Blowfish's Oceanopedia E-Book

Tom 'The Blowfish' Hird

• Herausgeber: Atlantic Books
• Kategorie: Lebensstil
• Sprache: Englisch

Seitenzahl: 503

Veröffentlichungsjahr: 2017

Beschreibung

A New Scientist Gift Pick 2017 From luminous squid to invisible plankton, from sandy shorelines to the bone-crushing pressure of the deep, marine conservationist Tom "The Blowfish" Hird takes us on an incredible journey revealing what lurks beneath the waves. A treasure chest of fascinating facts, full-colour photos and vintage line drawings, Blowfish's Oceanopedia is a stunningly beautiful guide to all we know about our oceans and the weird and wonderful creatures that inhabit them.

Leseprobe

Blowfish’sOceanopedia

Published in hardback in Great Britain in 2017 by Atlantic Books,an imprint of Atlantic Books Ltd.

Copyright © Tom Hird, 2017

The moral right of Tom Hird to be identified as the author of this work has been asserted by him in accordance with the Copyright, Designs and Patents Act of 1988.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior permission of both the copyright owner and the above publisher of this book.

Image copyright © Shutterstock, pages 43, 44, 45, 67, 71, 91, 93, 103, 108, 115, 118, 132, 144, 158, 167, 171, 179, 181, 192, 208, 228, 234, 238 and plates 1, 2, 3, 4, 5, 6, 7, 9, 10, 11, 13, 16.

Image copyright © Wikimedia Commons, page 106 and plates 8, 12, 14, 15.

Image copyright © Roger Hall, page 193.

10 9 8 7 6 5 4 3 2 1

A CIP catalogue record for this book is available from the British Library.

Hardback ISBN: 978 1 78649 2 401E-book ISBN: 978 1 78649 2 418

Designed by Carrdesignstudio.comPrinted in Great Britain.

Atlantic BooksAn imprint of Atlantic Books LtdOrmond House26–27 Boswell StreetLondon WC1N 3JZ

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Contents

Introduction

Acknowledgements

1    The Ways of the Sea

2    Shore

3    Coastal Seas

4    Coral Reef

5    Open Ocean

6    Deep Ocean

7    Frozen Seas

8    Threats to the Oceans

Further Reading

Index

Introduction

Welcome to my Oceanopedia! A wonderfully made-up name for a book about a wonderfully real world. First, I’d just like to say thanks to all of you who have spent your hard-earned cash on this book: I love you all. To those of you who have received this book as a gift or stocking filler . . . tough break. Be happy, at least, that it is heavy enough to be used to smite annoying insects, throw at door-to-door salesmen, or just prop up that wobbly table leg.

I wrote this book because I wanted to give you a glimpse into what the oceans have hidden deep within them. I have been fascinated by the seas for so long now I can’t really remember when my passion for poisson began. What I do know, though, is that I learn something new every day – and it’s not just the ordinary stuff we can often guess about terrestrial creatures, since a lot of them are, basically, pretty much like us. The stuff I’m talking about is truly unique, guaranteed to blow your mind.

My hope is that after reading this book you will love the oceans a little bit more and may start to realize that, even though you might not be wet right now (unless you’re reading this in the bath), the oceans and their health are the key to our own long-term survival. Don’t worry, this isn’t some kind of radical tome on Mother Ocean and how you need to start eating seaweed soup. But it should make you think twice next time a fish finger shows up on your plate.

Some of you may already have noticed that this isn’t your standard book on wildlife or the environment. The chapters and ‘nuggets’ of info are not meant to be a boring reference guide to getting a degree in marine biology, but rather a rough guide to the science that you can use to improve your own knowledge, impress your friends, and bore people at dinner parties.

But who is this handsome, bearded fellow who has so painstakingly written this impressive volume? Well, it’s me. Tom ‘The Blowfish’ Hird. A proud Yorkshire lad with more body hair that the average Wookiee. Growing up, I always loved nature and can’t remember a time in my life when I haven’t had some sort of animal around me. This is thanks to my mum and dad, who are also keen animal-lovers – though my mum now seems to be obsessed with collecting wire-haired dachshunds, while my dad has a bizarre penchant for various sizes of rubber and metal washers. Either way, my early days were spent travelling with my dad, who is a vet, to see horses, cows and other critters up and down the moors of West Yorkshire. At home, my mum would show me how to care for small animals, taking note of their different ways, meeting their daily needs, and thereby ensuring their long-term happiness within our family.

It goes without saying, then, that I wanted to emulate my parents and follow my dad into the veterinary profession. Sadly for me, I am not blessed with his prodigious intellect (although I am a damn sight better-looking), and after a trip through a famous aquarium at the age of twelve, decided to become a marine biologist. Perhaps this was fated, as I had already developed a terrible fear of sharks due to a particularly well-known film. So scared was I of being eaten by a massive shark that I wouldn’t hang my feet over the bed when sleeping, just in case! Yet, as is the way with most childhood fears, I became obsessed with sharks and just couldn’t read enough about them. Soon, I knew more about sharks as a thirteen-year-old than most people would ever learn in their whole lives, and one thing I knew for certain was that they needed our help.

Sharks have been persecuted to a truly apocalyptic extent. These incredible creatures are in decline worldwide thanks to a barrage of human influences, none of which show any immediate sign of stopping. I have dedicated my life to changing the way people think about sharks, and the oceans, in the hope that when I finally dance my last tango, there will be a few more sharks swimming around than there were when I came screaming into the world.

So what about The Blowfish then? Well, originally I was going to follow the righteous path of academia, getting a Master’s, PhD and more . . . writing papers which would change minds and laws, and defend my beloved sharks and rays. But in 2005, after taking part in a trip to the Adriatic to chum for sharks, and seeing precisely none over a two-week period, I realized I needed to make a more immediate impact. So I decided to use my voice to speak to you, the public, the people with the money who make the decisions at the grass-roots level. If we can change our ways when it comes to the fish we buy, the products we use and the waste we make, we can change the planet without the need for laws or politics. So it was time to stand up and give a voice to the creatures of the blue! However, ‘Tom Hird’ didn’t exactly have the right ring to it, so I settled on a nickname I had received from the surf club at my university and The Blowfish was born.

So, this is from The Blowfish, the world’s only heavy metal marine biologist (patent pending) to you, the awesome people of planet Earth! Enjoy this book, read it, share it, gift it, learn from it. But please, even if you only like one small section, think about what you can do to make a change and ensure this world remains a shining blue jewel for all the generations of little blowfishes to come.

Acknowledgements

There are too many people to properly thank for helping towards the completion of this book. Without a doubt, big thanks to Ben for his guidance and graft, to Mark for dealing with my biological terms, and to Andrew for sorting out the devil in the details. Thanks to Atlantic Books for giving me some paper to print the whole thing on and giving me a chance to tell my tales to the world at large. My huge and constant thank-yous to my mum and dad, who have supported me through all this TV and media madness with kind words, beers and roast dinners. And a special thank-you to Nick, who has kept me sane during these long months.

Finally, this book is dedicated to Alice, my beautiful, funny, intelligent and compassionate wife. You are the waves on my ocean, the sand of my beach and the water beneath my fins.

The Ways of the Sea

Water is an extraordinary molecule, vital for life as we know it. It first appeared on our planet around 4.5 billion years ago, and although science still hasn’t found a unifying reason for why Earth has so much water, its arrival began the planet’s transformation from spherical rock to a thriving Eden. Water allows chemicals to travel, offers electrons for reactions, dissolves salts and gases, stabilizes temperatures and provides buoyancy, giving relief from the harsh effects of gravity. In this highly active environment, the first life appeared – and evolution did the rest.

Although it is theoretically possible for water from all over the planet to mingle, in reality powerful physical forces and physical rules affect and restrict its movement. So, while some water dynamics are on a colossal scale, traversing the entire globe, others are small and predictable; but all have very specific attributes and associations, reflected in the way we designate distinct bodies of water. The oceans, seas and channels identified by humankind over the centuries are, at root, artificial separations – as man-made as the lines we scrawl over maps to divide countries and empires. But this doesn’t mean they have no merit. Although the physical, biological and chemical interactions of our blue planet have set the rules for all aquatic life, this doesn’t mean that a water molecule in the Bahamas is interchangeable with one in Bournemouth – you can’t just hop from one to the other.

Mapping the seas has not been an easy task, and it is true to say that the final frontier is the great oceans, where there is still much to learn. What we do know is that the oceans have many permutations of the basic physical factors, producing amazing environments to which life has adapted itself and then exploited. The Southern Ocean is a roaring mass of waves and wind, ensuring some of the harshest seafaring conditions on the planet; yet here we also find some of the densest concentrations of aquatic life. By contrast, water molecules further north, around the Equator, sit still and stagnant in the barren expanses of the Pacific: the warmness of these waters does not dictate that life will thrive in them. The picture is far more complicated than that, though, and each ocean has its own set of requirements, sometimes extremely testing, with which its denizens must comply in order to prosper.

All in all, living on our wet planet is complicated and difficult. The rules are strict, but can change in a heartbeat; they are fluid in every sense. Only the very strongest lifeforms survive, and even then you never know when the oceans might change the game all over again.

Once upon a time . . .

When the Earth first formed, there were no oceans at all, just a hot ball of rock spinning in space. All the water we now have was in gas form, in what developed into our atmosphere. Only after the Earth had cooled significantly did the water vapour get a chance to condense into clouds and dispense rain into the hollows below – and geologists believe there may have then been a centuries-long downpour (sound like Yorkshire?) as the primal oceans filled.

After this point in the planet’s evolution, the oceans’ shapes were decided not by water but by land, as continents shifted, and by the changing climate. In fact, 250 million years ago, when all the continents existed as one giant landmass known as Pangaea, there was consequently just the one vast ocean surrounding its coastline. After another 50 million years had passed by and Pangaea had started to break up, individual seas with more distinctive characteristics started to form, most famously the Tethys Sea. Splitting the northerly Laurasia continent from the southern Gondwana, the Tethys provided new ecological niches for life to colonize. Sediments and fossils from the Tethys give us great insight into what this forming world was doing during that geological age. As the continents continued to drift, more seas opened up, and in time the mighty Tethys itself closed, around 65 million years ago.

It is only in relatively recent geological time that today’s oceans took shape, when, as the continental drift slowed and the polar ice caps formed, currents started to connect and isolate different bodies of water. Continued movements in landmasses created relatively new seas, such as the Mediterranean, and in the twenty-first century the oceans continue to move, shift and adapt.

A tidal tale

‘Time and tide wait for no man . . .’ – a familiar phrase, but one that I have always enjoyed because of its honest simplicity, especially when it comes to the tide. Long before we invented clocks, nature had its own rhythm, the seasons giving colour to the year. And the tide provides the constant beating heart of the planet.

At a basic level, the tide is widely understood, for it flows in to reach high tide, and ebbs away to make low tide. In doing so, it swallows up the largest beaches, completely exposes harbours, and drives water through the smallest channels. But how does so much water move on a global scale?

Well, the first answer usually given is that the tides are controlled by the gravitational pull of the Moon. However, this is only half right. The tides are also controlled by the gravitational pull of the Sun, with both Sun and Moon exerting a similar control. As beach-goers know, the timing of tides differs each day, usually by around 50 minutes, depending on location. More than that, some shorelines can experience two high and two low tides daily, while others can have just one, and yet other shores vary depending on the time of the month. And then, twice a month respectively, there are spring tides and neap tides. Spring tides occur when the Sun and Moon are in alignment, either on opposite sides of the Earth or complementing each other on the same side. The combined gravitational pull of the celestial bodies brings higher high tides and lower low tides, covering and then exposing more shoreline than normal. But when the Sun and the Moon are 90 degrees apart when viewed from Earth, the opposite occurs. The gravitational pull is compromised and the result is a neap tide, in which little water moves in any direction.

The Blowfish goes deep ...

NOT MOVING, BUT WAVING

The ocean is never still. It constantly shifts and swells, ebbs and flows, as waves ripple and roll across its surface. Waves manifest themselves through tides, affected by the pull of the Moon and the Sun, and sometimes as surges, caused by large storms and hurricanes, or even more ferociously as tsunamis, caused by underwater geological disturbances.

Waves form as the wind blows over the surface of the ocean, creating friction and causing water molecules to begin moving in a circular direction. As they do so, they are replaced by molecules underneath, in turn dragging in yet more molecules alongside just as the original surface molecules are pulled around to join the chain. The result is numerous tiny circular motions, all stacked directly on top of one another, but decreasing in size and energy depending on the strength of the original wave-forming force.

Although waves have serious and sometimes catastrophic effects, they don’t technically move water; they are just energy transferring though water. To demonstrate this point, just get in the bath with your favourite rubber duck and make a wave. You’ll see how the wave travels across the whole bath, but the duck merely bobs up and down in the same spot as the wave passes.

When a wave hits a hard substance like a reef, beach or rocks, it breaks and forms surf – the circular motion of the water molecules is interrupted. But when unimpeded, waves are able to travel unchecked around the globe. In the Southern Ocean, where there are no landmasses lying between the inhabited continents and Antarctica, they do just that. The largest natural waves on the planet, reaching 30 metres in height, are found in these deadly, freezing waters.

Over thousands of years, humankind has studied the tides, acquiring a pretty good grasp of the whole phenomenon. More remarkable, though, is the way that marine animals are wonderfully in tune with the rhythm of the seas and in synchronicity with the tidal ebb and flow.

Tidal titans

Around the world, there are some extraordinary daily tidal events. The Bay of Fundy in Canada has the highest tide on the planet, exposing more than 26 kilometres of shoreline during the ebb of a high spring tide. Put another way, that’s an estimated 160 billion tonnes of seawater flowing in and out of the bay twice a day. Scientists attribute the phenomenon to the topography of the bay itself, which complements the wavelengths of the incoming tides to create an effect called tidal resonance.

Massive movements of water like this do not go unnoticed by man or beast, and areas of large tidal flow often exhibit great biodiversity. For us, the chance to harness the power of the tides is just too tempting, and across the globe tidal barriers are constructed as a method of producing clean, renewable energy.

By contrast, there are points around the planet where the arrangement of the continental shelves, landmasses and local topography result in there being very little tidal movement, and in some places almost nothing at all. These are termed amphidromic points. This is not to say that there are no low or high tides, but these points are like the fulcrum of a seesaw, never changing amid the contrasts on either side.

The current picture

Looking at a map of the ocean currents reveals a really quite incredible and intricate system, like some wonderful clockwork mechanism. You can see exactly where the water goes as it moves around Earth’s landmasses.

The major currents work in a reasonably uniform way. This means that in the northern hemisphere the currents move in clockwise whirls – gyres – while in the southern hemisphere they travel anticlockwise. This is due to the ‘coriolis effect’, a phenomenon produced by the Earth’s spinning rotation, pulling at both the water and the driving winds. As the currents move across the oceans, they are heated at the Equator, and then at higher latitudes their heat dissipates – and creates the weather we experience. Think of the Gulf Stream. This current begins in the tropical Gulf of Mexico and then moves across the Atlantic towards the UK; it typically brings with it the mild winters and warm summers a country at our latitude would not otherwise have, thanks to the heat it picked up at its Caribbean origin.

As warm water moves away from the Equator, it pulls in nutrient-rich cold water from the dark depths and/or the polar regions that is often directly responsible for an explosion of life. This phenomenon is evident in South America, where the bloom of plankton and the subsequent population explosion of anchoveta provide the basis for an entire ocean food chain, right up to humans, all of it originating in those cold waters.

There is only one current that seems to break all the rules – and this is known as the Antarctic circumpolar current. Driven by the turning of the Earth and the roaring winds, and without any landmass to stop it circulating, this current rips around the bottom of the planet in one huge loop. It can easily be ranked as the roughest sea on the planet.

Turn, turn, turn: the coriolis effect

Currents around the planet are driven by many factors – the wind, temperature, landmasses – but they’re also influenced by the constant spinning of the Earth. It’s hard to explain, but it’s really important, and it’s called the coriolis effect.

In a nutshell, as the Earth spins on its axis, objects near the Equator have to travel faster than objects nearer the poles to complete a single rotation. This is because they have further to travel to complete a single rotation than objects further away from the Equator, where the rotational distance is shorter. Water molecules are being subjected to this force all the time, and those molecules fractionally closer to the Equator move slightly faster than those further away. The effect of these fractional differences is to cause a spiral to form. While this effect is very weak on the Equator, where the large majority of water molecules are all subject to the same forces, as you move further towards the poles the effect increases.

The coriolis effect’s greatest impact is on the planet’s winds, as seen in weather patterns where large spirals of cloud can cover whole oceans. The winds then drive the oceans into the planet-spanning gyres and currents we rely on for our weather, for sea travel and for food. Without the coriolis effect and the spinning of the Earth, life would be dull indeed: our only major water movement would be the cycle of hot water to cold water in a very boring convection current.

Rip currents: a real drag

Knowing about rip currents could save your life. They are a powerful force to be reckoned with, and while they are found off some beaches all year round, they can appear anywhere under the right conditions.

Strong rip currents form when large waves and strong winds drive in towards the beach. Once a wave of water has broken, it wants to roll back into the sea; but behind it are more and more waves pushing in, trying to force it back towards the beach. So, the mass of water finds the path of least resistance back into the ocean. On long sandy beaches, this path can begin as a very slight depression in the sand and very quickly develop into a trench. Gulleys that form between rocks in the sand allow rip currents to establish themselves.

Although a rip current eventually merges back into the ocean to reappear as more waves, the problem is that their speed and strength can drag a swimmer out behind the breakers and into deep water very quickly indeed. Some rip currents will move at 8 kilometres an hour – faster than anyone trying to swim against it. So, if you do get caught in a rip, you have two options: either let it take you all the way out and then signal for help, or swim parallel to the beach until you get out of the current, before swimming back to shore.

Rip currents can be hard to spot, so local knowledge and looking out for warning signs are important. But if you see a thin strip of darker, calmer water at right-angles to the beach, cutting through white breaking waves, that’s a rip current.

Into the vortex: whirlpools

Whirlpools are awesome, be they the little ones in the bath when you pull the plug or the wilder ones in the natural world. I have been lucky enough to see the strongest whirlpools on the planet. In the Saltstraumen strait in Norway, currents of up to 40 kilometres an hour smash 400 million cubic litres of water through a gap only 150 metres across, producing the world’s strongest tide and a watery chaos truly living up to its name: the Maelstrom.

The formation of whirlpools is actually quite simple. They are just the meeting of two opposing currents, which, as they pass each other, interact and spiral downwards. The strength of the vortex, or downward pull, will depend on the power of the original currents. Most whirlpools struggle to pull down perhaps a metre or more; but the one at Saltstraumen can be 5 metres deep in just its cone. Getting pulled down into it would mean certain death for any swimmer, but fish don’t seem to be bothered by large whirlpools for the most part: any small fish or plankton sucked downwards are likely to resurface unharmed, while larger adult fish can simply skirt around the base of the vortex without concern.

More ingeniously, fish exploit smaller whirlpools for food: they use the eddying currents to minimize the effort needed to swim, while positioning themselves ready to feed rapidly on anything edible that the vortex brings down to them.

Tree-stripping tsunamis

The stuff of disaster movies, tsunamis are one of the most destructive and terrifying natural events that can be witnessed on Earth. Unpredictable and unstoppable, they are a constant reminder that we are guests on this planet and not its masters.

Tsunamis mainly occur through sudden movements in the Earth’s tectonic plates. These underwater earthquakes cause a massive shift in the water column above as one plate jerks suddenly beneath another, forcing the other plate to pitch upwards. This sends an enormous jolt of energy into the sea, and water is displaced either upwards or downwards. At the surface, directly above the epicentre of the quake, a single wave forms and radiates out in all directions. At first, this wave may not be very high at all, and the water column may have been displaced by less than a metre. But all the water down to the ocean floor will have been affected, and all that incredible energy means that the wave can travel at 800 kilometres an hour or faster. As the tsunami starts to reach land, its wave height drastically increases as all those energized water molecules start to bunch up on top of each other, reaching extraordinary heights. At the same time, as the wave height grows and the wavelength shortens, speed is lost – the wave might now be travelling at 50 kilometres an hour.

The 2004 Indian Ocean Tsunami formed waves of 30 metres in height, but this is a long way from the largest ever recorded. That honour belongs to a freak mega-tsunami in 1958, in Alaska. An earthquake and rockslide sent a wave across the ocean into the narrow bay of Lituya, reaching a mind-boggling height of 525 metres. In this case, the combination of the bay’s shallow water and a narrow channel allowed the tsunami to strip trees and other vegetation from the sides of the valley 500 metres up from the usual shoreline.

The riddle of the sands

What is a beach without the mesmerizing patterns found in the sand at low tide? These sand ripples are an artefact made by waves and currents, and they can tell us much about what is physically happening on the beach.

The ripples are formed when sand particles on the seabed are picked up by the circular movement of water molecules, accompanying the water on its oscillatory wave motion before being deposited back pretty much where they started. However, if the energy of the wave is not consistent – and it is very unlikely that it would be, especially at the coast – the sand does not complete a full circular journey. A sand particle, being naturally heavier than water, requires a given amount of wave energy to get picked up and carried; but if the wave, whether outgoing or incoming, doesn’t have the required energy to keep the particle in suspension, it gets dropped. Repeat this process countless times with a beach-worth of sand and the result is that the majority of sand particles are dropped in the same places, creating humps – the ripples in the sand. The distance between ripples reveals the wavelength of the energy at that particular time.

It can get a lot more complicated than this – but I’ll leave the rest for the physical oceanographers, as they like maths more than I do.

Delicate dunes

The physics behind sand-dune formation is fearsome! And just one look at the many individual kinds of dunes, not to mention the conditions in which they form, would give anyone an ulcer. But sand dunes are a critical part of coastal ecosystems, providing the land with life-saving protection from the sea.

An onshore breeze blowing onto a beach will pick up sand and take it away from the shoreline. Anything the breeze hits will cause the sand to stop and settle, which in turn will cause more sand to settle on top. Over sufficient time, a bank of sand will form, albeit remaining unstable and liable to shift and move with the wind and local climate. The pile of sand doesn’t form into a true dune until plants start to colonize it, providing stability with their deep roots and branching stems. Sand isn’t exactly the best home for most plants, for it’s not only soft and unstable, but fresh water drains through it very quickly. However, marram grass doesn’t seem to mind these conditions, which is why it is often the first pioneer species to colonize a new dune environment. These first settlers have to be hardy, as they also have to deal with salt spray from the nearby ocean. But those same seas bring a useful bounty in the form of organic matter like seaweed deposited by storm surges, which then rots down on the dunes to provide fertilizer for the plants fighting for survival.

Given time, sand dunes become more and more stable, and less hardy plants are able to move in behind the protection now afforded them. An established dune system then reduces the effects of land erosion and can protect coastal land from the ravages of future storm surges.

From pole to pole: the water molecule

Water – as seemingly simple as it is essential. While water has many properties that chemists and physicists might swoon over, for me it is the little molecule’s polar nature that equips it with such important biological abilities. How so?

To answer this question means getting technical about H2O. The oxygen atom, which is situated at the crux of the V-shaped water molecule, pulls so strongly on the molecule’s electrons that it ensures the two hydrogen atoms attached do not have a fair share of the electron spread. It’s like hogging the duvet in bed. But the extra time spent with negative electrons makes the oxygen atom slightly negatively charged, whereas the hydrogen atoms become slightly positive as their positive, proton-rich nucleus becomes mildly exposed. This leaves the whole water molecule with positive and negative poles.

The reason why this is so critical is that polar substances love to dissolve things. Anything with positive or negative ions that water molecules come across will be desperate to interact with them and move away from its original home. Look at salt: a positive sodium ion and a negative chloride ion, happy and bonded together, break apart into a solution when introduced to water. And it is when chemicals are dissolved in solution that they can really start to interact with each other. It is this key stage that allowed life on Earth to begin in the first place.

Put simply, the interaction and movement of chemicals is life – and without the polar nature of water shoving things around, it would never have started in the first place.

Oceanic gas-guzzling

Life takes advantage of a basic principle: when oxygen burns with a carbon source, energy is produced for biochemical reactions, and one of the by-products is carbon dioxide. This simple rule started in the oceans, where the role of dissolved gases isn’t just important to living and breathing biological life, but also to the planet’s climate.

All atmospheric gases are found dissolved in seawater. This mixing occurs at the ocean’s surface and is aided through the effects of waves and wind, driven by concentration gradients and controlled through factors such as salinity and temperature. For example, warm salty water cannot hold as much dissolved oxygen as cooler fresher water. Thanks to the movement of currents, gases exchanged at the surface can be transported down into the deep ocean, while upwellings from below can bring deep waters back to the surface for more chemical interaction. But there are also areas in the ocean called oxygen minimum zones, which usually lie between 200 and 1,000 metres in depth, and where restrictive currents and the presence of respiring, organic life mean that the oxygen gets used up and is not replenished via mixing. Life is constrained in these areas, though they are not completely barren, as some creatures have evolved to deal with the low oxygen levels.

In discussions of the watery gases, carbon dioxide currently attracts the most attention. For a start, it dissolves quite rapidly in seawater to form carbonic acids. The increase in greenhouse gases in the atmosphere has meant that more and more CO2 is dissolving into the seas, making them more acidic and causing great damage to ocean life. But there is also a limit to how far the seas can absorb the Earth’s CO2, and once that limit is reached, and less and less carbon dioxide dissolves in the ocean, there would be a pronounced jump in the amount of CO2 remaining in the atmosphere. The result of that would be significant climate change for us all.

A salty story

The sea is salty. Everyone knows that. But the seas are not uniformly salty – they vary, being affected by global position, currents, tides and landmasses. For example, the Mediterranean has a salinity of around 38 parts per thousand (ppt), essentially meaning a salt content of 3.8 per cent, whereas the waters around the UK have an average of 35 ppt. When you get closer to the poles, where meltwater dilutes the seas and the low temperatures mean less salt gets concentrated through evaporation, the proportion is even lower, at around 33 ppt.

Differing levels of salinity create challenges for fish and other ocean life. Salt attracts water molecules through the process of osmosis, and water can pass happily through most biological barriers. Sea creatures with thin biological barriers such as gills would rapidly lose water from their cells to the surrounding salty sea unless they had a clever way of dealing with the problem. Which, luckily, they do. Fish, for example, have specially designed cells that actively take in salt and move it around the body in an attempt to retain as much water as possible. The effort is biologically expensive, costing the animal a lot of energy; but it means fish can maintain a stable internal salinity, allowing them greater freedom to move around the oceans. By contrast, invertebrates such as shrimp or squid cannot adjust their internal salt levels, so they have to be content with mirroring the salinity of the water around them. While this means that they expend less energy in simply surviving, they are also very susceptible to rapid changes in salinity, which could be life-threatening. If an animal acclimated to the saltiness of one body of water attempts to move too rapidly across the gradients to a different level of salinity, it could easily die. In this way, these invisible salinity barriers play an important role in the diversity of many oceanic ecosystems.

In short, salt is the very first hurdle evolution had to overcome for life to thrive, and the way sea creatures deal with salts affects their reproduction, diets, habitat choices and life cycles.

Going all hot and cold: thermoclines

The temperature of the oceans may seem fairly straightforward: after all, anyone who takes a dip in the sea off Cornwall knows it’s not going to be as toasty as the water of Bali (that’s why most of us wise folk don a wetsuit before plunging into British waters). But rather more interesting, and certainly more biologically important than the whims of holidaymakers, is the phenomenon of the thermocline.

As the Sun beats down onto the oceans, its heat energy is transferred into the water. Yet the Sun’s rays can only penetrate so far, so the surface waters become uniformly warmer than the deeper waters beneath them. This distinct transition barrier between the cooler water and the warmer water is known as the thermocline, and it has a significant impact on the marine world.

As the warm waters on the surface are constantly being hammered by the Sun’s rays and mixed by choppy surface waves, they tend to become barren of the essential nutrients for life. In contrast, the cold, calm, deep waters are jam-packed with important compounds. The depth at which the thermocline occurs can vary from year to year, and between distinct regions. Still, regardless of the depth of the thermocline, the laws of physics will not allow the cold, dense water to push up into the warmer, lighter water above it, so thermoclines tend to stay relatively stable. For a thermocline to break down, there needs to be a shift in the amount of sunlight and energy being given to the surface, usually in the form of seasonal storms.

Eras of stagnation: El Niño

Everyone in recent years must have heard about the weather phenomenon called El Niño. Once touted by climate-change deniers as the reason for our changing weather, it is a periodic anomaly whose effects, as a result of man-made climate change, are becoming greater.

In the southern Pacific Ocean, water warmed at the Equator is usually driven by trade winds from the western coast of South America across the Pacific towards Indonesia, South-East Asia and Australia. As a result, rich and deep cold-water upwellings occur off the coast of Peru and Chile, rising to the surface and causing huge blooms of biodiversity, notably in the population explosion of anchoveta. But in El Niño years, the trade winds weaken, and the hot surface water is not blown across the ocean, instead stagnating off the coast and preventing the nutrient-rich cold water from reaching the surface.

Worldwide, a big patch of warm water languishing on the Equator doesn’t help the climate. The lack of hot, moist air moving across the Pacific can cause significantly reduced rainfall in places like Australia, and can lead to drought in many parts of South-East Asia. For marine life, there can be huge effects too. When the vital blooms of anchoveta fail to materialize, many seabirds, tuna and other ocean predators have to travel further in an attempt to find pockets of life where some cold water has made it to the surface. Fish stocks are disrupted, and in countries like Peru, where fishing is a key industry, there can be serious economic upheaval.

El Niño events eventually wear out, and the usual pattern of east–west trade winds establishes itself again. The problem today is that the oceans are in such a fragile state that El Niño episodes have the potential to inflict far more damage than they used to, and their frequency may be increasing.

Carbon sinks and climate stresses

I’ve said it before – but if we burned all the trees on Earth, it wouldn’t be the end of everything. Scientists estimate that up to 85 per cent of the world’s oxygen comes not from trees, but from the sea. The oceans control our climate, and we would do well to remember how.

First, tiny oxygen-producing phytoplankton cover a far greater surface of the globe than do the forests. Furthermore, although plants may create oxygen during the day, they consume much of that oxygen at night, when they cannot photosynthesize. Phytoplankton can photosynthesize at night and so, in some cases, can carry out round-the-clock oxygen production.

Second, the seas also act as a vitally important carbon sink, by sending carbon to the deep ocean floor in the form of the dead bodies of plankton, and through the molecular nature of seawater, which actively absorbs CO2 and turns it into carbonic acids.

But there are limits, and unfortunately we’re putting too much strain on our oceans. More and more greenhouse gases are being produced, and the ocean is reaching saturation point. Should we see yet more melting of the polar ice caps, the consequences will not just be rising sea levels swelling over low-lying islands and swamping coasts; the influx of fresh water could easily disrupt the vitally important currents that bring us our weather.

And there’s the rub. Those currents normally move hot water away from the Equator and towards the higher latitudes, where it can warm coastlines or evaporate into life-giving rain. But global warming may actually result in higher-latitude places, such as the UK, becoming colder rather than warmer, as currents break down and warm water stagnates around the Equator.

When reduced salt is bad: haloclines

Just as a thermocline is a barrier between waters of distinctly different temperatures, a halocline is a barrier between bodies of water with two different salinities. Salty water is heavy and tends to sink, whereas fresher water is less dense and so will rise to the surface. This is particularly important for the waters around the poles, where the cold but fresher water from the pole sits atop the warmer, saltier water below. The halocline helps to maintain this division, and it’s a good thing too. Fresher, colder water can form sea ice far more easily than it would if mixed with the saltier water from the deep.

Fresher water doesn’t always win the battle to be on top. Sometimes, a thermocline and halocline interact, as when surface waters around the tropics get heated by the Sun and experience increased evaporation, become saltier than the water beneath. This process does not tend to last long though. Eventually, small pockets of heated salty water become too salty and too dense; they sink down through the thermocline to be replaced by fresher, cooler water from below.

Haloclines can be particularly difficult barriers for fish to cross, because jumping from one salinity to another represents an extreme physiological process for any marine creature. For one thing, there are the lower levels of dissolved oxygen in saltier water. Unsurprisingly, in areas where haloclines are common – such as in fjords and estuaries – the fish and invertebrates that make them their home are often hardy and specialized. In truth, haloclines can be as varied and unique as the environment around them, leading to some amazing adaptations.

A dying sea

In the Middle East, on the borders of Israel, Palestine and Jordan, lies one of the strangest bodies of water on the planet: the Dead Sea. At 300 metres deep and lying some 430 metres below sea level, it is ten times saltier than the ocean and a lot denser than normal seawater. Swimming in the Dead Sea is a common bucket-list experience, mainly because you don’t have to try . . . you just lie back and float instead, held suspended by that super-salty water. Needless to say, such conditions prove almost impossible for life, and there’s a complete absence of large multicellular aquatic creatures. However, small bacterial blooms do occur, as do blooms of salt-loving red algae after it rains, when the high salinity drops just a little.

There are many theories about how the Dead Sea formed. Some believe it was once connected to the Red Sea or to the African Rift lakes; others think it’s a spillover from the Mediterranean that then became cut off when land levels rose. Either way, from the minute the Dead Sea became isolated, it started to dry up; and although this process had reached an equilibrium, because of an inflow of water from the River Jordan, it now seems that the Dead Sea is slipping away. Since the 1930s, when regular measurements and studies began, its area has dropped by 400 square kilometres. This drying-up is down to the diversion of rivers and the reduction in groundwater upwellings, caused by human development. Alas, the Dead Sea is in real danger of drying out completely.

Estuary life

The boundary between fresh water and salt water is a pretty stark one to cross, and not many fish can live in both worlds. There are, however, quite a few species that exploit the environments where fresh and salt water mix, and a classic case is the estuary.

In the tidal mouth of a river, there is a constant shifting and mixing of fresh and salt water, depending on local conditions and the position of the tide. All this variability requires that the animals, plants and algae that make their homes here be very tolerant of the ever-changing salinity. Even so, distinct biological barriers remain, for few aquatic species truly span the entire gradient of salinities. What makes an estuary so productive is the food supply. The ebb and flow of the tide regularly brings in fresh nutrients and organic material to be consumed, while the fresh water conveys sediments, detritus and chemicals whose properties change on entering seawater, becoming accessible to a whole different range of critters.

Estuaries are often quite sheltered, because their rivers have cut their way through a lot of rock to reach the ocean, and so the animals making their home here are often protected from the rough waves and harsher conditions of the open ocean. Making the best of these waters are often the invertebrates, such as the green shore crab, and different kinds of particulate filter-feeding worms. This abundance attracts predators, both above and below the water. Wading birds like oystercatchers and curlews have perfectly evolved beaks to access the tasty world beneath the sediments, and fish such as plaice and wrasse can access the shallows at high tide to hunt for prey.

Pining for the fjords

There are many truly wonderful and unique environments to be found in the seas of this world, each with its own set of biological rules and regulations that sets it apart. But when it comes to those areas where the ocean meets the land, there’s so much more than beaches.

Fjords, for example, are fascinating ecosystems found on certain coastlines around the world. A fjord is a narrow inlet, characterized by high-sided cliffs and formed through glacial erosion. So you will tend to find fjords where there have been, or still are, glaciers, and countries such as Norway, Iceland and New Zealand are famous for these geographical features.

Usually, there will be a river or stream running into the fjord at the landward end, perhaps even from the remnants of the glacier that carved it out. During the winter, the freshwater inflow tends to freeze up and the fjord becomes fully saline; but in the summer, with meltwaters flowing rapidly, a fjord exists in more of an estuarine condition, often with haloclines forming between the bodies of water. At the seaward-most end of a fjord, there is often a narrowing of the inlet and a sill, or deposit of rocks and moraine, left when the glacier could move no further. This is a choke point, leading into what are often extremely deep channels within the fjord proper, and sometimes the tidal current generates quite extreme effects in such specialized conditions, such as whirlpools.

All this shifting of cold, rich waters, not to mention the deep and protected environments typical of fjords, leads to high biodiversity: lots of seaweeds and static filter-feeders like anemones carpeting the rocks, and fish such as cod, pollack and halibut all dominate the fjord’s undersea world.

The white cliffs of coccoliths

It can be easy to forget that the rocks we walk over and build our houses on were once, eons ago, under the sea. Stranger still is the concept that the famous White Cliffs of Dover were once not just objects in the sea, but organisms of the sea.

The cliffs are white because they are made from chalk, a mineral derived from the accumulation of trillions of microscopic planktonic coccolithophores. A type of phytoplankton, these – like their photo-synthesizing brethren – have a protective shell or exoskeleton around their bodies. Looking like tea-strainers, the scales that surround coccolithophores allow water and vital chemicals access to the cell beneath the protective layer. Each scale, or coccolith, is made from calcium carbonate derived from seawater and formed by the coccolithophore itself.

The Blowfish goes deep ...

WHEN THE SEA SNOWS

The term ‘marine snow’ is a fancy metaphor for the particulates that fall to the ocean floor, a kind of monsoon of death; yet this blizzard of waste isn’t as grim as it may sound, for it provides a vital food source for millions of creatures and keeps carbon out of the atmosphere.

The dead bodies of plankton, especially phytoplankton, make up a large proportion of marine snow. Accordingly, the seasonal abundance of plankton means that marine snow is also seasonal, with the deep ocean getting inundated during the spring and autumn blooms. Faecal matter also makes up a large component of marine snow, but this is not so much the waste from large fish – it is mainly the constant excretions of creatures such as tiny crustaceans called copepods feeding in the plankton.

Just because marine snow doesn’t sound appetising to us doesn’t mean it is shunned in the murky depths. Many deep-sea animals have evolved with the direct purpose of collecting marine snow through particulate and filter-feeding methods. Indeed, so nutritious are the dead bodies of plankton and even the faeces of other animals that particles of marine snow may be consumed and excreted numerous times over before they finally get to the ocean floor.

As the particles fall, they tend to coagulate with sand, silt and other detritus; and as they get bigger, they fall faster, but even that doesn’t mean they will definitely reach the bottom. Because it can take several weeks for a ‘flake’ of marine snow to complete the downward trip, bacteria have plenty of time to work on it, possibly even to consume it completely en route. If the marine snow finally does makes it all the way down, it can settle into a fine ooze, which in turn can be the beginning of an incredible transformation over millions of years, into rocks like chalk or quartz. Then again, even at rest on the ocean floor there are more creatures waiting to hoover up whatever edible particles remain.

As the single-cell organism grows and divides, the coccoliths fall to the ocean floor, or the cell itself dies and takes the whole lot on a one-way trip. Either way, there is a constant rain of these calcium-based fragments falling to the ocean floor. Given enough time – and they need a hell of a lot, since each coccolithophore is barely one-tenth of a millimetre across – these deposits can build up into a thick layer. Give it even more time, along with some compression from heavier sediments settling over the top, and the result is chalk.

The White Cliffs of Dover started this process when dinosaurs roamed the Earth, and were later thrust to the surface when the Alps formed. It’s amazing to think that right now micro-algae in the ocean could be creating the lands of the future.

Water slides . . .

It’s not only on rainy, deforested hillsides that landslides can occur. Underwater landslides are quite common in the world’s oceans, and they can be as dangerous and devastating to undersea life as any similar event on land would be to terrestrial inhabitants.

The underlying concept is the same. In areas around the continental shelves, there are significant slopes that descend to the deep ocean below. But some may have an incline of just 1 per cent. When sediments build up on these slopes over time, they can reach critical mass before sliding down far below. Underwater landslides are actually a very important natural process: they move sediments and organic matter like carbon into the long-term storage and recycling facility that is the deep ocean. But there’s risk and danger involved for any sea life that happens to be in the way. As huge volumes of debris rapidly tumble or get stirred up into a suspension again, clouding the water, undersea habitats can be completely destroyed.

There are other reasons, apart from this gradual sediment loading, why an underwater landslide might occur. Earthquakes, volcanic eruptions, hurricanes and the collapse of a weaker substrate beneath the sediments are just some of the other causes. As far as humans are concerned, underwater landslides can weaken coastal areas, damage undersea cables and disrupt oceanic mining and drilling efforts. For the most part, it’s all hidden beneath the waves. But not always. About 8,000 years ago, the Storegga slides off Norway shifted 3,500 square kilometres of sediment down into the Norwegian Sea. This event was so intense that it caused a local tsunami, which slammed across the North Sea and hit the east coast of Britain.

. . . and bubble-baths

As familiar on British beaches as the slightly thuggish seagulls and obligatory ice-cream sellers are the flecks of light-brown foam kicked up along the waterline by the encroaching waves and onshore breeze. Sea foam, or spume – which is frankly a much better name for it – occurs thanks to the constant agitation of the ocean through wind and waves. It is, essentially, organic waste, the broken-down proteins, fats and sugars produced by many different forms of marine life. If the water is calm, you can see the dissolved organic matter as faint slicks on the surface. They are often concentrated at the meeting of currents, known as fronts; but when stirred by constant wave and wind action, they foam up into bubbles which are remarkably tough and hard to burst. The spume is then washed or blown up the beach, where microbes in the sand can feast on it. Sometimes, large algal blooms offshore can create spume at nearby beaches so intense that it can impede visibility or even be a danger to humans because of the irritating chemicals that certain algal strains contain in their bodies.

Spume is a by-product of the ocean and not one that really makes much dynamic impact; but those of us who love our aquariums are very keen on spume, and we make it ourselves. In marine aquariums, a device called a protein-skimmer can drastically reduce nitrogenous waste in the water. The idea is simple: water from the aquarium passes into a chamber where a strong pump vigorously aerates the water. This causes bubbles to form, and the resulting waste can be collected and removed, ensuring that the tanks and their inhabitants stay in tip-top condition.

The survivor: seaweed

Often dismissed as unsightly and smelly, seaweeds are the ocean’s vegetation. And yet they are not plants at all; they’re algae. They possess neither roots nor flowers, and lack the sort of tissues that your standard terrestrial plants have. However, to attempt to classify seaweeds any further would take a great deal of effort. They are extraordinarily diverse – a real pain for taxonomists – and debate rages over their finer details.

Seaweeds have unrivalled success when it comes to ocean ecosystems, thanks to a kaleidoscopic range of adaptations. For a start, the absence of a root system means they can grow almost anywhere, so we see everything from small encrusting growths on rocks to acid-boring seaweed that penetrates mollusc shells. Flexibility in how to respond to the water is just as important, and this is where seaweed’s famous floppiness comes in. Having flexible stipes and flowing blades (the flat main part of the seaweed) means they can move with the turbulent flow of the ocean, surviving the worst the weather can throw at them without breaking. In fact, in storms the rocks to which seaweeds are attached can give way before the seaweeds themselves. If you’re a seaweed, ensuring you get as much light as possible means you have to have some method of supporting a floppy blade, and many species have gas-filled bladders to raise them up towards the surface.

Able to colonize the ocean as well as intertidal areas, seaweeds can contain chemicals that stop them from freezing in the winter or baking in the summer sun at low tide. It’s the chemicals given off by heated seaweed that give the coast its signature smell – and, believe it or not, those same chemicals happen to play an important role in the formation of rainclouds too.

Generating more heat than light?

What is light? It’s just the rapid vibration of a particle travelling as a wave: energy in its purest form. The photons that make up light radiation react with whatever they hit, which, in the air, is not very much, until they reach the Earth.

In water, it’s a different matter altogether. The first problem is that a lot of light doesn’t even make it into the water in the first place. Depending on the angle of the Sun’s rays, light can reflect off the water’s surface and travel away in a different direction. For the photons that do penetrate the water’s surface, everything changes. Instead of flying along at nearly 300,000 kilometres a second, they suddenly collide with water molecules, and this slows them down and slightly skews their direction (depending on the angle of entry).

As light descends in water, it also starts to dissipate as heat energy. The photons possessing the lowest energy are always the ones to go first, since they’re already pretty close to heat themselves in terms of wavelength, and this means that red light starts to disappear from the visible spectrum. The deeper it goes, the weaker light becomes, until only the highest-energy blue wavelength remains; even then, it will eventually hit enough H2O molecules to be lost as heat. At around a kilometre, it’s all over. Sunlight cannot penetrate deeper than this, and beyond it lies an area that no photon has ever visited.

Super-charged sunbathing: photosynthesis

Only a few, unique and isolated parts of the Earth rely on energy derived from somewhere other than the Sun. Even so, photosynthesis isn’t all that easy to achieve and many adaptations have evolved to increase its potential wherever possible. Take seaweeds, for example. These macroalgae have modified the methods of sunlight collection to fit their lifestyles. As previously mentioned, sunlight rapidly diminishes in water, with the red end of the spectrum going first. So seaweeds directly under the surface or in rockpools tend to be bright-green, but, as the water depth increases and the wavelengths of light diminish, they become brown and then red. This change in the pigments, associated with photosynthesis, has a purpose: to maximize sugar production with all the available wavelengths.

Photosynthesis is such an attractive option for creating food that many animals have managed to hijack the process for themselves, by taking on living algae as lodgers. In this way, the algae can continue to do their full-time food-processing job, and the host creature, be it a coral, anemone, jellyfish or even a sea slug, can live life knowing it has food on tap whenever it wants it.

The psychedelic sea: oceanic colour-changers

The colours in the ocean can be truly breathtaking, from the bright and vivid corals to the enormous and beautiful variety seen in marine animals. Typically for the ocean, everything is in constant flux, and the colours of sea creatures are no exception.

The natural ability to change colour is perhaps best known in the chameleon, but the masters of colour change are fishes and invertebrates. Rather than relying on blood to initiate a colour change as does a chameleon, which is a slow business, fish and cephalopods also use nerves, generating an instant colour change. The cells responsible for producing this sudden makeover are called chromatophores, and they work in a wonderfully simple way.

If you close a colourful parasol and then point it horizontally at a friend, they will see little white dot at its end; but open it up, and the full array of colours appears. That is how chromatophores work. They are bags of pigment, which can be relaxed and expanded out between layers of the skin to reveal their colour, or quickly contracted to reveal the colour of the flesh beneath. From this basic premise, many different colour-changing cells have evolved. Iridiophores, for example, are cells of silvery crystals that produce iridescent blues and greens, while melanophores create blacks and browns, and cyanophores give out shades of blue.