Some people wonder why I bother going diving in the UK – after all it’s bloody cold
and you’re not going to see much wildlife, let alone any interesting wildlife. While
it’s true that UK diving requires more than a few of the warmest thermal layers ever invented,
the animals and algae you see when you’re down there more than make up for it.
I’m going to take you on an underwater safari of the best marine wildlife I’ve saw on
a single dive trip off the south coast of England. But as an evolutionary biologist,
I’m going to present them from least related to humans to most related to humans. This
isn’t to say that humans are in any way better than everything else (we’re not)
or that we are the pinnacle of evolution (we’re not) nor that we’re the most complex (we’re
not). It does mean we can see which adaptations happened a really long time ago and so are
found in most of the tree of life, and which adaptations happened more recently and so
only affect one or two branches. So squeeze into your drysuits and load up your lead as
we fall backwards into an underwater jungle.
I always thought of algae as the boring bit of the marine habitat; the frame in which
the beautiful animal picture hangs. Turns out their biology is so complex and interesting there’s
no way I can fit it all in here. Just as you may have heard there is no such thing as a fish
algae is a similarly meaningless word, as technically land plants
are a type of green algae, but there are also red and brown algae that are completely different
from plants that are also in the algae grouping. Much of the UK coastline is kelp forest, and
just like trees in a forest, the kelp provides shelter and structure while also absorbing
and fixing carbon. Globally, kelp forests capture 75% of the carbon fixed in the sea
and are one of the most productive ecosystems on earth. It’s honestly stunning swimming
through these enormous trunk like fronds, catching glimpses of fish, then seeing a mat
of reds and pinks and purple algae covering the rocks.
Leaving behind the plants and algae, we have
sponges, the most basal animal group, meaning they split off from the rest of the animals
ages ago and so lack many of the adaptations we see in other animals. They’re not lesser
animals for it; they have after all survived as a group for far longer than us mere mammals,
but when you look at a sponge, it’s hard not to call it primitive.
They don’t have true tissues or organs, there’s no head, and no anus. However, this
lack of complexity in the types of cells does give them one major superpower. You can pass
a sponge through a sieve to break it up into individual cells, and not only will the cells
survive, they will regroup and form a whole sponge again.
Just don't even imagine doing that to a human. It won't end well.
And we’re on to the cnidaria, that’s your
corals, anemones and jellyfish. We’ve gone up a level in cell complexity and have two
layers of cells with a jelly filling. That does mean we only have one orifice for eating
and excreting though – a mouth anus if you will. But although they have simple tissues,
they have evolved a wicked adaptation we don’t have. Cnidaria literally means nettle animals
because these have evolved stinging cells. And not just any stinging cells. These cnidocytes
are trigger activated, hydraulic propelled harpoons that can have piercing barbs, toxins,
lassos or glue. That’s hardly primitive. If they can pierce human skin the toxins are
some of the most fatal in the animal kingdom. If they can’t, like beadlet anemones, it
just feels sticky or grippy.
Ah we’ve reached the arthropods. From this point onwards, all the animals are bilateria.
We’ve got three cell layers during development which means we can now evolve a complete digestive
tract with a separate mouth and anus! Hooray! Biologists are so obsessed with mouths and
anuses that we split all the animals from this point into the ones that grow a mouth
first as an embryo (the protostomes) and the ones that grow an anus first and a mouth second
(the deuterostomes). Arthropods are a group of protostomes, and
boy are they a diverse group.
In the sea, we have malacostraca instead of
insects; the crabs, lobsters, crayfish, shrimp and woodlice. To once again drive home the
point that just because a group split off earlier along the evolutionary tree doesn’t
make it basic or primitive or less evolved, just listen to this parts list. They’ve
got 2 pairs of antennae, compound eyes, three pairs of mouthparts, eight pairs of legs from
the thorax, some of which might be specialised into pincers for feeding/defence, 6 pairs
of appendages on the abdomen or swimmerets, which might also be specialised into catching
food, brooding eggs, delivering sperm, bearing gills.
Special shout out to the spiny lobsters we saw in Cornwall. These were almost wiped out
from over fishing because they live so long and take so long to reproduce. But they’ve
been made a priority species on the UK Biodiversity Action Plan, and because we were diving next
to a Marine Conservation Zone where human activity is restricted, we were able to see
quite a few as the population is recovering.
We’ve reached the group where the anus forms first! The earliest branching of the deuterostomes
is the echinoderms or the spiny skinned; that’s your starfish, sea urchins and sea cucumbers.
Once again, they’ve evolved powers we lack; they have hydraulically powered tube feet
which they use to move around and grip onto food, and they can regenerate legs and internal
organs. You’ll often see starfish either missing a leg (or three) but they’ll be
absolutely fine and will just grow another one.
Sea cucumbers can also squirt long sticky tubes at threatening predators, entangling
and immobilising them for long enough for the cucumber to crawl away. However, I have
to read to you one description of how they do it: “it faces away from the attacker
and contracts its body wall muscles sharply. This causes the wall of the cloaca to tear
and the anus to gape and the free ends of some of the tubes to be ejected. Water is
forced into these tubules causing a rapid expansion and they elongate by up to twenty
times their original length”. Ouch.
Aaaand we’re finally at the more recognisable animals – the vertebrates. Vertebrates includes
your five big groups – the fish, amphibians, reptiles, birds and us mammals. And, as I
know you’re all wondering, we are deuterostomes which means our anus forms first! We start
off as a hollow ball of cells and that first invagination becomes the butt. We’ve now
evolved jaws and an adaptive immune system. Within the fish group, we have the chondrichthyes
and osteichthyes aka the fish with cartilage skeletons and the fish with bony skeletons.
The cartilaginous fish includes the sharks, skates and rays, and yes, sharks are fish
and yes there are sharks in the UK. I saw a couple of lesser spotted dogfish but we
also have basking sharks (the second largest fish in the world) plus about 30 other species
of shark that visit British waters and none of them will attack a human unless provoked.
Recent research on this type of shark found that sharks have personalities, aka a repeatable
behaviour across time and contexts that differ consistently among individuals. Social dogfish
were happy to hang out in conspicuous groups in a new habitat, whereas the less social
sharks preferred to camouflage on the gravel bottom, staying hidden on their own.
We have now evolved bone! And there’s also
an anal upgrade: we now have separate openings for the anus, urine and genitals. And if you
didn’t think there was already enough terminology with the osteichthyes and chondrichthyes, the
bony fish are also split into two, the actinopterygians and sarcopterygians aka the ray finned fish
and the lobe finned fish. I mean just take a second. I had to memorise all
of these terms for my undergrad degree. Take pity.
The ray finned fish, or actinopterygians, make up pretty much all
of what we think of when we think of a fish, including these wrasse. Wrasse are super common
and there are over 600 species, so when in doubt, we divers call every fish a wrasse!
The word wrasse comes from gwragh meaning old woman, which is the same root as the word
hag. Which is fitting, because like haggard old women, wrasse are colourful and beautiful.
All wrasse start off life as females and them some become males later in life. Usually there
is a single dominant male and when he dies, the most senior female will change sex and
take over. This is the opposite of the clownfish in Finding Nemo, where Nemo’s dad would
almost certainly have been Nemo’s mum by the time they reunited.
And finally the sarcopterygians, the lobe finned fish. You might
not think you know much about the sarcopterygians but in fact you know them intimately. And
that’s because humans are strictly speaking lobe finned fish, as are all the other land
vertebrates. Usually we exclude the land animals from this grouping but this is only for convenience,
and doesn’t make any biological sense when we’re considering who is most related or
who is evolved from whom. Around 380 million years ago, some fish found
their stubby bony fins were quite good at crawling through shallow water that was full
of mud and dead leaves. Being able to gulp air and hold it in lungs was really handy
for breathing in stagnant water. Fish were still living in the water when they evolved
legs and lungs, but once they had them, they were able to colonise the land.
Over the next few hundred million years, some of these land fish evolved hair and homeothermy
to keep warm, a big muscle called the diaphragm to breathe, and bigger brains to find food.
Then a few of these lobe finned fish decided they actually still like being able to go
under water after all. They weren’t very well adapted to life underwater and had to
invent these ridiculously heavy and complex tanks, masks, hoses and suits. But that’s
a story for my third and final scuba video in this series – how exactly DO you go scuba
diving in the UK?
Hello, and welcome to my highly professional voice-over recording booth.
Isn't this great? What's also great is this video is sponsored by New Scientist.
I love getting paid! Thumbs up!
So if you didn't grow up with New Scientist like I did, they are a science and technology magazine
both online and in print, and they write articles about new research, new papers that have just been published
technology, the environment, all these sort of things, but it's all for a general audience so it's all really easy to understand
And with the link in the description, you can get 10 editions of the magazine for just £10
which is in itself a great deal, but also at that link I have curated 3 articles that I think you'll enjoy
based on this video so they're all on marine biology and evolution
There's one on fish that have a dawn chorus and they have the audio file so you can listen to the dawn chorus
over a coral reef which has just been discovered
There's one that some sharks have been found to be glow in the dark
And my favourite one, and bear in mind that New Scientist have no editorial control over this video
They didn't know what this video was going to be about.
They already had an article about comb jelly anuses
So like jellyfish, an anus that comes and goes at will. How perfect is that for this video?
So if you want to say thank you to New Scientist for giving me money and helping me continue
to make a living making YouTube videos
If you want to get that amazing 10 for 10 deal and read more about jelly anuses
Then just go to the link in the description. Thanks!