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The Blue Planet – BNA Guide to British marine
life
The BBC’s breathtaking series ‘The
Blue Planet’ has allowed us all to enter the largely unexplored
undersea world, to gain views of animal life at depths of
over a mile down. Yet much of the series has viewed undersea
life closer to shore, where light can penetrate and form a
more direct plant and animal food chain. This is the world
of which most naturalists have more experience, but which
is no less exciting, just more accessible. For most of us
our early undersea exploration started when we collected shells
and seaweed on a beach, or peered at marine creatures in rockpools
during a seaside holiday.
British marine life
By Roger Tabor
We live on a blue planet, as over 60%
of the northern hemisphere, and over 80% of the southern hemisphere,
is mantled by seawater. Threequarters of that area of sea
has a depth of between 3000 and 6000 metres. Only a fraction,
some 1%, is deeper, in contrast some 16% makes up the shallower
areas of continental shelf that surrounds most land that forms
a plateau down to around 200 metres. The whole of the British
Isles are surrounded by a large continental shelf which is
continuous with that of mainland Europe. The entire North
Sea is bottomed by the N.W. Atlantic continental shelf.
Our western shores are bathed in the warm
Gulf Stream, which brings rich plankton food for fish which
then supports numbers of our coast’s seabird colonies.
(Elasmobranchii , the
sharks, cartiliginous skeleton)
You may be lucky enough to spot this huge
fish when looking out to sea from cliffs. These feed directly
on plankton, swimming slowly with a huge open mouth that nets
vast amounts of plankton. These fish can be up to 11 metres
long.
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Rocky or Muddy Shores?
- Seaweeds and Plants
Some parts of our coastline are cliff
edged, some with rockpools at their feet at low tide as at
Cornwall and N.W. Scotland. Other parts of our coastline have
flat muddy or sandy shores, such as around the Essex shores.
These widely differing habitats are home to very different
populations of wildlife. Both rocky and muddy shores have
a regular tide pattern, but rocky shores provide a range of
conditions that varies with rock type, and angles of exposure
on rockfaces to the sun. The seaweeds (algae) of the wrack
group have distinctly different amounts of bladder-floats
depending on species, and so they exploit different areas
of rocky coasts according to amounts of shelter.
Species of red
seaweeds are particularly abundant in reasonably sheltered
pools and tide gullies. Their distinctive red colour is an
adaptation to a significant factor of sea depth and light.
In the spectrum of light it is the blue wavelengths that can
travel further into the water, and the algae’s red pigment
has the best colour to absorb the blue light.
In most rockpools, and washed onto the
shore, you will find three distinctly coloured groups of algae
(seaweed), red, brown and green, and it is the red that can
live at the lower depths. Green
seaweeds’ pigments capture red wavelengths of light
that cannot penetrate far into the seawater. Off rocky shores
at low tide you can find forests of a type of brown
seaweed called oarweed,
which has big hand like flat fronds to maximise their light
gathering ability.
Off muddy shores there are vast areas
of eel grass, which perhaps
unexpectedly is a flowering plant that lives a submarine life.
The distinctive feature of a muddy shoreline
is a saltmarsh, and huge areas line places like the Wash in
East Anglia. The snaking channels of a saltmarsh have been
formed by the way silts are deposited around plants. The key
plant that begins the settlement of silt is glasswort
otherwise called marsh samphire.
There are a number of species of glasswort that are remarkably
similar.
Once the saltmarsh mud accumulates from
estuary waters, channels scour away between the areas bound
by plants. The one normally found all along the banks of the
saltmarsh channel is sea purslane
. As the table of the marsh becomes established then other
plants including sea lavender,
sea aster, sea
pink and scurvy grass
can become established.
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Coastal Marine Invertebrates.
Invertebrates are all those animals without
backbones. Generally invertebrates cannot reach the sizes
achieved by vertebrates, however, there are a few "monsters
of the deep", notably the Giant Squid that from top to tentacle
tip can reach up to 15 metres. There are many phyla of invertebrates,
but 5 key phyla include those species likely to be seen around
our coastline:
Arthropoda (includes marine crustaceans like crabs
and lobsters),
Mollusca (including the sea shells),
Annelida (includes the
marine segmented bristleworms like the ragworm),
Echinodermata (includes
sea urchins and starfishes) and
Coelenterata (includes
sea anemones and jellyfishes).
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Arthropods/crustacea.
Exoskeletal animals with jointed legs,
includes crabs and lobsters (the Decapopds), and barnacles
(Cirripedia).
There are number of different crabs along
the shores of the UK, including the Edible
Crab which is familiarly eaten. Along the shoreline
this pink coloured crab is only likely to be found up to 15cm
long, but further out to sea they reach the full size of almost
twice that. The typical small, green-brown, crab (up to 12cm)
commonly caught by children is usually the Shore
Crab. Some shore crabs have white patches.
The massive claws of lobsters are even
more pronounced than those of crabs. True
lobsters have pronounced abdomens and tails. There
are dark bodied in the sea, and emerge from shelter to feed
by scavenging. (Their pink colour seen in restaurants only
occurs during cooking).
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Coelenterata
Their bodies have an inner and outer layer
of cells with jelly between. Includes Jellyfish (Scyphozoa),
Portuguese Man of War (Siphonophora), and sea-anemones (Anthozoa).
These can often be seen washed up on the
beach as jelly-like structures. At sea they may have a pulsing
action, but their travel is largely due to drifting.
Aurelia aurita is commonly seen round Britain. Jellyfish
have stinging cells to immobilise prey. Although the Portuguese
Man of War is usually described as a jellyfish, technically
it is in a separate closely related group, and has been described
as a collaborating colony of different specialist polyps rather
than as a single animal.
Look into a rock pool and you will probably
find sea anemones, either
as dense coloured stumps with waving tentacles on top, or
as fleshy lumps when they retract their tentacles into their
body. Due to their colouration they appear more solid than
jellyfish, but their fundamental design is very similar, in
that they have a body with a simple cavity, and stinging tentacles
around the mouth.
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Mollusca
Molluscs are a huge group of animals,
with unsegmented bodies, and include the animals that made
the sea shells found washed up on beaches. These occur in
two main groups, the Gastropods
(slugs and snails) and the Lamellibranchs
(bivalve-shelled animals). Unexpectedly for many people, Cephalopods
(the octopus and cuttlefish) are also part of this grouping.
One of the most common groups of animals
found on rocky shores is Winkles.
These have a typical snail’s round-enclosed spiral shape of
shell. The carnivorous Dog Whelk
eats barnacles through their hunter’s tongues. Whelks typically
have a spiral cone shape of shell.
Although they occur as a simple low cone,
and do not have spiral shells Limpets
are also marine snails. They are famed for their tight and
tenacious grip on their rocks when exposed to air at low tide.
When the tide is up they grind their shell and the rock together
to a perfect fit, which becomes their base. During high tide
they release themselves and wander over the rock scraping
off the film of algae to feed on. By the time low tide returns
they also have returned to the security of their special spot.
Although generally marine snails are
commoner on rocky shores, in the mud of estuaries and sandy
shores bivalves are more common. However Whelks and other
snails can be readily found. Cockles
are the classic muddy shore bivalve, it burrows into mud up
to around 4cm deep using its extendable foot. Thinner, smoother
shelled Tellins are also
commonly encountered. Scallops
readily take to under water ‘flight’ by flapping their shells
together. Oysters prefer
the firm bottom of estuarine channels to live on rather than
shifting mud. (These form a significant part of my own ancestry,
as I come from at least ten generations of oystermen).
Mussels attach themselves to firm objects
by threads, and so are not just found on rocks, but commonly
attached around harbour posts.
To establish the age of a bivalve or univalve
animal from its shell, see: Young Naturalists Project Ideas
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Annelida – Marine Worms
Both of these have been dug for centuries
by fishermen as bait. The marine worms and shellfish are the
reason for the massive flocks of wintering waders, as they
exploit the marine species as food. (The length of the birds’
bills affects which bird catches which prey. See: Coastal
Waders section of BNA quick guides to identification).
Ragworms
are carniverous Nereid worms with many paddles on their sides.
In contrast the Lugworm
is a filter feeder that lives off a fine suspension of detritus
that it can pull through its tunnel in the sea bed.
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Echinoderms
These have a general circular pattern
(seen most clearly in sea urchins) but can be in a form with
radial arms (like starfishes). They all have tubefeet linked
to a system of tubes in the body. The phyla includes the classes
of: starfishes (Asteroidea), sea urchins (Echinoidea), brittle
stars (Ophiuroidea), sea cucumbers (Holothuroidea) and sea
lilies (Crinoidea).
A typical sea urchin is seen in the Rock
Urchin, which, although only being of up to some 6cm diameter,
has dramatic long spines. Colour is variable from brown to
green or purple-violet.
The Common Starfish regularly preys on
oysters, to the extent of being considered a pest by the oyster
fishing industry. They can be up to 30cm across and of variable
colour, from a pinky-fawn to purple-violet
Typically these have thinner arms than
starfish, radiating from a central hexagonal body block.
© Roger Tabor 2001
Roger Tabor is the Chairman
of the British Naturalists’ Association
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