Sponges
Starting with the most primitive animals we have the sponges. Sponges are found attached to rocks, plants and other animals. There are rich sponge communities on many of the rocky reefs around Scilly. They are colonial animals (a group of animals living together in a colony although they may appear to be one organism). They come in many different shapes and colours like the bright orange ‘shredded carrot sponge' and the upright, branching ‘chocolate finger sponge’. Sponges are fragile and easily damaged.
Cnidaria
The cnidaria is a group of animals with stinging cells which includes jellyfish, anemones, corals and others. They are some of the pretti
est animals in our waters, usually with soft fleshy bodies and long feeding tentacles. They dominate some of our reef walls; vivid jewel anemones and fluffy looking plumose anemones cloak the rock in places – a riot of colour in their underwater landscape. Corals are also found in this group and in Scilly we have healthy colonies of pink and white forms of the pink sea fan. Sea fans may have sea fan anemones and sea fan seaslugs living on them, both species are restricted to living on our pink sea fans. We also have other rare corals here, like sunset coral and scarlet and gold cup coral both of which are found in very few other places in the UK. Also found in Scilly are the strange stalked jellyfish which live on blades of seagrass.
Worms
Worms are common in the marine environment, of
ten they are found burrowing in mud or sandy sediments such as those in Scilly. Marine worms often construct tubes to live in and feed with tentacles in the water column. The large areas of sand flats in Scilly are home to many species of worm: sand mason worms make their tubes using mucus to stick sand grains together! Some marine worms are beautiful, like the eyelash worm which can shoot back into its tube very rapidly if it senses danger. Others such as lugworms are rarely seen but the casts which they leave on the surface of the sand (produced during feeding) are common.
Crustaceans
Crustaceans are the armoured tanks of the sea. Their
skeleton is on the outside of their body and it protects their soft tissues inside. Lobsters, crabs, prawns and even barnacles fall into this group. Hermit crabs have less protective armour than most of their relatives and have to borrow old shells from other animals to use as their mobile homes! The crawfish (or crayfish as it’s known locally) is an important species which has suffered from declines in the past. They resemble lobsters but without the large claws.
Molluscs
Sea shells, snails, slugs and clams all fall into the largest group of marine animals called the molluscs. Molluscs almost always have a hard shell, although in a few animals like the cuttlefish you can't see the shell because it is inside them. Others, like octopuses have completely lost their shell as they evolved. In Scilly we have a huge range of molluscs from the tiny lagoon snails in the spray zone at the top of the shore to the burrowing razor shells on the sandflats. Sea slugs can be very striking and there are slugs with all manner of spots, stripes and colourful patterns. Look out for a huge shell called the fan mussel, which used to be abundant here but seems to have disappeared.
Sea mats or bryozoans
Sea mats or bryozoans are a strange group. They are colonial animals like sponges but are more advanced than sponges. They may live on other plants or animals or attached to rocks, they often look like plants because they may be branched or bushy. Potato crisp bryozoan (also known as ross) is a brittle orange animal which grows slowly in a rosette shape. One important species, the orange peel seamat grows on seaweed around Scilly but is not known from anywhere else in the UK.
Echinoderms
The echinoderms (meaning spiny skin) are the starfish, sea urchins and sea cucumbers. Starfish like the bloody henry starfish and the common st
arfish which live in our waters are predators that move across the seabed using special organs called tube feet. Visible spines on the outside of urchins and on the skin of starfish and sea cucumbers are there to deter predators. On the sandflats at St Martin’s and Trescothere are important populations of burrowing heart urchins. Crevice sea cucumbers and featherstars are often seen on reefs by divers.
Sea squirts
Sea squirts may form colonies or grow as individuals; they are filter
feeders that are live in a fixed position. If they're disturbed they squirt a jet of water by contracting their muscles quickly. Lightbulb sea squirts are often found around Scilly, they have a bright band around them that looks like a filament. Some unusual species of seasquirt are found in Scilly, like the orange lights seasquirt which is normally found further south.
Fish
There are many kinds of fish around here like the sharks a
nd their relatives the rays. There are also the bony fish like the tiny gobies that you can find in rockpools and the brightly coloured and inquisitive cuckoo wrasse. Some sharks and rays lay eggs and their eggcases can be found washed up on local beaches. Learn how to identify an egg case. Keep an eye out for seahorses which also live in these waters and may end up washed up on beaches too.
Turtles
Sea turtles are occasionally seen around the Isles of Scilly, normally offshore in deep water. Leatherback turtles may pass by these islands on their migration routes as they search for shoals of jellyfish to eat. Sea turtles are globally threatened and their biggest threat in our waters is choking on plastic which they accidentally swallow. Rarely a turtle gets stranded in Scilly and needs assistance. If you ever come across a stranded turtle you should contact British Divers Marine Life Rescue (if it is alive) on their hotline 01825 765546 or the Cornwall Wildlife Trust Marine Strandings Network (if it is dead) on their 24 hour number 0845 201 2626.
Marine mammals
The Isles of Scilly are visited by a number of marine mammals and is a stronghold for grey seals. These charismatic and popular species are important for the tourism based economy of the islands and play important roles in marine ecosystems.
Cornwall Seal Group is actively studying seals in Scilly at the mome
nt and they have been able to recognise individuals from the mainland which have turned up in Scilly. Most of the seals live on the Eastern Isles, the Western Rocks and the Norrad Rocks. Whales, dolphins and porpoises are sometimes seen from the Scillonian or from boats moving around the islands. Common dolphins, bottlenose dolphins and harbour porpoises are seen most often. In 2008 a humpback whale was seen breaching near Scilly. If you see a marine mammal you can report your sighting to Seaquest Southwest.
Watch this seal video, filmed by Angie Gall at the Eastern Isles.
Plants
Plants are important in the underwater world around Scilly. Seagrass is unusual because it is a type of flowering plant which can reproduce underwater – it has waterproof pollen! Most other marine plants are much more primitive, these are the algae. Algae have no roots; instead they attach themselves to rocks or other algae or animals using a holdfast. In the clear waters of Scilly, algae can grow at a depth of over 30m. There are some rare species of algae in Scilly including a type of kelp which normally lives further south. Kelp forests provide a three dimensional habitat for many species of fish and invertebrates.
