Many novice divers who venture into Dublin Bay for the first time are surprised at the volume and variance of our local marine wildlife. Both the silty nature of Dublin Bay and the strong currents combine to create an ecosystem upon which marine life thrives. Visibility underwater rarely exceeds 5 – 10 meters so in order to observe the marine life it is necessary to stay close to the sand and silt bottom, boulders or underwater cliffs which comprise much of the underwater topography on many of the local dive sites. Wrecks, many of which are situated on sand banks or flat bottoms are therefore open to the full power of local currents. This attracts marine life as it provides a place to shelter or to attach on to.
An average club dive is generally restricted to 30 minutes underwater. It always seems to fly by as there is so much to see. Keeping a record of what you see and learning how to identify the various marine species is not particularly easy. For instance a notebook and pen is not a real option. However cheap digital cameras and underwater housings are a massive step forward in bulding up a knowledge of species as photographs of life, regardless of quality can be matched against one of the excellent marine life guides available today.
So if you’re new to diving you’re probably asking yourself ‘apart from an odd fish what is down there?’. Below is a summary of some of the classes of life to be found in Dublin bay as way of an introduction to our local marine life.

PORIFERA meaning ‘bearing pores’

PORIFER-WHAT. Yes , well these are basically sponges. Sponges are some of the most colourful animals in our waters. They are usually red, yellow or orange and pump water through the myriad openings feeding on microscopic organisms. They attach themselves usually to hard surfaces such as rocks and prefer areas of strong current.

CNIDARIA meaning ‘like nettles’

Cnidarians are more complex than sponges. Many can sting, swim, capture and swallow prey. This group of animals probably comprise the majority of life that you are likely to see in Dublin Bay. They include jellyfish, hydroids, sea pens, soft and hard corals and anemones.
Anemones are commonplace on Dalkey Island and the Muglins. Attached firmly to a hard substratum they open up like roses on a summers day and colour the underwater world in a dazzling variety of hues. With sticky stinging tentacles they capture passing plankton, crustaceans and even fish.
Soft corals are represented in profusion by the Dead Man’s Finger Alcyonium digitatum suspension feeders perfectly suited to the high currents of the Muglins.
Jellyfish are represented usually in the summer by large numbers of Moon Jellyfish, Lion’s Mane Jellyfish and Compass Jellyfish. Jellyfish are pelagic and are quite complex, some possessing ‘eyes’. Although divers are usually covered head to toe with wetsuits a common complaint is a jellyfish sting around the mouth – the only exposed piece of skin on a dive.

ARTHROPODA meaning ‘joint and foot’

Arthropoda include many familiar species and are a step up in complexity to the Cnidarians. They include sea spiders, shrimps, hermit crabs, crabs, lobsters, squat lobsters and surprise, surprise barnacles. They represent on a global scale 80 per cent of all known species. They are characterised by having a segmented body and an exoskeleton.

MOLLUSCA meaning ‘soft’

Molluscs range in size from 20m long squid to 1mm snails. Limpets, snails, whelks and my personal favourite of all underwater species, the opisthobranchs including the nudibranches. It takes many dives before you’ll even think about looking for nudibranches as they can be hard to spot but they’re worth the effort. Bright illuminescent colours do help to pick the tiny creatures out but knowing a little about what species they feed on also helps for instance the yellow spotted Limacia clavigera feeds exclusively on bryozoans which is subsequently found growing on seaweed!.
Also found in this group are tasty mussels and scallops. But the most incredible member of mollusca goes to the octupi and cuttlefish – highly intelligent creatures with sophisticated communication mechanisms. This group can change colour in front of your eyes.

ECHINODERMS meaning ‘hedgehog skin’

Starfishes, brittlestars(of which you may find millions scattered across the soft bottom near Dalkey Island like a carpet),sea urchins and sea cucumbers (starngely enough these last two are usually found in abundance where there is little or no other life i.e they eat all before them!).

FISHES

Yes we have fishes in Dublin despite the best efforts of our angling community. Speaking of which – I was chatting to an angler who told me that not 20 years ago the area around Dalkey could feed a large family on quality fish obtained on a leisurely hour’s angling in Dalkey Sound. Unfortunately that day is gone – is it time to make the special underwater paradise of Dalkey Island and the Muglins a marine park.
So what is the diver likely to see on a 30 minute dive in the area. Wrasse are the most obvious and colourful of fish. Ballan wrasse are most common along with rock cook, corkwing wrasse, goldsinny and the least common on the east coast is cuckoo wrasse – also the most colourful.
Gobies and shannies are cute and inquisitive little fish which hide away in rock crevices or sit atop boulders. The Tompot Blenny has to be every diver’s favourite.
Flatfish include dabs, topknot and sole. Mackeral can occasionally be seen in open water in large shoals. Dogfish are the only reresentative of the shark family you are likely to see on a dive however I have seen 6 foot long Tope caught only 100 meters off the Muglins – so watch out.
Usually the first fish that is mentioned post-dive is the conger eel and with Dalkey and the Muglins it’s a case of how many you have seen so common they are. These are giant, spooky eels found usually with their large heads protruding from a gap in a collection of boulders.
Other very noteworthy sightings are long tailed scorpion fish, ling, anglerfish, pipefish and tadpole fish (I have only seen twice on the Muglins in 12 years).
We hope you have enjoyed this introduction to the marine life of Dublin Bay but more specifically Dalkey Island and the Muglins.Now, why not contact the club, don that wetsuit and go see yourself.