The shore crab (Carcinus maenas).

Crustaceans are another common sight on rocky shores. This group includes crabs, lobsters, prawns and barnacles. One of the best known crabs inhabiting the Irish coast is the shore crab (Carcinus maenas). All crabs have an external skeleton made from chitin (a tough, semi-transparent substance) and this shell must be shed by moulting in order to allow the crab to grow. The shell of the shore crab is much broader than it is long and varies in colour from dark green to orange and red. Like starfish, crabs can generate new legs if necessary. The shore crab is considered an omnivore as it has an extremely varied diet. It consumes plants, algae, molluscs and worms. The diet of large shore The shore crab (Carcinus maenas) crabs mainly consists of molluscs however, and the common mussel (Mytilus edulis) is perhaps the most important of these.

Click here to see the main cockle-fishing areas in Ireland

The open sea is one of the most fascinating, yet poorly understood habitats in Ireland. In addition to this, much emphasis is placed on the study of the conspicuous vertebrates such as whales, dolphins and fish. In spite of this, the invertebrates are a diverse and abundant group in the seas around Ireland. In contrast to the previous two habitats, the open sea represents a much more stable environment for invertebrates. Temperature fluctuates little from day to night, animals are constantly immersed and so do not have to cope with desiccation, while the currents work to constantly distribute food and nutrients.

The Dublin Bay prawn (Nephrops norvegicus) is a small, pale orange lobster. It is known by a number of different names including nephrop, Norway lobster and, when its tasty tail meat is cooked in breadcrumbs, it is called scampi. It can grow to a total length of 25cm, although individuals are normally between 18-20cm. The relatively slender body ends in a broad fan-like tail. The Dublin Bay prawn lives in shallow burrows in fine mud, which it often shares with a small fish - Fries' Goby. The Goby acts as a guard of the burrow, warning the prawns of impending danger. The Dublin Bay prawn scavenges on scraps of food but also eats small fish. The Goby then eats the remaining scraps.

The curled octopus (Eledone cirrhosa) is thought to be present in the seas all around Ireland. It is instantly recognisable from its large, round body, long flowing tentacles and red and white colouring. Each tentacle bears a single row of suckers and when at rest, these arms are curled (the behaviour which gives this species its name (the behaviour which gives this its species name). Although the normal mode of transport for the curled octopus involves walking quickly on the seabed using the the tentacles, this mollusc is also capable of rapid swimming (when a predator appears, for example) by exhaling water from a siphon (tube) attached to the side of the body. Using the row of suckers on each tentacle, the curled octopus catches prey such as crabs and small fish.

Irish waters are home to a number of jellyfish species, one of the most striking of which is the compass jellyfish (Chrysaora hysoscella). The 'umbrella' or manubrium of the compass jellyfish is thickened and can grow up to 30cm in diameter. The upper surface of the manubrium is distinctive in having 16 v-shaped markings said to resemble the radii of a compass, from which this species gets its name. The stinging cells and venom of this jellyfish are strong and can produce painful weals in humans. Like most jellyfish, the compass jellyfish drifts through the water with limited control over its movements. However, jellyfish do have special muscles that allow them to contract the umbrella which enables vertical movement. Horizontal movement depends on ocean currents, tides and wind. the diet of the compass jellyfish consists of small fish and zooplankton (microscopic animals) that are caught on their tentacles. This particular species of jellyfish is hugely important in the diet of the endangered Leatherback turtle (Dermochelys coriacea).

Jellyfish Can Sting the Economy Tagging a giant jellyfish in the Irish Sea Jellyfish can severely impact many socio-economic sectors including aquaculture and tourism. Quantifying this impact and providing early warning are just some of the objectives of research undertaken at the Coastal and Marine Research Centre (CMRC). EcoJel, a partnership between the CMRC and Swansea University in Wales is exploring how increased jellyfish populations affect the tourism, aquaculture and fisheries sectors of the economy in the cross border area. The impact of jellyfish is being examined by tracking their movements and identifying the economic potential of harvesting jellyfish in a sustainable way as an eco-tourism attraction. The Irish salmon aquaculture industry, which is worth over €60 million to the economy, suffers severe losses each year as a result of gill pathologies. The causative agents are believed to be a combination of environmental parameters (e.g. water temperatures, oxygen levels.) and biological species such as phytoplankton and zooplankton swarms (jellyfish). The GillPat project, a consortium between the CMRC, the Marine Institute (lead partner), Vet-Aqua International, the Agri-Food and Biosciences Institute (Belfast), and the Irish Salmon Growers Association, has the objective of identifying these causative agents. The CMRC has established a pilot jellyfish monitoring programme with the aim of warning industry once a harmful species has been detected. Click here for more information on this research.

A gull sitting on a sewer oulet pipe

Threats

The Kerry slug (Geomalacus maculosis) - a terrestrial species, and the crayfish (Austropotamobius pallipes) - a freshwater species, are perhaps the most high-profile endangered invertebrates in Ireland. There are currently no endangered Irish marine or coastal invertebrates. However, with the threats to coastal and marine habitats growing in severity, increasing attention is being given to the protection of these habitats. The depletion of shellfish stocks through over-fishing is well-known in Ireland. Though once a common food, found widely around the coast, overfishing of oysters in the past resulted in them becoming a little known luxury. Over-fishing and disease caused a rapid decline of the native oyster throughout Europe. Pollution is also a significant problem. Marine dumping and waste disposal is a common practice and is subject to licensing by the relevant Department . Solid materials that have been dumped at sea include sewage and chemical sludges, fish processing waste and decommissioned vessels. In addition, accidental or unauthorised releases occur from time to time, and range from uncontrolled farmyard runoff to major oils spillages. Due to the vast nature of the open sea, it is difficult to investigate the effects of such events on the invertebrates inhabiting this environment.

The effects of the threat posed by climate change are perhaps the most difficult to predict. If the climate changes as forecast however, the environment of typical coastal invertebrates such as the cockle will be altered dramatically. Changes such as a rise in sea level and water temperature would undoubtedly impact negatively on the invertebrate fauna of the coast. The effects are most startling when the overall impact is taken into account. Changes in invertebrate populations would affect countless shorebird and fish species, which rely on them for food. That said, the effects of climate change on invertebrates represent mere speculation as we cannot accurately predict how these animals will respond to the changes.