| Overview | Data Sources | Links | References |
| Rocky Shores | • | Sandy/Muddy Shores | • | Open Seas | • | Threats |
The marine rocky intertidal zone is one of the best studied habitats, mainly due to its accessibility. Also, unlike sandy/muddy shores, the animals of rocky shores are not hidden in the substrate but are generally visible and slow-moving. Rocky shores are among the most physically stressful environments on Earth. When the tide is high, waves can sweep over plants and animals at velocities as high as 60 miles per hour, while at low tide, the same organisms dry up and bake in the sun. Yet despite this seeming inhospitality, rocky shores are exceptionally complex and biologically diverse. The rocky shore must therefore offer many advantages to its inhabitants. Boulders and loose rock in this habitat increase the degree of shelter available to invertebrate animals, the rocks themselves provide a stable substrate to which animals such as limpets can attach, and every times the waves roll in they bring a supply of water and nourishment.
Echinoderms such as the Common starfish(Asteria rubens) and Sun starfish (Crossaster pappossus) are perhaps amongst the most easily identifiable marine invertebrates. Starfish are characterised by their numerous arms, the base of which are covered in 'tube feet' used for both locomotion and prey capture. The number of arms varies between species with the common starfish having five arms while the sun starfish may have up to 14! Starfish are capable of regenerating these arms if they are lost. Starfish are omnivores but mostly feed on mussels.
The Molluscs represent a varied invertebrate group which includes limpets, periwinkles and mussels. The dogwhelk (Nucella lapillus) is quite common along the rocky shore in Ireland and can be significant as an indicator of pollution. The dogwhelk has a spiralled shell which varies in colour from ash-grey to cream. It is a voracious predator and the shell bears a radula (tooth) which is used to bore holes in the shells of prey. Digestive juices are then secreted to soften the body of the prey and the resulting 'soup' is sucked up through a proboscis (tube-like structure) by the dogwhelk. The prey of this mollusc most commonly includes mussels and barnacles.
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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.
Sandy/Muddy
Shores
The traditional view of sedimentary shores is one of a barren wasteland
with few signs of life. This may not be the case however, as is evidenced
by the countless shorebird species which rely on the invertebrate life of
sandy and muddy shores for food. Invertebrates of sandy and muddy shores
(and estuaries in particular) must cope with the mixing of seawater and
freshwater and the constant ebb and flow of the tide. In spite of these
conditions, these habitats also offer a number of benefits. Sandy/muddy
shores can often be more sheltered than neighbouring areas and hence do
not suffer extreme exposure to waves and currents. The soft substrate is
also crucial as it provides protection for burrowing animals which can take
refuge in the sand or mud when the tide is out.
Perhaps one of the most familiar sights on a beach at low tide is the coiled
castings of the lugworm. The lugworm (Arenicola marina) has a cylindrical,
segmented body quite similar to an earthworm. Adults can reach 120-200mm
in length and, although the colour varies, the lugworm is primarily red
and green. Lugworms dig a U-shaped burrow somewhere from the middle shore
downwards and can move backwards and forwards in this burrow by waves of
contraction and expansion, using the bristles on the middle part of the
body. With regard to diet, lugworms consume sand, which passes through the
stomach and intestine where small particles of dead plant and animal matter
in the sand are digested. The remaining sand is then ejected in the form
of the familiar cylindrical castings on the beach. Lugworms are important
as a prey species of many shorebirds (which may nip off the tail as it deposits
casts), and are also used as bait by anglers.
Another favoured food item of shorebirds is the mud shrimp (Corophium
volutator). This tiny crustacean has a long slender body that is white
with brown markings and grows up to 11mm in length. The mud shrimp has two
pairs of antennae on the head with the second pair being particularly long
and thick, almost as long as the body itself. Like the lugworm, the mud
shrimp occupies u-shaped burrows, rising to the surface on an incoming tide,
crawling over the mud surface at high tide and burrowing down on a receding
tide. It normally filters detritus from the water while in its burrow, but
can also pick up items directly from the surface when walking around at
high tide.
The common cockle (Cerastoderma edule) is a typical inhabitant
of the outer sandy parts of large estuaries. The shell of this mollusc is
roughly 3-5 cm long, oval in shape with an outer surface off-white, yellow
or brown. The shell is also thickened to help it withstand the pounding
of the waves, with distinctive ribs to assist in anchoring the cockle in
the sand. To alter their position cockles push out a fleshy foot and lock
it against an obstacle such as a pebble, then tightens the muscle pulling
the shell along. The cockle feeds using a pair of tube-like siphons which
filter suspended detritus when the tide is in.
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Click here to see the main cockle-fishing areas in Ireland |
Open
Seas
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).
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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. |
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| 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.
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