STUDIES OF THE SEA SHORE
AREAS CHOSEN FOR PROJECTS IN THE PAST • EFFECTS OF EXPOSURE ON ORGANISM DISTRIBUTION; MORPHOLOGY; BEHAVIOUR. • EFFECTS OF WAVE ACTION • INTERSPECIFIC & INTRASPECIFIC COMPETITION
• POPULATION DENSITIES
• INTRASPECIFIC VARIATION
• PREDATOR-PREY RELATIONSHIPS
• EXCLUSION ZONES
• EFFECTS OF ENVIRONMENTAL GRADIENT ON ORGANISM HABIT
• BIOTIC VS ABIOTIC FACTORS AND EFFECTS ON HABITATS / NICHES.
• ENERGY FLOW • ZONATION STUDIES • SUCCESSION
• SALTMARSH ADAPTATIONS
• ADAPTATIONS FOR IMPROVED PHOTOSYNTHESIS IN ALGAE
ZONATION • Zonation on a rocky seashore shows the preferred locations of the fauna and flora. Preferred meaning the optimal balance of abiotic and biotic conditions.
• The shore is divided into regions from the top down to the water’s edge as follows: • Splash zone; • Upper shore; • Middle shore; • Lower shore; • Sublittoral zone
• Top photo shows evidence of zonation on a UK rocky shore.
• Lower photo shows the splash zone which is NEVER covered by water at high tide.
• Top photo shows lichens that have been splashed by waves.
• Lower photo shows the uppermost limit of the barnacle zone.
• Top photo shows barnacles competing with mussels for space.
• Lower photo shows the mussels outcompeting the barnacles for space.
Examples of organisms commonly located on UK sea shores • PRIMARY PRODUCERS Included here are the algae of which there are 3 types: green, brown and red. Algae are NOT plants, but collections of individual cells with photosynthetic capability and thus act as the producers of CHEMICAL ENERGY.
• Examples of commonly found green algae are: • Enteromorpha a green alga commonly found higher up the shore where they use red light, that does not penetrate far into seawater, for photosynthesis Gutweed.jpg
• Sea lettuce (Ulva lactuca) this is made up of a sheet of unspecialised tissue 2 cells thick and of approximately 40 cm in length.It does not have a particular zone, though it can be dense under brown seaweeds for protection; nitrate fertiliser run-off in estuaries can lead to mud flats turning green in early summer.
• Brown seaweeds: These are more numerous than the green seaweeds and thus more important members of the shore population. Two main types the wracks which live on exposed rocks using a holdfast to anchor the stipe to the substratum and those confined to standing water in rock pools.
• Two main types the wracks which live on exposed rocks using a holdfast to anchor the stipe to the substratum and those confined to standing water in rock pools.
• Brown algae tolerate dehydration and are found typically in the middle shore. Examples of wracks are:
Bladderwrack (Fucus vesiculosis) which has a pair of air bladders on its fronds allowing it to float and intercept light. On exposed shores a bladderless form grows. The number of bladders varies with wave action. This alga lives for about 3 years, and can be pushed out by egg wrack, but only on sheltered shores.
Another wrack is egg or knotted wrack (Ascophylum nodosum) which has a single large air bladder in the centre of the frond. This wrack dominates the middle shore on SHELTERED rocky shores and can live for 15 years meaning it can compete favourably with other algae by forming a dominant blanket over the rocks, excluding new competitors, with few species growing under it because of the shade. It is not unpalatable for most grazers.
There is a red alga called Polysiphonia lanosa which grows as an epiphyte and can cause the death of the wrack by increasing the surface area and weight so wave action can pull the wrack of the rocks.
• Kelps (Laminaria spp) • Kelp grows in deeper water forming forests with layers of algae and animals. Kelp is more pigmented than other brown seaweeds because it grow where there is less light.
• There are 3 main types of kelp: • Sugar kelp (Laminaria saccharina) which can grow up to 2m in length. Unlike other kelps the frond is thickened in the middle, with a frilly edge and an uneven surface which induces turbulence around the frond allowing good exchange of gases and nutrients.
• The other 2 kelps are: • Oarweed (Laminaria digitata) shown here • and
• Laminaria hyperborea • Form of kelp commonly called Cuvie
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• Finally there are the red algae. Though these are not always an obvious red colour,some can be a dull purple through to green and yellow often as a result of the bleaching action of the sun.
• The red algae are generally less bulky than the brown ones but are much richer in species.
Red algae are so called because they have accessory or secondary pigments contained in organelles called phycobilisomes. The accessory pigments absorb light and the energy to chlorophyll for photosynthesis.
I have only chosen 3 types of red algae but there many species.
• Pepper dulse (Osmundea pinnatifida) is a red alga that is very tolerant of shade adapting by developing more pigments to absorb the little light present; this gives it a dark red / brown colour. When water drains away from large expanses of rock, leaving it exposed, it easily bleaches forming a dominant yellowygreen to white “turf” in midsummer. It is found from the middle to the lower shore on rocks.
• Another red alga is Laver (Porphyra spp) • which can live anywhere on the shore, especially near sand. When young it is dark purplish, but may be bleached to a green colour. It has an expanded frond which is just a few cells thick, forming a membrane over rocks. It is collected and fried with bacon in south Wales as laverbread; it is highly nutritious.
• Irish moss (Chondrus crispis) forms dense patches around the base of kelp, making it shade tolerant, in the lower shore as well as in rock pools of the middle shore. It is very common. Colour can vary but is generally a red-brown. It is not very palatable and few herbivores graze on it, causing it to dominate the smaller algae in rock pools.
• Animals located on the rocky shore can be divided into:
• Filter feeders;
• Herbivores;
• Sediment feeders.
• Carnivores;
• Examples of each now follow.
• Scavengers;
SEASHORE HERBIVORES
• Herbivores include: • Rough periwinkles • This group can be difficult to classify at the species level, but generally the ones shown here are Littorina saxatilis
• L.saxatilis survive high up on the shore and into the splash zone. • They have a shell and can breathe air by using a part of their body called the mantle cavity, which is highly vascularised and acts as a primitive lung. To save water they excrete nitrogenous waste as solid uric acid which is not very toxic.
• In very dry conditions they glue themselves onto the rock using mucous, withdraw their body into the shell, using their foot to block the entry hole or operculum. • Additionally they can move to find moist microhabitats such as crevices in rocks to hide in. • Survival in this difficult abiotic environment confers advantages such as little interspecific competition and lots of food in the form of lichen.
• Another example of a rough periwinkle is: • Littorina compressa
• Another herbivore are topshells, of which there are several. These animals are an important group that graze microalgae on the shore. • The genus Gibbula is common of which the purple topshell Gibbula umbilcalis is an example.
• The inside lip of the shell shows a “Mother of Pearl” effect with multiple colours. • The purple topshell has a shell that has a hollow spiral running through its central line with the shell height being about 15mm.
• The operculum is a horny plate that closes off the inside of the shell reducing water loss at LOW TIDE. • The operculum in topshells is CIRCULAR in shape, but in periwinkles it is TEAR-DROP or elongated shaped.
• Other examples of topshells include: • Grey Topshell (Gibbula cineraria)
Grey Topshell.jpg Grey Topshell.jpg
• Painted topshell (Calliostoma zizyphinum) • Lives on the lower shore, where dessication is not a problem; uses its foot to clean its shell.
• The toothed topshell (Osilinus lineata). • Large topshell possessing a small bump on the shell underside which protrudes slightly into the hole or aperture.
SEASHORE CARNIVORES
• Beadlet anemone (Actinia equina) • One of the few anemones able to survive on the UPPER SHORE. • Often found in rock crevices or pools where it is moist and to further reduce water loss when tide recedes it retracts its tentacles, reducing its body surface and trapping water inside its body. It now resembles a chewed wine gum.
• The beadlet anemone has special cells,called stinging cells or nematocysts,on its tentacles that contain coiled up microscopic “harpoons” which are released under tension if the protein coating the nematocyst is touched by prey.
• Some of the nematocysts release paralysing chemicals into the prey, whilst others lasso and hold the prey until the tentacles retract and pull the prey towards the mouth.
• The beadlet anemones (shown here in a rock pool) cannot actively seek their food but captures anything that falls or brushes into its tentacles. • Examples of prey include: • Small crabs; • Shrimps; • Small fish.
• Beadlets are very territorial and have been seen, over days, to nudge rivals until one of them moves, by slowly creeping along the floor.
• Snakeslock anemone ( Anemonia viridis) • Can occur in 2 colours, grey-purple (normal) and green due to symbiotic colonisation of its cells by an alga.
• Snakeslock anemone feeds like the beadlet one, but unlike the beadlet it cannot withdraw its tentacles as the tide recedes and is thus restricted to deeper rock pools in the middle and lower shore.
• Snakeslock often live under the larger brown fucus seaweeds to prevent dehydration. • Common on west but not east coasts of UK.
• Dogwhelks (Nucella lapillus) • Readily identified by having a groove along the underside edge of the shell. The groove allows gaseous exchange in water during shell boring operations.
• Great deal of variation in shell size, colour, thickness, shape.
• Dogwhelks eat barnacles, mussels and limpets. The mouth contains a structure called a radula which a rasping tool that has been adapted as a shell boring instrument with additional chemical secretion. Typical boring time for a barnacle shell is 48 hours. Photo shows dogwhelk feeding on a mussel.
• Dogwhelks are adaptive feeders according to prey availability.
• They are mainly located in the middle and lower shores.
• Blenny / Shanny(Lipophrys pholis) • Fish of length 5-10 cm, lives under algae in rock pools in the middle shore and can survive out of water for long periods by retaining water in its gill cavity.
• Carnivore with powerful jaws that allow it to crush barnacles, crabs and other prey. • Tompot blenny (Parablennis gattorugine) shown here is less able to survive dessication and lives lower down and off the shore in deeper water.
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FILTER FEEDERS, SCAVENGERS AND SEDIMENT FEEDERS
• Included here are sponges and mussels which are filter feeders, removing food from water taken into the animal filtered and expelled.
• Barnacles (Semibalanus balanoides) is the commonest species around Dale.
• This photograph is of another species of barnacle called Chthamalus.
• Barnacles are CRUSTACEANS and encrust the rocks making the surface razor sharp. • Filter feeders only when covered in water using feathery appendages on modified legs.
• Chthamalus and Semibalanus show the competitive exclusion principle where they compete for space on rocks; in conditions which suit Semibalanus they push Chthamalus off the rocks..
• On drier higher parts of the shore and on exposed shores Chthamalus is the superior competitor
• Common shore crab (Carcinus maenus) • Crustacean which is both a carnivore and scavenger eating most animals including periwinkles, topshells and dogwhelks. The crab holds its prey in one claw, snaps of the edge of the shell and eats the soft body inside.
• Carcinus is mobile and abundant in sheltered areas, under large algae and stones which helps it to reduce the impact of environmental stress.
• It can also osmoregulate thus controlling the water content of its body which allow it to live in estuaries where the salinity is c.0.6%; it cannot survive in freshwater. Only common crab able to do this in Europe.
• Edible crab ( Cancer pagurus). • Carnivore and scavenger. • Eats mostly molluscs and lives in similar conditions to the common shore crab. • Common on middle and lower shores. • Cannot osmoregulate.
• Examples of sediment feeders: • Lugworm ( Arenicola sp)
• Sand eels
• Paddleworms • (Phyllodoce spp)
• Edible cockle • (Cerastoderma edule) • One shown here is feeding.
SEASHORE LICHENS
• Lichens are 2 organisms living in a symbiotic relationship where both partners benefit. • The coloured part of the lichen is due to an ALGA which photosynthesises and makes sugars for itself and the host FUNGAL cells in which it lives.
• The fungus holds the lichen in the best position to intercept light and absorbs water and nutrients from the rock or substrate for both partners.
• Examples of lichens are: • Tar lichens • (Verrucaria maura) • The photo shows black tar lichen. • Found as a black band on all shores but is very abundant on exposed shores.
• Photo shows green tar lichen • (Verrucaria mucosa) • Found on the middle shore.
• Yellow and orange lichens are found in the SPLASH ZONE at the top of the shore. • The top photo shows Xanthoria parietina . • The lower photo is the same lichen in close up.
• The orange lichen shown here is Calopaca and next to it Lichina confinis a black tufted lichen as shown in the lower photo.
Bibliography The photos and accompanying text were taken from the FSC The Sea Shore and Environment online websites.