|Basic Information||Biotope classification||Ecology||Habitat preferences and distribution||Species composition||Sensitivity||Importance|
Image Keith Hiscock - Himanthalia elongata and Laminaria digitata on lower shore bedrock. Image width ca XX cm.
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LR.ELR.FR.Him recorded () and expected () distribution in Britain and Ireland (see below)
In the lower eulittoral zone, limpet grazing, which limits the upward extension of low-shore species in to the mid-eulittoral (e.g. Underwood, 1979; Underwood, 1980; Underwood & Jernakoff, 1981), becomes less effective and algal turfs of Himanthalia elongata, red algae and kelp species dominate the lower shore. Physical conditions in the lower eulittoral may be optimal for macroalgae. Several species of fucoids grow faster lower on the shore than higher on the shore (Schonbeck & Norton, 1980). Rapid growth to attain a size greater than 5 cm, grants immunity from limpet grazing and enhances survival (see Hawkins & Hartnoll, 1983 for review).
Brown algal canopy:Fucus serratus cannot withstand too much turbulence created by wave action, whilst Fucus serratus persists in the biotope, under wave exposed conditions the biotope is dominated by Himanthalia elongata. The cover provided by the 'straps' of Himanthalia elongata varies throughout the year (see recruitment processes) but the canopy it provides probably enhances the survival of an undergrowth of red algae by providing protection from excessive insolation, desiccation or by inhibiting the growth of potential rivals.
Himanthalia elongata supports a considerable epifauna and epiflora (see epiphytic species below) described by Kitching (1987).
Red algal turf and coralline algal crust: Red algae represent a major source of food for a variety of herbivores, including molluscs, crustaceans and sea urchins. Grazers may truncate the vertical distribution of some red algae or eliminate all but the most tolerant grazer-resistant species, but Chondrus crispus, Osmundea pinnatifida, and many calcareous crustose species in the biotope seem in some circumstances to be reliant upon browsing fauna to remove epiphytes or other competitors that might otherwise smother the plant (Kain & Norton, 1990).
Species such as Lomentaria articulata, Plumaria elegans and Cladophora rupestris prefer the shade of rocky overhangs or a screen of larger fucoids, and may become scarce if shaded surfaces are lacking. Osmundea pinnatifida can become more abundant further upshore in the eulittoral zone as long as it is shaded. Corallina officinalis, however, can rise further upshore in open sunlight than in shade provided that it is in damp depressions or runnels, indicating that strong sunlight does not harm it when desiccation is minimal (Lewis, 1964).
Epiphytic species:To obtain a better position in the 'struggle for light', smaller, non-parasitic algal species may grow as epiphytic algae on larger plants, and in most instances are only superficially attached to their host (Lüning, 1990). Epiphytic algae decrease the growth rate of their host, increase the probability of breakage, and may reduce reproductive output (d' Antonio, 1985).
On exposed shores the 'straps' of Himanthalia elongata have few epiphytes, however in slightly more sheltered locations they may develop a 'microforest' of filamentous algae, which provides a habitat for a variety of faunal epiphytes. Kitching (1987) recorded 105 species of flora and fauna on Himanthalia elongata plants in Lough Hyne. The upper surface of the buttons were very resistant to colonization by epiphytes while the underside of the buttons were usually colonized by Bryozoa and spirorbid worms. The straps were frequently covered in a microforest of filamentous algae, such as Ectocarpus siliculosus, Ceramium pedicellatum and Ulva prolifera. Fauna such as the gastropods Rissoa pavida, juvenile Helcion pellucidum and amphipods, were often associated with the filamentous epiphytes. The cushion-like brown algae Elachista scutulata occurs exclusively on Himanthalia elongata (Lüning, 1990). As a protection against epiphytes, young actively growing plants of Himanthalia elongata regularly shed off the outer layer of their outer-most cell wall (Filion-Myklebust & Norton, 1981). However, Elachista scutulata by-passes the cell shedding mechanism if its host by growing in cryptostomata (invaginations with hairs) and other natural breaks in the host thallus surface, where cells are not removed (Russell & Veltkamp, 1984).
Cell-shedding has also been detected in crustose coralline algae that grow beneath the brown algal canopy. In this instance, however, it is a case of ridding their surfaces of algal gametophytes (Masaki et al., 1981).
Where competition for space and light restricts the occurrence of Palmaria palmata on rock, the species often has an epiphytic habit on other algae, especially kelps.
Sessile and mobile epilithic species:Species such as the barnacles, Semibalanus balanoides and Chthamalus spp., limpet, Patella vulgata, gastropod molluscs, Littorina neglecta and Nucella lapillus, and the mussel, Mytilus edulis, are dominant species within the biotope, although as algal cover increases, so does competition for space.
Barnacles remain most numerous in the most wave exposed situations in the biotope, especially on vertical surfaces, steep slopes facing seawards and mounds rising above seaweed covered flats as recumbent fronds of macroalgae and red algal turf make flat surfaces less hospitable for barnacles. Algal competition for space in the lower eulittoral not only curtails the distribution of Semibalanus balanoides and Chthamalus spp. but also suppresses the penetration of Balanus perforatus up the shore (Lewis, 1964).
Density and size of Patella vulgata in the lower eulittoral is highly variable, and although a common species in the ELR.Him biotope, numbers in macroalgae dominated biotopes are usually less than on barnacle dominated biotopes but individuals can achieve a greater size (Lewis, 1964).
Nucella lapillus is an important intertidal predator and preys mainly on barnacles and mussels but may also prey on cockles, other bivalves and gastropods. Crothers (1985) suggested a mean annual consumption of 15-20 mussels per dog whelk (Largen, 1967a; Bayne & Scullard, 1978) and reported rates of 0.5 or 0.59 mussels/day or 1.1 Semibalanus balanoides /day in summer (Connell, 1961; Fretter & Graham, 1962; Anala, 1974). Dog whelks avoid dense mussel beds, preferring the diffuse margins between the mussel bed and the surrounding barnacle dominated substratum, or solitary mussels (Petraitis, 1987; Fretter & Graham, 1994; Davenport et al., 1996). This was partly because mussels can immobilise gastropods (Nucella lapillus and Littorina spp.) by entangling the gastropods with their byssus threads.
Many other animals are found in the biotope, but do not make a distinct contribution to the appearance of the shore. However, a species that may be apparent is the anemone Actinia equina that benefits from the damp conditions of pits and crevices amongst algae. Numerous small and specialised habitats exist within the biotope. On the algae or on damp rock beneath gammarid amphipods, the isopod Idotea, small hydroids and bryozoans (Dynamena pumila and Flustrellida hispida especially) and other small gastropod molluscs may be found.
This review can be cited as follows:
Budd, G.C. 2002. Himanthalia elongata and red seaweeds on exposed lower eulittoral rock. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 01/08/2014]. Available from: <http://www.marlin.ac.uk/habitatecology.php?habitatid=360&code=1997>