Zonation of algae and sessile invertebrates in the Glénan Archipelago. Biologic definition of bathymetric zones

Abstract

Zonation of algae and sessile invertebrates in the Gl6nan Archipelago. Biologic definition of bathymetric zones. The GI6nan Archipelago was investigated, from the surface to a depth of 60 m, by SCUBA diving. Four distinct communities ("peuptements") have been determined that fit into the system of zonation defined by the Genoa Symposium (1957). The results are compared with observations made in the English Channel (CA~IOCH 1968) and in the Atlantic Ocean (GLEMAI~C 1971). Since illumination depends upon the angle of the rocky face, photophilic species exhibit a maximum range when the rock surfaces are horizontal. The sublittoral zone is dominated by laminarians. They form two distinct communities with the animal and vegetal species they overshadow. The upper community is characterized by Laminaria digitata (LINNI~) L~ouRovx (horizontal rocky face from 0 to 6 m; vertical ro&y face from + 0.5 to --3 m). The lower cummunity, characterized by L. hyperborea (Gv~,mER) FOSLIE has a greater vertical extension (horizontal: --6 m to --26 m; vertical: --3 to --30 m). The circalittoraI zone is colonized by several animal species growing in a ramified manner: the upper community is characterized by Axinellidae (--30 m), the lower by DendrophyIlia eornigera (LAMAgCX) (--55 tO --60 m). Upright algae disappear somewhere between--40 and --47 m.

Development pattern of an infralittoral bryozoan community in the western Mediterranean Sea

“…A certain likeness is also found with the 'phases d e recruternent'and 'd'installation' described by Castric Fey (1974) and Castric (1977) for a community in the English Channel, where in 11 mo about 75 % of the species growing on the surrounding rocks settled on the artificial substrates.…”

“…The evolution of benthic populations on natural and artificial substrates was divided up into well-defined stages by determining the main categories of environmental factors governing the development process while looking for signs that the final stage or climax has been reached (Simon Papyn 1965, Bellan Santini 1970, Huve 1970, Castric Fey 1974, Castric 1977. The importance of some physical and biotic factors in controlling community development has been underlined by research in caves (Vacelet 1976, Harmelin 1980, 1983, a relatively simple environment due to the predominating influence of a comparatively small number of environmental factors and their stability.…”

Continuous underwater light measurement near Helgoland (North Sea) and its significance for characteristic light limits in the sublittoral region

“…12) 11 Jerlov water type calculated from data of authors 12 Boutler et al (1974) 13 depth below E.L.W.S. 14 measured by thermopile is Castric-Fey et al (1973) 16 Descatoire et al (1969) 17 young plants 18 Neushul (1971) 19 below canopy of…”

“…near Helgoland) has been recognized by more and more workers and regarded as the uppermost part of the sublittoral region (see Table 4). Laminaria digitata is a typical inhabitant of the infralittoral fringe (Castric-Fey et al, 1973) and is specially adapted for this habitat by its flexible stipe. Kain (1976) observed that this species, together with others, colonised cleared areas well below its usual zone, but was outcompeted after 4 years by L. hyperborea which finally overshadowed the other species due to its possession…”

Growth Strategies of Three Laminaria Species (Phaeophyceae) Inhabiting Different Depth Zones in the Sublittoral Region of Helgoland (North Sea)

“…On most European coasts Laminaria digitata inhabits the uppermost part of the sublittoral region, whereas L. hyperborea and (locally) L. saccharina dominate the middle and deeper parts of the kelp zone (Kain, 1962;Castric-Fey et al, 1973; Gayral & Cosson, 1973). L. digitata is well adapted for colonizing the upper sublittoral region, e.g.…”