South aegean (eastern mediterranean) continental slope benthos: macroinfaunal - environmental relationships  <B>South aegean (eastern mediterranean) continental slope benthos: macroinfaunal - environmental relationships</B><P></B><B>A.TSELEPIDES AND A. ELEFTHERIOU</B> <I><P> Institute of Marine Biology of Crete, P.0. Box 2214, 71003 Iraklio, Crete, Greece</I><B><P> ABSTRACT. </B> Macrobenthic faunal composition, abundance, biomass and diversity were investigated to determine factors regulating faunal distribution over the continental slope of the island of Crete in the oligotrophic South Aegean Sea (Eastern Mediterranean). Simultaneous sediment measurements of physicochemical characteristics and water column chemistry were undertaken.<BR> The hydrobiological profiles revealed the existence of a strongly stratified, oligotrophic two-layer water column, with a pronounced chlorophyll <I>a </I>(chl<I>a</I>) maximum at 70- to 100-m depth. In such a system energy transfer is considered to be conveyed to the traditional food chain via the "microbial loop."<BR> Mean benthic biomass, abundance and diversity decreased with depth, with a transition zone occurring at 400- to 500-m, beyond which values declined sharply. Polychaete feeding modes displayed a bimodal feeding trend, with surface deposit and carnivorous feeders dominating the shallow (200-, 300-, and 400-m) and deep (500- and 700-m) stations respectively. Classification and ordination analyses revealed the existence of four principal clusters divided by a faunal boundary between 400 and 500 m. Chemical sedimentary data declined with depth, chl<I>a</I> reaching almost undetectable levels beyond 700 m. Sediment particle size analysis produced an almost constant (85-98%) silt-clay fraction. Redox potential measurements proved sediments to be well oxygenated at all depths and, therefore, poor in organic loads.<BR> Significant correlations between macrofauna and sediment parameters (and especially with chl<I>a</I>) led to the conclusion that food availability is the principal regulating factor in the system. Such being the case, the prevailing hydrographic features which structure the pelagic food web directly affect the propagation of organic matter to the benthos.<I><P> In: G.T. Rowe and V. Pariente (eds.) Deep-Sea Food Chains and the Global Carbon Clycle, 139-156.</I> 1992 <I>Kluwer Academic Publishers. Printed in the Netherlands.</I><P>