(^) The New England slope study also shows, however, that the downward increase in
diversity does not extend indefinitely: E(S 100 ) values were 50–65 at 1250 m, and only
40–55 at 2250 m. Similar results have been obtained from many slope to abyss
transects. Olabarria (2005), sampling in the Porcupine Sea Bight (NE Atlantic) with
an epibenthic sled and trawls, found an increasing number of bivalve mollusk species
from 500 to 1200 m, then consistently 41–49 species to 3500 m, and finally a modest
decrease onto the adjacent abyssal plain (Fig. 13.19). Svavarsson (1997), also towing
sledge samplers to sample upper sediment layers, found a more dramatic rise then
decrease in isopod species numbers with depth in the Arctic Ocean north of Iceland
(Fig. 13.20). Total species per sample and E(S 200 ) both showed that pattern, with
E(S 200 ) less affected by the number of individuals per sample.
Fig. 13.19 Numbers of bivalve mollusk species, with ranges overlapping depths
plotted on the abscissa. Samples were collected with sledges and trawls from the
continental slope (500 m) to the abyss in the Porcupine Sea Bight, NE Atlantic.
(^) (Data extracted from Olabarria 2005.)
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