ECOLOGICAL GRADIENTS EXPRESSED BY BENTHIC FORAMINIFERAL ASSEMBLAGES ALONG THE E MEDITERRANEAN SHELF (40 M DEPTH) OFF ISRAEL

The shallow continental shelf of the SE Mediterranean off Israel constitutes the distal part of the siliciclastic Nile littoral cell. Foraminiferal faunas were collected from a N-S transect parallel to the coast at ~ 40 meter depth. Living (Rose Bengal stained) and dead benthic foraminifera were examined at intervals of 0.5 or 1.0 cm, from the surface down to 5 cm.

Abundance, diversity and composition of living and dead assemblages of benthic foraminifera vary according to substrate and location. Assemblages of the carbonate substrate north of Haifa grade into the more siliciclastic substrate of the southern shelf, controlled by Nilotic factors. Vertical distribution of living foraminifera in the top 5 cm of sediment is controlled by oxygen concentration, substrate and seasonal changes.

Sandy-silty sediments of the northern shelf are more carbonate-rich, seagrass dominated, are better ventilated, and have a more abundant and diverse fauna than do the equivalent sediments from south of Haifa. Living foraminifera are found right through the upper 5 cm of sediment. Hyaline plano-convex species are prominent.

To the south, Nile - derived silty-clayey sediments bear an assemblage dominated by thin, smooth-tested forms with rounded periphery, mostly planispiral to low trochospiral. More dysoxic, clayey sediments here had living benthics limited mostly to the uppermost 2 cm, although a few were found deeper, mimicking deep infaunal species. Some species known to be epiphytes were found free in clayey sediment between 4-5 cm, and appear highly tolerant to a variety of oxygen levels.

Taphonomy significantly affected assemblages of agglutinated foraminifera with organic cements. Some very abundant living species were absent or rare in the dead assemblages due to post-mortem disintegration of their delicate tests. Alternatively, some miliolids showing high abundances in the dead assemblage were rarely found alive, indicating seasonality or high rates of turnover.