HORIZONTAL AND VERTICAL SPATIAL MICRODISTRIBUTION OF FORAMINIFERS IN THE SHALLOW SUBTIDAL GULF OF TRIESTE, NORTHERN ADRIATIC SEA

The spatial microdistribution of foraminifers in the shallow subtidal zone of the northernmost Adriatic Sea was examined by the method of qu adratic sampling on a sample grid. In addition to the distributions at the sediment surface, the depth horizons down to 5 cm were also inves tigated in 1 cm steps. The distributions at the sediment surface are p atchy for all of the more commonly occurring species (Reophax nanus, L abrospira jeffreysii, Eggerelloides scabra, Spiroplectinella sagittula , Miliolinella subrotunda, Triloculina affinis, Brizalina striatula, B ulimina aculeata, Elphidium advenum, Ammonia tepida, Nonionella turgid a) except Epistominella vitrea which is randomly distributed. Nonionel la turgida is specialized to feed on diatoms; therefore, it is present only in the topmost two centimeters, which also represent the oxygena ted layer of the sediment. In addition to this oxygenated surface zone , all the other species inhabit burrows of infaunal macrobenthic organ isms; however, inside these burrows only the oxygenated halo will be c olonized. Elphidium granosum is frequently found exclusively in these burrows. In contrast, Spiroplectinella sagittula seems to burrow activ ely also in the anoxic sediment. The patchiness of the foraminifers ma y be caused by specific food requirements. The trophic modes are domin ated by detritus and deposit feeding, and diatoms may be an additional source of food for Miliolinella subrotunda and Triloculina affinis.