Modern benthic foraminifers at Northern shallow sites of Adriatic Sea and soft-walled, monothalamous taxa: a brief overview

Abstract

Sediment subsamples (0-2cm layer, >63µm fraction) from box cores taken at four sites (Stns 120, 121, 122, 123) located along a transect in theGulf of Trieste (water depth range 8-22m)were sorted for foraminifers, including soft-walledmonothalamous taxa (organic-walled allogromiids, agglutinated saccamminids and psammosphaerids). The distribution of foraminiferal species differed among samples, corresponding to differences in water depth, granulometry, distance from fresh water source and other chemical and physical parameters (temperature, salinity and dissolved oxygen). In general, the absolute and relative abundance of monothalamous foraminifers tended to decrease with distance from the coast, i.e. with distance from the inflow of the Isonzo River, whereas polythalamous taxa exhibited the opposite trend. Therewas also a switch in dominance by polythalamous agglutinated species at Stn 122 to polythalamous calcareous species at Stn 123. Among polythalamous foraminifers, the calcareous species Ammonia perlucida was dominant at the innermost station (Stn 120), together with the agglutinated species Cribrostomoides spp. and Haplophragmoides spp. These species were absent or less common at the other stations. Textularia agglutinans was abundant at the two inner stations (121, 122). Stn 122 was further characterized by Reophax nana, Leptohalysis scottii and the calcareous species Nonionella stella. The latter is also themost abundant taxa at the outer station (Stn 123) where the agglutinated taxa Reophax nana and Textularia conica are alsowell represented. All themonothalamous taxa found are previously unreported from North Adriatic waters; all are undescribed at the species level and, in most cases, at the generic level also. Two genera (Psammophaga, Vellaria), however, are common in other shallow-water settings and Micrometula, previously known from habitats ranging from coastal to deep sea, is also present. One of the allogromiid morphotypes closely resembles Goodayia rostellaum, recently described from the Black Sea. Psammophaga and Vellaria are also known from the Black Sea, but the populations are probably distinct at the species level.