Marginal marine environments of the Skagerrak and Kattegat: a baseline study of living (stained) benthic foraminiferal ecology

Abstract

This is the first detailed investigation of the distribution and ecology of living (stained) shallow water (0–6 m) foraminifera along the Skagerrak–Kattegat coast, eastern North Sea. A total of 25 species (13 agglutinated; 12 calcareous) are common in the 169 sediment surface samples which were collected from 27 geographic areas. The sediment grain size and total organic carbon (TOC) content are strongly variable and the salinity and temperature ranges were 10–31‰ and 9–30°C, respectively, at the time of sampling (July to October) but temperatures down to freezing occur during the winter. The species are divided into six environmental categories of which the first five comprise euryhaline and the sixth essentially stenohaline taxa: (1) species associated only with marsh plants, (2) species basically, but not entirely, associated with marsh plants, (3) species basically, but not entirely, restricted to non-marsh areas, (4) species solely recorded in non-marsh intertidal to subtidal environments, (5) species restricted to subtidal areas, (6) species basically living in the most open marine areas. In this region, marshes have a patchy distribution and they are small and compressed due to low tidal ranges (<40 cm). Balticammina pseudomacrescens (not reported here before) lives in the most elevated, landward, terrestrial parts of marshes and thus defines the uppermost limit of the influence of marine water. However, the marshes are generally dominated by Jadammina macrescens and Miliammina fusca at the landward and seaward sides, respectively. Jadammina macrescens is observed living epiphytically on decaying Carex leaf debris. The most widely distributed euryhaline species are Elphidium williamsoni, Miliammina fusca, Ammonia beccarii, and Haynesina germanica. The former two are common only in sediments with a mud content less than about 60%, whereas the latter two are common even in sediments with >80% mud. Ammoscalaria runiana is common only in coarse-grained sediments (<20% mud) with low TOC (≤0.7%). There are no marked biogeographic boundaries within the Skagerrak–Kattegat area but 10 of the 25 commonly occurring species have not been reported from the adjacent Baltic Sea, probably partly due to the brackish character of the water there. The southern limits of distribution of the northern species, Elphidium albiumbilicatum, Ammotium cassis, and Ophthalmina kilianensis, are in the Kattegat–Baltic Sea.