Quantitative ecological distribution of the Jaera albifrons group of species in the Baltic

Abstract

Abstract Habitat preferences based on quantitative samples are described for three species of the Jaera albifrons group in selected areas of the Skagerrak, Kattegat and Baltic. In all three regions J. ischiosetosa occurred most commonly beneath stones in shallow water and J. praehirsuta amongst fucoids, both in sheltered shores, whilst in the Skagerrak and Kattegat typical J. albifrons occurred most abundantly under stones on more exposed shores. Factors determining distribution seemed to be similar to those relating to the same three forms in Britain and confirm the view that they are distinct, sympatric species. In addition, as in Britain in sheltered brackish localities, J. albifrons showed a gradual but more pronounced change in body form until in the Baltic proper it was distinguishable as a separate brackish water form previously referred to as J.a. syei. This was particularly common amongst fucoids, especially in the absence of J. praehirsuta from that substrate.