Epibenthic fauna in Balsfjord. Potential food for the invasive red king crab (Paralithodes camtschaticus) with special attention to the deposit-feeding sea star Ctenodiscus crispatus

Abstract

After its introduction to the Barents Sea in the 1960’s, the red king crab Paralithodes camtschaticus has become an invasive species in northern Norwegian fjords and it is continuing to spread southward along the coast. Due to its negative effects on native benthic fauna through predation, establishing baseline studies in undisturbed fjords is important. In this study, the soft-bottom epibenthic macrofauna (> 5 mm) was investigated at four localities in Balsfjord, south of Tromsø, aiming at discussing potential prey for the red king crab. Samples were collected from the inner, outer and middle part of the fjord. The differences in species composition and biomass were linked to environmental conditions, biotic factors and general patchiness of benthic fauna. The similarities to invaded fjords, and observations of the red king crab in Balsfjord suggests that an invasion most likely will occur and the crab might reach high population densities in the next few years. An important prey item for the king crab is the mud star Ctenodiscus crispatus, which is a dominating species in northern Norwegian fjords, including Balsfjord, but whose abundance is strongly reduced in invaded areas. Little is known about its population dynamics, but this study attempts to provide some answers. Size-frequency distributions of mud stars collected during the year revealed no major recruitment events and were consistently dominated by a large mode of adult individuals, probably of many age classes. Low numbers of newly settled juveniles were observed between March and June, which could confirm spawning during mid-winter, suggested by previous studies. Patterns varied between investigated areas which indicates that depth, environmental conditions and biological interactions influence spawning, recruitment, growth and size-structures.