Abstract
Abstract The red king crab invaded Norwegian coastal waters in the early 1990s after having been introduced from the northern Pacific to the Russian Barents Sea coast. The crab stock increased rapidly in NE northern Norway in the latter half of the 1990s, and since 2002 there has been a commercial fishery in the eastern invaded areas. The crab is an active predator on benthic fauna especially feeding in deep soft-bottom environments. The present study is a follow-up of previous studies (2007–09) to assess the effects of the king crab predation on soft bottom species composition, ecological functioning and sediment quality. Macroinfauna (> 1 mm) was investigated in three fjord areas in the Varanger region with low, moderate and very high crab abundances, respectively. Compared with data from 1994, most benthic species were markedly reduced in abundance, in particular non-moving burrowing and tube-dwelling polychaetes, bivalves and echinoderms. However, a few species appeared to recover from 2007–09 to 2012. Changes in ecological functioning were assessed using ‘biological traits analysis (BTA)’. Following the crab invasion there was a relative reduction of suspension and surface deposit feeding species, an increase in mobile and predatory organisms and an increase in those with planktotrophic larval development. From low to high crab abundances functioning changed from tube-building, deep deposit feeding and fairly large size to free-living, shallow burrowing and rather small size. With regard to sediment reworking, downward and upward conveyors were reduced whereas surficial modifiers increased. The changes imply that sediment biomixing and bioirrigation were reduced leading to a degraded sedimentary environment. It is suggested that establishing relationships between ecosystem functioning and crab abundances may form the basis for estimating ecological costs of the crab invasion. Such knowledge is important for managing the crab in the Barents Sea area being both a non-indigenous species affecting native ecosystems as well as a valuable resource for commercial fishery.
Highlights
The red king crab (Paralithodes camtschaticus) is a non-indigenous species in the Barents Sea area
Annual scientific cruises are carried out to monitor the development of the crab stock both inside and outside the quota regulated area (QRA), which forms the basis for advice on fishery quota to the management authorities
Red king crabs were sampled at the annual cruises for monitoring of the crab stock using an enlarged version of an Agassiz trawl (6 m wide) and by traps (Stiansen et al, 2008; Hjelset et al, 2009)
Summary
The red king crab (Paralithodes camtschaticus) is a non-indigenous species in the Barents Sea area. Several impacts on benthic species assemblages in the Barents Sea area have been reported, notably loss of large specimens of prey species and changes in community composition (Falk-Petersen et al, 2011). The present study deals with effects on structure and function of soft bottom fauna in the Varanger area, located within the quota regulated area (QRA) of Norwegian management of the red king crab. It is a follow-up of previous studies of sediment infauna, epifauna and in situ sediment profile imagery (SPI) carried out in 2007–09 to assess the effects of the king crab on species composition and sediment quality (Oug et al, 2011). Data for bottom fauna from several other fjords in northern Norway without king crab were used as references for assessing the pattern and direction of changes in the Varangerfjord area
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