Species diversity, functional complexity and rarity in Arctic fjordic versus open shelf benthic systems

Abstract

We present a cross-system comparison of benthic species pools, species diversity, functional complexity and rarity in 2 typical Arctic coastal systems: an open shelf marginal sea and fjords (semi-enclosed, geologically younger basins remaining under strong terrestrial influences). A total of 388 van Veen grab samples were collected in the Barents Sea and 3 west Spitsbergen fjords (divided into inner and outer basins). Thirty percent of species were recorded only in fjords, questioning the common notion of the fjordic communities being merely subsets of the offshore species pools. Inner fjords, outer fjords and the open shelf hosted communities that differed significantly in terms of species composition and diversity. Species richness, examined at the scales of both the ecological zone and an individual sample, was severely depleted in inner fjordic basins. The congruence of the patterns across taxonomic groups employing different life histories (benthic vs. pelagic dispersal) pointed to habitat deterioration rather than dispersal barriers as a factor responsible for the fjordic diversity clines. The between-habitat differences in functional diversity were expressed in decreased functional evenness and a decline in suspension-feeding, sedentary and large tube-dwelling species in fjords, affecting infaunal habitat complexity. Species redundancy declined across the shelf − outer fjord − inner fjord environmental gradients, suggesting a higher resilience of shelf systems. The environmental deterioration of fjordic basins did not result in the reduction of rare species. These results should be applied to strategies for managing open shelf and fjordic habitats in the Arctic.KEY WORDS: Biodiversity · Rarity · Functional diversity · Redundancy · Benthos · Arctic Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 463: [73][74][75][76][77][78][79][80][81][82][83][84][85][86][87] 2012 They are geologically young areas (produced after the last glacial maximum some 17 000 years BP), and are regarded as ecologically immature, non-steadystate systems that have been evolving over relatively short time scales (Syvitski et al. 1987). Two mechanisms are usually cited as possible causes of the fjordic diversity impoverishment: (1) the barrier hypothesis points to the geomorphologic barriers that prevent a number of open shelf species from colonizing the fjordic habitats; (2) the habitat hypothesis states that lower diversity in fjords is due to the less favorable environment relative to offshore habitats (Buhl-Mortensen & Höisaeter 1993). The barrier hypothesis assumes that shelf seas serve as local species pools for fjordic biocenosis. Fjord communities are often regarded as range extensions of shelf communities that are filtered by barrier or habitat filters.In Arctic fjords, the main environmental gradients/ barriers are produced by the inflows of glacial meltwaters that are usually located in inner basins (Syvitski et al. 1987). Meltwaters are loaded with high levels of ...

From the worm’s point of view. I: Environmental settings of benthic ecosystems in Arctic fjord (Hornsund, Spitsbergen)

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