Disturbance effects of kelp thalli on structure and diversity of a coastal Arctic marine soft-bottom assemblage

The effects of biotic disturbances, like seaweed whiplash, on the diversity of benthic communities are well documented for temperate coastal systems, yet missing for Arctic benthos. In Arctic soft-bottom habitats, kelp thalli occur either continuously (e.g. trapped by sediment) or sporadically (by drifting on the sediment) after detachment from rocky shores. To explore whether a kelp thallus can disturb the structure and diversity of a coastal Arctic softbottom assemblage, we continuously fixed a single thallus of the kelp Saccharina latissima to or sporadically (i.e. biweekly) moved it on the sediment and compared treatment effects to unmanipulated plots (=controls). On 6 September 2013 (i.e. after 73 days of manipulation), one sediment core was taken from each of the 30 plots (n = 10), from which the number of individuals of each of the 45 encountered animal taxa was recorded. The continuous presence of an experimentally fixed kelp thallus significantly reduced the number of individuals on average by 27 %. This disturbance effect was even stronger, on average 49 %, where a kelp thallus was biweekly moved on the sediment. Likewise, taxon richness was lowered by an average of 19 and 36 % where a S. latissima thallus was continuously or sporadically present, respectively. While the composition of taxa was also significantly different among all treatment groups, evenness and biomass were unaffected by kelp treatments. We conclude that the presence and already movements of a single kelp thallus can promote small-scale patchiness in near-shore soft-bottom assemblage structure and diversity and exemplify a significant connection between rocky and sedimentary coastal habitats

Do bioturbation and consumption affect coastal Arctic marine soft-bottom communities?

Biotic factors such as bioturbation and predation affect abundance and species composition of marine soft-bottom communities from tropical to temperate regions, but their impact has been rarely investigated in Arctic coastal systems. By conducting a factorial manipulative field experiment, we excluded the bioturbating lugworm Arenicola marina and predacious consumers from a sedimentary nearshore area in Kongsfjorden (Spitsbergen) for 70 days to explore their role in structuring the benthic community. The removal of A. marina caused an increase in average species number by 25 %, a doubling increase in the average number of individuals and an increase in dry mass of benthic organisms by, on average, 73 % in comparison with untreated areas. Additionally, community composition was significantly modified by lugworm exclusion resulting in higher average densities of the cumacean Lamprops fuscatus (4.2-fold), the polychaete worms Euchone analis (3.7-fold) and Pygospio cf. elegans (1.5-fold), the bivalve Crenella decussata (2.8-fold) and the amphipod Crassicorophium crassicorne (1.2-fold), which primarily contribute to the observed differences. Consumer exclusion, by contrast, showed no effects on the response variables. This result was independent from bioturbation due to missing interaction between both biotic factors. We conclude that present levels of bioturbation may considerably affect Arctic coastal soft-bottom communities. In contrast, predation by macro-epibenthic consumers currently seems to be of minor importance. This might change in a predicted warmer Arctic with assumed higher predator abundances and a northward expansion of boreal consumers

Do bioturbators affect Arctic soft bottom communities?

A general understanding of drivers influencing biodiversity and the functioning of ecosystems is a central focus in ecology, especially in times of global change. Marine soft-bottom habitats as important food sources for higher trophic levels are expected to react to these global changes with alterations in composition and structure of benthic flora and fauna. However, little is known about the functioning of these habitats in high latitudes such as Arctic sedimentary environments. Bioturbation in a broad sense is the biological reworking of soils and sediments by all kinds of organisms. This process is, as well as consumption, an important driver of benthic species occurrence and dynamics. This study has determined the effects of bioturbation on benthic assemblages in a shallow Arctic soft-bottom habitat. A manipulative field experiment was conducted in l<ongsfjorden, Svalbard (79° N, 10° E), in summer 2012. Species composition in this fjord was dominated by crustaceans (50 %), polychaetes (32 %) and mollusks (13 %). The effects of bioturbation were determined using three bioturbation treatments, accomplished in an in-situ experiment: (i) exclusion of bioturbating animals by burying a plastic mesh into the sediment, (ii) procedural control treatments without a mesh but with the same disturbance as in areas with mesh, and (iii) un-treated areas as controls. Additionally, different cage treatments were installed at bioturbation areas to test for consumption effects, apart and combined with bioturbation. Exclusion of bioturbators showed significant effects on species richness, number of individuals and dry mass of benthic organisms, as well as on species composition, while predation had no effects. lt is suggested that bioturbation is a main driver shaping community patterns in Arctic softbottom environments, while predation seems to be of minor importance

Effects of thallus disturbance on abundance and biomass of soft-bottom species in Kongsfjorden in summer 2013

The effects of biotic disturbances, like seaweed whiplash, on the diversity of benthic communities are well documented for temperate coastal systems, yet missing for Arctic benthos. In Arctic soft-bottom habitats, kelp thalli occur either continuously (e.g. trapped by sediment) or sporadically (by drifting on the sediment) after detachment from rocky shores. To explore whether a kelp thallus can disturb the structure and diversity of a coastal Arctic soft-bottom assemblage, we continuously fixed a single thallus of the kelp Saccharina latissima to or sporadically (i.e. biweekly) moved it on the sediment and compared treatment effects to unmanipulated plots (= controls). On 6 September 2013 (i.e. after 73 days of manipulation), one sediment core was taken from each of the 30 plots (n = 10), from which the number of individuals of each of the 45 encountered animal species were recorded. The continuous presence of an experimentally fixed kelp thallus significantly reduced the number of individuals on average by 27 %. This disturbance effect was even stronger, on average 49 %, where a kelp thallus was biweekly moved on the sediment. Likewise, taxon richness was lowered by an average of 19 and 36 % where a S. latissima thallus was continuously or sporadically present, respectively. While the composition of taxa was also significantly different among all treatment groups, evenness and biomass were unaffected by kelp treatments. We conclude that the presence and already movements of a single kelp thallus can promote small scale patchiness in near-shore soft-bottom assemblage structure and diversity and exemplify a significant connection between rocky and sedimentary coastal habitats