Abstract
Climate change is influencing some environmental variables in the Southern Ocean (SO) and this will have an effect on the marine biodiversity. Peracarid crustaceans are one of the dominant and most species-rich groups of the SO benthos. To date, our knowledge on the influence of environmental variables in shaping abundance and species composition in the SO’s peracarid assemblages is limited, and with regard to ice coverage it is unknown. The aim of our study was to assess the influence of sea ice coverage, chlorophyll-a, and phytoplankton concentrations on abundance, distribution and assemblage structure of peracarids. In addition, the influence of other physical parameters on peracarid abundance was assessed, including depth, temperature, salinity, sediment type, current velocity, oxygen, iron, nitrate, silicate and phosphate. Peracarids were sampled with an epibenthic sledge (EBS) in different areas of the Atlantic sector of the SO and in the Weddell Sea. Sampling areas were characterized by different regimes of ice coverage (the ice free South Orkney Islands, the seasonally ice-covered Filchner Trough and the Eastern Antarctic Peninsula including the Prince Gustav Channel which was formerly covered by a perennial ice shelf). In total 64766 individuals of peracarids were collected and identified to order level including five orders: Amphipoda, Cumacea, Isopoda, Mysidacea, and Tanaidacea. Amphipoda was the most abundant taxon, representing 32% of the overall abundances, followed by Cumacea (31%), Isopoda (29%), Mysidacea (4%), and Tanaidacea (4%). The Filchner Trough had the highest abundance of peracarids, while the South Orkney Islands showed the lowest abundance compared to other areas. Ice coverage was the main environmental driver shaping the abundance pattern and assemblage structure of peracarids and the latter were positively correlated with ice coverage and chlorophyll-a concentration. We propose that the positive correlation between sea ice and peracarid abundances is likely due to phytoplankton blooms triggered by seasonal sea ice melting, which might increase the food availability for benthos. Variations in ice coverage extent and seasonality due to climate change would strongly influence the abundance and assemblage structure of benthic peracarids.
Highlights
Peracarids play an important role in marine ecosystems; they can influence the structure and composition of benthic communities (Duffy and Hay, 2000) and they are an important converter of biomass and organic matter in the biogeochemical cycles (Karlson et al, 2007; Dunn et al, 2009)
The expedition JR15005 with the RRS James Clark Ross worked at the South Orkney Islands in February-March 2016, a small archipelago located in the Northeast of the Antarctic Peninsula (Figures 1A,B, Griffiths, 2017)
Our study suggests that varying regimes of ice coverage and chlorophyll-a concentration strongly influence the abundance and assemblages’ structure of benthic peracarids from the continental shelf of the SO
Summary
Peracarids play an important role in marine ecosystems; they can influence the structure and composition of benthic communities (Duffy and Hay, 2000) and they are an important converter of biomass and organic matter in the biogeochemical cycles (Karlson et al, 2007; Dunn et al, 2009). Peracarid crustaceans can directly consume organic matter as deposit-feeders and feed on dead organisms from the sea bottom as scavengers; the assimilated biomass can be transferred to the higher trophic levels via direct consumption (Jeong et al, 2009; Thiel and Hinojosa, 2009; Duffy et al, 2012). Peracarids are an important source of food for benthic organisms as well as pelagic fauna such as fish and squid (Mouat et al, 2001; Padovani et al, 2012; Xavier et al, 2020). Amphipods represent a large percentage in the diet of many Antarctic species, from benthic invertebrates such as the polynoid polychaete Harmothoe spinosa, to bentho- and bathy-pelagic predators such as cephalopods (e.g., Galiteuthis glacialis), notothenioid fish (e.g., Notothenia coriiceps), and megafaunal predators like penguins (e.g., Eudyptes chrysolophus), and baleen whales (e.g., Balaenoptera borealis) (Dauby et al, 2003). It has been estimated that about 60 million tons of amphipods are consumed every year within the Antarctic food web (Dauby et al, 2003)
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