Mapping Antarctic Suspension Feeder Abundances and Seafloor Food-Availability, and Modeling Their Change After a Major Glacier Calving

Abstract

Seafloor communities are a critical part of the unique and diverse Antarctic marine life. Processes at the ocean-surface can strongly influence the diversity and abundance of these communities, even when they live at hundreds of meters water depth. However, even though we understand the importance of this link, there are so far no quantitative spatial predictions on how seafloor communities will respond to changing conditions at the ocean surface. Here, we map patterns in abundance of important habitat-forming suspension feeders on the seafloor in East Antarctica, and predict how these patterns change after a major disturbance in the icescape, caused by the calving of the Mertz Glacier Tongue. We use a purpose-built ocean model for the time-period before and after the calving of the Mertz-Glacier Tongue in 2010, data from satellites and a validated food-availability model to estimate changes in horizontal flux of food since the glacier calving. We then predict the post-calving distribution of suspension feeder abundances using the established relationships with the environmental variables, and changes in horizontal flux of food. Our resulting maps indicate strong increases in suspension feeder abundances close to the glacier calving site, fueled by increased food supply, while the remainder of the region maintains similar suspension feeder abundances despite a slight decrease in total food supply. The oceanographic setting of the entire region changes, with a shorter ice-free season, altered seafloor currents and changes in food-availability. Our study provides important insight into the flow-on effects of a changing icescape on seafloor habitat and fauna in polar environments. Understanding these connections is important in the context of current and future effects of climate change, and the mapped predictions of the seafloor fauna as presented for the study region can be used as a decision-tool for planning potential marine protected areas, and for focusing future sampling and monitoring initiatives.

Calving Event Led to Changes in Phytoplankton Bloom Phenology in the Mertz Polynya, Antarctica

“…This would therefore restrict the bloom to the eastern part of our study zone in these years, where we found significant higher biomass. A similar 50% to 80% increase in SIC (relative to the precalving period) was also observed (Campagne et al, 2015; Jansen et al, 2018) in the Mertz polynya. Interannual variability in SIC has been reported by Fraser et al (2019), where they demonstrated that fast ice regulates the size and the total sea ice production in the Cape Darnley polynya.…”

“…Iron is thought to be particularly enriched in the mCDW, as the mCDW comes in contact with the shelf before intruding between 100 and 300 m in the polynya (Moreau et al, 2019; Silvano et al, 2017). Biomass and net community production doubled in the shallow waters (<500 m) over the continental shelf in the eastern part of the polynya after calving (Jansen et al, 2018; Shadwick et al, 2017). Our results follow these previous observations.…”

“…SIC increased, especially between 140°E and 142°E, where the B9B grounded (Dragon et al, 2014). This is not the case where the MGT calved and further east (Jansen et al, 2018). It was suggested that in this area, the breakup of the sea ice postcalving occurs later in the year.…”

Integrated assessment of the spatial distribution and structural dynamics of deep benthic marine communities

“…Modeling work indicates widespread suspension feeder cover on the banks (Jansen et al. ), and distinct communities of benthic macroinvertebrates particularly along the steep edges of the banks and the coastal and continental slopes (Jansen et al. ).…”

“…Diverse and abundant benthic macrofaunal communities are found along the shelf-break and on the shallower section of the shelf between 200 and 600 m . Modeling work indicates widespread suspension feeder cover on the banks (Jansen et al 2018a), and distinct communities of benthic macroinvertebrates particularly along the steep edges of the banks and the coastal and continental slopes (Jansen et al 2018b). A more detailed descriptive analyses of the fish community inhabiting the George V shelf can be found in Causse et al (2011), and a detailed description of the benthic invertebrate communities in Post et al (2011).…”