Sediment organic carbon integrates changing environmental conditions to predict benthic assemblages in shallow Arctic seas

Abstract

In marine spatial planning, conserving adequate habitats and the food webs they support requires delineating habitats and projecting future trends. For bottom‐feeding marine birds and mammals, repeated benthic sampling over large areas to document changes and to develop predictive models of prey dispersion is quite costly. More easily monitored variables that relate strongly to the biomass and structure of benthic assemblages, and are more readily predicted from physical models of climate change, would facilitate planning efforts. The organic carbon (OC) content of sediments integrates diverse physical and biotic processes, and can be less variable over time than primary production, salinity, temperature, or position of water masses. Sediment OC further subsumes inputs at the base of food webs that can limit carbon flows to higher taxa. For the northern Bering Sea, this study explored the utility of sediment OC as a predictor of benthic assemblage types. Cluster analysis and multi‐dimensional scaling distinguished three main types along a gradient of sediment OC. The assemblage for highest sediment OC had a much greater biomass of brittlestars, diverse marine worms, and two mid‐sized, thinner‐shelled bivalves selected as prey by diving sea ducks. The assemblage for lowest sediment OC lacked brittlestars, had a much greater biomass of amphipods sought by gray whales (Eschrichtius robustus), and had a much higher biomass of two often larger or thicker‐shelled bivalves commonly targeted by walruses (Odobenus rosmarus). Areas of exceptionally low sediment OC tended towards dominance by sand dollars with low foraging value. Our study shows that sediment OC has promise as a proxy for monitoring and predicting changes in important prey assemblages in a given region. Models that link predicted hydrographic patterns to lateral advection of phytodetritus, and the resulting sediment OC, may further allow the use of physical climate models to project the future dispersion of benthic habitats for endothermic predators.

Trends in Benthic Macrofaunal Populations, Seasonal Sea Ice Persistence, and Bottom Water Temperatures in the Bering Strait Region

“…Results of this study suggest that indicators of carbon export (e.g., SCOC, sediment chl a) are correlated with higher benthic biomass, corroborating previous studies (Grebmeier et al, 2006a;Lovvorn et al, 2018). Bottom water temperature was correlated to higher benthic biomass overall, although the Mann-Kendall trend analysis didn't indicate significantly increasing temperature over time in our study for any of the three regions.…”

“…Some potential approaches include the Arctic Marine Pulses (AMP) model as well as ongoing efforts to model biological benthic hotspots and key drivers that maintain the benthic hotspots in the region (Feng et al, 2018). Lovvorn et al (2018) also recommend the development of models linking hydrographic patterns to lateral advection of phytodetritus and the descent of this material to the benthos as recorded in sediment organic carbon, which may allow the use of physical climate models to project the future expansion of benthic habitats for use by benthivorous predators.…”

“…Coincidently, increasing biomass was observed at the northern time series sites ( Figure B2). These findings highlight the importance of annual biological sampling together with physical parameter measurements to track environmental variability and change in order to develop models to help forecast future ecosystem change (Feng et al, 2018;Lovvorn et al, 2018).…”

“…Although temperature is known to be an important driver for faunal metabolic rates, bottom water temperature is less important for affecting benthic biomass compared to food supply in the northern Bering and Chukchi Seas (Grebmeier et al, 2015a). Seawater warming (Wood et al, 2015;Woodgate, 2018) and shifts in sediment composition and organic carbon content in the Pacific Arctic (Grebmeier et al, 2012(Grebmeier et al, , 2015bLovvorn et al, 2018) are physical changes that may potentially impact benthic macrofaunal community composition as well as biomass. Macrofaunal benthic biomass increases moving northward from south of St. Lawrence Island through the Chirikov Basin and Bering Strait into the Southeast Chukchi Sea, reflecting an increase in annual primary production and export of carbon to the benthos (Grebmeier et al, 2015a).…”

Climate-driven benthic invertebrate activity and biogeochemical functioning across the Barents Sea polar front

“…Whether climate-driven changes in the functional architecture of communities lead to the decline, maintenance or enhancement of ecosystem functioning will not only depend on the level of functional redundancy across multiple supporting processes [113,114] but also on the environmental circumstances under which faunal reorganization take place. As there is a strong coupling between export flux, including episodic events of sinking ice algae aggregates [115], community structure [116] and benthic carbon cycling [117], it follows that complex dependencies between trait composition and the timing and quality of organic matter are likely. A significant feature of our study was the dramatic contrast in ice cover between years, which we assume will have changed the timing of the primary production regime and the way in which energy and nutrients transit through the food web [11,31].…”