Explaining ecological shifts: the roles of temperature and primary production in the long‐term dynamics of benthic faunal composition

Abstract

Predicting the ecological consequences of environmental change requires that we can identify the drivers of long‐term ecological variation. Biological assemblages can exhibit abrupt deviations from temporal trends, potentially resulting in irreversible shifts in species composition over short periods of time. Such dynamics are hypothesised to occur as gradual forcing eventually causes biological thresholds to be crossed, but could also be explained by biota simply tracking abrupt changes to their environment. Here, we modelled temporal variation in a North Sea benthic faunal assemblage over a 40‐year period (1972–2012) to test for changes to temporal trends of biota and determine whether they could be explained by underlying patterns in sea temperature and primary production. These extrinsic factors were postulated to influence community dynamics through their roles in determining and sustaining the metabolic demands of organisms, respectively. A subset of mainly large and long‐lived taxa (those loaded on the first principal component of taxa densities) exhibited two significant changes to their temporal trends, which culminated in a shift in assemblage composition. These changes were explained by an increase in pelagic primary production, and hence detrital food input to the seabed, but were unrelated to variation in sea temperature. A second subset of mainly small and short‐lived taxa (those loaded on the second principal component) did not experience any significant changes to their temporal trends, as enhanced pelagic primary production appeared to mitigate the impact of warming on these organisms. Our results suggest that abrupt ecological shifts can occur as biota track underlying variation in extrinsic factors, in this case primary production. Changes to the structure of ecosystems may therefore be predictable based on environmental change projections.

Shifts in trait-based and taxonomic macrofauna community structure along a 27-year time-series in the south-eastern North Sea

“…However, for the hydroclimatic shift in 2014 no congruent changes in taxonomic and trait-based structures were found. The regimes and shifts in taxonomic and trait-based long-term variability, found in the study area, corresponded to shifts and changes, which were detected in the whole marine and North Sea ecosystem [49, 94, 95].…”

Uncovering the environmental drivers of short-term temporal dynamics in an epibenthic community from the Western English Channel

“…This pattern has been previously observed in the macro-infauna at L4, with deposit feeders rapidly responding to phytodetrital input with an increase in abundance, while predators and scavengers responded more slowly with an increase in biomass (Zhang et al ., 2015). While many studies have concluded that benthic communities can be structured by phytodetrital input over both short-term and decadal scales (Buchanan, 1993; Josefson et al ., 1993; Dauwe et al ., 1998; Wieking & Kröncke, 2005; Frid et al ., 2009 a , 2009 b ; Clare et al ., 2017) clear responses to organic input from benthic fauna can be difficult to detect (Graf et al ., 1982; Reiss & Kröncke, 2004). The ‘food bank’ hypothesis suggests that large reserves of labile organic matter in sediments can sustain benthic communities at constant levels of abundance on a year round basis, and clear responses to phytodetrital input are difficult to detect as a consequence (Mincks et al ., 2005; Kędra et al ., 2012; Włodarska-Kowalczuk et al ., 2016).…”

“…The trophic structure of North Sea macrofauna communities was found to reflect differences in the relative quality of organic matter received (Dauwe et al ., 1998; Wieking & Kröncke, 2005), and between 55% and 84% of year to year variability in benthic infaunal abundance off the coast of Northumberland was explained by changes in primary production (Buchanan, 1993). A marked increase in macrofaunal abundance in the same area in the 1980s was attributed to increases in phytodetrital input (Frid et al ., 1996), as were decadal-scale variations in taxonomic composition (Frid et al ., 2009 a , 2009 b ; Clare et al ., 2017). Josefson et al .…”

Comparison of biological and ecological long-term trends related to northern hemisphere climate in different marine ecosystems

“…Quantitative and qualitative changes in phytoplankton have unavoidable consequences at the other trophic levels. Several studies of benthic communities revealed that their diversity and function depended on the amount and quality of organic matter produced in the water column, even at extreme depths (Rowe and Pariente 1992;Clare et al 2017). The DFA's results of the Arctic HAUSGARTEN time-series (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016) revealed strong relationships between the phytoplankton composition and concentrations of biogenic sediment compounds, indicating organic matter in surface sediments with the explanatory variables chosen for our analysis.…”