Size differences of Arctic marine protists between two climate periods—using the paleoecological record to assess the importance of within‐species trait variation

Abstract

Mean body size decreases with increasing temperature in a variety of organisms. This size–temperature relationship has generally been tested through space but rarely through time. We analyzed the sedimentary archive of dinoflagellate cysts in a sediment record taken from the West Greenland shelf and show that mean cell size decreased at both intra‐ and interspecific scales in a period of relatively warm temperatures, compared with a period of relatively cold temperatures. We further show that intraspecific changes accounted for more than 70% of the change in community mean size, whereas shifts in species composition only accounted for about 30% of the observed change. Literature values on size ranges and midpoints for individual taxa were in several cases not representative for the measured sizes, although changes in community mean size, calculated from literature values, did capture the direction of change. While the results show that intraspecific variation is necessary to accurately estimate the magnitude of change in protist community mean size, it may be possible to investigate general patterns, that is relative size differences, using interspecific‐level estimates.

Intraspecific size variation in planktonic foraminifera cannot be consistently predicted by the environment

“…This result shows that contrasting patterns may be found when analysing different organizational levels, and emphasizes the importance of intraspecific variation. Indeed, recent evidence has been accumulating showing that variation within species is crucial for our understanding of macroecological and evolutionary patterns (Bolnick et al, 2011; Violle et al, 2012; Hart et al, 2016) and sometimes even surpasses the community-level effects related to variation among species (Mousing et al, 2017; Des Roches et al, 2018).…”

“…Organism size is a functional trait that influences biological processes across multiple levels of organisation: from individual physiology (Brown et al, 2004) and interactions (Emmerson and Raffaelli, 2004; Berlow et al, 2009) to populations (Damuth, 1981; Peters and Wassenberg, 1983; Jennings and Mackinson, 2003; Savage et al, 2004; Reuman et al, 2008), communities (Woodward et al, 2005; Petchey et al, 2008; Boyce et al, 2015; Gianuca et al, 2016) and ecosystems (Barton et al, 2013; Boyce et al, 2015). More specifically, size variation within species can affect species coexistence (Hart et al, 2016) and species’ responses to environmental change in marine communities (Sommer et al, 2017; Mousing et al, 2017). The ecological importance of trait variation within species is prominent (Bolnick et al, 2011; Violle et al, 2012; Des Roches et al, 2018), suggesting that our understanding of marine ecosystems might be incomplete when examined only at the level of species.…”

A review of the ecological affinities of marine organic microfossils from a Holocene record offshore of Adélie Land (East Antarctica)

“…This is also evident from the fossil record in which fossil prasinophyte phycomata have been found in sediment cores and surface sediments from the shelves of the Ross Sea, Prydz Bay, and the Antarctic Peninsula (Hannah et al, 1998;Wrenn et al, 1998;Hannah, 2006;Warny et al, 2006Warny et al, , 2009Warny, 2009;Clowes et al, 2016). In sea-ice-dominated environments, fossil prasinophyte phycomata have been associated with the sea-ice edge and increased stratification after sea-ice retreat (Mudie et al, 1992;Wrenn et al, 1998;Hannah, 2006). Pyramimonadales are considered important spring bloomers around Antarctica (Varela et al, 2002) and Greenland (Harðardóttir et al, 2014) and might be important in maintaining the heterotrophic microbial community dur-ing the winter (Harðardóttir et al, 2014).…”

“…The highest relative abundances of I. pallidum are observed in areas influenced by the melt-back of seasonal sea ice in both the Arctic and the Antarctic (Mudie, 1992;Marret and De Vernal, 1997;De Vernal et al, 2001;Kunz-Pirrung et al, 2001;Esper and Zonneveld, 2007;Bonnet et al, 2010;Pieńkowski et al, 2013b;Zonneveld et al, 2013). In the Southern Ocean, it is generally restricted to waters south of the Subtropical Front (Marret and De Vernal, 1997;Crouch et al, 2010;Verleye and Louwye, 2010;Prebble et al, 2013), but remarkably very low amounts of I. pallidum have been found in surface samples of the south-east Atlantic Ocean (Esper and Zonneveld, 2002).…”

“…In the Southern Ocean, it is generally restricted to waters south of the Subtropical Front (Marret and De Vernal, 1997;Crouch et al, 2010;Verleye and Louwye, 2010;Prebble et al, 2013), but remarkably very low amounts of I. pallidum have been found in surface samples of the south-east Atlantic Ocean (Esper and Zonneveld, 2002). In the Arctic, highest abundances of I. pallidum cysts are found in sediments of the deeper parts of the Arctic basins underlying the pack-ice margin (Mudie, 1992;Mudie and Harland, 1996). However, specimens of I. pallidum have been found in the Mediterranean and equatorial east Atlantic (Zonneveld et al, 2013).…”