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Abstract
Predicting the myriad effects of climate change on ecological communities is a major challenge for scientists, and to date relatively few studies have focused on the effects of sea freshening on species interactions. In particular, changes in keystone species predatory effects could be pervasive. Here, we assess the consequences of decreasing salinity on the ecological impact exerted by a keystone predatory sea star, Asterias rubens. We quantified sea star functional responses (FRs; per capita predation as a function of prey density) under decreasing salinity treatments aligned with climate change projections (18ppt, 15ppt, 12ppt). Furthermore, we combined FRs with larval recruitment estimates, i.e. ecological “Impact Potential”, to act as an ecological indicator of predator population-level responses under this environmental change. Attack and maximum feeding rates of sea stars were reduced by decreasing salinities, with no instances of predation found at 12ppt. Given that decreasing salinities also reduced larval sea star recruitment, the overall Impact Potential of this keystone predator species was lessened by decreased salinity. Sea freshening projections by the end of this century could thus drive significant decreases in the effects of this keystone predator, with serious implications for the structuring and functioning of ecological communities.
Highlights
Climate change is a major threat to global biodiversity (Thomas et al 2004; Harley 2011; IPBES 2019), predicting the extent of its role in driving biodiversity loss has proven difficult (Urban 2015), with a vast suite of biotic and abiotic consequences likely (Brook et al 2008)
Asterias rubens were collected from the Baltic Sea, Kiel Fjord (54.329577, 10.148900), between the 19th and 21st February 2018, using traps consisting of 50 × 50 × 20 cm PVC pipe structures, with an entrance on one side, covered with a 1 mm mesh and filled with crushed blue mussels (Mytilus edulis) as bait (Nour et al 2020)
Attack rates decreased and handling times increased with decreasing experimental salinity (Table 1; Fig. 1). These functional responses (FRs) parameter trends mirrored the larval recruitment data, with a mean of 2.67 larvae per 10 ml surviving to settlement under 18ppt conditions, a mean of 1.00 larva per 10 ml surviving under 15ppt conditions, and zero surviving at 12ppt (Table 1)
Summary
Climate change is a major threat to global biodiversity (Thomas et al 2004; Harley 2011; IPBES 2019), predicting the extent of its role in driving biodiversity loss has proven difficult (Urban 2015), with a vast suite of biotic and abiotic consequences likely (Brook et al 2008). Ocean acidification and changing weather patterns are well documented (Harley et al 2006), sea freshening is a neglected outcome of climate change (Bindoff & Hobbs 2013). Salinity changes occur as a result of water cycle strengthening, with warm air able to hold and distribute more water, meaning greater evaporation and greater precipitation This has been described as a “rich get richer” mechanism (Chou et al 2009), whereby the ocean surface in areas of net evapora tion is likely to become saltier, and areas of net precipitation likely to get fresher with amplified patterns of precipitation and evaporation (Held & Soden 2006; Durack et al 2012). The Baltic Sea is one area likely to freshen (Grawe et al 2013)
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