High climate velocity and population fragmentation may constrain climate‐driven range shift of the key habitat former Fucus vesiculosus

Abstract

Aim: The Baltic Sea forms a unique regional sea with its salinity gradient ranging from marine to nearly freshwater conditions. It is one of the most environmentally impacted brackish seas worldwide, and the low biodiversity makes it particularly sensitive to anthropogenic pressures including climate change. We applied a novel combination of models to predict the fate of one of the dominant foundation species in the Baltic Sea, the bladder wrack Fucus vesiculosus. Location:The Baltic Sea. Methods:We used a species distribution model to predict climate change-induced displacement of F. vesiculosus and combined these projections with a biophysical model of dispersal and connectivity to explore whether the dispersal rate of locally adapted genotypes may match estimated climate velocities to recolonize the receding salinity gradient. In addition, we used a population dynamic model to assess possible effects of habitat fragmentation. Results:The species distribution model showed that the habitat of F. vesiculosus is expected to dramatically shrink, mainly caused by the predicted reduction of salinity.In addition, the dispersal rate of locally adapted genotypes may not keep pace with estimated climate velocities rendering the recolonization of the receding salinity gradient more difficult. A simplistic model of population dynamics also indicated that the risk of local extinction may increase due to future habitat fragmentation. Main conclusions:Results point to a significant risk of locally adapted genotypes being unable to shift their ranges sufficiently fast considering the restricted dispersal and long generation time. The worst scenario is that F. vesiculosus may disappear from large parts of the Baltic Sea before the end of this century with large effects on the biodiversity and ecosystem functioning. We finally discuss how to reduce this risk through conservation actions, including assisted colonization and assisted evolution. K E Y W O R D SBaltic Sea, bladder wrack, climate change, connectivity, dispersal, fragmentation, local adaptation, range shift, salinity, species distribution modelThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Geographic variation in fitness‐related traits of the bladderwrack Fucus vesiculosus along the Baltic Sea‐North Sea salinity gradient

“…In light of our results, the predicted southward reduction of salinity (according to Jonsson et al, 2018) would be followed by a reduction in thallus size, photosynthetic activity and content of nutritious compounds in bladderwrack populations from central and western basins. In light of our results, the predicted southward reduction of salinity (according to Jonsson et al, 2018) would be followed by a reduction in thallus size, photosynthetic activity and content of nutritious compounds in bladderwrack populations from central and western basins.…”

“…However, these predictions based on species distribution models and occurrence data, show only the expected lethal effects of desalination and underestimate the consequences that future nonlethal but highly stressful conditions might have on the performance of F. vesiculosus and its interactions with competitors, grazers and epiphytes. In light of our results, the predicted southward reduction of salinity (according to Jonsson et al, 2018) would be followed by a reduction in thallus size, photosynthetic activity and content of nutritious compounds in bladderwrack populations from central and western basins. A decrease in algal size will likely impact the complexity of the habitat provided for invertebrates and fish, the lower photosynthetic activity will suppose a decrease in oxygen production and carbon fixation, and a decrease of palatability will impact the fitness and population growth of herbivores (e.g., I. balthica) and their consumers.…”

“…Thus, we hypothesize that the more are expected to convert the northern basins (currently at salinities of 4-5) into inhabitable areas for F. vesiculosus (Jonsson et al, 2018).…”

“…Notwithstanding the considerable drifting dispersal capacity of adults (see Jonsson et al, 2018;Rothäusler, Corell, & Jormalainen, 2015 for a detailed discussion), gene flow appears low and the genetic differentiation with the generation of population-specific phenotypic types is highly probable. Far from conclusive, our estimation KT acknowledges the Estonian Research Council (grant PUT1439) for founding.…”

“…active photosynthetic system of algae growing under favorable environmental conditions increases the synthesis of carbohydrates and other nutritious compounds, and therefore the palatability of F. vesiculosus for herbivores. This may be due to the inability of our bioassays to reliably detect the influences of highly watersoluble compounds(Jormalainen, Honkanen, Vesakoski, & Koivikko, 2005) or the less important role of phlorotannins in affecting the palatability of F. vesiculosus for I. balthica.The climate-induced desalination predicted for the end of the century is expected to produce a 30% contraction of the distribution of F. vesiculosus in the Baltic Sea(Jonsson et al, 2018;Kotta et al, 2019). Carbohydrates and mannitol in particular, are used by I. balthica and other crustaceans as feeding cues inthe assessment of the quality of different food items.…”