A climate vulnerability assessment of the fish community in the Western Baltic Sea

Abstract

Marine fisheries are increasingly impacted by climate change, affecting species distribution and productivity, and necessitating urgent adaptation efforts. Climate vulnerability assessments (CVA), integrating expert knowledge, are vital for identifying species that could thrive or suffer under changing environmental conditions. This study presents a first CVA for the Western Baltic Sea's fish community, a crucial fishing area for Denmark and Germany. Characterized by a unique mix of marine, brackish, and freshwater species, this coastal ecosystem faces significant changes due to the combined effects of overfishing, eutrophication and climate change. Our CVA involved a qualitative expert scoring of 22 fish species, assessing their sensitivity and exposure to climate change. Our study revealed a dichotomy in climate change vulnerability within the fish community of the Western Baltic Sea because traditional fishing targets cod and herring as well as other species with complex life histories are considered to face increased risks, whereas invasive or better adaptable species might thrive under changing conditions. Our findings hence demonstrate the complex interplay between life-history traits and climate change vulnerability in marine fish communities. Eventually, our study provides critical knowledge for the urgent development of tailored adaptation efforts addressing existing but especially future effects of climate change on fish and fisheries in the Western Baltic Sea, to navigate this endangered fisheries systems into a sustainable future.

Keywords: Climate change; Climate vulnerability assessment; Fish community; Trait-based sensitivity; Western Baltic Sea.

Figure 1

Study area. Map of the Western Baltic Sea with International Council for the Exploration of the Sea (ICES) management units (Sub-divisions: 22—Belt Sea, 23—Sound and 24—Arkona Sea).

Figure 2

Future temperature changes in the Western Baltic Sea. Example maps illustrating future bottom summer temperature changes used to assess the exposure of the fish community. (A) Temperature projections for mean bottom temperature under emission scenarios RCP 4.5 and RCP 8.5. (B) Map of Z-scores for the “mid of century” (MOC, 2040–2049) scenario. (C) Map of Z-scores for the “end of century” (EOC, 2080–2089) scenario under RCP 4.5. (D) Map of Z-scores for the “end of century” (EOC, 2080–2089) scenario under RCP 8.5. Z-scores in (B–D) are categorized into Low, Moderate, High and Very High.

Figure 3

Summary of thermal tolerances and attribute-based sensitivity scores of Western Baltic fish species. Species names are according to Table 1; thermal tolerance ranges reflect the needs of species for recruitment (R) and adult stages (A) as found in the literature (see species profiles); sensitivity scorings represent the means calculated over the values provided by all experts; RCP 4.5 and 8.5 represent emission scenarios (see “Materials and methods”); MOC middle of the century, EOC end of centrury.

Figure 4

Sensitivity of Western Baltic fish species to climate change. (A) Species’ sensitivity calculated as the weighted mean over 12 individual sensitivity attributes and using all expert scores; colours represent sensitivity scores according to the logic rule: red—very high, orange—high, yellow—moderate, blue—low. (B) Directional effects of climate change obtained as weighted means over all expert scores; colours represent categorization according to the logic rule: red—negative, yellow—neutral, blue—positive.

Figure 5

Relationships between sensitivity attributes and Western Baltic fish species. (A) Heatmap showing sensitivity attributes (rows) and species (columns); dendrograms and map splitting reflect the hierarchical clustering. (B) Principal Component Analysis biplot projecting attributes and species on the first two dimensions (Dim1, Dim2); colours of species groups assigned according to hierarchical clustering; complete attribute names and descriptions are provided in Table 2; species overplotted by “Habitat” is “Herring”.

Figure 6

Exposure of the Western Baltic fish species to climate change. Exposure scores for (A) RCP 4.5 mid-of-century climate scenario, (B) RCP 4.5 end-of-century climate scenario, and (C) RCP 8.5 end-of-century climate scenario. Colours represent sensitivity scores according to the logic rule: orange—high, yellow—moderate, blue—low.

Figure 7

Vulnerability of Western Baltic fish species to climate change. Vunerability scores are reporterd for (A) RCP 4.5 mid-of-century climate scenario, (B) RCP 4.5 end-of-century climate scenario, and (C) RCP 8.5 end-of-century climate scenario. Colours describe the intensity of sensitivity scores according to the logic rule: orange—high, yellow—moderate, blue—low. Certainty estimates derived by bootstrapping are added as numbers next to individual bars.