Species richness and functional attributes of fish assemblages across a large-scale salinity gradient in shallow coastal areas

[摘要] Coastal ecosystems are biologically productive, and their diversityunderlies various ecosystem services to humans. However, large-scale speciesrichness (SR) and its regulating factors remain uncertain for many organismgroups, owing not least to the fact that observed SR (SR obs ) depends onsample size and inventory completeness (IC). We estimated changes in SRacross a natural geographical gradient using statistical rarefaction andextrapolation methods, based on a large fish species incidence datasetcompiled for shallow coastal areas ( 30  m depth) from Swedish fishsurvey databases. The data covered a ca. 1300 km north–south distance and a12-fold salinity gradient along sub-basins of the Baltic Sea plus the Skagerrakand, depending on the sub-basin, 4 to 47 years of samplings during 1975–2021.Total fish SR obs was 144, and the observed fish species were of 74 %marine and 26 % freshwater origin. In the 10 sub-basins with sufficientdata for further analysis, IC ranged from 77 % to 98 %, implying that ca.2 %–23 % of likely existing fish species had remained undetected. Samplecoverage exceeded 98.5 %, suggesting that undetected species represented 1.5  % of incidences across the sub-basins, i.e. highly rarespecies. To compare sub-basins, we calculated standardized SR (SR std )and estimated SR (SR est ). Sub-basin-specific SR est varied between35  ±  7 (SE) and 109  ±  6 fish species, being ca. 3 timeshigher in the most saline (salinity 29–32) compared to the least salinesub-basins (salinity  3). Analysis of functional attributes showedthat differences with decreasing salinity particularly reflected adecreasing SR of benthic and demersal fish, of piscivores and invertivores,and of marine migratory species. We conclude that, if climate changecontinues causing an upper-layer freshening of the Baltic Sea, this mayinfluence the SR, community composition and functional characteristics offish, which in turn may affect ecosystem processes such as benthic–pelagiccoupling and connectivity between coastal and open-sea areas.

[学科分类] 大气科学