Dynamics and drivers of benthic crustaceans in Lake Mývatn

Abstract The community of benthic crustaceans in Lake Mývatn, Iceland, is dynamic, with different taxa showing different patterns of variation through time. Here, we analyze the dynamics of eight crustaceans collected during the summer from a central station in Mývatn over 29 years, 1995–2023. We investigated the hypothesis that fluctuations in the dominant benthic tube-forming midge, Tanytarsus gracilentus , drives fluctuations in benthic crustacean abundance. We also investigated two additional drivers: predatory three-spined stickleback ( Gasterosteus islandicus ) and water clarity as a measure of pelagic phytoplankton density. The analyses identified three groups of crustaceans whose populations are correlated with other members of the same group and which show similar responses to the drivers. The group of infaunal taxa fluctuated asynchronously with T. gracilentus , with the crustaceans reaching high abundances when T. gracilentus had low abundance. The bentho-pelagic taxa and Eurycercus lamellatus (treated as a group by itself) were not strongly influenced by T. gracilentus. These patterns derived from time-series data were supported by spatial data collected from a transect along a gradient of T. gracilentus abundance in 2024; those taxa that were present in the spatial transect showed similar responses to midge abundance. While stickleback and water clarity did have an impact on some taxa, this study largely confirms that T. gracilentus is the major driving force behind changes in the benthic crustacean community dynamics. The different responses of taxa to drivers and their asynchronous fluctuations increase the stability of the benthic crustacean community by ensuring that, in any given year, some taxa are relatively abundant.