Ichthyoplankton dynamics and biodiversity in the Gulf of Alaska: Responses to environmental change

Climate variation can cause major changes in the marine food web. We analyzed over 24 years of ichthyoplankton data from the Gulf of Alaska to evaluate lower trophic level responses to environmental change and judge their usefulness as ecological indicators. We standardized abundance data for each of 77 ichthyoplankton taxa, and used the Bray-Curtis distance measure and Flexible Beta linkage method, which grouped them into 22 discrete clusters. Variance Partitioning Analysis stressed the importance of geographical and seasonal processes for ichthyoplankton dynamics, and helped us identify the specific region(s) and month(s) for each response variable (cluster abundance, diversity) in which annual variation was maximized. Response variables were linked to environmental explanatory variables (atmospheric pressure, temperature, salinity and circulation indices) by Canonical Correspondence Analysis. The North Pacific Index (atmospheric pressure) and meso-scale climate variables like the El Niño Index (temperature), wind, and freshwater input (circulation) had the strongest impacts on ichthyoplankton species clusters. Specifically, the El Niño Index was negatively correlated with several ichthyoplankton clusters that were dominated by cold water species. Circulation was predominantly positively related to diversity and ichthyoplankton clusters, with the exception of clusters that mainly consisted of offshore taxa. The immediate response of ichthyoplankton to environmental forcing might make them suitable ecological indicators of environmental change although additional work is needed to assess affects on survival and recruitment.