Glacial meltwater influence on estuarine groundfish communities

Background/Question/Methods

The effects of climate change in terrestrial ecosystems on adjacent coastal ecosystems may have important implications for productivity of estuarine communities. Glaciers are retreating at high latitudes and the retreat rate is predicted to increase. Changes in inputs of glacial meltwater affect nutrient dynamics in estuaries. Habitat characteristics of estuarine nurseries are important to the success of young fishes, affecting the abundance of later adult cohorts. Fundamental differences in habitat characteristics of estuaries adjacent to watersheds with varying degrees of glacier cover may affect their suitability as nursery and spawning grounds for marine fishes. The objectives of this study are to determine if groundfish community structure differs among watersheds that vary in their glacial influence and to determine which geophysical variables are correlated with groundfish community structure. I sampled juvenile and adult groundfishes from estuaries in southeast Alaska that vary in their glacial influence, along with concurrent collection of geophysical variables from each location. Seven estuaries were sampled over two summers using a 50’ beach seine net with ¼” mesh. Sediment and water samples were collected at the time of fish capture. All fish captured were identified to species, and their abundance and body length recorded.

Results/Conclusions

Sediment grain sizes were smaller in estuaries with greater glacial influence. Number of groundfish species captured per estuary ranged from three to twelve, with no clear trend in richness as a function of glacial influence. However, there was a great degree of unevenness in the abundance of groundfish species at each estuary, and relative abundance of most species differed among estuaries. The most widely occurring species was starry flounder, which was most abundant in heavily glacially influenced estuaries. This pilot data suggests differences in community structure of groundfishes among estuaries that differ in glacial influence, implying that as glacial influence changes due to climate change, estuarine fish communities may change as well. Future work on this project will help inform predictions of climate change impacts on biological communities in nearshore marine ecosystems.