Influence of environmental attributes on intertidal community structure in glacial estuaries

Abstract

High-latitude coastal environments are experiencing dramatic changes due to climate warming, specifically enhanced glacier melt is modulating downstream environmental conditions in coastal watersheds and altering biological processes. Here, we examine rocky intertidal community structure, recruitment of key organisms, and environmental correlates at nine watersheds in two regions (Kachemak Bay and Lynn Canal) that bookend the Gulf of Alaska. Each watershed was part of a gradient in each of the regions that spanned 0–60% glacial coverage. Percent glacial cover, biomass surveys, and recruitment of intertidal organisms, along with environmental monitoring of salinity, temperature, dissolved oxygen, river discharge, turbidity, and nutrient loading were documented from April–September 2019 in each watershed. Biological community structure and variance were analyzed by taxa and by ecological group (i.e. primary producer, filter feeder, omnivore, grazer, predator) and then in relation to the local environmental gradients. In general, larger watersheds with more glacial coverage and river discharge resulted in more primary producers and less filter feeders. This pattern was more apparent in Kachemak Bay, the region with more oceanic influence, as compared to Lynn Canal, which is located within an inlet. In relation to specific environmental drivers, salinity was negatively correlated with primary producers, but positively associated with barnacle abundance. Additionally, turbidity was positively correlated with primary producer biomass, but negatively correlated with mussel abundance. In contrast, there was a positive relationship between mussel recruitment and discharge and turbidity. There was variability in within-ecological group response between regions that is speculated to be a response to local circulation and oceanic influences. Barnacles were the main filter feeder species driving patterns in the more saline regions located close to the open ocean, while mussels drove patterns in the other less oceanic regions. As glaciers recede, environmental conditions, such as salinity, will increase and turbidity will decrease, which may alter future intertidal community assemblages to be dominated by filter feeders.