Ecological Role of Intertidal Flats in Kachemak Bay, AK
ISSUE: Soft sediments, and particularly tidal flats, are a vital part of the coastal ecosystem and provide a number of important ecosystem services, such as:
- primary and secondary production;
- habitat for adult flatfish and shellfish;
- refuge and nursery habitat for juvenile fish; and
- interception and uptake of nutrients and contaminants from watershed drainage.
The Alaska coastline includes a large area of intertidal flats and shallow-water soft sediments. However, in contrast to the research done in such habitats as rocky shores, kelp beds and seagrass beds, little work has been done to examine the primary producer community occupying intertidal flats and their role in coastal ecosystem food webs. This is unfortunate given the position of these habitats near the land-sea interface, where they are particularly susceptible to changes in climate, sea level, increases in contaminant or nutrient loads, and direct physical impacts from storms and fishing activities. Kachemak Bay, Alaska is located on the lower reach of Cook Inlet, and has an average tidal amplitude of 5 meters. Broad mudflats extend up to 2.5 km from the entire north shore of the Bay, while the south shore is much steeper, and contains numerous bays, coves and lagoons. These tidal flats support productive plant communities, including microscopic benthic microalgae, macroalgae and eelgrass, and an abundant infauna community. The study area falls within the boundaries of the Kachemak Bay National Estuarine Research Reserve. Our objective is to describe the benthic microalgal community found on intertidal flats, and to determine their role in supporting secondary production in the bay. In particular, we assessed the role of tidal flat primary production in supporting littleneck clams (Protothaca staminea) and the Pacific blue mussel.
APPROACH: We collected water column samples, intertidal sediments and fauna from a series of stations located throughout Kachemak Bay. We characterized the benthic and planktonic microalgal communities in Kachemak Bay using pigment analysis and microscopy. Stable isotope analysis was used to examine the trophic linkages between tidal flat primary production and consumer organisms.
OUTCOME: The diatom assemblage occupying benthic habitats in Kachemak Bay exhibits both high biomass and biodiversity compared to assemblages reported in other locations. Based on microscopic examination of the communities, resuspended benthic microalgae are a relatively minor component of the phytoplankton. Nevertheless, our stable isotope results suggest that benthic primary production provides 50-80% of the food assimilated by several bivalves and infauna in the Kachemak Bay ecosystem, including littleneck clams and the blue mussel, which do not occur on tidal flats, but are found on adjacent rocky shorelines. Our data suggest that filter-feeding bivalves are selectively assimilating benthic microalgae, and therefore that resuspended benthic microalgae may be a more important food source for shellfish aquaculture than phytoplankton. Many of the intertidal fauna we sampled are common prey items for fish, birds, and marine mammals; thus linking tidal flat productivity to overall coastal production. For more information, contact Carolyn Currin.
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