Seagrass stems wave green
in shallow water currents
Hello, tanner crab
Why are we sampling?
We evaluate nearshore intertidal communities and sea otters as nearshore predators in Kachemak Bay as a means to determine if Kachemak Bay can be used as a control area for Prince William Sound if another oil spill were to occur. Our monitoring data also contributes to our overall understanding of the structure and ecological importance of nearshore ecosystems in the Gulf of Alaska.
Long-term, annual monitoring of these systems over a broad geographic area in the Gulf of Alaska is very important to understanding how the prominent weather and oceanic patterns in the region can result in changes every year. Once we have a good understanding of this inter-annual variability, we can tease apart changes that occur over the long-term from climate changes (at the scale of decades or longer) from those that occur suddenly from impacts such as an oil spill.
Where are we sampling?
We sample sites each year within Kachemak Bay, located on the southern Kenai Peninsula near Homer, Alaska. Our six rocky intertidal sites where we also assess mussel populations annually include Port Graham, Outside Beach near Seldovia, Cohen Island, and Elephant Island along the southern shore of Kachemak Bay, and Bluff Point and Bishop’s Beach near Homer on the northern shore of Kachemak Bay. The four seagrass beds we monitor are located near Homer Spit and Herring Island and in Jakolof and Peterson Bays. We also sample soft-sediment beaches in four places (Jakolof Bay, China Poot Bay, Port Graham, and Bear Cove) every other year for clams.
We collect sea otter foraging and scat data opportunistically within Kachemak Bay in places where sea otters are actively feeding.
How are we sampling?
We evaluate sea otters, plants and invertebrates on rocky intertidal beaches, seagrass beds, clams and mussels on gravel beaches, and environmental conditions such as water temperature and substrate composition. We use the same scientific met
hods in this project as are being used in the ongoing Gulf Watch Alaska Nearshore Ecosystems project in western Prince William Sound, Kenai Fjords National Park, and Katmai National Park and Preserve.
We sample the rocky intertidal and seagrass communities every summer for the percentage of coverage of the substrate by all organisms using transect surveys. On rocky sites, we also sample an adjacent mussel bed. Every other summer, we sample clams on gravel beaches. In 2015, we added sampling for sea star wasting disease.
During 2015, we compiled information on dead sea otters collected by the Alaska Marine Mammal Stranding Network in collaboration with the U.S. Fish and Wildlife Service Marine Mammals Management Office.
Watch this fun, short video to learn more about Nearshore Sampling in Kachemak Bay.
What are we finding?
- Rocky intertidal communities in Kachemak Bay are highly variable with respect to a suite of variables such as substrate, exposure to wave action, other environmental variables, rates of predation and exposure at low tide. In particular, intertidal communities along the south shore of the bay are significantly different from sites on the north shore, especially in the lowest tide zone.
- Seaweed and invertebrate species are different at each of the beaches we sample and the beaches themselves change from year to year. However, at each beach, species form distinct communities based on tidal level (high, mid, low, and -1 meter). One common trend among sites is low kelp coverage at the low and -1 meter strata in 2015, possibly associated with the warm water anomaly, the intense El Niño event that started in 2015, or some combination of factors.
- The abundance and size of mussels varies across rocky intertidal sites within Kachemak Bay and over time. Much of the variability is driven by small mussels and the strength of annual recruitment events. The magnitude of this variability was particularly obvious at Port Graham, where mussel density almost doubled or was halved from year to year.
- The incidence of sea star wasting disease increased in 2015. In comparison with no observations of disease during our 2014 surveys, at 11 survey sites in 2015, close to 6% of the sea stars we surveyed had severe white skin lesions, and, in some cases, their arms had completely disintegrated (see pictures). Species with disease symptoms included mottled stars (Evasterias troschelii), sunflower stars (Pycnopodia helianthoides), six-rayed stars (Leptasterias hexactis) and a rainbow star (Orthasterias koehleri). These observations suggest that either the disease took time to reach these northern regions from areas to the south where infection rates were much higher in 2014 or the warm water conditions during 2015 accelerated or even promoted spread of the disease.
• A record number (170) of dead sea otters were recovered in Kachemak Bay and lower Cook Inlet in 2015. Eighty-three percent of the stranded, dead sea otters that were necropsied presented symptoms of Strep Syndrome, a bacterial infection. The U.S. Fish and Wildlife Service has been tracking a Strep Syndrome unusual mortality event in Kachemak Bay sea otters since 2006, however, the sea otters dying from Strep Syndrome in late 2015 appeared healthier than those found in past years. In the future, we will use aging techniques to determine the age structure of moralities to determine the status of the sea otter population in Kachemak Bay in relation to carrying capacity and to compare the status of the Kachemak Bay population to that of populations in other locations where sea otters are being monitored as part of the Gulf Watch Alaska Nearshore Ecosystem Component.