Salt and fresh mix, in
diamond-tipped blue water
Why are we sampling?
The waters of Kachemak Bay and lower Cook Inlet are rich with plankton, kelp and seagrass, which form the base of the food web for the fish, shellfish, marine mammals and seabirds that live in this region. The primary production from plankton and marine plants is in turn driven by ocean conditions including temperature, salinity, oxygen, turbidity and nutrients. We are measuring oceanography and plankton in Cook Inlet to understand how changing environmental conditions affect species injured by the Exxon Valdez oil spill and the coastal ecosystem over the long term. We also aim to detect climate changes that may lead to ecosystem regime shifts and provide oceanographic information to Gulf Watch Alaska scientists and agency managers who monitor fish, marine mammal and bird populations.
Where are we sampling?
We are sampling at stations along five transects in lower Cook Inlet and Kachemak Bay and at stationary sites in Seldovia Harbor, Kasitsna Bay, Homer Harbor, and a mooring in Bear Cove near the head of Kachemak Bay.
How are we sampling?
We conduct boat surveys along repeated transects in lower Cook Inlet. We collect oceanographic data from the surface to the bottom, make zooplankton and phytoplankton tows in the upper water column and opportunistic seabird and marine mammal observations. We collect water quality measurements year-round at stations in Seldovia and Homer harbors and in ice-free months at a mooring in Bear Cove. We also collect phytoplankton samples every other month at the Kasitsna Bay Lab dock.
What are we finding?
We have measured how Cook Inlet waters respond to a range of climate patterns, including years of near-record snowfall (2012) and record warm temperatures (2014 and 2015). The current warm water anomaly in lower Cook Inlet and Kachemak Bay is consistent with findings in Prince William Sound and at GAK-1 and on the Seward Line. With persistent warm water temperatures, waters in Kachemak Bay become fresher, as demonstrated by anomalies in the monthly average salinities measured at the monitoring station in Seldovia Harbor.
While warm temperatures persisted from 2014 to 2015, the biological response was much more dramatic in 2015. Seabird and sea otter mortalities were extensive and, in September 2015, the first paralytic shellfish poisoning event and oyster farm closures in over a decade occurred in Kachemak Bay.
Throughout the summer of 2015, we recorded relatively low concentrations of Alexandrium fundyense at all Kachemak Bay sampling locations. This phytoplankton species produces the saxitoxin that causes paralytic shellfish poisoning. Higher concentrations of A. fundyense were significantly correlated with higher water temperature and lower salinity conditions . When we observed a late summer bloom of A. fundyense and sampled shellfish in Kachemak Bay sub-bays, we found saxitoxin present above the regulatory limit of 80 micrograms per 100 grams of tissue.
In addition, in the spring of 2015, we recorded a phytoplankton bloom of Pseudo-nitzschia diatoms (not identified to species) that occurred much earlier than usual. Pseudo-nitzschia produces domoic acid, a neurotoxin that bioaccumulates in shellfish and causes amnesic shellfish poisoning. This bloom occurred in May shortly after the normal diatom bloom . The Pseudo-nitzschia bloom persisted through most of the summer and our toxin testing of plankton and shellfish samples indicated that domoic acid toxins were present, but only in relatively low amounts, in contrast to the high domoic acid toxin levels that were observed along the coasts of California and Oregon during that same summer. We are collaborating with National Oceanographic and Atmospheric Administration colleagues to help understand what drives those differences.
Anecdotally, we observed more positive responses to the warm water anomaly from some fish and whale species. Local fishermen reported a high abundance of feeder king salmon in Kachemak Bay in both 2014 and 2015 and, in 2015 Kachemak Bay residents and visitors observed large and perhaps unprecedented numbers (more than 50) of actively feeding humpback whales in the bay all summer and into November. Fishermen, water taxi operators and local researchers also reported seeing significant numbers of herring in Kachemak Bay. Based on the sizes observed, most of the herring likely hatched that spring or summer (“age 0” year class). Fishermen also reported herring in the stomachs of salmon they caught; however, these observations were limited.