As we transition into warmer, sunnier, summer days, you may have noticed that Kachemak Bay has been inundated by an abundance of seasonal visitors. While the vast majority are a welcome addition to our area, some may cause seemingly undesirable, frightening or downright offensive effects.
A couple of weeks ago, for example, boaters were surprised to find the waters of Tutka Bay to be an unusually bright pea-green color. A few days later, portions of Halibut Cove Lagoon turned a dark, rusty brown.
As you may have guessed, the culprits of the kaleidoscope of colors in Kachemak Bay were blooms of phytoplankton — a diverse group of sun-loving, single-celled organisms that form the base of the ocean food chain.
Dense concentrations of certain phytoplankton species are not uncommon in the summer, especially because sunlight and higher temperatures fuel the growth of these photosynthetic organisms.
In Kachemak Bay, brightly colored phytoplankton blooms are generally naturally occurring and non-toxic. However, some species may develop into harmful algal blooms (HABs) without causing any visible changes to the water. Consuming shellfish that have accumulated toxins produced by HABs can have serious impacts on human health.
How do we know which phytoplankton species are causing a change in the Bay’s color, or if harmful species might be present? The Kachemak Bay National Estuarine Research Reserve (KBNERR), together with NOAA’s Kasitsna Bay Laboratory (KBL) and many trained partners such as the Center for Alaskan Coastal Studies and community volunteers, regularly monitor for HABs, in addition to documenting the seasonal shifts in beneficial phytoplankton community.
In fact, our team identified the cause of the striking green hues that developed in Tutka Bay within a day or so of their appearance. In this case, an initial observation by Curt Jackson of Mako’s Water Taxi precipitated a chain of phone calls and text messages among Bay-watching community members. When it reached Kris Holderied (KBL), she connected with Harmful Species Biologist Kim Schuster at KBNERR, who then put out a call to partners to collect samples from the affected areas.
Within hours, Curt had returned to collect a water sample. On the next day, KBL staff, including Biologist Paul Cziko and NOAA interns Maggie Harper and Grace Ellis, collected extensive samples from two more sites in Tutka Bay.
One day later, the soup was observed in Kasitsna Bay and, over the following week, green waters had spread more widely along the south side of the Kachemak Bay. A few days later, the bloom subsided.
Staff members at KBL and KBNERR quickly determined that a microscopic euglenid (possibly of a genus named Eutreptiella) was responsible for the unusual green color. This is the first time that a major bloom of this type of phytoplankton has been documented in Kachemak Bay.
Euglenids are protists with both plant and animal-like qualities. They multiply quickly and zip around using whip-like flagella. While the vivid green waters may have looked alarming, these euglenids have no known health impact on humans. Other species of euglenids have even been cultured as a human food supplement.
Similarly, the agents behind the dark brown waters in Halibut Cove — a diatom named Chaetoceros and a ciliate named Mesodinium rubrum — do not produce toxins. In fact, a red bloom of the latter species also made local headlines back in 2021.
Whether you were startled by the green water or appetized by its resemblance to a healthy green smoothie, remember that these tiny productive creatures keep humans breathing oxygen and our local shellfish well fed and happy as a clam!
Community members that notice characteristics of unusual plankton blooms in the Bay, including changes in water color or considerable amounts of seafoam, are encouraged to contact KBNERR and/or KBL. Together, we’ll be happy to investigate.
Weekly reports on phytoplankton in the Bay are distributed from KBNERR to state managers, private and public organizations, oyster farmers and tribal organizations. Reports are available at: kachemakbayreserve.org/science/monitoring/#algal-blooms.
To subscribe, or to get involved in the community monitoring project, please contact Jasmine Maurer at KBNERR.
Please note that neither the KBNERR nor KBL are regulatory agencies and do not test shellfish for the presence of toxins that could be harmful to human health. However, other entities regularly test commercially harvested shellfish and they are safe for consumption.
KBNERR in Homer is a partnership between NOAA and the University of Alaska Anchorage. kachemakbayreserve.org, 907-235-4799.
KBL, outside of Seldovia, is part of NOAA’s National Centers for Coastal Ocean Science (NCCOS). More information about the facility is available at www.coastalscience.noaa.gov/about/facilities/alaska.
Paul A. Cziko, PhD, is a marine biologist at the NOAA Kasitsna Bay Laboratory. Kim Schuster is a harmful species biologist for KBNERR. Grace Ellis and Maggie Harper are summer interns.
Correction: This article has been updated to note that Kim Schuster is a harmful species biologist for KBNERR, not a summer intern.
