How sea otters may be impacted by harmful algal blooms

A sea otter captured in Kachemak Bay, Alaska, getting examined by a veterinarian.

Photo courtesy of Grayson Conti

Harmful algal blooms (HABs) are of growing concern in marine environments. These toxic blooms can be detrimental to human and animal health, primarily through the consumption of shellfish species that concentrate these toxins. As the climate changes and waters warm, scientists expect the prevalence of HABs to increase in Alaskan coastal waters. Sea otters were captured in Kachemak Bay, Alaska, which afforded us an opportunity to assess their overall health by measuring quantities of gene transcription. Gene transcription (GT) is the process by which a DNA template is transcribed into mRNA; this is subsequently translated into a functional protein.

Specific GT responses can be attributed to specific stressors or conditions in the environment. Kachemak Bay sea otters appeared clinically normal during assessment, but blood samples were drawn to assess health through GT and were compared to sea otters from other regions. In comparison to the other sea otter populations, Kachemak Bay sea otter GT results indicated heightened activity of neurological, cardiac, immune, and detoxification systems. In addition, analyses of urine and fecal samples from the Kachemak Bay sea otters indicated the presence of domoic acid. Domoic acid is an algal toxin produced from the common algae, Pseudo-nitzschia. GT results point to chronic, low-level exposure to an algal toxin, such as domoic acid and may be a tool for early detection of environmental stressors. Developing analytical tools to help with health screening of animal populations may provide early indications of chronic exposure to stressors in environments undergoing changing climate scenarios.

Divergent Gene Expression Profiles in Alaskan Sea Otters: An Indicator of Chronic Domoic Acid Exposure?

Abstract

An opportunistic investigation into ecosystem instability in Kachemak Bay (KBay), Alaska, has led us to investigate exposure to toxic algae in sea otters. We used gene expression to explore the physiological health of sea otters sampled in KBay in May 2019. We found altered levels of gene transcripts in comparison with reference sea otters from clinically normal, oil-exposed, and nutritionally challenged populations sampled over the past decade. KBay sea otters were markedly divergent from the other groups for five genes, which indicated the involvement of neurological, cardiac, immune, and detoxification systems. Further, analyses of urine and fecal samples detected domoic acid in the KBay sea otters. In combination, these results may point to chronic, low-level exposure to an algal toxin, such as domoic acid. With a warming climate, the frequency and severity of harmful algal blooms in marine environments is anticipated to increase, and novel molecular technologies to detect sublethal or chronic exposure to algal toxins will help provide an early warning of threats to the stability of populations and ecosystems.

Bowen, L., S. Knowles, K. Lefebvre, M. St. Martin, M. Murray, K. Kloecker, D. Monson, B. Weitzman, B. Ballachey, H. Coletti, S. Waters, and C. Cummings. 2022. Divergent gene expression profiles in Alaskan sea otters: An indicator of chronic domoic acid exposure? Oceans 3(3): 401-418.