Project: Collaborative Research: Do diatom-derived polyunsaturated aldehydes directly or indirectly reduce embryonic and larval forage fish fitness?

NSF Award Abstract:
Forage fishes are a vital component of marine ecosystems. All life stages, from eggs to adults, are food for various marine and terrestrial predators, including salmon, seabirds, and marine mammals. Throughout life, forage fishes are exposed to toxins produced by diatoms, which are a type of single-celled algae. They frequently deposit their eggs on surfaces coated with benthic diatoms, and after hatching their larvae feed on pelagic diatoms. All forage fishes then continue to ingest diatoms at every life stage by eating zooplankton that have diatoms within their digestive tracts. Many diatom species produce defensive chemicals called polyunsaturated aldehydes (PUAs). After consuming PUA-producing diatoms, some marine animals produce fewer offspring, and those few offspring have impaired development and reduced survival. This project examines the impact of the most pervasive PUAs produced by diatoms on the embryos and larvae of ecologically, economically, and culturally important species of forage fishes in the North Pacific Ecosystem. It is currently unknown whether forage fishes suffer from the 'diatom effect' that reduces reproductive output in other marine animals. High forage fish abundance is crucial for the health of the Salish Sea ecosystem, which is located in the coastal waters of Washington State and British Columbia, where declines in Salish Sea forage fish stocks are of major concern to marine resource managers. This project is determining the prevalence of PUA-producing diatoms in both benthic and pelagic habitats within the Salish Sea and testing the effects of PUAs on the embryonic and larval health of Pacific herring and surf smelt in laboratory experiments. These two forage fish species were historically present in huge numbers in the Salish Sea. Whether their decline is at all linked to increased prevalence of diatoms, which can bloom dramatically in populated coastal areas with nitrogen-rich runoff, is not currently known. This work sheds light on a novel mechanism potentially driving reduced fitness and mortality in a foundational functional group in marine ecosystems. One postdoctoral fellow, two graduate students, and several undergraduate researchers are participating in the research. Educational outreach activities include the engagement of undergraduates from a variety of academic settings in internships and other collaborations, support for STEM education in K-Gray arenas such as laboratory open houses and community aquariums, and targeted outreach to students in a predominately LatinX public school district.

Forage fishes are critical food web components in most marine ecosystems. Many forage fishes spawn nearshore and are planktivorous throughout all exogenous feeding stages, placing them sympatric with benthic and pelagic diatoms. This project refines understanding of forage fish ecology and takes a novel approach to identifying mechanisms that elevate mortality in their early life history. The primary project goal is determining whether diatom-derived polyunsaturated aldehydes (PUAs) impair development, reduce fitness, and decrease survival in the embryos and larvae of two forage fishes of high ecological, commercial, and cultural importance in the North Pacific: surf smelt and Pacific herring. Although diatom-derived PUAs are known to have negative effects on the development of marine invertebrates, and laboratory studies have shown that these PUAs can be toxic to vertebrate models, no prior research has examined the effects of PUAs on fishes that are ecologically linked to diatoms. Because forage fishes are in close contact with diatoms throughout life, and because diatom blooms have increased in both extent and frequency due to nitrogen-rich runoff in coastal areas where forage fishes feed and reproduce, PUAs represent a plausible contributor to high early life history mortality. The team is 1) conducting field surveys at known Pacific herring and surf smelt spawning sites in the Salish Sea to quantify the prevalence, type, and concentration of both particulate and dissolved PUAs and 2) in laboratory experiments, exposing Pacific herring and surf smelt embryos and larvae to dissolved PUAs and diets containing PUA-producing diatoms and zooplankton gut loaded with diatoms to determine the potential of diatom PUAs to adversely affect forage fishes during their early life history. The results of this work are relevant to a diversity of marine and aquatic ecosystems and have implications for a wide range of fisheries.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.