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

OCE Award Pending summary

Overview
Historically, diatom diets were considered beneficial for high planktivore fecundity. Over the last quarter century that view has changed, and it is now recognized that diatom diets can have deleterious effects on zooplankton development and reproduction. These effects are due to naturally occurring cytotoxic compounds (polyunsaturated aldehydes, [PUAs]) produced by some pelagic diatoms.  Though PUA effects have been shown for several protist and invertebrate species, no direct studies have examined the effect of diatom PUAs on larval fishes, and little data exists for PUA production by benthic diatoms. Several species of marine forage fishes in the North Pacific Ecosystem (NPE) are obligate beach or nearshore spawners. This places them sympatric with communities of benthic and nearshore diatoms. We present here preliminary data showing that benthic diatom communities from a region in the NPE produce PUA derivatives known to be cytotoxic, and data showing detrimental effects of PUAs on a model fish, the zebrafish (Danio rerio). We suggest that through association with diatoms, both benthic and pelagic, ecologically important forage fishes from the NPE may suffer from the negative effects of diatom-derived PUAs, and that this mechanism may be another, yet unrecognized, source of larval forage fish mortality. We propose to test for the prevalence of PUAs, both in dissolved and particulate phases in the NPE, and to determine whether PUA diets negatively affect two foundational forage fishes, the Pacific herring and surf smelt. We hypothesize that PUAs are widespread in benthic diatoms (heretofore massively understudied regarding PUA production) and that associations between diatoms and forage fish embryos and larvae will reduce forage fish egg hatching, growth, development, larval fitness, and survival. We will conduct field surveys for the presence of particulate (pelagic and benthic diatom communities) and dissolved PUA speciation and concentration in the NPE’s Salish Sea. We will couple this field work with controlled laboratory experiments where Pacific herring and surf smelt embryos and larvae are exposed to dissolved PUAs and/or fed diets containing PUA-producing diatoms and diatom-laden zooplankton, to determine the potential of diatom PUAs to adversely affect forage fish early life history stages.

Intellectual Merit
This research explores the potential for naturally occurring diatom PUAs to negatively affect the early life history fitness of vertebrate consumers, specifically ecologically, economically, and culturally important species of NPE forage fishes. Diatoms and forage fishes are critical food web components in ecosystems ranging from subtropical to polar regions, and in oceanographic conditions dominated by coastal upwelling, estuarine circulation, and river plumes. Thus, findings from the proposed work are applicable across diverse ecosystems and have implications for multiple fisheries stakeholders. Furthermore, this work may illuminate another source of early-life history mortality in forage fishes that contributes to high annual variability in adult population demographics. If we find that PUA production by benthic diatoms is widespread, then the potential exists for PUAs to affect a broad and disparate consortium of benthic consumers who rely on diatoms for their reproductive output.  

Broader Impacts
This work will illuminate a novel mechanism potentially driving reduced fitness and mortality in a foundational functional group in marine ecosystems. Minimally, it will determine the prevalence of dissolved PUAs in nearshore environments of the NPE, the pervasiveness of benthic diatoms to produce them, and the impacts these have on forage fish embryos and larvae. Furthermore, this work will provide a more holistic understanding of embryonic and larval forage fish ecology. One postdoc, two graduate students, and several undergraduates will be trained during this project. Students and the postdoc will participate in all aspects of the project and be encouraged to present their own work at appropriate scientific and public venues. Educational outreach activities will be conducted at Western Washington University and its satellite institutions and programs, and in partnership with local public schools. Outreach activities will include participation of undergraduates from a variety of different academic settings in the research through internship and other formal avenues, to STEM education in K-Gray arenas such as laboratory open houses, aquariums, and through targeted outreach to students in a predominately LatinX school district.