Molecular biomonitoring has become an increasingly important tool in recent years, most notably in the form of metabarcoding of environmental DNA (eDNA) and dietary DNA (dDNA) (Sousa et al. 2019; Chavez et al. 2021). These methods have been used to identify prey from stomach and fecal contents from marine predators such as pelagic fishes, pinnipeds, and whales (Sousa et al. 2016).

Members of the Geospatial Ecology of Marine Megafauna (GEMM) Laboratory are currently investigating the dietary preferences of gray whales (Eschrichtius robustus) that feed along the Oregon Coast from June through October. Based on underwater video and light traps, these whales seem to target epibenthic or benthic invertebrates, most notably mysid shrimps and crab larvae (Hildebrand et al. 2021). Our own CCGL is collaborating with the GEMM Lab to expand on these results by metabarcoding remnant dDNA from gray whale fecal plumes.

Our initial results suggest that amphipods (Lysianassidae, Dexaminidae, Caprellidae, Photidae) and mysids (Mysidae) constitute the lion’s share of prey detected in Oregon Coast gray whale fecal samples (Fig. 1). There are also appreciable signals from polychaete worms (Phyllodocida, Sabellida, Spionida, Terebellida) and olive snails (Olivella spp.), and hydrozoans. All of these taxa have been previously reported from gray whale stomach contents or associated with gray whale feeding behavior (Oliver & Slattery 1985; Akmajian et al. in prep). As our sample size grows, we expect to characterize annual variation in primary prey types and perhaps individual preferences of these summertime visitors.

Figure1: The relative proportions of dietary DNA (dDNA) from fecal samples of Oregon Coast gray whales  (n = 36). Results are based on COI metabarcoding with an Illumina MiSeq. Taxonomic identification was assigned to 138,819 reads using a custom reference library and a search of NCBI GenBank. The species were generalized into higher-order taxonimic categories for data visualization purposes.

 

Chavez F, Min M, Pitz K, Truelove N, Baker J, LaScala-Grunewald D, Blum M, Walz K, Nye C, Djurhuus A, et al. 2021. Observing Life in the Sea Using Environmental DNA. Oceanog. 34(2):102-119. doi:10.5670/oceanog.2021.218.

Hildebrand L, Bernard KS, Torres LG. 2021. Do Gray Whales Count Calories? Comparing Energetic Values of Gray Whale Prey Across Two Different Feeding Grounds in the Eastern North Pacific. Front Mar Sci. 8:683634. doi:10.3389/fmars.2021.683634.

Oliver JS, Slattery PN. 1985. Destruction and Opportunity on the Sea Floor: Effects of Gray Whale Feeding. Ecology. 66(6):1965–1975. doi:10.2307/2937392.

Sousa LL, Silva SM, Xavier R. 2019. DNA metabarcoding in diet studies: Unveiling ecological aspects in aquatic and terrestrial ecosystems. Environmental DNA. 1(3):199–214. doi:10.1002/edn3.27.

Sousa LL, Xavier R, Costa V, Humphries NE, Trueman C, Rosa R, Sims DW, Queiroz N. 2016. DNA barcoding identifies a cosmopolitan diet in the ocean sunfish. Sci Rep. 6(1):28762. doi:10.1038/srep28762.

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