Github Repository for: European green crab predation in a Washington State estuary revealed with DNA metabarcoding

Fisher, MC, Grason, EW, Stote, A, Kelly, RP, Litle, K, & PS McDonald. (2024). Invasive European green crab (Carcinus maenas) predation in a Washington State estuary revealed with DNA metabarcoding. DOI:10.1371/journal.pone.0302518

Github release v1.1 of the repository for Fisher et al. 2024, "European green crab predation in a Washington State estuary revealed with DNA metabarcoding." For the most updated repository, see: github.com/mfisher5/Green-crab-dDNA

Contains the code and minimum dataset necessary to replicate study findings.

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Abstract: Predation by invasive species can threaten local ecosystems and economies. The European green crab (Carcinus maenas), one of the most widespread marine invasive species, is an effective predator associated with clam and crab population declines outside of its native range. In the U.S. Pacific Northwest, green crab has recently increased in abundance and expanded its distribution, generating concern for estuarine ecosystems and associated aquaculture production. However, regionally-specific information on the trophic impacts of invasive green crab is very limited. We compared the stomach contents of green crabs collected on shellfish aquaculture beds versus natural intertidal sloughs in Willapa Bay, Washington, to provide the first in-depth description of European green crab diet at a particularly crucial time for regional management. We first identified putative prey items using DNA metabarcoding of stomach content samples. We compared diet composition across sites using prey presence/absence and an index of species-specific relative abundance. For eight prey species, we also calibrated metabarcoding data to quantitatively compare DNA abundance between prey items, and to describe an ‘average’ green crab diet at an intertidal slough and an actively cultivated Manila clam bed. From the stomach contents of 61 green crabs, we identified 54 unique taxa belonging to nine phyla. The stomach contents of crabs collected from cultivated Manila clam beds were significantly different from the stomach contents of crabs collected at natural intertidal sloughs. Across all sites, arthropods were the most frequently detected prey, with the native hairy shore crab (Hemigrapsus oregonensis) the single most common prey item. Of the eight species included in the quantitative model, two ecologically-important native species – the sand shrimp (Crangon franciscorum) and the Pacific staghorn sculpin (Leptocottus armatus) – were the most abundant in crab stomach contents, when present. In addition to providing timely information on green crab diet, our research demonstrates the novel application of a recently developed model for more quantitative DNA metabarcoding. This represents another step in the ongoing evolution of DNA-based diet analysis towards producing the quantitative data necessary for modeling invasive species impacts.