Hull WW and Bourdeau PE (2017), Can crabs kill like a keystone predator? A fiel...

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PLoS One 2017 Aug 04;128:e0183064. doi: 10.1371/journal.pone.0183064.

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Can crabs kill like a keystone predator? A field-test of the effects of crab predation on mussel mortality on a northeast Pacific rocky shore.

Hull WW , Bourdeau PE .

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Predation can strongly influence community structure and ecosystem function, so the loss of key predators can have dramatic ecological consequences, unless other predatory species in the system are capable of playing similar ecological roles. In light of the recent outbreak of sea star wasting disease (SSWD) and subsequent depletion of west coast sea star populations, including those of the keystone predator Pisaster ochraceus, we examined whether large mobile crabs could play a role as predators on mussels (Mytilus californianus) on a rocky shore in Northern California. Using a combination of sea star removal and predator exclusion cages we found that mussel mortality was 43-294 times greater in uncaged treatments versus caged treatments. Mortality on uncaged mussels at low tidal elevations was due to predation by large mobile crabs (Cancer productus and Romaleon antennarium); confirmed by the presence of mussel shell fragments and documented attacks on wax snail replicas. Laboratory feeding assays indicated that crabs, on a per unit biomass basis, can consume almost twenty-five times as many mussels per day than sea stars, which together with the results of our field experiment, suggest that large predatory crabs could play an important role in maintaining ecosystem function through their predation on mussels on rocky shores where P. ochraceus are rare, absent, or have been depleted by SSWD.

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Species referenced: Echinodermata
Genes referenced: LOC100887844 LOC115925415 ROCK snai2

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References [+] :

Berger, Chytridiomycosis causes amphibian mortality associated with population declines in the rain forests of Australia and Central America. 1998, Pubmed

	Fig 1. Location of field study site on Cape Mendocino, on the northern coast of California.Partially wave-protected rocky bench just southeast of Mussel Rock, where experimental cages, wax snail models, and environmental loggers were deployed (inset).
	Fig 2. Mean (± 1 SE) abundance of Mytilus californianus across a tidal elevation gradient.
	Fig 3. Mean (± 1 SE) number of M. californianus lost per day in caged and uncaged plots in (A) low tidal elevation reference plots (Low) and high tidal elevation transplant plots (High) in Experiment 1; and in (B) low and high tidal elevation transplant plots.
	Fig 4. Frequency of attacked, incomplete, missing, and remaining wax snail replicas at low and high tidal elevations (‘0’ represents a frequency of zero).
	Fig 5. Photographic evidence of (A) crab attack on wax snail replica (B) crab-claw-induced damage to experimental cage, (C) crab attack on robo-mussel shell and temperature logger (inset).