Top-down and bottom-up controls on southern New England salt marsh crab populations

Kenneth B Raposa; Richard A McKinney; Cathleen Wigand; Jeffrey W Hollister; Cassie Lovall; Katelyn Szura; John A Gurak Jr; Jason McNamee; Christopher Raithel; Elizabeth B Watson

doi:10.7717/peerj.4876

Top-down and bottom-up controls on southern New England salt marsh crab populations

PeerJ. 2018 May 30:6:e4876. doi: 10.7717/peerj.4876. eCollection 2018.

Affiliations

¹ Narragansett Bay National Estuarine Research Reserve, Prudence Island, RI, United States of America.
² ORD-NHEERL, Atlantic Ecology Division, U.S. Environmental Protection Agency, Narragansett, RI, United States of America.
³ Department of Biological Sciences, College of the Environment and Life Sciences, University of Rhode Island, Kingston, RI, United States of America.
⁴ The Scripps Research Institute, La Jolla, CA, United States of America.
⁵ Rhode Island Department of Environmental Management, Jamestown, RI, United States of America.
⁶ Rhode Island Department of Environmental Management, Kingston, RI, United States of America.
⁷ Department of Biodiversity, Earth and Environmental Sciences, Academy of Natural Sciences, Drexel University, Philadelphia, PA, United States of America.

Abstract

Southern New England salt marsh vegetation and habitats are changing rapidly in response to sea-level rise. At the same time, fiddler crab (Uca spp.) distributions have expanded and purple marsh crab (Sesarma reticulatum) grazing on creekbank vegetation has increased. Sea-level rise and reduced predation pressure drive these changing crab populations but most studies focus on one species; there is a need for community-level assessments of impacts from multiple crab species. There is also a need to identify additional factors that can affect crab populations. We sampled crabs and environmental parameters in four Rhode Island salt marshes in 2014 and compiled existing data to quantify trends in crab abundance and multiple factors that potentially affect crabs. Crab communities were dominated by fiddler and green crabs (Carcinus maenas); S. reticulatum was much less abundant. Burrow sizes suggest that Uca is responsible for most burrows. On the marsh platform, burrows and Carcinus abundance were negatively correlated with elevation, soil moisture, and soil percent organic matter and positively correlated with soil bulk density. Uca abundance was negatively correlated with Spartina patens cover and height and positively correlated with Spartina alterniflora cover and soil shear strength. Creekbank burrow density increased dramatically between 1998 and 2016. During the same time, fishing effort and the abundance of birds that prey on crabs decreased, and water levels increased. Unlike in other southern New England marshes where recreational overfishing is hypothesized to drive increasing marsh crab abundance, we propose that changes in crab abundance were likely unrelated to recreational finfish over-harvest; instead, they better track sea-level rise and changing abundances of alternate predators, such as birds. We predict that marsh crab abundance will continue to expand with ongoing sea-level rise, at least until inundation thresholds for crab survival are exceeded.

Keywords: Community assessment; Crabs; New England; Predation; Salt marsh; Sea-level rise.

Grants and funding

Financial support was provided by (1) a grant under the Federal Coastal Zone Management Act, administered by the Office of Ocean and Coastal Management, National Oceanic and Atmospheric Administration, Silver Spring, MD, (2) the US Environmental Protection Agency, and (3) the Rhode Island Department of Environmental Management. There was no additional external funding received for this study. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.