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

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.

Pattern and scale: evaluating generalities in crab distributions and marsh dynamics from small plots to a national scale

“…Luk and Zajac (2013) suggested that landward expansion of low marsh vegetation species may facilitate increased distribution of fiddler crabs. Likewise, Crotty et al (2017) indicated the potential interaction between future SLR and Sesarma reticulatum impacts on marshes, as did Raposa et al (2018b) based on increases in crab burrows during recent periods of higher water levels. Likewise, Crotty et al (2017) indicated the potential interaction between future SLR and Sesarma reticulatum impacts on marshes, as did Raposa et al (2018b) based on increases in crab burrows during recent periods of higher water levels.…”

“…Szura et al (2017) found stronger effects of Sesarma reticulatum with increased inundation. Likewise, Crotty et al (2017) indicated the potential interaction between future SLR and Sesarma reticulatum impacts on marshes, as did Raposa et al (2018b) based on increases in crab burrows during recent periods of higher water levels. Vu and Pennings (2017) noted that crab burrowing that increases creek size may actually have a positive effect on marsh integrity in the face of SLR, by increasing drainage.…”

Peer Review #2 of "Distribution of crabs along a habitat gradient on the Yellow Sea coast after Spartina alterniflora invasion (v0.2)"

“…Recent studies have indicated that the reclamation of soil by S. alterniflora invasion can facilitate some taxa, such as fishes and crabs (Feng et al 2015;. Some studies confirm that the leaves of S. alterniflora can supply palatable food for C. dehaani and S. plicata (Gao et al 2018;Wang et al 2008) and that the abundance of U. arcuata is positively correlated with S. alterniflora cover (Raposa et al 2018). According to our results, the number of crab species in S. alterniflora marsh was lower than that in S. salsa marsh but greater than that in the mudflat and P. australis marsh.…”

Distribution of crabs along a habitat gradient on the Yellow Sea coast after Spartina alterniflora invasion

“…Recent studies have indicated that the reclamation of soil by S. alterniflora invasion can facilitate some taxa, such as fishes and crabs (Feng et al, 2015; Chen & Ma, 2018). Some studies confirm that the leaves of S. alterniflora can supply palatable food for C. dehaani and S. plicata (Gao et al, 2018; Wang et al, 2008) and that the abundance of U. arcuata is positively correlated with S. alterniflora cover (Raposa et al, 2018). According to our results, the number of crab species in S. alterniflora marsh was lower than that in S. salsa marsh but greater than that in the mudflat and P. australis marsh.…”