Long-term changes in an estuarine mud crab community: Evaluating the impact of non-native species

Abstract

Along the US Atlantic coast, oyster reefs support a large number of estuarine species including ecologically important and abundant mud crabs. Multiple factors including environmental conditions, the introduction of non-native species, parasites, and interspecific competition can change the structure of these communities over time. To examine long-term changes in mud crab communities, crabs were sampled quarterly for ten years in a mixed oyster/mud habitat in a northeast Florida estuary. A total of 6935 individuals comprised of 10 species were collected, including two non-native crab species: Petrolisthes armatus (Gibbes, 1850) and Charybdis hellerii (Milne-Edwards, 1867). Three species (Panopeus herbstii Milne Edwards, 1834, P. armatus, and Eurypanopeus depressus (Smith, 1869)) made up 97.3% of adult specimens collected, and were observed throughout the study period in varying abundances. Non-metric multi-dimensional scaling (MDS) conducted on species abundances revealed that the community underwent significant long-term, rather than cyclical seasonal, changes. Most noteworthy were the similarities in community assemblages observed in the years prior to, and soon after, the introduction of a nonnative parasite, Loxothylacus panopaei (Gissler, 1884), which preferentially infects E. depressus. The significance of the presence/absence of the parasite on the community structure was confirmed through an analysis of similarities test (ANOSIM). While E. depressus abundance declined in the early years of the study after the introduction of L. panopaei, and never recovered, abundance of P. herbstii did not significantly change. Temperature and salinity likely only briefly impacted individual species on a seasonal or yearly basis including P. armatus, whose abundance reached an all-time low in the winter of 2010-2011 along with extreme winter temperatures.