Effects of shoreline oiling on salt marsh epifaunal macroinvertebrates

Abstract

The Deepwater Horizon oil spill resulted in varying degrees of oiling in the salt marshes of northern Barataria Bay, Louisiana, USA. This study examines the effects of oiling intensity and recovery on two conspicuous marsh-platform macroinvertebrates, Uca spp., fiddler crabs, and Littoraria irrorata, the salt marsh periwinkle, from 2.5 to 4.5 years after the spill. The dominant fiddler crab within these marshes, Uca longisignalis, was the only species observed in field collections, and no significant difference in burrow density or burrow size was found among oiling levels over the study period indicating recovery from any negative effects of oiling already occurred for this species. The highest density of L. irrorata was found at moderately oiled sites compared to both reference (without visible oiling) and heavily oiled stations. Spartina alterniflora density recovered within two years after the spill at the moderately oiled stations facilitating recovery of L. irrorata approximately one year later. L. irrorata average shell length and length-frequency distributions were equivalent at moderately oiled and reference stations but snails were shorter at heavily oiled stations because of a greater proportion of subadults. Shell length data from the heavily oiled sites indicate that direct mortality due to oiling or oil-induced reductions in recruitment occurred in 2010 and that recovery was starting to occur at 48 months after the spill. The extent and duration of oil in the water during the spill and the biological responses we measured indicates that L. irrorata and Uca longisignalis were both affected in their ability to carry out their life cycle on the marsh and/or in the water column at all stations including the reference stations for some period following the entry of oil into the region.

Deepwater Horizon Oil Spill Impacts on Salt Marsh Fiddler Crabs (Uca spp.)

“…Our interpretation is greatly strengthened by results from experimental plantings of Spartina alterniflora at oiled sites: where marsh vegetation cover was restored, fiddler crab species composition returned to strong dominance by U. longisignalis (Zengel et al 2014). Qualitatively, Deis et al (2015) also observed strong dominance by U. longisignalis where Spartina alterniflora stem density recovered in their sites. These findings suggest that fiddler crab species composition will not recover at oiled sites until the vegetation recovers.…”

“…Studies We synthesized comparable results of all published studies and additional unpublished data including large NRDA and GoMRI data sets (Table 1). Detailed methods are included in each of the published studies and are available for the NRDA (Michel et al 2012;Zengel et al 2015b) and GoMRI (Deis et al 2015) sources. Study sites were widely distributed throughout the northern Gulf of Mexico (LA, MS, AL) with numerous sites concentrated in southeastern Louisiana (Barataria and Terrebonne Bays), where salt marsh oiling was most widespread and severe ( Fig.…”

“…By 2014, more than 4 years after initial oiling, overall burrow density had not recovered to reference levels at the marsh edge. There appeared to be possible signs of recovery in one study in 2014, where oiling levels were moderate to heavy (Deis et al 2015); however, the other study in 2014 displayed ongoing impacts, perhaps due to more persistent or heavier oiling (Zengel et al 2015a; see also Fleeger et al 2015). Longer-lasting impacts at the marsh edge are not surprising.…”