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.PeerJ PrePrints | https://dx.doi.org/10.7287/peerj.preprints.1480v1 | CC-BY 4.0 Open Access | recAbstract 17The Deepwater Horizon oil spill resulted in varying degrees of oiling in the salt marshes of 18 northern Barataria Bay, Louisiana, USA. This study examines the effects of oiling intensity and recovery 19 on two conspicuous marsh-platform macroinvertebrates, Uca spp., fiddler crabs, and Littoraria irrorata, 20 the salt marsh periwinkle, from 2.5 to 4.5 years after the spill. The dominant fiddler crab within these 21 marshes, Uca longisignalis, was the only species observed in field collections, and no significant 22 difference in burrow density or burrow size was found among oiling levels over the study period 23 indicating recovery from any negative effects of oiling already occurred for this species. The highest 24 density of L. irrorata was found at moderately oiled sites compared to both reference (without visible 25 oiling) and heavily oiled stations. Spartina alterniflora density recovered within two years after the spill 26 at the moderately oiled stations facilitating recovery of L. irrorata approximately one year later. L.27 irrorata average shell length and length-frequency distributions were equivalent at mod...

Five years of Deepwater Horizon oil spill effects on marsh periwinkles Littoraria irrorata

“…Even so, densities at their oiled sites appeared recovered by 2015 and were similar to mid-range to higher values typical for the region (see Zengel et al 2016a). However, even though densities appeared recovered in the Deis et al (2015) data, shifts in size distributions to smaller adults and sub-adults, and fewer large adults, were evident at their oiled sites across all years, similar to those observed in our combined analysis. This is likely due to initial losses of snails across all size classes, followed by subsequent recruitment or immigration of smaller (younger) snails that had not yet grown into the larger size classes.…”

“…Because of this, we consider recovery at the Silliman et al (2012) marsh edge sites to be inconclusive. Density differences between oiled and reference sites in the Deis et al (2015Deis et al ( ) data (2012Deis et al ( −2015 were not as large as observed elsewhere, although Deis et al (2015) indicated that a confounding influence of greater Juncus roemerianus plant dominance (and less Spartina alterniflora) may have resulted in lower periwinkle densities at their reference sites, affecting their comparisons. Even so, densities at their oiled sites appeared recovered by 2015 and were similar to mid-range to higher values typical for the region (see Zengel et al 2016a).…”

“…Detailed methods are included in each of the published studies and are available for the GoMRI data (Deis et al 2015). Study sites were widely distributed throughout the northern Gulf of Mexico (Louisiana, Mississippi, Alabama), with numerous sites concentrated in southeastern Louisiana (Barataria and Terrebonne Bays), where salt marsh oiling was most widespread and severe (Fig.…”

“…Preliminary analysis showed no major indications of seasonality in the density data, so we did not exclude any sampling dates. Where one study sampled 2 or more times per year (Deis et al 2015), we used an annual average for each site. We were able to compile density data for 22 study-zone-by-year combinations.…”

“…Because natural populations can be quite variable in space and time, it can be difficult in many cases for individual studies to clearly identify population and community changes even after large oil spills, hence the need for integration of data across multiple studies (Fodrie et al 2014). Here, we synthesize results of these 5 studies and other on going work in a meta-analysis, using published and unpublished sources spanning more than 5 yr, in cluding newly available Natural Resources Damage Assessment (NRDA) and Gulf of Mexico Research Initiative (GoMRI) (Deis et al 2015) data. We tested the hypotheses that the oil spill reduced periwinkle density (snail abundance), reduced mean periwinkle shell length (snail size), and altered periwinkle size distributions in salt marshes that were heavily oiled.…”