Deepwater Horizon was the largest marine oil spill in U.S. waters, oiling large expanses of coastal wetland shorelines. We compared marsh periwinkle (Littoraria irrorata) density and shell length at salt marsh sites with heavy oiling to reference conditions ∼16 months after oiling. We also compared periwinkle density and size among oiled sites with and without shoreline cleanup treatments. Densities of periwinkles were reduced by 80-90% at the oiled marsh edge and by 50% in the oiled marsh interior (∼9 m inland) compared to reference, with greatest numerical losses of periwinkles in the marsh interior, where densities were naturally higher. Shoreline cleanup further reduced adult snail density as well as snail size. Based on the size of adult periwinkles observed coupled with age and growth information, population recovery is projected to take several years once oiling and habitat conditions in affected areas are suitable to support normal periwinkle life-history functions. Where heavily oiled marshes have experienced accelerated erosion as a result of the spill, these habitat impacts would represent additional losses of periwinkles. Losses of marsh periwinkles would likely affect other ecosystem processes and attributes, including organic matter and nutrient cycling, marsh-estuarine food chains, and multiple species that prey on periwinkles.

Response actions associated with oil spills often have significant impacts on ecological communities. During the 87 d long Deepwater Horizon oil spill, the State of Louisiana (USA) released vast quantities of Mississippi River water into 2 estuarine basins (Barataria Bay and Black Bay/Breton Sound) in response to the approach of oil. We assessed the impact on subtidal oyster populations of this novel oil spill response action using 3 independent methods: (1) comparison of fisheries-independent post-spill densities to a pre-spill temporal baseline; (2) comparison of oyster density collected during natural resource damage assessment sampling between the area of maximal freshwater impact and reference areas in the 2 basins; and (3) estimation from a doseresponse model derived from an analysis of an in situ mark and recapture study conducted in 2010 to assess the relationship between salinity and oyster mortality. A substantial portion of both basins (483 km 2 of Barataria Bay and 362 km 2 of Black Bay/Breton Sound) experienced prolonged periods of very low (< 5 ppt) salinity in 2010 that lasted at least 1 mo longer than the average duration of low salinity between 2006 and 2009. The 3 approaches all indicate that dramatic losses occurred in the number of market-sized (> 75 mm) oysters as a result of a system-wide lowering of salinities, with an estimated 1.16 to 3.29 billion market-equivalent oysters lost. The efficacy of the large-scale response action of altering hydrographic conditions during the summer oyster growth period should be examined in light of the major perturbation to oyster communities.KEY WORDS: Estuary · Oil spill response · Natural resources damage assessment · Oyster reefs · Gulf of Mexico · Crassostrea virginica · Hydrography OPEN PEN ACCESS CCESS Contribution to the Theme Section 'Response of nearshore ecosystems to the Deepwater Horizon oil spill'Mar Ecol Prog Ser 576: [175][176][177][178][179][180][181][182][183][184][185][186][187] 2017 Too much freshwater reduces local salinity to levels where survivorship, growth, or reproduction of oysters is impaired, whereas too much ocean water generally elevates salinities and is associated with higher levels of predators (e.g. the oyster drill Stramonita haemastoma) or disease (e.g. the protozoan parasite Perkinsus marinus) that leads to reduced survivorship (e.g. Gunter 1955, Davis 1958, 1979, Chatry et al. 1983, Brown & Richardson 1988, Soniat & Brody 1988, Fodrie et al. 2008, La Peyre et al. 2009. Although the specific thresholds of these triggers varied from study to study, the general pattern of oysters thriving in waters whose average annual salinities fall be tween 8 and 22 ppt with frequent brief pulses of freshwater input is well established and accepted by oyster biologists. Because settlement of oysters is gregarious on existing oyster shells, sustainable populations of oysters require that the position of this green zone of water stays relatively fixed over time. A substantial perturbation of this salinity zone away from are...

No abstract

The Deepwater Horizon (DWH) oil spill affected more than 2000 km of shoreline. DWH oil entered the nearshore environment, stranding on shorelines as tar balls and/or emulsified oil, or forming submerged oil mats and integrating into nearshore sediments. The available chemistry data showed submerged sediments, especially within the first 50 m from oiled shorelines, displayed patchy distributions of elevated polycyclic aromatic hydrocarbon (PAH) concentrations in excess of ambient concentrations, which were quantified based on forensic findings establishing their source as being from the Macondo oil. Consistent with observed shoreline oiling conditions, PAH concentrations in the soils of affected Louisiana coastal wetlands were orders of magnitude higher than ambient concentrations, especially in locations along the seaward edge of the marsh. Both total and petrogenic PAHs decreased with distance from the shore in both inland and offshore directions. Although PAHs exhibited evidence of weathering over time, in the most heavily oiled areas, they continued to exceed ambient concentrations by orders of magnitude through fall of 2013.

Abstract. Marine species with planktonic larvae often have high spatial and temporal variation in recruitment that leads to subsequent variation in the ecology of benthic adults. Using a combination of published and unpublished data, we compared the population structure of the salt marsh snail, Littoraria irrorata, between the South Atlantic Bight and the Gulf Coast of the United States to infer geographic differences in recruitment and to test the hypothesis that the Deepwater Horizon oil spill led to widespread recruitment failure of L. irrorata in Louisiana in 2010. Size-frequency distributions in both ecoregions were bimodal, with troughs in the distributions consistent with a transition from sub-adults to adults at~13 mm in shell length as reported in the literature; however, adult snails reached larger sizes in the Gulf Coast. The ratio of sub-adults to adults was 1.5-2 times greater in the South Atlantic Bight than the Gulf Coast, consistent with higher recruitment rates in the South Atlantic Bight. Higher recruitment rates in the South Atlantic Bight could contribute to higher snail densities and reduced adult growth in this region. The ratio of sub-adults to adults in Louisiana was lower in 2011 than in previous years, and began to recover in 2012-2014, consistent with widespread recruitment failure in 2010, when large expanses of spilled oil were present in coastal waters. Our results reveal an important difference in the ecology of a key salt marsh invertebrate between the two ecoregions, and also suggest that the Deepwater Horizon oil spill may have caused widespread recruitment failure in this species and perhaps others with similar planktonic larval stages.