Recovery of the salt marsh periwinkle (Littoraria irrorata) 9 years after the Deepwater Horizon oil spill: Size matters

Severe ecological impacts caused by one of the worst orphan oil spills worldwide

Orphan oil spills pose a severe risk to ocean sustainability; however, they are understudied. We provide the first synthetic assessment of short-term ecological impacts of the most extensive oil spill in tropical oceans, which affected 2900 km of Brazil's coastline in 2019. Oil ingestion, changes in sex ratio and size of animals, morphological abnormalities of larvae and eggs, mutagenic, behavioral, and morphological alterations, contamination by polycyclic aromatic hydrocarbons, and mortality were detected. A decrease in species richness and abundance of oil-sensitive animals, an increase in opportunistic and oil-tolerant organisms, and simplification of communities was observed. The impacts were observed in sponges, corals, mollusks, crustaceans, polychaetes, echinoderms, turtles, birds, fish, and mammals. The majority of studies were conducted on bioindicator substrate-associated organisms, with 68.4% of the studies examining the benthos, 21.2% the nekton, and 10.4% the plankton. Moreover, most of the current short-term impacts assessment studies were focused on the species level (66.7%), with fewer studies on the community level (19%), and even fewer on oil-affected ecosystems (14.3%). Oil-related impacts were detected in five sensitive habitats, including blue-carbon ecosystems (e.g., mangroves and seagrass beds) and coastal reefs. These results call for the development of new ocean-basin observation systems for orphan spills. Finally, we discuss how these mysterious oil spills from unknown sources pose a risk to sustainable development goals and ocean-based actions to tackle global climate change.

Estuarine oiling increases a long-term decline in mussel growth

The ribbed mussel, Geukensia granosissima, cycles nutrients, contributes to soil stability, and can be a major component of predator-prey communities in salt marshes. Mussels were exposed to the 2010 Deepwater Horizon oil spill in the Gulf of Mexico, and salt marshes remain contaminated eight years later. We hypothesized that the oiled mussels had reduced annual growth, altered population size frequency, and perhaps changed valve morphometrics. We sampled 10 marshes near Port Sulphur, LA, to measure the morphometrics of 133 mussels and their age-specific growth rate, and also the marsh oil content and percent vegetative cover. The relationships between valve weight, length and biomass weight were stable as mussels aged. A Year 1 growth decline from 1994 to 2018 is not easily explained by estuarine acidification, flooding, and temperature rise; freshening of estuarine waters is suggested to be a probable causal factor in the declining growth rate. The average valve length and dry biomass per valve declined with oiling in 2010. A multiple regression equation using the percent cover and oil concentration in 2018 described 70% of the variation in valve length. Sites with the highest oiling had few mussels with 14 annual growth bands and more of the younger mussels compared to sites with the lowest oiling. Valve growth in Year 1 declined for four years after the oil spill and was not compensated by higher growth rates in older mussels. Annual growth was below the amount predicted in a regression equation for the five years after the oil spill. Mussel populations may also have been structured by predators that were also responsive to oiling in subtle ways.

Stable isotope analyses identify trophic niche partitioning between sympatric terrestrial vertebrates in coastal saltmarshes with differing oiling histories

Bioindicator species are commonly used as proxies to help identify the ecological effects of oil spills and other stressors. However, the utility of taxa as bioindicators is dependent on understanding their trophic niche and life history characteristics, as these factors mediate their ecological responses. Seaside sparrows (Ammospiza maritima) and marsh rice rats (Oryzomys palustris) are two ubiquitous terrestrial vertebrates that are thought to be bioindicators of oil spills in saltmarsh ecosystems. To improve the utility of these omnivorous taxa as bioindicators, we used carbon and nitrogen stable isotope analysis to quantify their trophic niches at saltmarshes in coastal Louisiana with differing oiling histories. We found that rats generally had lower trophic positions and incorporated more aquatic prey relative to seaside sparrows. The range of resources used (i.e.,trophic niche width) varied based on oiling history. Seaside sparrows had wider trophic niches than marsh rice rats at unoiled sites, but not at oiled sites. Trophic niche widths of conspecifics were less consistent at oiled sites, although marsh rice rats at oiled sites had wider trophic niches than rats at unoiled sites. These results suggest that past oiling histories may have imparted subtle, yet differing effects on the foraging ecology of these two co-occurring species. However, the temporal lag between initial oiling and our study makes identifying the ultimate drivers of differences between oiled and unoiled sites challenging. Even so, our findings provide a baseline quantification of the trophic niches of sympatric seaside sparrows and marsh rice rats that will aid in the use of these species as indicators of oiling and other environmental stressors in saltmarsh ecosystems.

How Do Indirect Effects of Contaminants Inform Ecotoxicology? A Review

Indirect effects in ecotoxicology are defined as chemical- or pollutant-induced alterations in the density or behavior of sensitive species that have cascading effects on tolerant species in natural systems. As a result, species interaction networks (e.g., interactions associated with predation or competition) may be altered in such a way as to bring about large changes in populations and/or communities that may further cascade to disrupt ecosystem function and services. Field studies and experimental outcomes as well as models indicate that indirect effects are most likely to occur in communities in which the strength of interactions and the sensitivity to contaminants differ markedly among species, and that indirect effects will vary over space and time as species composition, trophic structure, and environmental factors vary. However, knowledge of indirect effects is essential to improve understanding of the potential for chemical harm in natural systems. For example, indirect effects may confound laboratory-based ecological risk assessment by enhancing, masking, or spuriously indicating the direct effect of chemical contaminants. Progress to better anticipate and interpret the significance of indirect effects will be made as monitoring programs and long-term ecological research are conducted that facilitate critical experimental field and mesocosm investigations, and as chemical transport and fate models, individual-based direct effects models, and ecosystem/food web models continue to be improved and become better integrated.