Effects of oil exposure, plant species composition, and plant genotypic diversity on salt marsh and mangrove assemblages

Abstract

2018. Effects of oil exposure, plant species composition, and plant genotypic diversity on salt marsh and mangrove assemblages. Ecosphere 9(4):Abstract. Climate change is causing shifts in the distribution and abundance of many species.Because species vary in the rate and degree of these shifts, novel transition zones have developed where new combinations of species overlap. If climate-mediated range shifts result in greater diversity, transition communities could have enhanced resistance and/or resilience, particularly if the resident and colonizing species differ in their response to environmental change. The range expansion of the tropical black mangrove, Avicennia germinans, into salt marshes dominated by the temperate cordgrass, Spartina alterniflora, provides an opportunity to examine the responses of climate-mediated transition zones to disturbance. We conducted a yearlong mesocosm experiment testing the effects of plant species identity and composition (A. germinans, S. alterniflora), as well as plant genotypic diversity (S. alterniflora only), on the response of coastal wetlands to oiling disturbance. Oil negatively impacted S. alterniflora and A. germinans both above-and belowground, though the timing of these effects varied, with S. alterniflora showing more immediate declines than A. germinans. As hypothesized, the magnitude of the oil effect was reduced in the mixed plant species treatment compared to the single species treatment for A. germinans survival (12% vs. 21% reduction) and belowground biomass (19% vs. 71% reduction). In addition, when exposed to oil, A. germinans crown area and volume were greater in the mixed species treatment compared to the single species treatment at the end of the experiment. However, we did not detect any benefit of mixed species communities or S. alterniflora genotypic diversity for the S. alterniflora response to oil. Our results suggest that transition habitats in the northern Gulf of Mexico where A. germinans and S. alterniflora co-occur will be negatively impacted by future oiling events, but that they are no more susceptible, and perhaps slightly less so, than habitats dominated by either individual species.

Growth Responses of Avicennia germinans and Batis maritima Seedlings to Weathered Light Sweet Crude Oil Applied to Soil and Aboveground Tissues

“…The oil application was repeated and drained daily for 5 days, and a diurnal tidal regime was simulated throughout the one-year experimental duration. Similar to the ndings presented herein, Hughes et al (2018) detected no effect of oiling on A. germinans stem height. Further, a consistent negative impact of oiling was not detected for crown volume, a metric representative of A, germinans aboveground growth by Hughes et al (2018), which is consistent with the lack of impacts to A. germinans aboveground biomass reported here.…”

“…Similar to the ndings presented herein, Hughes et al (2018) detected no effect of oiling on A. germinans stem height. Further, a consistent negative impact of oiling was not detected for crown volume, a metric representative of A, germinans aboveground growth by Hughes et al (2018), which is consistent with the lack of impacts to A. germinans aboveground biomass reported here. Interestingly, reductions to A. germinans leaf number were detected with oiling application, but only after a full year of growth under oiled conditions; no impact of oiling to leaf number was detected at the three, seven, or nine month measurement periods (Hughes et al 2018).…”

“…The frequency of oiling in coastal wetland habitats necessitates studies that provide insight into how oiling exposure impacts the health and subsequent recovery of speci c coastal wetland vegetation species. The effects of oiling exposure on A. germinans have been addressed in a number of observational and controlled studies (Getter et al 1983;Pro t et al 1995;Chindah et al 2011;Hughes et al 2018). However, knowledge gaps exist in regard to the interactive effect of soil and aboveground tissue oiling for A. germinans seedlings.…”

A Synthesis of Deepwater Horizon Impacts on Coastal and Nearshore Living Marine Resources

“…Some impacts, however, were severe and obvious. For sedentary species including Eastern Oyster the combination of the toxicity of oil and the effects of freshening the marshes not only resulted in mass oyster mortalities (Powers et al, 2017a), but oiling of the marshes was also was associated with collapse of the marsh edges and the loss of oyster bars, which in turn resulted in increased soil erosion and other negative consequences for marsh ecosystems (Grabowski et al, 2012;Powers et al, 2017c;Hughes et al, 2018). Likewise, Bottlenose Dolphins' exposure to toxic oil concentrations presented a variety of negative health effects including reduced reproduction and associated morbidities and mortalities (Schwacke et al, 2014(Schwacke et al, , 2017.…”

Deepwater Horizon Oil Spill Impacts on Organisms and Habitats

“…However, damage was reduced when both species were present together. Therefore, researchers conclude that greater species diversity may mitigate some of the negative effects of an oil impact (Hughes et al 2018).…”