Investigating the sublethal effects of oil exposure on infaunal behavior, bioturbation, and sediment oxygen consumption

Abstract

Anthropogenic disturbances such as oil spills can cause mortality in benthic infaunal communities, reducing diversity and abundance and impeding sediment ecosystem functions. Sublethal effects of oil exposure have received less attention, however. We conducted a mesocosm experiment exposing 2 infaunal taxa, the polychaete Owenia fusiformis and the brittle star Hemipholis elongata, to sublethal concentrations of the water-accommodated fraction (WAF) of oil. We evaluated the effects of WAF on animal behavior, bioturbation, and sediment oxygen demand (SOD) in infaunal assemblages of both mixed and single species. WAF exposure did not affect O. fusiformis feeding behavior, nor did it influence bioturbation. Compared to O. fusiformis, the brittle star H. elongata mixed more surface sediments to greater depths and to a greater extent horizontally. Bioturbation in mesocosms with both taxa was consistent with predictions from monocultures for substitutive densities, but lower than predicted for additive densities. This indicates that taxa interacted (negatively) only at higher densities. SOD was higher in oiled than unoiled treatments initially (at 1-3 d), but this difference disappeared after the first sampling, consistent with a decrease in total petroleum hydrocarbons in the WAF treatment over the same time period. Higher SOD in WAF-exposed faunal treatments than sediments with no fauna suggested that faunal activities may enhance microbial degradation of hydrocarbons. These findings suggest that exposure to WAF stimulated microbial metabolism in the first few days of the experiment, but did not affect macrofaunal behavior/function, nor have lasting effects on sediment ecosystem functions.

Evidence of Rapid Functional Benthic Recovery Following the Deepwater Horizon Oil Spill

“…Microbial consortia capable of degrading petroleum-based hydrocarbons increased rapidly, while the Macondo well released oil, and biodegradation was faster than expected in the deep hydrocarbon plume in the water column. , Bioturbation enhances microbial biodegradation of organic matter in sediments, , including the degradation of oil and oil-derived compounds . Specifically, experiments using Macondo-like crude oil found that oil additions stimulated microbial degradation, an effect that was enhanced in the presence of bioturbation. , Experimental additions also indicated that short-term exposure to the water-accommodated fraction of oil did not affect bioturbation activity, and deep bioturbation has been suggested as an adaptive strategy in deep-sea environments that receive influxes of organic material. , These findings paired with SPI results of bioturbation deep within the sediment column throughout the area suggest that a positive feedback loop between microbial degradation and bioturbation may be a plausible mechanism for benthic recovery from the Deepwater Horizon oil spill.…”

“…61,62 Bioturbation enhances microbial biodegradation of organic matter in sediments, 47,63 including the degradation of oil and oil-derived compounds. 64 Specifically, experiments using Macondo-like crude oil found that oil additions stimulated microbial degradation, an effect that was enhanced in the presence of bioturbation. 64,65 Experimental additions also indicated that short-term exposure to the water-accommodated fraction of oil did not affect bioturbation activity, 66 and deep bioturbation has been suggested as an adaptive strategy in deep-sea environments that receive influxes of organic material.…”

“…64 Specifically, experiments using Macondo-like crude oil found that oil additions stimulated microbial degradation, an effect that was enhanced in the presence of bioturbation. 64,65 Experimental additions also indicated that short-term exposure to the water-accommodated fraction of oil did not affect bioturbation activity, 66 and deep bioturbation has been suggested as an adaptive strategy in deep-sea environments that receive influxes of organic material. 66,67 These findings paired with SPI results of bioturbation deep within the sediment column throughout the area suggest that a positive feedback loop between microbial degradation and bioturbation may be a plausible mechanism for benthic recovery from the Deepwater Horizon oil spill.…”

Transport of biodeposits and benthic footprint around an oyster farm, Damariscotta Estuary, Maine

“…In incubations, the cores were each submerged in separate 5-gallon buckets of seawater and watertight caps affixed to the tops (after methods and Fig 2 in Dorgan et al, 2020 ). The caps allowed for six cm of overlying water and were each equipped with a stir-bar to gently circulate the overlying water, inflow and outflow taps for water sampling, and an Atlas Scientific DO probe (Atlas Scientific LLC, Long Island City, NY) that measured oxygen concentrations in the overlying water of each core every ∼12 s. The buckets containing the cores were covered with foil to prevent oxygen production by photosynthesis from corrupting oxygen consumption rate measurements.…”

Biodiversity influences the effects of oil disturbance on coastal ecosystems

“…Schrandt et al (2018).bHughes et al (2018).cDorgan et al (2020).| 5 of 15TA B L E 2 Total number of experiments included both oil-only (n = 10) and oil + dispersant experiments (n Spartina belowground biomass, Spartina leaf growth, Flower production, Seed production B. Nitrite reductase (denitrifer) microbial Abundance, Nitrous oxide reductase (denitrifer) microbial Abundance, Chlorophyll a concentration, Bacterial Shannon Diversity A. Denitrification Potential Rate, N2 fixation potential; B. Sediment oxygen demandParentheses denote the number of effect sizes (k) for both monoculture and polyculture in total within oil and oil + dispersant experiments. Responses were categorized into 3 levels of biological organization: Population: fitness and production metrics of target taxa or genotype manipulated in diversity treatment; Community: response of associated species in response to changes in target diversity; or Ecosystem: change in ecosystem functions or processes in response to variation in target diversity.…”