Response of a benthic food web to hydrocarbon contamination

Abstract

Direct and indirect effects of diesel-contaminated sediment on microalgae, meiofauna, and meiofauna-microalgae trophic interactions were examined in a microcosm study of the sediment community from a Spartina aZterniJora salt marsh. Microcosms of natural sediment were given small daily doses of contaminated sediment over a 28-d period, creating low-, medium-, and high-diesel treatment concentrations of -0.5, 5.5, and 55 ppm PAH, respectively. Diesel caused initial (within 7 h) reductions in microalgal grazing by meiobenthic harpacticoid copepods. Over longer periods of exposure (7-28 d), grazing on microalgae by copepods as a group was reduced in highdiesel treatments, primarily because of high copepod mortality. In contrast, grazing by and abundance of Cletocamptus deitersi (a copepod) was significantly enhanced in high-diesel treatments. Concurrent with reduced grazing by copepods, nematode grazing rates increased significantly in high-diesel treatments, indicating possible competition for microalgae between copepods and nematodes. In spite of transiently enhanced grazing by nematodes and C. deitersi, total meiofaunal grazing on microalgae was reduced in high-diesel treatments. Increased Chl a: pheopigment ratios in contaminated sediments were also indicative of reduced grazing pressure. A large (10X) increase in microalgal biomass was observed in high-diesel treatments and was likely a consequence of reduced meiofaunal grazing. The general responses observed in microcosms were also observed in a field study of polycyclic aromatic hydrocarbon contamination. Collectively, our data indicate that benthic microalgal biomass is controlled by meiofaunal grazing and that meiofauna may compete for limited algal resources. Furthermore, consideration of multiple trophic levels and their interactions allows a more complete and ecologically meaningful understanding of the mechanisms by which contaminants induce changes in natural communities.

Functional and structural responses of marine plankton food web to pyrene contamination

“…Other studies showed no effects of PAHs on copepod grazing (Carman et al 1997, and references herein), which was attributed to tolerance variability, within and among species, or to positive indirect effects from changes in phytoplankton (Carman et al 2000). These possible causes could also be valid in our study, where no severe effects of pyrene exposure were observed on zooplankton community grazing after Day 2.…”

“…This is especially true for high-molecular-weight PAHs, but also for other PAHs, such as pyrene, since they all have a high affinity to particulate matter. Studies on the biological effects of PAHs have therefore been focused on the benthic environment (Carman et al 1997, Lotufo 1997, Selck et al 2003. The few reported measurements of environmental concentrations of pyrene in the pelagic zone range from < 0.04 to 5.45 nmol l -1 pyrene (Dachs et al 1997, Law et al 1997, Rudnick & Chen 1998, Witt 2002, Latimer & Zheng 2003.…”

Impacts of permethrin contamination on nematode density and diversity: A microcosm study on benthic meiofauna from a Mediterranean coastal lagoon

“…Stimulation of selected nematode species has been observed in several studies of trace metals (GyeduAbabio & Baird 2006;Austen et al 1994;Mahmoudi et al 2007), hydrocarbons (Coull et Chandler 1992;Peterson et al 1996;Carman et al 1997;Beyrem et Aďssa 2000;Mahmoudi et al 2005) lubricants (Thompson et al 2007;Beyrem et al 2010) and pesticide (Boufahja et al 2011). These species take advantage of the stressed situation at a particular site to dominate in numbers at the expense of other nematode species.…”

Effects of the bioturbating crab <i>Macrophthalmus</i> <i>japonicus</i> on abiotic and biotic tidal mudflat characteristics in the Tama River, Tokyo Bay, Japan

“…In other words, M. japonicus maintained a high level of primary production of MPB (despite the low biomass of the controls) by stabilizing the sediment through the maintenance of finer particles, akin to gardening by bioturbators (Hylleberg 1975). In a related example, Arenicola marina, an upward conveyor , induces MPB blooming around their burrows by supplying nutrients from the reworked sediment (Chennu et al 2015). In the present situation, however, the blooming of MPB in the exclusion treatments suggests that nutrients may not be similarly implicated, and that M. japonicus may instead be gardening MPB by maintaining the level of finer particles in the sediment surface and, consequently, sediment stability.…”

“…MPB biomass was expressed as chlorophyll-a content (chla) and total phaeopigments (phaeo), and the turnover rate of MPB was estimated from the ratio of chl-a to phaeo (chl-a/phaeo). Although Carman et al (1997) used this ratio as an indirect qualitative measure of feeding pressure on MPB, it was defined here as the turnover ratio of MPB against feeding, with a lower chl-a/phaeo ratio indicating a higher MPB turnover. Sediment samples for the chl-a and phaeo analyses were taken with a plastic corer (2 cm diameter) to a depth of 0.5 cm.…”