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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2006.05.007 Byline: J.W. Fleeger (a), K.R. Carman (a), P.B. Weisenhorn (a), H. Sofranko (a), T. Marshall (a), D. Thistle (b), J.P. Barry (c) Keywords: Carbon dioxide; Meiobenthos; Nematodes; Size distribution; Biovolume; Monterey Canyon Abstract: One proposal for ameliorating global warming is to sequester large amounts of carbon dioxide in the deep ocean, but the environmental consequences of sequestration for sediment-dwelling animals are poorly known. In a previous publication, we reported that [approximately equal to]80% of benthic copepods were killed in an experimental release of CO.sub.2 off northern California at 3262m. The effects of this release on nematodes are reported here. We examined samples of nematodes taken inside two 'corrals' into which CO.sub.2 was directly injected (providing an extreme endpoint for CO.sub.2 exposure) and taken near to and far from this CO.sub.2 source. After 30 days, pore-water pH was unchanged ([approximately equal to]7.8) at the sediment-water interface far ([approximately equal to]40m) from corrals, but pH profiles were reduced by [approximately equal to]0.75 near ([approximately equal to]2m) corrals. Corral pH was highly acidic (5.4 in a measurement from a subsequent experiment). Fifty randomly selected nematodes from each of four vertical layers from the 14 cores were photographed. They were assigned to a tail group (based on morphology), and individual biovolume was estimated from measurements of body length and width. Although nematode abundance (expressed as total nematodes and by tail group) was not affected, length, width, and individual biovolume significantly differed between near and far samples. Median nematode biovolume examined across tail group and core layer increased by [approximately equal to]48% inside and near corrals. Differences between near and corral samples were always less than differences between near and far samples. However, nematode length:width ratio did not differ between near and far, and the shapes of length, width, and biovolume frequency distributions were similar in all samples. We postulate that the nematode community throughout the upper 3cm suffered a high rate of mortality after exposure to CO.sub.2, and that nematodes were larger because postmortem expansions in body length and width occurred. Decomposition rates were probably low and corpses did not disintegrate in 30 days. The observable effects of a reduction in pH to about 7.0 after 30 days were as great as an extreme pH reduction (5.4), suggesting that 'moderate' CO.sub.2 exposure, compared to the range of exposures possible following CO.sub.2 release, causes high mortality rates in the two most abundant sediment-dwelling metazoans (nematodes and copepods). Author Affiliation: (a) Department of Biological Sciences, Louisiana State University, Baton Rouge, LA 70803-1725, USA (b) Department of Oceanography, Florida State University, Tallahassee, FL 32306-4320, USA (c) Monterey Bay Aquarium Research Institute, Moss Landing, CA 95039, USA Article History: Received 4 August 2005; Revised 17 May 2006; Accepted 20 May 2006

Xenotrichula intermedia populations present in the Mediterranean Sea, the northwestern Atlantic and the Gulf of Mexico are genetically different but morphologically similar. Analysis of 16 morphological features shows that the populations in the Gulf of Mexico differ from the others in having a smaller pharynx. However, the nucleotide sequence of the mitochondrial cytochrome oxidase I gene is different in different populations. This indicates that the different populations are separate sibling species rather than a single species.

A study investigates the settlement behavior of suspended meiofaunal copepods into shallow depressions. A large, recirculating laboratory flume is used. Meiobenthic copepods display a significant preference for algal-enriched sediments over non-enriched sediment in still water. However, non of the four species used are able to exercise initial habitat selection in moving water. Furthermore, under high shear conditions copepods are either unable to locate algal-enriched pits because they settled passively without re-emergence, or even if the re-emerge they could not overcome the shear velocity required for active habitat selection and consequently re-entered the flowing water.

Abstract: One proposed approach to ameliorate the effects of global warming is sequestration of the greenhouse gas CO2 in the deep sea. To evaluate the environmental impact of this approach, we exposed the sediment-dwelling fauna at the mouth of the Monterey Submarine Canyon (3262m) and a site on the nearby continental rise (3607m) to CO2-rich water. We measured meiobenthic nematode population and community metrics after ∼30-day exposures along a distance gradient from the CO2 source and with sediment depth to infer the patterns of mortality. We also compared the nematode response with that of harpacticoid copepods. Nematode abundance, average sediment depth, tail-group composition, and length: width ratio did not vary with distance from the CO2 source. However, quantile regression showed that nematode length and diameter increased in close proximity to the CO2 source in both experiments. Further, the effects of CO2 exposure and sediment depth (nematodes became more slender at one site, but larger at the other, with increasing depth in the sediment) varied with body size. For example, the response of the longest nematodes differed from those of average length. We propose that nematode body length and diameter increases were induced by lethal exposure to CO2-rich water and that nematodes experienced a high rate of mortality in both experiments. In contrast, copepods experienced high mortality rates in only one experiment suggesting that CO2 sequestration effects are taxon specific. [Copyright &y& Elsevier]

Abstract: A microcosm experiment was conducted using a replicated factorial design to determine if a benthic fish modifies the effects of sediment-bound contaminants (diesel fuel and two levels of a Cu, Cr, Pb, Hg and Cd mixture) on saltmarsh benthic primary producers and consumers. The naked goby, Gobiosoma bosc, a burrowing fish that preys on small macrofauna, was added to experimental microcosms. Goby burrowing and foraging significantly increased turbidity and disrupted the sediment surface. Results were typified by complex and varied responses with many statistically significant effects and interactions among treatments. Although G. bosc modified the responses to both diesel and metal pollution in invertebrates (but not microalgae), bioturbation did not increase or decrease the toxic effects of metals or diesel, and diesel–metal interactions did not vary in response to G. bosc. Specifically, G. bosc inhibited a trend toward diesel-induced increases in nematode abundance, and diesel toxicity inhibited increases in ostracod abundance stimulated by G. bosc. Diatoms, nematodes and the copepod Pseudostenhelia wellsi decreased in treatments with G. bosc. However, G. bosc lead to increases in cyanobacteria and ostracods and a trend toward increases in the copepod Pseudobradya sp. Our findings suggest that microcosm experiments are potentially poor mimics of natural systems without bioturbation. Conclusions about the direct and indirect effects of contaminants may differ with and without bioturbation. Finally, our work suggests that the direct effects of toxicants may inhibit or mask bioturbation effects that stimulate population growth of some meiofauna. [Copyright &y& Elsevier]