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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

Abstract: One proposal for alleviating global warming is to sequester large amounts of industrial carbon dioxide on the deep-sea floor, but the environmental consequences of sequestration for the animals living in the sediment are poorly known. In an earlier publication, we reported that, during an experimental sequestration off central California (36.378°N, 122.676°W, 3262 m depth), most individuals of our target taxon (the harpacticoid copepods) were killed, but ∼20% survived. Because knowledge of which species survived and how they did so could clarify the effects of sequestration on the fauna, we have now identified the individuals from that experiment to species. Although most were adversely affected, species differed significantly in the degree of their susceptibility. Unexpectedly, six species showed no effect and may be resistant. The hypothesis that harpacticoids could escape the effects of carbon dioxide-rich seawater by moving deeper into the seabed was not supported. Exposure to carbon dioxide-rich seawater created partially defaunated areas, but we found no evidence that disturbance-exploiting harpacticoid species invaded during the recovery of the affected area. Because the environmental effects of the carbon dioxide (e.g. unusually acidic pore water) were still present, however, the opportunity for invasion might not yet have occurred. Differences among species in susceptibility increase the complexity of the effects of carbon dioxide sequestration on the deep-sea fauna. [Copyright &y& Elsevier]