Recruitment response of methane-seep macrofauna to sulfide-rich sediments: An in situ experiment

• Published in: Journal of experimental marine biology and ecology 2006-03, Vol.330 (1), p.132-150
• Main Authors: Levin, Lisa A., Ziebis, Wiebke, Mendoza, Guillermo F., Growney-Cannon, Valerie, Walther, Shelly
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Annelida; Biological and medical sciences; Colonization; Continental slope; Dorvilleidae; Fundamental and applied biological sciences. Psychology; Hydrogen sulfide; In situ experiments; Infauna; Marine; Mediomastus; Nephtys cornuta; Nerillidae; Paraonidae; Sea water ecosystems; Settlement; Synecology
• ISSN: 0022-0981; 1879-1697
• DOI: 10.1016/j.jembe.2005.12.022

Hydrodynamically unbiased colonization trays were deployed for 6 months (Oct. 2000 to April 2001) on the northern California margin (Eel R. region; 525 m) to examine macrofaunal colonization rates at methane seeps. The influence of sulfide on recruitment and survival was examined by deploying sediments with and without sulfide added; effect of seep proximity was evaluated by placing trays inside and outside seeps. The trays contained a two-layer system mimicking vesicomyid clam bed habitat geochemistry, with 8–9 mM sulfide in a lower agar layer at the start of the experiment. After 6 month on the seabed, the lower agar layer contained 2–4 mM H 2S. We observed rapid macrofaunal colonization equivalent to 50% of initial non-seep ambient densities. There was no difference in total colonizer densities, number of species, or rarefaction diversity among 3 treatments: (1) controls (no sulfide added) placed outside seeps, (2) trays with sulfide added placed outside seeps and (3) trays with sulfide added placed inside seep patches. Colonization trays with sulfide placed at seeps had different species composition from trays without sulfide place outside seeps; there were more amphipods (non-ampeliscid) and cumaceans in the seep/sulfide treatment and more nemerteans, Nephtys cornuta and tanaids in the non-seep/no-sulfide treatment. Outside seeps, annelids comprised < 15% of tray colonists; within seep patches, annelids comprised 5 of the top 10 dominant colonizing taxa (24% of the total). The polychaetes Mediomastus sp., Aphelochaeta sp., Paraonidae sp., and Nerillidae sp. exhibited significantly higher densities in sulfide additions. Tanaids, echinoderms, and N. cornuta exhibited sulfide avoidance. At least 6 dorvilleid polychaete species colonized the experiments. Of these, 4 species occurred exclusively in trays with sulfide added and 80% of all dorvilleid individuals were found in trays with sulfide placed inside seep sediments. Counts of large sulfur bacterial filaments were positively correlated with maximum sulfide concentration in each tray, and with proximity of sulfide to the sediment surface. However, total macrofaunal densities were not correlated with tray sulfide concentrations. As a group, tray assemblages achieved some but not all characteristics of ambient seep assemblages after 6-month exposure on the sea floor. Distinctive colonization patterns at methane seeps contribute to the dynamic mosaic of habitat patches that characterize the eastern Pacifi