Ecological implications of surficial marine gas hydrates for the associated small-sized benthic biota at the Hydrate Ridge (Cascadia Convergent Margin, NE Pacific)

• Published in: Marine ecology. Progress series (Halstenbek) 2002-11, Vol.243, p.25-38
• Main Authors: Sommer, Stefan, Pfannkuche, Olaf, Rickert, Dirk, Kähler, Anja
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Applied ecology; Bacteria; Beggiatoa; Biofilms; Biological and medical sciences; Biota; Calyptogena; Clams; Exploitation and management of natural biological resources (hunting, fishing and exploited populations survey, etc.); Fundamental and applied biological sciences. Psychology; Hydrates; Marine; Methane; Oxidation; Sea water ecosystems; Sediments; Sulfates; Sulfides; Synecology
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps243025

The effect of methane released from decomposing surficial gas hydrates (SGH) on standing stocks and activities of the small-sized benthic biota (SSBB; i.e. bacteria, fungi, protozoa, and meiobenthic organisms) was studied at about 790 m water depth, at the Hydrate Ridge, Cascadia subduction zone. Presence of SGH and elevated sulfide concentrations in the sediment were indicated by extensive bacterial mats ofBeggiatoasp. and clam fields of the bivalve mollusc Calyptogenasp. Vertical and horizontal distribution patterns of the SSBB biomass were derived from DNA and total adenylate (TA) sediment assays. Potential bacterial exoenzymatic hydrolytic activity was measured using fluorescein-di-acetate (FDA) as substrate. Estimates of chemoautotrophic production of particulate organic carbon (POC) were determined by14CO₂ uptake incubations. Inventories of chlaand pheopigments were determined as parameters of surface water primary produced POC input. Average SSBB biomass in clam field sediments integrated over the upper 10 cm (765.2 g C m–2, SD 190.1) was 3.6 times higher than in the adjacent control sites (213 g C m–2, SD 125). Average SSBB biomass in bacterial mat sediments, which were almost devoid of eukaryotic organisms > 31 μm, was 209 g C m–2(SD 65). Significant correlations between FDA, DNA and plant pigments imply that productivity of the SSBB at SGH sites is only partially uncoupled from the primary production of the surface water. Areal estimates of autotrophic Corgproduction at control sites, bacterial mat sites and in clam field sites were 5.7, 59.7 and 190.0 mg C m–2d–1, respectively. Based on different models predicting vertical POC fluxes from surface water primary production and water depth, these autotrophic POC productions account for 5 to 17% (controls), 35 to 68% (bacterial mats), and 63 to 87% (clam fields) of the bulk POC (sum of allochthonous POC input through the water column and sedimentary autochthonous autotrophic POC production) provided at the various sites. At SGH sites inventories of chlaand pheopigments, integrated over the upper 10 cm of the sediment, were half of that found at the control sites. This might be due to enhanced degradation of phytodetritally associated organic matter. The resulting low molecular weight organic carbon compounds might stimulate and fuel sulfate reduction, which is conducted in a microbial consortium with anaerobic methane consuming archaea. This syntrophic consortium might represent a prominent interfac