The ecology, biogeochemistry and phylogeny of methane seep and non-seep benthic foraminifera from the Pacific margin.

摘要

In an effort to understand the relationships between active methane seep and adjacent non-seep (inactive) populations of the deep-sea foraminifera Cibicidoides wuellerstorfi, a common paleo-indicator species, from methane seeps in the Pacific were analyzed and compared to one another for genetic similarities of small subunit rDNA (SSU rDNA) sequences. Pacific Ocean C. wuellerstorfi were also compared to those collected from other localities around the world (based on 18S gene available on Genbank, e.g., Schweizer et al., 2009). Results from this study revealed that C. wuellerstorfi living in seeps near Costa Rica and Hydrate Ridge are genetically similar to one another at the species level. Individuals collected from the same location that display opposite coiling directions (dextral and sinistral) had no species level genetic differences. Comparisons of specimens with genetic information available from Genbank (SSU rDNA) showed that Pacific individuals, collected for this study, are genetically similar to those previously analyzed from the North Atlantic and Antarctic. These observations provide strong evidence for the true cosmopolitan nature of C. wuellerstorfi and highlight the importance of understanding how these microscopic organisms are able to maintain sufficient genetic exchange to remain within the same species between seep and non-seep habitats and over global distances.;Although organic matter degradation rates have been studied for some time, in situ rates of protoplasm degradation in deep-sea foraminiferal tests have been estimated based on laboratory experiments and sediment distribution patterns. Information regarding degradation rates of foraminiferal protoplasm is essential in the use of non-vital stains in identifying the amount and character of protoplasm in tests which remains the most commonly used method to assess living populations of benthic foraminifera (e.g., Murray and Bowser, 2000). In an effort to examine the retention potential of foraminiferal protoplasm on the deep seafloor 36 frozen, protoplasm filled Cibicidoides wuelllerstorfi were placed in natural sediments inside experimental containers and deployed on for 390 to 396 days. Despite oxygen-poor conditions (0.24 mL/L to 0.37 mL/L) that would be expected to promote preservation of organic matter, and experimental container protection from macro- and megafauna, 72% of deployed tests containing protoplasm were destroyed beyond recognition within 396 days. Of the 10 specimens (28%) recovered, 9 retained at least some protoplasm, but only 1 individual had the potential to be identified as living based on Rose Bengal staining techniques. However, in this specimen, protoplasm was clearly altered or missing in some chambers. The results of this study suggest that it is unlikely that many, if any, benthic foraminiferal specimens containing protoplasm terminated by freezing would be conservatively considered as recently living using Rose Bengal as an indicator of the extent and character of protoplasm within the test after 396 days or less exposed to in situ conditions in deep-seafloor habitats. (Abstract shortened by UMI.).