Many of the world's productive deepwater hydrocarbon basins experience significant and ongoing vertical migration of fluids and gases to the modern seafloor. These products, which are composed of hydrocarbon gases, crude oil, formation fluids, and fluidized sediment, dramatically change the geologic character of the ocean floor, and they create sites where chemosynthetic communities supported by sulfide and hydrocarbons flourish.Unique fauna inhabit these sites, and the chemosynthetic primary production results in communities with biomass much greater than that of the surrounding seafloor.

The activity rhythm of the cold seep shrimp Alvinocaris stactophila from the Gulf of Mexico slope (650 m depth) was investigated in the laboratory in relation to an artificial 12 h light-dark regime. Animals were sampled with a submersible and transferred into individual aquaria where their activity was monitored for 5 d by taking digital video snapshots every 30 s. An observer analysed the footage by counting the number of times an animal crossed two perpendicular lines drawn on a PC screen per 30 min interval. Resulting time series were represented over consecutive days and the waveform analysis was used to precisely assess the phase (i.e. the peak timing) and its limits (i.e. onset and offset) in relation to light ON and OFF. The majority (73%) of animals showed a marked nocturnal pattern of activity with number of movements close to zero during the photophase. Waveform analysis showed that the behavioural transition from activity to inactivity after light ON occurred within approximately 1 h. Considering the general lack of knowledge on the regulation of activity rhythms of crustaceans from subtidal areas, the present data provide a new insight on the role played by light in the regulation of animal activity rhythm in deep-water environments such as those of the cold seeps in the Gulf of Mexico.

Peepers are a common alternative to push cores for collecting porewater from shallow aquatic environments such as lakes, streams, and wetlands but are infrequently used to sample deep‐sea sediments due to design limitations. In this study, a peeper was developed to obtain porewater from precisely located positions on the deep‐sea floor using remotely operated or manned submersibles. The sample cells of the peepers can be sealed closed after they are deoxygenated on board a ship to ensure that they remain anoxic until peepers are deployed at the deep‐sea sampling location. Similarly, peeper cells can be closed at the end of an incubation period to maintain sample integrity during submersible recovery and until sample processing. Each peeper can be used to collect samples from 10 cm above the sediment water interface and at 10 cm intervals down to 60 cm depth in the sediment, and can provide sufficient volume for multiple chemical analyses, including stable isotope ratio determinations.

Previous studies have shown clear, predictable successional trends in habitat characteristics and community structure in tubeworm aggregations at 3 similar hydrocarbon-seep sites on the central upper Louisiana slope of the Gulf of Mexico. In this study, we examine these trends in quantitative community collections from 7 additional hydrocarbon-seep sites widely distributed in the northern Gulf of Mexico. The relative proportions and sizes of Lamellibrachia luymesi and Seepiophila jonesi in tubeworm aggregations were similar at new and central sites, though S. jonesi dominated some collections from new sites, a situation not previously observed at central sites. In general, sulfide declined with increasing aggregation age (average size of tubeworms), but there was more variability in this trend at the new sites. Tubeworm-associated community composition was similar at new and central sites, with only a few rare species collected at the new sites for the first time. The most significant differences in the communities at new sites were the lower relative abundance of various gastropod species, and the absence of gastropods from collections made at the Viosca Knoll site. This community type was largely restricted to young aggregations at new sites that were more isolated from other tubeworm aggregations and consisted of higher proportions of S. jonesi. As succession proceeds from young to old aggregations, many of the previously described processes were apparent at the new sites including a reduction in biomass and a shift in trophic structure from endemic primary consumers to non-endemic higher order predators. Regardless of community composition in young aggregations, succession converges on similar late-stage community types.