Spatial distribution of seepages and associated biological communities within Haima cold seep field, South China Sea

More than 30 cold seeps have been discovered on the northern continental slope of the South China Sea (SCS), but only two cold seep sites actively harbor living cold seep communities. One is the Haima cold seep, which is located at a water depth of approximately 1360–1400 m at the northern slope of the SCS. To date, however, the scale of seepage activity, the spatial distribution of seepages, and the biodiversity of benthic fauna associated with this field remain largely unknown because of the absence of a high-resolution seafloor investigation. Here, we report the spatial distribution of individual seepage areas within the Haima cold seep field and their associated biological community structures. Huge gas flares 100 to 200 m inwidth and ascending ~200–800 m into the water column were identified. Seventeen dives conducted by the manned submersible Shenhaiyongshi showed that the Haima consists of at least six individual patch of communities and(or) carbonate mound (HM-1 to HM-6). Outcrops of gas hydrates were observed at HM-3, where active seepage causes dense seep communities to flourish. We found that Mytilidae and Vesicormyidae were predominant, together with Ophiuridae, Chiridotidae, Siboglinidae, Turridae, Actinernidae, Galatheidae, Alvinocarididae, and Lithodidae. Spatially varying patterns of the Haima fauna are attributed to the supply of methane and sulfides, which could provide useful information regarding dynamical seep change and the carbon and sulfur cycles of cold seep areas.