the Johnson Sea Link were funded by the Mineral Management 

 Service (MMS) in September 1986. These dives were followed by a 

 larger survey using the NR-1 (March 1987). Based on these 

 results, the National Undersea Research Program ( NURP ) funded a 

 series of dives (Dives 2053-2077) in June 1987 aboard the Johnson 

 Sea Link . The goals of these dives were continued studies to 

 refine the description of the distribution and abundance of 

 organisms around the seep sites; description of the sediment, 

 water and hydrocarbon chemistry around the animals; and 

 documentation of the importance of chemosynthesis to these 

 communities using biochemical, physiological and isotopic 

 methods. The ecological components of the Sea-Link series of 

 dives were designed to describe the distribution of organisms 

 within these ecosystems and the factors controlling the observed 

 distributions . 



RESULTS AND DISCUSSION 



Ecology (Including Isotopes) 



Four sites have been intensively surveyed by the Johnson Sea 

 Link and a broader regional survey was conducted by the 

 NR-1. The Johnson Sea Link dives produced 87 video tapes (20 

 minute tapes) of faunal transects and of assemblage structure. 

 Eighteen (18) rolls of 35 mm film were taken to provide 

 high-resolution spatial data. At present, data from Dives 

 2052 to 2056 have been analyzed and work is progressing on 

 other samples. 



Significant progress was made in better understanding 

 the relationship between background, heterotrophic fauna and 

 chemosynthetic fauna. Progress in this area is one of the 

 most exciting aspects of the NURP-sponsored Johnson Sea Link 

 cruise. The mussel and tubeworm clumps form distinct 

 assemblages which are exploited by "background" browsers and 

 predators. Due to the relative ease of sampling the mussel 

 assemblages, the best information is currently available about 

 this system (Fig. 4). Both sessile suspension feeders 

 ( gorgonians ) , epifaunal browsers (urchins) and predators can 

 derive carbon from the chemosynthetic community. 



The composition and spatial distribution of the faunal 

 assemblages in the seep area were found to be more complex 

 than previously suspected. Whereas it is increasingly clear 

 that methane and petroleum support and regulate these 

 communities, why the different assemblages are distributed 

 as they are over a topographically complex landscape is not 

 clear. On a smaller scale, it is not known what controls 

 variations within assemblage clumps. However, there appear 

 to be important ecological differences between the tubeworm 

 and mussel assemblages. High mussel cover density is 

 significantly correlated to methane levels in the water 



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