Ch. 6— Environmental Considerations • 245 



MMH.: 



Box 6-H. — Gorda Ridge Study Results 



Plankton 



Most work on the study area is now 10-20 years old. No information exists on feeding ecology, secondary 

 production, and reproduction. The phytoplankton community is dominated by diatoms. Many estimates of 

 phytoplankton abundance were made in the 1960s;' they indicate productivity in this region is low (e.g., chlo- 

 rophylla concentration ranges from 0.1-0.8 mg/m' throughout the year). 



Nekton 



Only one species-albacore (Thunnus alalunga) is commercially fished in the Gorda Ridge Lease area. 

 Larvae and juvenile forms of other commercially important species (the Dover and Rex sole) occur within 

 the area. These larvae are far west of the shelf and slope areas where the adult populations live, and their 

 survival and input to the commercial fishery population is unknown. While occurrences of species of fish, 

 shrimps, swimming mollusks (cephalopods), and mammals with the Gorda Ridge area are fairly well-known, 

 their abundances, reproduction, growth rates, food habits, and vertical and horizontal migratory patterns are not. 



Benthos 



Litde is known about the benthos of the Gorda Ridge area. Until recently, these rocky environments were 

 avoided by benthic ecologists because of the difficulty in sampling them. Photographic surveys from the sub- 

 mersibles Advin (1984) and Sea Cliff (1986) as well as from a towed-camera vehicle behind the S.P. Lee (1985) 

 provide most of the benthic information for this area. The Gorda Ridge rift valley animals appear to be primarily 

 filter feeders and detritus feeders. Soft sediment and rocky epifaunal communities appear to differ in species 

 composition; however, quantitative data from controlled photographic transects across the Ridge and taken 

 close to the substrate (3-6 ft. off the bottom) are needed to permit identification of smaller organisms. Non- 

 vent areas may represent several types of environment with some areas of high particulate organic material 

 concentrated by topographic features juxtaposed with off-axis rocky surfaces. 



'S.G. Ellis, and J.H. Garber, The State of ScientiUc Information Relating to the Biology and Ecology of the Gorda Ridge Study Area, Northeast 

 Pacific Ocean: Plankton, Open-File Report 0-86-8, State of Oregon, Department of Geology and Mineral Industries (Portland, OR: February 1986). 



plankton,^' seabirds, ^^ and epifaunal and infaunal 

 community structure.^' The information contained 

 in these reports was collected from a variety of 

 sources such as peer-reviewed journals, government 



"S.G. Ellis and J.H. Garber, The State of Scientific Information 

 Relating to the Biology and Ecology of the Gorda Ridge Study Area, 

 Northeast Pacific Ocean: Plankton, State of Oregon, Department of 

 Geology and Mineral Industries, Portland, OR, Open-File Report 

 0-86-8, February 1986. 



°^L.D. Krasnow, The State of Scientific Information Relating to 

 the Biology and Ecology of the Gorda Ridge Study Area, Northeast 

 Pacific Ocean: Seabirds, State of Oregon, Department of Geology 

 and Mineral Industries, Portland, OR, Open File Report 0-86-9, Feb- 

 ruary 1986. 



"A.G. Carey, Jr., D.L. Stein, andG.L. Taghon, Anaiysis o/Ben- 

 thic Epifaunal and Infaunal Community Structure at the Gorda Ridge, 

 State of Oregon, Department of Geology and Mineral Industries, Port- 

 land, OR, Open FUe Report 0-86-11, July 1986. 



investigators, and active researchers, as well as less 

 traditional sources such as fishing records, etc. The 

 reports are useful compendia identifying what base- 

 line information exists for biota at and near the pro- 

 posed lease area and what missing information 

 needs to be developed before the effects of a min- 

 ing operation can be fuUy characterized (see box 

 6-H). 



While active vent sites such as the Gorda Ridge 

 area often contain lush communities of unique spe- 

 cies, the MMS has decided it will not lease such 

 areas for mining should they be encountered.^* 

 Thus, their discussion is not included here. 



"Thus far, none have been found on the Gorda Ridge sites. 



I 



