Videotapes made from the submersible Alvin on Baby Bare, a 2600-m-deep North Pacific basalt outcrop, and at two other deep-sea localities document that octopuses of the genera Graneledone and Benthoctopus attach their eggs to hard substrate and apparently brood them through development. The behavior of brooding females was generally similar to that of shallow-water octopuses, but the genera showed apparent differences. In addition to the high density of brooding females observed at Baby Bare, which may relate to the increased availability of exposed hard substrates for egg attachment and of prey, females are suggested to increasingly associate with hard substrates as they mature. The biology of Baby Bare may seem unduly unique because the outcrop is isolated on a sedimented plain and is among the few exposures of hard substrate other than hydrothermal vents that have been explored by submersible. On the sediment-covered ocean floor, the availability of hard substrate may strongly affect the distribution of brooding octopuses. The size and shape of boreholes in 19 of over 400 thyasirid clam shells collected from Baby Bare support the hypothesis that octopuses had preyed upon the clams.

This study used seafloor imaging, near-surface sampling and drilling results to examine hydrological constraints on vent organism distribution and productivity in a sedimented hydrothermal setting at Middle Valley, Juan de Fuca Ridge in the northeast Pacific, where venting is focused around seafloor mounds. A vesicomyid clam bed on one of these mounds (Chowder Hill) was reconstructed from imagery acquired by the remotely operated vehicle ROPOS, using a new image enhancement/ mosaicking system. The mosaic was fitted to a Universal Trans-Mercator (UTM) coordinate grid and a contour map of clam density and local bathymetry was derived from visual counts within grid squares and ROPOS navigation logs. Highest clam density occurred on a slightly raised area of seafloor in the upper-central portion of the clam bed, where sediment temperatures suggested hydrothermal flux to be greater than further downslope. Results from Ocean Drilling Program (ODP), College Station, Texas, USA, Leg 139 suggested that a local hydrothermal reservoir exists within Chowder Hill and that erosion of low-permeability surface sediments may be critical to allowing fluids to escape. A l-dimensional advection-diffusion model was used to derive an estimate for HIS supply to the clam bed from a subsurface reservoir, based on sediment temperature profiles and pore-water H,S concentrations. Estimated H,S flux (250 m01 m-2 yr-'1 would support a maximum chemosynthetic CO2 fixation rate of 8.3 gC m-2 yr-'. More detailed in situ data are required to study links between local fluid flow variations and clam density, and to resolve near-surface processes that laterally delimit the fluid conduit beneath the clam colony.