DEEP SEA MINERALS - Vol 1 - Sea-Floor Massive Sulphides

3.4

Defining characteristics of SMS systems

The description in Section 2 of faunal communities associated with SMS highlights several key characteristics to be considered specifically for this environment when assessing potential im- pacts. These considerations, and others, are summarised here. Knowledge of species composition and biodiversity at hydro- thermal vent sites is incomplete. Many species are poorly un- derstood, and likely many are still undiscovered (German et al . 2011). Observations to date indicate that the dominant species and faunal communities vary through the western Pacific. Sometimes, parts of an SMS deposit are still actively venting, while other parts are dormant. At locations in the Pacific Island region where active venting occurs, typical biomass-dominant sessile animals include gastropods (snails), barnacles, and bathymodiolid mussels. More mobile animals include shrimp, crabs, and eel-pout fish. Many species from hydrothermal vent sites are considered endemic to the vent environment and reliant on venting activity and its particular environmental characteris- tics (such as depth, temperature, and chemical composition). These endemic species are localized, so their populations could be severely affected by relatively small-scale mining activities.

inant megafauna can colonize new vent sites relatively quickly following such disturbances as volcanic eruptions. Evidence for this has been observed at the East Pacific Rise and Juan de Fuca Ridge hydrothermal vent systems (Tunnicliffe et al . 1997; Shank et al . 1998). Because venting activity is ephemeral and often variable at a local scale, the animal populations associ- ated with vents must be adapted to, or at least tolerant of, this natural variability. For example, because hydrothermal vent activity is transient at various time scales, animals have to be adapted to move (or disperse their eggs and larvae) between sites if venting stops. Animals associated with dormant SMS sites are non-chemo- synthetic fauna, dominated by standard sea-floor/hard-sub- strate taxa, such as attached barnacles, stony corals, octocor- als, sponges, and slow-moving feather stars and brittle stars. Many of these fauna are slow-growing and long-lived. These animals are part of a wider regional pool of species, typical of deep sea animals found elsewhere, including on basalt (and other) outcrops. Recovery of these fauna from disruptive hu- man activities may take decades to centuries because of their slow growth, and this factor needs to be balanced against the likelihood that mining activity will have less impact on the wider species pool.

There is much to learn about the dispersal and colonization potential of vent species. It has been suggested that the dom-

THE GEOLOGY OF SEA-FLOOR MASSIVE SULPHIDES 35