THE GEOLOGY OF SEA-FLOOR MASSIVE SULPHIDES
35
Defining characteristics
of SMS systems
3.4
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.
There is much to learn about the dispersal and colonization
potential of vent species. It has been suggested that the dom-
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.
