standardization of environmental data and information - International ...

A participant observed that, if only 30% of an area was mined in
patches about 30-50 km wide, much of the area surrounding the highly
disturbed portion might give organisms the chance to recolonise.
Craig Smith commented that 3-5 km did not sound far but it was a
much greater distance than in the DISCOL area, which had taken seven
years or more to recover. He did not think any macrofauna would survive
after being picked up in a nodule harvester and blown up into the water
column. When samples were washed, they had to be treated with a low
flow rate on a screen to keep from destroying most of the polychaetes. Yet,
the shear forces involved in washing sediments on a sieve were orders of
magnitude lower than the shears produced in any kind of mining head to
separate water from the nodules. Thus, while recolonisation of an area 5
km in diameter area would be fast when compared to an area 100 km
across, it would still be slow. If the surface sediment were stripped from an
area 5 km across, he would expect recovery to take at least two or three
times longer than in the case of DISCOL. No information was available
about rates of recovery in the middle of a large-scale, devastating
disturbance. It could take 100 years or more.
A questioner, noting that in DISCOL the sediment had been shifted
aside by up to 10 m compared to the 10-12 km that would be shifted by
mining, asked whether the time required for recolonisation could be
calculated by dividing 12 km by 10 m and multiplying the quotient by seven
years. Schriever replied that the processes were non-linear.
Another questioner, citing data to the effect that meiofauna had
reached a steady state by the time they were sampled three years after the
impact, wondered whether a steady state would have been found if
sampling had occurred two years after impact. Schriever responded that
steady state in this case referred to abundance, not species composition.
In any case, species composition and diversity were still different from the
baseline. He added that the researchers had tried without success to find
any correlation between these data and the shift from El Niño to La Niña
conditions.
Asked whether the control sites had changed along with the impact
site, Schriever replied that neither the nematodes nor the megafauna at the
control sites had changed much. The tremendous change in abundance
had occurred only within the DISCOL area.
INTERNATIONAL SEABED AUTHORITY 361