Application 124771 - Ministry of Fisheries

MAY 2012 REPORT NO. 2134 | CAWTHRON INSTITUTE
3. BACKGROUND TO SEABED AND WATER COLUMN
EFFECTS
4
The ecological effects from farming mussels and other filter-feeding bivalves on the
benthic and wider environment have recently been reviewed in a New Zealand
context (Figure 2, Keeley et al. 2010). Below we provide a summary of the effects of
mussel farms on the seabed and water column, taken from Keeley et al. 2010 (with
minor changes).
Figure 2. Summary of potential wider ecological effects, localised benthic effects, and water
column effects of mussel farming on the environment (from Keeley et al. 2010).
3.1. Seabed effects
The main ecological effects on the seabed from farming mussels and other filterfeeding
bivalves arise from biodeposits (Giles et al. 2006) and drop-off of mussels,
shell and associated biota (Wong & O’Shea 2011). In most instances, the severity of
seabed effects have been assessed as low to moderate (Keeley et al. 2010). The
effects exhibit as minor enrichment of the seabed sediments (organic content
increases of up to ~7.5%) (Hartstein & Stevens 2005), increased build-up of shell litter
directly beneath the site and, in some instances, increased aggregations of seastars
and other epifauna taxa (Kaspar et al. 1985). Sediment enrichment, in-turn, affects the
composition of sediment dwelling biota with productivity generally enhanced (i.e.
some smaller species, like polychaete worms, become more prolific). Changes to the
surface dwelling biota (e.g. seastars) have been documented but are difficult to
quantify and vary significantly between sites (Kaspar et al. 1985). Seabed effects are
most pronounced directly beneath farm sites, reduce rapidly with distance, and are