Environmental Engineering Reference
In-Depth Information
decreasing the growth rate of plant shoots (Craig et al., 2008). Conversely, deposition
of organic matter in the wakes of marine energy devices could encourage the growth
of benthic invertebrate communities that are adapted to that substrate. Mussel shell
mounts that slough off from oil and gas platforms may create surrounding artificial
reefs that attract a large variety of invertebrates (e.g., crabs, sea stars, sea cucumbers,
anemones) and fish (Love et al., 1999). Accumulation of shells and organic matter
in the areas would depend on the wave and current energy, activities of biota, and
numerous other factors (Widdows and Brinsley, 2002). Although the new habitats
created by energy conversion structures may enhance the abundance and diversity of
invertebrates, predation by fish attracted to artificial structures can greatly reduce the
numbers of benthic organisms (Davis et al., 1982).
Movements of mooring or electrical transmission cables along the bottom (sweep-
ing) could be a continual source of habitat disruption during operation of the project.
For example, Kogan et al. (2006) found that shallow water wave action shifted a
6.6-cm-diameter, armored coaxial cable that was laid on the surface of the seafloor.
The strumming action caused incisions in rocky outcrops, but effects on seafloor
organisms were minor. Anemones colonized the cable itself, preferring the hard
structure over the nearby sediment-dominated seafloor. Some flatfishes were more
abundant near the cable than at control sites, probably because the cable created a
more structurally heterogeneous habitat. Sensitive habitats that may be particularly
vulnerable to the effects of cable movements include macroalgae and seagrass beds,
coral habitats, and other biogenic habitats such as worm reefs and mussel mounds.
Renewable energy projects may also have benefits for some aquatic habitats and
populations. The presence of a marine energy conversion project will likely limit
most fishing activities and other access in the immediate area. Bottom trawling can
disrupt habitats, and benthic communities in areas that are heavily fished tend to be
less complex and productive than in areas that are not fished in that way (Jennings et
al., 2001; Kaiser et al., 2000). Blyth et al. (2004) found that cessation of towed-gear
fishing resulted in significantly greater total species richness and biomass of benthic
communities compared to sites that were still fished. The value of these areas in
which fishing is precluded (or, at least limited to certain gear types) by the energy
project would depend on the species of fish and their mobility. For relatively sed-
entary animals, reserves less than 1 km across have augmented local fisheries, and
reserves in Florida of 16 km 2 and 24 km 2 have sustained more abundant and sizable
fish than nearby exploited areas (Gell and Roberts, 2003). On the other hand, the
protection of long-lived, late-maturing, or migratory marine fish species may require
much larger marine protected areas (greater than 500 km 2 ) than those envisioned for
most energy developments (Blyth-Skyrme et al., 2006; Kaiser, 2005; Nelson, 2008).
i MpaCTs oF n oise
Freshwater and marine animals rely on sound for many aspects of their lives includ-
ing reproduction, feeding, predator and hazard avoidance, communication, and
navigation (Popper, 2003; Weilgart, 2007). Consequently, underwater noise gener-
ated during installation and operation of a hydrokinetic or ocean energy conver-
sion device has the potential to impact these organisms. Noise may interfere with
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