37
concentrated oil patches from the Prestige wreck, impeding their entrance into the
Rías Baixas (Álvarez-Salgado et al. 2006). In the Seto Inland Sea (Japan), tidal
and thermohaline fronts showed elevated concentrations of persistent organochlorines in surface waters, and also in organisms and sediments (Tanabe et al. 1991).
In fact fronts are able to concentrate not only floating pollutants near the surface
but also other pollutants such as heavy metals, which tend to accumulate in the
sediments. For example, the highest concentrations of Cu, Zn, Pb, Cd and Ag in
marine sediments from Gdansk Bay, Poland, occur near the mouth of the Vistula
River. These elements are probably scavenged at the hydrological front by Mn and
Fe oxyhydroxides where mixing of Vistula river water with brackish Baltic Sea
water takes place (Glasby and Szefer 1998).
At smaller spatial scales, in absence of sufficiently strong winds or tides, primary
treated sewage (domestic and industrial) discharged through shoreline and deepwater outfalls into coastal waters, form visible surface plumes that intrude some kilometers seaward and along the coast from their point of discharge. Such sewage plumes
are lenses of low-salinity waters a few meters deep that overlay high-salinity shelf
waters. Small scale fronts usually develop between plumes and shelf waters where
young fishes may concentrate, as a result of advection at fronts as well as behavioral
responses. Surface sewage plumes therefore affect small-scale (<1 km) patterns of
distribution and density of young fishes and may increase and prolong their exposure
to pollutants that can cause sub-lethal and lethal effects (Gray 1996).
Though not marine fronts properly, internal waves show another example of
pollutant concentration in small scale convergence zones. Tidal currents flowing
off the continental shelf (or across reefs or banks) produce large internal waves
that propagate onshore. Surface current over the waves produce alternating zones
of convergence and divergence, and oil spills (and other flotsams) swept into such
convergences will be trapped there and carried onshore (Shanks 1987).
As a result of the potential for increased survival and growth of planktonic
larvae, together with reduced dispersal, fronts experience increased ecological
resilience due to increased recruitment across a range of taxa from ecosystem
engineers (kelps, corals, barnacles, mussels, scallops) to top predators. In addition,
this predictability makes regions of high front probability particularly amenable
to marine conservation and spatial planning efforts (Etnoyer et al. 2004; Woodson
et al. 2012; Scales et al. 2014). Moreover, because of their role in the amplification of interactions between fisheries and endangered species; and their ability to
concentrate pollutants, marine fronts may be seen as highly valuable ecosystems
for wildlife conservation actions such as the implementation of high seas marine
protected areas (Queiroz et al. 2012).
4.3 Climate Change
In marine ecosystems, rising atmospheric CO 2 and climate change are associated
with concurrent shifts in temperature, circulation, stratification, strength and direction of prevailing wind, precipitation, river run-off and groundwater contribution,
4.2 Conservation Issues
concentrated oil patches from the Prestige wreck, impeding their entrance into the
Rías Baixas (Álvarez-Salgado et al. 2006). In the Seto Inland Sea (Japan), tidal
and thermohaline fronts showed elevated concentrations of persistent organochlorines in surface waters, and also in organisms and sediments (Tanabe et al. 1991).
In fact fronts are able to concentrate not only floating pollutants near the surface
but also other pollutants such as heavy metals, which tend to accumulate in the
sediments. For example, the highest concentrations of Cu, Zn, Pb, Cd and Ag in
marine sediments from Gdansk Bay, Poland, occur near the mouth of the Vistula
River. These elements are probably scavenged at the hydrological front by Mn and
Fe oxyhydroxides where mixing of Vistula river water with brackish Baltic Sea
water takes place (Glasby and Szefer 1998).
At smaller spatial scales, in absence of sufficiently strong winds or tides, primary
treated sewage (domestic and industrial) discharged through shoreline and deepwater outfalls into coastal waters, form visible surface plumes that intrude some kilometers seaward and along the coast from their point of discharge. Such sewage plumes
are lenses of low-salinity waters a few meters deep that overlay high-salinity shelf
waters. Small scale fronts usually develop between plumes and shelf waters where
young fishes may concentrate, as a result of advection at fronts as well as behavioral
responses. Surface sewage plumes therefore affect small-scale (<1 km) patterns of
distribution and density of young fishes and may increase and prolong their exposure
to pollutants that can cause sub-lethal and lethal effects (Gray 1996).
Though not marine fronts properly, internal waves show another example of
pollutant concentration in small scale convergence zones. Tidal currents flowing
off the continental shelf (or across reefs or banks) produce large internal waves
that propagate onshore. Surface current over the waves produce alternating zones
of convergence and divergence, and oil spills (and other flotsams) swept into such
convergences will be trapped there and carried onshore (Shanks 1987).
As a result of the potential for increased survival and growth of planktonic
larvae, together with reduced dispersal, fronts experience increased ecological
resilience due to increased recruitment across a range of taxa from ecosystem
engineers (kelps, corals, barnacles, mussels, scallops) to top predators. In addition,
this predictability makes regions of high front probability particularly amenable
to marine conservation and spatial planning efforts (Etnoyer et al. 2004; Woodson
et al. 2012; Scales et al. 2014). Moreover, because of their role in the amplification of interactions between fisheries and endangered species; and their ability to
concentrate pollutants, marine fronts may be seen as highly valuable ecosystems
for wildlife conservation actions such as the implementation of high seas marine
protected areas (Queiroz et al. 2012).
4.3 Climate Change
In marine ecosystems, rising atmospheric CO 2 and climate change are associated
with concurrent shifts in temperature, circulation, stratification, strength and direction of prevailing wind, precipitation, river run-off and groundwater contribution,
4.2 Conservation Issues