119
7 Ecosystem Health in the Context of Fisheries and Aquaculture…
Aquaculture Increasing Diversity, Complexity and Impacts
on Ecosystem Health
Another major coastal transformation is induced by aquaculture. Enterprises of different types, sizes and technology have spread around the globe, generating impacts
on ecosystem health. Aquaculture development increases system complexity with
its presence in areas previously devoted to fi shing or other activities. It brings new
stakeholders with different images of reality and visions for the future of the coastal
area, marginalizing traditional users who have little capital or may not be eager to
join (Pascual 2004 ) , and thus increasing the diversity of the system-to-be-governed
and the governability challenges.
From an ecosystem perspective, great diversity and complexity can also be found
in the aquaculture system, with huge differences between herbivorous, carnivorous
and omnivorous species. The latter two depend, to some extent, on compound feed,
made up of fi shmeal and fi sh oil, among other ingredients. Carp and shrimp, for
instance, consume more than 40 and 18% of the total world production of this aquafeed, respectively (FAO 2009 ) . Problems with this are related to the fact that raw
materials used in the production of fi shmeal are comprised of small and juvenile
fi sh, some of which may have little to no value but are often important sources of
protein for the poor (Tacon and Hasan 2007 ) . Furthermore, they are mostly caught
with destructive gear such as bottom trawling and push net. Another concern resulting from aquaculture development is environmental health. For instance, the early
development of intensive shrimp culture, mainly tiger prawn ( Penaeus monodon ) in
Southeast Asia in the late 1980s involved clear-cutting of large areas of mangrove
forests. Large amount of feed is input into ponds that are densely stocked with larvae from hatcheries. The high density culture system and the intensive feeding,
coupled with use of fertilizers, biocides and antibiotics for disease control, has compromised their long term viability and created side effects such as high concentrations of nitrogen and organic wastes. Euthrophication due to the excess nutrients
may also constitute a risk, because some algae species can be toxic to humans or
marine organisms.
Another side effect of aquaculture is the introduction of alien species; typically
those that have suf fi cient market value ensure the culture is pro fi table. However, all
ecosystems are subject to the arrival of alien species, and recent increases in water
temperature have fostered this process in the oceans. Ballast water in cargo ships
also contributes to such introductions. No less relevant are the intentional or accidental releases from different sources, as in the case of a tropical green alga
( Caulerpa taxifolia ), which was released from the Monaco Oceanographic Museum
before 1984 and colonized large areas of the Mediterranean Sea (Meinesz et al.
2001 ; Valiela 2006 ) . Some of these introductions are controversial. For instance,
zebra mussels ( Dreissena polymorpha ) brought to the Great Lakes by ballast water
was considered by some to have helped clean up the water. This, however, means
that they have fi ltered out most of the phytoplankton and small zooplankton in the
waters, leaving larval and juvenile fi sh without any food. Debate about the bene fi ts
7 Ecosystem Health in the Context of Fisheries and Aquaculture…
Aquaculture Increasing Diversity, Complexity and Impacts
on Ecosystem Health
Another major coastal transformation is induced by aquaculture. Enterprises of different types, sizes and technology have spread around the globe, generating impacts
on ecosystem health. Aquaculture development increases system complexity with
its presence in areas previously devoted to fi shing or other activities. It brings new
stakeholders with different images of reality and visions for the future of the coastal
area, marginalizing traditional users who have little capital or may not be eager to
join (Pascual 2004 ) , and thus increasing the diversity of the system-to-be-governed
and the governability challenges.
From an ecosystem perspective, great diversity and complexity can also be found
in the aquaculture system, with huge differences between herbivorous, carnivorous
and omnivorous species. The latter two depend, to some extent, on compound feed,
made up of fi shmeal and fi sh oil, among other ingredients. Carp and shrimp, for
instance, consume more than 40 and 18% of the total world production of this aquafeed, respectively (FAO 2009 ) . Problems with this are related to the fact that raw
materials used in the production of fi shmeal are comprised of small and juvenile
fi sh, some of which may have little to no value but are often important sources of
protein for the poor (Tacon and Hasan 2007 ) . Furthermore, they are mostly caught
with destructive gear such as bottom trawling and push net. Another concern resulting from aquaculture development is environmental health. For instance, the early
development of intensive shrimp culture, mainly tiger prawn ( Penaeus monodon ) in
Southeast Asia in the late 1980s involved clear-cutting of large areas of mangrove
forests. Large amount of feed is input into ponds that are densely stocked with larvae from hatcheries. The high density culture system and the intensive feeding,
coupled with use of fertilizers, biocides and antibiotics for disease control, has compromised their long term viability and created side effects such as high concentrations of nitrogen and organic wastes. Euthrophication due to the excess nutrients
may also constitute a risk, because some algae species can be toxic to humans or
marine organisms.
Another side effect of aquaculture is the introduction of alien species; typically
those that have suf fi cient market value ensure the culture is pro fi table. However, all
ecosystems are subject to the arrival of alien species, and recent increases in water
temperature have fostered this process in the oceans. Ballast water in cargo ships
also contributes to such introductions. No less relevant are the intentional or accidental releases from different sources, as in the case of a tropical green alga
( Caulerpa taxifolia ), which was released from the Monaco Oceanographic Museum
before 1984 and colonized large areas of the Mediterranean Sea (Meinesz et al.
2001 ; Valiela 2006 ) . Some of these introductions are controversial. For instance,
zebra mussels ( Dreissena polymorpha ) brought to the Great Lakes by ballast water
was considered by some to have helped clean up the water. This, however, means
that they have fi ltered out most of the phytoplankton and small zooplankton in the
waters, leaving larval and juvenile fi sh without any food. Debate about the bene fi ts