1 Fish Farm Wastes in the Ecosystem
35
Suppose that the whole of a sea-loch was given over to mussel farming, so that
mussels took by far the largest share of the available primary production and their
pseudo-faeces began to buildup a loose layer of mainly inorganic particles on and
near the sea bed. Under such conditions the loch would become a “sink” for phytoplankton, consuming more than it produced, and the depletion of food, and benthic
changes, might mean that the biomass of plankton and benthos decreased and that
some species were eliminated. The increase in turbidity due to the resuspended
matter might prevent seaweeds from growing where the sea bed was below the
low tide mark. Or, suppose the amount of salmon farmed in Creran was greatly
increased, so that nutrient enrichment caused eutrophication, with many algal
blooms and increased downwards flow of organic matter, causing many locally
impacted areas on the seabed, and depletion of oxygen in the deeper parts of the
loch. Again, the effect might be to degrade the structure of the benthic community
and suppress the natural extent of seaweed primary production. In all these cases
the loch’s ecosystem would have suffered an undesirable disturbance that can be
described in terms of the ecosystem’s resistance being overwhelmed, so that ecosystem state plunges over the “cliff” in Fig. 1.6, bringing about a state of ill health
in which self-regulation is poor.
In such a state there would be little resilience within the loch’s ecosystem to
bring about recovery if mariculture was removed. However, this hypothetically
impacted water body is, fortunately, part of a larger world, and it is reasonable to
assume that the import of plankton, seaweed spores, and the pelagic larvae of benthic animals, would eventually restore the ecosystem. Nevertheless, we know little
about the processes of ecosystem reassembly, and it is possible that the resulting
system would be unlike that which was made unwell. Nor do we know how long it
would take to restore a zone B ecosystem: very likely, much longer than the 1–2
years required to restore an impacted AZE beneath a fish cage. And finally, as the
reader may already have spotted, pressures on zone C scales that lead to a weakening of the health of ecosystems over large parts of coastal seas, will damage the
recovery prospects for any zone B scale waterbody for which the zone C scale
ought to offer the reseeding potential.
1.13 Phytoplankton Community Index
Ecosystem vigour is easy to understand: it refers to the intensity of life, including
its production and consumption of organic matter, its turnover of nutrient elements,
and its ability to restore a good state after local disturbance. Organization is more
complicated. If we were dealing with a coral reef, its organization would include the
physical structure of the reef, together with the diversity of the organisms living
there and there food web interrelationships. A similar account could be written for the
benthic community, as shown in Fig. 3(a) where increasing organic loading results
in organizational degradation. But what about the plankton? Plankters are passive
riders on water motion, and their population abundances can change rapidly.
35
Suppose that the whole of a sea-loch was given over to mussel farming, so that
mussels took by far the largest share of the available primary production and their
pseudo-faeces began to buildup a loose layer of mainly inorganic particles on and
near the sea bed. Under such conditions the loch would become a “sink” for phytoplankton, consuming more than it produced, and the depletion of food, and benthic
changes, might mean that the biomass of plankton and benthos decreased and that
some species were eliminated. The increase in turbidity due to the resuspended
matter might prevent seaweeds from growing where the sea bed was below the
low tide mark. Or, suppose the amount of salmon farmed in Creran was greatly
increased, so that nutrient enrichment caused eutrophication, with many algal
blooms and increased downwards flow of organic matter, causing many locally
impacted areas on the seabed, and depletion of oxygen in the deeper parts of the
loch. Again, the effect might be to degrade the structure of the benthic community
and suppress the natural extent of seaweed primary production. In all these cases
the loch’s ecosystem would have suffered an undesirable disturbance that can be
described in terms of the ecosystem’s resistance being overwhelmed, so that ecosystem state plunges over the “cliff” in Fig. 1.6, bringing about a state of ill health
in which self-regulation is poor.
In such a state there would be little resilience within the loch’s ecosystem to
bring about recovery if mariculture was removed. However, this hypothetically
impacted water body is, fortunately, part of a larger world, and it is reasonable to
assume that the import of plankton, seaweed spores, and the pelagic larvae of benthic animals, would eventually restore the ecosystem. Nevertheless, we know little
about the processes of ecosystem reassembly, and it is possible that the resulting
system would be unlike that which was made unwell. Nor do we know how long it
would take to restore a zone B ecosystem: very likely, much longer than the 1–2
years required to restore an impacted AZE beneath a fish cage. And finally, as the
reader may already have spotted, pressures on zone C scales that lead to a weakening of the health of ecosystems over large parts of coastal seas, will damage the
recovery prospects for any zone B scale waterbody for which the zone C scale
ought to offer the reseeding potential.
1.13 Phytoplankton Community Index
Ecosystem vigour is easy to understand: it refers to the intensity of life, including
its production and consumption of organic matter, its turnover of nutrient elements,
and its ability to restore a good state after local disturbance. Organization is more
complicated. If we were dealing with a coral reef, its organization would include the
physical structure of the reef, together with the diversity of the organisms living
there and there food web interrelationships. A similar account could be written for the
benthic community, as shown in Fig. 3(a) where increasing organic loading results
in organizational degradation. But what about the plankton? Plankters are passive
riders on water motion, and their population abundances can change rapidly.