2009
ICM: The Interdisciplinary Contest in Modeling
Creating Food Systems: Re-Balancing Human-Influenced
Ecosystems
Background
Less than 1% of the ocean floor is covered by coral. Yet, 25% of the ocean’s biodiversity
is supported in these areas. Thus, conservationists are concerned when coral
disappears, since the biodiversity of the region disappears shortly thereafter.
Consider an area in the Philippines located in a narrow channel between Luzon Island
and Santiago Island in Bolinao, Pangasinan, that used to be filled with coral reef and
supported a wide range of species (Figure 1). The once plentiful biodiversity of the area
has been dramatically reduced with the introduction of commercial milkfish (Chanos
chanos) farming in the mid 1990’s. It's now mostly muddy bottom, the once living corals
are long since buried, and there are few wild fish remaining due to over fishing and loss
of habitat. While it is important to provide enough food for the human inhabitants of the
area, it is equally important to find innovative ways of doing so that allow the natural
ecosystem to continue thriving; that is, establishing a desirable polyculture system that
could replace the current milkfish monoculture. The ultimate goal is to develop a set of
aquaculture practices that would not only support the human inhabitants financially and
nutritionally, but simultaneously improve the local water quality to a point where reef-
building corals could recolonize the ocean floor and co-exist with the farms.
A desirable polyculture is a scenario where multiple economically valuable species are
farmed together and the waste of one species is the food for another. For example, the
waste of a fin-fish can be eaten by filter feeders and excess nutrients from both fish and
filter feeders can be absorbed by algae which can also be sold, either as food or
commercially useful by-products. Not only does this reduce the amount of nutrient input
from the fish farming into the surrounding waters, it also increases the amount of profit a
farmer can make by using the fish waste to generate a greater quantity of usable
products (mussels, seaweed, etc.)
For modeling purposes, the primary animal organisms involved in these biodiverse
environments can be partitioned into predatory fish (phylum Chordata, subphylum
Vertebrata); herbivorous fish (phylum Chordata, subphylum Vertebrata); molluscs (such
as mussels, oysters, clams, snails, etc., phylum Mollusca); crustaceans (such as crabs,
lobsters, barnacles, shrimp, etc., phylum Arthropoda, subphylum Crustacea);
echinoderms (such as star fish, sea cucumbers, sea urchins, etc.; phylum
Echinodermata); and algae. By feeding types, there are primary producers
(photosynthesizers—these can be single cell phytoplankton, cyanobacteria, or
multicellular algae); filter feeders (strain plankton, organic particles, and sometimes
bacteria out of the water); deposit feeders (that eat mud and digest the organic
molecules and nutrients out of it); herbivores (eat primary producers); and predators
(carnivores). Just as on land, most of the carnivores eat herbivores or smaller
carnivores, but in the ocean they can also eat many of the filter feeders and deposit
feeders. Most animals have growth efficiencies of 10–20%, so 80–90% of what they
ingest ends up as waste in one form or another (some dissipated heat, some physical