Effects of Changing Environmental Conditions on Lagoon Ecology - Coastal Lagoons: Ecosystem Processes and Modeling for Sustainable Use and Development - page 201

waters high densities of small omnivorous copepods would be expected as they can
effectively feed on small phytoplankton cells, small flagellates from the microbial
loop, and some detritus. The rate of filtering generally increases with body size, both
within and between species. It decreases for some species when food concentration
is above or below certain limits.
The food consumed ( R ) by zooplankton can be expressed in terms of amount
of food available by the Ivlev model:

R = R max (1 − e − kp ) (5.4)

where R max is the maximum ration (maximum amount of food that an organism can
consume during a certain period of time), p is the prey concentration, and k is a
proportionality constant. Although the main factors determining the grazing rate are
the size of the organisms and their oral pieces, 46-48 they have a certain ability to
choose the food based on its quality, with each species grazing preferentially over
a certain particle size range.
From an ecological point of view, other approaches to population dynamics
are frequently used to explain the evolution of both phytoplankton and zoop-
lankton populations based on predator-prey type of models. Basic equations
describing predator-prey models can be found in any ecology textbook. A min-
imal model applicable to the eutrophication process should consider logistic
growth for preys, in this case phytoplankton, but with carrying capacity depend-
ing on nutrient concentration in water. When considering models with three
variables (nutrients, phytoplankton, and zooplankton) the outputs show limit
cycles and unstable equilibrium points with complex dynamics introducing some
degree of uncertainty in predictions. 16

5.2.1.4 Benthic Fauna

As mentioned above, seagrass meadows subsidize not only the microbial webs and
zooplankton community but also the benthic filter and detritus feeder organisms.
These organisms also benefit from seagrass meadows by efficiently retrieving their
energetic requirements from its fragmented debris. The equilibrium between stability
of the substrate, refuge provided, and moderate supply of organic matter, all together
favored by aerobic conditions, gives the benthic fauna community a balance between
their filter feeders and detritivorous organisms. Benthic fauna may vary depending
on the lagoon characteristics as they adapt to substrate, with major groups being
deposit feeders and other detritivorous, filter feeders and predatory annelids, mol-
luscs, and crustaceans. High abundance of filter feeders including mainly sponges,
bivalves, and ascidians are frequently found in oligotrophic lagoons, providing the
water with high filtering rates that retrieve many of its particles, including phy-
toplankton. It has been reported that in shallow waters the entire water column may
be turned over in a few days by filter feeders. 8,49
Benthic macrofauna play an important role, by bioturbation, in the microbial
communities in sediment, directly due to burrowing and ventilation 50 and indirectly
by feeding on detritus and microorganisms. 51,52 Increased transport due to ventilation