Effects of Changing Environmental Conditions on Lagoon Ecology - Coastal Lagoons: Ecosystem Processes and Modeling for Sustainable Use and Development - page 202

of burrow water usually enhances reaction rates and solute fluxes whereas reworking
during burrowing is responsible for displacement of organic particles. 8

5.2.1.5 Fish Assemblages

Oligotrophic lagoons also have extensive areas of sandy and muddy bottoms without
vegetation coverage that provide extensive feeding resources to several fishes (such
as grey mullet and sparid). Open sandy areas are frequently inhabited by small fishes
such as Pomatoschistus spp., Gobius spp., Callyonimus spp. and Solea spp. Sea-
grasses not only provide small fishes (mainly gobiids, singnatids, and some blennies)
with food as well as shelter from large predators, but also cover the needs of
migratory species that require protected habitats for breeding and nursery. 53 Addi-
tionally, more intense waterfowl grazing may occur at sheltered areas than at exposed
sites.
The growth rate of fish is influenced by several factors, such as temperature,
food availability, population density, and competition. 54 In oligotrophic waters pri-
mary and secondary production is low, so the food will be scarce, increasing the
competition among the different species present and also among individuals of the
same species.
Several growth models can be used to describe fish growth, the most commonly
used being the von Bertalanffy model. 55 However, in lagoon environments, the
majority of fishes only stay inside the lagoon during their first years. Other models,
such as the parabolic or the Gompertz models, are more appropriate to describe
their growth. 56
At the ecosystem level, the relationship among the several trophic groups is
generally given by

d trophic group i / dt = U i ± J i − U i +1 − L i − E i (5.5)

where U i represents the food uptake by trophic group i , J i denotes migration rates
of group i , U i +1 represents group losses due to group i consumption by higher trophic
groups, L i denotes loss rates by defecation and natural mortality and E i corresponds
to excretion rates of group i (adapted from Gurney and Nisbet). 57 If i corresponded
to zooplankton, then we would have phytoplankton uptake by zooplankton, and
zooplankton consumption by the carnivorous group, which could be composed, for
example, of fishes and benthic invertebrates. Migration rates for some trophic groups
might be equal to zero.
This equation is relatively similar to the net growth equation of the “standard
organism” proposed by Baretta-Bekker et al.: 58

STc/dt = (uptake − (respiration + mortality + excretion + grazing))STc (5.6)

where STc is the carbon biomass of the standard organism. Despite the simplicity
of their biological representation, these models need an enormous number of bio-
logical parameters. Each term of these equations is described by a relatively complex
equation, which might be related to some environmental or biotic factors such as
temperature, dissolved oxygen content, or food availability.