and phytobenthos (red, green, and brown algae)
(Lindeman, 1942). These components, along with detritus, constitute the main energy source for organisms in
estuaries (Kennish, 1990). Zooplankton is comprised
mainly of crustaceans such as copepods, as well as molluscs, coelenterates, and chaetognaths. The phytoplankton
is consumed by zooplankton; about 50 % of phytoplankton
is not consumed and goes into detritus. The zoobenthos
consists of a wide range of organisms, mostly invertebrates
such as sponges, crabs, echinoderms, polychaetes, snails,
clams, and sea stars, which feed on the phytobenthos as well
as on detritus. The zoobenthos is one of the main food
sources for fish, which compose the most conspicuous and
dominant community in estuaries. The abundance, biomass,
and diversity of the ichthyofauna are regulated by the size
of the estuary, the season (wet or dry), latitude (tropical
and subtropical zones), and changes in abiotic factors
(temperature, freshwater input, salinity changes, pH, currents
within the estuary, and evaporation). These factors can lead
to changes in the fish community structure through migration
or immigration of less eurytopic species. However, most of
the population is comprised by highly tolerant species that
have a clear tendency toward an r strategy (Pianka, 1970).
In general, four fish feeding categories can be observed
(Claro, 1994):
Herbivores: This trophic category includes fish that feed
exclusively on plants (algae). Fish from the Kyphosidae
family are very well represented in estuaries.
Detritivores: This group contains species that consume
detritus, which consists of vegetal and animal material
that has not been consumed and gets deposited on the
benthos. The most typical fish family in estuaries is
the Mugilidae family.
Benthophagous: Fish that feed on small organisms that
inhabit the substrate. Most fish species present in estuaries are found in this category (e.g., Mullidae and
Chaetodontidae families).
Carnivores: Consumers of animal prey, they feed mainly
on fish and invertebrates. The most representative species belong to the families Lutjanidae, Serranidae,
Haemulidae, Carangidae, and Balistidae.
A practical way to analyze the trophic dynamics of estuaries is by performing functional diversity studies that provide a rapid characterization of communities, reducing
complex ecosystems into species groups (functional
groups) with ecological equivalence, thereby facilitating
comparative community studies (Root, 1967; Root, 2001).
Species that comprise a functional group are those that
overlap in the highest number of variables in the
multidimensional niche, being ecologically equivalent in
function (Nagelkerken and Van der Velde, 2004). From
the functional viewpoint, biological communities can be
represented as a mosaic of functional groups, or as bricks
with which communities are built (Krebs, 2003). The presence of multiple species (dominant and subordinates)
within each functional group increases functional
redundancy and contributes to the resilience of the estuary
or ecosystem studied (Hooper et al., 2005).
With a higher number of functionally similar species,
each with different responses to environmental factors,
there is a higher probability of at least one species surviving possible perturbations (Hooper et al., 2005). If there is
no functional redundancy, the loss of a single species
could result in the complete loss of a functional group;
therefore, at least one species per functional group is
essential for ecosystem functioning (Díaz et al., 2005).
Currently, due to urban and touristic development, anthropogenic impacts affect negatively coastal areas and especially estuaries, so that immediate and continued
evaluations of these effects on the local fauna and flora
are extremely important. The study of functional diversity
is therefore an effective and precise tool to evaluate these
effects.
The most important inputs for the development and
evolution of trophodynamic perspectives over the last
decades have occurred mainly in the field of aquatic ecology (Lindeman, 1942; Ulanowicz, 2004). The mass balance model ECOPATH with Ecosim has been the most
extensively used tool for analyzing trophic webs
(Polovina, 1984; Christensen and Pauly, 1992). This
model describes quantitatively the energy flows
(biomass) within food webs and facilitates an approximation to the structure and function of the ecosystem. Additionally, the model outputs allow the calculation of
several ecological indicators of the state of the trophic
web, such as ascendancy, surplus, and development potential (Ulanowicz, 1986; Libralato et al., 2006), that can be
used to follow up an ecosystem’s development through
time and to compare the ecological maturity of systems
located in different parts of the world.
Summary
Estuarine trophic dynamics is one of the most complex
processes of estuarine science. Its complexity lies in the
high environmental heterogeneity and biodiversity of
these coastal systems, which includes all trophic levels
from the smallest autotrophs to the largest predators. The
microbial decomposers must be considered as well.
Among the most important components in the flow of
energy in estuaries are fish communities due to the great
diversity of finfish eating habits which has resulted in
a large number of direct and indirect trophic interactions
with other biotic components present within networks that
structure and determine the energy dynamics of these
valuable ecosystems.
Bibliography
Claro, R., 1994. Características generales de la ictiofauna. In Claro, R.
(ed.), Ecologı ´a de los peces marinos de Cuba. Capı ´tulo 2. México:
Instituto de Oceanología y CIQRO, pp. 124–143.
Christensen, V., and Pauly, D., 1992. ECOPATH II: a software for
balancing steady-state models and calculating network characteristics. Ecological Modeling, 61, 169–185.
TROPHIC DYNAMICS
719
(Lindeman, 1942). These components, along with detritus, constitute the main energy source for organisms in
estuaries (Kennish, 1990). Zooplankton is comprised
mainly of crustaceans such as copepods, as well as molluscs, coelenterates, and chaetognaths. The phytoplankton
is consumed by zooplankton; about 50 % of phytoplankton
is not consumed and goes into detritus. The zoobenthos
consists of a wide range of organisms, mostly invertebrates
such as sponges, crabs, echinoderms, polychaetes, snails,
clams, and sea stars, which feed on the phytobenthos as well
as on detritus. The zoobenthos is one of the main food
sources for fish, which compose the most conspicuous and
dominant community in estuaries. The abundance, biomass,
and diversity of the ichthyofauna are regulated by the size
of the estuary, the season (wet or dry), latitude (tropical
and subtropical zones), and changes in abiotic factors
(temperature, freshwater input, salinity changes, pH, currents
within the estuary, and evaporation). These factors can lead
to changes in the fish community structure through migration
or immigration of less eurytopic species. However, most of
the population is comprised by highly tolerant species that
have a clear tendency toward an r strategy (Pianka, 1970).
In general, four fish feeding categories can be observed
(Claro, 1994):
Herbivores: This trophic category includes fish that feed
exclusively on plants (algae). Fish from the Kyphosidae
family are very well represented in estuaries.
Detritivores: This group contains species that consume
detritus, which consists of vegetal and animal material
that has not been consumed and gets deposited on the
benthos. The most typical fish family in estuaries is
the Mugilidae family.
Benthophagous: Fish that feed on small organisms that
inhabit the substrate. Most fish species present in estuaries are found in this category (e.g., Mullidae and
Chaetodontidae families).
Carnivores: Consumers of animal prey, they feed mainly
on fish and invertebrates. The most representative species belong to the families Lutjanidae, Serranidae,
Haemulidae, Carangidae, and Balistidae.
A practical way to analyze the trophic dynamics of estuaries is by performing functional diversity studies that provide a rapid characterization of communities, reducing
complex ecosystems into species groups (functional
groups) with ecological equivalence, thereby facilitating
comparative community studies (Root, 1967; Root, 2001).
Species that comprise a functional group are those that
overlap in the highest number of variables in the
multidimensional niche, being ecologically equivalent in
function (Nagelkerken and Van der Velde, 2004). From
the functional viewpoint, biological communities can be
represented as a mosaic of functional groups, or as bricks
with which communities are built (Krebs, 2003). The presence of multiple species (dominant and subordinates)
within each functional group increases functional
redundancy and contributes to the resilience of the estuary
or ecosystem studied (Hooper et al., 2005).
With a higher number of functionally similar species,
each with different responses to environmental factors,
there is a higher probability of at least one species surviving possible perturbations (Hooper et al., 2005). If there is
no functional redundancy, the loss of a single species
could result in the complete loss of a functional group;
therefore, at least one species per functional group is
essential for ecosystem functioning (Díaz et al., 2005).
Currently, due to urban and touristic development, anthropogenic impacts affect negatively coastal areas and especially estuaries, so that immediate and continued
evaluations of these effects on the local fauna and flora
are extremely important. The study of functional diversity
is therefore an effective and precise tool to evaluate these
effects.
The most important inputs for the development and
evolution of trophodynamic perspectives over the last
decades have occurred mainly in the field of aquatic ecology (Lindeman, 1942; Ulanowicz, 2004). The mass balance model ECOPATH with Ecosim has been the most
extensively used tool for analyzing trophic webs
(Polovina, 1984; Christensen and Pauly, 1992). This
model describes quantitatively the energy flows
(biomass) within food webs and facilitates an approximation to the structure and function of the ecosystem. Additionally, the model outputs allow the calculation of
several ecological indicators of the state of the trophic
web, such as ascendancy, surplus, and development potential (Ulanowicz, 1986; Libralato et al., 2006), that can be
used to follow up an ecosystem’s development through
time and to compare the ecological maturity of systems
located in different parts of the world.
Summary
Estuarine trophic dynamics is one of the most complex
processes of estuarine science. Its complexity lies in the
high environmental heterogeneity and biodiversity of
these coastal systems, which includes all trophic levels
from the smallest autotrophs to the largest predators. The
microbial decomposers must be considered as well.
Among the most important components in the flow of
energy in estuaries are fish communities due to the great
diversity of finfish eating habits which has resulted in
a large number of direct and indirect trophic interactions
with other biotic components present within networks that
structure and determine the energy dynamics of these
valuable ecosystems.
Bibliography
Claro, R., 1994. Características generales de la ictiofauna. In Claro, R.
(ed.), Ecologı ´a de los peces marinos de Cuba. Capı ´tulo 2. México:
Instituto de Oceanología y CIQRO, pp. 124–143.
Christensen, V., and Pauly, D., 1992. ECOPATH II: a software for
balancing steady-state models and calculating network characteristics. Ecological Modeling, 61, 169–185.
TROPHIC DYNAMICS
719