pycnogonids, chitons, bivalves, gastropods, echinoderms,
bryozoans, and urochordates. Macrofauna that are
commonly found in the water column include jellyfish,
ctenophores, salps, and some larvae of benthic invertebrates such as sponges, mollusks, polychaetes, and
crustaceans that exceed 0.5 mm in length. Benthic
macrofauna can play an important role in the detoxification of estuarine and marine environments because
they store and transform many types of pollutants
(Greenway, 1995; Schlacher and Wooldridge, 1996;
Beaumont et al., 2007).
Bibliography
Beaumont, N. J., Austen, M. C., Atkins, J. P., Burdon, D., Degraer,
S., Dentinho, T. P., Derous, S., Holm, P., Horton, T., Lerland, E.,
Marboe, A. H., Starkey, D. J., Townsend, M., and Zarzycki, T.,
2007. Identification, definition and quantification of goods
and services provided by marine biodiversity: implications
for the ecosystem approach. Marine Pollution Bulletin, 54,
253–265.
Greenway, M., 1995. Trophic relationships of macrofauna within
a Jamaican seagrass meadow and the role of the echinoid
Lytechinus variegatus (Lamarck). Bulletin of Marine Science,
56(3), 719–736.
Schlacher, T. A., and Wooldridge, T. H., 1996. How sieve mesh size
affects sample estimates of estuarine benthic macrofauna. Journal of Experimental Marine Biology and Ecology, 201,
159–171.
Cross-references
Benthic Ecology
Infauna
Meiofauna
Microfauna
Soft Sediment Communities
MACRONUTRIENTS
Manuel Flores Montes
Department of Oceanography, Federal University of
Pernambuco, Recife, Pernambuco, Brazil
Synonyms
Inorganic nutrients; Limited nutrients
Definition
Macronutrients are chemical elements required by an
organism in relatively large amounts (e.g., N and
P required by plants). They are seldom in excess of
a few micromolar concentrations.
Description
Inputs. Most biologically important compounds entering
an estuary are derived from riverine sources. After the
industrial era, the use of fertilizers and fossil fuels
increased dramatically, leading to a substantial increase
in nutrient concentrations in estuarine systems.
Demand. Estuarine primary production requires the
availability of a variety of nutrient elements. The chemical
elements essential for primary producers are carbon (C),
oxygen (O), nitrogen (N), phosphorus (P), and silicon
(Si). Carbon, nitrogen, and phosphorus are the most
important elements for forming molecules vital to organisms (Day et al., 2012).
Stoichiometry. Nutrient elements accumulate in
phytoplankton to a relatively constant internal composition. As described by the Redfield ratio, the marine phytoplankton intracellular O:C:N:P ratio is 138:106:16:1.
Inadequate levels of a nutrient element in the environment can limit an organism’s metabolic activities.
Limitation. Carbon is abundant in the marine environment (carbonate, bicarbonate, and carbon dioxide)
and thus is rarely limiting. The N:P ratio best represents
the macronutrient limitations (Redfield et al., 1963).
According to Liebig’s Law of the Minimum, the concentration of a nutrient present at the lowest relative
levels required for an organism’s growth is typically
the limiting factor, which explains why the N:P ratio
is a limiting factor compared with carbon (Bianchi,
2007).
Estuarine Behavior. Certain estuarine microorganisms
may have variable internal N:P ratios because the internal
composition reflects the ratio in the environment and
N and P concentrations are highly variable in estuaries.
Therefore, changes in bioavailability of such elements
can significantly limit organic carbon production.
Nitrogen is the limiting nutrient in most estuaries because
it is assimilated more rapidly and in greater amounts than
other nutrients. It also has a more complex biogeochemical cycle than phosphorus. Reactive dissolved silicon is
a key component in the composition of diatom and
silicoflagellate shells as well as exoskeletons of other
organisms, such as certain sponges. Reactive dissolved
silicon is assimilated by diatoms at ratios similar to those
at which N is assimilated.
Eutrophication. Eutrophication caused by nutrient
enrichment (i.e., N and P) is a major problem in many
estuaries (Kennish, 1997). Excessive loading of N to estuarine waters can result in P limitation in systems that are
generally considered to be N limited.
Bibliography
Bianchi, T. S., 2007. Biogeochemistry of Estuaries. Oxford: Oxford
University Press.
Day, J. W., Kemp, M. W., Yánez-Arancibia, A., and Crump, B. C.,
2012. Estuarine Ecology, 2nd edn. Hoboken, New Jersey:
Wiley-Blackwell.
Kennish, M. J., 1997. Practical Handbook of Estuarine and Marine
Pollution. Boca Raton, Florida: CRC Press.
Redfield, A. C., Ketchum, B. H., and Richards, F. A., 1963. The
influence of organisms on the composition of seawater. In Hill,
M. N. (ed.), The Sea. New York: John Wiley & Sons,
Vol. 2, pp. 26–77.
MACRONUTRIENTS
389
bryozoans, and urochordates. Macrofauna that are
commonly found in the water column include jellyfish,
ctenophores, salps, and some larvae of benthic invertebrates such as sponges, mollusks, polychaetes, and
crustaceans that exceed 0.5 mm in length. Benthic
macrofauna can play an important role in the detoxification of estuarine and marine environments because
they store and transform many types of pollutants
(Greenway, 1995; Schlacher and Wooldridge, 1996;
Beaumont et al., 2007).
Bibliography
Beaumont, N. J., Austen, M. C., Atkins, J. P., Burdon, D., Degraer,
S., Dentinho, T. P., Derous, S., Holm, P., Horton, T., Lerland, E.,
Marboe, A. H., Starkey, D. J., Townsend, M., and Zarzycki, T.,
2007. Identification, definition and quantification of goods
and services provided by marine biodiversity: implications
for the ecosystem approach. Marine Pollution Bulletin, 54,
253–265.
Greenway, M., 1995. Trophic relationships of macrofauna within
a Jamaican seagrass meadow and the role of the echinoid
Lytechinus variegatus (Lamarck). Bulletin of Marine Science,
56(3), 719–736.
Schlacher, T. A., and Wooldridge, T. H., 1996. How sieve mesh size
affects sample estimates of estuarine benthic macrofauna. Journal of Experimental Marine Biology and Ecology, 201,
159–171.
Cross-references
Benthic Ecology
Infauna
Meiofauna
Microfauna
Soft Sediment Communities
MACRONUTRIENTS
Manuel Flores Montes
Department of Oceanography, Federal University of
Pernambuco, Recife, Pernambuco, Brazil
Synonyms
Inorganic nutrients; Limited nutrients
Definition
Macronutrients are chemical elements required by an
organism in relatively large amounts (e.g., N and
P required by plants). They are seldom in excess of
a few micromolar concentrations.
Description
Inputs. Most biologically important compounds entering
an estuary are derived from riverine sources. After the
industrial era, the use of fertilizers and fossil fuels
increased dramatically, leading to a substantial increase
in nutrient concentrations in estuarine systems.
Demand. Estuarine primary production requires the
availability of a variety of nutrient elements. The chemical
elements essential for primary producers are carbon (C),
oxygen (O), nitrogen (N), phosphorus (P), and silicon
(Si). Carbon, nitrogen, and phosphorus are the most
important elements for forming molecules vital to organisms (Day et al., 2012).
Stoichiometry. Nutrient elements accumulate in
phytoplankton to a relatively constant internal composition. As described by the Redfield ratio, the marine phytoplankton intracellular O:C:N:P ratio is 138:106:16:1.
Inadequate levels of a nutrient element in the environment can limit an organism’s metabolic activities.
Limitation. Carbon is abundant in the marine environment (carbonate, bicarbonate, and carbon dioxide)
and thus is rarely limiting. The N:P ratio best represents
the macronutrient limitations (Redfield et al., 1963).
According to Liebig’s Law of the Minimum, the concentration of a nutrient present at the lowest relative
levels required for an organism’s growth is typically
the limiting factor, which explains why the N:P ratio
is a limiting factor compared with carbon (Bianchi,
2007).
Estuarine Behavior. Certain estuarine microorganisms
may have variable internal N:P ratios because the internal
composition reflects the ratio in the environment and
N and P concentrations are highly variable in estuaries.
Therefore, changes in bioavailability of such elements
can significantly limit organic carbon production.
Nitrogen is the limiting nutrient in most estuaries because
it is assimilated more rapidly and in greater amounts than
other nutrients. It also has a more complex biogeochemical cycle than phosphorus. Reactive dissolved silicon is
a key component in the composition of diatom and
silicoflagellate shells as well as exoskeletons of other
organisms, such as certain sponges. Reactive dissolved
silicon is assimilated by diatoms at ratios similar to those
at which N is assimilated.
Eutrophication. Eutrophication caused by nutrient
enrichment (i.e., N and P) is a major problem in many
estuaries (Kennish, 1997). Excessive loading of N to estuarine waters can result in P limitation in systems that are
generally considered to be N limited.
Bibliography
Bianchi, T. S., 2007. Biogeochemistry of Estuaries. Oxford: Oxford
University Press.
Day, J. W., Kemp, M. W., Yánez-Arancibia, A., and Crump, B. C.,
2012. Estuarine Ecology, 2nd edn. Hoboken, New Jersey:
Wiley-Blackwell.
Kennish, M. J., 1997. Practical Handbook of Estuarine and Marine
Pollution. Boca Raton, Florida: CRC Press.
Redfield, A. C., Ketchum, B. H., and Richards, F. A., 1963. The
influence of organisms on the composition of seawater. In Hill,
M. N. (ed.), The Sea. New York: John Wiley & Sons,
Vol. 2, pp. 26–77.
MACRONUTRIENTS
389