Bibliography
Cohen, D. M., 1970. How many recent fish are there? Proceedings
of the California Academy of Sciences, 38, 341–346.
McDowall, R. M., 1987. The occurrence and distribution of
diadromy among fishes. In Dadswell, M. J., Klauda, R. J.,
Moffitt, C. M., Saunders, R. L., Rulifson, R. A., and Cooper,
J. E. (eds.), Common Strategies of Anadromous and Catadromous Fishes. American Fisheries Society Symposium,
Vol. 1, Bethesda, MD.
Meek, A., 1916. The Migrations of Fishes. London: Edward
Arnold.
Meyers, G. S., 1949. Usage of anadromous, catadromous and allied
terms for migratory fishes. Copeia, 11, 89–97.
Subnikov, D. A., 1976. Types of migrations of diadromous and
semidiadromous fishes. Journal of Ichthyology, 16, 531–535.
ANAEROBIC ENVIRONMENTS
Ayman A. Elgamal
Marine Geology Department, Coastal Research Institute,
National Water Research Center, Alexandria, Egypt
Synonyms
Non-aerial environment
Definition
An anaerobic environment is characterized by the absence
of free oxygen but may contain atomic oxygen bound in
compounds such as nitrate (NO 3 ), nitrite (NO 2 ), and sulfites (SO 3 ), in contrast to an aerobic environment where
free oxygen is available (WKU, 2013).
Description
Some organisms are successfully adapted to anaerobic
environments (EPA, 2012). These organisms do not use
O 2 as their electron acceptors. There are a number of substances that they will use as a substitute for O 2 , including
(among others) nitrate (NO 3 ), ferric iron (Fe 3
+ ), manganese (Mn 2
+ ), sulfate (SO 4
2À
), and carbon dioxide (CO 2 )
(Scharf, 2000). Bacteria use sulfate as an acceptor for electrons in place of oxygen under anaerobic conditions. As
the reduced organic tissue is oxidized to CO 2 , the sulfate
is reduced to sulfide (Nietch, 2000).
In bottom waters of stratified estuaries, oxygen consumed primarily by bacteria will exceed oxygen input via
atmospheric and photosynthetic reoxygenation. While the
anoxia/hypoxia that develops will eliminate almost all estuarine and marine organisms, a large number of bacteria and
protists can still remain active in these areas by changing
their metabolism to anaerobic respiration (Dang et al.,
2008). If oxygen becomes so low that the system becomes
anoxic, which occurs frequently in shallow turbid estuaries
in the summer time, anaerobic mechanisms for decomposition become important. Carbon turnover occurs continuously in subtidal and intertidal sediments where oxygen is
depleted just a few millimeters below the sediment surface.
Much of the organic matter undergoes decomposition in an
estuarine anaerobic environment via sulfate reduction
(Nietch, 2000). Preservation of skeletal remains in these
environments appears to be correlated with the abundance
of dissolved organic matter rather than with high sedimentation rates (Simon et al., 1994).
Bibliography
Dang, H., Zhang, X., Sun, J., Li, T., Zhang, Z., and Yang, G., 2008.
Diversity and spatial distribution of sediment ammoniaoxidizing crenarchaeota in response to estuarine and environmental gradients in the Changjiang Estuary and East China
Sea. Microbiology, 154, 2084–2095.
EPA, 2012. Glossary of technical terms. Underground storage
tanks, U.S. Environmental Protection Agency, http://www.epa.
gov/oust/cat/tumgloss.htm.
Nietch, C., 2000. Biogeochemistry. University of South Carolina.
http://www.nerrs.noaa.gov/Doc/SiteProfile/ACEBasin/html/
envicond/biogeo/bgtext.htm.
Scharf, R., 2000. Soil Composition and Formation: Wetland Soils.
SCDNR Land, Water, and Conservation Division. http://www.
nerrs.noaa.gov/Doc/SiteProfile/ACEBasin/html/envicond/soil/
slwetlnd.htm.
Simon, A., Poulicek, M., Velimirov, B., and MacKenzie, F. T., 1994.
Comparison of anaerobic and aerobic biodegradation of mineralized skeletal structures in marine and estuarine conditions.
Biogeochemistry, 25(3), 167–195.
WKU, 2013. Physiological Requirements of Oxygen. 208 Microbiology, Section 3, Laboratory Week 11, Western Kentucky
University (WKU), http://bioweb.wku.edu/courses/Biol208/
Lab_Manual/208%20week%2011.pdf
Cross-references
Anaerobic Environments
Anoxia, Hypoxia, and Dead Zones
ANOXIA, HYPOXIA, AND DEAD ZONES
Robert J. Diaz
College of William and Mary, Virginia Institute of
Marine Science, Gloucester Point, VA, USA
Synonyms
Anoxic; Anoxic basins; Euxina; Hypoxic, Low dissolved
oxygen; Oxygen minimum layer; Oxygen minimum zone
Definition
Anoxia is a condition of no, or at times very little,
dissolved oxygen in marine or freshwater systems, which
has drastic consequences to normal ecosystem functioning
including biogeochemical cycling.
Hypoxia is a condition of low dissolved oxygen concentrations in marine or freshwater systems, which has
adverse consequences to normal ecosystem functioning
ANOXIA, HYPOXIA, AND DEAD ZONES
19
Cohen, D. M., 1970. How many recent fish are there? Proceedings
of the California Academy of Sciences, 38, 341–346.
McDowall, R. M., 1987. The occurrence and distribution of
diadromy among fishes. In Dadswell, M. J., Klauda, R. J.,
Moffitt, C. M., Saunders, R. L., Rulifson, R. A., and Cooper,
J. E. (eds.), Common Strategies of Anadromous and Catadromous Fishes. American Fisheries Society Symposium,
Vol. 1, Bethesda, MD.
Meek, A., 1916. The Migrations of Fishes. London: Edward
Arnold.
Meyers, G. S., 1949. Usage of anadromous, catadromous and allied
terms for migratory fishes. Copeia, 11, 89–97.
Subnikov, D. A., 1976. Types of migrations of diadromous and
semidiadromous fishes. Journal of Ichthyology, 16, 531–535.
ANAEROBIC ENVIRONMENTS
Ayman A. Elgamal
Marine Geology Department, Coastal Research Institute,
National Water Research Center, Alexandria, Egypt
Synonyms
Non-aerial environment
Definition
An anaerobic environment is characterized by the absence
of free oxygen but may contain atomic oxygen bound in
compounds such as nitrate (NO 3 ), nitrite (NO 2 ), and sulfites (SO 3 ), in contrast to an aerobic environment where
free oxygen is available (WKU, 2013).
Description
Some organisms are successfully adapted to anaerobic
environments (EPA, 2012). These organisms do not use
O 2 as their electron acceptors. There are a number of substances that they will use as a substitute for O 2 , including
(among others) nitrate (NO 3 ), ferric iron (Fe 3
+ ), manganese (Mn 2
+ ), sulfate (SO 4
2À
), and carbon dioxide (CO 2 )
(Scharf, 2000). Bacteria use sulfate as an acceptor for electrons in place of oxygen under anaerobic conditions. As
the reduced organic tissue is oxidized to CO 2 , the sulfate
is reduced to sulfide (Nietch, 2000).
In bottom waters of stratified estuaries, oxygen consumed primarily by bacteria will exceed oxygen input via
atmospheric and photosynthetic reoxygenation. While the
anoxia/hypoxia that develops will eliminate almost all estuarine and marine organisms, a large number of bacteria and
protists can still remain active in these areas by changing
their metabolism to anaerobic respiration (Dang et al.,
2008). If oxygen becomes so low that the system becomes
anoxic, which occurs frequently in shallow turbid estuaries
in the summer time, anaerobic mechanisms for decomposition become important. Carbon turnover occurs continuously in subtidal and intertidal sediments where oxygen is
depleted just a few millimeters below the sediment surface.
Much of the organic matter undergoes decomposition in an
estuarine anaerobic environment via sulfate reduction
(Nietch, 2000). Preservation of skeletal remains in these
environments appears to be correlated with the abundance
of dissolved organic matter rather than with high sedimentation rates (Simon et al., 1994).
Bibliography
Dang, H., Zhang, X., Sun, J., Li, T., Zhang, Z., and Yang, G., 2008.
Diversity and spatial distribution of sediment ammoniaoxidizing crenarchaeota in response to estuarine and environmental gradients in the Changjiang Estuary and East China
Sea. Microbiology, 154, 2084–2095.
EPA, 2012. Glossary of technical terms. Underground storage
tanks, U.S. Environmental Protection Agency, http://www.epa.
gov/oust/cat/tumgloss.htm.
Nietch, C., 2000. Biogeochemistry. University of South Carolina.
http://www.nerrs.noaa.gov/Doc/SiteProfile/ACEBasin/html/
envicond/biogeo/bgtext.htm.
Scharf, R., 2000. Soil Composition and Formation: Wetland Soils.
SCDNR Land, Water, and Conservation Division. http://www.
nerrs.noaa.gov/Doc/SiteProfile/ACEBasin/html/envicond/soil/
slwetlnd.htm.
Simon, A., Poulicek, M., Velimirov, B., and MacKenzie, F. T., 1994.
Comparison of anaerobic and aerobic biodegradation of mineralized skeletal structures in marine and estuarine conditions.
Biogeochemistry, 25(3), 167–195.
WKU, 2013. Physiological Requirements of Oxygen. 208 Microbiology, Section 3, Laboratory Week 11, Western Kentucky
University (WKU), http://bioweb.wku.edu/courses/Biol208/
Lab_Manual/208%20week%2011.pdf
Cross-references
Anaerobic Environments
Anoxia, Hypoxia, and Dead Zones
ANOXIA, HYPOXIA, AND DEAD ZONES
Robert J. Diaz
College of William and Mary, Virginia Institute of
Marine Science, Gloucester Point, VA, USA
Synonyms
Anoxic; Anoxic basins; Euxina; Hypoxic, Low dissolved
oxygen; Oxygen minimum layer; Oxygen minimum zone
Definition
Anoxia is a condition of no, or at times very little,
dissolved oxygen in marine or freshwater systems, which
has drastic consequences to normal ecosystem functioning
including biogeochemical cycling.
Hypoxia is a condition of low dissolved oxygen concentrations in marine or freshwater systems, which has
adverse consequences to normal ecosystem functioning
ANOXIA, HYPOXIA, AND DEAD ZONES
19