SOFT SEDIMENT COMMUNITIES
Francisco Barros
Laboratório de Ecologia Bentônica, Instituto de Biologia,
Universidade Federal da Bahia, Salvador, Bahia, Brazil
Synonyms
Soft bottom communities
Definition
Estuarine soft sediment communities consist of groups of
benthic species that frequently co-occur and show
interdependence.
Description
Soft sediments – mud, silt, and sand – cover a large portion of the world’s estuarine benthic environments and
provide habitat for a multitude of benthic invertebrate species. Soft sediments are three-dimensional environments
inhabited by many benthic species. It is well documented
that soft sediment communities are not only influenced by
environmental factors (e.g., sediment size, pH, organic
content) but also by biotic factors (e.g., bioturbation)
(see the pioneer work of Rhoads and Young, 1970). Bioturbation is linked to deposit feeding, sediment reworking,
construction of burrows and tubes, and irrigation, with
important effects on biogeochemical processes in surface
sediments and at the sediment-water interface and on
redox conditions in deeper sediments (Rosenberg, 2001).
Estuaries provide essential ecological functions (e.g.,
nutrient cycling), and soft sediment communities are integral to these functions (Levin et al., 2001). A large fraction
of primary consumers in an estuary are found in the bottom sediments (McLusky and Elliott, 2004). The
macrofauna of estuarine soft sediment communities are
dominated by crustaceans, mollusks, and annelids, and
there are many studies showing that the structure of these
communities is an essential tool for assessing impacts on
estuaries.
While the meaning of the term “soft sediment” is
straightforward, the meaning of the term “community”
has been a matter of debate for decades. This debate
involves disagreement about populations versus communities as the appropriate level of organization to study
(see Underwood, 1986 and references therein). In the estuarine ecological literature, the terms “community” and
“assemblage” are often used synonymously. However,
the term “community” not only refers to groups of species
that co-occur in a similar habitat but also to the
interdependence between those species. In contrast, the
term “assemblage” refers to a collection of co-occurring
species that does not require links to a specific
habitat, and it does not imply interdependency (Gray and
Elliott, 2009).
Summary
In the estuarine ecological literature, the terms “community” and “assemblage” are often used synonymously,
but community not only refers to groups of species that
co-occur in a similar habitat but also to the
interdependence between those species. In the absence
of experimental evidence of interdependence
(or interaction), these groups should be called assemblages. Soft sediment communities are affected by the
physical, chemical, and biological characteristics of the
benthic habitat, and they are frequently used to assess
human impacts on estuaries. Many primary consumers in
estuaries are part of benthic communities that provide
essential ecological functions to the system.
Bibliography
Gray, J. S., and Elliott, M., 2009. Ecology of Marine Sediments:
From Science to Management. Oxford: Oxford University Press.
Levin, L. A., Boesch, D. F., Covich, A., Daham, C., Erséus, C.,
Ewel, K. C., Kneib, R. T., Moldenke, A., Palmer, M. A.,
Snelgrove, P., Strayer, D., and Welawski, J. M., 2001. The function of marine critical transitional zones and the importance of
sediment biodiversity. Ecosystems, 4, 430–451.
McLusky, D. S., and Elliott, M., 2004. The Estuarine Ecosystem:
Ecology, Threats and Management. Oxford: Oxford University
Press.
Rhoads, D. C., and Young, D. K., 1970. The influence of deposit
feeding organisms on sediment stability and community trophic
structure. Journal of Marine Research, 28, 150–178.
Rosenberg, G., 2001. Marine benthic faunal successional stages and
related sedimentary activity. Scientia Marina, 65, 107–119.
Underwood, A. J., 1986. What is a community? In Raup, M. P., and
Jablonsky, D. (eds.), Patterns and Processes in the History of
Life. Berlin: Springer, pp. 351–367.
Cross-references
Benthic Ecology
Biogenic Sedimentary Structures
Infauna
SOLDIER CRABS (MICTYRIDAE)
Joy Unno and Vic Semeniuk
V & C Semeniuk Research Group, Warwick,
WA, Australia
Definition
The mictyrid soldier crab is easily identified by a number
of distinctive characteristics including its relatively small
body size (marble to golf ball diameter); blue coloring;
prominent black eyes on short stalks; round, spider-like
appearance; chelipeds (front claws) orientated in the vertical plane; and forward-walking locomotion style. McNeill
(1926) provides a more detailed taxonomic description of
the genus.
606
SOFT SEDIMENT COMMUNITIES
Francisco Barros
Laboratório de Ecologia Bentônica, Instituto de Biologia,
Universidade Federal da Bahia, Salvador, Bahia, Brazil
Synonyms
Soft bottom communities
Definition
Estuarine soft sediment communities consist of groups of
benthic species that frequently co-occur and show
interdependence.
Description
Soft sediments – mud, silt, and sand – cover a large portion of the world’s estuarine benthic environments and
provide habitat for a multitude of benthic invertebrate species. Soft sediments are three-dimensional environments
inhabited by many benthic species. It is well documented
that soft sediment communities are not only influenced by
environmental factors (e.g., sediment size, pH, organic
content) but also by biotic factors (e.g., bioturbation)
(see the pioneer work of Rhoads and Young, 1970). Bioturbation is linked to deposit feeding, sediment reworking,
construction of burrows and tubes, and irrigation, with
important effects on biogeochemical processes in surface
sediments and at the sediment-water interface and on
redox conditions in deeper sediments (Rosenberg, 2001).
Estuaries provide essential ecological functions (e.g.,
nutrient cycling), and soft sediment communities are integral to these functions (Levin et al., 2001). A large fraction
of primary consumers in an estuary are found in the bottom sediments (McLusky and Elliott, 2004). The
macrofauna of estuarine soft sediment communities are
dominated by crustaceans, mollusks, and annelids, and
there are many studies showing that the structure of these
communities is an essential tool for assessing impacts on
estuaries.
While the meaning of the term “soft sediment” is
straightforward, the meaning of the term “community”
has been a matter of debate for decades. This debate
involves disagreement about populations versus communities as the appropriate level of organization to study
(see Underwood, 1986 and references therein). In the estuarine ecological literature, the terms “community” and
“assemblage” are often used synonymously. However,
the term “community” not only refers to groups of species
that co-occur in a similar habitat but also to the
interdependence between those species. In contrast, the
term “assemblage” refers to a collection of co-occurring
species that does not require links to a specific
habitat, and it does not imply interdependency (Gray and
Elliott, 2009).
Summary
In the estuarine ecological literature, the terms “community” and “assemblage” are often used synonymously,
but community not only refers to groups of species that
co-occur in a similar habitat but also to the
interdependence between those species. In the absence
of experimental evidence of interdependence
(or interaction), these groups should be called assemblages. Soft sediment communities are affected by the
physical, chemical, and biological characteristics of the
benthic habitat, and they are frequently used to assess
human impacts on estuaries. Many primary consumers in
estuaries are part of benthic communities that provide
essential ecological functions to the system.
Bibliography
Gray, J. S., and Elliott, M., 2009. Ecology of Marine Sediments:
From Science to Management. Oxford: Oxford University Press.
Levin, L. A., Boesch, D. F., Covich, A., Daham, C., Erséus, C.,
Ewel, K. C., Kneib, R. T., Moldenke, A., Palmer, M. A.,
Snelgrove, P., Strayer, D., and Welawski, J. M., 2001. The function of marine critical transitional zones and the importance of
sediment biodiversity. Ecosystems, 4, 430–451.
McLusky, D. S., and Elliott, M., 2004. The Estuarine Ecosystem:
Ecology, Threats and Management. Oxford: Oxford University
Press.
Rhoads, D. C., and Young, D. K., 1970. The influence of deposit
feeding organisms on sediment stability and community trophic
structure. Journal of Marine Research, 28, 150–178.
Rosenberg, G., 2001. Marine benthic faunal successional stages and
related sedimentary activity. Scientia Marina, 65, 107–119.
Underwood, A. J., 1986. What is a community? In Raup, M. P., and
Jablonsky, D. (eds.), Patterns and Processes in the History of
Life. Berlin: Springer, pp. 351–367.
Cross-references
Benthic Ecology
Biogenic Sedimentary Structures
Infauna
SOLDIER CRABS (MICTYRIDAE)
Joy Unno and Vic Semeniuk
V & C Semeniuk Research Group, Warwick,
WA, Australia
Definition
The mictyrid soldier crab is easily identified by a number
of distinctive characteristics including its relatively small
body size (marble to golf ball diameter); blue coloring;
prominent black eyes on short stalks; round, spider-like
appearance; chelipeds (front claws) orientated in the vertical plane; and forward-walking locomotion style. McNeill
(1926) provides a more detailed taxonomic description of
the genus.
606
SOFT SEDIMENT COMMUNITIES