Variety of refuge hole sizes
Holes are very important to small fish on coral reefs as refuges from predators. The number of holes is also counted
within the same five 1 m
2 quadrats on each transect from
which surface indices are calculated. They are classified into
the following size ranges (entrance diameter): 1–5, 6–15,
16–30, 31–50, and >50 cm (Roberts and Ormond, 1987).
Vertical relief or height of substratum architecture
A surface can be topographically complex in a number of
ways, and there are correspondingly many ways of measuring such complexity. For comparative studies, variation in complexity is usually described with a univariate
index. Researchers have a choice of indices with complexity values typically calculated from a transect across the
surface. There are essentially two ways in which the complexity of the surface can be translated into an index.
The distance traveled along the surface compared to the
linear distance between the ends of the transect gives
a measure of the extra surface introduced by following
cracks and protrusions on the surface. Typically chains
are used to follow the surface profile and calculate this
type of index. As an alternative to surface following techniques, some form of measurement of the surface can be
taken, with statistics calculated from the resulting profile.
Typically these surface measurements involve recording
the different heights of pins in a profile gauge or the use
of a stereophoto to reconstruct heights. Statistics calculated from these profiles include the sum of consecutive
height differences between horizontally adjacent points
and indices based on the variance of change in slope angle
between consecutive measurements. Separate indices
measure slightly different properties of a surface but tend
to be correlated for the same profile (Frost et al., 2005).
Percentage live cover, including corals and
seagrasses
Percentage live cover throughout the area is visually
assessed along 50 m of reef around the perimeter of a basin
at points on a 1-km grid. Cover is estimated using the following scale: 0 % (dead), <2 %, 2 to <5 %, 5–10 %, and
>10 %. This method of measuring coral cover is preferred
to more quantitative techniques due to the limited time
available and because data from abundance categories
have proved reliable in quantifying changes in other
assemblages (Bell and Galzin, 1984).
Percentage hard substratum
Hard substratum refers to the percentage of substratum
that is not mud, sand, or rubble (Gratwick and Speight,
2005).
How to measure the complexity of the habitat
Understanding the relationships between species biological
traits and the environment is crucial to predicting the effect
of habitat perturbations on communities. Habitat complexity is a multivariate problem; one of the characteristics of
environmental data is the complex relationships that
exist between them. In order to elucidate the relationships
between biological assemblages and the environmental
variables, multivariate tests can be applied: canonical correspondence analysis (CCA), multiple regression analysis,
non-metric multidimensional scaling (nMDS), multivariate
analysis of variance (MANOVA), and others.
Many studies have assessed local effects of habitat complexity, reporting increased richness and abundance in more
complex habitats. Greater habitat complexity is often associated with a greater abundance and diversity of organisms.
High complexity habitats may reduce predation and competition, thereby allowing more individuals to occupy a given
area. However, the relationship between habitat complexity
and species diversity is still unclear. In essence, quantitative
indices of habitat complexity are available for most habitat
types and should be more widely employed in future studies
to better understand the mechanistic role of habitat structure. Some of these indices can be developed further to
enable consistent comparison among different habitats, thus
alleviating the problem of the lack of integration between
fields (Kovalenko et al., 2012).
Summary
The analysis of habitat complexity is an important aspect
of understanding the dynamics of estuarine communities.
This analysis should consider a multivariate approach, as
the habitat is determined by the synergy of environmental
factors such as topographic complexity or rugosity of the
substratum, substratum diversity, variety of refuge hole
sizes, vertical relief or height of substratum architecture,
percentage live cover (including corals and seagrasses),
and percentage hard substratum. Furthermore, it is necessary to develop and implement the use of new indices that
help discern more clearly the relationship of diversity to
habitat complexity.
Bibliography
Bell, J. D., and Galzin, R., 1984. Influence of live coral cover on
coral reef fish communities. Marine Ecology Progress Series,
15, 265–274.
Frost, N. J., Burrows, M. T., Johnson, M. P., Hanley, M. E., and Hawkins, S. J., 2005. Measuring surface complexity in ecological studies. Limnology and Oceanography: Methods, 3, 203–210.
Gratwick, B., and Speight, M. R., 2005. The relationship between
fish species richness, abundance and habitat complexity in
a range of shallow tropical marine habitats. Journal of Fish
Biology, 66, 650–667.
Kovalenko, K. E., Thomaz, S. M., and Warfe, D. M., 2012. Habitat
complexity: approaches and future directions. Hydrobiologia,
685, 1–17.
Krebs, C., 1994. Ecology. The Experimental Analysis of Distribution and Abundance, 4th edn. New York: Harper Collins College
Publishers.
Roberts, C. M., and Ormond, R. F. G., 1987. Habitat complexity and
coral reef fish diversity and abundance on Red Sea fringing reefs.
Marine Ecology Progress Series, 41, 1–8.
Walker, B. K., Jordan, L. K. B., and Spieler, R. E., 2009. Relationship of reef fish assemblages and topographic complexity on
southeastern Florida coral reef habitats. Journal of Coastal
Research, 53, 39–48.
348
HABITAT COMPLEXITY
Holes are very important to small fish on coral reefs as refuges from predators. The number of holes is also counted
within the same five 1 m
2 quadrats on each transect from
which surface indices are calculated. They are classified into
the following size ranges (entrance diameter): 1–5, 6–15,
16–30, 31–50, and >50 cm (Roberts and Ormond, 1987).
Vertical relief or height of substratum architecture
A surface can be topographically complex in a number of
ways, and there are correspondingly many ways of measuring such complexity. For comparative studies, variation in complexity is usually described with a univariate
index. Researchers have a choice of indices with complexity values typically calculated from a transect across the
surface. There are essentially two ways in which the complexity of the surface can be translated into an index.
The distance traveled along the surface compared to the
linear distance between the ends of the transect gives
a measure of the extra surface introduced by following
cracks and protrusions on the surface. Typically chains
are used to follow the surface profile and calculate this
type of index. As an alternative to surface following techniques, some form of measurement of the surface can be
taken, with statistics calculated from the resulting profile.
Typically these surface measurements involve recording
the different heights of pins in a profile gauge or the use
of a stereophoto to reconstruct heights. Statistics calculated from these profiles include the sum of consecutive
height differences between horizontally adjacent points
and indices based on the variance of change in slope angle
between consecutive measurements. Separate indices
measure slightly different properties of a surface but tend
to be correlated for the same profile (Frost et al., 2005).
Percentage live cover, including corals and
seagrasses
Percentage live cover throughout the area is visually
assessed along 50 m of reef around the perimeter of a basin
at points on a 1-km grid. Cover is estimated using the following scale: 0 % (dead), <2 %, 2 to <5 %, 5–10 %, and
>10 %. This method of measuring coral cover is preferred
to more quantitative techniques due to the limited time
available and because data from abundance categories
have proved reliable in quantifying changes in other
assemblages (Bell and Galzin, 1984).
Percentage hard substratum
Hard substratum refers to the percentage of substratum
that is not mud, sand, or rubble (Gratwick and Speight,
2005).
How to measure the complexity of the habitat
Understanding the relationships between species biological
traits and the environment is crucial to predicting the effect
of habitat perturbations on communities. Habitat complexity is a multivariate problem; one of the characteristics of
environmental data is the complex relationships that
exist between them. In order to elucidate the relationships
between biological assemblages and the environmental
variables, multivariate tests can be applied: canonical correspondence analysis (CCA), multiple regression analysis,
non-metric multidimensional scaling (nMDS), multivariate
analysis of variance (MANOVA), and others.
Many studies have assessed local effects of habitat complexity, reporting increased richness and abundance in more
complex habitats. Greater habitat complexity is often associated with a greater abundance and diversity of organisms.
High complexity habitats may reduce predation and competition, thereby allowing more individuals to occupy a given
area. However, the relationship between habitat complexity
and species diversity is still unclear. In essence, quantitative
indices of habitat complexity are available for most habitat
types and should be more widely employed in future studies
to better understand the mechanistic role of habitat structure. Some of these indices can be developed further to
enable consistent comparison among different habitats, thus
alleviating the problem of the lack of integration between
fields (Kovalenko et al., 2012).
Summary
The analysis of habitat complexity is an important aspect
of understanding the dynamics of estuarine communities.
This analysis should consider a multivariate approach, as
the habitat is determined by the synergy of environmental
factors such as topographic complexity or rugosity of the
substratum, substratum diversity, variety of refuge hole
sizes, vertical relief or height of substratum architecture,
percentage live cover (including corals and seagrasses),
and percentage hard substratum. Furthermore, it is necessary to develop and implement the use of new indices that
help discern more clearly the relationship of diversity to
habitat complexity.
Bibliography
Bell, J. D., and Galzin, R., 1984. Influence of live coral cover on
coral reef fish communities. Marine Ecology Progress Series,
15, 265–274.
Frost, N. J., Burrows, M. T., Johnson, M. P., Hanley, M. E., and Hawkins, S. J., 2005. Measuring surface complexity in ecological studies. Limnology and Oceanography: Methods, 3, 203–210.
Gratwick, B., and Speight, M. R., 2005. The relationship between
fish species richness, abundance and habitat complexity in
a range of shallow tropical marine habitats. Journal of Fish
Biology, 66, 650–667.
Kovalenko, K. E., Thomaz, S. M., and Warfe, D. M., 2012. Habitat
complexity: approaches and future directions. Hydrobiologia,
685, 1–17.
Krebs, C., 1994. Ecology. The Experimental Analysis of Distribution and Abundance, 4th edn. New York: Harper Collins College
Publishers.
Roberts, C. M., and Ormond, R. F. G., 1987. Habitat complexity and
coral reef fish diversity and abundance on Red Sea fringing reefs.
Marine Ecology Progress Series, 41, 1–8.
Walker, B. K., Jordan, L. K. B., and Spieler, R. E., 2009. Relationship of reef fish assemblages and topographic complexity on
southeastern Florida coral reef habitats. Journal of Coastal
Research, 53, 39–48.
348
HABITAT COMPLEXITY