Chapter 21 Seagrasses, Fish, and Fisheries
515
occurred in seagrass and oyster shell habitats, such
that there was no additive effect on overall species
richness (Eggleston et al., 1999).
The abundance and growth of pinfish (Lagodon
rhomboides, Sparidae) were greater where intertidal
salt marsh was adjacent to seagrass beds rather than
non-vegetated habitats (Irlandi and Crawford, 1997).
Movement of fish also was affected by the type of
subtidal habitat adjacent to the marsh. For example, fish moved between marsh and seagrass more
readily than they did between marsh and mudflat
(Irlandi and Crawford, 1997). Linkages between
habitats may, however, depend on the distance between habitats. These results suggest that for restoration of marsh habitats, managers may want to restore
marsh habitats that are adjacent to subtidal seagrass
beds (Irlandi and Crawford, 1997).
C. Regional and Biogeographic Scales
Investigations over large spatial scales (tens to hundreds of km and greater) also show significant differences in fish abundance (Ferrell and Bell, 1991; Gray
et al., 1996; Goldberg et al., 2002). Observations
among multiple estuaries, between tropical and temperate systems, and among different biogeographic
regions may be necessary to determine if there are
distinct patterns of habitat use at these large spatial
scales. The generality of any observed patterns and
mechanisms responsible for patterns could then be
determined (Table 1).
1. Comparisons Among Estuaries
Significant variation in abundances and species richness among estuaries has been found (Worthington
et al., 1992; Ferrell et al., 1993; Wyda et al., 2002).
In one study that sampled three estuaries spanning
300 km of coastline, each estuary had 14 or 15
species that occurred only in that estuary (Ferrell
et al., 1993). In contrast, 37 species occurred in all
estuaries. Assemblages of fish from within an estuary were, however, more similar to each other than
to samples from different estuaries (Ferrell et al.,
1993). At large spatial scales (e.g. among 3–4 sites
separated by greater than 1 km within 3–4 estuaries
spanning 400 km of coast), most variation in abundances of individual species was explained by larval supply rather than density of seagrass shoots, as
variation in density of shoots explained less than 5%
of the variation in abundances (Worthington et al.,
1992). Other factors (e.g. wave exposure) may also
be correlated with larval supply meaning that determining factors that influence abundance of organisms will be difficult. In addition, attributes of seagrass structure other than density may be more important. Studies often focus on only one estuary (or
location) and further research is needed to determine
the generality of results among multiple estuaries.
2. Generality Across Large
Biogeographic Scales
In a recent review, geographical differences were
noted in the degree to which seagrass meadows support greater densities of organisms than other habitats (Heck et al., 2003). For example, 75% (58 of 77
comparisons) of studies in the northern hemisphere
showed greater abundances in seagrass, whereas
only 36% (42 of 116) from the southern hemisphere
did. It should, however, be noted that most studies from the northern hemisphere were conducted
in USA, and most studies from the southern hemisphere were conducted in Australia. Determining
generality at large biogeographic scales is likely to be
difficult due to differences in sampling designs and
methodologies across studies and the lack of studies
in some regions. Approaches using published studies and meta-analyses would be useful where studies
exist for a wide range of regions, but other initiatives will be needed where existing studies are lacking. For example, a comparative study using similar
techniques could be planned that enlists researchers
from several countries.
3. Comparisons Between Tropical
and Temperate Seagrass Systems
Relatively few studies have compared fish assemblages between tropical and temperate seagrass beds,
and most of these studies only compare one tropical
region to one temperate region. Frequently, numerous variables in a study differ between temperate
and tropical systems (e.g. species of seagrass, patch
scale variables). Therefore, determining whether latitude or some other variable is more important is difficult. Panamanian seagrass beds had significantly
more species than similar habitats in the Gulf of
515
occurred in seagrass and oyster shell habitats, such
that there was no additive effect on overall species
richness (Eggleston et al., 1999).
The abundance and growth of pinfish (Lagodon
rhomboides, Sparidae) were greater where intertidal
salt marsh was adjacent to seagrass beds rather than
non-vegetated habitats (Irlandi and Crawford, 1997).
Movement of fish also was affected by the type of
subtidal habitat adjacent to the marsh. For example, fish moved between marsh and seagrass more
readily than they did between marsh and mudflat
(Irlandi and Crawford, 1997). Linkages between
habitats may, however, depend on the distance between habitats. These results suggest that for restoration of marsh habitats, managers may want to restore
marsh habitats that are adjacent to subtidal seagrass
beds (Irlandi and Crawford, 1997).
C. Regional and Biogeographic Scales
Investigations over large spatial scales (tens to hundreds of km and greater) also show significant differences in fish abundance (Ferrell and Bell, 1991; Gray
et al., 1996; Goldberg et al., 2002). Observations
among multiple estuaries, between tropical and temperate systems, and among different biogeographic
regions may be necessary to determine if there are
distinct patterns of habitat use at these large spatial
scales. The generality of any observed patterns and
mechanisms responsible for patterns could then be
determined (Table 1).
1. Comparisons Among Estuaries
Significant variation in abundances and species richness among estuaries has been found (Worthington
et al., 1992; Ferrell et al., 1993; Wyda et al., 2002).
In one study that sampled three estuaries spanning
300 km of coastline, each estuary had 14 or 15
species that occurred only in that estuary (Ferrell
et al., 1993). In contrast, 37 species occurred in all
estuaries. Assemblages of fish from within an estuary were, however, more similar to each other than
to samples from different estuaries (Ferrell et al.,
1993). At large spatial scales (e.g. among 3–4 sites
separated by greater than 1 km within 3–4 estuaries
spanning 400 km of coast), most variation in abundances of individual species was explained by larval supply rather than density of seagrass shoots, as
variation in density of shoots explained less than 5%
of the variation in abundances (Worthington et al.,
1992). Other factors (e.g. wave exposure) may also
be correlated with larval supply meaning that determining factors that influence abundance of organisms will be difficult. In addition, attributes of seagrass structure other than density may be more important. Studies often focus on only one estuary (or
location) and further research is needed to determine
the generality of results among multiple estuaries.
2. Generality Across Large
Biogeographic Scales
In a recent review, geographical differences were
noted in the degree to which seagrass meadows support greater densities of organisms than other habitats (Heck et al., 2003). For example, 75% (58 of 77
comparisons) of studies in the northern hemisphere
showed greater abundances in seagrass, whereas
only 36% (42 of 116) from the southern hemisphere
did. It should, however, be noted that most studies from the northern hemisphere were conducted
in USA, and most studies from the southern hemisphere were conducted in Australia. Determining
generality at large biogeographic scales is likely to be
difficult due to differences in sampling designs and
methodologies across studies and the lack of studies
in some regions. Approaches using published studies and meta-analyses would be useful where studies
exist for a wide range of regions, but other initiatives will be needed where existing studies are lacking. For example, a comparative study using similar
techniques could be planned that enlists researchers
from several countries.
3. Comparisons Between Tropical
and Temperate Seagrass Systems
Relatively few studies have compared fish assemblages between tropical and temperate seagrass beds,
and most of these studies only compare one tropical
region to one temperate region. Frequently, numerous variables in a study differ between temperate
and tropical systems (e.g. species of seagrass, patch
scale variables). Therefore, determining whether latitude or some other variable is more important is difficult. Panamanian seagrass beds had significantly
more species than similar habitats in the Gulf of