Chapter 21 Seagrasses, Fish, and Fisheries
529
E. Links between Seagrass and Fish
Trophic links between seagrass and other habitats
(e.g. coral reefs, non-vegetated), particularly involving commercially important species preying on
small non-commercial species, are only just starting to be investigated. Further studies are required
that sample both predatory fishes and their prey over
the same spatial and temporal scales. Such studies
should also incorporate dietary analysis of piscivorous fish. Isotope studies may be particularly useful
in this area. Stable isotopes may also help trace the
contribution of material from within seagrass beds to
fishery species elsewhere (e.g. Thresher et al., 1992).
If seagrass material is being utilized and assimilated
by species elsewhere, then this may have implications for loss of seagrass. At present, the importance
of exported seagrass material to organisms in other
habitats is poorly known.
Links between seagrass habitats and other habitats
are still poorly known. In particular no studies have
examined the contribution of seagrass beds from different estuaries or regions to commercial fisheries
(e.g. Gillanders, 2002) and few studies have examined the contribution of differing juvenile habitats
to adult populations (e.g. Gillanders and Kingsford,
1996). Likewise, few if any studies have examined
relative differences in the contribution of larvae
from different regions to seagrass beds. Thus, larval sources and transport pathways are completely
unknown. With developments in the field of isotopic
and elemental chemistry, determining origins, movement, and contributions from different areas/habitats
should be possible. This approach requires empirical
determination of spatial and temporal differences in
chemistry over the range of the organism of interest. Depending on spatial and temporal differences
in chemistry it may be necessary to track adults
back to the cohort of recruits from which they originated (e.g. Gillanders, 2002). Once seagrass beds
that contribute more individuals to adult populations
are identified it will then be possible to focus conservation strategies (e.g. estuarine protected areas)
on these areas.
F. Larval Studies
Further information is required on larval dynamics
which should enable a better understanding of larval supply processes (see above). All aspects of the
biology and ecology of larvae (of fish found within
seagrass beds) require further study. In many cases,
even the taxonomy of larvae is poorly known. Larval
behavior has only recently been examined but there
is still much work to be done. While larvae are able
to control where they are and where they will settle,
it is not known at what stage they assume this control. One of the limitations of many larval studies is
that extensive sampling then requires considerable
effort to process samples. Methods that overcome
such limitations are required (e.g. molecular techniques).
G. Impacts of Fishing
Impacts of fishing on fish stocks and seagrass habitats have been investigated in some areas of the
world, but have been largely unexplored in other
regions (e.g. Africa, Asia). Although a number of
studies have investigated by-catch of fishing gear and
altering gear to reduce by-catch, few of these studies
have focused specifically on seagrass habitats or determined potential mortality rates of fish returned to
the water. Investigations of fishing-induced mortality and how this varies by species, size of fish, and
gear type are needed. Such information combined
with by-catch data would enable us to determine the
quantitative impact of fishing on fish within seagrass
habitats. The indirect effect of fishing on seagrass
inhabitants also requires further investigation. For
example, the effects of propeller scarring (e.g. Bell
et al., 2002) and trampling in seagrass (e.g. Eckrich
and Holmquist, 2000) on faunal assemblages have
only recently been investigated. A range of manipulative experiments have examined sediments and turbidity within seagrass, but few studies have focused
on seagrass inhabitants. Thus, further research that
investigates both the direct and indirect effects of
fishing on seagrass inhabitants, including commercially important species is needed. Such research
needs to be done for a range of seagrass species.
H. Seagrass Restoration and Fisheries
Much literature is appearing on restoration of seagrass habitats (e.g. see chapters within this book),
but few studies investigate whether planted or restored seagrass provides similar resources to natural seagrass. Studies that monitor the effectiveness of planted/restored seagrass should monitor not
just the plants themselves, but also the inhabitants,
529
E. Links between Seagrass and Fish
Trophic links between seagrass and other habitats
(e.g. coral reefs, non-vegetated), particularly involving commercially important species preying on
small non-commercial species, are only just starting to be investigated. Further studies are required
that sample both predatory fishes and their prey over
the same spatial and temporal scales. Such studies
should also incorporate dietary analysis of piscivorous fish. Isotope studies may be particularly useful
in this area. Stable isotopes may also help trace the
contribution of material from within seagrass beds to
fishery species elsewhere (e.g. Thresher et al., 1992).
If seagrass material is being utilized and assimilated
by species elsewhere, then this may have implications for loss of seagrass. At present, the importance
of exported seagrass material to organisms in other
habitats is poorly known.
Links between seagrass habitats and other habitats
are still poorly known. In particular no studies have
examined the contribution of seagrass beds from different estuaries or regions to commercial fisheries
(e.g. Gillanders, 2002) and few studies have examined the contribution of differing juvenile habitats
to adult populations (e.g. Gillanders and Kingsford,
1996). Likewise, few if any studies have examined
relative differences in the contribution of larvae
from different regions to seagrass beds. Thus, larval sources and transport pathways are completely
unknown. With developments in the field of isotopic
and elemental chemistry, determining origins, movement, and contributions from different areas/habitats
should be possible. This approach requires empirical
determination of spatial and temporal differences in
chemistry over the range of the organism of interest. Depending on spatial and temporal differences
in chemistry it may be necessary to track adults
back to the cohort of recruits from which they originated (e.g. Gillanders, 2002). Once seagrass beds
that contribute more individuals to adult populations
are identified it will then be possible to focus conservation strategies (e.g. estuarine protected areas)
on these areas.
F. Larval Studies
Further information is required on larval dynamics
which should enable a better understanding of larval supply processes (see above). All aspects of the
biology and ecology of larvae (of fish found within
seagrass beds) require further study. In many cases,
even the taxonomy of larvae is poorly known. Larval
behavior has only recently been examined but there
is still much work to be done. While larvae are able
to control where they are and where they will settle,
it is not known at what stage they assume this control. One of the limitations of many larval studies is
that extensive sampling then requires considerable
effort to process samples. Methods that overcome
such limitations are required (e.g. molecular techniques).
G. Impacts of Fishing
Impacts of fishing on fish stocks and seagrass habitats have been investigated in some areas of the
world, but have been largely unexplored in other
regions (e.g. Africa, Asia). Although a number of
studies have investigated by-catch of fishing gear and
altering gear to reduce by-catch, few of these studies
have focused specifically on seagrass habitats or determined potential mortality rates of fish returned to
the water. Investigations of fishing-induced mortality and how this varies by species, size of fish, and
gear type are needed. Such information combined
with by-catch data would enable us to determine the
quantitative impact of fishing on fish within seagrass
habitats. The indirect effect of fishing on seagrass
inhabitants also requires further investigation. For
example, the effects of propeller scarring (e.g. Bell
et al., 2002) and trampling in seagrass (e.g. Eckrich
and Holmquist, 2000) on faunal assemblages have
only recently been investigated. A range of manipulative experiments have examined sediments and turbidity within seagrass, but few studies have focused
on seagrass inhabitants. Thus, further research that
investigates both the direct and indirect effects of
fishing on seagrass inhabitants, including commercially important species is needed. Such research
needs to be done for a range of seagrass species.
H. Seagrass Restoration and Fisheries
Much literature is appearing on restoration of seagrass habitats (e.g. see chapters within this book),
but few studies investigate whether planted or restored seagrass provides similar resources to natural seagrass. Studies that monitor the effectiveness of planted/restored seagrass should monitor not
just the plants themselves, but also the inhabitants,