178
M. A. Mateo, J. Cebri ´
an, K. Dunton, and T. Mutchler
Fig. 11. δ
15 N values (%, mean ±95% confidence intervals) of Halodule wrightii and epiphytic algae in seagrass beds exposed to control,
water column, and sediment fertilization during 20 days (see text).
(∼31%; averages calculated from a compilation by
Daehnik et al., 1992).
4. From the Individual to the Landscape Level
Also overlooked in traditional studies of food web
dynamics is the contribution of individual species in
a community: measurements of primary production,
biomass, and isotopic composition are often performed on samples containing complex assemblages
of species, where the measurements integrate the
functional properties as single points on a graph and
ignore the individual contribution of each species.
This practice is most common with microalgae and
small invertebrates, both of which have been shown
to be functionally important (Klumpp et al., 1992;
Moncreiff et al., 1992). Although this ‘guild-level’
approach is a necessary starting point, much ecological information is lost when groups of species
are combined; measuring the production, biomass,
turnover time, density, consumption rate, and assimilation efficiency of individual species would permit
quantification of the contribution by each species to
the overall flux of matter within the system.
Addressing questions at larger scales is also possible: for example, in the trophic pathways between
beds and other communities. Thus, stable isotopes
will be useful in evaluating the residency time of
individuals in particular beds (Fry et al., 2003).
Knowing how organisms move between seagrass
beds, unvegetated sediments, salt marshes, and other
nearshore habitats as well as the degree to which they
feed in each habitat will help to elucidate how organic matter production in these habitats is linked
(see Valentine and Duffy, Chapter 20; Heck and
Orth, Chapter 22; Kenworthy el al., Chapter 25; and
Bell et al., Chapter 26). Landscape-level maps of
production could be generated to relate areas of high
productivity and carbon flux to landscape variables
so that areas of greatest value to fisheries and the
health of coastal ecosystems can be identified (see
Bell et al., Chapter 26).
5. Stable Isotopes: Future Developments
A particularly strong approach for the future is a
balanced combination of natural abundance analyses and isotope addition experiments. Natural abundance analyses can provide an assessment of the
background conditions while creatively targeted isotope additions would afford opportunities to resolve
trophic ambiguities, monitor changes in trophic dynamics in response to environmental factors (e.g. nutrient enrichment, fragmentation, and disturbance),
M. A. Mateo, J. Cebri ´
an, K. Dunton, and T. Mutchler
Fig. 11. δ
15 N values (%, mean ±95% confidence intervals) of Halodule wrightii and epiphytic algae in seagrass beds exposed to control,
water column, and sediment fertilization during 20 days (see text).
(∼31%; averages calculated from a compilation by
Daehnik et al., 1992).
4. From the Individual to the Landscape Level
Also overlooked in traditional studies of food web
dynamics is the contribution of individual species in
a community: measurements of primary production,
biomass, and isotopic composition are often performed on samples containing complex assemblages
of species, where the measurements integrate the
functional properties as single points on a graph and
ignore the individual contribution of each species.
This practice is most common with microalgae and
small invertebrates, both of which have been shown
to be functionally important (Klumpp et al., 1992;
Moncreiff et al., 1992). Although this ‘guild-level’
approach is a necessary starting point, much ecological information is lost when groups of species
are combined; measuring the production, biomass,
turnover time, density, consumption rate, and assimilation efficiency of individual species would permit
quantification of the contribution by each species to
the overall flux of matter within the system.
Addressing questions at larger scales is also possible: for example, in the trophic pathways between
beds and other communities. Thus, stable isotopes
will be useful in evaluating the residency time of
individuals in particular beds (Fry et al., 2003).
Knowing how organisms move between seagrass
beds, unvegetated sediments, salt marshes, and other
nearshore habitats as well as the degree to which they
feed in each habitat will help to elucidate how organic matter production in these habitats is linked
(see Valentine and Duffy, Chapter 20; Heck and
Orth, Chapter 22; Kenworthy el al., Chapter 25; and
Bell et al., Chapter 26). Landscape-level maps of
production could be generated to relate areas of high
productivity and carbon flux to landscape variables
so that areas of greatest value to fisheries and the
health of coastal ecosystems can be identified (see
Bell et al., Chapter 26).
5. Stable Isotopes: Future Developments
A particularly strong approach for the future is a
balanced combination of natural abundance analyses and isotope addition experiments. Natural abundance analyses can provide an assessment of the
background conditions while creatively targeted isotope additions would afford opportunities to resolve
trophic ambiguities, monitor changes in trophic dynamics in response to environmental factors (e.g. nutrient enrichment, fragmentation, and disturbance),