Roles of Sea Turtles in Marine Ecosystems: Reconstructing the Past
269
How much of this decline was a result of decreased hawksbill predation on
sponges? The relatively high coral cover on some modern Caribbean reefs indicates that sponges are somehow prevented from overwhelming the corals. With
hawksbill populations seriously depleted, predation by other spongivores — fish,
especially parrotfish (Wulff, 1997; Dunlap and Pawlik, 1998; Hill, 1998), and
invertebrates — has apparently played this role. Redundancy in ecosystems can
mask the effect of species removal until all species performing a given function
are lost (Jackson et al., 2001). As humans “fish down the food web” (Pauly et al.,
1998), and spongivorous fish populations are depleted, the role of all sponge
predators in maintaining the structure and function of coral reef ecosystems may
become more apparent.
10.5 CONCLUSIONS
We present three general conclusions:
1. All species of sea turtles in the Caribbean were once extremely abundant.
Despite enormous uncertainties, we can conclude that they occurred in
the millions or tens of millions. These are conservative estimates.
2. Past sea turtle populations consumed large quantities of prey species,
many of which are consumed only to a limited extent by other species.
Sea turtles in the Caribbean were once the major consumers of seagrasses,
sponges, and jellyfish.
3. Therefore, the virtual ecological extinction of sea turtles in the Caribbean
must have resulted in major changes in the structure and function of the
marine ecosystems they inhabited.
The roles of sea turtles in the evolution and maintenance of the structure and
dynamics of marine ecosystems have gone largely unrecognized because their populations were seriously depleted long ago. Their ecological functions have been
essentially unstudied, although sea turtles were an integral part of the interspecific
interactions in marine ecosystems as prey, consumer, competitor, and host; served
as significant conduits of nutrient and energy transfer within and among ecosystems;
and substantially modified the physical structure of marine ecosystems. Research
effort should be directed to these ecological questions as a high priority. Sea turtles
should be integrated into models of trophic interactions and restoration plans for
marine ecosystems.
ACKNOWLEDGMENTS
This work was conducted as part of the Long-Term Ecological Records of Marine
Environments, Populations and Communities Working Group supported by the
National Center for Ecological Analysis and Synthesis (funded by NSF grant DEB0072909, the University of California, and the University of California, Santa Barbara). We thank Alan Bolten and Jeffrey Seminoff for their constructive comments
on the manuscript.
1123 book.book Page 269 Monday, November 11, 2002 11:11 AM
269
How much of this decline was a result of decreased hawksbill predation on
sponges? The relatively high coral cover on some modern Caribbean reefs indicates that sponges are somehow prevented from overwhelming the corals. With
hawksbill populations seriously depleted, predation by other spongivores — fish,
especially parrotfish (Wulff, 1997; Dunlap and Pawlik, 1998; Hill, 1998), and
invertebrates — has apparently played this role. Redundancy in ecosystems can
mask the effect of species removal until all species performing a given function
are lost (Jackson et al., 2001). As humans “fish down the food web” (Pauly et al.,
1998), and spongivorous fish populations are depleted, the role of all sponge
predators in maintaining the structure and function of coral reef ecosystems may
become more apparent.
10.5 CONCLUSIONS
We present three general conclusions:
1. All species of sea turtles in the Caribbean were once extremely abundant.
Despite enormous uncertainties, we can conclude that they occurred in
the millions or tens of millions. These are conservative estimates.
2. Past sea turtle populations consumed large quantities of prey species,
many of which are consumed only to a limited extent by other species.
Sea turtles in the Caribbean were once the major consumers of seagrasses,
sponges, and jellyfish.
3. Therefore, the virtual ecological extinction of sea turtles in the Caribbean
must have resulted in major changes in the structure and function of the
marine ecosystems they inhabited.
The roles of sea turtles in the evolution and maintenance of the structure and
dynamics of marine ecosystems have gone largely unrecognized because their populations were seriously depleted long ago. Their ecological functions have been
essentially unstudied, although sea turtles were an integral part of the interspecific
interactions in marine ecosystems as prey, consumer, competitor, and host; served
as significant conduits of nutrient and energy transfer within and among ecosystems;
and substantially modified the physical structure of marine ecosystems. Research
effort should be directed to these ecological questions as a high priority. Sea turtles
should be integrated into models of trophic interactions and restoration plans for
marine ecosystems.
ACKNOWLEDGMENTS
This work was conducted as part of the Long-Term Ecological Records of Marine
Environments, Populations and Communities Working Group supported by the
National Center for Ecological Analysis and Synthesis (funded by NSF grant DEB0072909, the University of California, and the University of California, Santa Barbara). We thank Alan Bolten and Jeffrey Seminoff for their constructive comments
on the manuscript.
1123 book.book Page 269 Monday, November 11, 2002 11:11 AM