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Effects of Predation on Candidate Species Acropora palmata (elkhorn coral)
in the Florida Keys National Marine Sanctuary (FKNMS) |
Elkhorn coral is one of the primary
builders of reef structure and habitat on shallow Caribbean reefs. However, it
(and its congener Acropora cervicornis, staghorn coral) have been
undergoing major population declines over the last decade throughout the
Caribbean region due to multiple factors including hurricanes, disease (),
bleaching events, and predation. Elkhorn coral populations in the Florida Keys
are no exception. This regional decline led NMFS to designate both Acropora
species as candidates under the Endangered Species Act in 1999 (For the past two years, with support from
the National Undersea Research Center (UNCW)
and the NMFS Recover
Protected Species program, we have been investigating the impact of snail
predators on remnant elkhorn coral populations in the FKNMS. These snails can
occur in large aggregations and consume substantial amounts of live coral
tissue. The snails were found to be feeding on elkhorn coral at all seven sites
sampled. Population and physiological studies indicate that a single,
average-sized snail on elkhorn coral stands in the FKNMS can consume up to 8 cm2
of live tissue per day. Thus, a large aggregation of snails can cause
significant loss of tissue on its host colony.
 
Another aspect of the project examined the
possible protective effects of snail removal from elkhorn coral colonies. When a
snail aggregation was removed from a colony, 75% more live tissue was preserved
on that colony than a colony where a snail aggregation was left alone. This
suggests that targeted snail removal efforts may be effective in preserving
remnant elkhorn coral stands. However, other sources of mortality (e.g.
bleaching or a hurricane) could negate any beneficial effects of snail removal.
Collaborators: Iliana Baums, Univ of Miami, RSMAS
Dr. Alina Szmant, Univ of North Carolina- Wilmington
Status of Coral Reefs of Navassa Island:
"A typical view of Navassa Island.
Undercut, eroded cliffs surround the island (no mangroves nor beaches) make
landing extremely treacherous."
In March 2000, reef team member Margaret
Miller was an invited participant on an expedition to Navassa Island sponsored
by the Center for Marine Conservation ().
Navassa is a tiny island between Jamaica and Haiti which is a US protectorate
and has recently been placed under the jurisdiction of the US Fish and Wildlife
Service as part of the Caribbean Islands National Wildlife Refuge.
The reefs of Navassa, as expected given
its remoteness and low level of current human development, are in good
condition. Mean percent cover of live coral ranged from 17-26 % for the five
sites surveyed (compared to less than 10% for most reefs in the Florida Keys).
Most of the observed coral colonies (including reasonable stands of elkhorn
coral) were healthy and abundant small recruits suggest that the coral
populations are self-sustaining. Another point of interest - the black grazing
sea urchin, Diadema antillarum, was observed to be moderately abundant
(mean of about 3 urchins per 30m2 transect). These were important
grazers on Caribbean reefs before a regional die-off in the early 1980's from
which they have largely failed to recover. At least 36 species of hard corals
were observed. 
"An upward view of the
reef wall at Navassa showing abundant and healthy growth of elkhorn coral (Acropora
palmata) and waves crashing above."
Despite its remoteness, the marine communities around Navassa are not completely undisturbed. Subsistence fishers from Haiti travel the 5-6 hour trip in small open boats from their homes to fish around Navassa. Subsistence fishing is permitted in National Wildlife Refuges. So far, these activities do not seem to have had the large impacts that have been observed in other Caribbean islands as fish were abundant and large
snapper, grouper, and parrot fish were observed. However, this clearly
represents the greatest management challenge for conserving the coral reef
resources in Navassa as effective management approaches to limiting subsistence
fisheries from another country in such a remote place are not evident.
 "These
open boats travel from Haiti (>60 miles of open ocean) to fish the waters
around Navassa. They spend about one week on each trip. The large container on
the boat on the right contains ice which will aid in getting their catch back to
their village."
,
"This Haitian artesanal fisher is cleaning a large snapper."
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