Coral reefs have been well documented to be ecosystems of high biological
diversity. Because substratum space is generally regarded as the primary
limiting resource for sessile reef organisms, biological characterization
of local reef systems will concentrate on the provision, acquisition,
and retention of space. Natural and anthropogenic stresses are expected
to be manifested through space-related processes. For example, the
provision of space following coral mortalities may reflect direct
effects of stresses (hurricanes, disease, bleaching and sedimentation)
or biological interactions (predation and competition). In addition,
other stresses as nutrient inputs may affect biological interactions
(e.g., competition between algae and corals).
The benthic biology component of the CRES program involves high resolution
examination of the stability of the coral community structure and
demography (recruitment, growth, survivorship, etc.) of major coral
reef organisms. These studies are currently being conducted at La
Parguera, Puerto Rico, on the southwest coast near the Magueyes Island
laboratory of the UPR Department of Marine Sciences. Fish, macroalgal
and macroinvertebrate (principally including corals, gorgonians and
sea urchins) populations are all being studied at the same transects.
Eight reef sites: three near shore, three mid-shelf and two shelf
edge reefs were selected and permanent transects at four depths (per
reef site) with permanent quadrats have been established. Community
structure will be assessed with repeated surveys of the same permanent
transect/quadrats, thus allowing a documentation of change. Photo-quadrats
along the permanent transect lines at each reef locality will be conducted
to support the quantitative surveys. These field sites include reefs
within and outside a proposed local marine reserve. Although other
studies have been conducted previously in Puerto Rico, this represents
the first time that all major components of coral reef communities
will be examined in the same locations simultaneously. It is expected
that these studies will provide new insights into the dynamics of
coral reef communities.
The purpose of these studies is to characterize the distribution,
cover and abundance of reef organisms within the study area, understand
their population dynamics and detect spatial and temporal changes
in reef composition and live cover. Comparison of the biology of reef
systems as a function of position on the insular shelf, will provide
insight into watershed effects. It is expected that by assessing possible
changes in terms of the physical and chemical information gathered
in CRES studies, we will be able to identify responsible stress factors.
Diadema Transplant Experiment: An underlying theme of the
CRES demographic studies are the direct and indirect linkages between
various biological, physical and chemical processes on coral reefs.
The importance of certain coral reef organisms may be highly complex.
We will study biological effects of one of these, the long spined
sea urchin Diadema antillarum, which can be regarded as a
keystone grazer based on its ecology and consequences of its mass
mortality. Diadema grazes on turf and macroalgae and in the
process it can ingest coral tissue and other sessile recruits; thus,
it may be beneficial for larger corals via the removal of macroalgae
but unfavorable for (sexual) coral recruitment when the densities
of this urchins are high. Diadema is also a major bioeroder,
producing 'clean', easily transportable sediments that can smother
recruit colonies. Thus, an increase in gorgonian recruitment occurring
shortly after the Diadema mass mortality was evidently due
to decreased grazing as well as the decreased production of sediments
and its consolidation by microflora. We will monitor an experimental
site for 1 y prior to transplanting Diadema. In experimental
sites, high density of urchins will be maintained for 1 y and then,
urchins will be removed. The subsequent recovery processes will then
be followed for 2 y. Sediment transport regimes as well as algal,
coral, gorgonian and fish populations will be monitored during the
entire period. We expect higher recruitment of corals and other sessile
invertebrates in the experimental areas following the removal of Diadema,
with a gradual (2 y) decline in recruitment due to changes in the
sediment transport regime.
