[Coral-List] Acropora cervicornis in Broward County

[Bernardo Vargas-Angel]

The occurrence of dense Acropora cervicornis thickets off the coast of Fort
Lauderdale, Florida, is both unusual and ecologically valuable: 1) they
represent the largest and northernmost Acropora cervicornis population in
the continental United States (Vargas-Angel et al in press); and 2) they
develop in close proximity to highly urbanized coastal features and
potential anthropogenic stressors (Thomas et al. 2000).

For the last two and a half years, the National Coral Reef Institute has
been involved in the scientific investigation of this valuable resource.
Based on anecdotal accounts and supplementary exploration surveys, over a
dozen thickets have been identified, georeferenced and mapped, between Port
Everglades, and Hillsboro Inlet, at approximately 3–7 m depth, and ranging
between ~0.1 and 0.8 ha in size. Detailed quantitative studies have been
conducted at seven of these thickets (Vargas-Angel & Thomas 2002,
Vargas-Angel et al. Coral Reefs, in press) to document the composition and
structure of the assemblages, as well as the reproductive dynamics of the
species, and the incidence of white band disease (WBD) and predation by the
fire worm Hermodice carunculata.

With regards to disease, our studies indicate that WBD is present at all the
study thickets, and in many colonies within thickets. However, the estimated
percent mortality of A. cervicornis due to WBD is relatively low: ~1.8%,
June–August 2002, and 1.7% for October 2003 (total live coral cover;
Vargas-Angel et al., in press). Predation by the fire worm Hermodice
carunculata is also commonly observed at these thickets, with an overall
average of ~2 scars per m2, and a mean scar size close to 4 cm (Vargas-Angel
et al. in press).

Fire worm predation can be easily misidentified as WBD. It is generally
accepted that fire worm predation is, to a great extent, restricted to
branch tips, while WBD commonly ‘moves’ from the base of the colony toward
the end of the branches. Studies are underway to quantify the potential
short- and long-term effects of H. carunculata on A. cervicornis.
Preliminary results suggest that at the present predation rates, H.
carunculata poses no threat to the local A. cervicornis population (Berkle,
in progress). Additionally, histopathological studies are being conducted to
assess the effects of WBD on A. cervicornis reproduction.

Over the time that I have been studying the Broward County staghorn coral
thickets, I have never observed bleaching of Acropora cervicornis at any of
the study sites. On occasions, other scleractininas such as Porites
astreoides, Montastrea cavernosa and Dichocoenia stokesi have exhibited
patchy bleaching, however, never extensively.

Although there is currently no active reef accretion in the coastal waters
of Broward County, the thriving population of Acropora cervicornis off Fort
Lauderdale provides an interesting research opportunity, and counterpoint to
the declining and disease-stricken A. cervicornis populations throughout the
Caribbean, and especially in the Florida Keys National Marine Sanctuary.
NCRI’s research has helped established a baseline against which to compare
the ‘normal’ limits of coral development within the region. Our work
pertains to the study of impacted and threatened reef corals, and its aimed
to develop, test, and implement the best scientific hypotheses and response,
relevant to understanding, evaluation, protection, and preservation of coral
reefs.


Bernardo Vargas-Angel, Ph.D.
Research Scientist
National Coral Reef Institute
NSU Oceanographic Center
8000 N. Ocean Drive
Dania Beach, FL 33004
Phone: (954) 262-3677
Fax: (954) 262-4027