11th ICRS Abstract book - Nova Southeastern University

Poster Mini-Symposium 10: Ecological Processes on Today's Reef Ecosystems
10.379
Comparison of Sedimentation in Bays and Reefs below Developed vs. Undeveloped
Watersheds, St. John, US Virgin Islands
Sarah C. GRAY* 1 , Kimbrie L. GOBBI 1 , Patricia V. NARWOLD 1 , Michael D. FOX 1 ,
Kara A. MILLER 1
1 Marine Science and Environmental Studies, University of San Diego, San Diego, CA
Increased terrestrial runoff associated with development is one of the most serious threats
to coral reefs. Here we present preliminary data from an ongoing study to evaluate if
development on St John, US Virgin Islands has impacted the quantity (flux rate), quality
(mineralogy, grain size and organic matter content) and spatial variability of
sedimentation. Our approach is to compare sedimentation in reefs and bays below
developed watersheds to reefs and bays below undeveloped watersheds and to compare
bottom sediment and substrate cover today to data from sediment surveys conducted 20
years ago.
For each of seven 10-23 day sediment-trap sampling periods over the rainy season,
unsieved sediment flux rates (normalized to watershed area) were at least 1 and up to 51
times higher on the reefs below developed watersheds compared to reefs below
undeveloped watersheds. The developed watershed sediment flux rates (3-630 mg cm -2 d -
1 ) were sometimes within range of rates previously shown to cause “severe to
catastrophic” sediment stress to corals. The proportionate increase in sediment flux in
response to a major rainfall event was much greater at the developed compared to the
undeveloped bays and reefs (storm/baseline flux rate = 210 for the developed vs. 3 for the
control reef). Carbonate was the most abundant sediment constituent at all sampling sites
except those nearest the shore. Mean siliceous mineral (terrestrially derived) flux rates
were 15 times higher (5 vs. 0.3 mg cm -2 d -1 ) and mean organic matter flux rates were 10
times higher (3 vs. 0.3 mg cm -2 d -1 ) on the reefs below the developed watershed.
Analyses of the textural variability, specific mineralogy, and organic matter source of the
sediments are underway.
Detailed monitoring of sedimentological processes affecting individual reefs is a critical
compliment to ecological monitoring and necessary to evaluate the effectiveness of
erosion mitigation strategies.
10.380
Habitat Partitioning By Territorial Pomacentrids
Andreza PACHECO* 1 , Ferreira BEATRICE 2
1 Departamento de Oceanografia, Universidade Federal de Pernambuco, Tamandare,
Brazil, 2 Departamento de Oceanografia, Universidade de Pernambuco, Tamandare, Brazil
Territorial pomacentrids are very abundant on shallow reefs of the northeastern Brazilian
coast. The influence of habitat on the distribution and abundance of juveniles and adults
of three territorial species of Pomacentrid (Stesgastes fuscus, S. variabilis and
Microspathodon chrysurus) was investigated on four reefs in the Tamandare reef
complex. Four categories of reef tops were defined according rugosity and algal cover:
low and medium rugosity, both with algae assemblage dominated by Halimeda, Dictyota
and Gellidiela; and two high rugosity types dominated by turf algae and by Amphiroa
mat, respectively. Fish censuses were conducted using belt-transect method while
substrate cover was estimated by point-base method and contour measurements
(rugosity). The density of sea urchin Echinometra lucunter was also estimated. S. fuscus
was the dominant species in the reef flats with higher rugosity, independent of the
prevailing kind of algal cover, with density positively correlated to rugosity. Juveniles of
S. fuscus occurred in all types of reef flats, with no significant difference in density. S.
variabilis juveniles settled in all reef types, but were less abundant on tops dominated
by adults S. fuscus. Adults of S. variabilis occurred only on low and medium rugosity
habitats, with higher abundances on medium rugosity flats, being absent on S. fuscus
dominated flats, indicating ontogenetic migration or post settlement. There was a
negative correlation between densities of adults of Stegastes species, indicating a possible
exclusion effect. Abundance of E. lucunter was higher in turf covered habitats. In these
areas higher densities of S. fuscus were inversely correlated to higher E. lucunter
abundances indicating herbivory competition. Although adults of M. chysurus occurred
in flats dominated by Amphiroa mat, they were mostly found at flats dominated by turf
algae, coexisting with adults of S. fuscus, while juveniles were restricted to hydrocoral
Millepora colonies.
10.381
Competitive Directs Interactions in A Caribbean Reef: Comparing The Competitive
Networks in Three Zones Of A Venezuela Reef
Jeannette PÉREZ-BENÍTEZ* 1 , Estrella VILLAMIZAR 2 , Humberto CAMISOTTI 3
1 LEMAC - UCV, Caracas, Venezuela, 2 IZT - UCV, Caracas, Venezuela, 3 FCLR, Caracas,
Venezuela
Most scleractinians corals show a wide range of ecological adaptations, which allows them to
colonize virtually all areas of the reef. Variations in species diversity, distribution and
abundance on a coral reef are often attributed to processes occurring within the community such
as competition and predation (Sammarco, 1982; Connell, 1983) and physical disturbances
(Karlson & Hurd, 1993). This study was carried out at the fringing reef off Key Dos Mosquises
located south-west of National Park Archipielago Los Roques, Venezuela. The objective of this
study was to characterize and compare the different zones of coral reefs (flat, crest and slope),
based on “in-situ” observations of the evidence of competitive relationship between
scleractinian corals. In each zone were evaluated 5 belt transects of 2 x 10, where each found
direct competitive interactions were counted. Among the most relevant results were obtained
that competitive relations in the first two zones were very similar, considering the classification
of corals according to their degree of aggressiveness, proposed by Lang (1973). In the slope
zone the competitive network was more complex because the Presence of more species in direct
competition, being much larger number of links or ties between competing species. In general,
the "aggressive species" on the reef were: M. mirabilis and M. annularis (flat), M. aliciae (crest
and slope) and A. lamarcki (slope), followed by the species M. faveolata, M. cavernosa and M.
franksi which were characterized by high frequency of harming its neighbors; while the
"subordinate species" were S. iIntersepta and S. siderea. The competitive relationships vary
with the zone of the reef, mainly due to the distribution of species in the depth and possibly
differences in the resource constraint in each area.
10.382
Differential Effect Of Early Post-Settlement Processes On The Abundance Of Two
Concurrently Settling Coral Reef Fishes
Henri VALLES* 1 , Donald KRAMER 1 , Wayne HUNTE 2
1 Biology, McGill University, Montreal, QC, Canada, 2 Biology, University of the West Indies,
Cave Hill, Barbados
To examine the magnitude, spatial variability and causes of early density-independent (DI) and
density-dependent (DD) post-settlement losses in coral reef fishes, we monitored density of
Sparisoma (Scaridae) and Stegastes partitus (Pomacentridae) on three reefs in Barbados (West
Indies) for 3-3.5 months following a period of high recruitment and fitted the data to a modified
Beverton-Holt model. To assess whether surveys missed early DD mortality, we compared
recruitment on reefs to that on standard monitoring units (SMURFs) that excluded predators.
Recruitment was >11x (Sparisoma) and >3x (S. partitus) greater than the initial number of large
juveniles/ adults. Mortality was very high (Sparisoma 97%; S. partitus 91%), indicating that
post-settlement processes were more important than settlement in determining local density.
Mortality did not vary significantly across sites. After 3-3.5 months, Sparisoma densities were
similar to those before recruitment. S. partitus densities increased, but increases did not match
among-site differences in recruitment, indicating that post-settlement processes differed
spatially. DI effects did not vary significantly between taxa or sites. DD effects were one order
of magnitude higher for Sparisoma than for S. partitus, possibly due to lower availability of
refuge microhabitat for Sparisoma. DD effects varied significantly across sites for S. partitus,
but not Sparisoma, perhaps because of lower precision in density estimates for Sparisoma.
Among-site differences in DD effects for S. partitus were associated with differences in
recruitment rates and substrate. Predator density was similar across sites. Recruit density on the
reefs mirrored captures in SMURFs, indicating that surveys did not miss important DD
predation. Our findings suggest that substrate influences rates of DD mortality and therefore
local population dynamics, but with markedly different strength for different taxa.
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