Dissertations / Theses on the topic 'Corals – Barbados'

This study investigates effects of eutrophication on settlement, abundance, mortality and community structure of soleractinian corals on fringing reefs on the west coast of Barbados, W.I. Juvenile abundance was lower, but juvenile size larger, on eutrophic than less eutrophic reefs. The lower abundance results at least in part from a higher juvenile mortality on eutrophic reefs. Algae were more abundant and grazers (Diadema antillarum and herbivorous fish) less abundant on eutrophic reefs. Juvenile community structure on all reefs, and adult community structure on eutrophic reefs, was dominated by type 1 corals (high recruitment, high natural mortality). Type 2 corals (low recruitment, low natural mortality) were common in adult communities on less eutrophic reefs. Settlement of coral recruits on artificial substrates was lower on more eutrophic reefs.

Effects of variation in eutrophication and in Diadema antillarum densities (grazing pressure) on the abundance and life history characteristics of Favia fragum on seven reefs along the west coast of Barbados were investigated. Densities of D. antillarum were negatively correlated with eutrophication levels, and interpretations of their effects have been made simultaneously. Abundance of F. fragum was lower on more eutrophic reefs with lower D. antillarum densities. This may result from effects of eutrophication and of D. antillarum on algal cover on reefs. Macrophytic algae were more abundant, and crustose coralline algae less abundant, on eutrophic reefs with lower D. antillarum densities; and macrophytic algal cover was negatively correlated with crustose coralline algal cover across reefs. F. fragum abundance was positively correlated with crustose coralline algal cover, and F. fragum occurred less frequently on reef areas where macrophytic algae were abundant. High eutrophication and low D. antillarum density (grazing pressure) may therefore reduce F. fragum abundance by increasing the cover of macrophytic algae relative to crustose coralline algae on reefs. Neither planulation periodicity, colony fecundity, nor polyp fecundity in F. fragum differed at different eutrophication levels and D. antillarum densities. Moreover, adult growth and adult mortality did not differ with eutrophication levels and D. antillarum densities on reefs. However, growth of juveniles appeared slower and mortality higher on eutrophic reefs with low D. antillarum densities. Moreover, larvae of F. fragum preferred to settle on crustose coralline algae than on turf algae (macrophytic algae), and the former are comparatively scarce on eutrophic reefs with low D. antillarum densities. The results suggest that the negative correlation between adult abundance of F. fragum and eutrophication levels/grazing pressure (D. antillarum densities) on Barbados reefs are caused primarily by effects

Multivariate ordination techniques were used to characterize the direction and magnitude of coral community changes on west coast reefs in Barbados between 1982 and 1992, and to relate these changes to coastal eutrophication and variation in Diadema antillarum densities (grazing pressure). D. antillarum densities were substantially lower in 1992 than in 1982, reflecting the 1983 mass mortality event. Reductions in urchin density were greater on less eutrophic reefs than eutrophic reefs. Cover by macrophytic algae increased, cover by crustose coralline algae decreased, and the number of coral species decreased between 1982 and 1992. With the notable exception of the most eutrophic reef, coral cover decreased over the 10 year period. Changes in algal cover across reefs between 1982 and 1992 were strongly correlated with decreases in D. antillarum densities, and were therefore typically greater on less eutrophic reefs, indicating that reduced grazing pressure has more strongly influenced algal cover changes than prevailing eutrophication levels. Coral species composition changed at all sites between 1982 and 1992, and except at the most eutrophic site, the direction of change was directly related to reduced D. antillarum densities and associated algal cover changes. Temporal change at the most eutrophic site was best explained by the prevailing high level of eutrophication, and resulted primarily from a substantial increase in the cover of one species, Porites porites. The decrease in coral cover that occurred on most of the study reefs in the face of the increasing cover by macrophytic algae was typically accompanied by an increase in the relative abundance of Type 1 (high recruitment, high natural juvenile mortality) to Type 2 (low recruitment, low natural juvenile mortality) corals.

This study examined whether movements of fishes across reserve boundaries reduced the difference in density and size of fish between reserve and non-reserve areas. Visual censuses, experimental trapping, habitat measurements and tagging were performed at 10 sites on two nearly contiguous fringing coral reefs at the northern edge of the Barbados Marine Reserve and at 10 sites on the two fringing reefs closest to the boundary in the non-reserve. The visual censuses showed that overall density and size of fishes large enough to be caught in Antillean fish traps were higher on reserve reefs than on non-reserve reefs. The differences in density and size varied considerably among species and were not statistically significant for individual species. In contrast to a previous study, experimental trap catches were not higher in the reserve than in the non-reserve. Visual censuses, trap catches, and their ratio (trappability) were affected by habitat variables. Species mobility, estimated by the maximum distance between locations at which an individual was captured, corrected for the sampling effort at that distance, was highly variable among species (medians 0--116m). For the more mobile species, movements within fringing reefs and between the nearly contiguous reserve reefs was high but extremely rare among reefs separated by expanses of sand and rubble. For this discrete fringing reef system, there is no evidence that movement across the reserve boundary influences the relative density or size of fish between the reserve and non-reserve.

Samples of Porites porites rubble were collected from across three fringing reefs which lie along a eutrophication gradient in Barbados, West Indies. The coral skeleton fragments were examined for clionid sponges. Data collected from the reef crest and fore reef zones and from across the range of distances and depths were pooled for each reef to compare indices of sponge abundance along the eutrophication gradient. Significant differences between the reefs were found for the proportion of rubble invaded (ANCOVA, p = 0.004), number of invasions per sample (ANCOVA, p = 0.002), and number of species per sample (ANCOVA, p = 0.018) but not for total surface area of sponge invasions per sample (ANCOVA, p = 0.064). All the indices demonstrated an increase with increasing eutrophication level. Clionids were found in nearly twice as many of the pieces collected from the most eutrophic site (41%) as from the least eutrophic (24%). Since clionids may be the principal bioeroders of coral reefs, an increase in their abundance due to excessive pollution likely results in greater bioerosion of affected reefs. The mean abundance of Type 3 corals was found to be positively related to the frequency of boring sponge invasion, suggesting that increased bioeroision may be partly responsible for community shifts toward Type 3 corals in polluted waters. One new variety and three new species of boring sponges of the genus Cliona were found. A new variety of C. amplicavata Rutzler is described, Cliona species 2 of MacGeachy is redescribed and Cliona species 4 and Cliona species 5 are described for the first time. Cliona species 5 may become an important bioeroder in Barbados and other Caribbean islands since it flourishes under high eutrophic conditions which are beginning to plague West Indian reefs. (Abstract shortened by UMI.)

This study investigates the characteristics and use of spawning sites by the bluehead wrasse Thalassoma bifasciatum in Barbados, and movements of wrasses from source reefs to proximate and isolate recipient reefs. Pair spawning rate increased with increasing projection height; group spawning rate increased with increasing proximity to the downcurrent reef edge. Daily group spawning rates, but not pair-spawning rates, were higher when daily current speeds were lower, suggesting that fertilisation rates in group spawns may be more sensitive to current speed than fertilisation rates in pair spawns. Migration rate to isolated reefs was 16% that to proximate reefs. Immigration rate to recipient reefs decreased with increasing distance from the source reef and increased with increasing population density on the source reef. Immigration rates to proximate reefs were phase, sex, and size-specific, and were strongly influenced by phase, sex, and size-specific differences in home range size of wrasses. Immigration to isolated reefs was also phase and sex-specific. (Abstract shortened by UMI.)

This study used trapping and visual census surveys to assess whether a marine reserve in Barbados effectively protected coral reef fish stocks and whether there was evidence of emigration from the reserve. Fish abundance and sizes were higher in the reserve than in surrounding non-reserve areas. Relative differences in abundance and size between reserve and non-reserve of different taxa were positively correlated to vulnerability to traps (the most common fishing method) but not to mobility of fish. Gradients of abundance across the reserve boundaries (decreasing abundance with distance from the reserve center) were apparent for total abundance but not for individual taxa. These patterns suggest that the reserve does protect fish stocks and that emigration is of minor importance.

The effects of terrestrial runoff on the Bellairs fringing reef environment were assessed by a study of water quality. This study is partitioned into two components. The first documents terrestrial discharge of sediments and nutrients into coastal waters and maps the resulting seawater quality by analyzing samples taken from a grid of stations. Terrestrial water samples were analyzed for turbidity, total suspended solids (TSS), nitrate-nitrite-nitrogen (NOx-N), and soluble reactive phosphorus (SRP). Seawater was analyzed for turbidity, TSS, and salinity while sedimentation rates were measured upon the seafloor. Results indicated that on all four events, water above the reef exceeded the guidelines for turbidity, TSS, or both. Post-discharge changes in seawater quality around the outlet depend on a runoff event's TSS load and total discharge, though above the reef which lies 600m from the outlet, there is the added dependence of the prevailing winds. Spatial trends were not observed across the reef, though directly in front of the outlet there was an apparent northward trend for plumes. Sedimentation rates on the reef were much higher than guidelines for 35 of the 118 days monitored. The second component of this study characterizes the watershed draining to the aforementioned coastal outlet in terms of hydrology and water quality, and the latter's relation to landuse. Water samples were taken at the outlet over time as well as at four upstream locations on two events, and were analyzed for turbidity, TSS, NOx-N, and SRP. Observed hydrological characteristics included spatially heterogeneous rainfall, flash floods, internal drainage of runoff into the karstic aquifer, and a correlation between event total runoff volumes and event runoff coefficients (r = 0.89). Water quality results identified a first flush phenomenon for TSS, and sources of high TSS, turbidity, and SRP to be industry, urban areas, and agriculture. Considering the low proportion of agr
Les effets de ruissellement de surface sur l'environnement des récifs de Bellairs ont été évaluer par une étude de la qualité de l'eau. Cette étude est divisée en deux composantes. La premiere documente les déversements terrestres des éléments nutritifs et des sédiments dans les eaux côtières. De plus, la mer est divisée en grille, permettant l'analyse d'échantillons survenant de chaque région et des tendances de ces résultats. Des prélèvements de ruisellement de surface ont également été analysées pour leur turbidité, le totale des matieres solides en suspension (TSS), les nitrates-nitrites-nitrogen (NOX - N), et de phosphore soluble réactif (PSR). La turbidité, TSS, salinité, et le taux de sédimentation sur le fond marin ont toutes été obtenus des échantillons maritimes. Les résultats ont démontré que pour les quatre occasions de déchargements terrestres, l'eau au dessus des récifs excédés les limites de conseil de TSS, turbidité ou les deux. Après un événement de déchargement, les changements de qualité d'eau maritime autour d'une sortie dépendent sur le TSS. Par contre, au dessus des récifs, à 600m de la sortie, il y a le facteur supplementaire de vent. Des tendances spatiales n'ont pas été observés a travers le récif, mais une apparente direction des décharges envers le nord a été remarqué en avant des sorties. Le taux de sédimentation excédé les limites de conseil pendant 35 jours des 118 jours d'observations totales. La deuxième composante de cette étude caractérise le bassin d'évacuation lié à la sortie maritime mentionné en terme d'hygrologie, qualités des eaux, et de la relation entre ce dernier et l'utilisation des terres. Des échantillons d'eaux ont été pris à travers le temps à la sortie, ainsi qu'à quatre endroits d'amont à deux reprise chacune. Les analyses incluent la turbidité, TSS, PSR et NOX-N. Les caractéristiques hydrologiques observées sont une distribution sp

A reef-associated zooplankton community was monitored at weekly intervals for 53 weeks. Samples were collected from quadrats of dense coral cover using emergence net traps. The numerical and biomass fluctuations of 15 taxonomic groups, 7 size classes and 5 feeding groups of the community were determined both temporally and spatially. The community was composed of abundant and diverse taxa (81) with cyclopoid copepods being the most important taxon. Larger-sized fauna (e.g. amphipods, decapods, mysids, etc.) were the second most important abundance and biomass contributors. Size class analysis illustrated a bimodal size distribution spectrum. The well developed second mode of the spectrum was attributed to substratum characteristics which permitted an enhanced macrofaunal/detritivore presence. Although week to week fluctuations of the abundance/biomass data were marked, diversity indices indicated a persistent and resilient community. The nocturnal vertical migrations of the fauna did not show a persistent pattern with the varying phases of 12 sequentially monitored lunar cycles. Substratum heterogeneity was primarily responsible for the spatial distribution pattern of the fauna. Although the data variance suggested stochasticity, time-series procedures determined that cross-correlations between the numerical abundances of taxa, size classes and feeding groups occurred without a lead or lag. Similar analyses identified chlorophyll a as the important environmental variable and also as a leading indicator of particular taxonomic, size and feeding group abundances. It was concluded that reef-associated zooplankton communities are abundant, diverse assemblages structured by periodicities which in combination act to form important links between tropical, inshore benthic and pelagic ecosystems.