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A comparison of the ecology of shallow subtidal gastropods between western Indian Ocean and Caribbean coral reefs
Author(s): T. McClanahan
Year: 2002
Description/Abstract: I studied the ecology of snails inhabiting shallow wave-protected subtidal coral reef seascapes on the down-welling eastern edge of the American (Florida Keys and Belize) and African (Kenya and Madagascar) continents. Snail population abundance (CPUE), body sizes, modes of feeding, numbers of species, and species diversity were compared between regions and ocean basins. The Caribbean region had a third the number of species above 50 h or 5,000 individuals of sampling and higher dominance. When analyzed as numbers of individuals, the Caribbean community had a greater abundance of herbivorous and detritivorous individuals compared to the western Indian Ocean region. When analyzed as a percentage of species, there were no trophic differences, with two thirds of the species being carnivorous and one third herbivorous or detritivorous in both ocean basins. Body sizes were also not different in analyses based on either species or population abundance, but the Caribbean sites had higher variation in body size than the western Indian Ocean. The trophic, dominance, and species richness data suggest that the Caribbean assemblage has been influenced by environmental stress, but body-size data do not reflect this pattern unless stress increases variation rather than decreases body size. Recent environmental conditions may account for differences in the population dominance of trophic categories, but differences in species richness has required many millions of years of differential species origination and extinction.
Journal/Source: Coral Reefs
Publisher: Springer-Verlag
Full Citation: McClanahan, T.R. (2002) A comparison of the ecology of subtidal gastropods between western Indian Ocean and Caribbean coral reefs. Coral Reefs 21: 399-406.
Algal growth and species composition under experimental control of herbivory, phosphorus and coral abundance in Glovers Reef, Belize
Author(s): T.R. McClanahana, B.A. Cokosb, E. Salac
Year: 2002
Description/Abstract: The proliferation of algae on disturbed coral reefs has often been attributed to (1) a loss of large-bodied herbivorous fishes, (2) increases in sea water nutrient concentrations, particularly phosphorus, and (3) a loss of hard coral cover or a combination of these and other factors. We performed replicated small-scale caging experiments in the offshore lagoon of Glovers Reef atoll, Belize where three treatments had closed-top (no large-bodied herbivores) and one treatment had open-top cages (grazing by large-bodied herbivores). Closed-top treatments simulated a reduced-herbivory situation, excluding large fishes but including small herbivorous fishes such as damselfishes and small parrotfishes. Treatments in the closed-top cages included the addition of high phosphorus fertilizer, live branches of Acropora cervicornis and a third unmanipulated control treatment. Colonization, algal biomass and species composition on dead A. palmata “plates” were studied weekly for 50 days in each of the four treatments. Fertilization doubled the concentration of phosphorus from 0.35 to 0.77 μM. Closed-top cages, particularly the fertilizer and A. cervicornis additions, attracted more small-bodied parrotfish and damselfish than the open-top cages such that there was moderate levels of herbivory in closed-top cages. The open-top cages did, however, have a higher abundance of the chemically and morphologically defended erect algal species including Caulerpa cupressoides, Laurencia obtusa, Dictyota menstrualis and Lobophora variegata. The most herbivore-resistant calcareous green algae (i.e. Halimeda) were, however, uncommon in all treatments. Algal biomass increased and fluctuated simultaneously in all treatments over time, but algal biomass, as measured by wet, dry and decalcified weight, did not differ greatly between the treatments with only marginally higher biomass (p<0.06) in the fertilized compared to open-top cages. Algal species composition was influenced by all treatments with a maximum between-treatment Bray–Curtis similarity of only 29%. The fertilized cages showed rapid colonization by a mixed turf community largely composed of the filamentous brown (Hincksia mitchelliae) and green (Enteromorpha prolifera) species. Algal cover in the fertilized cages leveled at 80% after 20 days compared to less than 50% in the other treatments. There was no evidence that A. cervicornis suppressed algal colonization compared to the unmanipulated controls. Instead, the herbivore susceptible Padina sanctae-crucis was the most abundant algae followed by Jania capillacea in this treatment in contrast to the more chemically defended Dictyota menstrualis that dominated the unmanipulated controls. We conclude that A. cervicornis was not suppressing algae as a group and its loss cannot account for the observed changes in algal abundance in most reefs except for creating space. In contrast, A. cervicornis appears to attract aggressive damselfish that may reduce herbivory by larger herbivores. Phosphorus enrichment can lead to rapid colonization of space by filamentous turf communities but not high biomass and dominance of erect frondose algae within 50 days. Moderate levels of herbivory by large-bodied herbivores promoted moderately herbivore-resistant erect brown and green algae that are commonly reported on disturbed reefs. Consequently, all the studied factors influenced algal communities but seldom as commonly predicted.
Journal/Source: Marine Pollution Bulletin
Publisher: Elsevier Science
Full Citation: McClanahan, T.R., Cokos, B.A., and Sala, E. (2002) Algal growth and species composition under experimental control of herbivory, phosphorus and coral abundance in Glovers Reef, Belize. Marine Pollution Bulletin 44: 441-45.
An ecological shift in a remote coral atoll of Belize over 25 years
Author(s): Timothy R. McClanahan, Nyawira A. Muthiga
Year: 1998
Description/Abstract: Many coral reefs in the Caribbean, and elsewhere, have undergone changes from hard coral to fleshy algal dominance over the past two decades which has often been interpreted as a localized response to eutrophication and fishing. Here, data on the abundance of hard corals and algae from lagoonal patch reefs distributed throughout a large (260 km2) remote reef atoll located approximately 30 km offshore from the sparsely-populated coast of Belize, Central America, are compared with a study of these patch reefs conducted 25 years previously. Data and observations indicate that these patch reefs have undergone a major change in their ecology associated with a 75% reduction in total hard coral, a 99% loss in the cover of Acropora cervicornis and A. palmata, and a 315% increase in algae, which are mostly erect brown algae species in the genera Lobophora, Dictyota, Turbinaria and Sargassum. Such changes have been reported from other Caribbean reefs during the 1980s, but not on such a remote reef and the present changes may be attributed primarily to both a disease that began killing Acropora in this region in the mid 1980s and a reduction in herbivory. The low level of herbivory may be attributable to the disease-induced loss of the sea urchin Diadema antillarum in 1983, or fishing of herbivorous fishes, but both explanations are speculative. The present density of fisherfolk is low, and their efforts are not targetted at herbivorous fishes, and population densities of D. antillarum 14 years after the mortality are <1 individual per 1000 m2, but there is no comparative data from before the die off. There is, however, no indication that these major changes occurred on the fore reef, because A. palmata is abundant and erect algal abundance is low. We suggest that reported changes in other Caribbean reefs are not necessarily or exclusively influenced by local human factors such as localized intense eutrophication or fishing.
Journal/Source: Environmental Conservation
Publisher: Cambridge University Press
Full Citation: McClanahan, T.R. and Muthiga, N.A. (1998) An ecological shift in a remote coral atoll Belize over 25 years. Environmental Conservation 25: 122-130.
Benthic dispersal of Caribbean spiny lobsters among insular habitats- implication for the conservation of exploited marine species
Author(s): Charles A. Acosta
Year: 1999
Description/Abstract: Understanding how populations of target species interact with their habitats is necessary for developing an effective conservation strategy. During its complex life history, the Caribbean spiny lobster ( Panulirus argus) uses a variety of benthic marine habitats, but how habitat characteristics affect their dispersal is unclear. To assess how habitat insularity affects the benthic dispersal of spiny lobsters, I compared lobster abundance, size class structure, and migration among insular mangrove and coral reef habitats that were surrounded by bare rubble fields or by seagrass meadows. Lobsters were significantly more abundant on mangrove and coral islands surrounded by seagrass. The size-class distributions of lobsters in these habitats had higher proportions of juveniles, whereas islands surrounded by sand and rubble had skewed distributions dominated by adult lobsters. Seagrass is known to serve as settlement habitat for larval recruits and is likely associated with the higher abundances of lobsters found in seagrass-isolated habitats. Immigration and emigration rates were three to four times higher on seagrass-isolated islands than on rubble-isolated islands, reflected in the significantly greater number of juveniles moving into and from seagrass-isolated islands. Rubble fields appeared to function as a barrier to benthic dispersal for all lobsters except adults. Vegetated substrates may function as movement corridors for juvenile lobsters and may facilitate dispersal to areas containing new resources. The effects of insularity on a population may be lessened by the nature of the surrounding habitats if those habitats have important functional roles as larval settlement areas, foraging grounds, or movement corridors. Protection of insular habitats like coral reefs may be ineffective if related habitats like seagrass meadows are left unprotected. Conservation strategies for mobile benthic species need to incorporate the protection of areas with heterogenous habitats that are important to meet the changing habitat requirements in complex life cycles
Journal/Source: Conservation Biology
Publisher: John Wiley & Sons
Full Citation: Acosta, C.A. (1999) Benthic dispersal of Caribbean spiny lobsters among insular habitats: implication for the conservation of exploited marine species. Conservation Biology 13:603-612
Bleaching and hurricane disturbances to populations of coral recruits in Belize
Author(s): Peter J. Mumby
Year: 1999
Description/Abstract: In 1998, coral populations in Belize were disturbed sirnultaneously by a severe coral bleaching event and Hurricane Mitch. The impact of these disturbances was assessed for naturally occurring populations of coral recruits (2 to 20 mm diameter), at a depth of 8 to 10 m on the forereef of Glovers Atoll. Bleaching took place at aii 4 study sites but the hurricane only affected 2 sites, enabling the effects of bleaching to be compared to those arising from bleaching plus hurncane damage. Predisturbance recruit density, size-frequency distribution, and cornmunity structure were similar between sites (at kiiometre scales). The bleaching event lasted ca 3.5 mo. From 70 to 90% of adult colonies bleached and at least 25% of recruits exhibited signs of bleaching. A month after adult colonies had regained usual colouration, only 1 % of recruits showed even partial bleaching. Surprisingly, coral bleaching alone had no measurable effect on either recruit density or community structure. The combination of bleaching and hurricane disturbance reduced total recruit densities to 20% of pre-&sturbance levels. Effects of bleaching/hurricane disturbance on community structure were spatially patchy, and I suggest that such patchiness may arise from variable Cover of protective rnicrohabitat and/or different storm conditions mediated by proximity to reef cuts (breaks in the reef crest).
Journal/Source: Marine Ecology Progress Series
Publisher: Inter-Research
Full Citation: Mumby, P.J. (1999) Bleaching and hurricane disturbances to populations of coral recruits in Belize. Marine Ecology Progress Series 190: 27-35.
Comparative spatial ecology of fished spiny lobsters Panulirus argus and an unfished congener P. guttatus in an isolated marine reserve at Glover's Reef atoll, Belize
Author(s): C. Acosta, D. Robertson
Year: 2003
Description/Abstract: Palinurid lobsters are being exploited with increasing intensity in coral reef ecosystems, but marine protected areas may play a key role in preventing overfishing and local extinctions. In order to define the spatial requirements for protection, we compared the spatial and temporal patterns in distribution, density, biomass, size structure, and reproductive seasonality of Caribbean spiny lobsters Panulirus argus and the congeneric spotted lobsters P. guttatus on coral patch reef, forereef, and deep reef habitat at Glover's Reef, Belize. The relative impact of fishing on P. argus was also examined in an isolated marine reserve and adjacent fished habitats, in comparison with the relatively unfished distribution of P. guttatus. Over a 5-year period, both species co-occurred in all major reef habitats, but aspects of their population dynamics differed markedly due to both habitat and fishing effects. All size classes of spiny lobsters P. argus occupied shallow patch reefs, but large adults were predominant on the deep wall reef. Panulirus guttatus also occupied patch reefs in the lagoon, but spur-and-groove forereef appeared to be the primary habitat of this species. Density and exploitable (adult) biomass of P. argus increased significantly over time in the protected patch reef habitat of the lagoon but remained stable on deep reef habitat. The biomass of spotted lobsters P. guttatus in all habitats was at least an order of magnitude less than that of exploitable P. argus. Reproductive activity by both species was evident most of the year in all habitats, but breeding P. argus females were concentrated on the deep reef. Commercial fisheries for spotted lobsters P. guttatus are currently being considered for development, but data from this and other studies suggest that such a fishery may be relatively unproductive and may lead to rapid localized extinctions. Spiny lobsters P. argus used a variety of coral reef habitats, but spotted lobsters P. guttatus were habitat specialists restricted to shallow reef habitat. The protection needs of both species are similar in one aspect: large protected areas. However, P. argus required large areas with heterogeneous habitats including coral reefs and seagrass beds, whereas P. guttatus required large areas of coral reef habitat.
Journal/Source: Coral Reefs
Publisher: Springer
Full Citation: Acosta, C.A. and Robertson, D.N. (2003) Comparative spatial ecology of fished spiny lobsters Panulirus argus and an unfished congener P. guttatus in an isolated marine reserve at Glover's Reef atoll, Belize. Coral Reefs 22:1-9.
Comparisons between abundance estimates from underwater visual census and catch-per-unit-effort in a patch reef system
Author(s): Mandy Karnauskas, Elizabeth A. Babcock
Year: 2012
Description/Abstract: Methods of underwater visual censuses (UVC) and catch-per-unit-effort (CPUE) are both commonly used to estimate abundance of fish stocks. While each method is subject to certain biases, in theory they should produce related measures of fish abundance for a specific site at a given point in time, for species targeted by both methods. We tested relationships between estimates of abundance and biomass from UVC and experimental hook-and-line CPUE in a spatially complex coral patch reef system. Fishes targeted by the CPUE method were significantly larger than those sampled by UVC. Abundance estimates from UVC and CPUE were significantly correlated when the data were collected simultaneously—and over small spatial scales (<20 m). However, this correlation was reduced when collection of UVC and CPUE data was separated by either time or space. Spatial autocorrelation in the fish community composition was not detected for most species, and abundance estimates were highly variable over time and space. Our results show that differences among monthly sampling periods were responsible for the greatest amount of variability in the data, and we recommend that abundance estimates should be derived from surveys carried out over multiple months to improve accuracy. While the UVC method is useful to detect a wide variety of species, some species are more efficiently assessed using CPUE. Development of cost-effective monitoring programs is crucial to document changes in reef fish populations and support the implementation of management regulations that may prevent further degradation of reef fisheries worldwide.
Journal/Source: Marine Ecology Progress Series
Publisher: Inter-Research
Full Citation: Karnauskas, M., Babcock, E. A. (2012). Comparisons between abundance estimates from underwater visual census and catch-per-unit-effort in a patch reef system. Marine Ecology Progress Series 468: 217-230.
Coral reef management and conservation in light of rapidly evolving ecological paradigms
Author(s): Peter J. Mumby and Robert S. Steneck
Year: 2008
Description/Abstract: The decline of many coral reef ecosystems in recent decades surprised experienced managers and researchers. It shattered old paradigms that these diverse ecosystems are spatially uniform and temporally stable on the scale of millennia. We now see reefs as heterogeneous, fragile, globally stressed ecosystems structured by strong positive or negative feedback processes. We review the causes and consequences of reef decline and ask whether management practices are addressing the problem at appropriate scales. We conclude that both science and management are currently failing to address the comanagement of extractive activities and ecological processes that drive ecosystems (e.g. productivity and herbivory). Most reef conservation efforts are directed toward reserve implementation, but new approaches are needed to sustain ecosystem function in exploited areas.
Journal/Source: Trends in Ecology and Evolution
Publisher: Cell Press
Full Citation: Mumby, P.J., Steneck, R. (2008) Coral reef management and conservation in light of rapidly evolving ecological paradigms. Trends in Ecology and Evolution 23: 555-63.
Coral responses to macroalgal reduction and fisheries closure on Caribbean patch reefs
Author(s): T. R. McClanahan, B. E. Huntington, B. Cokos
Year: 2011
Description/Abstract: To determine the effects of algal reduction and fisheries closure, a crossed experimental design was undertaken over a 516 d period on the remote patch reefs of Glover’s Reef Atoll, Belize. We investigated (1) the effects on health, growth, and survivorship of 2 transplanted coral species, Porites asteroides and Siderastrea siderea, and (2) the changes in the benthic and fish communities. Algal reduction (98% reduction by physical removal kept low by monthly removal) increased the abundance of all fish and slightly elevated herbivore bite rates. P. asteroides showed a temporal response to environmental conditions opposite of predictions, with higher bleaching and mortality in the unfished reefs cleared of algae. This may be due to reduced water flow at these sites as the growth rate of P. asteroides was positively related to water flow (R2 = 0.35, p = 0.04). S. siderea growth showed no relationship with water flow and bleached slightly more in the control reefs. Nevertheless, there were no patterns in mortality, and growth rates were twice as high in the fished than unfished reefs for this species. This reef-scale study contrasts with results of small-scale experiments that found rapid, indirect coral mortality from erect algae. Rather, our results suggest that environmental conditions, notably reef location in relation to water flow, can be a considerably stronger factor influencing coral health than erect algae.
Journal/Source: Marine Ecology Progress Series
Publisher: Inter-Research
Full Citation: McClanahan, T.R. B.E. Huntington, Cokos, B. (2011) Coral responses to macroalgal reduction and fishery closure on Caribbean patch reefs. Marine Ecology Progress Series 437: 89-102.
Corals fail to recover at a Caribbean marine reserve despite ten years of reserve designation
Author(s): B. E. Huntington, M. Karnauskas, D. Lirman
Year: 2011
Description/Abstract: The ability of reserves to replenish fish stocks is relatively well documented, but the evidence of their ability to induce positive effects on benthic communities remains inconclusive. Here, we test whether 10 years of reserve designation have translated into positive effects on coral communities in Glover’s Reef, Belize. Surveys of 87 patch reefs inside and outside the reserve revealed no clear indication of reserve implementation benefitting coral cover, coral colony size, or abundance of juvenile corals. Furthermore, massive broadcasting coral species exhibited greater losses over time than their smaller-sized counterparts across all sites, suggesting that local management actions have not alleviated the regional trend of high mortality for these species. We detected no difference in herbivorous fish abundances or macroalgal cover between reserve and fished sites, providing a potential explanation for the lack of cascading positive effects on the coral community. We conclude that patterns of regional coral decline are evident at Glover’s Reef, including a shift in dominance from broadcasting species to brooding species and declines in mean colony size. Our findings suggest that regional stressors are overwhelming local management efforts and that additional strategies are required to improve local coral condition.
Journal/Source: Coral Reefs
Publisher: Springer-Verlag
Full Citation: Huntington, B.E., Karnauskas, M., Lirman, D. (2011) Corals fail to recover at a Caribbean marine reserve despite ten years of reserve designation. Coral Reefs 30: 1077-1085.
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