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- McClanahan, Tim, et al.
(författare)
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Response of fishes to algal reductions at Glovers Reef, Belize
- 2000
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Ingår i: Marine Ecology Progress Series. - : Inter-Research. - 0171-8630 .- 1616-1599. ; 206, s. 273-282
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Tidskriftsartikel (refereegranskat)abstract
- Many Caribbean coral reefs have experienced an increase in erect brown algae (species of Sargassum, Turbinaria and Lobophora) over the past 18 yr. We explored the effects of fleshy algal overgrowth on coral reef fishes by reducing erect algae by ~2.5 kg(wet) m-2 on 8 patch reefs (average size ~1000 m2) whereby half were in a new no-fishing zone and half in an unrestricted fishing zone. Another 8 reefs were left as unmanipulated controls in the respective zones. Multivariate ordination indicated that the algal removal had marginal effect on whole-fish assemblages but that effect was highly significant on the biomass of common herbivores. The reduction of erect algae resulted in a rapid increase in the abundance of the blue-headed wrasse Thalassoma bifasciatum (Labridae), in the biomass of the blue tang Acanthurus coeruleus (Acanthuridae), and in both the abundance and biomass of the spotlight parrotfish Sparisoma viride (Scaridae). Bite rates and intra- and inter-specific aggressive encounters were used as measures of resource quality, and we found that these measures increased for surgeonfishes and damselfishes after the algal reduction, particularly in the center of the patch reefs, where most erect algae was originally located. Increased accessibility, net production and palatability of the early successional turf algae on the manipulated reefs are likely to account for the increased numbers, biomass and feeding rates of the dominant herbivorous fishes.
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| 3. |
- McClanahan, Tim, et al.
(författare)
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Responses of algae, corals and fish to the reduction of macroalgae in fished and unfished patch reefs of Glovers Reef Atoll, Belize
- 2001
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Ingår i: Coral Reefs. - : Springer. - 0722-4028 .- 1432-0975. ; 19:4, s. 367-379
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Tidskriftsartikel (refereegranskat)abstract
- Macroalgae were experimentally reduced by approximately 2.5 kg/m2 on eight similar-sized patch reefs of Glovers Reef Atoll, Belize, in September 1998. Four of these reefs were in a protected "no-take" zone and four were in a "general use" fishing zone. Eight adjacent reefs (four in each management zone) were also studied as unmanipulated controls to determine the interactive effect of algal reduction and fisheries management on algae, coral, fish, and rates of herbivory. The 16 reefs were sampled five times for 1 year after the manipulation. We found that the no-fishing zone had greater population densities for 13 of 30 species of fish, including four herbivorous species, but lower herbivory levels by sea urchins. However, there was lower stony coral cover and higher macroalgal cover in the "no-take" zone, both prior to and after the experiment. There were no significant effects of management on the percent cover of fleshy macroalgae. The algal reduction resulted in an increase in six fish species, including four herbivores and two which feed on invertebrates. One species, Lutjanus griseus, declined in experimental reefs. Macroalgal biomass quickly recovered from the reduction in both management areas within a few months, and by species-level community measures within 1 year, while stony coral was reduced in all treatments. Coral bleaching and Hurricane Mitch disturbed the site at the beginning of the study period and may explain the loss of stony coral and rapid increase in erect algae. We suggest that reducing macroalgae, as a technique to restore turf and encrusting coralline algae and stony corals, may work best after reefs have been fully protected from fishing for a period long enough to allow herbivorous fish to recover (i.e. >5 years). Further ecological studies on Glovers Reef are required to understand the shift from coral to algal dominance that has occurred on this reef in the last 25 years.
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- Nordemar, Ingrid, 1968-, et al.
(författare)
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Effects of estimated herbivory on the reproductivepotential of four East African algal species – a mechanismbehind ecosystem shifts on coral reefs?
- 2007
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Ingår i: Hydrobiologia. - : Springer Science and Business Media LLC. - 0018-8158 .- 1573-5117. ; 575:1, s. 57-68
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this field study was toinvestigate effects of estimated fish- and seaurchin herbivory on the reproductive potential offour species of macroalgae; Halimeda macroloba(Decasine), H. renschii (Hauck), Turbinaria ornata(Turner) and Padina boergesenii (Allender etKraft). Fish and sea urchin herbivory were calculatedbased on reported consumption rates fortheir biomass estimates. We hypothesized thatreduced herbivory would increase algal size andthe reproductive potential, which may promotealgal recruitment and be one of the drivingmechanisms behind algal shifts and persistent algae-dominated reefs. Algae were investigated infield sites where the estimated fish- and or seaurchin herbivory differed. Our results suggest thatalgal fecundity of T. ornata and P. boergesenii arepositively correlated to their size. Fecundity ofT. ornata was higher and individuals grew largerin areas where estimated fish herbivory was lower.The two species of Halimeda grew larger andhad higher fecundity in areas where estimatedsea urchin herbivory was lower. P. boergeseniiresponded ambiguously to patterns in herbivory.Due to species-specific responses to differentherbivores, it is difficult to generalize abouteffects of overfishing on algal fecundity.
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| 5. |
- Nordemar, Ingrid, 1968-
(författare)
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Human Abuses of Coral Reefs- Adaptive Responses and Regime Transitions
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During the last few decades, coral reefs have become a disappearing feature of tropical marine environments, and those reefs that do remain are severely threatened. It is understood that humans have greately altered the environment under which these ecosystems previously have thrived and evoloved. Overharvesting of fish stocks, global warming and pollution are some of the most prominent threats, acting on coral reefs at several spatial and temporal scales. Presently, it is common that coral reefs have been degraded into alternative ecosystem regimes, such as macroalgae-dominated or sea urchin-barren. Although these ecosystems could potentially return to coral dominance in a long-term perspective, when considdering current conditions, it seems likely that they will persist in their degraded states. Thus, recovery of coral reefs cannot be taken for granted on a human timescale. Multiple stressors and disturbances, which are increasingly characteristic of coral reef environments today, are believed to act synergistically and produce ecological surprises. However, current knowledge of effects of compounded disturbances and stress is limited. Based on five papers, this thesis investigates the sublethal response of multiple stressors on coral physiology, as well as the effects of compounded stress and disturbance on coral reef structure and function. Adaptive responses to stress and disturbance in relation to prior experience are highlighted. The thesis further explores how inherent characteristics (traits) of corals and macroalgae may influence regime expression when faced with altered disturbance regimes, in particular overfishing, eutrophication, elevated temperature, and enhanced substrate availability. Finally, possibilities of affecting the resilience of macroalgae-dominaed reefs and shifting the community composition towards a coral-dominated regime are explored.
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