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11.
T. R. McClanahan V. Hendrick M. J. Rodrigues N. V. C. Polunin 《Coral reefs (Online)》1999,18(3):195-203
The consequences of macroalgal overgrowth on reef fishes and means to reverse this condition have been little explored. An
experimental reduction of macroalgae was conducted at a site in the Watamu Marine National Park in Kenya, where a documented
increase in macroalgal cover has occurred over the last nine years. In four experimental 10 m by 10 m plots, macroalgae were
greatly reduced (fleshy algal cover reduced by 84%) by scrubbing and shearing, while four similar plots acted as controls.
The numerical abundance in all fish groups except wrasses and macroalgal-feeding parrotfishes (species in the genera Calotomus and Leptoscarus) increased in experimental algal reduction plots. Algal (Sargassum) and seagrass (Thalassia) assays, susceptible to scraping and excavating parrotfishes, were bitten more frequently in the algal reduction plots one
month after the manipulation. Further, surgeonfish (Acanthurus leucosternon and A. nigrofuscus) foraging intensity increased in these algal reduction plots. The abundance of triggerfishes increased significantly in experimental
plots relative to control plots, but densities remained low, and an index of sea urchin predation using tethered juvenile
and adult Echinometra mathaei showed no differences between treatments following macroalgal reduction. Dominance of reefs by macrofleshy algae appears
to reduce the abundance of fishes, mostly herbivores and their rates of herbivory, but also other groups such as predators
of invertebrates (triggerfishes, butterflyfishes and angelfishes).
Accepted: 2 February 1999 相似文献
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Carbon and nitrogen stable isotope ratios are used to assess diet composition by determining bounds for the relative contributions of different prey to a predator's diet. This approach is predicated on the assumption that the isotope ratios of predator tissues are similar to those of dominant food sources after accounting for trophic discrimination (Δ(x)X), and is formulated as linear mixing models based on mass balance equations. However, Δ(x)X is species- and tissue-specific and may be affected by factors such as diet quality and quantity. From the different methods proposed to solve mass balance equations, some assume Δ(x)X to be exact values whilst others (based on Bayesian statistics) incorporate variability and inherent uncertainty. Using field data from omnivorous reef fishes, our study illustrates how uncertainty may be taken into account in non-Bayesian models. We also illustrate how dietary interpretation is a function of both absolute Δ(x)X and its associated uncertainty in both Bayesian and non-Bayesian isotope mixing models. Finally, collated literature illustrate that uncertainty surrounding Δ(x)X is often too restricted. Together, these data suggest the high sensitivity of mixing models to variation in trophic discrimination is a consequence of inappropriately constrained uncertainty against highly variable Δ(x)X. This study thus provides guidance on the interpretation of existing published mixing model results and in robust analysis of new resource mixing scenarios. 相似文献
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Fisheries exploitation provides the opportunity to examine the ecosystem‐scale biodiversity consequences of predator removal. We document predatory reef fish densities, coral‐eating starfish densities and coral reef structure along a 13‐island gradient of subsistence exploitation in Fiji. Along the fishing intensity gradient, predator densities declined by 61% and starfish densities increased by three orders of magnitude. Reef‐building corals and coralline algae declined by 35% and were replaced by non‐reef building taxa (mainly filamentous algae), as a result of starfish predation. Starfish populations exhibited thresholds and Allee‐type dynamics: population growth was negative under light fishing intensities and high predator densities, and positive on islands with higher fishing intensities and low predator densities. These results suggest the depletion of functionally important consumer species by exploitation can indirectly influence coral reef ecosystem structure and function at the scale of islands. 相似文献
16.
M. H. Ledlie N. A. J. Graham J. C. Bythell S. K. Wilson S. Jennings N. V. C. Polunin J. Hardcastle 《Coral reefs (Online)》2007,26(3):641-653
Cousin Island marine reserve (Seychelles) has been an effectively protected no-take marine protected area (MPA) since 1968
and was shown in 1994 to support a healthy herbivorous fish assemblage. In 1998 Cousin Island reefs suffered extensive coral
mortality following a coral bleaching event, and a phase shift from coral to algal dominance ensued. By 2005 mean coral cover
was <1%, structural complexity had fallen and there had been a substantial increase in macroalgal cover, up to 40% in some
areas. No clear trends were apparent in the overall numerical abundance and biomass of herbivorous fishes between 1994 and
2005, although smaller individuals became relatively scarce, most likely due to the loss of reef structure. Analysis of the
feeding habits of six abundant and representative herbivorous fish species around Cousin Island in 2006 demonstrated that
epilithic algae were the preferred food resource of all species and that macroalgae were avoided. Given the current dominance
of macroalgae and the apparent absence of macroalgal consumers, it is suggested that the increasing abundance of macroalgae
is reducing the probability of the system reverting to a coral dominated state. 相似文献
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Understanding the strength and diversity of predator‐prey interactions among species is essential to understand ecosystem consequences of population‐level variation. Directly quantifying the predatory behaviour of wild fishes at large spatial scales (>100 m) in the open sea is fraught with difficulties. To date the only empirical approach has been to search for correlations in the abundance of predators and their putative prey. As an example we use this approach to search for predators of the keystone crown‐of‐thorns starfish. We show that this approach is unlikely to detect predator–prey linkages because the theoretical relationship is non‐linear, resulting in multiple possible prey responses for single given predator abundance. Instead we suggest some indication of the strength and ecosystem importance of a predator–prey relationship can be gained by using the abundance of both predators and their putative prey to parameterize functional response models. 相似文献
18.
Christina Skinner Steven P. Newman Stephen Box Andrzej Narozanski Nicholas V. C. Polunin 《Journal of fish biology》2019,94(4):585-594
The grazing behaviour of two Caribbean parrotfish, a fished species, the stoplight parrotfish Sparisoma viride and a non-fished species, the striped parrotfish Scarus iseri, were studied in the presence (fished site) and absence (marine reserve) of chronic spearfishing activity. Diurnal feeding periodicity did not differ between the sites in either species: roving individuals had significantly higher bite rates in the afternoon, while territorial individuals foraged consistently throughout the day. Mean bite rate varied between sites in both species. Abundance, biomass and bite rates of S. viride were all significantly higher within the reserve, except for roving S. viride which had a higher mean bite rate in the afternoon outside the reserve compared with within it, attributable to maximisation of feeding in the afternoon when fishing risk was lower. Scarus iseri mean abundance and bite rate were greater outside the reserve, potentially because reduction in large territorial herbivores allowed S. iseri to feed more rapidly. By reducing the grazing potential of the remaining S. viride individuals the effect of fishing is greater than would be predicted from biomass changes alone. Less grazing by S. viride would not be compensated for by the increase in grazing by S. iseri because the latter feeds on different algae. Spearfishing of key parrotfish species reduces grazing potential directly by extraction and indirectly by changing behaviour. 相似文献
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N. A. J. Graham S. K. Wilson M. S. Pratchett N. V. C. Polunin M. D. Spalding 《Biodiversity and Conservation》2009,18(12):3325-3336
As climate change increasingly threatens biodiversity, identifying specific drivers of species loss as well as the attributes
of species most vulnerable to climatic disturbances is a key challenge to ecologists and conservationists. Here we assess
the effects of coral loss versus declines in structural complexity on obligate and facultative coral feeding butterflyfishes
on coral reefs in the central and western Indian Ocean. In the inner Seychelles, the abundance of the obligate coral feeding
group declined markedly in response to live coral mortality (r
2 = 0.48), but showed no further decline with respect to erosion of the physical matrix of the reef. Conversely, the facultative
feeding group showed no decline in response to live coral loss, reflecting their feeding versatility; however they did decline
in response to structural erosion of the reef framework (r
2 = 0.26). There were no significant changes in either obligate or facultative corallivore abundances at a reference location
(Chagos archipelago), highlighting that butterflyfish populations are stable in the absence of habitat disturbance. While
specialised coral dependant fishes are highly vulnerable to coral loss caused by climate-induced coral bleaching, the structural
collapse of dead coral colonies may have significant, but more variable, impacts across a wide range of fishes. If conservation
and mitigation planning are to be effective, there is a clear need to better understand the mechanisms of reef structural
collapse and the dynamics of system recovery following large-scale disturbance. 相似文献