Abstract
Aim
Strong social‐ecological trade‐offs between resource extraction and protection have created challenges for large, protected area management in natural resource‐dependent countries. ...Therefore, local governments and community conservation activities are becoming common and information about low environmental exposure and high biodiversity can provide for planning localized conservation activities.
Location
The western Indian Ocean.
Methods
Coral reef sites were evaluated for local‐scale environmental and species richness to elucidate local patterns in spatial heterogeneity. Local coral and fish taxonomic richness and coral community susceptibility to stress were normalized to partially account for common and heterogenous disturbances to coral cover and fish biomass. Residuals of these three response variables were evaluated for local geographic patterns and specific relationships with 21 environmental variables using machine learning methods.
Results
Richness was highly variable at local geographies and had a double‐peaked shape with latitudes. Thirteen of the 21 examined variables were selected and indicated complex, spatially heterogeneous and weak cumulative predictive relationships with specific environmental and human influences. For example, each selected variable contributed 7% to 25% of the variance but with different relationships for the three responses. Coral fish richness and coral community susceptibility correlations were positive but weak and therefore produced different local spatial patterns. Nevertheless, these spatial patterns exhibited some coarse‐scale similarities indicating locations with shared positive community attributes and potential climate refugia. Shared richness variables included depth and wave energy, temperature variables of SST skewness, excess heat and rate of rise. Human influences of distance to shore, human populations and cities were also selected for richness and community susceptibility responses.
Main Conclusions
Planning to include local stress and richness patterns variability could contribute to species persistence. From these specific data, sites in the Pemba Channel between the Tanzanian mainland and Pemba Island, and northern Mozambique and Madagascar fit refugia characteristics.
Abstract
Negative trade-offs between food production and biodiversity and the positive functional diversity–productivity relationships are potentially conflicting paradigms that are frequently evoked ...in conservation and sustainability science and management. While the complementary niches of species could potentially increase fisheries yields, stark food-diversity trade-offs have been proposed for wild-caught fisheries. Nevertheless, this first evaluation of stock biomass, yields, and species relationships in 115 coral reef locations in the Western Indian Ocean found that management for multispecies-maximum sustained yield (MMSY) will increase both food production and numbers of species relative to open access fisheries. A precipitous loss of >50% of species did not occur until >70% of the fishable and target biomasses was depleted. At MMSY, 6%–15% of total predicted number of fish species were lost indicating a need for other conservation mechanisms. These patterns occurred because the best-fit to the yield-numbers of species relationship was either a saturation or convex parabolic relationship. Fishing at MMSY in coral reefs should provide considerable diversity required to support many ecosystem services. Low biomass and overfishing were common and around 80% of studied locations were losing ∼2.0–2.5 tons km
−2
yr
−1
and 15%–40% of their species relative to MMSY.
The emerging world crisis created by declining fish stocks poses a challenge to resource users and managers. The problem is particularly acute in poor nations, such as those in East Africa, where ...fishing is an important subsistence activity but high fishing intensity and use of destructive gear have resulted in declining catches. In this context developing effective management strategies requires an understanding of how fishers may respond to declines in catch. We examined the readiness of 141 Kenyan fishers to stop fishing under hypothetical scenarios of declines in catch and how socioeconomic conditions influenced their decisions. As expected, the proportion of fishers that would exit the fishery increased with magnitude of decline in catch. Fishers were more likely to say they would stop fishing if they were from households that had a higher material style of life and a greater number of occupations. Variables such as capital investment in the fishery and the proportion of catch sold had weak, nonsignificant relationships. Our finding that fishers from poorer households would be less likely to exit a severely declining fishery is consistent with the literature on poverty traps, which suggests the poor are unable to mobilize the necessary resources to overcome either shocks or chronic low-income situations and consequently may remain in poverty. This finding supports the proposition that wealth generation and employment opportunities directed at the poorest fishers may help reduce fishing effort on overexploited fisheries, but successful interventions such as these will require an understanding of the socioeconomic context in which fishers operate.
Coral reef communities exposed to rapid temperature rises and frequent thermal anomalies were evaluated for taxonomic turnover via presence/absence information over a 27-year period experiencing ...large changes in the dominant taxa. Temporal turnover of the taxa within sites was consistently high (~ 40%) due to both inter-annual episodic and directional changes. Turnover with time displayed a rapid increase and slow decline after sequential cool and warm thermal anomalies between 1996 and 1998. Subsequent warm temperature anomalies caused fewer broad-scale changes. Directional change for all sites combined indicated three overall gains and losses in taxa—
Montipora
being the only dominant taxon that declined in both abundance and presence/absence. The studied marine reserves had higher local but lower between-site taxonomic richness than fished reefs. Despite similar mean turnover, there were fewer gains than losses in marine reserves (7 gains and 20 losses in 5 sites) than fished sites (16 gains and 15 losses in 7 sites). Changes in taxonomic cover and presence/absence turnover data were not correlated, indicating that turnover detects finer scale taxonomic change likely to be missed when the cover of the dominant taxa is evaluated—especially in the higher richness marine reserves. High spatial richness, community change, and thermal acclimation in these shallow reef lagoons may have prevented higher net losses of taxa. Consequently, the probabilities of reducing local extirpations of taxa may be best achieved by planning and management that promotes spreading more evenly-spread access restrictions to reef areas with high between-site diversity rather than focusing restrictions to sites with high within-site diversity.
AIM: Numbers of coral reef species are broadly influenced by historical, physical and geographical factors that are often the basis for prioritizing conservation and management investments. In ...contrast, the number of species at a site is often influenced by site‐specific factors, including abundance, benthic cover and other habitat features (depth and exposure), fishing pressure and resource management. Conservation policies and programmes often prioritize geographies or specific management systems within specific geographies. I evaluate the variance in number of species at the site scale and estimate the contributions of fishing pressure, local habitat factors and regional geography to local diversity. LOCATION: Coral reefs of the south‐western Indian Ocean (SWIO). METHODS: Site‐level species richness data from an extensive field sample of common coral reef fish at 266 sites in seven SWIO countries were analysed to create four species richness metrics to evaluate the effects of local site, geography and management. RESULTS: The local number of species was strongly predicted by an asymptotic relationship with fish biomass, followed by habitat variables, and lastly by the geographical positions of latitude and longitude. A species richness centre or ‘hotspot’ was found between Madagascar and the African coastline, but the variance attributable to geography when biomass and habitat effects were removed was small. Evaluation of the number of species in five existing fisheries management categories indicated that differences were chiefly influenced by biomass rather than habitat factors. MAIN CONCLUSIONS: Although the centre of species richness may indicate a climate refugium that should be considered in conservation prioritization, this diversity‐centre effect can weaken if habitat and biomass features are reduced by climate disturbances and fishing. Consequently, the highest priority for conserving local numbers of reef fish species is to maintain biomass above the c. 600 kg ha⁻¹ threshold found in this study.
Changes in the cover of the dominant hard coral taxa were studied on seven Kenyan back reefs over 20 yr. All factors of time, taxa, site, and their interactions were statistically significant and the ...1998 temperature anomaly caused the greatest community changes. The 1998 disturbance changes reflected a classic coral succession, which included partial or little mortality and persistence of stress tolerant (massive and submassive growth forms) and early colonization by weedy taxa (pocilloporids). Nevertheless, competitive taxa had high and full mortality and the expected dominance of acroporids was inhibited even ~13 yr after the disturbance. So, while total hard coral cover displayed the expected logistic recovery where maximum cover was reached <10 yr after the disturbance, the poor recovery of competitive dominants resulted in less than expected coral cover. A number of stress-resistant and weedy taxa (poritids, agaricidae, faviids, and pocilloporids) are expected to dominate the composition of these reefs in the future. Nevertheless, three submassive faviids and branching
Porites
began to decline toward the end of the time series, indicating further stress after 1998. Increased algal cover and other unstudied factors, including milder warming, may explain these changes. The patterns of change on this continental fringing reef differ from recovery of more remote, offshore islands. This probably reflects low acroporid dominance and recruitment limitations associated with greater anthropogenic influences of high sea urchin grazing and terrestrial runoff.
The 1998 and 2016 thermal anomalies were among the 2 most severe global-scale anomalies in recent history, with broad-scale impacts on reef condition. In 2 Kenyan fully protected national park reef ...lagoons, the water flow, light, and temperature exposure severity of these 2 events was grossly similar at 7.3 cm s−1, ∼50 Einsteins m−2 d−1 and ∼85 degree-days above summer baseline. Yet, despite similarities in the coral communities’ metrics over this time, the bleaching responses were diminished considerably across this 17 yr period. For example, the numbers of pale and bleached colonies declined from 73 to 27% and from 96 to 60% in the low and high thermal exposure reefs, respectively. A metric that weights bleaching by the intensity of the response and the number of individuals of each taxon also found a decline from 35 to 10% and from 65 to 33%. Of the 21 most common coral taxa, 11, including major contributors to coral cover such as Porites and Acropora, showed declines in their sensitivity. Ten taxa, including Montipora and Pocillopora, showed either little or weak evidence for change in sensitivity, and 1 taxon, Acanthastrea, was more sensitive to the exposure in 2016 than in 1998. Sampling limitations and qualitative differences in the pre-peak temperature conditions did not allow separating the influences of genetic adaptation, acclimatization, and community change.
Trophic cascades caused by a reduction in predators of sea urchins have been reported in Indian Ocean and Caribbean coral reefs. Previous studies have been constrained by their siteâspecific nature ...and limited spatial replication, which has produced site and speciesâspecific understanding that can potentially preclude larger communityâorganization nuances and generalizations. In this study, we aimed to evaluate the extent and variability of the cascade community in response to fishing across
Reef corals are likely to have many subtle but four gross responses to anomalous warm water. These are (1) not bleach and live (mortality <10%), (2) not bleach and die (mortality >20%), (3) bleach ...and live, and (4) bleach and die. The frequency of these four possible gross responses was determined for 18 common coral taxa over an exceptionally warm 1998 El Nino where intense bleaching was observed, and mortality determined from line transects averaged 41.2+/-34.7 (+/-SD). Field studies included (1) recording the loss of color (bleaching) and observing recently dead individuals among 6,803 colonies during five sampling periods and (2) estimating mortality based on 180 m of line-intercept transects completed 4 months before and near the end of the bleaching episode. There was no clear relationship between the loss of color and either direct observation or transect-based estimates of mortality for the 18 taxa. The morphology of the taxa did not influence color loss but branching and encrusting taxa had higher mortality than massive and submassive taxa. Loss of color and mortality are the most common responses to warm water as only Pavona did not lose color or die and only two taxa, Cyphastrea and Millepora, did not significantly lose color but died. Of the 15 taxa that lost color, five taxa, Astreopora, Favia, Favites, Goniopora, and Leptoria, did not die. These taxa are those most likely to have reduced potential mortality by the loss of pigments and associated algal symbionts. Death of the branching taxa was detected reasonably by direct field observation but some taxa were underestimated when compared with mortality estimates based on line transects. Death of encrusting and massive taxa including Echinopora, Galaxea, Hydnophora, Montipora, Platygyra, and massive Porites was poorly detected from direct observations but they proved to have modest to high mortality (20-80%) based on line transects. There was no single response of these common corals to warm water but these data, collected during an extreme warm-water anomaly, indicate that the loss of color is most frequently a sign of morbidity, particularly for branching and encrusting taxa. PUBLICATION ABSTRACT
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