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1.
Habitat specialists form tight relationships with their host habitat and are able to make microscale decisions when selecting final habitat locations. The obligate coral-dwelling fish, Gobiodon histrio, is thought to make habitat choices based on the coloration and structural characteristics of Acropora nasuta, their preferred coral host. Yet, most studies on the habitat preference of G. histrio have been conducted on Australia’s Great Barrier Reef with no understanding if geographic differences in preferences exist. Here, we tested the habitat preference of G. histrio toward A. nasuta on the reefs of Kadavu and Tavewa Islands, Fiji. First, to assess the natural distribution, belt transect surveys of all acroporid corals were conducted. Transects indicated that, while G. histrio is most frequently found in A. nasuta over other acroporid corals, the coral’s structural characteristics rather than the coral’s color variation were the preferred characteristic. In contrast, the Australian G. histrio have been found to be more frequent in blue A. nasuta opposed to the brown color variation, suggesting a geographic difference in habitat preferences among the species. In addition, we conducted two in situ behavioral field experiments to determine whether G. histrio would (1) move from dead A. nasuta to a live brown or blue A. nasuta and (2) preferentially select between the brown- or blue-colored A. nasuta when placed on a dead A. nasuta. The results of the in situ experiments support the finding that Fijian G. histrio does not discriminate between A. nasuta using color but uses only structural morphologies to guide its habitat selection process. Habitat selection is a complex process, and microscale habitat preferences within a species can vary between geographic locations. This study sheds light on the need to expand research findings to incorporate large geographic regions when attempting to understand the preferences of coral reef symbionts. 相似文献
3.
Coral bleaching is an increasingly prominent threat to coral reef ecosystems, not only to corals, but also to the many organisms that rely on coral for food and shelter. Coral-feeding fishes are negatively affected by coral loss caused by extensive bleaching, but it is unknown how feeding behaviour of most corallivorous fishes changes in response to coral bleaching. In this study, coral bleaching was experimentally induced in situ to examine the feeding response of two obligate corallivorous fish, Labrichthys unilineatus (Labridae) and Chaetodon baronessa (Chaetodontidae). Feeding rates were monitored before, during, and immediately after experimental bleaching of prey corals. L. unilineatus significantly increased its feeding on impacted corals during bleaching, but showed a steady decline in feeding once corals were fully bleached. Feeding response of L. unilineatus appears to parallel the expected stress-induced mucous production by bleaching colonies. In contrast, C. baronessa preferentially fed from healthy colonies over bleached colonies, although bleached colonies were consumed for five days following manipulation. Feeding by corallivorous fishes can play an important role in determining coral condition and mortality of corals following stress induced bleaching. 相似文献
4.
Techniques that utilize sea surface temperature (SST) observations to predict coral reef bleaching are in common use and form the foundation for predicted global coral reef ecosystem demise within this century. Yet, quality assessments of these methods are typically qualitative or anecdotal. Quality is the correspondence of forecasts with observations and has standard quantitative measures. Here a forecast verification method, commonly used in meteorology, is presented and used to measure the quality of the degree heating weeks (DHW) technique as an exploration of insights that can be gleaned from this methodology. DHW values were calculated from NOAA Optimum Interpolation SST version 2 data and compared to a database of bleaching observations from 1990–2007. Quality is expressed with an objective measure, the Peirce Skill Score (PSS). The quality at varying DHW thresholds above which bleaching was projected to occur is calculated. By selecting the thresholds that maximize quality, the predictive technique is objectively optimized. This results in optimal threshold maps, showing reefs more prone and more resistant to bleaching. Optimization increases the quality of DHW as a predictor of bleaching from PSS = 0.55 to PSS = 0.83, in global average, but the optimal PSS and corresponding DHW values vary significantly from location to location. The coral reef research and management community are urged to adopt the simple, but rigorous tools of forecast verification routinely used in other disciplines so that bleaching forecasts can be quantitatively compared and their quality improved. 相似文献
5.
Future widespread coral bleaching and subsequent mortality has been projected using sea surface temperature (SST) data derived
from global, coupled ocean–atmosphere general circulation models (GCMs). While these models possess fidelity in reproducing
many aspects of climate, they vary in their ability to correctly capture such parameters as the tropical ocean seasonal cycle
and El Ni?o Southern Oscillation (ENSO) variability. Such weaknesses most likely reduce the accuracy of predicting coral bleaching,
but little attention has been paid to the important issue of understanding potential errors and biases, the interaction of
these biases with trends, and their propagation in predictions. To analyze the relative importance of various types of model
errors and biases in predicting coral bleaching, various intra- and inter-annual frequency bands of observed SSTs were replaced
with those frequencies from 24 GCMs 20th century simulations included in the Intergovernmental Panel on Climate Change (IPCC)
4th assessment report. Subsequent thermal stress was calculated and predictions of bleaching were made. These predictions
were compared with observations of coral bleaching in the period 1982–2007 to calculate accuracy using an objective measure
of forecast quality, the Peirce skill score (PSS). Major findings are that: (1) predictions are most sensitive to the seasonal
cycle and inter-annual variability in the ENSO 24–60 months frequency band and (2) because models tend to understate the seasonal
cycle at reef locations, they systematically underestimate future bleaching. The methodology we describe can be used to improve
the accuracy of bleaching predictions by characterizing the errors and uncertainties involved in the predictions. 相似文献
6.
This study examines patterns of susceptibility and short-term recovery of corals from bleaching. A mass coral bleaching event began in March, 1991 on reefs in Moorea, French Polynesia and affected corals on the shallow barrier reef and to >20 m depth on the outer forereef slope. There were significant differences in the effect of the bleaching among common coral genera, with Acropora, Montastrea, Montipora, and Pocillopora more affected than Porites, Pavona, leptastrea or Millepora. Individual colonies of the common species of Acropora and Pocillopora were marked and their fate assessed on a subsequent survey in August, 1991 to determine rates of recovery and mortality. Ninety-six percent of Acropora spp. showed some degree of bleaching compared to 76% of Pocillopora spp. From March to August mortality of bleached colonies of Pocillopora was 17%, 38% recovered completely, and many suffered some partial mortality of the tissue. In contrast, 63% of the Acropora spp. died, and about 10% recovered completely. Generally, those colonies with less than 50% of the colony area affected by the bleaching recovered at a higher rate than did those with more severe bleaching. Changes in community composition four months after the event began included a significant decrease only in crustose algae and an increase in cover of filamentous algae, much of which occupied plate-like and branching corals that had died in the bleaching event. Total coral cover and cover of susceptible coral genera had declined, but not significantly, after the event. 相似文献
9.
We present a refined genetic map of the obligate methylotroph Methylobacillus flagellatum. New, Hfr (high-frequency-of-transfer) donors, and pulsed-field gel electrophoresis, were used to determine that M.␣flagellatum contains one ∼3.1-Mb circular chromosome, and no plasmids. A correlation between time-of-entry units and DNA length was established. Using in vivo and in vitro cloning, and sequencing, a number of new genetic markers were identified and mapped; in addition, the nature of some of the previously mapped markers was elucidated. Received: 11 August 1997 / Accepted: 11 December 1997 相似文献
11.
There is no simple explanation for the unusual increase in coral reef bleaching events that have been occurring on a global scale over the last 2 decades. Recent studies focusing on this problem reveal that mass bleaching events have a strong periodic component, arising every 3-4 yr in step with the El Ni?o climatic phenomenon. To explore this possibility further, we examine a simple oceanographic-ecological model designed to simulate the warm and cool phases of the Pacific Ocean cycle and gauge its effect on local coral reefs. This allows us to identify causes for localized 'hot spots' in the ocean, whose high sea surface temperatures have disastrous consequences for corals. The underlying wave dynamics of the model lead to chaotic oscillations (every 3-4 yr), which help explain the coexistence of both order and irregularity in the dynamics of mass bleaching. The model makes use of a temperature threshold mechanism-a bleaching event is triggered whenever temperature anomalies exceed a critical level. In a variable environment, the threshold mechanism is sensitive to background fluctuations, and their effects are studied by making use of a 'stochastic resonance' formulation. Global climate change and other trends in external background environmental conditions are all shown to strongly influence the distribution of mass coral bleaching events. 相似文献
12.
Coral Reefs - Coral bleaching as a response to increased sea surface temperature is regularly surveyed, but our understanding of species-specific differences in response is limited. We compiled... 相似文献
13.
‘Resilience’, the capacity of the coral symbiosis with dinoflagellate algal symbionts (‘zooxanthellae’) to recover after bleaching, is a little-studied but crucial aspect of coral responses to bleaching stressors. This study investigated the response of the zooxanthella population in the coral Porites cylindrica after bleaching either naturally on a shallow subtidal reef or experimentally in response to elevated temperature and darkness. Coral resilience was influenced by the nature and duration of the stressor. Corals strongly bleached by natural stressors were less resilient than those that had been partially bleached; and a similar recovery profile was obtained for corals experimentally bleached by exposure to elevated temperature, in which recovery was slower for corals thermally-stressed 96 h than for 72 h. The opposite trend was evident for corals exposed to darkness, indicating that the bleaching trigger had a strong impact on coral resilience. When P. cylindrica recently recovered from bleaching was subjected to a repetition of bleaching stressors, it did not display acclimation, i.e. experience-mediated acquisition of resistance to bleaching stressors. The zooxanthella populations in all corals tested throughout the experiments were typed by PCR-RFLP as clade C, indicating that coral responses were not accompanied by any substantial change in zooxanthella composition at the cladal level. 相似文献
15.
Annual bleaching of Oculina patagonica on the Israeli Mediterranean coastline has been reported since 1993, although the cellular mechanisms underlying the bleaching
have not yet been investigated. This survey examined 48 coral colonies of O. patagonica (bleached and unbleached) from various sites along the Israeli coast. Histopathological investigations of bleached lesions
revealed a loss of endosymbionts, and an apparent in situ degradation of the endosymbionts. In situ end labelling of bleaching
lesions did not provide evidence of apoptotic cell death. Electron microscopy of bleaching lesions also demonstrated an apparent
in situ degradation and no evidence of apoptotic cell death of the host. 相似文献
16.
Coral Reefs - Coral health depends on a fragile partnership between the coral hosts and the endosymbiotic dinoflagellate symbionts. Sequence-level omics techniques are revolutionizing many aspects... 相似文献
19.
The shore crab, Carcinus maenas L. (Portunidae), is a coastal and estuarine species, which can live and reproduce under brackish water conditions; freshly hatched larvae have been observed in the field at salinities below 15‰. In the present laboratory study, the tolerance of hypo-osmotic stress was experimentally investigated in early larvae of a marine (North Sea) population of C. maenas reared at four different salinities (15, 20, 25, 32‰). Two and 4 days after hatching, the Zoea I larvae were moult-staged microscopically, and their rates of respiration and growth (changes in dry weight, W, carbon, C, nitrogen, N, and hydrogen, H) were measured. Survival and development were monitored until the megalopa was reached: 15‰ did not allow for development beyond the first zoeal stage, while metamorphosis to the megalopa was reached at salinities ≥20‰. At 20‰, development was significantly delayed and mortality enhanced as compared with 25 and 32‰. Rates of growth and respiration decreased during exposure to reduced salinities ≤25‰. Hence, the suppression of growth could not be explained as a consequence of enhanced metabolic losses per larva. Instead, a partial C budget indicates that the Zoea I larvae suffered from decreased capabilities of assimilating ingested and subsequently converting assimilated matter to tissue growth. Net growth efficiency ( K2, C-based) was at 25 and 32‰ initially high (>60% during the postmoult and intermoult stages of the Zoea I moult cycle), but decreased during the later stages (down to ≤30% in premoult). An inverse pattern of C partitioning was observed at ≤20‰, with initially low K2 values (≤21% during the first 2 days of the moult cycle), and a later increase (up to ≥46% in premoult). Thus, larval growth was initially suppressed under conditions of reduced salinity, but this was later (during premoult) partially compensated for by an increase in C assimilation and K2. Our observations indicate that Zoea I shore crab larvae react during the late stages of their moulting cycle less sensitively against reduced salinities than during postmoult and intermoult. This suggests that the transition between moult cycle stages C and D 0 may be a critical point for effects of hypo-osmotic stress, similarly as already known in relation to effects of nutritional stress. Negative effects were found also when freshly hatched Zoea I shore crab larvae were exposed only transitorily (for 24–72 h) to 20‰, with significantly lower rates of survival, development, growth, respiration, and K2. These effects increased with increasing duration of initial exposure to reduced salinity. 相似文献
20.
Coral Reefs - Reef-building corals are surrounded by complex microenvironments (i.e. concentration boundary layers) that partially isolate them from the ambient seawater. Although the presence of... 相似文献
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