Simulation of recovery of pre-disturbance size structure in populations of Porites spp. damaged by the crown of thorns starfish Acanthaster planci

Outbreaks of the crown of thorns starfish Acanthaster planci (L.) have caused high levels of mortality and injury in corals on the Great Barrier Reef. In surveys conducted in 1985 and 1986, it was estimated that a quarter of the massive Porites spp. corals surveyed at five reefs — John Brewer, Rib, Potter, Feather and Green Island — had been killed outright. In addition, there was minor to severe injury to colonies throughout the coral's size range. A population model was used to evaluate this damage. The evaluations were based on simulations of the time necessary for prior abundances of large colonies (>2 m diam) to be re-established and on simulations of the number of additional disturbances the populations could withstand before becoming locally extinct. The affect of recurrent disturbances on populations receiving recruits was also simulated. Assuming no further disturbance, the model predicts minimum recovery times in excess of 50 yr for most of the populations, and 9 to 100 yr for sub-populations within reefs. For populations subjected to repeated disturbance every 10 to 30 yr, it predicted that all large colonies would soon be lost unless there was both low background mortality and a major recruitment of Porites spp. between outbreaks. In the worst-case scenario of failed recruitment and high background mortality, four of the five populations could withstand as few as two to three additional disturbances equivalent to those earlier in this decade.     

Recovery of corals a decade after a bleaching event in Dubai, United Arab Emirates

Elevated sea surface temperatures in the late 1990s were associated with widespread coral mortality in the Arabian Gulf, particularly in Acropora dominated areas. This study investigates the composition, condition, and recruitment patterns of coral communities in Saih Al-Shaib, Dubai, United Arab Emirates, a decade after mass bleaching. Five statistically distinct communities were identified by cluster analysis, with grouping optimized from 17 significant indicator species. Overall, 25 species of scleractinian coral were observed, representing 35 ± 1.6% coral cover. Densities of recruits were low (0.8 ± 0.2 m⁻²), and composition generally reflected that of the surrounding adult community. Ten years after mass mortality, Acropora dominated assemblages were observed in three of the six sites examined and coral cover (41.9 ± 2.5%) was double post-bleaching cover. One shallow near-shore site appears to have had recovery of Acropora reset by a further bleaching event in 2002. However, the prevalence of young Acropora colonies here indicates that recovery may recur in several years. One area formerly dominated by Acropora is now dominated by faviids and poritids, with adult and juvenile composition suggesting this dominance shift is likely to persist. Porites lutea and Porites harrisoni dominated communities were negligibly impacted by the bleaching events, and the limited change in coral cover and composition in intervening years likely results from slow growth and low recruitment. Despite strong recovery of several dominant Acropora species, five formerly common species from this area were not observed suggesting local extinction. Dubai coral communities exhibit both resistance and resilience to elevated sea temperatures. The conservation of these patch reefs is warranted given the predicted increase in bleaching events, and the role that these communities may play in regional recovery.     

Shifts in coral community structures following cyclone and red tide disturbances within the Gulf of Oman (United Arab Emirates)

This study documents the effects of two consecutive disturbances on coral community structures in the Gulf of Oman (United Arab Emirates); Cyclone Gonu in June 2007 and the Cochlodinium polykrikoides harmful algal bloom (HAB) that persisted from August 2008 until May 2009. Coral cover, colony densities, size class frequency distributions, and geometric growth rates derived from size class transition probability matrices were used to assess the post-Gonu and post-HAB recovery trajectories at four sites. The net effects of these disturbances were fourfold: (i) storm damage caused >50% losses of live branching and tabular coral cover by fragmentation and dislodgment of pocilloporid and acroporid colonies; (ii) Pocillopora damicornis colonies that survived the cyclone experienced mass mortality during the first 3?months of the HAB, resulting in localized extirpation of this species; (iii) variable Acropora mortality during the HAB indicated individual colony, rather than taxa-wide, susceptibility; and (iv) massive colony coral taxa were resistant to both disturbances.     

Major bleaching events can lead to increased thermal tolerance in corals

Climate change is a major threat to coral reef ecosystems worldwide. A key determinant of the fate of reef corals in a warming climate is their capacity to tolerate increasing thermal stress. Here, an increase in thermal tolerance is demonstrated for three major coral genera (Acropora, Pocillopora and Porites) following the extensive mass bleaching event that occurred on the Great Barrier Reef (Australia) in 1998. During the subsequent and more severe thermal stress event in 2002, bleaching severity was 30–100% lower than predicted from the relationship between severity and thermal stress in 1998, despite higher solar irradiances during the 2002 thermal event. Coral genera most susceptible to thermal stress (Pocillopora and Acropora) showed the greatest increase in tolerance. Although bleaching was severe in 1998, whole-colony mortality was low at most study sites. Therefore, observed increases in thermal tolerance cannot be explained by selective mortality alone, suggesting a capacity for acclimatization or adaptation. Although the vulnerability of coral reefs remains largely dependent on the rate and extent of climate change, such increase in thermal tolerance may delay the onset of mass coral mortalities in time for the implementation of low-emission scenarios and effective management.     

Ecological versatility and the decline of coral feeding fishes following climate driven coral mortality

Coral reefs are under threat due to climate-mediated coral mortality, which affects some reef coral genera more severely than others. The impact this has on coral reef fish is receiving increasing attention, with one focal area assessing impacts on fish that feed directly on live coral. It appears that the more specialised a species of corallivore, the more susceptible it is to coral declines. However data are sparse for the Indian Ocean, and little is known about why some corals are preferentially fed upon over others. Here I assess feeding specialisation in three species of coral feeding butterflyfish in the Chagos Archipelago, central Indian Ocean, assess the food quality of the coral genera they target and document patterns of decline in the Seychelles following a severe coral mortality event. Cheatodon trifascialis was the most specialised coral feeder, preferentially selecting for Acropora corals, however, when Acropora was scarce, individuals showed considerable feeding plasticity, particularly for the dominant Pocillopora corals. C. trifasciatus also preferentially fed on Acropora corals, but fed on a much more diverse suite of corals and also displayed some selectivity for Porites. C. auriga is a facultative corallivore and consumed ∼55% live coral, which lies within the wide range of coral dependence reported for this species. C:N ratio analysis indicated Lobophyllia and Acropora have the highest food quality, with Pocillopora having the lowest, which conforms with diet selection of corallivores and helps explain preferential feeding. Obligate specialist feeders displayed the greatest declines through coral mortality in the Seychelles with obligate generalists also declining substantially, but facultative feeders showing little change. Clearly a greater understanding of the species most vulnerable to disturbance, their habitat requirements and the functional roles they play will greatly assist biodiversity conservation in a changing climate.     

Coral mortality following extreme low tides and high solar radiation

Extreme tidal events are one of the most predictable natural disturbances in marine benthic habitats and are important determinants of zonation patterns in intertidal benthic communities. On coral reefs, spring low tides are recurrent disturbances, but are rarely reported to cause mass mortality. However, in years when extremely low tides coincide with high noon irradiances, they have the potential to cause widespread damage. Here, we report on such an event on a fringing coral reef in the central Great Barrier Reef (Australia) in September 2005. Visual surveys of colony mortality and bleaching status of more than 13,000 corals at 14 reef sites indicated that most coral taxa at wave-protected sites were severely affected by the event. Between 40 and 75% of colonies in the major coral taxa (Acropora, Porites, Faviidae, Mussidae and Pocilloporidae) were either bleached or suffered partial mortality. In contrast, corals at wave-exposed sites were largely unaffected (<1% of the corals were bleached), as periodic washing by waves prevented desiccation. Surveys along a 1–9 m depth gradient indicated that high coral mortality was confined to the tidal zone. However, 20–30% of faviid colonies were bleached throughout the depth range, suggesting that the increase in benthic irradiances during extreme low tides caused light stress in deeper water. Analyses of an 8-year dataset of tidal records for the area indicated that the combination of extended periods of aerial exposure and high irradiances occurs during May–September in most years, but that the event in September 2005 was the most severe. We argue that extreme low-tide, high-irradiance events are important structuring forces of intertidal coral reef communities, and can be as damaging as thermal stress events. Importantly, they occur at a time of year when risks from thermal stress, cyclones and monsoon-associated river run-off are minimal.     

Microhabitat association in white-streaked grouper Epinephelus ongus: importance of Acropora spp.

Microhabitat associations are considered to be important for juvenile survivorship and growth of coral reef fishes. The aim of the study was to quantify microhabitat associations between juvenile and adult white-streaked grouper Epinephelus ongus, which supports important fisheries in coral reef areas. Underwater observations revealed that most juveniles were found in bottlebrush Acropora spp., staghorn Acropora spp. and coral rubble and there was a significant positive use of bottlebrush Acropora spp. and a significant negative use of coral rubble. For adults, most individuals were found in bottlebrush Acropora spp. and staghorn Acropora spp., and there was a significant positive use of staghorn Acropora spp. and significant negative use of coral rubble. A habitat choice experiment by using pre-settlement individuals revealed that both bottlebrush Acropora spp. and staghorn Acropora spp. were used as settlement sites, whereas coral rubble was rarely used as a settlement site. Results of the study suggest that juvenile and adult E. ongus showed significantly positive microhabitat associations with bottlebrush Acropora spp. and staghorn Acropora spp., respectively, in the field. Bottlebrush Acropora spp. has smaller inter-branch spaces than staghorn Acropora spp., which could drive patterns of microhabitat associations. In addition, post-settlement processes such as predation may influence the spatial distribution of juveniles. Because Acropora corals are very susceptible to coral bleaching, we predict that rising temperatures from climate change will negatively impact populations of E. ongus.     

Importance of Habitat Quality and Landscape Connectivity for the Persistence of Endangered Natterjack Toads

Abstract: The natterjack toad (Bufo calamita) is endangered in several parts of its distribution, including Belgium, where it occurs mainly in artificial habitats. We parameterized a general model for natterjack population viability analysis (PVA) and tested its sensitivity to changes in the values of basic parameters. Then we assessed the relative efficiency of various conservation measures in 2 situations: a small isolated population and a system of 4 populations connected by rare dispersal movements. We based the population viability analysis on a stage‐structured model of natterjack population dynamics. We parameterized the model in the RAMAS GIS platform with vital rates obtained from our own field experience and from published studies. Simulated natterjack populations were highly sensitive to habitat quality (particularly pond drying), to dispersal from surrounding local populations, and to a lesser extent to values of fecundity and survival of terrestrial stages. Population trajectories were nearly insensitive to initial abundances, carrying capacities, and the frequency of extreme climatic conditions. The simulations showed that in habitats with highly ephemeral ponds, where premetamorphosis mortality was high, natterjack populations nearly always had a very high extinction risk. We also illustrated how low dispersal rates (<1 dispersing individual/generation) efficiently rescued declining local populations. Such source‐sink dynamics demonstrate that the identification and management of source populations should be a high priority.     

Porites and the Phoenix effect: unprecedented recovery after a mass coral bleaching event at Rangiroa Atoll,French Polynesia

The 1997/1998 El Niño Southern Oscillation (ENSO) was the most severe coral bleaching event in recent history, resulting in the loss of 16 % of the world’s coral reefs. Mortality was particularly severe in French Polynesia, where unprecedented mortality of massive Porites was observed in lagoonal sites of Rangiroa Atoll. To assess the recovery of massive Porites 15 years later, we resurveyed the size structure and extent of partial mortality of massive Porites at Tivaru (Rangiroa). Surveys revealed an abundance of massive Porites colonies rising from the shallow lagoonal floor. Colony width averaged 2.65 m, reaching a maximum of 7.1 m (estimated age of ~391 ± 107 years old). The relative cover of recently dead skeleton within quadrats declined from 42.8 % in 1998 to zero in 2013, yet the relative cover of old dead skeleton increased only marginally from 22.1 % in 1998 to 26.1 % in 2013. At a colony level, the proportion of Porites dominated by living tissue increased from 34.9 % in 1998 to 73.9 % in 2013, indicating rapid recovery of recent dead skeleton to living tissue rather than transitioning to old dead skeleton. Such rapid post-bleaching recovery is unprecedented in massive Porites and resulted from remarkable self-regeneration termed the ‘Phoenix effect’, whereby remnant cryptic patches of tissue that survived the 1997/1998 ENSO event regenerated and rapidly overgrew adjacent dead skeleton. Contrary to our earlier predictions, not only are large massive Porites relatively resistant to stress, they appear to have a remarkable capacity for recovery even after severe partial mortality.     

Assessing the effects of disease and bleaching on Florida Keys corals by fitting population models to data

Coral diseases have increased in frequency over the past few decades and have important influences on the structure and composition of coral reef communities. However, there is limited information on the etiologies of many coral diseases, and pathways through which coral diseases are acquired and transmitted are still in question. Furthermore, it is difficult to assess the impacts of disease on coral populations because outbreaks often co-occur with temperature-induced bleaching and anthropogenic stressors. We developed spatially explicit population models of coral disease and bleaching dynamics to quantify the impact of six common diseases on Florida Keys corals, including aspergillosis, dark spots, white band, white plague, white patch, and Caribbean yellow band. Models were fit to an 8-year data set of coral abundance, disease prevalence, and bleaching prevalence. Model selection was used to assess alternative pathways for disease transmission, and the influence of environmental stressors, including sea temperature and human population density, on disease prevalence and coral mortality. Classic disease transmission from contagious to susceptible colonies provided the best-fit model only for aspergillosis. For other diseases, external disease forcing, such as through a vector or directly from pathogens in the environment, provided the best fit to observed data. Estimates of disease reproductive ratio values (R₀) were less than one for each disease, indicating coral colonies were below densities required for diseases to become established through contagious spread alone. Incidences of white band and white patch disease were associated with greater susceptibility or slower recovery of bleached colonies, and no disease outbreaks were associated with periods of elevated sea temperatures alone. Projections of best-fit models indicated that, atleast during the period of this study, disease and bleaching did not have substantial impacts on populations and impaired rates of population growth appeared to be attributable to other stressors. By applying epidemiological models to field data, our study gives qualitative insights into the dynamics of coral diseases, relative stressor impacts, and directions for future research.     

Seasonality of coral reproduction in the Dampier Archipelago,northern Western Australia

Coral spawning in Western Australia (WA) occurs predominantly in the austral autumn in contrast to the Great Barrier Reef (GBR) on Australia’s east coast where most spawning occurs in spring. Recent work, however, suggests a second spawning period in northern WA with at least 16 Acropora spp spawning in spring or early summer. This discovery has initiated a re-examination of reproductive seasonality in northern WA, particularly on inshore reefs adjacent to large development projects, such as the site of this study in Mermaid Sound, in the Dampier Archipelago. Three locally abundant taxa, Porites spp, Pavona decussata and Turbinaria mesenterina were sampled monthly from September 2006 to May 2007 to determine sexuality, the mode of reproduction and the time of gamete maturity. All three taxa were gonochoric broadcast spawners. Porites spp. colonies were mature in November and December, P. decussata in March and April. In contrast, most colonies of T. mesenterina contained mature gametes for up to 5 months beginning in November, suggesting either individuals are releasing gametes on multiple occasions, or they retain mature gametes for more than 1 month. Field surveys to determine the reproductive status of the remaining coral assemblage were conducted prior to the full moon in October 2006 and March 2007. Only four species contained mature gametes in October 2006. In contrast, 55 species contained mature gametes in March 2007. We conclude that the major spawning season of corals on shallow-inshore reefs in the Dampier Archipelago is autumn, although taxa that spawn in spring and summer include Porites spp., Acropora spp. and possibly T. mesenterina that are numerically dominant at many of these sites. Consequently, management initiatives to limit the exposure of coral spawn to stressors associated with coastal development may be required in up to five months per year.     

Use of individual-based models for population parameters estimation

A method for parameters estimation of stage-specific mortality and fecundity rate functions in poikilotherm organisms, and in particular for arthropod structured population, is proposed. The application of this method requires three types of information: stage-frequency data of a sampled population, development rate function and time evolution of forcing variables affecting the rate functions. By means of an individual-based model (a microscopic model) the number of eggs produced by the adults is generated starting from the number of individuals collected at each sampling time. Using a compartmental model (a macroscopic model) a stage-structured population dynamics is described and compared with observations. Non-linear regression methods based on least square principle are used to estimate the optimal parameters of the mortality and fecundity rate functions combining microscopic and macroscopic models. As a case study, the parameter estimation of the temperature-dependent mortality function of olives fruit fly Bactrocera oleae is presented.     

Photosynthate partitioning by phytoplankton in a New Zealand coastal upwelling system

A stimulation model of copepod population dynamics (development rate, fecundity, and mortality) was used to compute the predatory consumption necessary to control population growth in three dominant copepod species (Pseudocalanus sp., Paracalanus parvus, and Calanus finmarchicus) on Georges Bank, given observed seasonal cycles of copepod and predator populations. The model also calculated secondary production of each species. Copepod development rate and fecundity were functions of temperature while mortality was a function of predator abundance and consumption rate. Daily inputs of temperature and predator abundance (chaetognaths, ctenophores, and Centropages spp.) were derived from equations fit to field data. Model runs were made with various consumption rates until the model output matched observed copepod seasonal cycles. Computed consumption rates were low compared with published values from field and laboratory studies indicating that, even at conservative estimates of consumption, predators are able to control these copepod populations. Combined annual secondary production by the small copepod species, Pseudocalanus sp. and P. parvus, was nearly twice that of the larger C. finmarchicus with P. parvus having the highest total annual production.     

Dynamics of a coral reef community after mass mortality of branching <Emphasis Type="Italic">Acropora</Emphasis> corals and an outbreak of anemones

Dynamics of a coral reef community at Tiao-Shi Reef, southern Taiwan were studied using permanent transects to examine coral recovery and successive cascades to collapse stage resulting from chronic anthropogenic impacts and typhoons. Three distinct zones were recognized within a relatively small study area (250 m across) formerly dominated by large stands of branching Acropora corals. The first zone still retains the dominance of branching Acropora corals, although they show a significant decreasing tendency. The second zone exhibits recovery with a significant increase in branching Montipora stellata, which is recruited and grows faster than branching Acropora corals. The third zone is occupied by anemone, Condylactis sp., and demonstrates a stable phase of coral deterioration without recovery. Such differences in coral reef community dynamics within a small spatial scale illustrate mosaic dynamics which have resulted from degradation of the water quality, patchy mortality of large branching Acropora thickets caused by typhoons, the rapid asexual fragmentation and growth of M. stellata making it a successful colonizer, and occupation by anemone, Condylactis sp., together with unstable remnants of dead Acropora rubbles have not allowed coral recruits to survive.     

Long-term changes in coral colony size distributions on Kenyan reefs under different management regimes and across the 1998 bleaching event

Colony size is an important life-history characteristic of corals and changes in colony size will have significant effects on coral populations. This study summarizes ∼21,000 haphazard colony size measurements of 26 common coral taxa (mostly coral genera) collected annually between 1992 and 2006 in seven Kenyan reef lagoons. There was a major coral bleaching and mortality event in early 1998 and all seven reefs were affected. The seven locations include two long-protected Marine National Parks (Malindi and Watamu), one relatively recently established park (Mombasa), and four unprotected locations (Vipingo, Kanamai, Ras Iwatine, and Diani). They span about 150 km and represent three distinct fishery management regimes: old protected (OP), newly protected (NP), and unprotected (UP). Seventeen taxa had statistically significant different sizes for comparisons of the management regimes, with only one genus, Pavona, having larger sizes in the unprotected reefs. The size of eight coral genera showed a significant time and management interaction, and size frequency differences that existed in management areas prior to 1998 were further increased after the bleaching event. Time alone was a significant factor for eleven genera, and in all cases colonies were smaller after 1998. For most taxa, colony size distributions were significantly skewed and had right-tailed distributions. After 1998, the right-tailed distributions of Acropora, Hydnophora, and Montipora were significantly reduced. Most taxa had peaky distributions and only Acropora experienced a statistically significant change from peaky to flat. The mean sizes of taxa were not related to their mortality across 1998, which indicates that the size effect was within rather than between taxa. Astreopora and Platygyra were well-sampled taxa that did not show an effect of management, but had reduced median sizes across 1998. Consequently, no taxa were tolerant of both fishing and bleaching disturbances and the combined effect was to reduce the size of all corals.     

Reproduction,recruitment and fragmentation in nine sympatric species of the coral genus Acropora

Multispecies assemblages of the coral genus Acropora occur commonly throughout the Indo-Pacific Ocean. Nine species from such an assemblage comprising 41 species of Acropora, at Big Broadhurst Reef on the Great Barrier Reef, were studied during 1981–1983. Similarities and differences in reproductive modes and timing, oocyte dimensions and fecundity, recruitment by larvae and by fragments, and mortality were recorded. All species had an annual gametogenic cycle, were simultaneous hermaphrodites, and had the same arrangement of gonads in polyps. In six species, most colonies released gametes on the same night of the year, in early summer, during a mass spawning event involving many coral genera. A seventh species had colonies spawning at this as well as other times of the year. Another species spawned in late summer, and gametes were not observed to mature in the last species. Eggs were very large (601 to 728 m geometric mean diameter) and fecundity of polyps low, compared with other corals; no reduction in oocyte numbers occurred during oogenesis. Reef-flat species had slightly bigger and fewer eggs than reef-slope species. All species recruited by larvae, but four also multiplied by fragmentation, either year-round or during occasional rough weather. Yearround fragmenters had few larval recruits; non-fragmenters had many, and a rough-weather fragmenter had an intermediate number of larval recruits. It was concluded that larval recruitment largely determined species composition, and that reduced larval recruitment was responsible for sparse distribution of fragmenting species. Subsequent mortality in some species and increase by fragmentation in others probably determined relative abundances.     

Effects of the 1996 and 1998 positive sea-surface temperature anomalies on corals,coral diseases and fish in the Arabian Gulf (Dubai,UAE)

Two positive sea-surface temperature anomalies occurred in the Arabian Gulf in short sequence. Between May and August 1996 and 1998, sea-surface temperatures in the southern Arabian Gulf were elevated by 2°C above average. The consequences for coral fauna, coral diseases and coral regeneration were studied in Dubai (United Arab Emirates) between Jebel Ali and Ras Hasyan. In 1996, coral death was widespread, affecting primarily the genus Acropora. In Acropora-dominated areas, live coral cover was reduced from 90% to about 26% in 1996, while in 1998 only a reduction from 26% to 22% of the remaining coral cover occurred. In the study area, all six Acropora species suffered total mortality in 1996, thus the coral fauna was reduced from 34 species to 27. The nearest areas with surviving Acropora were 30 km to the east (Deira) and 20 km to the west (Al Jazira). Massive coral species suffered negligible mortality, and slowly increased in space cover. The Acropora overkill turned 7.9 km² (19.7% of total coral-covered area) of previously lush coral gardens into a dead framework that was increasingly bioeroded. Acropora recruitment only started in 1998, average recruit size in 1999 was 7Dž cm, and recruits were rare. Prior to the mass mortality event, coral diseases were common and seasonal (14LJ% of corals, mainly Acropora, affected in summer, in winter 7Lj%, mainly massives), after the mortality event seasonality was lost and infection remained below winter levels (6LJ%, only massives infected). In fish, overall species richness decreased from 95 to 64 species in point counts, but frequency only decreased in one species (Pseudochromis persicus). Guild structure changed inasmuch as herbivores and planktivores increased, and invertivores decreased, although differences were not statistically significant. The most abundant family, both prior to and after the coral mass mortality, was Lutjanidae. It appears that even though much of the coral was dead, the maintenance of structural complexity allowed the fish assemblage to avoid a similar catastrophic change to that experienced by the coral assemblage.     

Fitting probability models to population dynamics data

Methods for modeling population dynamics in probability using the generalized point process approach are developed. The life history of these populations is such that seasonal reproduction occurs during a short time. Several models are developed and analyzed. Data about two species: colonial spiders (Stegodyphus dumicola) and a migratory bird (wood thrush, Hylocichla mustelina) are used to estimate model parameters with appropriate log maximum likelihood functions. For the spiders, the model is fitted to provide evolutionary feasible colony size based on maximum likelihood estimates of fecundity and survival data. For the migratory bird species, a maximum likelihood estimates are derived for the fecundity and survival rates of young and adult birds and immigration rate. The presented approach allows computation of quantities of interest such as probability of extinction and average time to extinction.     

Mathematical modelling for conservation and management of gorgonians corals: youngs and olds,could they coexist?

Gorgonian corals are long-lived, slow-growing marine species dominating Mediterranean rocky bottoms. Endowed with complex morphologies they give a structure to the whole community, moreover, being efficient suspension feeders, they play a key role in plankton-benthos energy flow and CO₂${\text{CO}}_2$ storage. Thus, the structure and the development of benthic, hard bottom communities are linked to gorgonian survival. The red coral Corallium rubrum (L. 1758) is a precious gorgonian endemic to the Mediterranean Sea. Harvested and traded world-wide since ancient times red coral is a clear example of overexploited marine resource. This species is structured into self-seeding, genetically differentiated populations, some of which, living in the shallower part of the species bathymetric distribution, was recently affected by anomalous mortality events linked to global climate change. The co-occurrence of overharvesting and mass mortality could dramatically affect such populations. Demographic population models, widely applied by conservation biologists to check population viability and to project population trends over time are fundamental to foster survival of such populations matching harvesting to population growth rates. Therefore we set out a dynamic model of a genetically differentiated red coral population living in shallow waters. This population is characterised by small/young, crowded colonies and high recruitment rate. On the basis of the size–age structure determined for this population, a static life-history table, in which survival and reproduction coefficients of the different size–age classes were reported, has been set out. Demographic data were included in a non-linear, discrete, age-structured dynamic model, based on a Leslie-Lewis transition matrix. Our field data indicate that the recruits-to-larvae ratio is actually density-dependent. Such dependence, positive for low and negative for high density values, was included into the model and the effect of colonies of different size–age classes on recruits-to-larvae ratio was considered to be proportional to the number of polyps they have. We applied such model to simulate the trends of the studied population under different increases of survival and life-span. As some populations of gorgonians actually show the dominance of sparse, big/old colonies and low recruitment rate, while others are characterised by crowded, small/young colonies and high recruitment rate, we simulated the shift from the former to the latter structure increasing survival and life-span. Our results suggest that a dramatic mortality increase of bigger–older colonies (due, in the case of red coral to overfishing) could have determined the population structure we found.     

Is acclimation beneficial to scleractinian corals,Porites spp.?

With coral reefs impacted by climate change, attention is turning to the extent to which scleractinian corals can acclimatize to new physical conditions. The implicit assumption that acclimatization is beneficial has not been tested for scleractinians, although it has been investigated in other systems and has been referred to as the beneficial acclimation hypothesis (BAH). This study tests this hypothesis for scleractinians in experiments on massive Porites spp. from Moorea, French Polynesia (17° 28.564S, 149° 49.018 W). Corals were acclimated for 15–21 days to three temperatures within the range experienced in the collection habitat and then transferred to each of the same temperatures for a treatment period of 14–15 days. The response of the holobiont was measured as growth, the response of the Symbiodinium populations as maximum photochemical efficiency of open reaction centers II (F _v/F _m). An ANOVA with polynomial contrasts was used to distinguish among the BAH, three alternative hypotheses and a null hypothesis describing the consequences of acclimation. In the first experiment (2009), massive Porites spp. were unresponsive to temperature. In the second experiment (2013), the BAH was not supported, but growth of the holobiont conformed to the “hotter is better” (HIB) hypothesis; the response of Symbiodinium populations conformed to developmental buffering. These results suggest that acclimation by massive Porites spp. to temperatures experienced routinely in the natural environment does not have clear beneficial value for growth or photochemical efficiency (i.e., BAH was not supported), but they reveal that acclimation to increased temperature can have value in responding to a variety of subsequent temperatures (i.e., support for HIB).