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The frequency and severity of marine heatwaves causing mass mortality events in tropical and temperate coral species increases every year, with serious consequences on the stability and resilience of coral populations. Although recovery and persistence of coral populations after stress events is closely related to adult fitness, as well as larval survival and settlement, much remains unknown about the effects of thermal stress on early life history stages of temperate coral species. In the present study, the reproductive phenology and the effect of increased water temperature (+4 °C and +6 °C above ambient, 20 °C) on larval survival and settlement was evaluated for two of the most representative Mediterranean octocoral species (Eunicella singularis and Corallium rubrum). Our study shows that reproductive behavior is more variable than previously reported and breeding period occurs over a longer period in both species. Thermal stress did not affect the survival of symbiotic E. singularis larvae, but drastically reduced the survival of the non‐symbiotic C. rubrum larvae. Results on larval biomass and caloric consumption suggest that higher mortality rates of C. rubrum exposed to increased temperature were not related to depletion of endogenous energy in larvae. The results also show that settlement rates of E. singularis did not change in response to elevated temperature after 20 days of exposure, but larvae may settle fast and close to their native population at 26 °C (+6 °C). Although previous experimental studies found that adult colonies of both octocoral species are mostly resistant to thermal stress, our results on early life history stages suggest that the persistence and inter‐connectivity of local populations may be severely compromised under continued trends in ocean warming.
Climate change is causing an increase in the frequency and intensity of marine heatwaves (MHWs) and mass mortality events (MMEs) of marine organisms are one of their main ecological impacts. Here, we show that during the 2015–2019 period, the Mediterranean Sea has experienced exceptional thermal conditions resulting in the onset of five consecutive years of widespread MMEs across the basin. These MMEs affected thousands of kilometers of coastline from the surface to 45 m, across a range of marine habitats and taxa (50 taxa across 8 phyla). Significant relationships were found between the incidence of MMEs and the heat exposure associated with MHWs observed both at the surface and across depths. Our findings reveal that the Mediterranean Sea is experiencing an acceleration of the ecological impacts of MHWs which poses an unprecedented threat to its ecosystems' health and functioning. Overall, we show that increasing the resolution of empirical observation is critical to enhancing our ability to more effectively understand and manage the consequences of climate change. During the 2015‐2019 period, the Mediterranean Sea has experienced exceptional marine heatwaves conditions resulting in the onset of five consecutive years of widespread MMEs across the basin. These MMEs affected thousands of kilometers of coastline from the surface to 45 m depth, across a range of marine habitats and taxa (50 taxa across 8 phyla). By assessing and integrating temperature data with mass mortality records across the basin, our study provides the most up‐to‐date account of the impacts of extreme warming events on Mediterranean marine organisms and ecosystems.
Understanding the resilience of temperate reefs to climate change requires exploring the recovery capacity of their habitat-forming species from recurrent marine heatwaves (MHWs). Here, we show that, in a Mediterranean highly enforced marine protected area established more than 40 years ago, habitat-forming octocoral populations that were first affected by a severe MHW in 2003 have not recovered after 15 years. Contrarily, they have followed collapse trajectories that have brought them to the brink of local ecological extinction. Since 2003, impacted populations of the red gorgonian Paramuricea clavata (Risso, 1826) and the red coral Corallium rubrum (Lin-naeus, 1758) have followed different trends in terms of size structure, but a similar progressive reduction in density and biomass. Concurrently, recurrent MHWs were observed in the area during the 2003-2018 study period, which may have hindered populations recovery. The studied octocorals play a unique habitat-forming role in the coralligenous assemblages (i.e. reefs endemic to the Mediterranean Sea home to approximately 10%
The survival, behavior and competence period of lecithotrophic larvae depends not only on the energy allocation transferred by maternal colonies but also on the amount of energy consumed to sustain embryonic, larval, and post-larval development. The objective of the present work is to understand the effect of energy consumption on the performance of lecithotrophic larvae. To this aim, we analyzed free fatty acid (FFA) content and composition of the larvae of three Mediterranean octocorals (Corallium rubrum, Eunicella singularis and Paramuricea clavata) as a proxy for energy consumption. Results showed that C. rubrum larvae consume more FFA than P. clavata, whereas the energy consumed by E. singularis larvae is high but highly variable. These results are in accordance with the larval behavior of these three species since C. rubrum larvae are characterized by their high swimming activity frequency, P. clavata larvae are almost inactive, and the swimming activity frequency of E. singularis larvae is high, although variable. The differences in FFA composition of the larvae suggest contrasting energetic strategies that could explain the differences in survival and recruitment rates. In fact, high dispersal and recruitment capacities for E. singularis larvae can be inferred from the FFA composition, whereas the high spatial and temporal variability of recruitment observed in C. rubrum may be related to the non-selective transfer of fatty acid (FA) from maternal colonies. Finally, the high recovery rates after mass mortality events observed in P. clavata could be favored by the presence of a specific FA (22:6(n-3)) related to adaptation mechanisms under environmental stresses during the first developmental stages.
Deep-sea octocorals are common habitat-formers in deep-sea ecosystems, however, our knowledge on their early life history stages is extremely limited. The present study focuses on the early life history of the species Dentomuricea aff. meteor , a common deep-sea octocoral in the Azores. The objective was to describe the embryo and larval biology of the target species under two temperature regimes, corresponding to the minimum and maximum temperatures in its natural environment during the spawning season. At temperature of 13 ±0.5 °C, embryos of the species reached the planula stage after 96h and displayed a median survival of 11 days. Planulae displayed swimming only after stimulation, swimming speed was 0.24 ±0.16 mm s ⁻¹ and increased slightly but significantly with time. Under a higher temperature (15 °C ±0.5 °C) embryos reached the planula stage 24 h earlier (after 72 h), displayed a median survival of 16 days and had significantly higher swimming speed (0.3 ±0.27 mm s ⁻¹ ). Although the differences in survival were not statistically significant, our results highlight how small changes in temperature can affect embryo and larval characteristics with potential cascading effects in larval dispersal and success. In both temperatures, settlement rates were low and metamorphosis occurred even without settlement. Such information is rarely available for deep-sea corals, although essential to achieve a better understanding of dispersal, connectivity and biogeographical patterns of benthic species.
Estimating long-term modifications of the sea surface temperature (SST) is crucial for evaluating the current state of the oceans and to correctly assess the impact of climate change at regional scales. In this work, we analyze SST variations within the Mediterranean Sea and the adjacent Northeastern Atlantic box (west of the Strait of Gibraltar) over the last 37 years, by using a satellite-based dataset from the Copernicus Marine Environment Monitoring Service (CMEMS). We found a mean warming trend of 0.041 ± 0.006 • C/year over the whole Mediterranean Sea from 1982 to 2018. The trend has an uneven spatial pattern, with values increasing from 0.036 ± 0.006 • C/year in the western basin to 0.048 ± 0.006 • C/year in the Levantine-Aegean basin. The Northeastern Atlantic box and the Mediterranean show a similar trend until the late 1990s. Afterwards, the Mediterranean SST continues to increase, whereas the Northeastern Atlantic box shows no significant trend, until ~2015. The observed change in the Mediterranean Sea affects not only the mean trend but also the amplitude of the Mediterranean seasonal signal, with consistent relative increase and decrease of summer and winter mean values, respectively, over the period considered. The analysis of SST changes occurred during the "satellite era" is further complemented by reconstructions also based on direct in situ SST measurements, i.e., the Extended Reconstructed SST (ERSST) and the Hadley Centre Sea Ice and Sea Surface Temperature dataset (HadISST), which go back to the 19th century. The analysis of these longer time series, covering the last 165 years, indicates that the increasing Mediterranean trend, observed during the CMEMS operational period, is consistent with the Atlantic Multidecadal Oscillation (AMO), as it closely follows the last increasing period of AMO. This coincidence occurs at least until 2007, when the apparent onset of the decreasing phase of AMO is not seen in the Mediterranean SST evolution.
Anthropogenic climate change, and global warming in particular, has strong and increasing impacts on marine ecosystems (Poloczanska et al., 2013; Halpern et al., 2015; Smale et al., 2019). The Mediterranean Sea is considered a marine biodiversity hotspot contributing to more than 7% of world’s marine biodiversity including a high percentage of endemic species (Coll et al., 2010). The Mediterranean region is a climate change hotspot, where the respective impacts of warming are very pronounced and relatively well documented (Cramer et al., 2018). One of the major impacts of sea surface temperature rise in the marine coastal ecosystems is the occurrence of mass mortality events (MMEs). The first evidences of this phenomenon dated from the first half of ’80 years affecting the Western Mediterranean and the Aegean Sea (Harmelin, 1984; Bavestrello and Boero, 1986; Gaino and Pronzato, 1989; Voultsiadou et al., 2011). The most impressive phenomenon happened in 1999 when an unprecedented large scale MME impacted populations of more than 30 species from different phyla along the French and Italian coasts (Cerrano et al., 2000; Perez et al., 2000). Following this event, several other large scale MMEs have been reported, along with numerous other minor ones, which are usually more restricted in geographic extend and/or number of affected species (Garrabou et al., 2009; Rivetti et al., 2014; Marbà et al., 2015; Rubio-Portillo et al., 2016, authors’ personal observations). These events have generally been associated with strong and recurrent marine heat waves (Crisci et al., 2011; Kersting et al., 2013; Turicchia et al., 2018; Bensoussan et al., 2019) which are becoming more frequent globally (Smale et al., 2019). Both field observations and future projections using Regional Coupled Models (Adloff et al., 2015; Darmaraki et al., 2019) show the increase in Mediterranean sea surface temperature, with more frequent occurrence of extreme ocean warming events. As a result, new MMEs are expected during the coming years. To date, despite the efforts, neither updated nor comprehensive information can support scientific analysis of mortality events at a Mediterranean regional scale. Such information is vital to guide management and conservation strategies that can then inform adaptive management schemes that aim to face the impacts of climate change.
Our changing climate is a threat to corals, causing disfiguring bleaching and mortality to reefs that once teemed with life. Shlesinger and Loya alert us to an equally dangerous yet nearly invisible hazard to coral: loss of breeding synchrony (see the Perspective by Fogarty and Marhaver). They found that environmental changes have resulted in shifts in the timing of gamete release in several species of broadcast-spawning corals in the Red Sea. Similar changes are likely occurring globally. Such a loss of spawning synchrony could result in reproductive failure, a much less obvious but no less insidious threat to coral reefs.
Science , this issue p. 1002 ; see also p. 987
Climate change threatens coastal benthic communities on a global scale. However, the potential effects of ongoing warming on mesophotic temperate reefs at the community level remain poorly understood. Investigating how different members of these communities will respond to the future expected environmental conditions is, therefore, key to anticipating their future trajectories and developing specific management and conservation strategies. Here, we examined the responses of some of the main components of the highly diverse Mediterranean coralligenous assemblages to thermal stress. We performed thermotolerance experiments with different temperature treatments (from 26 to 29°C) with 10 species from different phyla (three anthozoans, six sponges and one ascidian) and different structural roles. Overall, we observed species‐specific contrasting responses to warming regardless of phyla or growth form. Moreover, the responses ranged from highly resistant species to sensitive species and were mostly in agreement with previous field observations from mass mortality events (MMEs) linked to Mediterranean marine heat waves. Our results unravel the diversity of responses to warming in coralligenous outcrops and suggest the presence of potential winners and losers in the face of climate change. Finally, this study highlights the importance of accounting for species‐specific vulnerabilities and response diversity when forecasting the future trajectories of temperate benthic communities in a warming ocean.
Extreme ocean warming events, known as marine heatwaves (MHWs), have been observed to perturb significantly marine ecosystems and fisheries around the world. Here, we propose a detection method for long-lasting and large-scale summer MHWs, using a local, climatological 99th percentile threshold, based on present-climate (1976–2005) daily SST. To assess their future evolution in the Mediterranean Sea we use, for the first time, a dedicated ensemble of fully-coupled Regional Climate System Models from the Med-CORDEX initiative and a multi-scenario approach. The models appear to simulate well MHW properties during historical period, despite biases in mean and extreme SST. In response to increasing greenhouse gas forcing, the events become stronger and more intense under RCP4.5 and RCP8.5 than RCP2.6. By 2100 and under RCP8.5, simulations project at least one long-lasting MHW every year, up to three months longer, about 4 times more intense and 42 times more severe than present-day events. They are expected to occur from June-October and to affect at peak the entire basin. Their evolution is found to occur mainly due to an increase in the mean SST, but increased daily SST variability also plays a noticeable role. Until the mid-21st century, MHW characteristics rise independently of the choice of the emission scenario, the influence of which becomes more evident by the end of the period. Further analysis reveals different climate change responses in certain configurations, more likely linked to their driving global climate model rather than to the individual model biases.
Sexual reproduction characteristics of Stylophora pistillata, one of the most common coral species in the Gulf of Eilat, Red Sea, were extensively studied in the 1970s and 1980s. Four decades later, we examined possible changes in reproductive patterns in this species by placing planula traps over S. pistillata colonies during the 2015 and 2016 reproductive seasons. In total, 708 larval traps (222 traps in 2015 and 486 in 2016) were used, collecting 31,396 planulae overall (12,455 in 2015 and 18,852 in 2016). The results of this 2-year study indicated (a) lengthening of the reproductive season by up to 2 months (until mid-September 2015 and August 2016), (b) an extension of peaks in larval release from 2–3 to 5–6 months, (c) an increase in the percentage of colonies that release planula larvae, and (d) a high variability in larval release among different colonies and between consecutive collecting dates. All the above reflect decadal differences in the reproductive effort in S. pistillata. Furthermore, this study reveals that S. pistillata colonies stop releasing planulae after sea surface temperature (SST) reaches its annual peak, contrasting with the earlier finding that planula release ended before the annual SST peak. We propose that global change impacts and an increase in anthropogenic activities in the Gulf of Eilat are the culprit behind the reported changes in coral reproductive traits over the past 4 decades.
The effects of multiple stressors on the early life stages of reef-building corals are poorly understood. Elevated temperature is the main physiological driver of mass coral bleaching events, but increasing evidence suggests that other stressors, including elevated dissolved inorganic nitrogen (DIN), may exacerbate the negative effects of thermal stress. To test this hypothesis, we investigated the performance of larvae of Orbicella faveolata and Porites astreoides, two important Caribbean reef coral species with contrasting reproductive and algal transmission modes, under increased temperature and/or elevated DIN. We used a fluorescence-based microplate respirometer to measure the oxygen consumption of coral larvae from both species, and also assessed the effects of these stressors on P. astreoides larval settlement and mortality. Overall, we found that (1) larvae increased their respiration in response to different factors (O. faveolata in response to elevated temperature and P. astreoides in response to elevated nitrate) and (2) P. astreoides larvae showed a significant increase in settlement as a result of elevated nitrate, but higher mortality under elevated temperature. This study shows how microplate respirometry can be successfully used to assess changes in respiration of coral larvae, and our findings suggest that the effects of thermal stress and nitrate enrichment in coral larvae may be species specific and are neither additive nor synergistic for O. faveolata or P. astreoides. These findings may have important consequences for the recruitment and community reassembly of corals to nutrient-polluted reefs that have been impacted by climate change.
Many marine invertebrates provide their offspring with symbionts. Yet the consequences of maternally inherited symbionts on larval fitness remain largely unexplored. In the stony coral Favia fragum (Esper 1797), mothers produce larvae with highly variable amounts of endosymbiotic algae, and we examined the implications of this variation in symbiont density on the performance of F. fragum larvae under different environmental scenarios. High symbiont densities prolonged the period that larvae actively swam and searched for suitable settlement habitats. Thermal stress reduced survival and settlement success in F. fragum larvae, whereby larvae with high symbiont densities suffered more from non-lethal stress and were five times more likely to die compared with larvae with low symbiont densities. These results show that maternally inherited algal symbionts can be either beneficial or harmful to coral larvae depending on the environmental conditions at hand, and suggest that F. fragum mothers use a bet-hedging strategy to minimize risks associated with spatio-temporal variability in their offspring's environment.
Coral reefs support immense biodiversity and provide important ecosystem services to many millions of people. Yet reefs are degrading rapidly in response to numerous anthropogenic drivers. In the coming centuries, reefs will run the gauntlet of climate change, and rising temperatures will transform them into new configurations, unlike anything observed previously by humans. Returning reefs to past configurations is no longer an option. Instead, the global challenge is to steer reefs through the Anthropocene era in a way that maintains their biological functions. Successful navigation of this transition will require radical changes in the science, management and governance of coral reefs.
Frequency and severity of heat waves is expected to increase as a consequence of climate change with important impacts on human and ecosystems health. However, while many studies explored the projected occurrence of hot extremes on terrestrial systems, few studies dealt with marine systems, so that both the expected change in marine heat waves occurrence and the effects on marine organisms and ecosystems remain less understood and surprisingly poorly quantified. Here we: i) assess how much more frequent, severe, and depth-penetrating marine heat waves will be in the Mediterranean area in the next decades by post-processing the output of an ocean general circulation model; and ii) show that heat waves increase will impact on many species that live in shallow waters and have reduced motility, and related economic activities. This information is made available also as a dataset of temperature threshold exceedance indexes that can be used in combination with biological information to produce risk assessment maps for target species or biomes across the whole Mediterranean Sea. As case studies we compared projected heat waves occurrence with thermotolerance thresholds of low motility organisms. Results suggest a deepening of the survival horizon for red coral (Corallium rubrum, a commercially exploited benthic species already subjected to heat-related mass mortality events) and coralligenous reefs as well as a reduction of suitable farming sites for the mussel Mythilus galloprovincialis. In recent years Mediterranean circalittoral ecosystems (coralligenous) have been severely and repeatedly impacted by marine heat waves. Our results support that equally deleterious events are expected in the near future also for other ecologically important habitats (e.g. seagrass meadows) and aquaculture activities (bivalvae), and point at the need for mitigation strategies.
Recent research has documented phenotypic differences among larvae released from corals with a brooding reproductive mode, both among species and within broods from a single species. We studied larvae released from the common Atlantic coral Porites astreoides in Bermuda to further evaluate phenotypic variability. Inter-site differences were investigated in larvae from conspecifics at a rim and patch reef site. Larvae were collected daily for one lunar cycle from several colonies per site each year over 5 yr. Larval volume varied with reef site of origin, with colonies from the rim reef site producing larger larvae than colonies from the patch reef site. This inter-site variation in larval size could not be explained by corallite size and may be a response to different environmental conditions at the sites. Larvae from both reef sites also varied in size depending on lunar day of release over 4 yr of study. Regardless of site of origin, smaller larvae were released earlier in the lunar cycle. Over 1 yr of study, lipid and zooxanthellae content and settlement success after 48 h covaried with larval size. However, there may be a trade-off between larger larvae and reduced fecundity. Overall, larvae released from colonies from the rim reef site were larger and had greater settlement success than those from colonies from the patch reef site. This study documents larval phenotypic variability and a distinct inter-site difference in larval ecology among conspecifics within the same geographic area, which may have implications for recruitment success, population dynamics, and resilience.
Events in the early life history of reef-building corals, including fertilisation and larval survival, are susceptible to changes in the chemical and physical properties of sea water. Quantifying how changes in water quality affect these events is therefore important for understanding and predicting population establishment in novel and changing environments. A review of the literature identified that levels of salinity, temperature, pH, suspended sediment, nutrients and heavy metals affect coral early life-history stages to various degrees. In this study, we combined published experimental data to determine the relative importance of sea water properties for coral fertilisation success and larval survivorship. Of the water properties manipulated in experiments, fertilisation success was most sensitive to suspended sediment, copper, salinity, phosphate and ammonium. Larval survivorship was sensitive to copper, lead and salinity. A combined model was developed that estimated the joint probability of both fertilisation and larval survivorship in sea water with different chemical and physical properties. We demonstrated the combined model using water samples from Sydney and Lizard Island in Australia to estimate the likelihood of larvae surviving through both stages of development to settlement competency. Our combined model could be used to recommend targets for water quality in coastal waterways as well as to predict the potential for species to expand their geographical ranges in response to climate change.
Gorgonian species show a high morphological variability in relation to the environment in which they live. In coastal areas, parameters such as temperature, light, currents, and food availability vary significantly with depth, potentially affecting morphology of the colonies and the structure of the populations, as well as their connectivity patterns. In tropical seas, the existence of connectivity between shallow and deep populations supported the hypothesis that the deep coral reefs could potentially act as (reproductive) refugia fostering re-colonization of shallow areas after mortality events. Moreover, this hypothesis is not so clear accepted in temperate seas. Eunicella singularis is one of the most common gorgonian species in Northwestern Mediterranean Sea, playing an important role as ecosystem engineer by providing biomass and complexity to the coralligenous habitats. It has a wide bathymetric distribution ranging from about 10 m to 100 m. Two depth-related morphotypes have been identified, differing in colony morphology, sclerite size and shape, and occurrence of symbiotic algae, but not in mitochondrial DNA haplotypes. In the present study the genetic structure of E. singularis populations along a horizontal and bathymetric gradient was assessed using microsatellites and ITS1 sequences. Restricted gene flow was found at 30-40 m depth between the two Eunicella morphotypes. Conversely, no genetic structuring has been found among shallow water populations within a spatial scale of ten kilometers. The break in gene flow between shallow and deep populations contributes to explain the morphological variability observed at different depths. Moreover, the limited vertical connectivity hinted that the refugia hypothesis does not apply to E. singularis. Re-colonization of shallow water populations, occasionally affected by mass mortality events, should then be mainly fueled by larvae from other shallow water populations.
The life cycle of the gorgonian Eunicella singularis has been studied with emphasis on larval behaviour, metamorphosis and annual growth. Planulae are found to have a mobile phase lasting from several hours to several days. Once settled, they metamorphose into a complete primary polyp in approximately four days. In the first year, budding will yield colonies of a height between 10 and 30 mm. Subsequently, average growth rates range from 14 to 33 mm year ⁻¹ . Death may be due to several causes. Predators may partly denude the gorgonian branches, thus facilitating the settlement of epibionts, which in turn may invade the entire skeleton, slowly pushing back the living tissue of the gorgonian. Colonies may also be torn off their substratum by wave or current action, this process sometimes being speeded up when tall epibionts such as fast growing bryozoans enhance resistance to water movement. Once toppled, the gorgonians die by necrosis of their living tissues, or by being buried under sediment. Colonies of E. singularis are estimated to reach an age of approximately 25 to 30 years. Some data have been obtained on growth rates and life spans of two other Mediterranean gorgonians, Lophogorgia ceratophyta and Paramuricea clavata .
Increase in atmospheric CO2 is the main driver of global climate change and is projected to elevate sea surface temperature by at least 2°C and to decrease oceanic pH by 0.3 to 0.4 units by the end of the century. These factors seriously threaten coral reef ecosystems worldwide. In Okinawa, solitary corals are an important feature of the coral community structure. While previous studies on the effects of ocean warming (OW), ocean acidification (OA) and its combination on larval survival focused on colonial coral species, the present study assessed the effect of high temperature on larvae from solitary corals. In this study, we examined the influence of OW (control = 28°C; control +3 = 31°C; control + 6 = 34°C) and OA (control, pCO2 = 400 to 500 μatm; medium, pCO2 = 1000 to 1300 μatm; high, pCO2 = 1700 to 2200 μatm) on the larval survival of two solitary corals, Fungia fungites and Lithophyllon repanda for eight days. Results showed that F. fungites was neither affected by OW, OA, nor its combination. Similarly, survival of L. repanda was not affected by OA however it was significantly affected by temperature. Temperature tolerance varies between species; L. repanda (+3°C above ambient) has lower tolerance than F. fungites (+6°C above ambient). This observation suggests that fungiid larvae had higher tolerance to elevated temperature stress relative to other scleractinian corals. With the projected increase in OW and OA in the future, fungiidsmay retain good potential to widely disperse and successfully recruit to natal and other neighbouring reefs.
The Mediterranean Sea ranks among the ocean regions warming fastest. There is evidence for impacts of climate change on marine Mediterranean organisms but a quantitative assessment is lacking. We compiled the impacts of warming reported in the literature to provide a quantitative assessment for the Mediterranean Sea. During the last three decades the summer surface temperature has increased 1.15 oC. Strong heat wave events have occurred in years 1994, 2003 and 2009. Impacts of warming are evident on growth, survival, fertility, migration and phenology of pelagic and benthic organisms, from phytoplankton to marine vegetation, invertebrates and vertebrates. Overall, 50 % of biological impacts in the Mediterranean Sea occur at summer surface temperature anomaly ≤ 4.5 ºC and at summer surface temperature of 27.5 ºC. The activation energy (geometric mean 1.58 ± 0.48 eV), the slope of the Arrhenius equation describing the temperature-dependence of biological processes, for the response of Mediterranean marine biota to warming reveals that these responses in the Mediterranean are far steepest than possibly explained by the direct effect of warming alone. The observations are biased toward the northern and western sectors of the basin, likely underestimating the impacts of warming in areas where warming is particularly intense.
Human pressures on the ocean are thought to be increasing globally, yet we know little about their patterns of cumulative change, which pressures are most responsible for change, and which places are experiencing the greatest increases. Managers and policymakers require such information to make strategic decisions and monitor progress towards management objectives. Here we calculate and map recent change over 5 years in cumulative impacts to marine ecosystems globally from fishing, climate change, and ocean- and land-based stressors. Nearly 66% of the ocean and 77% of national jurisdictions show increased human impact, driven mostly by climate change pressures. Five percent of the ocean is heavily impacted with increasing pressures, requiring management attention. Ten percent has very low impact with decreasing pressures. Our results provide large-scale guidance about where to prioritize management efforts and affirm the importance of addressing climate change to maintain and improve the condition of marine ecosystems.
What are the determinant factors of community assemblies in the most diverse ecosystem in the ocean? Coral reefs can be divided in continental (i.e., reefs that develop on the continental shelf, including siliciclastic reefs) and oceanic (i.e., far off the continental shelf, usually on volcanic substratum); whether or not these habitat differences impose community-wide ecological divergence or species exclusion/coexistence with evolutionary consequences, is unknown.
Studying Caribbean octocorals as model system, we determined the phylogenetic community structure in a coral reef community, making emphasis on species coexistence evidenced on trait evolution and environmental feedbacks. Forty-nine species represented in five families constituted the species pool from which a phylogenetic tree was reconstructed using mtDNA. We included data from 11 localities in the Western Caribbean (Colombia) including most reef types. To test diversity-environment and phenotype-environment relationships, phylogenetic community structure and trait evolution we carried out comparative analyses implementing ecological and evolutionary approaches.
Phylogenetic inferences suggest clustering of oceanic reefs (e.g., atolls) contrasting with phylogenetic overdispersion of continental reefs (e.g., reefs banks). Additionally, atolls and barrier reefs had the highest species diversity (Shannon index) whereas phylogenetic diversity was higher in reef banks. The discriminant component analysis supported this differentiation between oceanic and continental reefs, where continental octocoral species tend to have greater calyx apertures, thicker branches, prominent calyces and azooxanthellate species. This analysis also indicated a clear separation between the slope and the remaining habitats, caused by the presence or absence of Symbiodinium. K statistic analysis showed that this trait is conserved as well as the branch shape.
There was strong octocoral community structure with opposite diversity and composition patterns between oceanic and continental reefs. Even habitats with similar depths and overall environmental conditions did not share similar communities between oceanic and continental reefs. This indicates a strong regional influence over the local communities, probably due to water transparency differences between major reef types, i.e., oceanic vs. continental shelf-neritic. This was supported by contrasting patterns found in morphology, composition and evolutionary history of the species between atolls and reef banks.
The integration of ecological and evolutionary data is highly valuable for conservation planning. However, it has been rarely used in the marine realm, where the adequate design of marine protected areas (MPAs) is urgently needed. Here, we examined the interacting processes underlying the patterns of genetic structure and demographic strucuture of a highly vulnerable Mediterranean habitat-forming species (i.e. Paramuricea clavata (Risso, 1826)), with particular emphasis on the processes of contemporary dispersal, genetic drift, and col-onization of a new population. Isolation by distance and genetic discontinuities were found, and three genetic clusters were detected; each submitted to variations in the relative impact of drift and gene flow. No founder effect was found in the new population. The interplay of ecology and evolution revealed that drift is strongly impacting the smallest, most isolated populations, where partial mortality of individuals was highest. Moreover, the eco-evolutionary analyses entailed important conservation implications for P. clavata. Our study supports the inclusion of habitat-forming organisms in the design of MPAs and highlights the need to account for genetic drift in the development of MPAs. Moreover, it reinforces the importance of integrating genetic and demographic data in marine conservation.
For octocorals, sexual reproductive processes are fundamental to maintaining populations and influencing macroevolutionary processes. While ecological data on octocorals have lagged behind their scleractinian counterparts, the proliferation of reproductive studies in recent years now enables comparisons between these important anthozoan taxa. Here we review the systematic and biogeographic patterns of reproductive biology within Octocorallia from 182 species across 25 families and 79 genera. As in scleractinians, sexuality in octocorals appears to be highly conserved. However, gonochorism (89%) in octocorals predominates, and hermaphroditism is relatively rare, in stark contrast to scleractinians. Mode of reproduction is relatively plastic and evenly split between broadcast spawning (49%) and the 2 forms of brooding (internal 40% and external 11%). External surface brooding which appears to be absent in scleractinians may represent an intermediate strategy to broadcast spawning and internal brooding and may be enabled by chemical defenses. Octocorals tend to have large oocytes, but size bears no statistically significant relationship to sexuality, mode of reproduction, or polyp fecundity. Oocyte size is significantly associated with subclade suggesting evolutionary conservatism, and zooxanthellate species have significantly larger oocytes than azooxanthellate species. Based on biogeographic patterns, reef scleractinians appear to disperse longer distances over ecological timescales compared to reef octocorals. However, differences in reproductive characteristics between the 2 taxa do not offer an obvious explanation for these different biogeographic patterns.
The Mediterranean climate is expected to become warmer and drier during the twenty-first century. Mediterranean Sea response to climate change could be modulated by the choice of the socio-economic scenario as well as the choice of the boundary conditions mainly the Atlantic hydrography, the river runoff and the atmospheric fluxes. To assess and quantify the sensitivity of the Mediterranean Sea to the twenty-first century climate change, a set of numerical experiments was carried out with the regional ocean model NEMOMED8 set up for the Mediterranean Sea. The model is forced by air-sea fluxes derived from the regional climate model ARPEGE-Climate at a 50-km horizontal resolution. Historical simulations representing the climate of the period 1961-2000 were run to obtain a reference state. From this baseline, various sensitivity experiments were performed for the period 2001-2099, following different socio-economic scenarios based on the Special Report on Emissions Scenarios. For the A2 scenario, the main three boundary forcings (river runoff, near-Atlantic water hydrography and air-sea fluxes) were changed one by one to better identify the role of each forcing in the way the ocean responds to climate change. In two additional simulations (A1B, B1), the scenario is changed, allowing to quantify the socio-economic uncertainty. Our 6-member scenario simulations display a warming and saltening of the Mediterranean. For the 2070-2099 period compared to 1961-1990, the sea surface temperature anomalies range from +1.73 to +2.97 °C and the SSS anomalies spread from +0.48 to +0.89. In most of the cases, we found that the future Mediterranean thermohaline circulation (MTHC) tends to reach a situation similar to the eastern Mediterranean Transient. However, this response is varying depending on the chosen boundary conditions and socio-economic scenarios. Our numerical experiments suggest that the choice of the near-Atlantic surface water evolution, which is very uncertain in General Circulation Models, has the largest impact on the evolution of the Mediterranean water masses, followed by the choice of the socio-economic scenario. The choice of river runoff and atmospheric forcing both have a smaller impact. The state of the MTHC during the historical period is found to have a large influence on the transfer of surface anomalies toward depth. Besides, subsurface currents are substantially modified in the Ionian Sea and the Balearic region. Finally, the response of thermosteric sea level ranges from +34 to +49 cm (2070-2099 vs. 1961-1990), mainly depending on the Atlantic forcing.
Abstract Using empirical analyses of the effects of global climate change (GCC) and ocean acidification (OA) on the survival and calcification of early life stages of Pocillopora damicornis, we employed a demographic approach to forecast the consequences of GCC and OA on the population dynamics of this coral. We constructed a size-based demographic model using life-history tables and transition probabilities for a population in Southern Taiwan, and projected the population structure over *100 yr under scenarios of warming and acidification. The simulations incorporated stochastic variability of the parameters (±5 %), decline in larval survival due to increases in temperature and pCO2, modified growth rates due to rising temperature, and larval input from distant populations. In a closed population, an increase of pCO2 from 40.5 to 91.2 Pa reduces density, and an increase in temperature from 26 to 29 �C results in population extirpation within 100 yr. With a larval supply of 10 % from distant populations, the population persisted regardless of high temperature (?3 �C). These results indicate that: (1) populations of P. damicornis may be resistant to GCC and OA so long as it persists as part of a metapopulation capable of supplying larvae from spatially separated populations and (2) early life stages can regulate the population dynamics of P. damicornis.
Studies of the benthos between 30 and 60 m at Cape Armitage, McMurdo Sound. Antarctica, reveal an epifaunal community in which sponges and their asteroid and nudibranch predators predominate. Field experiments demonstrated that, with the exception of Mycale accrata, the growth rates of the sponges are too slow to measure in one year. Mycale, however, was observed to increase its mass as much as 67%. Because of its more rapid growth rate, Mycale appears to be the potential dominant in competition for substratum space, the resource potentially limiting to the sessile species. This conclusion is supported by observations of Mycale growing over and, in some cases, apparently having smothered many other sessile species representing at least three phyla. The densities and size frequency distributions of all the predators were measured; numerous feeding observations allowed an accurate appraisal of dietary compositions. Because of the predators' very slow consumption rates, however, direct measures of ingestion and its impact on prey populations were not possible. Estimates of the ingestion rates were derived from measurements of predator respiration rates, growth rates, and gonad growth. Data from the field surveys and the energetics studies suggest that Mycale is prevented from dominating the space resource by the predation of two asteroids. Perknaster fuscus antarcticus and Acodontaster conspicuus. Adult Perknaster specialize on Mycale, and the sponge provides a small proportion of the diet of A. conspicuus. Acodontaster conspicuus and the dorid nudibranch Austrodoris memurdensis are the most important predators on three species of rossellid sponges (Rossella racovitzae, R. nuda, and Scolymastra joubini). Despite this relatively heavy consumption and despite the fact that none of these sponges has a refuge in growth from potential mortality from A. conspicuus, very large standing crops of the rossellid sponges have accumulated. This accumulation appears to result from predation on larval and young A. conspicuus and Austrodoris by Odontaster validus, which is primarily a detrital feeder and apparently acts as a filter against the settlement and survival of the A. conspicuus and Austrodoris larvae. In addition, predation upon adult A. conspicuus by O. validus and the actinian urticinopsis antarcticus annually kills approximately 3.5% of the A. conspicuus population. This mortality exceeds the apparent rate at which A. conspicuus escape the larval filter.
Larval dispersal is the process enabling connectivity between populations of marine species with a sedentary adult stage. This transportation results from the coupling between flow and larval biological traits. This experimental study aims to quantify these larval biological traits, namely pelagic larval duration (PLD), buoyancy, and larval vertical motility behavior, for Corallium rubrum. Larval vertical motility behavior was split into active behavior (swimming) and passive behavior (free fall). A particle tracking routine was applied to video recordings of the active and passive motility behavior of C. rubrum larvae to quantify their free fall speeds, swimming activity frequency and swimming speeds. The experiment was repeated under different light conditions and at different larval ages. Pelagic larval duration (PLD) ranged from 16 days (95% survival) to 42 days (5% survival). Larvae exhibited negative buoyancy with a free fall speed decreasing linearly with age, at a velocity varying from – 0.09 ± 0.026 cm s-1 on day 1, to – 0.05 ± 0.026 cm s-1 on day 10. No significant difference was found either in the activity frequency or in the mean swim velocities during active periods for age (up to 12 days old) or under different light conditions. C. rubrum larvae maintained active swimming behavior for 82% of the time. This activity frequency was combined with age-varying free fall periods in the motility behavior model extrapolated up to 15 days old, resulting in a mean upward speed that increased from 0.045 cm s-1 (day 1) to 0.056 cm s-1 (day 15). This larval motility behavior, combined with the extended PLD, confers on C. rubrum larvae an unsuspectedly high dispersive potential in open waters.
Climate change will alter many aspects of the ecology of organisms, including dispersal patterns and population connectivity. Understanding these changes is essential to predict future species distributions, estimate potential for adaptation, and design effective networks of protected areas. In marine environments, dispersal is often accomplished by larvae. At higher temperatures, larvae develop faster, but suffer higher mortality, making the effect of temperature on dispersal difficult to predict. Here, we experimentally calibrate the effect of temperature on larval survival and settlement in a dynamic model of coral dispersal. Our findings imply that most reefs globally will experience several-fold increases in local retention of larvae due to ocean warming. This increase will be particularly pronounced for reefs with mean water residence times comparable to the time required for species to become competent to settle. Higher local retention rates strengthen the link between abundance and recruitment at the reef scale, suggesting that populations will be more responsive to local conservation actions. Higher rates of local retention and mortality will weaken connectivity between populations, and thus potentially retard recovery following severe disturbances that substantially deplete local populations. Conversely, on isolated reefs that are dependent on replenishment from local broodstock, increases in local retention may hasten recovery.
Many corals obtain their obligate intracellular dinoflagellate symbionts from the environment as larvae or juveniles. The process of symbiont acquisition remains largely unexplored, especially under stress. This study addressed both the ability of Fungia scutaria (Lamarck 1801) larvae to establish symbiosis with Symbiodinium sp. C1f while exposed to elevated temperature and the survivorship of aposymbiotic and newly symbiotic larvae under these conditions. Larvae were exposed to 27, 29, or 31°C for 1 h prior to infection, throughout a 3-h infection period, and up to 72 h following infection. Exposure to elevated temperatures impaired the ability of coral larvae to establish symbiosis and reduced larval survivorship. At 31°C, the presence of symbionts further reduced larval survivorship. As sea surface temperatures rise, coral larvae exposed to elevated temperatures during symbiosis onset will likely be negatively impacted, which in turn could affect the establishment of future generations of corals.
The precious octocoral, Corallium rubrum , endemic to the Mediterranean, has long been overexploited. A demographic approach to the conservation and management of this species would therefore be highly valuable. To this end, a coastal population of red coral was studied in detail. The population represents a true "genetic unit", as it is mainly "self-seeding". It is moreover gonocoric, and the sex ratio is significantly biased toward females. For this study, 4408 colonies, collected from 28, 300-cm 2 samples, were divided into 10 size (age) classes. Recruits represent about half the population. The frequency of colonies in each class decreases exponentially with colony size. On these bases, an "ad hoc" life history table has been updated to include the mortality and reproduction coefficients actually measured in the population. The major reproductive output is due to the first 3 reproductive classes (79%), while larger colonies, although having higher reproductive coefficients, are sparse and only account for a small portion of the population overall reproductive output. The ratio of larval survival to adult density found indicates that some density-dependent limitation of population growth is likely at play in the population under study. Such results will be important for understanding dynamics of red coral disturbed or exploited populations.
Climate change is one of the biggest emerging threats to marine biodiversity in the Mediterranean Sea. In this chapter, we focus on the recurrent and large scale mass mortality events (MMEs) induced by marine heatwaves (MHWs), and their immediate and long-term impacts on structural octocorals from highly diverse coralligenous communities. By combining an accurate characterization of present and expected thermal stress conditions in coastal seawater from the surface down to 40 m depth with the state of the art on demography, population genetics, and responses to thermal stress, we analyze the ongoing eco-evolutionary impacts and explore future trajectories of these emblematic Mediterranean communities.
Structured demographic models are among the most common and useful tools in population biology. However, the introduction of integral projection models (IPMs) has caused a profound shift in the way many demographic models are conceptualized. Some researchers have argued that IPMs, by explicitly representing demographic processes as continuous functions of state variables such as size, are more statistically efficient, biologically realistic, and accurate than classic matrix projection models, calling into question the usefulness of the many studies based on matrix models. Here, we evaluate how IPMs and matrix models differ, as well as the extent to which these differences matter for estimation of key model outputs, including population growth rates, sensitivity patterns, and life spans. First, we detail the steps in constructing and using each type of model. Second, we present a review of published demographic models, concentrating on size‐based studies, that shows significant overlap in the way IPMs and matrix models are constructed and analyzed. Third, to assess the impact of various modeling decisions on demographic predictions, we ran a series of simulations based on size‐based demographic data sets for five biologically diverse species. We found little evidence that discrete vital rate estimation is less accurate than continuous functions across a wide range of sample sizes or size classes (equivalently bin numbers or mesh points). Most model outputs quickly converged with modest class numbers (≥ 10), regardless of most other modeling decisions. Another surprising result was that the most commonly used method to discretize growth rates for IPM analyses can introduce substantial error into model outputs. Finally, we show that empirical sample sizes generally matter more than modeling approach for the accuracy of demographic outputs. Based on these results, we provide specific recommendations to those constructing and evaluating structured population models. Both our literature review and simulations question the treatment of IPMs as a clearly distinct modeling approach or one that is inherently more accurate than classic matrix models. Importantly, this suggests that matrix models, representing the vast majority of past demographic analyses available for comparative and conservation work, continue to be useful and important sources of demographic information.
Coral reefs are threatened worldwide by global climate change, manifested in anthropogenic ocean warming and acidification. Despite the importance of coral sexual reproduction for the continuity of coral reefs, our understanding of the extent of the impact of climate change on coral sexual reproduction, particularly on coral reproductive phenology and early life stages, is limited. Here, we experimentally examined the effects of predicted end-of-the-century seawater conditions on the sexual reproduction and photosynthetic capacity of a Red-Sea zooxanthellate octocoral, Rhytisma fulvum. Sexually mature colonies were exposed to ambient temperature and pH conditions and to Representative Concentration Pathway (RCP) conditions (4.5 and 8.5), five weeks prior to their expected surface-brooding event. The reproductive phenology of the colonies under the simulated seawater conditions was compared to that on the natural reef. In addition, subsequent planulae development and their metamorphosis into primary polyps under the same RCP conditions as their parent colonies were monitored in a running seawater system. The results reveal that both RCP conditions led to a change in the timing of onset of the surface-brooding event and its synchronicity. In contrast, the surface-brooding event under ambient conditions co-occurred with that of the in-situ reef colonies and maintained its synchrony. Similarly, planula survival and polyp metamorphosis rate were significantly reduced under both RCP conditions compared to propagules reared under ambient conditions. In addition, the photosynthetic capacity of the parent colonies under both RCPs showed a reduction relative to that under the ambient conditions in the experiment, suggesting a reduction in carbon fixation during the late stages of gametogenesis. While our findings indicate that octocoral reproductive phenology is affected by environmental changes, further work is required in order to elucidate the long-term implications for the R. fulvum population in the northern Red Sea.
Larvae released into the water column rely on chemical cues from the benthos for successful settlement. However , larval preference for substrates may be affected by rising seawater temperature brought about by global climate change. In this study, we examined the effect of elevated temperature on chemical cue preference by larvae of the scleractinian coral, Acropora tenuis, and the octocoral, Heliopora coerulea, collected from northwestern Philippines. At ambient temperature (28 • C), both H. coerulea and A. tenuis larvae showed preference for substrates containing either crustose coralline algae or crude ethanolic extracts from conspecific or congeneric corals. In contrast, at higher temperature (30 • C), greater preference was shown for substrates containing the crude extract from conspecific or congeneric corals. These results demonstrate that elevated temperature can change larval substrate preference, which will have downstream impacts on crucial biological processes, such as larval settlement and recruitment.
Sessile marine species such as Anthozoans act as ecosystem engineers due to their three-dimensional structure. Gorgonians, in particular, can form dense underwater forests that give shelter to other species increasing local biodiversity. In the last decades, several Mediterranean gorgonian populations have been affected by natural and anthropogenic impacts which drastically reduced their size. However, some species showed unexpected resilience, mainly due to the supply of new individuals. To understand the mechanisms underlying recovery processes, studies on the first life history stages (i.e. larval dispersal, settlement and recruitment) are needed. In tropical coral reefs, crustose coralline algae (CCA) are known to influence coral larvae habitat selection and settlement. This capacity however is not ubiquitous among CCA species and larvae of different coral species may have different preferences. The present work focuses on three Mediterranean gorgonians (Eunicella singularis, Paramuricea clavata and Corallium rubrum) with the objective of quantifying settlement and recruitment in presence of two common CCA species (Litophyllum stictaeforme and Litophyllum incrustans). Results showed that the presence of CCA activates earlier settlement in E. singularis and increases the density of recruits, with different trends for the three species. Our results suggest that CCA should be taken into account in the implementation of conservation strategies. Moreover, a deeper comprehension of settlement mechanisms could help improving restoration techniques based on sexual reproduction.
Recurrent thermal stress events and intensified precipitation alter the ocean environment resulting in the decline of coral populations. However, the influence of these changes on larval survival and settlement is not well understood. We examined the effect of salinity (15, 20, 25, 30, 35, and 40 ppt) and temperature (27 °C, 30 °C, and 33 °C) on settlement and survival of larvae of the octocoral, Heliopora coerulea. Larvae settled successfully at salinities from 25 to 30 ppt. On the other hand, larval survival and settlement decreased with increasing temperature. A combination of 25-35 ppt and 27-30 °C resulted in highest survival and settlement. These results indicate that early life stages of H. coerulea are negatively impacted by thermal stress but may be able to survive at reduced salinity. The wider tolerance range of H. coerulea larvae compared to most scleractinian larvae may thus contribute to the success of this coral on disturbed reef ecosystems.
1.Global warming and overexploitation both threaten the integrity and resilience of marine ecosystems. Many calls have been made to at least partially offset climate change impacts through local conservation management. However, a mechanistic understanding of the interactions of multiple stressors is generally lacking for habitat‐forming species; preventing the development of sound conservation strategies. 2.We examined the effectiveness of no‐take marine protected areas (MPAs) at enhancing structural complexity and resilience to climate change on populations of an overexploited and long‐lived octocoral. We used long‐term data over eight populations, subjected to varying levels of disturbances, and Integral Projection Models to understand how the interaction between overfishing and mass‐mortality events shapes the stochastic dynamics of the Mediterranean red coral Corallium rubrum. 3.MPAs largely reduced colony partial mortality (i.e. shrinkage), enhancing the structural complexity of coral populations. However, there were no significant differences in individual mortality or population growth rates between protected and exploited populations. In contrast, warming had detrimental consequences for the long‐term viability of red coral populations, driving steady declines and potential local extinctions due to sharp effects in survival rates. Stochastic demographic models revealed only a weak compensatory effect of MPAs on the impacts of warming. 4.Policy implications. Our results suggest that marine protected areas (MPAs) are an effective local conservation tool for enhancing the structural complexity of red coral populations. However, MPAs may not be enough to ensure red coral's persistence under future increases in thermal stress. Accordingly, conservation strategies aiming to ensure the persistence and functional role of red coral populations should include management actions at both local (well‐enforced MPAs) and global scales (reductions in greenhouse gas emissions). Finally, this study unravels the divergent demographic consequences that can arise from multiple stressors and highlights the key role of demography in better understanding and predicting the consequences of combined impacts for vulnerable ecosystems. This article is protected by copyright. All rights reserved.
Predicted increases in sea-surface temperatures due to climate change are likely to alter the physiology of marine organisms and ultimately influence the distribution and abundance of their populations. The consequences of increased temperatures for marine species, including decreased survival and altered rates of development, growth and settlement, are well known and often attributed to imbalances between energy supply and demand. To test this hypothesis, we calibrated the effect of temperature on rates of survival and lipid depletion for larvae of the common stony coral Acropora tenuis over a 7 °C temperature range. Temperature had a pronounced, linearly increasing effect on larval mortality, with a sixfold decrease in median survival time. Contrary to expectation, however, temperature had a quasi-parabolic effect on lipid use; rates declined as temperatures either increased above or decreased below the ambient temperature at the time of spawning. This contrasts with previous work suggesting that increased energy depletion is the cause of larval mortality at higher temperatures. Our results highlight the sensitivity of coral larvae to temperature and have implications for dispersal potential because fewer larvae will survive to disperse. Such projected declines in connectivity among coral populations are likely to undermine reef resilience.
This study investigates the energetic investment during spawning of two Mediterranean gorgonians characterized by different reproductive strategies: Corallium rubrum (internal brooder) and Paramuricea clavata (surface brooder). Sexual products (number of oocytes and spermatic sacs) were quantified, and biochemical characteristics (lipid content and free fatty acid content and composition) were determined to investigate the parental energetic investment and demand in reproduction. Results suggested that the majority of the energetic cost was due to reproductive activity (i.e., gametogenesis and spawning). The two species exhibited different life history strategies, with P. clavata investing more energy in reproduction than C. rubrum. However, P. clavata is reproductively more sensitive to inter-annual changes in environmental conditions.
The behaviour of Mediterranean octocoral planulae was studied in light-dark situations and in a light gradient. Larvae of Eunicella singularis (Esper, 1794) reacted photopositively but it is uncertain which mechanism (klinotaxis or klinokinesis) determines this property. The blind larvae probably possess a dermal light sense, but it cannot be excluded that the yolk contains photosensitive carotenoids while the symbiotic zooxanthellae may also play a role. The photopositive behaviour of planulae of this species explains some aspects of the distributional ecology of adult colonies. It was also found that for the induction of settlement and metamorphosis the chemical properties of a given substratum seem to be far more important than its roughness. Larvae of Corallium rubrum (Linnaeus, 1758) are geonegative and indifferent to light. This latter fact is surprising, since in nature the colonies are exclusively found in dark places. It is supposed, therefore, that tolerance of the colonies rather than larval choice determines light-dependent zonation of this species in nature.
Interactions between organisms are a major determinant of the distribution and abundance of species. Ecology textbooks (e.g., Ricklefs 1984, Krebs 1985, Begon et al. 1990) summarise these important interactions as intra- and interspecific competition for abiotic and biotic resources, predation, parasitism and mutualism. Conspicuously lacking from the list of key processes in most text books is the role that many organisms play in the creation, modification and maintenance of habitats. These activities do not involve direct trophic interactions between species, but they are nevertheless important and common. The ecological literature is rich in examples of habitat modification by organisms, some of which have been extensively studied (e.g. Thayer 1979, Naiman et al. 1988).
The combined effects of disparate impacts on population health are a continuing problem in risk assessment and management for threatened species. Populations of red gorgonian Paramuricea clavata in the NW Mediterranean Sea are threatened both by chronic and localized increases in mortality due to high diving activity and by widespread but episodic mass mortality events related to climatic anomalies. Using demographic data obtained from 3 populations (2 under contrasting levels of diving and one affected by a 1999 mass mortality event), we developed size-structured matrix models to forecast the long-term consequences of both disturbances and their combined effects. When we considered only the effects of diver damage, our results showed that population stability could be achieved with an increase in the annual survival of adult colonies of between 3 and 7%, demonstrating the need for diving reduction in the study locations, where there are estimated to be between 30000 and 70000 dives yr(-1). Modeling the effects of mass mortality events alone showed a low annual population growth rate (0.886) and near certain extinction risk over even short time scales. Considering these 2 types of impacts together, we found that the effects of mass mortality events aggravate the decline in gorgonian populations subjected to high diving impact, reaching the extinction threshold after 36 to 55 yr under the actual frequency of mass mortality events. Simulated reduction of diving effects dramatically increased the time to quasi-extinction for populations subjected to realistic frequencies of mass mortality events. Our simulations reveal the need of management actions to ensure the gorgonian viability in the face of climate change, and suggest that management of more controllable impacts, such as diving, can help buffer populations against the less controllable effects of climate change.
Satellite observations from 1985-2006 indicate that in the last 2 decades the temperature in the upper layer of the Mediterranean Sea has been increasing at an average (+/- SD) rate of 0.03 +/- 0.008 degrees C yr(-1) for the western basin and 0.05 +/- 0.009 degrees C yr(-1) for the eastern basin. The increases in temperature are not constant throughout the year but occur primarily during May, June and July. Maximum increases of 0.16 degrees C yr(-1) are found in June in the Tyrrhenian, Ligurian and Adriatic Seas and close to the African coast. The Aegean Sea shows maximum change in sea surface temperature during August. Only the statistically significant results are presented.