Increasing Seawater Temperature Research Articles

Spatiotemporal Dynamics of Vibrio spp. within the Sydney Harbour Estuary.

Vibrio are a genus of marine bacteria that have substantial environmental and human health importance, and there is evidence that their impact may be increasing as a consequence of changing environmental conditions. We investigated the abundance and composition of the Vibrio community within the Sydney Harbour estuary, one of the most densely populated coastal areas in Australia, and a region currently experiencing rapidly changing environmental conditions. Using quantitative PCR (qPCR) and Vibrio-specific 16S rRNA amplicon sequencing approaches we observed significant spatial and seasonal variation in the abundance and composition of the Vibrio community. Total Vibrio spp. abundance, derived from qPCR analysis, was higher during the late summer than winter and within locations with mid-range salinity (5–26 ppt). In addition we targeted three clinically important pathogens: Vibrio cholerae, V. Vulnificus, and V. parahaemolyticus. While toxigenic strains of V. cholerae were not detected in any samples, non-toxigenic strains were detected in 71% of samples, spanning a salinity range of 0–37 ppt and were observed during both late summer and winter. In contrast, pathogenic V. vulnificus was only detected in 14% of samples, with its occurrence restricted to the late summer and a salinity range of 5–26 ppt. V. parahaemolyticus was not observed at any site or time point. A Vibrio-specific 16S rRNA amplicon sequencing approach revealed clear shifts in Vibrio community composition across sites and between seasons, with several Vibrio operational taxonomic units (OTUs) displaying marked spatial patterns and seasonal trends. Shifts in the composition of the Vibrio community between seasons were primarily driven by changes in temperature, salinity and NO2, while a range of factors including pH, salinity, dissolved oxygen (DO) and NOx (Nitrogen Oxides) explained the observed spatial variation. Our evidence for the presence of a spatiotemporally dynamic Vibrio community within Sydney Harbour is notable given the high levels of human use of this waterway, and the significant increases in seawater temperature predicted for this region.

Effects of warm acclimation on physiology and gonad development in the sea urchin Evechinus chloroticus

The physiology of the New Zealand sea urchin Evechinus chloroticus was evaluated through feeding, respiration, growth and gonad growth in adult animals acclimated for 90days at 18°C (annual mean temperature) and 24°C (ambient summer temperature (21°C) +3°C). Measured parameters with representative rates of assimilation efficiency were used to calculate scope for growth (SfG) for each treatment. All physiological parameters were negatively affected at 24°C, showing a decrease in feeding rate which coincided with negative growth and gonad development at the end of the acclimation period, and a decrease in respiration rate suggesting metabolic depression. Histology of gonad samples after the acclimation period also showed no gametic material in animals acclimated at 24°C. All animals acclimated at 24°C had negative growth, differing from the calculated SfG which indicated that the animals had sufficient energy for production. The results suggest that calculated SfG in echinoderms should be used together with actual measurements of growth in individuals as, by itself, SfG may underestimate the actual effect of ocean warming when animals are exposed to stressful conditions. Overall, considering the total loss of reproductive output observed in E. chloroticus at higher temperatures, an increase in seawater temperature could dramatically influence the persistence of northern populations of this species, leading to flow-on effects in the subtidal ecosystem.

Relative summer abundances and distribution of Pseudocalanus spp. (Copepoda: Calanoida) adults in relation to environmental variables in the Nordic Seas and Svalbard fjords

North Atlantic average sea surface temperatures have increased since the 1970s, and how the marine environment is responding to the temperature increase is of considerable interest. Several zooplankton taxa have been reported to have undergone shifts in distributional ranges driven by climate change. We present a study on interannual variability of adult Pseudocalanus spp. from the Norwegian Sea and two fjords of Spitsbergen, collected between 2003 and 2009. Species are identified based on the combination of morphological features and molecular methods (mitochondrial cytochrome oxidase I gene, COI and nuclear internal transcribed spacer 1, ITS 1 sequences). Based on multivariate statistics, our observations suggest that Pseudocalanus species differ markedly in their environmental preferences; three species appear to be oceanic: P. elongatus is associated with relatively high temperatures and shares domain with P. minutus, P. moultoni tolerates a wide range of temperatures and is widely distributed, while P. acuspes is a coastal/shelf species that is strongly associated with cold and less saline waters. We conclude that with a climate change and increasing sea water temperatures, P. elongatus is likely to shift its distribution northward; for P. acuspes, it may result in smaller populations in the future; while P. minutus and P. moultoni may not be affected.

Expression pattern of heat shock proteins during acute thermal stress in the Antarctic sea urchin, Sterechinus neumayeri

Antarctic marine organisms have evolved a variety of physiological, life-history and molecular adaptations that allow them to cope with the extreme conditions in one of the coldest and most temperature-stable marine environments on Earth. The increase in temperature of the Southern Ocean, product of climate change, represents a great challenge for the survival of these organisms. It has been documented that some Antarctic marine invertebrates are not capable of generating a thermal stress response by means of an increase in the synthesis of heat shock proteins, which could be related with their low capacity for acclimatization. In order to understand the role of heat shock proteins as a compensatory response in Antarctic marine species to projected scenarios of increased seawater temperatures, we assessed the expression of the genes Hsp90, Grp78, Hyou1 and Hsc70 in the Antarctic sea urchin Sterechinus neumayeri under three thermal treatments (1 °C, 3 °C and 5 °C), for a period of exposure of 1, 24 and 48 h. The results obtained showed that these genes were expressed themselves in all of the tissues analyzed in a constitutive form. During acute thermal stress, an overexpression of the Hsp90, Grp78 and Hyou1 genes was observed in coelomocyte samples at 3 °C after 48 h, while in esophageal samples, an increase in Hsp90 and Grp78 expression was observed after 48 h. Thermal stress at 5 °C, in general, did not produce a significant increase in the expression of the genes that were studied. The expression of Hsp70 did not show modifications in its expression as a result of thermal stress. S. neumayeri is capable of overexpressing stress proteins as a result of thermal stress, however, this response is delayed and to a lesser degree compared to other Antarctic or temperate species. These results indicate that adult individuals could cope with the expected impacts caused by an increase in coastal sea temperatures in the Southern Ocean.

In hospite Symbiodinium photophysiology and antioxidant responses in Acropora muricata on a coast-reef scale: implications for variable bleaching patterns

Understanding susceptibility to bleaching may indicate how corals cope with increasing seawater temperatures resulting from climate change. In Belle Mare lagoon, Mauritius, Acropora muricata colonies at reef sites but not near the coast exhibited bleaching. We compared seawater temperatures and light intensity both on a summer day and a winter day at a reef station and a near-coast station. The total phenolic contents, non-enzymatic antioxidant activities of the coral holobiont, in situ photophysiological parameters of in hospite Symbiodinium as well as their cladal diversity were assessed. Both sites had comparable maximum temperatures but fluctuations were higher in the near-coast station (2–3 °C) compared to the reef station (1–1.5 °C) on both days. Light intensity was higher on the summer day than the winter day at both stations. Higher total phenolic contents and ferrous reducing antioxidant potential were observed in near-coast colonies than in reef colonies on the summer day. Only Clade A-like Symbiodinium sp. variants were detected at both locations, but higher maximum relative electron transport rates and maximum non-photochemical quenching were measured in near-coast colonies. Our data show that the near-coast colonies exhibited enhanced photophysiological responses, antioxidant activities and increased total phenolic contents in response to higher thermal and light fluctuations. This acclimatization may explain the variability in bleaching along a coast-reef scale.

Ocean warming and elevated carbon dioxide: multiple stressor impacts on juvenile mussels from southern Chile

Abstract The combined effect of increased ocean warming and elevated carbon dioxide in seawater is expected to have significant physiological and ecological consequences at many organizational levels of the marine ecosystem. In the present study, juvenile mussels Mytilus chilensis were reared for 80 d in a factorial combination of two temperatures (12 and 16°C) and three pCO2 levels (380, 700, and 1000 µatm). We investigated the combined effects of increasing seawater temperature and pCO2 on the physiological performance (i.e. feeding, metabolism, and growth). Lower clearance rate (CR) occurred at the highest pCO2 concentration (1000 µatm) compared with the control (380 µatm) and with the intermediate concentration of pCO2 (700 µatm). Conversely, CR was significantly higher at 16°C than at 12°C. Significant lower values of oxygen uptake were observed in mussels exposed to 1000 µatm pCO2 level compared with those exposed to 380 µatm pCO2. Scope for growth (SFG) was significantly lower at the highest pCO2 concentration compared with the control. Mussels exposed to 700 µatm pCO2 did not show significantly different SFG from the other two pCO2 treatments. SFG was significantly higher at 16°C than at 12°C. This might be explained because the experimental mussels were exposed to temperatures experienced in their natural environment, which are within the range of thermal tolerance of the species. Our results suggest that the temperature rise within the natural range experienced by M. chilensis generates a positive effect on the processes related with energy gain (i.e. feeding and absorption) to be allocated to growth. In turn, the increase in the pCO2 level of 1000 µatm, independent of temperature, adversely affects this species, with significantly reduced energy allocated to growth (SFG) compared with the control treatment.

Cardiorespiratory responses in an Antarctic fish suggest limited capacity for thermal acclimation.

Polar fishes are at high risk from increasing seawater temperatures. Characterising the physiological responses to such changes may both clarify mechanisms that permit life under extreme conditions and identify limitations in the response to continued global warming. We hypothesised that Notothenia coriiceps would show physiological compensation after an acute exposure to 5°C, and following 6 weeks warm acclimation, compared with ambient temperature (0°C). However, initial tachycardia (22.4±2.8 versus 12.8±1.1 min(-1); P<0.01) was not reversed by acclimation (21.0±1.9 min(-1)). Hyperventilation (45.5±3.1 versus 21.4±2.4 breaths min(-1); P<0.001) showed a modest reduction following acclimation (38.0±2.9 min(-1); P<0.05), while resting oxygen consumption (0.52±0.08 mmol kg(-1)h(-1)) was acutely increased at 5°C (1.07±0.10 mmol kg(-1)h(-1); P<0.001) but unchanged with acclimation. Autonomic blockade showed initial responses were mainly of vagal origin, with little subsequent withdrawal or recovery in long-term heart rate variability after 6 weeks. Given the limited cardiorespiratory capacity to withstand sustained warming, effective physiological compensation probably requires a more prolonged acclimation period.

Growth of the sword razor (Ensis magnus) early stages: modelling juvenile seasonal growth

Growth of the sword razor (Ensis magnus) early stages: modelling juvenile seasonal growth

Performance analysis of an organic Rankine cycle for a reverse osmosis desalination system using zeotropic mixtures

The use of low-grade thermal energy to power desalination processes by coupling an organic Rankine cycle (ORC) with seawater reverse osmosis (RO) is a promising technology to reduce the cost and environmental impact associated with the use of fossil fuel sources. A low-enthalpy geothermal ORC for a RO desalination system with zeotropic mixtures is proposed. Zeotropic mixtures can improve the thermodynamic performance of ORC systems owing to their excellent temperature glide characteristics during evaporation and condensing processes. A case study with butane/pentane (R600/R601) and butane/isopentane (R600/R601a) is investigated, aiming to analyze the effect of seawater temperature increase on the cycle performance. In the temperature range investigated, the power profit first increases rapidly then decreases. For the mixture R600/R601 at a mole fraction of 0.9/0.1, the maximum power profit value of 29.3kW occurred with the temperature rise of 26K, and for the mixture R600/R601a at a mole fraction of 0.9/0.1, the maximum power profit value of 30.9kW occurred with the temperature rise of 27K. The results show that, it is necessary to consider the effects of seawater temperature increase in both the ORC and RO simultaneously to design the ORC-RO system.

Global change and climate‐driven invasion of the Pacific oyster (Crassostrea gigas) along European coasts: a bioenergetics modelling approach

AbstractAimThe spread of non‐indigenous species in marine ecosystems world‐wide is one of today's most serious environmental concerns. Using mechanistic modelling, we investigated how global change relates to the invasion of European coasts by a non‐native marine invertebrate, the Pacific oyster Crassostrea gigas.LocationBourgneuf Bay on the French Atlantic coast was considered as the northern boundary of C. gigas expansion at the time of its introduction to Europe in the 1970s. From this latitudinal reference, variations in the spatial distribution of the C. gigas reproductive niche were analysed along the north‐western European coast from Gibraltar to Norway.MethodsThe effects of environmental variations on C. gigas physiology and phenology were studied using a bioenergetics model based on Dynamic Energy Budget theory. The model was forced with environmental time series including in situ phytoplankton data, and satellite data of sea surface temperature and suspended particulate matter concentration.ResultsSimulation outputs were successfully validated against in situ oyster growth data. In Bourgneuf Bay, the rise in seawater temperature and phytoplankton concentration has increased C. gigas reproductive effort and led to precocious spawning periods since the 1960s. At the European scale, seawater temperature increase caused a drastic northward shift (1400 km within 30 years) in the C. gigas reproductive niche and optimal thermal conditions for early life stage development.Main conclusionsWe demonstrated that the poleward expansion of the invasive species C. gigas is related to global warming and increase in phytoplankton abundance. The combination of mechanistic bioenergetics modelling with in situ and satellite environmental data is a valuable framework for ecosystem studies. It offers a generic approach to analyse historical geographical shifts and to predict the biogeographical changes expected to occur in a climate‐changing world.

해수 온도에 따른 S355ML 강재의 부식 경향 평가

Machinery Technology Research Team, Korean Register, 36, Myeongji ocean city 9-ro, Gangseo-gu, Busan, Republic of Korea, 46762(Received June 16, 2015; Revised October 08, 2015; Accepted October 13, 2015)Corrosion is of greatest concern for metallic materials exposed to corrosive seawater or aggressive marine atmospheres. Marine structures and components made of metallic materials incur an initial cost and additional large costs for corrosion control and maintenance. There have been worldwide efforts to minimize marine corrosion and extend service life of the materials. It is believed that various factors are associated with corrosion of marine grade metallic materials, particularly the temperature of the solution affecting the corrosion rate by changing dissolved oxygen solubility and concentrations of chloride. In the present study, the electrochemical characteristics of S355ML steel are investigated to identify corrosion acceleration tendencies with changes in solution temperature under marine environments. It was found that increasing seawater temperature, promoted not only activation of chloride ion transfer, but also the formation of porous Fe(OH)

A preliminary analysis of fishery resource exhaustion in the context of biodiversity decline

Marine biodiversity in almost all oceans is being threatened at the genetic, species, and ecosystem levels. The marine ecosystem is being degraded and the extinction rate of marine organisms has accelerated. In this paper, the potential causes of fishery resource exhaustion in the East China Sea are analyzed, including the change in the stoichiometric composition of seawater with regard to the concentrations of N and P, toxic effects of marine pollution, marine habitat destruction, increased seawater temperatures caused by climate warming, ocean acidification, pressure from overfishing, and the spread of marine pathogenic bacteria. It is believed that the factors mentioned above have significant impact on the exhaustion of fishery resources in the East China Sea. However, considering the cumulative, synergistic, and superimposed effects as well as the amplification effects resulting from their interactions, the actual risk of ecological extinction of marine organisms might be even more severe than that previously estimated. Hence, ecosystem management and research focused on a single risk factor or influencing factor is not enough to prevent marine ecosystem degradation and fishery resource exhaustion. A comprehensive, systematic, effective, and ecosystem-based management policy is imperative for healthy and sustainable fishery development in the East China Sea.

Temporal variability in epifaunal assemblages associated with temperate gorgonian gardens

The present study is one of the few that investigate the temporal variability of epifaunal assemblages associated with coral species, particularly the octocorals Eunicella gazella and Leptogorgia lusitanica in south Portugal. The results suggest time rather than colony size as a primary driver of the ecological patterns of these assemblages, which were dominated by amphipods, molluscs and polychaetes. Temporal variability was linked to changes in environmental parameters, namely temperature, chlorophyll a and particulate organic carbon. Hence, temporal variability must be taken into account for the design of future biodiversity assessment studies, as different patterns may be observed depending on the sampling time. Associated epifaunal assemblages were consistently dominated by resident species (i.e. species present in all sampling periods) and a peak of rare species was observed in the transition from spring to summer following the increase in seawater temperature. Turnover was particularly high in the transition between the spring and summer periods. In both hosts, turnover was higher in the small sized colonies, which harboured less diverse and less abundant assemblages that also differed from those inhabiting larger size colonies. The high levels of diversity associated with gorgonian colonies highlight the need for the conservation of this priority habitat.

An empirically derived inorganic sea spray source function incorporating sea surface temperature

Abstract. We have developed an inorganic sea spray source function that is based upon state-of-the-art measurements of sea spray aerosol production using a temperature-controlled plunging jet sea spray aerosol chamber. The size-resolved particle production was measured between 0.01 and 10 μm dry diameter. Particle production decreased non-linearly with increasing seawater temperature (between −1 and 30 °C) similar to previous findings. In addition, we observed that the particle effective radius, as well as the particle surface, particle volume and particle mass, increased with increasing seawater temperature due to increased production of particles with dry diameters greater than 1 μm. By combining these measurements with the volume of air entrained by the plunging jet we have determined the size-resolved particle flux as a function of air entrainment. Through the use of existing parameterisations of air entrainment as a function of wind speed, we were subsequently able to scale our laboratory measurements of particle production to wind speed. By scaling in this way we avoid some of the difficulties associated with defining the "white area" of the laboratory whitecap – a contentious issue when relating laboratory measurements of particle production to oceanic whitecaps using the more frequently applied whitecap method. The here-derived inorganic sea spray source function was implemented in a Lagrangian particle dispersion model (FLEXPART – FLEXible PARTicle dispersion model). An estimated annual global flux of inorganic sea spray aerosol of 5.9 ± 0.2 Pg yr−1 was derived that is close to the median of estimates from the same model using a wide range of existing sea spray source functions. When using the source function derived here, the model also showed good skill in predicting measurements of Na+ concentration at a number of field sites further underlining the validity of our source function. In a final step, the sensitivity of a large-scale model (NorESM – the Norwegian Earth System Model) to our new source function was tested. Compared to the previously implemented parameterisation, a clear decrease of sea spray aerosol number flux and increase in aerosol residence time was observed, especially over the Southern Ocean. At the same time an increase in aerosol optical depth due to an increase in the number of particles with optically relevant sizes was found. That there were noticeable regional differences may have important implications for aerosol optical properties and number concentrations, subsequently also affecting the indirect radiative forcing by non-sea spray anthropogenic aerosols.

Host Coenzyme Q Redox State Is an Early Biomarker of Thermal Stress in the Coral Acropora millepora.

Bleaching episodes caused by increasing seawater temperatures may induce mass coral mortality and are regarded as one of the biggest threats to coral reef ecosystems worldwide. The current consensus is that this phenomenon results from enhanced production of harmful reactive oxygen species (ROS) that disrupt the symbiosis between corals and their endosymbiotic dinoflagellates, Symbiodinium. Here, the responses of two important antioxidant defence components, the host coenzyme Q (CoQ) and symbiont plastoquinone (PQ) pools, are investigated for the first time in colonies of the scleractinian coral, Acropora millepora, during experimentally-induced bleaching under ecologically relevant conditions. Liquid chromatography-mass spectrometry (LC-MS) was used to quantify the states of these two pools, together with physiological parameters assessing the general state of the symbiosis (including photosystem II photochemical efficiency, chlorophyll concentration and Symbiodinium cell densities). The results show that the responses of the two antioxidant systems occur on different timescales: (i) the redox state of the Symbiodinium PQ pool remained stable until twelve days into the experiment, after which there was an abrupt oxidative shift; (ii) by contrast, an oxidative shift of approximately 10% had occurred in the host CoQ pool after 6 days of thermal stress, prior to significant changes in any other physiological parameter measured. Host CoQ pool oxidation is thus an early biomarker of thermal stress in corals, and this antioxidant pool is likely to play a key role in quenching thermally-induced ROS in the coral-algal symbiosis. This study adds to a growing body of work that indicates host cellular responses may precede the bleaching process and symbiont dysfunction.

The relationship between heterotrophic feeding and inorganic nutrient availability in the scleractinian coralT. reniformisunder a short-term temperature increase

Worldwide increase in seawater temperature represents one of the major threats affecting corals, which experience bleaching, and thereafter a significant decrease in photosynthesis and calcification. The impact of bleaching on coral physiology may be exacerbated when coupled with eutrophication, i.e., increasing plankton, inorganic nutrient concentrations, sedimentation and turbidity due to coastal urbanization. Whereas zooplankton provision (heterotrophy) may alleviate the negative consequences of thermal stress, inorganic nutrient supply may exacerbate them, which creates a paradox. Our experimental study aims to disentangle the effects of these two components of eutrophication on the physiological response of Turbinaria reniformis subject to normal and to a short-term temperature increase. Additionally, three different inorganic nutrient ratios were tested to assess the influence of nutrient stoichiometry on coral physiology: control (ambient SW 0.5 μM N and 0.1 μM P), N only (ambient + 2 μM N) and N + P (ambient + 2 μM N and + 0.5 μM P). Our results show a deleterious effect of a 2 μM nitrate enrichment alone (N) on coral photosynthetic processes under thermal stress as well as on calcification rates when associated with heterotrophy. On the contrary, a coupled nitrate and phosphorus enrichment (N + P) maintained coral metabolism and calcification during thermal stress and enhanced them when combined with heterotrophy. Broadly, our results shed light on the tight relationship existing between inorganic nutrient availability and heterotrophy. Moreover, it assesses the relevance of N: P stoichiometry as a determining factor for the health of the holobiont that may be adapted to specific nutrient ratios in its surrounding environment.

갈조류 감태(Ecklonia cava)의 포자체와 배우체 생장에 영향을 주는 수온과 pCO&lt;sub&gt;2&lt;/sub&gt; 농도의 상호작용

To examine the effects of increased CO₂ concentration and seawater temperature on the photosynthesis and growth of forest forming Ecklonia cava (Laminariales, Phaeophyta), sporophytic discs and gametophytes were cultured under three pCO₂ concentrations (380, 750, 1000 ppm), four temperatures (5, 10, 15, 20℃ for sporophytes; 10, 15, 20, 25℃ for gametophytes), and two irradiance levels (40, 80 μmol photons m ?2 s ?1 ) for 5 days. Photosynthetic parameter values (ETR max , E k , and α) were generally higher as sporophytic discs were grown under low temperature and increased CO₂ concentration at 750 ppm. However, photosynthesis of Ecklonia sporophytes was severely inhibited under a combination of high temperature (20℃) and 1000 ppm CO₂ concentration at the two photon irradiance levels. The growth of gametophytes was maximal at the combination of 380 ppm (present seawater CO₂ concentration) and 25℃. Minimal growth of gametophytes occurred at enriched pCO₂ concentration levels (750, 1000 ppm) and high temperature of 25℃. The present results imply that climate change which is increasing seawater temperature and pCO₂ concentration might diminish Ecklonia cava kelp beds because of a reduction in recruitments caused by the growth inhibition of gametophytes at high pCO₂ concentration. In addition, the effects of increased temperature and pCO₂ concentration were different between generations - revealing an enhancement in the photosynthesis of sporophytes and a reduction in the growth of gametophytes.

Carbonic anhydrase activity changes in response to increased temperature and pCO2 in Symbiodinium–zoanthid associations

Carbon dioxide (CO2) makes up less than 1% of dissolved inorganic carbon (DIC) in the ocean. To acquire carbon dioxide for photosynthesis, many marine autotrophs rely on the enzyme carbonic anhydrase (CA) to catalyze the conversion of bicarbonate ions (HCO3−) to CO2. In zoanthids and other cnidarians with Symbiodinium spp. endosymbionts, CA is essential for transporting CO2 to symbionts for photosynthesis. Temperature and ambient DIC affect CA activity, therefore, increased sea water temperatures and ocean acidification (OA) will alter CO2 transport in symbiotic cnidarians. However, these effects are likely to be species specific for both host and symbiont, as different cnidarians and Symbiodinium spp. vary in their mechanisms of DIC transport and utilization of CA. In this study, host and symbiont CA activity in the zoanthids Palythoa sp. and Zoanthus sp. varied with thermal stress and low pH. Increased temperature inhibited algal, but not host CA activity in Zoanthus sp. polyps with A4 Symbiodinium, while temperature had no effect on CA activity in Palythoa sp. with C1 Symbiodinium. High pCO2/low pH altered algal CA activity in both zoanthid species, but host CA activity changed in Zoanthus sp. polyps only. This study shows that thermal stress and OA induce species-specific changes in CA activity, and thus DIC transport in symbiotic zoanthids. These observations suggest that CA activity in symbiotic cnidarians will be altered by climate conditions predicted for the future, and for some cnidarians, changes in CA activity may inhibit photosynthesis.

Effect of elevated temperature on fecundity and reproductive timing in the coral Acropora digitifera.

The synchrony of spawning is of paramount importance to successful coral reproduction. The precise timing of spawning is thought to be controlled by a set of interacting environmental factors, including regional wind field patterns, timing of the sunset, and sea surface temperatures (SST). Climate change is resulting in increased SST, which is causing physiological stress in corals and could also be altering spawning synchrony and timing. In this study, we examined the effect of increasing seawater temperature by 2°C for 1 month prior to the predicted spawning time on reproduction in the coral Acropora digitifera. This short period of elevated temperature caused spawning to advance by 1 day. In animals incubated at elevated temperature, egg number per egg bundle did not change, however, egg volume significantly decreased as did sperm number. Our results indicate that temperature is acting both as a proximate cue to accelerate timing and as a stressor on gametogenesis to reduce fecundity. This finding suggests that increasing SSTs could play a dramatic role in altering reproductive timing and the success of corals in an era of climate change.

Asynchronous reproduction and multi-spawning in the coral-excavating sponge Cliona delitrix

Cliona delitrix is one of the most abundant and destructive coral-excavating sponges on Caribbean reefs. However, basic aspects of its reproductive biology, which largely determine the species propagation potential, remain unknown. A 2-year study (October 2009 to September 2011) was conducted to determine the reproductive cycle and gametogenesis of a C. delitrix population located in a shallow reef in Florida, USA. Mesohyl tissue collected from randomly chosen and tagged sponge individuals was sampled one to several times a month, and analysed by light and transmission electron microscopy (TEM). Cliona delitrix is oviparous and gonochoric, except for a few simultaneous hermaphroditic individuals. The C. delitrix reproductive cycle in Florida is from April to December, and is triggered by an increase in seawater temperature to 25°C. Oogenesis and spermatogenesis were asynchronous among individuals; with different cohorts of oocytes co-occurring in females, and spermatic cysts in males. Granulose cells acted as nurse cells, contributing to the growth and maturation of both female and male gametes. Spawning of gametes was not always synchronized with full moon phase. Unlike most other oviparous sponges, the reproductive cycle of C. delitrix is versatile and includes multiple spawning events during the summer of each year. This characteristic maximizes sponge propagation on coral reefs during the warmer months of the year, particularly when thermal stress induces coral mortality. This aspect, combined with its success on polluted areas, make C. delitrix a suitable bioindicator of coral reef health.