Effects of temperature and UV radiation increases on the photosynthetic efficiency in four scleractinian coral species

Experiments were performed on coral species containing clade A (Stylophora pistillata, Montipora aequituberculata) or clade C (Acropora sp., Pavona cactus) zooxanthellae. The photosynthetic efficiency (F(v)/F(m)) of the corals was first assessed during a short-term increase in temperature (from 27 degrees C to 29 degrees C, 32 degrees C, and 34 degrees C) and acute exposure to UV radiation (20.5 W m(-2) UVA and 1.2 W m(-2) UVB) alone or in combination. Increasing temperature to 34 degrees C significantly decreased the F(v)/F(m) in S. pistillata and M. aequituberculata. Increased UV radiation alone significantly decreased the F(v)/F(m) of all coral species, even at 27 degrees C. There was a combined effect of temperature and UV radiation, which reduced F(v)/F(m) in all corals by 25% to 40%. During a long-term exposure to UV radiation (17 days) the F(v)/F(m) was significantly reduced after 3 days' exposure in all species, which did not recover their initial values, even after 17 days. By this time, all corals had synthesized mycosporine-like amino acids (MAAs). The concentration and diversity of MAAs differed among species, being higher for corals containing clade A zooxanthellae. Prolonged exposure to UV radiation at the nonstressful temperature of 27 degrees C conferred protection against independent, thermally induced photoinhibition in all four species.     

Elevated temperature reduces survivorship and settlement of the larvae of the Caribbean scleractinian coral, Favia?fragum (Esper)

The effect of elevated seawater temperatures, such as those plaguing tropical seas during the summers of anomalously warm years, on early life stages of reef corals remains poorly studied. To redress this situation, survivorship of larvae of the brooding coral, Favia fragum, was studied in the laboratory, using both short term (48 h) and long term (156–191 h) exposures to 28, 29, and 31°C. Ability to settle when presented with induction substrates and survival after settlement, at the same exposure temperature and after reciprocal transfers to the other experimental temperatures, were also measured. No significant effect of temperature on survivorship was detected after 48 h of exposure, but larvae incubated for 156 h at the highest temperature (31°C) exhibited a 13% reduced survivorship compared to larvae at 28°C. Induction of settlement further increased mortality at the highest temperature (31°C); survivorship after settlement at 31°C was 27% lower than when larvae were simply maintained at the elevated temperature. These results indicate that elevated temperatures are more detrimental to coral larvae undergoing the developmentally complex settlement process than to the swimming planula stage. This may bode poorly for Caribbean corals with late summer reproductive seasons. Communicated by Ecology Editor Prof. Peter Mumby     

Effects of intermittent flow and irradiance level on back reef Porites corals at elevated seawater temperatures

Corals inhabiting shallow back reef habitats are often simultaneously exposed to elevated seawater temperatures and high irradiance levels, conditions known to cause coral bleaching. Water flow in many tropical back reef systems is tidally influenced, resulting in semi-diurnal or diurnal flow patterns. Controlled experiments were conducted to test effects of semi-diurnally intermittent water flow on photoinhibition and bleaching of the corals Porites lobata and P. cylindrica kept at elevated seawater temperatures and different irradiance levels. All coral colonies were collected from a shallow back reef pool on Ofu Island, American Samoa. In the high irradiance experiments, photoinhibition and bleaching were less for both species in the intermittent high-low flow treatment than in the constant low flow treatment. In the low irradiance experiments, there were no differences in photoinhibition or bleaching for either species between the flow treatments, despite continuously elevated seawater temperatures. These results suggest that intermittent flow associated with semi-diurnal tides, and low irradiances caused by turbidity or shading, may reduce photoinhibition and bleaching of back reef corals during warming events.     

Experimental responses to elevated water temperature in genotypes of the reef coral<Emphasis Type="Italic"> Pocillopora damicornis</Emphasis> from upwelling and non-upwelling environments in Panama

The authors investigated the response to experimentally elevated water temperature in genotypes of Pocillopora damicornis from three coral reefs in the upwelling Gulf of Panama and four coral reefs in the non-upwelling Gulf of Chiriquí, Panamanian Pacific. Sea-surface temperature in the Gulf of Panama declines below 20 °C during seasonal upwelling, while in the thermally stable Gulf of Chiriquí, the temperature ranges from 27 to 29 °C. Genotypes of P. damicornis from the seven locations were determined by allozyme electrophoresis. The most abundant genotype at each location was selected for a thermal tolerance experiment where corals were exposed to water temperature of 30 °C (1 °C above ambient) for 43 days. Four site coral genotypes can be uniquely differentiated by the GPI locus, two by the LGG-2 locus, and two by a combination of the MDH-1, LGG-2, and LTY-3 loci. A visual assessment of the coral condition after exposure to an elevated temperature showed that corals from localities in the non-upwelling environment retained a normal to slightly pale appearance, while corals from the upwelling environment bleached and their polyps were mostly retracted. A two-way ANOVA confirmed that corals were significantly affected by water temperature and locality. The zooxanthellae were also significantly affected by the interaction of elevated temperature and locality of the corals. Mean zooxanthellae density decreased by 25 and 55%, respectively, in experimentally heated corals from the non-upwelling and upwelling environments. Low concentrations of photosynthetic pigments per live area of the corals were the norm in corals under elevated temperature. The mean concentration of chlorophyll a per live area of the corals was reduced by 17 and 49%, respectively, in heated corals from the non-upwelling and upwelling sites. Coral genotypes from the upwelling Gulf of Panama demonstrated higher vulnerability to thermal stress than coral genotypes from the non-upwelling Gulf of Chiriquí. However, the latter showed greater differences in their responses. Thus, even at small geographic scales, corals can display different levels of tolerance to thermal stress. The difference in thermal tolerance between corals from upwelling and non-upwelling environments is concomitant with greater genetic differences in experimental corals from the thermally stable Gulf of Chiriquí compared with corals from the upwelling Gulf of Panama.Communicated by K.S. Sealey     

Effect of temperature on the settlement choice and photophysiology of larvae from the reef coral Stylophora pistillata

To better understand the consequences of climate change for scleractinian corals, Stylophora pistillata was used to test the effects of temperature on the settlement and physiology of coral larvae. Freshly released larvae were exposed to temperatures of 23 degrees C, 25 degrees C (ambient), and 29 degrees C at light intensities of approximately 150 micromol photons m(-2) s(-1). The effects were assessed after 12 h as settlement to various substrata (including a choice between crustose coralline algae [CCA] and limestone) and as maximum quantum yield of PSII (F(v)/F(m)) in the larvae versus in their parents. Regardless of temperature, 50%-73% of the larvae metamorphosed onto the plastic of the incubation trays or in a few cases were drifting in the water, and 14% settled on limestone. However, elevated temperature (29 degrees C) reduced the percentage of larvae swimming by 81%, and increased the percentage choosing CCA nearly 7-fold, both relative to the outcomes at 23 degrees C. Because temperature did not affect settlement on limestone or plastic, increased settlement on CCA reflected temperature-mediated choices by larvae that otherwise would have remained swimming. Interestingly, F(v)/F(m) was unaffected by temperature, but it was 4% lower in the larvae than in the parents. These results are important because they show that temperature can affect the settlement of coral larvae and because they reveal photophysiological differences between life stages that might provide insights into the events associated with larval development.     

The effect of sub-lethal increases in temperature on the growth and population trajectories of three scleractinian corals on the southern Great Barrier Reef

To date, coral death has been the most conspicuous outcome of warming tropical seas, but as temperatures stabilize at higher values, the consequences for the corals remaining will be mediated by their demographic responses to the sub-lethal effects of temperature. To gain insight into the nature of these responses, here I develop a model to test the effect of increased temperature on populations of three pocilloporid corals at One Tree Island, near the southern extreme of the Great Barrier Reef (GBR). Using Seriatopora hystrix, S. caliendrum and Pocillopora damicornis as study species, the effects of temperature on growth were determined empirically, and the dynamics of their populations determined under natural temperatures over a 6-month period between 1999 and 2000 [defined as the study year (SY)]. The two data sets were combined in a demographic test of the possibility that the thermal regime projected for the southern GBR in the next 55–83 years—warmer by 3°C than the study year (the SY+3 regime), which is equivalent to 1.4°C warmer than the recent warm year of 1998—would alter coral population trajectories through the effects on coral growth alone; the analyses first were completed by species, then by family after pooling among species. Laboratory experiments showed that growth rates (i.e., calcification) varied significantly among species and temperatures, and displayed curvilinear thermal responses with growth maxima at ∼27.1°C. Based on these temperature-growth responses, the SY+3 regime is projected to: (1) increase annualized growth rates of all taxa by 24–39%, and defer the timing of peak growth from the summer to the autumn and spring, (2) alter the intrinsic rate of population growth (λ) for S. hystrix (λ decreases 26%) and S. caliendrum (λ increases 5%), but not for P. damicornis, and (3) have a minor effect on λ (a 0.3% increase) for the Pocilloporidae, largely because λ varies more among species than it does between temperatures. Ten-year population projections suggest that the effects of a sub-lethal increase in temperature (i.e., the SY+3 regime) are relatively small compared to the interspecific differences in population dynamics, but nevertheless will alter the population size and increase the relative abundance of large colonies at the expense of smaller colonies for all three species, as well as the Pocilloporidae. These effects may play an important role in determining the nuances of coral population structure as seawater warms, and their significance may intensity if the coral species pool is depleted of thermally sensitive species by bleaching.     

Identity and diversity of coral endosymbionts (zooxanthellae) from three Palauan reefs with contrasting bleaching, temperature and shading histories

The potential of corals to associate with more temperature-tolerant strains of algae (zooxanthellae, Symbiodinium) can have important implications for the future of coral reefs in an era of global climate change. In this study, the genetic identity and diversity of zooxanthellae was investigated at three reefs with contrasting histories of bleaching mortality, water temperature and shading, in the Republic of Palau (Micronesia). Single-stranded conformation polymorphism and sequence analysis of the ribosomal DNA internal transcribed spacer (ITS)1 region was used for genotyping. A chronically warm but partly shaded coral reef in a marine lake that is hydrographically well connected to the surrounding waters harboured only two single-stranded conformation polymorphism profiles (i.e. zooxanthella communities). It consisted only of Symbiodinium D in all 13 nonporitid species and two Porites species investigated, with the remaining five Porites harbouring C*. Despite the high temperature in this lake (> 0.5 degrees above ambient), this reef did not suffer coral mortality during the (1998) bleaching event, however, no bleaching-sensitive coral families and genera occur in the coral community. This setting contrasts strongly with two other reefs with generally lower temperatures, in which 10 and 12 zooxanthella communities with moderate to low proportions of clade D zooxanthellae were found. The data indicate that whole coral assemblages, when growing in elevated seawater temperatures and at reduced irradiance, can be composed of colonies associated with the more thermo-tolerant clade D zooxanthellae. Future increases in seawater temperature might, therefore, result in an increasing prevalence of Symbiodinium phylotype D in scleractinian corals, possibly associated with a loss of diversity in both zooxanthellae and corals.     

The physiological response of reef corals to diel fluctuations in seawater temperature

An opportunity to explore the effects of fluctuating temperatures on tropical scleractinian corals arose when diurnal warming (as large as 4.7 °C) was detected over the rich coral communities found within the back reef of Moorea, French Polynesia. In April and May 2007, experiments were completed to determine the effects of fluctuating temperature on Pocillopora meandrina and Porites rus, and consecutive trials were used to expose them for 13 days to 26 °C, 28 °C (ambient conditions), 30 °C, or a fluctuating treatment ranging from 26 to 30 °C over 24 h. The multivariate response was assessed using maximum dark-adapted quantum yield of PSII (F_V/F_M), Symbiodinium density, chlorophyll-a content, and calcification. In trial 1, multivariate physiology of both species was significantly affected by treatments, with the fluctuating temperature resulting in a 17-45% decline in Symbiodinium density (relative to the ambient) matching that occurring at a constant 30 °C; F_V/F_M, chlorophyll-a content, and calcification, did not differ between the fluctuating and the steady treatments. In contrast, in trial 2 that utilized corals collected two weeks after those used in trial 1, the corals were unaffected by the treatments, likely due to an environment × trial interaction caused by seasonal declines in Symbiodinium density. Together, these results demonstrate that short transgressions to ecologically relevant high and low temperatures can elicit a potentially detrimental response equivalent to that occurring upon exposure to a constant high temperature. The dissimilar responses among dependent variables and consecutive trials underscore the importance of temporal replication and multivariate approaches in coral ecophysiology. It is likely that recent history has a stronger effect on the response of corals to treatments than is currently recognized.     

Seasonal and local spatial patterns in the upper thermal limits of corals on the inshore Central Great Barrier Reef

 Experimental studies of the upper thermal limits of corals from Orpheus Island, an inshore reef in the central Great Barrier Reef, show that Acropora formosa has a 5-day 50%-bleaching threshold of between 31 and 32 °C in summer, only 2 to 3 °C higher than local mean summer temperatures (29 °C). Summer bleaching thresholds for Pocillopora damicornis and A. elseyi were 1 °C higher (between 32 and 33 °C). The winter bleaching threshold of Pocillopora damicornis was 1 °C lower than its summer threshold, indicating that seasonal acclimatisation may take place. This seasonal difference raises the possibility that at least some corals may be capable of short-term thermal acclimatisation. Neither P. damicornis nor A. elseyi showed habitat-specific (reef flat versus reef slope) differences in bleaching thresholds. Further, colonies of P. damicornis collected from sites 3 km apart also showed no difference in bleaching threshold despite populations of this species responding differently at these two sites during a natural bleaching event. The bleaching thresholds determined in this study are best considered as the maximum tolerable temperatures for local populations of these species because they were determined in the absence of additional stressors (e.g. high light) which often co-occur during natural bleaching events. We consider the 5-day 50% bleaching thresholds determined in these experiments to be fair indicators of upper thermal limits, because >50% of a sample population died when allowed to recover in situ. We found a delay of up to a month in the bleaching response of corals following thermal stress, a result that has implications for identifying the timing of stressful conditions in natural bleaching events. Accepted: 26 May 1999     

Real-time PCR reveals a high incidence of <Emphasis Type="Italic">Symbiodinium </Emphasis>clade D at low levels in four scleractinian corals across the Great Barrier Reef: implications for symbiont shuffling

Reef corals form associations with an array of genetically and physiologically distinct endosymbionts from the genus Symbiodinium. Some corals harbor different clades of symbionts simultaneously, and over time the relative abundances of these clades may change through a process called symbiont shuffling. It is hypothesized that this process provides a mechanism for corals to respond to environmental threats such as global warming. However, only a minority of coral species have been found to harbor more than one symbiont clade simultaneously and the current view is that the potential for symbiont shuffling is limited. Using a newly developed real-time PCR assay, this paper demonstrates that previous studies have underestimated the presence of background symbionts because of the low sensitivity of the techniques used. The assay used here targets the multi-copy rDNA ITS1 region and is able to detect Symbiodinium clades C and D with >100-fold higher sensitivity compared to conventional techniques. Technical considerations relating to intragenomic variation, estimating copy number and non-symbiotic contamination are discussed. Eighty-two colonies from four common scleractinian species (Acropora millepora, Acropora tenuis, Stylophora pistillata and Turbinaria reniformis) and 11 locations on the Great Barrier Reef were tested for background Symbiodinium clades. Although these colonies had been previously identified as harboring only a single clade based on SSCP analyses, background clades were detected in 78% of the samples, indicating that the potential for symbiont shuffling may be much larger than currently thought.     

High zooxanthella density shortens the survival time of coral cell aggregates under thermal stress

To investigate bleaching mechanisms in coral-zooxanthella symbiotic systems, it is important to study the cellular- or tissue-level responses of corals to stress. We established an experimental system to study the stress responses of coral cells using coral cell aggregates. Dissociated coral cells aggregate to form spherical bodies, which rotate by ciliary movement. These spherical bodies (tissue balls) stop rotating and disintegrate when exposed to a thermal stress. Tissue balls prepared from dissociated cells of Fungia sp. and Pavona divaricata were exposed to either elevated temperature (31 °C, with 25 °C as the control) or elevated temperature in the presence of exogenous antioxidants (ascorbic acid and catalase, or mannitol). The survival curves of tissue balls were markedly different between 31 and 25 °C. At 31 °C, most tissue balls disintegrated within 24 h, whereas at 25 °C, most tissue balls survived for more than 24 h. There was a negative correlation between survival time and the zooxanthella density of tissue balls at 31 °C, but no significant relationship was found at 25 °C. Antioxidants extended the survival time of tissue balls at high temperature, suggesting that zooxanthellae produce reactive oxygen species under stress. These results indicate that zooxanthellae produce harmful substances and damage coral cells under high-temperature stress. Tissue balls provide a good experimental system with which to study the effects of stress and various chemical reagents on corals cells.     

Effects of constant and fluctuating incubation temperatures on hatching success and hatchling traits in the diamondback terrapin (Malaclemys terrapin) in the context of the warming climate

As global temperatures continue to rise, so too will the nest temperatures of many species of turtles. Yet for most turtle species, including the estuarine diamondback terrapin (Malaclemys terrapin), there is limited information on embryonic sensitivity to elevated temperature. We incubated eggs of M. terrapin at three, mean temperatures (31, 34, 37 °C) under two thermal exposure regimes (constant or semi-naturally fluctuating temperature) and measured hatching success, developmental rate, and hatchling size. Hatching success was 100% at 31 °C and 67% at 34 °C, respectively; at 37 °C, all eggs failed early in the incubation period. These values were unaffected by exposure regime. The modeled LT₅₀ (temperature that was lethal to 50% of the test population) was 34.0 °C in the constant and 34.2 °C in the fluctuating thermal regime, reflecting a steep decline in survival between 33 and 35 °C. Hatchlings having been incubated at a constant 34 °C hatched sooner than those incubated at 31 °C under either constant or fluctuating temperature. Hatchlings were smaller in straight carapace length (CL) and width after having been incubated at 34 °C compared to 31 °C. Larger (CL) hatchlings resulted from fluctuating temperature conditions relative to constant temperature conditions, regardless of mean temperature. Based upon recent temperatures in natural nests, the M. terrapin population studied here appears to possess resiliency to several degrees of elevated mean nest temperatures, beyond which, embryonic mortality will likely sharply increase. When considered within the mosaic of challenges that Maryland's M. terrapin face as the climate warms, including ongoing habitat losses due to sea level rise and impending thermal impacts on bioenergetics and offspring sex ratios, a future increase in embryonic mortality could be a critical factor for a population already experiencing ecological and physiological challenges due to climate change.     

Seawater temperature measured at the surface and at two depths (7 and 12 m) in one coral reef at Culebra Bay, Gulf of Papagayo, Costa Rica

Superficial seawater temperature (SST) and at two depths (7 and 12 m) were measured non-continuously during the study of the corals and coral reefs of Culebra Bay (1993-1996). SST showed seasonal variations of approximately 4 degrees C. The highest average temperatures (27.0 +/- 0.1, range 23-29 degrees C) were during the rainy season from May to November and the lowest (22.9 +/- 0.3 degrees C, 15.5-29 degrees C) during the dry season from December to April. Cold fronts with 2-3 degrees C differences in SST frequently pass into the bay and remain there for several hours according to the tidal cycles. Differences of approximately 3 degrees C between SST and the bottom (5-10 m depth) were usually found, particularly at locations where bottom topography and tidal circulation produced tidal bores. The average temperatures recorded by data loggers placed at 7 and 12 m depth on a coral reef at the outer shores of Culebra Bay, were 27.1 +/- 0.02 degrees C (20.5-31.6 degrees C) and 25.8 +/- 0.04 (9.9-31.5 degrees C) respectively. The seasonal pattern of higher and lower temperatures corresponds respectively to the rainy and dry season of the northern Pacific coast of Costa Rica. Water temperature at 12 m was < 14 degrees C for some hours during an upwelling event whilst minimum temperatures at 7 m were > or = 22 degrees C. Negative temperature anomalies coincided with an increase of the NE-E winds intensity and there is a lunar and tidal component which influence diumal variations of temperature. These results suggest that coral reefs built by branching species (e.g. Pocillopora spp.) in Culebra Bay could be limited by both the influence of cold fronts and by seasonal upwellings which affect negatively those coral species, as reported for other locations in the tropical eastern Pacific.     

New insights into patterns of coral spawning on Western Australian reefs

On reefs around Australia, coral mass spawning typically occurs during the austral spring (October/November) on the east coast, and during autumn (March/April) on the west coast. However, to investigate the incidence of a secondary spawning event in spring on the west coast, the reproductive state of corals was assessed on two reefs. The results indicated that of the 29 species of Acropora investigated, multiple colonies of 11 species spawned in late spring or in early summer, in contrast to previous reports of spawning during autumn. Additionally, of four species that were followed through time at one reef, two spawned in both spring and autumn, however, individual colonies had only one gametogenic cycle. Within a single site, conspecific colonies were reproductively isolated and may not interbreed, potentially representing the initial stage of sympatric speciation in these populations.     

Measuring antioxidant potential in corals using the FRAP assay

In this paper, we standardized a method for determining antioxidant potential in corals. This was determined using a simple, reproducible and inexpensive method: the ferric reducing/antioxidant potential (FRAP) assay. This procedure involves the reduction of Fe^III-TPTZ to a blue colored Fe^II-TPTZ by biological antioxidants and chemical reductants, some of which might have no antioxidant activity in a sample. The FRAP assay compares the change in absorbance at 600 nm of a sample compared with the change in absorbance of a known standard (FeSO₄·7H₂O) to determine antioxidant levels. This assay was used to determine changes in antioxidant potential in the corals Pocillopora damicornis and Pocillopora meandrina exposed to different temperatures (28, 29, 30 and 31 °C) for 3 h. Corals were also incubated at 31 °C for time intervals of a 0.5, 1 and 3 h. Antioxidant potential in the coral host increased with temperature and time, as indicated by FRAP values, compared to control samples at ambient sea surface temperatures (26.5-27 °C). Lower FRAP values could be a response to lower production of reactive oxygen species (ROS) or the result of an increase in ROS that react with the antioxidants. Because of the complex interactions within cells, one test is normally not enough to understand precisely what is going on within the cell. Rather, a broad array of tests is required to determine the different cellular parameters that are occurring within a biological system. To our knowledge, this is the first time that FRAP has been used to determine antioxidant status in a marine organism. The FRAP technique can potentially be a useful and inexpensive tool for marine biologists engaged in ecotoxicological studies.     

Thermal compensation of metabolism in the temperate coral, Plesiastrea versipora (Lamarck, 1816)

Plesiastrea versipora is a hermatypic coral with a distribution that extends to the southern limit for hermatypic corals. The normal annual temperature range for this coral in Port Phillip Bay (Victoria) (approximately 10-21 degrees C) is well below the physiological optimum for the majority of hermatypic corals (25-29 degrees C). The rate of photosynthesis and respiration in Plesiastrea generally increased with temperature before levelling out at the higher temperatures, with Q(10) data suggesting that both photosynthesis and respiration in Plesiastrea acclimate to changing temperatures. Respiration showed a similar trend to photosynthesis, with respect to temperature, but with a slightly lower rate of increase. Photosynthetic rate in Plesiastrea is comparable with that of reef corals despite lower temperatures and irradiance. When expressed as a function of chlorophyll a content photosynthesis approached perfect temperature compensation with prolonged exposure to various temperatures. Temperature-dependent changes with chlorophyll content may be responsible for temperature related changes in photosynthetic rate. This may be a mechanism for stabilising the symbiotic relationship over a wide temperature range. Autotrophic ability, estimated from photosynthesis/respiration (P/R) ratios, was greatest at higher temperatures and was only slightly less than that of reef corals. At low temperatures Plesiastrea may be dependent on heterotrophic feeding.     

Interactive effects of climate change and eutrophication on the dinoflagellate-bearing benthic foraminifer <Emphasis Type="Italic">Marginopora vertebralis</Emphasis>

Elevated sea surface temperatures caused by global climate change and increased nutrient concentrations resulting from land runoff both are stressors for calcifying coral reef organisms. Here, we test the hypothesis that increased temperature leads to bleaching in dinoflagellate-bearing foraminifera similar to corals and that increased nutrients through runoff can exaggerate stress on the holobiont. In an experiment manipulating temperatures alone, we have shown that mortality of Marginopora vertebralis increased with temperatures. Most individuals died after 7 days at 34°C, ~5°C above current summer maxima. Survival at 37 days was >98% at 28°C. After 7 days of exposure to 31 or 32°C, photosynthesis of the endosymbionts was compromised, as indicated by several photophysiological parameters (effective quantum yield and apparent photosynthetic rate). In a flow-though experiment manipulating both temperature (three levels, 26, 29 and 31°C) and nitrate concentrations (3 levels, ~0.5, 1.0 and 1.4 μmol l⁻¹ NO₃ ⁻), elevated temperature had a significant negative effect on most parameters measured. At 31°C, most photopigments (measured by UPLC) in the foraminifera were significantly reduced. The only pigment that increased was the photoprotective diatoxanthin. Several other parameters measured (maximum and effective quantum yield, O₂ production in light, organic carbon contents) also significantly decreased with temperature. Optode-based respirometry demonstrated that the presence of symbionts at elevated temperatures represents a net carbon loss for the host. Growth rates of M. vertebralis and mortality at the end of the experiment were significantly affected by both temperature increase and nitrate addition. We conclude that these foraminifera bleach in a similar fashion to corals and that global sea surface temperature change and nitrate increases are stressors for these protists. Furthermore, this provides support for the hypothesis that management of local stressors elevates resilience of coral reefs to global stressors.     

The genetic identity of dinoflagellate symbionts in Caribbean octocorals

Many cnidarians (e.g., corals, octocorals, sea anemones) maintain a symbiosis with dinoflagellates (zooxanthellae). Zooxanthellae are grouped into clades, with studies focusing on scleractinian corals. We characterized zooxanthellae in 35 species of Caribbean octocorals. Most Caribbean octocoral species (88.6%) hosted clade B zooxanthellae, 8.6% hosted clade C, and one species (2.9%) hosted clades B and C. Erythropodium caribaeorum harbored clade C and a unique RFLP pattern, which, when sequenced, fell within clade C. Five octocoral species displayed no zooxanthella cladal variation with depth. Nine of the ten octocoral species sampled throughout the Caribbean exhibited no regional zooxanthella cladal differences. The exception, Briareum asbestinum, had some colonies from the Dry Tortugas exhibiting the E. caribaeorum RFLP pattern while elsewhere hosting clade B. In the Caribbean, octocorals show more symbiont specificity at the cladal level than scleractinian corals. Both octocorals and scleractinian corals, however, exhibited taxonomic affinity between zooxanthella clade and host suborder.Communicated by R.C. Carpenter     

Viability and rate of development at different temperatures in Drosophila: a comparison of constant and alternating thermal regimes

Populations belonging to the sibling species Drosophila melanogaster and D. simulans were collected in Southwestern France and Southern Spain, and investigated under constant (CT) and alternating (AT) temperature regimes. Development under CT was possible between 11 and 32 degrees C and egg-to-adult viability curves were almost 'rectangular', with a sharp decrease below 14 and above 29 degrees C. Rate of development followed a complex non-linear curve. A model described the curve as an exponential below a critical temperature (T(C)), and above T(C) as the difference between this function and another exponential which is assumed to show deleterious effects of heat. Developmental rates under two daily 12-h phases with various mid-temperatures and thermal amplitudes were compared to expected rates calculated from the above model. Acceleration effects were observed at four AT (in increasing order: 12-30, 9-21, 11-21, 16-26 degrees C); retardation occurred at three other ones (in increasing order, 7-21, 5-15, 7-29 degrees C). When expressed by the ratio observed/expected, the effects could be predicted using a multiple regression, as a positive function of the thermal amplitude and a negative one of the mid-temperature. Viability under AT was analysed considering an equivalent developmental temperature (EDT), that is the CT which would produce the same rate or development. Very low viabilities occurred under broad amplitude regimes, but the deleterious effects of some extreme temperatures, that would be lethal under CT, could be recovered by daily return to a moderate temperature. The two species exhibited slight but significant differences in their characteristic temperatures: developmental zero, critical temperature, temperature of maximum rate, upper developmental limit. All data may be interpreted by considering that D. simulans compared to D. melanogaster is more tolerant to cold but less tolerant to heat.