Effects Of Elevated Seawater Temperature Research Articles

How does heat stress affect sponge microbiomes? Structure and resilience of microbial communities of marine sponges from different habitats

IntroductionSponges are key components of marine benthic communities, providing many ecosystem functions and establishing close relationships with microorganisms, conforming the holobiont. These symbiotic microbiotas seem to be host species-specific and highly diverse, playing key roles in their sponge host. The effects of elevated seawater temperature on sponges and their microbiota are still poorly known, and whether sponges from polar areas are more sensitive to these impacts respect to temperate and tropical species is totally unknown.MethodsWe analyzed the microbiomes of different sponge species in their natural habitat and after exposure to heat stress in aquaria by 16S rRNA amplicon sequencing to (1) characterize the sponge microbiota covering a latitudinal gradient (polar, temperate and tropical environments), and (2) asses the effects of thermal stress on their microbial communities.ResultsBacterial communities’ structure was different in the different sponge species and also respect the surrounding seawater. The core microbiome is maintained in most sponge species after a heat stress, although whether they would recover to the normal conditions previous to the stress remains yet to be further investigated. We observed increased abundances of transient bacteria from unknown origin in sponge species exposed to heat stress.DiscussionSome of the transient bacteria may be opportunistic bacteria that may benefit from the heat stress-associated dysregulation in the sponge by occupying new niches in the holobiont. According to our results, sponges from Antarctic waters could be more resilient than tropical and temperate sponges. Both the microbiome composition and the changes produced by the heat stress seem to be quite host species-specific, and thus, depend on the sponge species. Under a global change scenario, the microbiomes of the tropical and temperate sponges will probably be those suffering the most the heat stress, and therefore the effects of global change may be dramatic for benthic ecosystems since sponges are a fundamental part of them.

Fluorescence signatures of persistent photosystem damage in the staghorn coral Acropora cf. pulchra (Anthozoa: Scleractinia) during bleaching and recovery

ABSTRACT Staghorn corals represent dominant reef-builders in lagoons and back reefs in Guam. These habitats experience peak seawater temperatures close to 36°C during the hottest months of the year which causes increasingly frequent bleaching episodes that have led to major staghorn coral declines. To study the photo-physiological response of staghorn corals to bleaching conditions, pulse amplitude modulated (PAM) fluorometry was used to record signatures of chlorophyll fluorescence in Acropora cf. pulchra. Fragments of A. cf. pulchra were subjected to a week-long heat treatment some 2–3°C above average ambient seawater temperatures of 30°C; a four-week long recovery period at ambient temperatures followed treatment. While heat-treated coral fragments exposed to full sun responded with immediate and lasting declines in photosynthetic efficiency, shading of coral fragments largely mitigated the effects of elevated seawater temperatures. Of particular concern to reef management efforts is the finding that the strongest effects of heat stress were observed during the recovery period following the initial heat stress. Indeed, it took three times as long as the initial stress event lasted for photosynthesis to return to baseline levels. This lengthy recovery period appears to be driven by photodamage, likely requiring time-consuming protein synthesis-dependent repair of damaged photosystems and replacement of damaged zooxanthellae. These results highlight the importance of developing and implementing coral bleaching intervention efforts well beyond the end of bleaching conditions to facilitate recovery of affected reefs.

Crawling and righting behavior of the subtropical sea star Echinaster (Othilia) graminicola: effects of elevated temperature

Sea stars exhibit discrete neuromuscular-mediated behaviors, such as crawling and righting, which are critical to daily functioning and survival. As global seawater temperatures rise, subtidal asteroids such as Echinaster (Othilia) graminicola on the Gulf Coast of Florida are increasingly subjected to elevated temperatures, which may compromise their neuromuscular health. To better understand the neuromuscular biology of E. graminicola and the effects of elevated seawater temperature on behavior, we first describe their righting mechanism and identify the arms used in righting and crawling. Together, this allowed us to determine if they exhibit any bilateral tendencies, related to their anterior–posterior ancestry, by measuring the frequency with which each arm led in righting and crawling. To determine the effect of elevated seawater temperature on their described righting behavior, we tested the effects of acute (1 day) and chronic (7 day) exposure to seawater temperatures ranging from 28 to 36 °C on righting time in a laboratory experiment. We found that E. graminicola rights by somersaulting, but exhibits no lead arm preference during this behavior. In crawling, Arm E, located adjacent to the madreporite, led most frequently, indicating a partial tendency toward bilateralism. Sea stars righted significantly faster with increasing temperature and exposure time as temperatures increased from 28 to 34 °C, suggesting some capacity for acclimatization to elevated temperatures. However, at 36 °C, righting time increased dramatically and sea stars experienced high mortality, suggesting E. graminicola may be living near the upper limits of its thermotolerance. As seawater temperatures rise beyond an organism’s thermal tolerance, their neuromuscular responses may become critically impaired, reducing their capacity to survive in a warming ocean.

The response of a boreal deep-sea sponge holobiont to acute thermal stress

Effects of elevated seawater temperatures on deep-water benthos has been poorly studied, despite reports of increased seawater temperature (up to 4 °C over 24 hrs) coinciding with mass mortality events of the sponge Geodia barretti at Tisler Reef, Norway. While the mechanisms driving these mortality events are unclear, manipulative laboratory experiments were conducted to quantify the effects of elevated temperature (up to 5 °C, above ambient levels) on the ecophysiology (respiration rate, nutrient uptake, cellular integrity and sponge microbiome) of G. barretti. No visible signs of stress (tissue necrosis or discolouration) were evident across experimental treatments; however, significant interactive effects of time and treatment on respiration, nutrient production and cellular stress were detected. Respiration rates and nitrogen effluxes doubled in responses to elevated temperatures (11 °C & 12 °C) compared to control temperatures (7 °C). Cellular stress, as measured through lysosomal destabilisation, was 2–5 times higher at elevated temperatures than for control temperatures. However, the microbiome of G. barretti remained stable throughout the experiment, irrespective of temperature treatment. Mortality was not evident and respiration rates returned to pre-experimental levels during recovery. These results suggest other environmental processes, either alone or in combination with elevated temperature, contributed to the mortality of G. barretti at Tisler reef.

Elevated temperature has adverse effects on GABA-mediated avoidance behaviour to sediment acidification in a wide-ranging marine bivalve

Sediment acidification is known to influence the burrowing behaviour of juvenile marine bivalves. Unlike the alteration of behaviour by ocean acidification (OA) observed in many marine organisms, this burrowing response to present-day variation in sediment pH is likely adaptive in that it allows these organisms to avoid shell dissolution and mortality. However, the consequences of global climate stressors on these burrowing responses have yet to be tested. Further, while neurotransmitter interference appears to be linked to the alteration of behaviour by OA in marine vertebrates, the mechanism(s) controlling the burrowing responses of juvenile bivalves in response to present-day variation in sediment acidification remain unknown. We tested the interactive effects of elevated seawater temperature and sediment acidification on juvenile soft-shell clam burrowing behaviour (measured as the proportion of clams burrowed into sediment) to test for effects of elevated temperature on bivalve burrowing responses to sediment acidification. We also examined whether GABAA-like receptor interference could act as a potential biological mechanism underpinning the burrowing responses of these clams to present-day variation in sediment acidification. Results showed that both elevated temperature and gabazine administration reduced the proportion of clams that avoided burrowing into low pH sediment. These results suggest that CO2 effects on neurophysiology (GABAA receptors) can act to mediate adaptive behaviours in juvenile marine bivalves to elevated CO2, but that these behaviours may be adversely affected by elevated temperature.

The effects of elevated seawater temperatures on Caribbean gorgonian corals and their algal symbionts, Symbiodinium spp.

Global climate change not only leads to elevated seawater temperatures but also to episodic anomalously high or low temperatures lasting for several hours to days. Scleractinian corals are detrimentally affected by thermal fluctuations, which often lead to an uncoupling of their mutualism with Symbiodinium spp. (coral bleaching) and potentially coral death. Consequently, on many Caribbean reefs scleractinian coral cover has plummeted. Conversely, gorgonian corals persist, with their abundance even increasing. How gorgonians react to thermal anomalies has been investigated utilizing limited parameters of either the gorgonian, Symbiodinium or the combined symbiosis (holobiont). We employed a holistic approach to examine the effect of an experimental five-day elevated temperature episode on parameters of the host, symbiont, and the holobiont in Eunicea tourneforti, E. flexuosa and Pseudoplexaura porosa. These gorgonian corals reacted and coped with 32°C seawater temperatures. Neither Symbiodinium genotypes nor densities differed between the ambient 29.5°C and 32°C. Chlorophyll a and c2 per Symbiodinium cell, however, were lower at 32°C leading to a reduction in chlorophyll content in the branches and an associated reduction in estimated absorbance and increase in the chlorophyll a specific absorption coefficient. The adjustments in the photochemical parameters led to changes in photochemical efficiencies, although these too showed that the gorgonians were coping. For example, the maximum excitation pressure, Qm, was significantly lower at 32°C than at 29.5°C. In addition, although per dry weight the amount of protein and lipids were lower at 32°C, the overall energy content in the tissues did not differ between the temperatures. Antioxidant activity either remained the same or increased following exposure to 32°C further reiterating a response that dealt with the stressor. Taken together, the capability of Caribbean gorgonian corals to modify symbiont, host and consequently holobiont parameters may partially explain their persistence on reefs faced with climate change.

Response of Subtropical Coastal Sediment Systems of Okinawa, Japan, to Experimental Warming and High pCO2

Increasing seawater temperatures and CO2 levels associated with climate change affect the shallow marine ecosystem function. In this study, the effects of elevated seawater temperature and partial pressure of CO2 (pCO2) on subtropical sediment systems of mangrove, seagrass, and coral reef lagoon habitats of Okinawa, Japan, were examined. Sediment and seawater from each habitat were exposed to four pCO2-temperature treatments, including ambient pCO2- ambient temperature, ambient pCO2-high temperature (ambient temperature + 4°C), high pCO2 (936 ppm)-ambient temperature, and high pCO2-high temperature. Parameters including primary production, nutrient flux, pigment content, photosynthetic community composition, and bacterial abundance were examined. Neither high temperature nor high pCO2 alone impacted mangrove and seagrass sediment primary production significantly (Tukey’s test, P > 0.05). However, the combined stress significantly (Tukey’s test, P 0.05) under the combined stress, suggesting that heterotrophic processes were less affected by the combined stress than autotrophic processes. In summary, mangrove and seagrass sediments minimize the negative impacts of elevated temperature and pCO2 via increased primary production and carbon storage. Lagoonal sediments also act as a carbon sink under temperature and ocean acidification stress.

Testing Antarctic resilience: the effects of elevated seawater temperature and decreased pH on two gastropod species

AbstractOcean acidification has been hypothesized to increase stress and decrease shell calcification in gastropods, particularly in cold water habitats like the western Antarctic Peninsula (WAP). There is limited information on how calcified marine benthic invertebrates in this region will respond to these rapidly changing conditions. The present study investigated the effects of elevated seawater temperature and decreased pH on growth (wet mass and shell morphometrics), net calcification, and proximate body composition (protein and lipid) of body tissues in two common benthic gastropods. Individuals of the limpet Nacella concinna and the snail Margarella antarctica collected from the WAP were exposed to seawater in one of four treatment combinations: current ambient conditions (1.5°C, pH 8.0), near-future decreased pH (1.5°C, pH 7.8), near-future elevated temperature (3.5°C, pH 8.0), or combination of decreased pH and elevated temperature (3.5°C, pH 7.8). Following a 6-week exposure, limpets showed no temperature or pH effects on whole body mass or net calcification. Despite no significant differences in whole body mass, the shell length and width of limpets at elevated temperature tended to grow less than those at ambient temperature. There was a significant interaction between the sex of limpets and pH. There were no significant temperature or pH effects on growth, net calcification, shell morphologies, or proximate body composition of snails. Our findings suggest that both gastropod species demonstrate resilience to initial exposure to temperature and pH changes predicted to occur over the next several hundred years globally and perhaps sooner along the WAP. Despite few significant impacts of elevated temperature or decreased pH, any response to either abiotic variable in species with relatively slow growth and long lifespan is of note. In particular, we detected modest impacts of reduced pH on lipid allocation in the reproductive organs of the limpet N. concinna that warrants further study.

Seawater Acidification and Elevated Temperature Affect Gene Expression Patterns of the Pearl Oyster Pinctada fucata

Oceanic uptake of anthropogenic carbon dioxide results in decrease in seawater pH and increase in temperature. In this study, we demonstrated the synergistic effects of elevated seawater temperature and declined seawater pH on gene expression patterns of aspein, calmodulin, nacrein, she-7-F10 and hsp70 in the pearl oyster Pinctada fucata. Under ‘business-as-usual’ scenarios, four treatments were examined: (1) ambient pH (8.10) and ambient temperature (27°C) (control condition), (2) ambient pH and elevated temperature (+3°C), (3) declined pH (7.70) and ambient temperature, (4) declined pH and elevated temperature. The results showed that under warming and acidic seawater conditions, expression of aspein and calmodulin showed no significant differences among different time point in condition 8.10 T. But the levels of aspein and calmodulin in conditions 8.10 T+3, 7.70 T and 7.70 T+3, and levels of nacrein, she-7-F10 in all the four treatments changed significantly. Low pH and pH×temperature interaction influenced the expression of aspein and calmodulin significantly after hours 48 and 96. Significant effects of low pH and pH×temperature interaction on the expression of nacrein were observed at hour 96. The expression level of she-7-F10 was affected significantly by pH after hours 48 and 96. The expression of hsp70 was significantly affected by temperature, pH, temperature×pH interaction at hour 6, and by temperature×pH interaction at hour 24. This study suggested that declined pH and pH×temperature interaction induced down regulation of calcification related genes, and the interaction between declined seawater pH and elevated temperature caused up regulation of hsp70 in P. facata. These results demonstrate that the declined seawater pH and elevated temperature will impact the physiological process, and potentially the adaptability of P. fucata to future warming and acidified ocean.

Differences in physiological response to increased seawater temperature in nearshore and offshore corals in northern Vietnam

Effects of elevated seawater temperature show high spatial heterogeneity and variation within and among coral species. The objective of this study was to investigate how two coral species, Porites lutea and Galaxea fascicularis, from two high latitude reefs differently exposed to chronic disturbance, respond to elevated seawater temperatures. Corals were collected from reefs nearshore (i.e. subjected to high sediment load, higher chlorophyll α concentrations, turbidity etc.) and offshore (i.e. less exposed). The corals were exposed in the lab to gradually increasing temperatures (25.5–33.5 °C) for 72 h after which they were allowed to recover to ambient temperature (25.5 °C) for 24 h. Production and respiration were measured after 24, 48, 72 and 96 h. The results show that P. lutea from nearshore reefs suffered an initial decrease in gross primary production/respiration (GP/R) ratio after 24 h, after only a moderate temperature increase (+2 °C, from 25.5 to 27.5 °C), while there was no difference in GP/R ratio between heat-exposed and controls the other days, indicating that the chronic disturbance in the nearshore reef had no effect on their thermotolerance. Furthermore, P. lutea from the offshore reef showed a decrease in GP/R ratio both after 24 h and 72 h (33.5 °C) of exposure. In comparison, G. fascicularis showed a decrease in GP/R ratio after 48 h, 72 h and 96 h of exposure for the nearshore corals. Also, after 72 h these corals had withdrawn their polyps. There were no differences between heat-treated and controls for the offshore G. fascicularis. This implies that the chronically disturbed G. fascicularis had lower thermotolerance when exposed to a temperature increase. This study, hence, shows that the response of corals to elevated seawater temperature varies with species and environmental background history.

Metagenomic analysis of the coral holobiont during a natural bleaching event on the Great Barrier Reef

Understanding the effects of elevated seawater temperatures on each member of the coral holobiont (the complex comprised of coral polyps and associated symbiotic microorganisms, including Bacteria, viruses, Fungi, Archaea and endolithic algae) is becoming increasingly important as evidence accumulates that microbial members contribute to overall coral health, particularly during thermal stress. Here we use a metagenomic approach to identify metabolic and taxonomic shifts in microbial communities associated with the hard coral Acropora millepora throughout a natural thermal bleaching event at Magnetic Island (Great Barrier Reef). A direct comparison of metagenomic data sets from healthy versus bleached corals indicated major shifts in microbial associates during heat stress, including Bacteria, Archaea, viruses, Fungi and micro-algae. Overall, metabolism of the microbial community shifted from autotrophy to heterotrophy, including increases in genes associated with the metabolism of fatty acids, proteins, simple carbohydrates, phosphorus and sulfur. In addition, the proportion of virulence genes was higher in the bleached library, indicating an increase in microorganisms capable of pathogenesis following bleaching. These results demonstrate that thermal stress results in shifts in coral-associated microbial communities that may lead to deteriorating coral health.

Physiological response of the blue mussel Mytilus edulis to differences in food and temperature in the Gulf of Maine

Studies performed in the Gulf of Maine (GOM) during the spring of 2006 examined populations of the blue mussel, Mytilus edulis at several intertidal locations. Several parameters were measured including maximum length, diet (stable isotope composition), and the physiological performance of individual mussels using condition indices and RNA/DNA ratios. These same mussels were also assessed for their response to differences in seawater temperature by quantifying the expression of heat shock proteins (HSP70) and the activities of the antioxidant enzyme, superoxide dismutase (SOD). These data were then interpreted in the context of sea surface and air temperatures as well as chlorophyll a concentration and the genetic structure of mussel populations. Populations of M. edulis throughout the GOM were found to be genetically homogenous and consumed a mixed diet of phytoplankton and detritus. Mussels exposed to higher seawater temperatures also showed a significant increase in the expression of HSP70 and activities of SOD. The site-specific interplay between the amount of energy gained from the available food resources and the costs associated with protection against the effects of elevated seawater temperatures shows that these mussels exhibit phenotypic plasticity at different sites which could play an important role in the population dynamics of this key member of the rocky intertidal.

Potential Effects of Elevated Sea-Water Temperature on Pelagic Food Webs

The effect of temperature changes on the marine pelagic food web was studied in three successive mesocosm experiments, performed during the spring bloom 2001 in the northern Baltic Sea. The temperature was varied from 5 to 20 °C in each experiment, running over a 3-week period. The experiments included food webs of at least four trophic levels: (1) phytoplankton-bacteria, (2) flagellates, (3) ciliates and (4) metazooplankton. The results showed that heterotrophic to autotrophic biomass ratio (H/A) increased 5 times when temperature was raised from 5 to 10 °C. In agreement, the carbon fixation to respiration ratio indicated a decrease of six times over the same temperature range. Furthermore, the sedimentation decreased by 45% when the temperature was elevated from 5 to 10 °C, probably as a consequence of the increased respiration losses and bacterial biodegradation of settling material. Analyzed parameters, thus, indicated that the degree of heterotrophy increased in the temperature interval of 5–10 °C. Above 10 °C, the analyzed parameters in general were more stable. Our results indicate that moderately elevated seawater temperatures, due to climate change or weather alterations, may affect the entire ecosystem function in temperate sea areas by altering the balance between autotrophy and heterotrophy.

Effects of elevated seawater temperature and nitrate enrichment on the branching coral Porites cylindrica in the absence of particulate food

Compounded disturbances are becoming increasingly common on coral reefs. Impacts of global warming, which is generally perceived as the most serious threat to coral reefs today, often coincide with various common anthropogenic disturbances, such as pollution and overharvesting. To better evaluate the impact of global warming, interactions between elevated temperature and background disturbance should be investigated. In this study, the physiological response of the reef-building coral Porites cylindrica was investigated, when exposed to enrichment of dissolved inorganic nitrate (+15 μM for 14 days) and elevated seawater temperature (+2oC for 48 h), in the absence of particulate food. It was shown that P. cylindrica was able to tolerate the temperature exposure without losing symbiotic microalgae or chlorophyll pigments, although the photosynthetic capacity was affected. Nitrate enrichment significantly reduced primary production rate, although zooxanthella population density and chlorophyll concentrations were not affected. The combination of elevated temperature and nitrate enrichment produced an even more pronounced reduction of the production rate. Since coral respiration rate remained unaffected by the treatments, this implies that the corals were unable to acclimate to impaired photosynthesis. However, there was no indication of subsequently reduced tissue growth or increased host catabolism based on tissue biomass measurements. On the other hand, all corals, including controls, lost tissue biomass during the exposure, suggesting a dependence on particulate food. Our results imply that corals on nutrient-exposed reefs may be more stressed during periods of elevated temperature, compared to corals in more pristine areas.