Posts Tagged 'reproduction'

The combined effects of increased temperature and ocean acidification on the early life history stages of Caribbean coral and its implication for the recovery potential of Florida reefs

The early life history stages of coral are an essential component determining the recovery potential of coral reefs through sexual reproduction and recruitment. The pelagic larval phase is inherent in all coral species regardless of differing reproductive strategies and is the only time in coral life history where large scale movement is possible allowing for the repopulation of reef areas both within and outside the natal reef habitat. In the face of climate change, the larval dispersal and recruitment phase will take place in a warmer more acidic ocean if we continue on the path of unabated fossil fuel emissions. While much research has focused on how increased temperature or ocean acidification affect coral larvae independently, our understanding of how these factors interact to shape larval response is limited, especially in regards to Caribbean coral species.

To gain a better understanding of how the early life history stages of Caribbean coral may be affected by climate change, this dissertation investigates the effects of increased temperature (2.5 °C above historical averages in the Florida Keys) and carbon dioxide levels (900-1000 parts per million CO2) on corals from the Florida Reef tract by investigating the effects on larval metabolism, survivorship, settlement, and post-settlement growth and survival. Additionally, a coupled biophysical model was developed to determine the potential changes in connectivity that may result from the biological effects of increased temperature and ocean acidification on the larval phase. The larval respiratory response of three Caribbean coral species revealed Orbicella faveolata as the most environmentally responsive with significant increases in respiration after 1 day exposure to increased temperature (68% greater than control conditions) with a counteracting effect of ocean acidification significantly decreasing respiration. The changes in metabolism over time correlated with decreased time to competency under elevated temperature in O. faveolata larvae, resulting in a greater number of settlers (76% greater than control) and a relative increase in local retention and self-recruitment rates as revealed by the biophysical model (5 and 7% greater than control respectively). However, when increased temperature occurred in combination with elevated CO2 levels, respiration was not significantly increased relative to control conditions and development of competency is minimally impacted. This resulted in a smaller increase in settlers (13% greater than control) and no significant changes in connectivity patterns. The post-settlement phase was similarly impacted with counteracting effects of increased temperature and ocean acidification on recruit growth.

Overall, this dissertation reveals the potential for adaptation to increased temperature in at least one important coral species (Orbicella faveolata) that is greatly diminished when encountered in combination with ocean acidification. These results encourage the reduction of carbon emissions to give coral species the chance to adapt to elevated temperatures through the recruitment of more resilient individuals without the additional stress of ocean acidification.

Continue reading ‘The combined effects of increased temperature and ocean acidification on the early life history stages of Caribbean coral and its implication for the recovery potential of Florida reefs’

Effects of current and future coastal upwelling conditions on the fertilization success of the red abalone (Haliotis rufescens)

Acidification, deoxygenation, and warming are escalating changes in coastal waters throughout the world ocean, with potentially severe consequences for marine life and ocean-based economies. To examine the influence of these oceanographic changes on a key biological process, we measured the effects of current and expected future conditions in the California Current Large Marine Ecosystem on the fertilization success of the red abalone (Haliotis rufescens). Laboratory experiments were used to assess abalone fertilization success during simultaneous exposure to various levels of seawater pH (gradient from 7.95 to 7.2), dissolved oxygen (DO) ($60 and 180 mm. kg SW) and temperature (9, 13, and 18 C). Fertilization success declined continuously with decreasing pH but dropped precipitously below a threshold near pH 7.55 in cool (9 C—upwelling) to average (13 C) seawater temperatures. Variation in DO had a negligible effect on fertilization. In contrast, warmer waters (18 C) often associated with El Nino Southern Oscillation conditions in central California acted antagonistically with decreasing pH, largely reducing the strong negative influence below the pH threshold. Experimental approaches that examine the interactive effects of multiple environmental drivers and also strive to characterize the functional response of organisms along gradients in environmental change are becoming increasingly important in advancing our understanding of the real-world consequences of changing ocean conditions.

Continue reading ‘Effects of current and future coastal upwelling conditions on the fertilization success of the red abalone (Haliotis rufescens)’

Naturally acidified habitat selects for ocean acidification–tolerant mussels

Ocean acidification severely affects bivalves, especially their larval stages. Consequently, the fate of this ecologically and economically important group depends on the capacity and rate of evolutionary adaptation to altered ocean carbonate chemistry. We document successful settlement of wild mussel larvae (Mytilus edulis) in a periodically CO2-enriched habitat. The larval fitness of the population originating from the CO2-enriched habitat was compared to the response of a population from a nonenriched habitat in a common garden experiment. The high CO2–adapted population showed higher fitness under elevated PCO2 (partial pressure of CO2) than the non-adapted cohort, demonstrating, for the first time, an evolutionary response of a natural mussel population to ocean acidification. To assess the rate of adaptation, we performed a selection experiment over three generations. CO2 tolerance differed substantially between the families within the F1 generation, and survival was drastically decreased in the highest, yet realistic, PCO2 treatment. Selection of CO2-tolerant F1 animals resulted in higher calcification performance of F2 larvae during early shell formation but did not improve overall survival. Our results thus reveal significant short-term selective responses of traits directly affected by ocean acidification and long-term adaptation potential in a key bivalve species. Because immediate response to selection did not directly translate into increased fitness, multigenerational studies need to take into consideration the multivariate nature of selection acting in natural habitats. Combinations of short-term selection with long-term adaptation in populations from CO2-enriched versus nonenriched natural habitats represent promising approaches for estimating adaptive potential of organisms facing global change.

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Symbiodinium mitigate the combined effects of hypoxia and acidification on a non-calcifying cnidarian

Anthropogenic nutrient inputs enhance microbial respiration within many coastal ecosystems, driving concurrent hypoxia and acidification. During photosynthesis, Symbiodinium spp., the microalgal endosymbionts of cnidarians and other marine phyla, produce O2 and assimilate CO2, and thus potentially mitigate the exposure of the host to these stresses. However, such a role for Symbiodinium remains untested for non-calcifying cnidarians. We therefore contrasted the fitness of symbiotic and aposymbiotic polyps of a model host jellyfish (Cassiopea sp.) under reduced O2 (~2.09mgL−1) and pH (~pH 7.63) scenarios in a full factorial experiment. Host fitness was characterised as asexual reproduction and their ability to regulate internal pH and Symbiodinium performance characterised by maximum photochemical efficiency, chla content, and cell density. Acidification alone resulted in 58% more asexual reproduction of symbiotic polyps than aposymbiotic polyps (and enhanced Symbiodinium cell density) suggesting Cassiopea sp. fitness was enhanced by CO2-stimulated Symbiodinium photosynthetic activity. Indeed, greater CO2 drawdown (elevated pH) was observed within host tissues of symbiotic polyps under acidification regardless of O2 conditions. Hypoxia alone produced 22% fewer polyps than ambient conditions regardless of acidification and symbiont status, suggesting Symbiodinium photosynthetic activity did not mitigate its effects. Combined hypoxia and acidification, however, produced similar numbers of symbiotic polyps compared with aposymbiotic kept under ambient conditions, demonstrating that the presence of Symbiodinium was key for mitigating the combined effects of hypoxia and acidification on asexual reproduction. We hypothesise that this mitigation occurred because of reduced photorespiration under elevated CO2 conditions where increased net O2 production ameliorates oxygen debt. We show that Symbiodinium play an important role in facilitating enhanced fitness of Cassiopea sp. polyps, and perhaps also other non-calcifying cnidarian hosts, to the ubiquitous effects of ocean acidification. Importantly we highlight that symbiotic, non-calcifying cnidarians may be particularly advantaged in productive coastal waters that are subject to simultaneous hypoxia and acidification.

Continue reading ‘Symbiodinium mitigate the combined effects of hypoxia and acidification on a non-calcifying cnidarian’

Global proteome profiling of a marine copepod and the mitigating effect of ocean acidification on mercury toxicity after multigenerational exposure

Previously, we found that ocean acidification (OA) mitigates mercury (Hg) toxicity to marine copepod Tigriopus japonicus under multigenerational exposure (four generations, F0-F3). To determine the response mechanisms of T. japonicus against long-term exposure to OA and Hg pollution, we investigated the proteome of F3 copepods after multigenerational exposure to four conditions: pCO2 400 μatm + control; pCO2 1000 μatm + control; pCO2 400 μatm + 1.0 µg/L Hg; and pCO2 1000 μatm + 1.0 µg/L Hg. Functional enrichment analysis indicated that OA enhanced the copepod’s energy production mainly by increasing protein assimilation and proteolysis as a compensatory strategy, which explained its physiological resilience to reduced pH. Conversely, Hg treatment decreased many critical processes, including ferric iron binding, antioxidant activity, cellular homeostasis, and glutathione metabolism, and these toxic events could translate into higher-level responses, i.e., restrained reproduction in copepods. Importantly, the mediation of Hg toxicity in T. japonicus by OA could be explained by the enhanced lysosome-autophagy pathway proteomes that are responsible for repairing/removing damaged proteins/enzymes under stress. Overall, this study provided molecular insights into the response of T. japonicus to long-term exposure of OA and Hg, with a particular emphasis on the mitigating impact of CO2-driven acidification on Hg toxicity.

Continue reading ‘Global proteome profiling of a marine copepod and the mitigating effect of ocean acidification on mercury toxicity after multigenerational exposure’

High pCO2 and elevated temperature reduce survival and alter development in early life stages of the tropical sea hare Stylocheilus striatus

Elevated temperature (ocean warming) and reduced oceanic pH (ocean acidification) are products of increased atmospheric pCO2, and have been shown in many marine taxa to alter morphology, impede development, and reduce fitness. Here, we investigated the effects of high pCO2 and elevated temperature on developmental rate, hatching success, and veliger morphology of embryos of the tropical sea hare, Stylocheilus striatus. Exposure to high pCO2 resulted in significant developmental delays, postponing hatching by nearly 24 h, whereas exposure to elevated temperature (in isolation or in combination with high pCO2) resulted in accelerated development, with larvae reaching several developmental stages approximately 48 h in advance of controls. Hatching success was reduced by ~20 and 55% under high pCO2 and warming, respectively, while simultaneous exposure to both conditions resulted in a nearly additive 70% reduction in hatching. In addition to these ontological and lethal effects, exposure of embryos to climate change stressors resulted in significant morphological effects. Larval shells were nearly 40% smaller under high pCO2 and warming in isolation and up to 53% smaller under multi-stressor conditions. In general, elevated temperature had the largest impact on development, with temperature-effects nearly 3.5-times the magnitude of high pCO2-effects. These results indicate that oceanic conditions congruent with climate change predictions for the end of the twenty-first century suppress successful development in S. striatus embryos, potentially reducing their viability as pelagic larvae.

Continue reading ‘High pCO2 and elevated temperature reduce survival and alter development in early life stages of the tropical sea hare Stylocheilus striatus’

Ocean acidification effects on mesozooplankton community development: Results from a long-term mesocosm experiment

Ocean acidification may affect zooplankton directly by decreasing in pH, as well as indirectly via trophic pathways, where changes in carbon availability or pH effects on primary producers may cascade up the food web thereby altering ecosystem functioning and community composition. Here, we present results from a mesocosm experiment carried out during 113 days in the Gullmar Fjord, Skagerrak coast of Sweden, studying plankton responses to predicted end-of-century pCO2 levels. We did not observe any pCO2 effect on the diversity of the mesozooplankton community, but a positive pCO2 effect on the total mesozooplankton abundance. Furthermore, we observed species-specific sensitivities to pCO2 in the two major groups in this experiment, copepods and hydromedusae. Also stage-specific pCO2 sensitivities were detected in copepods, with copepodites being the most responsive stage. Focusing on the most abundant species, Pseudocalanus acuspes, we observed that copepodites were significantly more abundant in the high-pCO2 treatment during most of the experiment, probably fuelled by phytoplankton community responses to high-pCO2 conditions. Physiological and reproductive output was analysed on P. acuspes females through two additional laboratory experiments, showing no pCO2 effect on females’ condition nor on egg hatching. Overall, our results suggest that the Gullmar Fjord mesozooplankton community structure is not expected to change much under realistic end-of-century OA scenarios as used here. However, the positive pCO2 effect detected on mesozooplankton abundance could potentially affect biomass transfer to higher trophic levels in the future.

Continue reading ‘Ocean acidification effects on mesozooplankton community development: Results from a long-term mesocosm experiment’

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Ocean acidification in the IPCC AR5 WG II

OUP book