Posts Tagged 'reproduction'

Reduced seawater pH alters marine biofilms with impacts for marine polychaete larval settlement

Highlights

• Reduced seawater pH strongly influences biofilm community composition, at both eukaryotic and prokaryotic level

• For older biofilms, biofilm age plays no role in community composition

• Incubation under different pH treatments results in variations in apparent colour and structural complexity of marine biofilms

• Incubation of marine biofilms under different pH treatments alters the settlement response in marine invertebrates

• The changes in marine biofilm community composition induced by seawater pH are most likely responsible for the changes observed in invertebrate settlement selectivity

Abstract

Ocean acidification (OA) can negatively affect early-life stages of marine organisms, with the key processes of larval settlement and metamorphosis potentially vulnerable to reduced seawater pH. Settlement success depends strongly on suitable substrates and environmental cues, with marine biofilms as key settlement inducers for a range of marine invertebrate larvae. This study experimentally investigated (1) how seawater pH determines growth and community composition of marine biofilms, and (2) whether marine biofilms developed under different pH conditions can alter settlement success in the New Zealand serpulid polychaete Galeolaria hystrix. Biofilms were developed under six pH(T) treatments (spanning from 7.0 to 8.1 [ambient]) in a flow-through system for up to 14 months. Biofilms of different ages (7, 10 and 14 months) were used to assay successful settlement of competent G. hystrix larvae reared under ambient conditions. Biofilm microbiomes were characterized through amplicon sequencing of the small subunit ribosomal rRNA gene (16S and 18S). Biofilm community composition was stable over time within each pH treatment and biofilm age did not affect larval settlement selectivity. Seawater pH treatment strongly influenced biofilm community composition, as well as subsequent settlement success when biofilms were presented to competent Galeolaria larvae. Exposure to biofilms incubated under OA-treatments caused a decrease in larval settlement of up to 40% compared to the ambient treatments. We observed a decrease in settlement on biofilms relative to ambient pH for slides incubated at pH 7.9 and 7.7. This trend was reversed at pH 7.4, resulting in high settlement, comparable to ambient biofilms. Settlement decreased on biofilms from pH 7.2, and no settlement was observed on biofilms from pH 7.0. For the first time, we show that long-term incubation of marine biofilms under a wide range of reduced seawater pH treatments can alter marine biofilms in such a way that settlement success in marine invertebrates can be compromised.

Continue reading ‘Reduced seawater pH alters marine biofilms with impacts for marine polychaete larval settlement’

Effects of salinity, pH and alkalinity on hatching rate of fertilized eggs of Penaeus monodon

The fertilized eggs of “Nanhai 2” Penaeus monodon bred by our research group were incubated at the same temperature (30°C), different salinity (20, 25, 30, 35, 40), different pH (7.0, 7.5, 8.0, 8.5, 9.0) and different alkalinity (2.0 mmol/L, 2.5 mmol/L, 3.0 mmol/L, 3.5 mmol/L, 4.0 mmol/L) to explore the effects of salinity, pH and alkalinity on hatching rate of fertilized eggs of P. monodon. The results showed that the hatching rate of fertilization rate of P. monodon was closely related to salinity, and the best hatching rate was obtained when the seawater salinity was 30 with the average hatching rate was 82.60%. The hatching rate was very low when the salinity was as low as 20 or as high as 40, which was significantly lower than that of other treatments (P<0.05). The hatching effect of the fertilized eggs of P. monodon was closely related to the pH value of seawater, and the slightly alkaline seawater was conducive to the normal development of the fertilized eggs. Among them, the hatching effect of the seawater pH value of 8.0 was the best, and the average hatching rate of the fertilized eggs was 80.62%. Too low or too high pH value of the seawater was not conducive to the development of the embryo, and the hatching rate of the fertilized eggs decreased in varying degrees. There was no significant correlation between the hatching effect of fertilized eggs and the change of seawater alkalinity. The average hatching rate of fertilized eggs ranged from 78.65% to 83.12% in the alkalinity range of 2.0-4.0 mmol/L

Continue reading ‘Effects of salinity, pH and alkalinity on hatching rate of fertilized eggs of Penaeus monodon’

Invariant gametogenic response of dominant infaunal bivalves from the Arctic under ambient and near-future climate change conditions

Arctic marine ecosystems are undergoing a series of major rapid adjustments to the regional amplification of climate change, but there is a paucity of knowledge about how changing environmental conditions might affect reproductive cycles of seafloor organisms. Shifts in species reproductive ecology may influence their entire life-cycle, and, ultimately, determine the persistence and distribution of taxa. Here, we investigate whether the combined effects of warming and ocean acidification based on near-future climate change projections affects the reproductive processes in benthic bivalves (Astarte crenata and Bathyarca glacialis) from the Barents Sea. Both species present large oocytes indicative of lecithotrophic or direct larval development after ∼4 months exposure to ambient [<2°C, ∼400 ppm (CO2)] and near-future [3–5°C, ∼550 ppm (CO2)] conditions, but we find no evidence that the combined effects of acidification and warming affect the size frequency distribution of oocytes. Whilst our observations are indicative of resilience of this reproductive stage to global changes, we also highlight that the successful progression of gametogenesis under standard laboratory conditions does not necessarily mean that successful development and recruitment will occur in the natural environment. This is because the metabolic costs of changing environmental conditions are likely to be offset by, as is common practice in laboratory experiments, feeding ad libitum. We discuss our findings in the context of changing food availability in the Arctic and conclude that, if we are to establish the vulnerability of species and ecosystems, there is a need for holistic approaches that incorporate multiple system responses to change.

Continue reading ‘Invariant gametogenic response of dominant infaunal bivalves from the Arctic under ambient and near-future climate change conditions’

Feedback mechanisms stabilise degraded turf algal systems at a CO2 seep site

Human activities are rapidly changing the structure and function of coastal marine ecosystems. Large-scale replacement of kelp forests and coral reefs with turf algal mats is resulting in homogenous habitats that have less ecological and human value. Ocean acidification has strong potential to substantially favour turf algae growth, which led us to examine the mechanisms that stabilise turf algal states. Here we show that ocean acidification promotes turf algae over corals and macroalgae, mediating new habitat conditions that create stabilising feedback loops (altered physicochemical environment and microbial community, and an inhibition of recruitment) capable of locking turf systems in place. Such feedbacks help explain why degraded coastal habitats persist after being initially pushed past the tipping point by global and local anthropogenic stressors. An understanding of the mechanisms that stabilise degraded coastal habitats can be incorporated into adaptive management to better protect the contribution of coastal systems to human wellbeing.

Continue reading ‘Feedback mechanisms stabilise degraded turf algal systems at a CO2 seep site’

Gene expression responses of larval gopher (Sebastes carnatus) and blue (S. mystinus) rockfish to ocean acidification and hypoxia

Global climate change is driving shifts in ocean chemistry, which combined with intensification of coastal upwelling, reduces ocean pH and dissolved oxygen (DO) content in the nearshore habitats of the California Current System. Physiological plasticity, within and across generations, might be especially important for long-lived, late-to-mature species, like rockfishes (genus Sebastes), that may be unable to keep pace with climate change via genetic adaptation. Rockfishes exhibit matrotrophic viviparity and may be able to buffer their offspring from environmental stress through early developmental exposure or transgenerational plasticity (non-genetic inheritance of phenotypes). In this study, mature female gopher (S. carnatus) and blue (S. mystinus) rockfish were pre-exposed to one of four treatments; 1) control conditions, 2) low pH, 3) low DO, or 4) combined low pH/DO stressors during embryonic growth (i.e. fertilization and gestation), followed by a 5-day larval exposure after birth in either the same or a different treatment received by mothers. I used RNA sequencing to determine how the maternal environment affected larval rockfish gene expression (GE) at birth, after the 5-day larval exposure in either the same maternal treatment or a novel pH/DO environment, and between larvae sampled at birth and after the 5-day larval exposure within each treatment. For both species, I found that the maternal exposure drove larval GE patterns regardless of sampling time point or treatment. Furthermore, the maternal environment continued to strongly influence larval GE for at least the first five days after birth. In gopher rockfish, larvae differentially expressed fewer genes at birth between the control and hypoxic groups than larvae that gestated in and remained in the same treatment and were sampled after the 5-day larval exposure. Gene functions also shifted; at day 5, there was an increase in differentially expressed genes that were related to metabolic pathways, implying that the larvae in the hypoxic treatment are responding to the stressor. In both species, I found that larvae which experienced a pH and/or hypoxic stressor during the maternal exposure had fewer differentially expressed genes across time compared to larvae that experienced control conditions. This pattern remained consistent, even if the larvae were placed into control conditions for the 5-day larval exposure, indicating that exposure to low pH/DO stressors might cause a delay in development. These data suggest that rockfish may not be able to buffer their offspring from environmental stressors, highlighting the important role of the maternal environment during gestation. Between the two species, however, blue rockfish may in fact fare better in future conditions as their reproductive season occurs before the onset of strong spring upwelling, when more hypoxic and low pH water intrudes the nearshore. However, if future climate models are correct, shifts in the timing and intensity of upwelling season may overlap with the reproductive season in blue rockfish. Elucidating the critical role of the maternal environment on offspring physiology can help us better understand how economically and ecologically important species will fare in the face of climate change.

Continue reading ‘Gene expression responses of larval gopher (Sebastes carnatus) and blue (S. mystinus) rockfish to ocean acidification and hypoxia’

American lobster postlarvae alter gene regulation in response to ocean warming and acidification

Anthropogenic carbon emissions released into the atmosphere is driving rapid, concurrent increases in temperature and acidity across the world’s oceans. Disentangling the interactive effects of warming and acidification on vulnerable life stages is important to our understanding of responses of marine species to climate change. This study evaluates the interactive effects of these stressors on the acute response of gene expression of postlarval American lobster (Homarus americanus), a species whose geographic range is warming and acidifying faster than most of the world’s oceans. In the context of our experiment, we found two especially noteworthy results: First, although physiological end points have consistently been shown to be more responsive to warming in similar experimental designs, our study found gene regulation to be considerably more responsive to elevated pCO2. Furthermore, the combined effect of both stressors on gene regulation was significantly greater than either stressor alone. Using a full factorial experimental design, lobsters were raised in control and elevated pCO2 concentrations (400 ppm and 1,200 ppm) and temperatures (16°C and 19°C). A transcriptome was assembled from an identified 414,517 unique transcripts. Overall, 1,108 transcripts were differentially expressed across treatments, several of which were related to stress response and shell formation. When temperature alone was elevated (19°C), larvae downregulated genes related to cuticle development; when pCO2 alone was elevated (1,200 ppm), larvae upregulated chitinase as well as genes related to stress response and immune function. The joint effects of end‐century stressors (19°C, 1,200 ppm) resulted in the upregulation of those same genes, as well as cellulase, the downregulation of calcified cuticle proteins, and a greater upregulation of genes related to immune response and function. These results indicate that changes in gene expression in larval lobster provide a mechanism to respond to stressors resulting from a rapidly changing environment.

Continue reading ‘American lobster postlarvae alter gene regulation in response to ocean warming and acidification’

Impacts of hypoxic events surpass those of future ocean warming and acidification

Over the past decades, three major challenges to marine life have emerged as a consequence of anthropogenic emissions: ocean warming, acidification and oxygen loss. While most experimental research has targeted the first two stressors, the last remains comparatively neglected. Here, we implemented sequential hierarchical mixed-model meta-analyses (721 control–treatment comparisons) to compare the impacts of oxygen conditions associated with the current and continuously intensifying hypoxic events (1–3.5 O2 mg l−1) with those experimentally yielded by ocean warming (+4 °C) and acidification (−0.4 units) conditions on the basis of IPCC projections (RCP 8.5) for 2100. In contrast to warming and acidification, hypoxic events elicited consistent negative effects relative to control biological performance—survival (–33%), abundance (–65%), development (–51%), metabolism (–33%), growth (–24%) and reproduction (–39%)—across the taxonomic groups (mollusks, crustaceans and fish), ontogenetic stages and climate regions studied. Our findings call for a refocus of global change experimental studies, integrating oxygen concentration drivers as a key factor of ocean change. Given potential combined effects, multistressor designs including gradual and extreme changes are further warranted to fully disclose the future impacts of ocean oxygen loss, warming and acidification.

Continue reading ‘Impacts of hypoxic events surpass those of future ocean warming and acidification’

Effect of climate change on endocrine regulation of fish reproduction

Climate change is a serious concern for aquatic environment which alters physical and chemical properties of the water causing negative impacts on the aquatic organisms including fish. Temperature alteration, ocean acidification, and hypoxia are the major factors associated with climate change, which affects the endocrine regulation of fish reproduction profoundly. Fish being poikilothermic animals, the change in environmental temperature directly affects their body temperature. Seasonal change in temperature has either fastened the spawning process or delayed the process depending upon the species and their spawning window. Ocean acidification and hypoxia had caused threat to larval survival by impairing larval behavior and sensory capacity. Often climate change shows extreme effect of the demography of fishes by leading to a non-spawning season in some species. Depending upon species, geographic location, and spawning ground, exogenous factors possess significant threat on fish reproduction. The present chapter will provide baseline information on effect of different factors of climate change such as temperature, ocean acidification, and hypoxia on fish reproduction and early ontogenesis phase of fish.

Continue reading ‘Effect of climate change on endocrine regulation of fish reproduction’

Ocean acidification boosts reproduction in fish via indirect effects

Ocean acidification affects species populations and biodiversity through direct negative effects on physiology and behaviour. The indirect effects of elevated CO2 are less well known and can sometimes be counterintuitive. Reproduction lies at the crux of species population replenishment, but we do not know how ocean acidification affects reproduction in the wild. Here, we use natural CO2 vents at a temperate rocky reef and show that even though ocean acidification acts as a direct stressor, it can indirectly increase energy budgets of fish to stimulate reproduction at no cost to physiological homeostasis. Female fish maintained energy levels by compensation: They reduced activity (foraging and aggression) to increase reproduction. In male fish, increased reproductive investment was linked to increased energy intake as mediated by intensified foraging on more abundant prey. Greater biomass of prey at the vents was linked to greater biomass of algae, as mediated by a fertilisation effect of elevated CO2 on primary production. Additionally, the abundance and aggression of paternal carers were elevated at the CO2 vents, which may further boost reproductive success. These positive indirect effects of elevated CO2 were only observed for the species of fish that was generalistic and competitively dominant, but not for 3 species of subordinate and more specialised fishes. Hence, species that capitalise on future resource enrichment can accelerate their reproduction and increase their populations, thereby altering species communities in a future ocean.

Continue reading ‘Ocean acidification boosts reproduction in fish via indirect effects’

Effect of CO2 driven ocean acidification on calcification, physiology and ovarian cells of tropical sea urchin Salmacis virgulata – a microcosm approach

In the present study, we depict the structural modification of test minerals, physiological response and ovarian damage in the tropical sea urchin Salmacis virgulata using microcosm CO2 (Carbon dioxide) perturbation experiment. S. virgulata were exposed to hypercapnic conditions with four different pH levels using CO2 gas bubbling method that reflects ambient level (pH 8.2) and elevated pCO2 scenarios (pH 8.0, 7.8 and 7.6). The variations in physical strength and mechanical properties of S. virgulata test were evaluated by thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray diffraction analysis and scanned electron microscopy analysis. Biomarker enzymes such as glutathione-S-transferase, catalase, acetylcholine esterase, lipid peroxidase and reduced glutathione showed physiological stress and highly significant (p < 0.01) towards pH 7.6 and 7.8 treatments. Ovarian cells were highly damaged at pH 7.6 and 7.8 treatments. This study proved that the pH level 7.6 and 7.8 drastically affect calcification, physiological response and ovarian cells in S. virgulata.

Continue reading ‘Effect of CO2 driven ocean acidification on calcification, physiology and ovarian cells of tropical sea urchin Salmacis virgulata – a microcosm approach’

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