The future is now: marine aquaculture in the anthropocene

Aquaculture now produces more seafood than wild capture fisheries and this production is expected to at least double by 2050. Representing almost half of global production, marine aquaculture will contribute to sustainably feeding the growing humanity. However, climate change will undoubtedly challenge the future growth of marine aquaculture. Temperature and sea-level rise, shifts in precipitation, freshening from glacier melt, changing ocean productivity, and circulation patterns, increasing occurrence of extreme climatic events, eutrophication, and ocean acidification are all stressors that will influence marine aquaculture. The objective of this themed article set was to bring together contributions on the broad theme of the potential impacts, adaptation, and mitigation strategies of marine aquaculture to climate change. Here we present 14 papers covering a diverse set of approaches including experimentation, modelling, meta-analysis and review, and disciplines like biology, ecology, economics, and engineering. These articles focus on the impacts of climate change-related stressors on the aquaculture potential itself and on the resulting ecological interactions (e.g. parasitism and predation), on phenotypic plasticity and adaptation potential of species, and on measures to mitigate the effects of climate change on aquaculture and vice versa. Considering this, adaptation of the aquaculture sector relies on anticipating the biogeographical changes in the distribution of species, determining their potential for adaptation and selective breeding for resistance or tolerance to climate-induced stressors, and fostering ecosystem resilience by means of conservation, restoration, or remediation. By will or by force, aquaculture will contribute to the low carbon economy of tomorrow. Aquaculture must move towards a new paradigm where the carbon footprint and the analysis of the life cycle of products are at least as important as economic profitability.

Continue reading ‘The future is now: marine aquaculture in the anthropocene’

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 ocean acidification on calcification of the sub-Antarctic pteropod Limacina retroversa

Ocean acidification is expected to impact the high latitude oceans first, as CO2 dissolves more easily in colder waters. At the current rate of anthropogenic CO2 emissions, the sub-Antarctic Zone will start to experience undersaturated conditions with respect to aragonite within the next few decades, which will affect marine calcifying organisms. Shelled pteropods, a group of calcifying zooplankton, are considered to be especially sensitive to changes in carbonate chemistry because of their thin aragonite shells. Limacina retroversa is the most abundant pteropod in sub-Antarctic waters, and plays an important role in the carbonate pump. However, not much is known about its response to ocean acidification. In this study, we investigated differences in calcification between L. retroversa individuals exposed to ocean carbonate chemistry conditions of the past (pH 8.19; mid-1880s), present (pH 8.06), and near-future (pH 7.93; predicted for 2050) in the sub-Antarctic. After 3 days of exposure, calcification responses were quantified by calcein staining, shell weighing, and Micro-CT scanning. In pteropods exposed to past conditions, calcification occurred over the entire shell and the leading edge of the last whorl, whilst individuals incubated under present and near-future conditions mostly invested in extending their shells, rather than calcifying over their entire shell. Moreover, individuals exposed to past conditions formed larger shell volumes compared to present and future conditions, suggesting that calcification is already decreased in today’s sub-Antarctic waters. Shells of individuals incubated under near-future conditions did not increase in shell weight during the incubation, and had a lower density compared to past and present conditions, suggesting that calcification will be further compromised in the future. This demonstrates the high sensitivity of L. retroversa to relatively small and short-term changes in carbonate chemistry. A reduction in calcification of L. retroversa in the rapidly acidifying waters of the sub-Antarctic will have a major impact on aragonite-CaCO3 export from oceanic surface waters to the deep sea.

Continue reading ‘Effects of ocean acidification on calcification of the sub-Antarctic pteropod Limacina retroversa’

New version of the R package seacarb available

The R package seacarb calculates parameters of the seawater carbonate system and includes functions useful for ocean acidification research. It has just been updated to v3.2.16. It is recommended to use this version rather than any of the earlier ones. The new or updated functions are listed below; the seacarb Change Log provides more details:

Update: all functions using K1 and K2 now provide the additional formulation of Shockman & Byrne (2021) to calculate these constants.

Schockman K.M. & Byrne, R.H., Spectrophotometric Determination of the Bicarbonate Dissociation Constant in Seawater, Geochimica et Cosmochimica Acta (2021), doi: https://doi.org/10.1016/j.gca.2021.02.008

Continue reading ‘New version of the R package seacarb available’

Calcifying phytoplankton demonstrate an enhanced role in greenhouse atmospheric CO2 regulation

The impact of calcifying phytoplankton on atmospheric CO2 concentration is determined by a number of factors, including their degree of ecological success as well as the buffering capacity of the ocean/marine sediment system. The relative importance of these factors has changed over Earth’s history and this has implications for atmospheric CO2 and climate regulation. We explore some of these implications with four “Strangelove” experiments: two in which soft-tissue production and calcification is stopped, and two in which only calcite production is forced to stop, in idealized icehouse and greenhouse climates. We find that in the icehouse climate the loss of calcifiers compensates the atmospheric CO2 impact of the loss of all phytoplankton by roughly one-sixth. But in the greenhouse climate the loss of calcifiers compensates the loss of all phytoplankton by about half. This increased impact on atmospheric CO2 concentration is due to the combination of higher rates of pelagic calcification due to warmer temperatures and weaker buffering due to widespread acidification in the greenhouse ocean. However, the greenhouse atmospheric temperature response per unit of CO2 change to removing ocean soft-tissue production and calcification is only one-fourth that in an icehouse climate, owing to the logarithmic radiative forcing dependency on atmospheric CO2 thereby reducing the climate feedback of mass extinction. This decoupling of carbon cycle and temperature sensitivities offers a mechanism to explain the dichotomy of both enhanced climate stability and destabilization of the carbonate compensation depth in greenhouse climates.

Continue reading ‘Calcifying phytoplankton demonstrate an enhanced role in greenhouse atmospheric CO2 regulation’

Interactive effects of elevated CO2 concentration and light on the picophytoplankton Synechococcus

Synechococcus is a major contributor to the primary production in tropic and subtropical oceans worldwide. Responses of this picophytoplankton to changing light and CO2 levels is of general concern to understand its ecophysiology in the context of ocean global changes. We grew Synechococcus sp. (WH7803), originally isolated from subtropic North Atlantic Ocean, under different PAR levels for about 15 generations and examined its growth, photochemical performance and the response of these parameters to elevated CO2 (1,000 μatm). The specific growth rate increased from 6 μmol m–2 s–1 to reach a maximum (0.547 ± 0.026) at 25 μmol m–2 s–1, and then became inhibited at PAR levels over 50 μmol m–2 s–1, with light use efficiency (α) and photoinhibition coefficient (β) being 0.093 and 0.002, respectively. When the cells were grown at ambient and elevated CO2 concentration (400 vs. 1,000 μatm), the high-CO2 grown cells showed significantly enhanced rates of electron transport and quantum yield as well as significant increase in specific growth rate at the limiting and inhibiting PAR levels. While the electron transport rate significantly increased at the elevated CO2 concentration under all tested light levels, the specific growth did not exhibit significant changes under the optimal growth light condition. Our results indicate that Synechococcus WH7803 grew faster under the ocean acidification (OA) treatment induced by CO2 enrichment only under limiting and inhibiting light levels, indicating the interactive effects and implying that the picophytoplankton respond differentially at different depths while exposing changing light conditions.

Continue reading ‘Interactive effects of elevated CO2 concentration and light on the picophytoplankton Synechococcus’

Removing carbon dioxide through ocean alkalinity enhancement and seaweed cultivation: legal challenges and opportunities

Scientists increasingly agree that carbon dioxide removal will be needed, alongside deep emissions cuts, to stave off the worst impacts of climate change. A wide variety of technologies and strategies have been proposed to remove carbon dioxide from the atmosphere. To date, most research has focused on terrestrial-based approaches, but they often have large land requirements, and may present other risks and challenges. As such, there is growing interest in using the oceans, which have already absorbed more than a quarter of anthropogenic carbon dioxide emissions, and could become an even larger carbon sink in the future.

This paper explores two ocean-based carbon dioxide removal strategies—ocean alkalinity enhancement and seaweed cultivation. Ocean alkalinity enhancement involves adding alkalinity to ocean waters, either by discharging alkaline rocks or through an electrochemical process, which increases ocean pH levels and thereby enables greater uptake of carbon dioxide, as well as reducing the adverse impacts of ocean acidification. Seaweed cultivation involves the growing of kelp and other macroalgae to store carbon in biomass, which can then either be used to replace more greenhouse gas-intensive products or sequestered.

Continue reading ‘Removing carbon dioxide through ocean alkalinity enhancement and seaweed cultivation: legal challenges and opportunities’

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’

Ocean acidification compromises energy management in Sparus aurata (Pisces: Teleostei)

Highlights

• Gilthead seabream (Sparus aurata) increased catabolic routes to face long-term hypercapnia.

• Glycogen stored in liver and white muscle is consumed at high environmental pCO2.

• Amino acids are relevant energy sources at higher pCO2 environments.

• Long-term hypercapnia may lead to delayed growth rates in teleost fish.

Abstract

The effects of ocean acidification mediated by an increase in water pCO2 levels on marine organisms are currently under debate. Elevated CO2 concentrations in the seawater induce several physiological responses in teleost fish, including acid-base imbalances and osmoregulatory changes. However, the consequences of CO2 levels enhancement on energy metabolism are mostly unknown. Here we show that 5 weeks of exposure to hypercapnia (950 and 1800 μatm CO2) altered intermediary metabolism of gilthead seabream (Sparus aurata) compared to fish acclimated to current ocean values (440 μatm CO2). We found that seabream compromises its physiological acid-base balance with increasing water CO2 levels and the subsequent acidification. Intestinal regions (anterior, mid, and rectum) engaged in maintaining this balance are thus altered, as seen for Na+/K+-ATPase and the vacuolar-type H+-ATPase activities. Moreover, liver and muscle counteracted these effects by increasing catabolic routes e.g., glycogenolysis, glycolysis, amino acid turnover, and lipid catabolism, and plasma energy metabolites were altered. Our results demonstrate how a relatively short period of 5 weeks of water hypercapnia is likely to disrupt the acid-base balance, osmoregulatory capacity and intermediary metabolism in S. aurata. However, long-term studies are necessary to fully understand the consequences of ocean acidification on growth and other energy-demanding activities, such as reproduction.

Continue reading ‘Ocean acidification compromises energy management in Sparus aurata (Pisces: Teleostei)’

Effect of ocean acidification on bacterial metabolic activity and community composition in oligotrophic oceans, inferred from short-term bioassays

Increasing anthropogenic CO2 emissions in recent decades cause ocean acidification (OA), affecting carbon cycling in oceans by regulating eco-physiological processes of plankton. Heterotrophic bacteria play an important role in carbon cycling in oceans. However, the effect of OA on bacteria in oceans, especially in oligotrophic regions, was not well understood. In our study, the response of bacterial metabolic activity and community composition to OA was assessed by determining bacterial production, respiration, and community composition at the low-pCO2 (400 ppm) and high-pCO2 (800 ppm) treatments over the short term at two oligotrophic stations in the northern South China Sea. Bacterial production decreased significantly by 17.1–37.1 % in response to OA, since bacteria with high nucleic acid content preferentially were repressed by OA, which was less abundant under high-pCO2 treatment. Correspondingly, shifts in bacterial community composition occurred in response to OA, with a high fraction of the small-sized bacteria and high bacterial species diversity in a high-pCO2 scenario at K11. Bacterial respiration responded to OA differently at both stations, most likely attributed to different physiological responses of the bacterial community to OA. OA mitigated bacterial growth efficiency, and consequently, a larger fraction of DOC entering microbial loops was transferred to CO2.

Continue reading ‘Effect of ocean acidification on bacterial metabolic activity and community composition in oligotrophic oceans, inferred from short-term bioassays’

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