54. Who is the master? Trade-off between competitive ability and resistance to elevated pCO2

Giannina S.I. Hattich

Background
Ocean acidification negatively impacts calcification and growth rate of calcifying phytoplankton species. Under future conditions species and genotypes
that are more resistant towards elevated pCO should thus have an advantage.

Theory, however, states that “a jack in every trait is a master of none”. Applying this theory, highly resistant species and genotypes towards elevated pCO might be weaker competitors. If selection in nature acts along such a trade-off curve the
selective outcome under competition between all genotypes and elevated CO at the same time should reflect the expectations raised by the trade-off curve.

Methods
We set out to test if a trade-off between competitive ability and the resistance to ocean acidification exists among nine genotypes of the planktonic calcifier Emiliania huxleyi. The resistance to elevated pCO
was assessed by comparing the plastic response in growth rate and carrying capacity among genotypes. The relative competitive ability was assessed in a separate experiment by measuring competitive exclusion in all 36 two-genotype combinations and ranking the competitive ability of each of the genotypes accordingly.

Findings
The resistance to elevated pCO conditions differed significantly between the tested genotypes. Preliminary results also show that genotypes differed in competitive ability and that competitive ability was further altered under high pCO. Awaiting the final analyses, these results point towards the existence of a trade-off between competitive ability and resistance to enhanced seawater CO concentrations.

Conclusions

Knowledge of the selective force of pCO including a potential tradeoff in competitive phytoplankton assemblages will enhance the predictive power for
projecting future changes In phytoplankton
communities in a high-CO world.

49. Effect of Ocean Acidification on the Nutritional Quality of Phytoplankton for Copepod Reproduction

Morgan T Meyers (1), Edward J Carpenter (1), William P Cochlan (1), Wim J Kimmerer (1)

1 Romberg Tiburon Center for Environmental Studies, Tiburon, CA, 94920, USA

Background
Phytoplankton are the oceans’ primary producers of polyunsaturated fatty acids (PUFA), which support the health and reproduction of heterotrophic marine organisms at higher trophic levels. It is hypothesized that future ocean acidification (OA) conditions could change the availability of phytoplankton PUFAs for ecologically significant consumers such as copepods, affecting their reproductive success in an increasingly acidified environment.

Methods
Three species of phytoplankton (Rhodomonas salina, Skeletonema marinoi, Prorocentrum micans) were grown under present-day (400ppm CO2, pH~8.1) and predicted future (1000ppm CO2, pH~7.8) oceanic conditions using nitrate-limited semi-continuous batch cultures. For four days, female Acartia tonsa copepods were fed a phytoplankton mixture from either the present-day or predicted-future treatment cultures. To assess changes in phytoplankton PUFA content, fatty acid profiles were analysed via capillary gas chromatography. Copepod egg production (EP), hatching success (HS), and egg viability (EV) were analysed to assess changes in copepod reproductive success.

Findings
CO2 concentration changed the composition of fatty acids in the phytoplankton used for the copepod diet. Under high pCO2 conditions, the relative proportion of PUFAs to total fatty acids was smaller (R. salina 21.5%; S. marinoi 14.1%; P. micans 14.4%) compared to that found in phytoplankton cultured under present-day pCO2 conditions (R. salina 28.8%, S. marinoi 32.7%, P. micans 39.3%). Copepod reproduction analyses show that females fed the high pCO2 phytoplankton had lower EP (median=13 eggs female-1), HS (median=12%), and EV (median=0%) compared to reproductive success of females fed the present-day pCO2 phytoplankton (EP median=25 eggs female-1; HS median=91.5%; EV median=98%).

Conclusions
This laboratory study demonstrates that OA can change the nutritional quality of primary producers, which affects the potential reproductive success of fundamental primary consumers.

Responses of marine organisms to climate change and ocean acidification across ocean regions

Chair: Ken Caldeira

Elvira Poloczanska(1)

1 CSIRO Oceans and Atmosphere, Brisbane, Qld 4072, Australia

Background
Ocean acidification is occurring concurrently with other physical and chemical changes in the ocean as a result of anthropogenic greenhouse gas emissions, with serious implications for marine species and concomitant risks to marine industries dependent on those species. I present the results of a meta-analysis of the responses of marine ecosystems and species to climate change and ocean acidification across ocean regions, from the boreal and polar systems to oligotrophic tropical seas.

Methods
I draw on a marine climate-change impacts database comprising of >1900 observations of marine ecological impacts of climate change from >230 peer-reviewed publications. Observations of ecological responses were classified as changes in abundance, distribution, phenology, demography and calcification. Each observation was assessed for consistency with theoretical expectations from climate change and includes examples where responses were equivocal or zero

Findings
I present a global map of species responses to climate change and ocean acidification. The volume and type of evidence of species responses to climate change is variable across ocean regions and taxonomic groups, with much evidence from high latitude northern hemisphere oceans. In contrast, observations of changing calcification were predominantly from tropical oceans, reflecting the dominance of coral studies. At a species level, impacts on the abundance and distribution (including depth shifts) of marine species are widely reported (41%), while less evidence exists for phenology change (14%) and few observations of demography (3%) and changing calcification (2%), presumably reflecting the very recent emergence of ocean acidification as a concern and in the development of technologies for long-term monitoring of ocean acidification.

Future ecosystem resistance to a high-CO2 world: stabilising effect of ecological compensation

Chair: Ken Caldeira

Sean D. Connell (1)*, Giulia Ghedini (2), Bayden Russell (3)

1,2 The University of Adelaide, Adelaide, South Australia, 5005, Australia
3 The University of Hong Kong, Kong Hong

Background
The natural processes that stabilise ecosystems against change from enriched CO2 can be powerful, but there is almost no recognition for them among those that study climate change in the sea. In the absence of tests of compensatory processes to enriched CO2, we run the risk of over-estimating the effects of a high-CO2 world.

Methods
We tested the strength of compensatory processes that counter the effects of enriched CO2 to prevent community change. Experimental tests observed the countervailing strength of trophic compensation (i.e. herbivory) to absorb ecosystem change (i.e. the expansion of mat-forming algae to displace kelp forests).

Findings
CO2 drove a reversal in competitive dominance of habitat (from kelp to mats), but in the presence of herbivores this switch is countered by a proportional countervailing response that eliminates its otherwise unchecked effect. This capacity for adjustment in strength of trophic interactions, whilst acting as a relatively imperceptible mechanism to absorb global and local disturbances, enhances community stability well before significant loss of species occurs.

Conclusions
This capacity of natural systems to absorb the effects of CO2 without undergoing major change is a critical and almost unstudied aspect of future ecosystem stability. Compensatory effects are likely to maintain the resistance of communities to a high-CO2 world more deeply than current thinking allows.

Variability in response of Antarctic marine microbes to enhanced pCO2

Chair: Sean Connell

Andrew Davidson (1,2,3), Karen Westwood (1,2,3), Paul Thomson (4), Stacy Deppeler (3), Penelope Pascoe (1), Simon Wright (1,2,3), Imojen Pearce (1,2,3), Rick van den Enden (1,2,3), Rob Johnson (5), Kai Schulz(6), Bronte Tilbrook (7), Miguel DeSalas (8)
1Australian Antarctic Division, Kingston, Tasmania, 7050, Australia
2Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Hobart, Tasmania, 7001, Australia
3Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, 7001, Australia
4The University of Western Australia, Crawley, Western Australia, 6009, Australia
5Bureau of Meteorology, Melbourne, Victoria, 3001, Australia
6Southern Cross University, East Lismore, NSW, 2480, Australia
7Commonwealth Scientific and Industrial Research Organisation (CSIRO) Marine and Atmospheric Research, Hobart, Tasmania, 7001, Australia
8Tasmanian Herbarium, Tasmanian Museum and Art Gallery, Hobart, Tasmanian 7005, Australia

Background
The response of organisms to enhanced pCO 2 can differ with changes in environment and among strains/species. Consequently, spatial and temporal changes in community structure, and physical or chemical environment, can alter the response of organisms to CO2. Establishing the nature and extent of these changes is vital if we are to predict the effects of ocean acidification on ecosystems and the services they provide.

Methods
The effect of elevated pCO2 on natural communities of marine microbes was determined within and between seasons at Davis Station, Antarctica. Four experiments were performed, in which coastal sea water was incubated at different CO2 concentrations in 6 x 650 L minicosm tanks.

Findings
The effects of CO 2 on coastal Antarctic microbial communities were similar in nature (sign) for all 4 experiments. This was despite changes in the microbial community and the physical and chemical environment among experiments. The threshold CO2 concentration required to elicited changes in the microbial community was ~2 x current pCO2 (800-1200 µatm). Above this threshold, rates of biomass accumulation and primary productivity fell and picoplankton abundance (autotrophs and prokaryotes) increased in all experiments. The magnitude of the CO2-induced change was apparently mediated by nutrient availability, acclimation, community composition and grazing.

Conclusions
The consistent nature of microbial responses to elevated pCO2 simplifies attempts to model and predict the effects of OA on the microbial loop in Antarctic coastal waters over time.

Ocean acidification alters marine food chains

Chair: Ana Queiros

Ivan Nagelkerken(1), Sean D. Connell(1)

1 School of Biological Sciences, The University of Adelaide, Adelaide SA 5005, Australia

Background
Ocean acidification has detrimental effects on a wide range of species, but we know relatively little about how it affects species interactions, particularly trophic interactions.

Methods
We performed a meta-analysis, a large mesocosm study, and a study on natural CO 2 vents to evaluate how ocean acidification – and its combination with ocean warming – affects species at different trophic levels.

Findings
Our meta-analysis shows that ocean warming causes a shift towards smaller pico-/nanoplankton species to the detriment of microplankton, which are less suitable as a food source for zooplankton. Total primary production by temperate non-calcifying plankton increases with elevated temperature and CO 2, whereas tropical plankton decreases productivity due to acidification. Temperature increases consumption by and metabolic rates of herbivores, but this response does not translate to greater secondary production, which instead decreases with acidification. This effect creates a mismatch with carnivores whose metabolic and foraging costs increase with temperature. Our mesocosm study supports this analysis by showing that elevated temperature and CO₂ increased energetic demands of sharks but also reduced their ability to locate food through olfaction, leading to a considerable reduction in shark growth rate. On natural CO2 vents, we found that predators such as groupers showed a steep reduction in their abundances which was associated with a strong increase in some prey species.

Conclusions
Our results suggest that species at higher trophic levels are particularly vulnerable to the combination of ocean warming and acidification due to elevated energetic demands, which are contrasted by reduced food intake resulting from a diminished ability to effectively hunt. This can lead to reduced top-down control over food webs, favouring some prey species at lower trophic levels. We find that ocean warming and acidification increase the potential for an overall simplification of ecosystem structure and function with reduced energy flow among trophic levels.

Effects of in situ CO2 Enrichment on Structural Characteristics, Photosynthesis, and Growth of the Mediterranean Seagrass Posidonia oceanica

Chair: Sean Connell

T. Erin Cox (1), Frédéric Gazeau (1), Samir Alliouane (1), Iris E. Hendriks (2), Paul Mahacek (1), Arnaud Le Fur (1), and Jean-Pierre Gattuso (1,3)*

1 Sorbonne Universités, UPMC Univ Paris 06, CNRS-INSU, Laboratoire d’Océanographie de Villefranche, 181 chemin du Lazaret, F-06230 Villefranche-sur-mer, France
2 Global Change Department, IMEDEA (CSIC-UIB), Instituto Mediterraneo de Estudios Avanzados, C/Miquel Marques 21, 07190 Esporles, Mallorca, Spain
3 Institute for Sustainable Development and International Relations, Sciences Po, 27 rue Saint Guillaume, F-75007 Paris, France

Background
Seagrass are expected to benefit from increased carbon availability under future ocean acidification. This hypothesis has been little tested by in situ manipulation.

Methods
To test for ocean acidification effects on seagrass meadows under controlled CO2/pH conditions, we used a Free Ocean Carbon Dioxide Enrichment (FOCE) system which allows for the precise manipulation of pH as an offset from ambient. This system was deployed in a Posidonia oceanica meadow at 11 m depth. It consisted of two benthic enclosures, an experimental and a control unit both 1.7 m3, and an additional reference plot in the ambient (2 m2) to account for structural artifacts. The meadow was monitored from April to November. The pH of the experimental enclosure was lowered by 0.26 pH units for the second half of the eight-month study. The diel change in pHT for the ambient meadow was ~ 0.1 units, while the diel change in the experimental enclosure during the pertubation was two to three times greater.

Findings
Changes in P. oceanica leaf biometrics, photosynthesis, and leaf growth accompanied seasonal changes recorded in the environment but no differences were found between the two enclosures. Leaf thickness may change in response to lower pH but this requires further testing. Results suggest any benefit from ocean acidification, over the next century, on Posidonia physiology and growth may be minimal.

Conclusions
The limited stimulation and increased diel pH variation casts doubts on speculations that elevated CO2 would confer resistance to thermal stress and increase buffering capacity of meadows.

Can corals acclimate to the high CO2 world?

Chair: Sean Connell

Haruko Kurihara (1), Asami Tsugi (1), Takashi Kawai (1), Izumi Mimura (1), Chuki Hongo (1), Atsushi Watanabe (2), Marine Gouezo (3), Yimnang Golbuu (3)

1 University of the Ryukyus, Okinawa, 903-0213, Japan
2 Tokyo Institute of Technology, Tokyo, 152-8552, Japan
3 Palau International Coral Reef Center, Koror, PW96940, Palau

Background
It has been clearly shown that global warming and ocean acidification that result from the increase in atmospheric CO2 will affect a wide range of marine organisms and it is now threatening the whole ocean ecosystem. However, several gaps still remain in our knowledge for better predict and address impacts of climate change to the ocean: 1. Synergistic impacts of high temperature and low pH on marine organisms, 2. Impacts in the field, 3. Impacts at community level, and 4. Possible acclimation and adaptation responses to the high-CO2 world. In this presentation we will introduce studies conducted at coral reefs in Nikko Bay, located in the rock islands of Palau, western Pacific. Nikko Bay is a unique site that provides us an opportunity to address the gaps in knowledge.
Methods
Nikko Bay is a highly sheltered bay with spatially heterogeneous seawater chemistry due to the complex topography and high water residence time. The seawater pH within the bay ranges from 7.6 to 8.1, aragonite saturation (Ω) from 1.8 to 3.6 and the average temperature from 28.5 to 32.0°C degrees. For the evaluation of the effect of pH/temperature at community level, we conducted benthic community surveys along the gradient of the seawater pH and temperature among sites. We also conducted coral (Porites cylindrica) transplantation experiment along this gradient. Lastly, low pH/ high temperature tank experiment using P. cylindrica collected from different sites was also performed.
Findings
We found that the coral communities living in the highest temperature and lowest pH site had the highest resistance to the high temperature and low pH. However, we also found that coral growth rate collected from all the sites increases when transplanted to higher pH condition or cultured under high pH seawater. These results first suggest potential adaptation capacity of corals to the high-CO2 world, albeit with limitation. In the presentation, we also discuss the possible variability of coral reef community responses to the climate change.
Conclusions
Nikko Bay offers a potential living laboratory for the evaluation of global warming and ocean acidification at community level and adaptation capacity of the organisms to the high CO2 world. Results suggest possible adaptation capacity of corals and we suggest the evaluation of climate change on reef community and marine ecosystems should be a next step.

Reversal of ocean acidification enhances net coral reef calcification

Chair: Jean-Pierre Gattuso

Rebecca Albright(1), Ken Caldeira(2)

1 Carnegie Institution for Science, Stanford, CA, 94305, USA
2 Carnegie Institution for Science, Stanford, CA, 94305, USA

Background
Ocean acidification is projected to shift reefs from a state of net accretion to one of net dissolution sometime this century. While retrospective studies show large-scale changes in coral calcification over the last several decades, determining the contribution of ocean acidification to these changes is difficult due to the confounding factors of temperature and other environmental parameters. Here, we quantified the calcification response of a coral reef flat to alkalinity enrichment to test whether reef calcification increases when ocean chemistry is restored closer to pre-industrial conditions.

Methods
We used sodium hydroxide (NaOH) to increase the total alkalinity of seawater flowing over a reef flat, with the aim of increasing carbonate ion concentrations [CO32-] and the aragonite saturation state (Ωarag) closer to values that would have been attained under pre-industrial atmospheric pCO2 levels. We developed a dual tracer regression method to estimate alkalinity uptake (i.e., net calcification) in response to alkalinity addition. This approach uses the change in ratios between a non-conservative tracer (alkalinity) and a conservative tracer (non-reactive dye, Rhodamine WT) to assess the fraction of added alkalinity that is taken up by the reef.

Findings
Using this method, we estimate that an average of 17.3% ± 2.3% of the added alkalinity was taken up by the reef community, inferring a 6.9 ± 0.9% increase in net community calcification.

Conclusions
In providing results from the first seawater chemistry manipulation experiment performed on a natural (i.e., unconfined) coral reef community, we demonstrate that, upon increase of [CO32-] and Ωarag closer to pre-industrial values, net reef calcification increases. Thus, we conclude that ocean acidification may already be impairing coral reef growth. This work is the culmination of years of work in the Caldeira lab at the Carnegie Institution for Science, involving many people including Jack Silverman, Kenny Schneider, and Jana Maclaren.

Effect of Ocean Acidification on the Nutritional Quality of Phytoplankton for Copepod Reproduction

Chair: Ana Queiros

Morgan T Meyers (1)*, Edward J Carpenter (1), William P Cochlan (1), Wim J Kimmerer (1)

1 Romberg Tiburon Center for Environmental Studies, Tiburon, CA, 94920, USA

Background
Phytoplankton are the oceans’ primary producers of polyunsaturated fatty acids (PUFA), which support the health and reproduction of heterotrophic marine organisms at higher trophic levels. It is hypothesized that future ocean acidification (OA) conditions could change the availability of phytoplankton PUFAs for ecologically significant consumers such as copepods, affecting their reproductive success in an increasingly acidified environment.

Methods
Three species of phytoplankton (Rhodomonas salina, Skeletonema marinoi, Prorocentrum micans) were grown under present-day (400ppm CO2, pH~8.1) and predicted future (1000ppm CO2, pH~7.8) oceanic conditions using nitrate-limited semi-continuous batch cultures. For four days, female Acartia tonsa copepods were fed a phytoplankton mixture from either the present-day or predicted-future treatment cultures. To assess changes in phytoplankton PUFA content, fatty acid profiles were analysed via capillary gas chromatography. Copepod egg production (EP), hatching success (HS), and egg viability (EV) were analysed to assess changes in copepod reproductive success.

Findings
CO2 concentration changed the composition of fatty acids in the phytoplankton used for the copepod diet. Under high pCO2 conditions, the relative proportion of PUFAs to total fatty acids was smaller (R. salina 21.5%; S. marinoi 14.1%; P. micans 14.4%) compared to that found in phytoplankton cultured under present-day pCO2 conditions (R. salina 28.8%, S. marinoi 32.7%, P. micans 39.3%). Copepod reproduction analyses show that females fed the high pCO2 phytoplankton had lower EP (median=13 eggs female-1), HS (median=12%), and EV (median=0%) compared to reproductive success of females fed the present-day pCO2 phytoplankton (EP median=25 eggs female-1; HS median=91.5%; EV median=98%).

Conclusions
This laboratory study demonstrates that OA can change the nutritional quality of primary producers, which affects the potential reproductive success of fundamental primary consumers.

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