Habitat choice and settlement of coral larvae of high latitude coral species under ocean acidification

Project leaders

Fabio Badalamenti, Sylvain Agostini

Agreement

GIAPPONE - JSPS - Japan Society for the Promotion of Science

Call

CNR/JSPS biennio 2018-2019 2018-2019

Department

Earth system science and environmental technologies

Thematic area

Earth system science and environmental technologies

Status of the project

New

Research proposal

Shifts of coral reef communities in response to direct and indirect anthropogenic activities and a range of bio-physical stressors have been observed since '60s. Classic explorations of this issue focused on coral reef where main disturbances of interest included overfishing, outbreaks of coral-eating predators, disease, coastal water pollution, hurricanes, extreme temperatures and large-scale coral bleaching. Key evidences underlying these trends are widespread declines in scleractinians cover at global scale, changes in species composition towards algal or non-scleractinian coral species.
At the same time, species ranges are shifting with corals moving to marginal subtropical/temperate areas in the attempt to follow their thermal envelope, as it was observed in Japan and other parts of the world. This shift from temperate macroalgae to coral and other tropical species - known as "tropicalisation" - is predicted to highly impact marine ecosystems at the edge between subtropical and temperate regions. However, modelling and in situ observations suggest that ongoing declines of aragonite saturation state (Omega arag) - a process termed as Ocean Acidification (OA), i.e. the changes in the ocean's carbonate system resulting from increasing anthropogenic CO2 emissions - will halt the expansion of corals at higher latitudes. By contrast, the biomass of seaweeds, which are able to exploit the fertilization effect of CO2, is expected to increase. At present experimental evidence supporting such mechanisms is scant, and awaits further study specifically focusing on sensitive processes regulating early life stages such as larval recruitment and settlement or interspecific competition.

Recruitment is a fundamental process to maintain population replenishment and hence local persistence of a given species or the poleward colonization of novel environments to track thermal optima. Documented neurosensory disruptions of organisms under OA make early stages unable to recognize olfactory, visual and auditory stimuli, decreasing their survival and settlement success. The downstream consequences of such impaired processes are expected to affect the ecological outcomes at community- and ecosystem-level. Indeed, some organisms will adapt to OA, while several others will not. Seaweeds and soft corals seem to be the main survivors, whereas hard corals (particularly at early stages) and other key calcifying taxa (e.g., crustose coralline algae, which trigger corals recruitment) can be out-competed or cannot survive. This likely allows seaweed to substitute calcifying reef species, shifting ecosystem towards non-reef forming algal states, reduced habitat complexity and biodiversity loss. Indeed, once seaweeds become dominant, coral recovery is suppressed as their larvae are repelled by algal chemical cues.
Coral juveniles having an unbalanced control of the calcification required for somatic growth could be highly sensitive to OA as the energy cost of calcification will be increased. However, the effect on juveniles has only been tested in laboratory conditions where in addition to intrinsic biases (e.g. tanks), other important processes such as recruitment and interaction with algae cannot be tested.

We propose to use well-established CO2 seep sites in Japan and Italy, to identify the direct and indirect effect of OA on coral recruitment at high latitudes regions, which are considered thermal refugia for shifting coral species, and assess their competition with algal species, which are in turn boosted by antropogenic CO2 enrichment of the ocean.

Project strength
It is difficult to mimic OA conditions in situ for sufficient periods to affect whole marine communities. Work to date mainly involved short-term, usually rapid perturbation experiments on isolated elements of the ecosystem (e.g. single species or small groups of species). Areas with naturally high CO2 represent the most ecologically realistic tool for predicting responses of marine species to OA and should be harnessed to investigate long-term changes in ecological communities.

Indeed, Italian and Japanese scientists do require networked research to take scientific advantage of the fact that their many active volcanoes are of global significance in geological CO2 flux, but at the same time provide unique opportunities to scale-up from laboratory studies and improve predictions about the long-term effects of CO2 on coastal ocean system functioning. Studies such as the one proposed here relies on the uniqueness of the sites as CO2 seeps are scarce around the world.

The project will equip a new cohort of early career scientists with the skills required to expand their research experience in natural analogue systems, hence offering them the chance to increase their field experience and to acquire new competences through the collaboration with senior researchers with knowledge and technical skills in different disciplines from physiology to ecology.

By combining our efforts and research expertise, we expect to provide a robust understanding of OA consequences on reef forming species at high latitudes, which will greatly contribute to the knowledge required at regional scale (Eastern Pacific Ocean and Mediterranean Sea) for the prediction of OA effects. Indeed this will meet some of the principal targets on the Convention for Biological Diversity of both the Italian and the Japanese governments and during the COP 21 meeting in Paris.

The two research teams have extensive experience on benthic community ecology, coral biology/ecology, biomineralization, and developmental biology. Importantly researchers from both teams have pioneered the use of submarine CO2 seeps in Italy and Japan and have recently undertaken successful collaborative research under the JSPS invitation fellowship framework. As such, a well-established and solid collaborative partnership does exist.

Research goals

In situ and lab approaches will study how OA affects 1)habitat choice and settlement of high-latitude scleractinian larvae through chemical cue experiments and imaging technologies, 2)pre and post-settlement survival, calcification, metabolisms of coral early life stages and their competition with algae using field transplantations and microsensors technologies
Hypotheses are that OA will lead to:
1a) a reduction of coral relative abundance and crustose coralline algae (CCA) cover. Hence, since an non-reef forming algal states will dominate in High CO2 conditions, this will result in a decrease of positive cues (CCA) and an increase of negative cues (algal turf) for coral recruits
1b) Impairment of sensory system in larvae, reducing their ability to move towards the cue
1c) Decreased coral settlement success
2a) Increased energy cost for calcification and reduced successful settlement and growth of the coral recruits
2b) Increased post-settlement competition with algae resulting in reduced survival rates of recruits
Field trials will be based on Vulcano (Italy) and Shikine (Japan) islands natural laboratories for OA research. The corals to be used are brooder, i.e. they release planulae. The Pacific species are the symbiotic Alveopora japonica and the asymbiotic Tubastrea coccinea. The Mediterranean species is the asymbiotic Astroides calycularis. They are abundant in the control zones and mostly absent in the high pCO2 zones (~1000 ppm) at the two CO2 seeps respectively

Last update: 16/08/2025