Project

Ecosystem functioning and trophic interactions in a pristine coral reef

Goal: This project started in 2011and aims at better understanding the structure of a near-pristine coral reef food web. The atoll of Fakarava located in French Polynesia represents a unique research location to investigate the natural functioning of a healthy reef. Its southern pass host a population of up to 900 reef sharks and is the arena every year for one of the largest grouper spawning aggregation.

The main aims are:
- to determine the structure of the food web and its dynamics
- to study the behaviour of the largest aggregation of reef sharks
- to investigate the predator-prey direct and indirect trophic interactions
- to better solve the mysteries of grouper spawning

Methods: Acoustic Telemetry, Biotelemetry, Underwater Observations

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Project log

Johann Mourier
added a research item
Social predation allows groups of predators to search for, pursue, and capture prey with greater efficiency than using solitary hunting. During ~3,000 hours of underwater observations of nocturnal shark foraging activity, we report for the first time a heterospecific association between two shark species, with the nature of the interaction ranging from commensalism to kleptoparasitism and mutual-ism. These foraging associations with whitetip reef sharks offer grey reef sharks the opportunity to access different types of prey and increase their predation success. These findings add more evidence that heterospecific social associations may exist across animal groups including large marine predators.
Johann Mourier
added a research item
Social foraging allows groups of predators to search for, pursue, and capture prey with greater efficiency than using solitary hunting. It can vary in complexity and take many forms ranging from cooperative hunting, to social information sharing and local enhancement (Lang and Farine 2017). Theoretical and empirical studies support the advantages of group foraging, although there will be trade‐offs between benefits, such as increased prey detection or capture success, and costs such as increased competition amongst group members (Gil et al. 2017).
Johann Mourier
added an update
We are proud to announce that 700 Sharks, the film illustrating our research in Fakarava, is nominated in the Outstanding Cinematography Category at the International Emmy Awards!
After 14 awards in international festivals, this is a huge reward to all the great team work involved in this project!
 
Johann Mourier
added a research item
Many species of groupers form transient fish spawning aggregations (FSAs) that are both spatially and temporally predictable, making them highly vulnerable to fishing. Consequently, many known aggregations have disappeared, making the collection of additional baseline data imperative to inform management actions and decisions that have the capacity to protect these important areas in the long term. Using acoustic telemetry and underwater observations, we document the spatio-temporal dynamics of the camouflage grouper Epinephelus polyphekadion at a FSA in Fakarava, French Polynesia. We show that grouper arrival at the aggregation site started 2 weeks before the full moon with a core area density that increased from 0.13 to 1.25 fish m−2 during the observation period. Following reproduction, almost all camouflage groupers left the FSA site within 48 h. Among 30 tagged groupers in 2011 and despite a relatively low receiver coverage in the pass, 30% returned to the FSA the following year confirming patterns of FSA site fidelity of the species found in previous studies at other locations. Our results confirm that the current management procedures protecting the FSA under the UNESCO biosphere reserve are critical in maintaining the functional role of the FSA by ensuring the persistence and sustainability of large and healthy populations of groupers and sharks.
Johann Mourier
added an update
Here is a preliminary work on animated movements of grey reef sharks during a day in the Fakarava pass based on acoustic transmitter with acceleration and depth sensors.
 
Johann Mourier
added an update
The May issue of National Geographic Magazine is covering our research conducted on the Fakarava unique ecosystem including the predator-prey game between sharks and fishes and it is magnificently illustrated by talented photographer Laurent Ballesta.
 
Johann Mourier
added an update
Find out what we have done during our 40 days expedition to study reef shark behaviour, including methods used (tagging, observations, animal-borne cameras, acoustic cameras..etc):
 
Johann Mourier
added an update
We've just finished a new 40 days expedition in Fakarava to work on the population of grey reef sharks and observed grouper spawning aggregation in full moons of June and July. This expedition was also the opportunity to make another big documentary focused on shark hunting behaviour.
Other shark count sessions were conducted, but this year we also successfully tagged 38 grey reef sharks with acoustic transmitters and accelerometers. Receivers will record shark mouvement and activity for a year. We were able to deploy 4 CatCam (animal borne cameras) attached to the dorsalfin and recording for 2 or 3 days small scale accelerometry and recording videos from a shark's view. We also were able to collect muscle samples for stable isotope analysis and to investigate the real trophic position of sharks in the local food web. In addition we collected hours of videos of natural hunting behaviour during night dive which also allows us to describe their diet by identifying prey items.
 
Johann Mourier
added an update
The team is ready for the new 2017 #GOMBESSA4 expedition and will investigate for 2 months the hunting behaviour of reef sharks and their role in structuring the coral reef ecosystem of Fakarava atoll. More than 2 tonnes of materials and up to 30 persons involved in the project to conduct great shark science!
 
Johann Mourier
added an update
Good News followers! We are planning a new 2017 expedition in June and July to investigate in better details the hunting behaviour of reef sharks using biologging technologies, underwater observations and many more techniques.
A new film will be produced and best on the success of our previous documentary "the Grouper Mystery" we hope it will be another nice illustration of the wildness of French Polynesia and its pristine reefs!
 
Johann Mourier
added an update
Here is a preview of the new 2017 expedition. Our aim is to better understand shark hunting behaviour at a very fine-scale but also to determine what is the role of reef sharks in healthy reef with incomparable predator densities.
Check the teaser: https://vimeo.com/194482561
 
Johann Mourier
added 3 research items
The extent of the global human footprint [ 1 ] limits our understanding of what is natural in the marine environment. Remote, near-pristine areas provide some baseline expectations for biomass [ 2, 3 ] and suggest that predators dominate, producing an inverted biomass pyramid. The southern pass of Fakarava atoll—a biosphere reserve in French Polynesia—hosts an average of 600 reef sharks, two to three times the biomass per hectare documented for any other reef shark aggregations [ 4 ]. This huge biomass of predators makes the trophic pyramid inverted. Bioenergetics models indicate that the sharks require ∼90 tons of fish per year, whereas the total fish production in the pass is ∼17 tons per year. Energetic theory shows that such trophic structure is maintained through subsidies [ 5–9 ], and empirical evidence suggests that sharks must engage in wide-ranging foraging excursions to meet energy needs [ 9, 10 ]. We used underwater surveys and acoustic telemetry to assess shark residency in the pass and feeding behavior and used bioenergetics models to understand energy flow. Contrary to previous findings, our results highlight that sharks may overcome low local energy availability by feeding on fish spawning aggregations, which concentrate energy from other local trophic pyramids. Fish spawning aggregations are known to be targeted by sharks, but they were previously believed to play a minor role representing occasional opportunistic supplements. This research demonstrates that fish spawning aggregations can play a significant role in the maintenance of local inverted pyramids in pristine marine areas. Conservation of fish spawning aggregations can help conserve shark populations, especially if combined with shark fishing bans.
Johann Mourier
added an update
Our research led to the production of a documentary entitled "The Grouper Mystery" that was already awarded a few times.
ARTE, Les Films d'Ici, Andromede Oceanologie
 
Johann Mourier
added an update
Here is a graphical abstract of our recent paper showing the dynamic nature of ecosystem functioning and predator/prey interactions
 
Johann Mourier
added an update
Cover of Current Biology: Grey reef sharks predating on groupers at night. Groupers gather in mass spawning aggregation every year for 2 months and are in turn targeted by sharks.
 
Johann Mourier
added an update
Here is a video summarising the first results of this project recently published in Current Biology:
 
Johann Mourier
added a project goal
This project started in 2011and aims at better understanding the structure of a near-pristine coral reef food web. The atoll of Fakarava located in French Polynesia represents a unique research location to investigate the natural functioning of a healthy reef. Its southern pass host a population of up to 900 reef sharks and is the arena every year for one of the largest grouper spawning aggregation.
The main aims are:
- to determine the structure of the food web and its dynamics
- to study the behaviour of the largest aggregation of reef sharks
- to investigate the predator-prey direct and indirect trophic interactions
- to better solve the mysteries of grouper spawning