Résumé: In coral reef lagoons, microphytobenthos (MPB) primary production can be of the same order of magnitude as coral or macroalgal production. As they are situated in oligotrophic waters, sediments receive low amount of allochtonous nutrients, and their high metabolism cannot be achieved without an efficient nutrient recycling. In oligotrophic environments nutrient exchange between sediments and the water column is considered to be low. However, physical forcing that disturbs the sediment interface may accelerate nutrient exchange. The objectives of this work were to: (i) characterize the benthic trophic status and associated nutrient diffusion fluxes as a function of terrestrial and anthropogenic influence and (ii) investigate the impact of physical forcing on the exchanges at the interface and the response of the water column. For that purpose, a multidisciplinary study was performed in the southwest lagoon of New Caledonia combining field survey, laboratory experiments and mathematical modelling. The field survey indicated that most of the lagoon sediments were autotrophic and presented negligible nutrient fluxes. This suggests an apparent decoupling between the sediment and the water column as long as diffusion is the dominant nutrient exchange mode process. This was confirmed by experimental ex situ incubations that showed bacterial production in the water column was not affected by the presence of sediment. The modelling approach showed that physical forcing, such as sediment erosion or wave driven pore water advection, might enhance the coupling between the sediment and the water column through the release of nutrients and organic matter leading to the stimulation of the bacterioplankton and phytoplankton compartments.

Résumé: Connectivity is a crucial process underpinning the persistence, recovery, and productivity of marine ecosystems. The Convention on Biological Diversity, through the Aichi Target 11, has set the ambitious objective of implementing a ‘well connected system of protected areas’ by 2020. This paper identifies eight challenges toward the integration of connectivity into MPA network management and planning. A summary table lists the main recommendations in terms of method, tool, advice, or action to address each of these challenges. Authors belong to a science–management continuum including researchers, international NGO officers, and national MPA agency members. Three knowledge challenges are addressed: selecting and integrating connectivity measurement metrics; assessing the accuracy and uncertainty of connectivity measurements; and communicating and visualizing connectivity measurements. Three management challenges are described: integrating connectivity into the planning and management of MPA networks; setting quantitative connectivity targets; and implementing connectivity-based management across scales and marine jurisdictions. Finally, two paths toward a better integration of connectivity science with MPA management are proposed: setting management-driven priorities for connectivity research, bridging connectivity science, and MPA network management. There is no single method to integrate connectivity into marine spatial planning. Rather, an array of methods can be assembled according to the MPA network objectives, budget, available skills, data, and timeframe. Overall, setting up ‘boundary organizations’ should be promoted to organize complex cross-disciplinary, cross-sectoral and cross-jurisdiction interactions that are needed between scientists, managers, stakeholders and decision-makers to make informed decision regarding connectivity-based MPA planning and management.