Marine ecosystems are among the most biodiverse and productive environments on Earth, yet they face unprecedented threats from climate change, overfishing, pollution, and habitat destruction. Active or passive restoration efforts aim to reverse these damages, but many projects fail to consider a critical factor: ecological connectivity. Without it, even well-intentioned restoration efforts may fall short.
Connectivity refers to the physical and biological linkages between different marine habitats that allow the movement of species, nutrients, and energy.
Mobile species navigate among different habitats supporting different functions such as nursing, mating, refuging or simply feeding along their life cycle. Many fish and invertebrates rely on mangroves and seagrasses as nurseries before migrating to coral reefs as adults (Nagelkerken et al. 2000). Restoring one habitat without the other disrupts this cycle. Species like sea turtles, sharks, and whales depend on migratory pathways to reproduce (Hays et al. 2016). Fragmentation from coastal development or degraded habitats can block these routes, reducing population recovery. Restoring connectivity ensures that species can migrate, reproduce, and recolonize degraded areas, boosting biodiversity and ecosystem recovery.
All fixed organisms, such as corals, oysters, and seagrasses, rely on ocean currents to disperse larvae (Cowen and Sponaugle, 2009). As a consequence, the diversity of species colonizing artificial reefs will depend to which natural habitat those artificial reefs are connected (Blouet et al. 2022). If natural habitats are out of reach, larval supply to restored sites may be insufficient. Similarly, transplantation to disconnected locations will not benefit to the natural populations. Strategic placement of restoration sites within connected networks improves recruitment and long-term sustainability. Isolated populations face higher risks of inbreeding and reduced genetic diversity, making them more vulnerable to diseases and climate change (Frankham, 2005). Connectivity allows gene flow between populations, enhancing their ability to adapt to environmental stressors. Healthy marine ecosystems depend on predator-prey relationships and nutrient cycling. Restoring connectivity between mangroves, seagrass beds, and coral reefs, for example, ensures that species can access feeding grounds, maintaining balanced food webs (Mumby et al. 2004).
Colonization of artificial reefs more than 10 years after their deployment in the Gulf of Lion (NW Mediterranean Sea). The pictures exemplify different type of colonization of artificial reefs: on the left, the reef is mainly colonized by the highly dispersive and opportunist polychaete Sabella spallanzanii, abundant in ports and on the right, the reef is colonized by the less dispersive white gorgonian Eunicella singularis, a characteristic species of the coralligeneous natural habitat. Pictures credits: Sylvain Blouet.
Focusing restoration efforts in areas with high ecological connectivity ensures that benefits spread beyond the immediate site. This “spillover effect” makes passive restoration more impactful and cost-efficient in the long run. It was shown recently that expanding a marine protection network integrating connectivity by larval dispersal is more profitable than based on habitat continuity (Blouet et al. 2025). Connectivity is not just a bonus in active restoration—it’s a necessity. Active restoration projects will only lead to resilient marine ecosystems that thrive for generations if their design considers ocean currents, migratory pathways, and habitat linkages. Ignoring connectivity risks fragmented, unsustainable outcomes, while embracing it leads to healthier oceans and more successful restoration.
Cited references
Blouet, S., Bramanti, L., Guizien, K. (2022) Artificial reefs geographical location matters more than shape, age and depth for sessile invertebrate colonization in the Gulf of Lion (NorthWestern Mediterranean Sea), Peer Community Journal, 2: e24.
Blouet, S., Tournadre, T., Hentati, S., Guizien, K. (2025) Expanding a network of marine protected areas based on functional rather than structural connectivity is more profitable. Biological Conservation 306:111112 https://doi.org/10.1016/j.biocon.2025.111112
Cowen RK, Sponaugle S. (2009) Larval dispersal and marine population connectivity. Ann Rev Mar Sci. 1:443-66. doi: 10.1146/annurev.marine.010908.163757.
Frankham, R. (2005) Genetics and extinction Biological Conservation, 126(2), 131-140. doi: 10.1016/j.biocon.2005.05.002
Hays GC, Ferreira LC, Sequeira AMM, et al. (2016) Key Questions in Marine Megafauna Movement Ecology. Trends Ecol Evol. 31(6):463-475. doi: 10.1016/j.tree.2016.02.015. Epub 2016 Mar 12.
Mumby, P., Edwards, A., Ernesto Arias-González, J. et al. Mangroves enhance the biomass of coral reef fish communities in the Caribbean. Nature 427, 533–536 (2004). https://doi.org/10.1038/nature02286
Nagelkerken I., van der Velde G., Gorissen M.W., Meijer G.J., Van’t Hof T., den Hartog C. (2000) Importance of Mangroves, Seagrass Beds and the Shallow Coral Reef as a Nursery for Important Coral Reef Fishes, Using a Visual Census Technique, Estuarine, Coastal and Shelf Science. 51(1):31-44, ISSN 0272-7714, https://doi.org/10.1006/ecss.2000.0617.
