Experimental coral nursery in an extremely shallow degraded lagoon: macroalgal shading‐mediated coral survival, growth, and biodiversity dynamics at La Preneuse, Mauritius

Abstract Introduction Coral nurseries are increasingly employed to restore degraded reefs and support biodiversity in degraded lagoon systems. Experimental coral nurseries offer a viable means of enhancing coral survivorship and promoting ecosystem resilience, yet their performance in extremely shallow, sediment‐impacted environments remains insufficiently documented. Objectives This study evaluated (1) species‐specific survival and growth of Acropora humilis and A. muricata , (2) environmental and biological factors affecting fragment performance, and (3) biodiversity responses associated with shallow‐water nursery structures over 17 months. Methods A total of 211 fragments of A. humilis and A. muricata were deployed across five experimental tables. Survivorship, planar growth, pigmentation patterns, and bleaching were monitored through underwater photography and ImageJ‐based analysis. Results Acropora humilis exhibited consistently high survival (92–100% across tables) and moderate growth (mean increase = 70.0 mm 2 ), whereas A. muricata showed site‐specific mortality, with complete loss on two tables and full survival on others; surviving fragments displayed a mean growth of 72.8 mm 2 . Periods of elevated sea surface temperature and high irradiance coincided with paling and mortality in exposed fragments, whereas those engulfed by the macroalgae Padina spp. retained darker pigmentation and survived, suggesting a shading‐mediated buffering effect. Biodiversity surveys recorded 27 species and revealed stable benthic communities and increased fish presence around nursery structures. Conclusions These findings demonstrate that natural shading interactions with Padina spp. can enhance fragment survivorship under high light and temperature stress, while nursery structures simultaneously enhance functional reef biodiversity. The nursery provides a scalable model for ecosystem‐based coral restoration in very shallow areas within the small island developing states of the Western Indian Ocean.