Stress-tolerance trade-offs in mangrove oysters: evidence for compensatory growth under habitat degradation in Gazi Bay, Kenya

Habitat degradation typically reduces individual fitness, but some organisms may exhibit compensatory responses that mask ecosystem-level impacts. We tested the stress-tolerance trade-off hypothesis by examining morphological and physiological responses of mangrove oysters Saccostrea cuccullata across a degradation gradient in Gazi Bay, Kenya. Between March 2023 and February 2024, we measured shell morphology, condition indices, and environmental parameters for 4680 oysters from 18 sites across natural forests, plantation forests, and degraded areas. Using hierarchical Bayesian models, we found that oysters in degraded forests were 15% larger but had 23% higher mortality and 18% lower condition indices than those in natural forests. Principal component analysis revealed that degraded sites had higher turbidity and nutrient concentrations but lower structural complexity. Path analysis indicated that increased resource availability in degraded areas promotes individual growth, but elevated stress reduces survival probability. These findings demonstrate that compensatory growth can obscure population-level costs of habitat degradation, challenging the use of individual size as an ecosystem health indicator. Our results emphasize the importance of multi-metric approaches incorporating physiological stress indicators for accurate assessment of anthropogenic impacts on coastal ecosystems.