Unravelling ecological connectivity and natural capital in Essex’s salt marshes

Temperate estuarine salt marshes provide important ecosystem services, including carbon storage, carbon sequestration, nutrient removal, flood protection and biodiversity support. While natural capital assessments commonly consider habitat extent and condition, the influence of habitat connectivity on ecosystem service provision remains poorly understood, particularly within temperate estuarine systems. Furthermore, it is unclear how the spatial framework used to define the landscape influences estimates of structural connectivity. This thesis investigated the relationships between structural connectivity and natural capital within the Blackwater and Colne estuaries, Essex, UK, using salt marshes as a case study. Structural connectivity was quantified using landscape metrics describing habitat area, patch isolation, patch cohesion and patch geometry. These metrics were compared with spatially explicit natural capital indicators representing carbon storage, carbon sequestration, nitrogen removal, wave attenuation and species richness. A second analysis examined how connectivity metrics varied across four spatial frameworks: the whole estuary, Water Framework Directive water bodies, nutrient management zones and Shoreline Management Plan policy units. Habitat area showed the strongest and most consistent positive relationships with carbon storage, carbon sequestration and wave attenuation under current conditions, while greater patch isolation was generally associated with lower ecosystem service provision. In contrast, patch cohesion and shape exhibited weaker and less consistent relationships with natural capital indicators. Under a future habitat creation scenario, these relationships largely disappeared, reflecting reduced spatial variability and the assumptions underlying projected ecosystem service estimates. Structural connectivity metrics were also highly sensitive to analytical scale, with finer spatial frameworks revealing greater heterogeneity than broader landscape-scale assessments. These findings demonstrate that habitat extent remains the strongest predictor of several natural capital indicators, while structural connectivity provides complementary information regarding habitat configuration and fragmentation. The study highlights the importance of considering analytical scale when quantifying connectivity and demonstrates how landscape ecological approaches can strengthen natural capital assessment, habitat restoration planning and coastal management within temperate estuarine ecosystems.