Disturbance and Recovery of Intertidal Mixed Seagrass Communities

Disturbances are a key driver in determining the structure and function of the ecological landscape by altering resource availability, community composition and species interactions. For seagrass habitats, most research has focused on subtidal temperate or subtropical systems. Because tropical systems tend to have higher species diversity and are exposed to more types of disturbances, we have a weak understanding of how species-rich intertidal seagrasses recover from different types of disturbances or how these disturbances influence habitat heterogeneity within the landscape. This dissertation investigated the responses, including recovery, of mixed-species intertidal seagrass communities to disturbances at the population, community and landscape level. Key findings include: (1) both macro-scale (tidal gradient) and microscale (disturbance) factors influence seagrass zonation and species diversity patterns across the intertidal landscape in the species-rich Indo-Pacific region; (2) seagrass recolonization in mixed species intertidal meadows is complex, suggesting that recovery prediction using two dimensional seagrass succession models is limited and should incorporate a third dimension – elevation changes produced by specific disturbance types and placement along a tidal gradient; (3) infauna abundance and diversity does not return to original levels even when seagrass biomass returns to pre-disturbance levels, suggesting that the return of ecosystem functions such as habitat utilization may lag behind plant recovery and that monitoring of above-ground plant components is not an accurate indication of full community recovery; (4) changes in sediment organic content iii following seagrass removal in intertidal meadows is not an important factor in smallscale recovery, which differs from experimental studies in subtidal seagrass habitats that found negative affects on seagrass growth; (5) intertidal seagrass meadows are highly dynamic, and the creation of bare gaps within vegetated areas by disturbances can influence habitat heterogeneity at local and landscape scales; and (6) small-size gaps created by disturbances can persist for years and in some cases even expand, and therefore should be included in studies of spatial patterns and landscape dynamics. These findings build upon our general understanding of disturbance ecology in seagrass ecosystems, underline differences between subtidal and intertidal systems, and have applications to prediction efforts and restoration activities in seagrass ecosystems throughout the world.

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