Abstract:
The coexistence and interactions among mangrove prop-root-associated communities are dependent on
the degree and frequency of disturbances (wave action) occurring in the underwater root environment.
The intermediate Disturbance Hypothesis (IDH) suggests that species diversity peaks at intermediate
levels of disturbance. Although the IDH has been applied to several ecosystems, its relevance to
mangrove prop root ecosystems, characterised by tidal variations and biotic interactions that create
dynamic microhabitats, remains unsubstantiated. The primary aim of this study was to experimentally
test the applicability of the IDH in mangrove prop-root-associated communities, using wave action as
a physical disturbance proxy, and to evaluate how spatial orientation influences disturbance diversity
relationships. Gypsum balls placed horizontally and vertically across the root system were used to
measure the disturbance caused by wave action. Gypsum ball dissolution was measured after a fixed
24-hour deployment period, with multiple replicate gypsum balls placed at the sampling site. Along
the horizontal gradient, the highest diversity occurred in the intermediate zone (H′=0.61±0.04),
compared with dense (0.31±0.05) and sparse (0.22±0.03) root zones. While root density modified
disturbance in a way that facilitated classic competition-disturbance trade-offs based on IDH, vertical
position imposed a steep physical stress gradient and biogenic habitat modification that constrain
species diversity irrespective of competitive dynamics. The dominance of Saccostrea sp. and their role
as secondary colonizers were considered as the primary drivers shaping community composition,
structure, and generating enhanced habitat complexity. It demonstrated that disturbance in mangrove
underwater root ecosystems was not a single, uniform process, but operated differently depending on
spatial orientation, structural mediation, and proximity to sediment-driven resource pools. Overall, this
research provided compelling evidence that the IDH was conditionally validated in mangrove
underwater prop-root systems, functioning effectively only where disturbance interacts with habitat
complexity to regulate competition, rather than where disturbance acts primarily as a physiological
stressor.
