Differential size frequency distribution of hard coral colonies across physical reef health gradients in Northeast Peninsula Malaysia

This study elucidates the health status of coral reefs in Pulau Lang Tengah and presents demographic population data for the first time for a Malaysian coral reef.

Full article available here: Differential size frequency distribution of hard coral colonies across physical reef health gradients in Northeast Peninsula Malaysia - ScienceDirect

Abstract

The size structure of a hard coral population reflects key demographic processes such as death, growth, and recruitment, and provides clues into recent ecological dynamics. Shrinking time intervals between mass disturbances (e.g., mass coral bleaching) result in demographic events that impact coral reef health and functionality. Analysis of size frequency distribution (SFD) of hard corals enables post hoc assessments of such demographic events and improves monitoring of coral reef health. Here, we present the first demographic study of Malaysian coral reefs and show the SFD of 36 morpho-taxa (n=4066 colonies), recorded along 27 × 10 m belt transects across three distinctive sites. We demonstrate a preponderance of small colonies (i.e., <20 cm, 84% of recorded colonies) and significant differences of taxon-specific SFD across physical reef health gradients (i.e., coral dominated to rubble dominated reefs). Physically degraded sites were significantly and consistently lower in coral recruitment, density, and diversity, while cover of coral rubble was higher. SFDs of abundant taxa were more negatively skewed (i.e., large colonies) and leptokurtic (i.e., peaky) at physically degraded sites. However, intra-taxonomic comparison revealed that absolute colony size was generally smaller at physically degraded sites, specifically for slow-growing massive colonies, but was larger for fast-growing Acropora and Fungia. Importantly, absolute colony size ranges were narrower at rubble dominated reefs and colony abundance declined across all size classes, resulting in the preponderance of medium-sized colonies in populations with more negatively skewed SFD. Therefore, our results support the notion that coral dominated reefs are assembled by predominantly smaller colonies. Conclusively, these results manifest that both the largest and the smallest individuals are eliminated at low cover reefs and community heterogeneity is impoverished. Ultimately, we highlight taxa with a balanced SFD (e.g., massive Dipsastraea, Porites spp. (rus), and massive Porites) despite the more frequent recurrence of mass disturbances.