Influence of monsoonal storm disturbance on the diversity of intertidal macroalgae along the eastern coast of Johor (Malaysia)

Abstract

The effects of cyclical disturbances towards macroalgal community structure could reveal the progression of short-term colonisation but are understudied in tropical settings, especially in Malaysia. The storms associated with monsoon events modify the local macroalgal community structure, and this study aims to determine the variation in species, assemblage and cover of macroalgae during the monsoonal cycle of 2015 to 2016. Four locations (Pantai Pasir Lanun, Pulau Mawar, Telok Gorek and Tanjung Lompat) along the eastern coast of Johor were surveyed during the post-monsoon (January–April 2015), pre-monsoon (May–August 2015), monsoon (September–December 2015) and the beginning of the subsequent post-monsoon (January–February 2016) periods. Line transects (25 m) were deployed at the study sites, and along each line, square quadrats (50 × 50 cm) were placed alternately at every 1 m. These transects provided data on macroalgal cover, frequency and diversity indices. Overall, macroalgal species richness was highest at Tanjung Lompat (n = 31) and lowest at Pulau Mawar (n = 5). The physical disturbances associated with the storm event were most profound at Pantai Pasir Lanun and Pulau Mawar. Here, macroalgal cover reduced to 0% at the end of the monsoon period in December 2015. The highest Shannon index value was observed at Tanjung Lompat (1.54) and lowest at Telok Gorek (0.52). Comparisons between the monsoonal periods revealed that the highest Shannon index value was found during the pre-monsoon period of 2015 (up to 2.13) compared with the monsoon period of 2015 (up to 1.49). We report that the species Chaetomorpha spp. and Cladophoropsis membranacea played a dominant role as first-colonisers, appearing within 1 month from the onset of the post-monsoon period. This study suggests that despite a loss of local macroalgal diversity after storm events, natural re-establishment of the macroalgal community would ensue in cyclical patterns.