Habitat complexity affects benthic harmful dinoflagellate assemblages in the fringing reef of Rawa Island, Malaysia

•Microhabitat heterogeneity is one of the driving factors leading to the variation in species composition and abundance of benthic harmful dinoflagellate assemblages.•While most taxa were present on healthy reefs, higher cell abundances were observed in degraded reefs with the exception of Ostreopsis.•Ostreopsis was the taxonomic group least influenced by substrate complexity, with cells found in all the microhabitat types examined.•Gambierdiscus were not favoured by habitats with high macroalgal cover as commonly anticipated, but instead reached highest abundances in habitats dominated by turf algae.