Epiphytic algal cover and sediment deposition as determinants of arthropod distribution and abundance on mangrove pneumatophores

Abstract

We report here an investigation on intertidal mangrove pneumatophores, examining the relationships between arthropod abundance (for ten taxa, mostly belonging to the meiofaunal size-class), algal biomass and sediment cover. There was a strong correlation between the mass of sediment and the mass of macroalgae, supporting the assumption that pneumatophore sediment cover depends on algal growth. These two components of pneumatophore cover were negatively related to elevation, an effect probably relating to desiccation-limited algal growth towards the pneumatophore tips. Total arthropod abundance and that of some taxa (particularly, Uropodidae (Acari), Metidae (Crustacea), Ceratopogonidae (Insecta) and Empidoidea (Insecta)), was negatively correlated with elevation and positively correlated with sediment and algal cover, suggesting a good relationship between abundance and habitat availability. Other arthropod taxa (particularly, Halacaridae (Acari)) however, showed the opposite pattern of relationships. When the pneumatophore cover was physically removed, in an experiment to assess assemblage recovery rates, some arthropod taxa (Halacaridae (Acari), Harpacticoidea (Crustacea) and Ceratopogonidae (Insecta)) had completely recovered by 25 weeks, while others (Tanaididae (Crustacea) and Empidoidea (Insecta)) only partially recovered.