Zonal and seasonal variation in the distribution and abundance of mangrove macroalgae in the Parramatta River, Australia

The purpose of this study was to examine the spatial and temporal variation of macroalgae epiphytic on pneumatophores of the Grey mangrove, Avicennia marina (Forsk.) Vierh., in the Parramatta River, the major estuarine system flowing into Sydney Harbour. No previous studies have examined algal distribution in three spatial dimensions (along the mid-saline length of a river, from front to back of mangrove stand, and from bottom to top of pneumatophores), simultaneously with their temporal variation within mangrove stands. Three sites in the Parramatta River, Australia, were surveyed seasonally on four occasions over a two-year period, and algal distribution and biomass assessed with respect to temporal, site, intertidal and vertical variation. Sediment and water characteristics, including nutrient levels, were also assessed in order to examine all variables that may be influencing algal distribution and abundance. The results indicated that intertidal position within sites (front, middle and back zones of the intertidal mangrove stands) was the factor of greatest influence on algal frequency and biomass, with individual species dominating in different zones. This observation together with the identification of four species of macroalgae that fulfill the criteria for bioindicators of environmental impacts are discussed.