BENTHIC MICROALGAE AND NUTRIENT DYNAMICS IN WAVE-DISTURBED ENVIRONMENTS IN MARMION LAGOON, WESTERN-AUSTRALIA, COMPARED WITH LESS DISTURBED MESOCOSMS

The relationships between the standing stock of marine benthic microal gae and physical variables and nutrients in the water column and porew aters were explored by comparing a wave-exposed field location at Marm ion Lagoon, Western Australia, to less disturbed benthic mesocosms. Fo r field stations in Marmion Lagoon, multiple regressions of chlorophyl l a concentrations against the PCA scores (PCA1, PCA2, PCA3) indicated chlorophyll a was only significantly negatively related to PCA1 score s, which itself was dominated by temperature, salinity, DO, NOx, SiO4 and SRP from the water column. Concentrations of chlorophyll a in surf ace sediments at field stations were significantly positively correlat ed to decreased temperature and salinity and negatively correlated to increased water column nutrients over the duration of the experiment. For mesocosms, chlorophyll a concentrations were not significantly rel ated to any of the PC axes, indicating that shifts in temperature, sal inity and nutrients in water column and porewaters were not responsibl e for the observed distribution of chlorophyll a in surface sediments. Benthic microalgae standing stock did not respond in similar ways in mesocosms and field stations to changes in nutrient status in the wate r column and surface sediments. There was a visible difference in the level of disturbance of surface sediments. In field stations, sand was resuspended and ripples developed on surface sediments in response to winter storm swells. In mesocosms, where disturbance of sediment was reduced, a surface layer of detritus and living benthic microalgae dev eloped on the sediment surface and appeared to reduce the rate of nutr ient efflux out of the sediment. (C) 1998 Elsevier Science BN. All rig hts reserved.