Benthic Microalgae (BMA)

Benthic Microalgae (= microphytobenthus) are microscopic single celled algae (diatoms and dinoflagellates) and cyanobacteria that inhabit the top 0-3 cm of aquatic sediments. Benthic microalgae biomass is detected and quantified by sediment chlorophyll a analysis. A comprehensive survey of chlorophyll a content of Moreton Bay sediments has shown that Benthic microalgae are ubiquitous, although concentrations vary greatly. Benthic microalgae biomass is highly variable and ranged from 1 - 120 mg chl a m-2 and was influenced by water depth and turbidity. Moreton Bay Biota poster series The highest biomass detected was on the intertidal banks of the Brisbane River, which appeared green with densities greater than 40 mg chl a m-2, and at depths shallower than 5 m throughout Moreton Bay. High concentrations and bay wide distribution of Benthic microalgae suggest that these microscopic plants are potentially important vectors in carbon and nutrient cycling within the bay.

Paralia sp. Prorocentrum lima Pleurosignma sp. Navicula sp.

Ecological significance of benthic microalgae Benthic microalgae (BMA) are ecologically significant in coastal marine environments from corals reefs to estuaries. They are a major food source for benthic feeders such as prawns and other crustaceans, bivalves and polychaete worms. Suspension feeders, such as polychaete worms and oysters, may also graze on them when they are resuspended into the water column due to current or tides BMA excrete polysaccharides which bind the sediment and minimise the influence of overlying water movements. This results in an increase in sediment stability reducing the potential for sediment erosion and resuspension. BMA communities also modify nutrient exchange, particularly nitrogen, between the water column and sediments and hence may play an important role in regulating water quality. Despite these crucial ecological roles, BMA communities in Moreton Bay remain relatively unstudied. Clearly, they are a component of the marine flora which requires further research and understanding.

Benthic microalgae conceptual model

Conceptual model depicting the ecological role of benthic microalgae. Benthic microalgae are important for nutrient absorption, sediment binding and contribute to the benthic food webs. Benthic microalgae distribution and concentration Benthic microalgal distribution and concentration as determined by sediment chlorophyll a concentrations. The highest concentrations were found at the mouth of Pumicestone Passage and the lowest concentrations were recorded in central Bay. (click on image to maximise)