The potential of benthic iron and phosphorus fluxes to support the growth of a bloom forming toxic cyanobacterium Lyngbya majuscula, Moreton Bay, Australia

Lyngbya majuscula is a bloom-forming toxic marine cyanobacterium. Most research on L. majuscula growth in Moreton Bay has focussed on water column supplies of iron and phosphorus with little consideration of benthic sources and supply. This study investigates the potential for sandy sediments in a shallow, well mixed subtropical embayment (Deception Bay, Moreton Bay, Australia) to supply iron and phosphorus for L. majuscula growth after significant benthic community change following a major flood event. Measurements of benthic oxygen, iron and nutrient fluxes were obtained by incubating intact sediment cores sampled from Deception Bay. Results suggest that post-flood sediment communities are capable of supplying >1300% of daily L. majuscula Fe requirements and up to 9.2% of daily P demands, suggesting that L. majuscula growth in Deception Bay is likely to be P limited. The benthic release of PO43- and Fe-II only occurred after water column DO became depleted below 3 mg L-1. This study suggests that the benthic release of PO43- and Fe-II could support the initiation and growth of L. majuscula blooms in Deception Bay.