Allelopathic Interactions Between the Tropical Macrophyte Enhalus Acoroides and Epibenthic HAB Dinoflagellate Prorocentrum Concavum

A benthic harmful dinoflagellate bloom caused by Prorocentrum concavum occurred at Xincun Bay, a lagoon characterized by a tropical seagrass ecosystem in the southern China, in summer 2018. Both abiotic and biotic factors may affect the abundance dynamics of P. concavum. One of the biotic factors, allelopathy, is known to be especially common among aquatic species and is suggested to be an economical and environmentally-friendly way to eliminate Benthic Harmful Algal Blooms (BHABs). To investigate the possible allelopathic interactions between seagrasses and P. concavum , a field survey was conducted to study the cell densities of P. concavum on four major substrates over 12 months. In laboratory, fresh Enhalus acoroides leaves and a crude aqueous extract of dry E. acoroides leaves were added to the culture of P. concavum respectively to assess possible effects on the growth and photosynthesis activities of P. concavum cells. Our results showed that the average abundance of P. concavum on E. acoroides leaves was statistically lower than that on the sediment outside the seagrass meadow and that on Thalassia hemperichii leaves. Both the growth and photosynthesis activities of P. concavum cells were inhibited in the two experiments, which can be attributed to the release and production of allelochemicals by E. acoroides. Our results offer new insights into the interaction between the submerged seagrass E. acoroides and the benthic harmful algal bloom dinoflagellate P. concavum , which can influence the abundance dynamics of P. concavum and provide an alternative for reducing potential threat of BHABs.