Dinoflagellate Tripos furca and Tripos fusus niches in the South China Sea: Maximum entropy assessment of environmental factors

Abstract

Two dinoflagellate species, Tripos furca and T. fusus commonly co-occur in different marine waters. Both species often bloomed and caused mortalities of natural and culture marine organisms, but T. furca was more often suggested as the causative species. However, the ecological characteristics of these two species are not well understood. The present study applied the MaxEnt (maximum entropy) model using input data obtained from four surveys during 2003–2006 for estimating and comparing entropies of T. furca and T. fusus based on impact levels of six environmental factors (nitrate, phosphate, silicate, salinity, temperature and dissolved oxygen). PCA analysis on in situ data sets including abundance of the two species and the environmental factors were performed to compared with the model data. MaxEnt model results indicated that there was a significant difference between the two species on entropy values and impact levels of environmental factors to their occurring probabilities. The strongest environmental factor was salinity and nitrate (contributing 37.5% and 24.5% effect) for T. furca and T. fusus, respectively. PCA analysis of density of the two species and environmental variables showed comparable results with the MaxEnt model simulation, that the most important environmental variable being salinity to T. furca and nitrate/phosphate to T. fusus. Tripos furca can be dominant over T. fusus in lower but broader salinity and lower nitrate and phosphate concentrations. The present study results demonstrated applicability of this model for assessing ecological characteristics of species provided adequate input data.