Scales of temporal and spatial variability in the distribution of harmful algae species in the Indian River Lagoon, Florida, USA

Abstract This paper describes the results of a harmful algal bloom (HAB) monitoring effort in the Indian River Lagoon. The goal of the study was to describe spatial and temporal variability in the distribution, frequency of occurrence, and composition of HABs, along with an examination of potential driving factors, such as hydrologic conditions and nutrient concentrations. Six sampling sites in the northern lagoon were selected for the study. The composition and abundance of the phytoplankton community was determined microscopically. Water column parameters measured in the study included salinity, water temperature, Secchi depth, total phosphorus, and total nitrogen. Dinoflagellates, diatoms or cyanobacteria dominated the phytoplankton communities in terms of biovolume at all six sampling sites. Five potential toxin producing species were observed at bloom levels during the study period, including the diatom Pseudo-nitzschia calliantha and the dinoflagellates Pyrodinium bahamense var. bahamense , Prorocentrum rathymum , Cochlodinium polykrikoides , and Karlodinium veneficum . The saxitoxin-producing dinoflagellate P. bahamense var. bahamense had the highest biovolume observed over the study period, 33.9 × 10 6  μm 3  ml −1 , and was present in almost half of the samples collected. Three non-toxic HAB species were observed at bloom levels of biovolume, including Akashiwo sanguinea , Peridinium quinquecorne , and Kryptoperidinium foliaceum . As part of this study, a statistical approach to estimating the probability of detecting HAB events was explored, using three common and important HAB species in the IRL, P. bahamense var. bahamense , A. sanguinea and P. calliantha , as exemplars. The potential driving factors for HAB events are discussed within the context of the hydrological, meteorological and watershed characteristics of the lagoon.