Abstract
Mesozooplankton, as abundant grazers of microalgae in coastal systems, have the potential to prevent or mitigate harmful algal blooms (HABs) and their effects. The Indian River Lagoon (IRL) is a subtropical estuary in eastern Florida (United States) where repeated blooms, dominated by the toxic dinoflagellatePyrodinium bahamense, the brown tide speciesAureoumbra lagunensis, pico/nano planktonic cyanobacteria and other nano-eukaryotes, have highlighted the need to better understand fluctuations in the grazing potential of mesozooplankton populations across bloom cycles. Mesozooplankton and abiotic environmental data were collected at five sites in the northern IRL system at 6-week intervals from November 2013 through June 2016. A total of 107 taxa from 14 phyla were detected. Communities varied across sites, dates and between bloom and non-bloom periods, with densities up to 338 individuals L–1. Eight taxa comprising 85–94% of the total population at each site were identified as primary potential grazers, including barnacle nauplii, cladocerans, adult copepods, gastropod veligers, larvaceans, and polychaete metatrochophores. Although abundant, the estimated grazing potential of the primary taxa, calculated from their measured densities and previously published grazing rates, suggest that mesozooplankton lack the capacity to suppress phytoplankton once they reach bloom levels. These findings illustrate the utility of monitoring data and underscore the importance of systematically evaluating algal bloom controls with a consideration for the dynamic conditions of each unique ecosystem.
Highlights
Mesozooplankton are important grazers of phytoplankton in a wide variety of marine systems
Mesozooplankton were sampled at five sites across the northern Indian River Lagoon (IRL) system (Figure 1) that were selected because of previous phytoplankton bloom activity (Phlips et al, 2015): the southern Mosquito Lagoon (MLA), the IRL at Titusville (TIV) and Cocoa (COA), Banana River North (BRN) and Banana River Central (BRC)
Eight taxa comprising 85–94% of the total population at each site were identified as primary potential grazers: Amphibalanus spp. barnacle nauplii, Evadne sp. cladocerans, gastropod veligers, Oikopleura sp. larvaceans, polychaete metatrochophores, and the copepods A. tonsa, O. colcarva, and P. crassirostris
Summary
Mesozooplankton are important grazers of phytoplankton in a wide variety of marine systems. In 2011, picocyanobacteria and Pedinophyceae species bloomed throughout the northern IRL, followed by repeated intense blooms of the brown tide pelagophyte Aureoumbra lagunensis, and other small-celled taxa (Phlips et al, 2021). None of these taxa were documented at such levels in the estuary prior to 2011 but have occurred repeatedly in the years since (Phlips et al, 2015, 2020; Schaefer et al, 2019). The blooms have decreased light penetration and dissolved oxygen concentrations, leading to large-scale losses of habitat and changes in biological communities (Phlips et al, 2015; Lapointe et al, 2020; Lewis et al, 2020, 2021; Lazensky et al, 2021) that have defined the IRL for decades
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