Grazing by the Copepod Parvocalanus crassirostris on Picochlorum sp. at Harmful Bloom Densities and the Role of Particle Size

Abstract

Harmful blooms of nanophytoplankton (2–20 μm) are increasingly common and sometimes severe, but requirements and controls of such blooms (e.g., water quality constraints, requirements for nutrients, and the presence of different guilds of grazers) are poorly understood. Laboratory grazing experiments were conducted to evaluate the potential for top-down control by the copepod Parvocalanus crassirostris on a small harmful algal species (an unidentified chlorophyte Picochlorum, 1–4 μm) and to test the effects of cell sizes on grazing rates. The Picochlorum sp. is a strain isolated from a long-lasting harmful algal bloom in the Indian River Lagoon that reached high densities (>1 × 106 cells ml–1). Experiments contrasted grazing on Picochlorum sp. with grazing on the palatable prymnesiophyte Isochrysis galbana (4–6 μm) in monocultures and mixed cultures. When presented in monocultures, grazing rates on Picochlorum sp. were lower than grazing rates on the palatable alternative. When Picochlorum sp. were presented alongside I. galbana, copepods essentially ceased feeding on the former. In additional experiments, P. crassirostris were fed plastic beads with diameters of 2.0–17.9 μm to control for differences in taste, toxicity, production of mucilage and shape of potential food. Paracalanus crassirostris fed most efficiently on beads with diameters of 7.0–7.9 μm. Results revealed that P. crassirostris can consume Picochlorum sp., but small size and the presence of palatable cells reduces the likelihood of top-down control of blooms of Picochlorum sp.

B vitamins supplementation induced shifts in phytoplankton dynamics and copepod populations in a subtropical coastal area

“…Copepoda typically preferred phytoplankton that were nutritious and within a suitable size range (Liu et al, 2010;Lee et al, 2012;Fridolfsson et al, 2019). Picochlorum has been reported to be too small for Copepoda to graze effectively, making top-down control of their bloom less likely (Ma et al, 2021). Thus, our study suggests that B vitamin-induced changes in phytoplankton community composition may also negatively affect Copepoda through feeding inhibition.…”

Characterization of Pseudochloris wilhelmii potential for oil refinery wastewater remediation and valuable biomass cogeneration

“…It is plausible that during days 14-20 the bacterial, as well as P. wilhelmii, secondary toxic metabolites accumulate in the medium shadowing the toxicity reduction effect (Costelli, 2014). Although there is no record of P. wilhelmii being able to synthesize toxic metabolites, some strains of the Picochlorum genus were reported to have been avoided by copepods as a food source (Ma et al, 2021), or to express cytotoxic activity against cancer cell line (Abolhasani et al, 2018). Since P. wilhelmii has been shown as promising strain for cultivation and isolation of valuable bioproducts, a deeper insight into the toxicity aspects is needed, particularly in a light of the adverse Microtox ® results presented herein, as well as literature reports.…”