Growth response of the ichthyotoxic haptophyte, Prymnesium parvum Carter, to changes in sulfate and fluoride concentrations

Abstract

Golden alga Prymnesium parvum Carter is a euryhaline, ichthyotoxic haptophyte (Chromista). Because of its presumed coastal/marine origin where SO42- levels are high, the relatively high SO42- concentration of its brackish inland habitats, and the sensitivity of marine chromists to sulfur deficiency, this study examined whether golden alga growth is sensitive to SO42- concentration. Fluoride is a ubiquitous ion that has been reported at higher levels in golden alga habitat; thus, the influence of F- on growth also was examined. In low-salinity (5 psu) artificial seawater medium, overall growth was SO42—dependent up to 1000 mg l-1 using MgSO4 or Na2SO4 as source; the influence on growth rate, however, was more evident with MgSO4. Transfer from 5 to 30 psu inhibited growth when salinity was raised with NaCl but in the presence of seawater levels of SO42-, these effects were fully reversed with MgSO4 as source and only partially reversed with Na2SO4. Growth inhibition was not observed after acute transfer to 30 psu in a commercial sea salt mixture. In 5-psu medium, F- inhibited growth at all concentrations tested. These observations support the hypothesis that spatial differences in SO42- –but not F-–concentration help drive the inland distribution and growth of golden alga and also provide physiological relevance to reports of relatively high Mg2+ concentrations in golden alga habitat. At high salinity, however, the ability of sulfate to maintain growth under osmotic stress was weak and overshadowed by the importance of Mg2+. A mechanistic understanding of growth responses of golden alga to SO42-, Mg2+ and other ions at environmentally relevant levels and under different salinity scenarios will be necessary to clarify their ecophysiological and evolutionary relevance.

Growth of the harmful alga,Prymnesium parvum(Prymnesiophyceae), after gradual and abrupt increases in salinity

“…The present study determined and compared acute and long‐term effects of transfer to high salinity (>5) on growth of Prymnesium parvum . Consistent with observations by Rashel and Patiño (2017, 2019), abrupt transfer of P. parvum from salinity of 5 to 30 (by adding NaCl) in modified ASM resulted in the acute suppression of r and maximum abundance. In the present study, however, the initial suppression in r was followed by a return to control values (compensation) as early as during the second culture round.…”

“…Modified ASM at salinity of 5 (ASM‐5) is a relatively simple, brackish medium that has been used previously to study Prymnesium parvum growth (Rashel and Patiño 2017, 2019, Dabney and Patiño 2018, Patiño et al. 2018).…”

“…This study used ASM‐5 as the starting medium to study the effects of acutely or gradually increasing salinity by adding NaCl. This approach allows an examination of the effects of salinity (NaCl) on growth while avoiding confounding effects of other major ions (e.g., sulfate or magnesium) that also influence growth independently of salinity (Rashel and Patiño 2019). The ecological relevance of this approach is suggested by the finding that acute transfer of P. parvum to various NaCl‐dependent salinities in ASM‐5 yields salinity‐dependent abundance profiles (Rashel and Patiño 2017) that closely match salinity‐abundance profiles in nature (e.g., Gou 1983, Guo et al.…”

“…Prymnesium parvum was grown over five sequential batch cultures under the following salinity treatments: (i) ASM‐5 as the control (same as stock culture medium); (ii) modified ASM with salinity incrementally increased from 5 to 30 by adding NaCl (increments of 5 per batch; ASM‐5 to 30); (iii) abrupt transfer into modified ASM at a salinity of 30, raised with NaCl (ASM‐30) during the first batch culture and subsequently maintained in ASM‐30; and (iv) abrupt transfer into IO‐30 during the first batch culture and subsequently maintained in IO‐30. The latter treatment does not acutely affect P. parvum growth (Rashel and Patiño 2019) but the possibility of long‐term adjustments in this medium (e.g., increased growth) has not been explored. All experimental media contained f /2 levels of nutrients and vitamins (the IO salt mixture contains little if any nitrates or phosphates; Atkinson and Bingman 1998; manufacturer's product description, https://pentairaes.com/instant-ocean-salt.html).…”

“…When natural or artificial seawater is proportionally diluted to create different salinity levels, however, the acute suppression of P. parvum growth at high salinity can be reduced or eliminated (Hambright et al. 2014, Rashel and Patiño 2019) due to an undefined cellular mechanism associated with the higher levels of sulfate and hardness cations in these media (Rashel and Patiño 2019). These observations suggest that the ionic composition of natural waters or culture media is important to consider in studies of the effects of salinity on P. parvum distribution and growth.…”