Influence of Environmental Variables on Gambierdiscus spp. (Dinophyceae) Growth and Distribution

Abstract

Benthic dinoflagellates in the genus Gambierdiscus produce the ciguatoxin precursors responsible for the occurrence of ciguatera toxicity. The prevalence of ciguatera toxins in fish has been linked to the presence and distribution of toxin-producing species in coral reef ecosystems, which is largely determined by the presence of suitable benthic habitat and environmental conditions favorable for growth. Here using single factor experiments, we examined the effects of salinity, irradiance, and temperature on growth of 17 strains of Gambierdiscus representing eight species/phylotypes (G. belizeanus, G. caribaeus, G. carolinianus, G. carpenteri, G. pacificus, G. silvae, Gambierdiscus sp. type 4–5), most of which were established from either Marakei Island, Republic of Kiribati, or St. Thomas, United States Virgin Island (USVI). Comparable to prior studies, growth rates fell within the range of 0–0.48 divisions day-1. In the salinity and temperature studies, Gambierdiscus responded in a near Gaussian, non-linear manner typical for such studies, with optimal and suboptimal growth occurring in the range of salinities of 25 and 45 and 21.0 and 32.5°C. In the irradiance experiment, no mortality was observed; however, growth rates at 55μmol photons · m-2 · s-1 were lower than those at 110–400μmol photons · m-2 · s-1. At the extremes of the environmental conditions tested, growth rates were highly variable, evidenced by large coefficients of variability. However, significant differences in intraspecific growth rates were typically found only at optimal or near-optimal growth conditions. Polynomial regression analyses showed that maximum growth occurred at salinity and temperature levels of 30.1–38.5 and 23.8–29.2°C, respectively. Gambierdiscus growth patterns varied among species, and within individual species: G. belizeanus, G. caribaeus, G. carpenteri, and G. pacificus generally exhibited a wider range of tolerance to environmental conditions, which may explain their broad geographic distribution. In contrast, G. silvae and Gambierdiscus sp. types 4–5 all displayed a comparatively narrow range of tolerance to temperature, salinity, and irradiance.

Phenotypic diversity within two toxic dinoflagellate genera: environmental and transcriptomic studies of species diversity in Alexandrium and Gambierdiscus

“…When water was sampled at depth of Gambierdiscus growth and natural substrates, salinity values were more constant across sites though there was still moderate evidence of lower salinities closer to shore at low tide. However, previous laboratory data have shown many Gambierdiscus species to be relatively tolerant of large ranges of salinity values (Xu et al, 2016). Nutrient concentrations also increase closer to shore.…”

“…A. Tester, Feldman, Nau, Kibler, & Wayne Litaker, 2010;Villareal et al, 2007). Gambierdiscus species have been shown to have different temperature ranges of growth as well as different ranges in toxicity Xu, Richlen, Liefer, Robertson, & Kulis, 2016). Therefore as seawater temperatures shift, Gambierdiscus species ranges will change, affecting not only total abundance of Gambierdiscus as a genus but also Gambierdiscus community composition.…”

“…Experiments were performed in triplicate over a temperature range of 16 to 35 °C using two temperature-gradient bars, and growth rates were measured by in vivo fluorescence using a 10-AU Fluorometer (Turner Designs, USA) (Watras, Chisholm, & Anderson, 1982;Xu et al, 2016). Fluorescence measurements (log) over time were plotted to calculate the growth rate from the exponential portion of the curve using the following equation from (Guillard, 1973):…”

“…At Wai'Ōpae, G. belizeanus was more abundant at lower temperatures. Since the Xu et al, 2016 andKibler et al, 2012 G. belizeanus data were collected from strains isolated from the Caribbean, Pacific strains may have different growth rates. In Xu et al, 2016, G. carpenteri had consistently lower growth rates across both high and low temperatures.…”

“…Prior studies have shown that multiple Gambierdiscus species co-occur, and have significant differences in toxicity and optimum temperature growth ranges Xu et al, 2016). However, most Gambierdiscus species are indistinguishable under the light microscope.…”