Effects of temperature and irradiance on growth of strains belonging to sevenSkeletonemaspecies isolated from Dokai Bay, southern Japan

Abstract

The effect of temperature on the growth of Skeletonema ardens, S. costatum sensu stricto, the S. marinoi-dohrnii complex, S. japonicum, S. menzelii, S. pseudocostatum and S. tropicum isolated from Dokai Bay in southern Japan were examined under five to seven different temperatures and an irradiance of 150 mmol m À2 s À1. The effect of irradiance on the growth of the seven Skeletonema species was also examined under a wide range of irradiances ranging from 7-700 mmol m À2 s À1 at 20 C. AllSkeletonema species were able to grow at temperatures ranging from 15 to 25 C. Intra-species differences in specific growth rates of four strains for S. menzelii, and five strains for S. ardens, the S. marinoi-dohrnii complex, S. japonicum and S. tropicum were not significant (Kruskal-Wallis test, P > 0.05). Significant inter-species differences in specific growth rates were observed at 10, 15, 25 and 30 C (Kruskal-Wallis test, P < 0.01; Steel-Dwass test, P < 0.01). The S. marinoi-dohrnii complex and S. japonicum grew faster than other species at the lower temperatures of 10 and 15 C, and S. ardens and S. menzelii grew at the highest temperature of 35 C. The maximum specific growth rates ( max ) from growth-irradiance curves ranged from 1.50 to 3.44 d À1. Threshold values of irradiance (I 0 ) and saturation irradiance (S) for growth ranged from 3.9 to 7.6 mmol m À2 s À1, and from 250 to 740 mmol m À2 s À1, respectively. In Dokai Bay, our results suggested that the occurrence of Skeletonema species should be affected mainly by temperature and less by irradiance. In particular, only two species, the S. marinoi-dohrnii complex and S. japonicum could maintain their populations in the surface water during the cold season, whereas during other periods, all seven species could maintain their population under the strong influence of estuarine circulation, which rapidly flushed the surface water out of Dokai Bay. Temperature and irradiance dependent growth values were in good agreement with their geographical distributions. The S. marinoi-dohrnii complex and S. japonicum were capable of growing in cold regions, but our results suggested that S. ardens and S. menzelii will tend to prefer tropical regions.

Temporal variation of Skeletonema community composition from a long-term time series in Narragansett Bay identified using high-throughput DNA sequencing

“…Temperature is thought to influence phytoplankton species richness and diversity (Graham et al 2004), in part because temperature strongly influences the growth rates of individual species (Thomas et al 2012), including those in the genus Skeletonema. A comparison of growth rates under different temperatures revealed that cultures of S. marinoi grew faster than other Skeletonema species at the lowest tested temperatures (10 and 15°C) (Kaeriyama et al 2011). This could explain the dominance of S. marinoi in winter-spring samples, although wintertime temperatures in NBay drop into the single digits, lower than previously examined.…”

“…Rapid changes in species composition over a period of weeks could be due to stochastic effects. However, given the observation of physiological variation within the genus (Kaeriyama et al 2011), it is more likely that rapid compositional changes may indicate that diversification within the genus Skeletonema has led to species with finely tuned differences in their physiologies, allowing the genus to dominate the microplankton across a range of environmental conditions.…”

“…Field observations of species distributions have been supported by physiological studies showing different growth rates among cryptic species in response to environmental conditions such as temperature and light (Kaeriyama et al 2011), salinity (Jackson et al 1992) and nutrients (Maldonado et al 2002). Studies of Pseudo-nitzschia have also described how cryptic species respond to unique environmental cues that induce sexual reproduction (Quijano-Scheggia et al 2009).…”

Species composition of Skeletonema (Bacillariophyceae) in planktonic and resting-stage cells in Osaka and Tokyo Bays

“…We therefore applied the SSU rDNA analysis to 50 strains (27 from Osaka Bay and 23 from Tokyo Bay) of the 420 strains identified as S. dohrnii by LSU rDNA. In previous papers (Yamada et al 2010, Kaeriyama et al 2011) the name S. marinoi-dohrnii complex was used for this species, but S. sp. cf.…”

Molecular species discovery in the diatom Sellaphora and its congruence with mating trials.

“…More recently, the application of molecular tools in taxonomy has revealed a large number of previously unrecognized species (e.g. Coleman 2001;Montresor et al 2003;Šlapeta et al 2005;Darling & WaDe 2008;EVans et al 2008), with potentially restricted geographical ranges (Pawlowski & Holzmann 2008) and niche breadths (De Vargas et al 1999;Lewis & FleChtner 2004;VanelslanDer et al 2009;Kaeriyama et al 2011). Sometimes, molecular evidence for lineage splitting has been backed up by breeding data and detailed morphological investigations.…”