Effects of a marine diatom Skeletonema costatum extract on Luminescence disease causing Vibrio harveyi during penaeus monodon larviculture

The crude extract of Skeletonema costatum obtained through cold extraction method was characterized for its phytochemicals, using FTIR and GC-MS. The antagonism of S. costatum extract was tested against Vibrio harveyi, its various virulence factors, and also tested against Vibrio harveyi during Penaeus monodon larviculture. S. costatum extract, controlled the growth of V. harveyi. The zones of inhibition were 12.6 ± 0.2, 6.6 ± 0.1 and 3.7 ± 0.1 mm at 300, 200 and 100 μg, respectively. The production of bio-luminescence was also reduced to 10.0, 11.0, 20.0, 25.0 CPS. The extract contained fatty acids such as 16-octadecanoic acid (48.05%) and pentadecanoic acid (18.94%) as evidenced by GC-MS. S. costatum extract revealed various compounds viz., alcohols, phenols, etc, which are responsible for controlling V. harveyi and virulence factors. During P. monodon larviculture, S. costatum extract at 200 μg/ml showed reduction (p < 0.05) in the cumulative percentage of mortality caused by V. harveyi (35.20 ± 0.6%) as compared to control (76.30 ± 0.8%). It can be concluded that S. costatum extract may be used to control disease-causing V. harveyi during shrimp larviculture.

Physiological responses of <i>Skeletonema</i> <i>costatum</i> to the interactions of seawater acidification and combination of photoperiod and temperature

Ocean acidification (OA), which is a major environmental change caused by increasing atmospheric CO2, has considerable influences on marine phytoplankton. But few studies have investigated interactions of OA and seasonal changes in temperature and photoperiod on marine diatoms. In the present study, a marine diatom Skeletonema costatum was cultured under two different CO2 levels (LC, 400 μatm; HC, 1000 μatm) and three different combinations of temperature and photoperiod length (8:16 L:D with 5 ℃, 12:12 L:D with 15 ℃, 16:8 L:D with 25 ℃), simulating different seasons in typical temperate oceans, to investigate the combined effects of these factors. The results showed that specific growth rate of S. costatum increased with increasing temperature and daylength. However, OA showed contrasting effects on growth and photosynthesis under different combinations of temperature and daylength: while positive effects of OA were observed under spring and autumn conditions, it significantly decreased growth (11 %) and photosynthesis (21 %) in winter. In addition, low temperature and short daylength decreased the proteins of PSII (D1, CP47 and RubcL) at ambient pCO2 level, while OA alleviated the negative effect. These data indicated that future ocean acidification may show differential effects on diatoms in different cluster of other factors.