Abstract
<p>The genus <em>Ostreopsis</em> includes species largely distributed from tropical to temperate marine areas worldwide. Among the nine species of the genus, <em>O. siamensis</em>, <em>O. mascarenensis</em>, <em>O. lenticularis</em> and <em>O. </em>cf.<em> ovata</em> can produce toxins of the palytoxin group. In the last decade <em>Ostreopsis</em> cf. <em>ovata</em> and <em>O</em>. cf. <em>siamensis</em> originated intense blooms in all the rocky Mediterranean Sea coastal areas, typically during summer-late summer. The correct identification of <em>Ostreopsis</em> species in field samples is often problematic as <em>Ostreopsis</em> species are morphologically plastic and hardly discriminable under light microscopy and, therefore, molecular analyses are required. <em>Ostreopsis</em> blooms are often associated with noxious effects on health of both humans and benthic marine organisms mainly carried by aerosol and direct contact with seawater. Environmental factors have been shown to affect toxin content of <em>Ostreopsis</em> which generally produces more toxins per cell when growing under suboptimal conditions.<em> O</em>. cf. <em>ovata</em> is able to produce both temporary and resting cysts. In particular, the resting cysts are able to germinate in laboratory conditions for as long as 5 months after their formation at 25°C, but not at 21°C; the presence of a temperature threshold affecting cyst germination in the laboratory suggests that temperature represents a key factor for <em>Ostreopsis</em> cf. <em>ovata</em> bloom onset in natural environments as well. Several studies conducted to assess the role of abiotic factors (mainly hydrodynamics, water temperature and nutrients) on the bloom dynamics, revealed that the synergic effects of hydrodynamics, temperature and N:P ratios would lead the <em>Ostreopsis</em> blooms in temperate areas. <em>Ostreopsis</em> abundances showed a significant decrease with depth, likely related to light availability, although there are conflicting data about the relationship between light intensity and <em>Ostreopsis</em> growth in experimental conditions. The relationship between <em>Ostreopsis</em> blooms and salinity is not completely clear, complicated by the influence of high nutrient levels often associated to low salinity waters. Finally,<em> Ostreopsis</em> colonize a variety of substrata, although living substrata seems to allow lower concentration of epibionts than any other substrate, probably due to the production of some allelopathic compounds.</p>
Subject
Aquatic Science,Oceanography