Spatio-temporal distribution of the dominant Diatom and Dinoflagellate species in the Bay of Tunis (SW Mediterranean Sea)

Abstract

Microphytoplankton composition and its relationships with hydrology and nutrient distributions were investigated over 24 months (December 1993 -November 1995 in the Bay of Tunis (SW Mediterranean Sea). A new index, the 'Specific Preference Index' (SPI) obtained by computing the median value of each parameter weighed by the numerical value of each species density was developed. Using this index, the relationships between each species and temperature, salinity and major nutrients were analysed.The distribution of chlorophyll a did not show a clear correlation with microplankton abundance suggesting that other factors contribute to chlorophyll concentration, such as smaller phytoplankton size fractions or detritus. The winter-spring diatom blooms did not show a regular pattern during both years. High nutrient inputs in late summer, associated with mild meteorological conditions, contributed to the development of a large diatom bloom in autumn 1995 where significant silicate depletion was witnessed. Generally, diatoms were more stenotherm than dinoflagellates in the Bay, whereas dinoflagellates were more stenohaline than diatoms. The statistical analyses showed that the two species, Bellerochea horologicalis and Lithodesmioides polymorpha var. tunisiense, appeared in a wide range of environmental conditions. An excess of phosphate versus nitrate appeared to be associated with red tides of Gymnodinium spp, whereas Peridinium quinquecorne showed the opposite. Phosphate concentrations appear to be crucial in this coastal environment, where diatom blooms are often limited by low silicate availability.

A new recorded of red tide forming species; Heterocapsa triquetra, Gymnodinium impudicum, Heterosigma akashiwo and Thalassiosira rotula in Alexandria Waters, Egypt

“…Its intensive occurrence at the measured high temperature and low salinity correspond well with previous data (Chang et al, 2001), and the species seems dependent on water stability (∆ sigma-t value at 120.11). The relatively high nitrate and low phosphate accompanied the bloom peak are in contrary to the observations of Giacobbe et al (1996) andYahia-Kéfi et al (2005) that maximum abundance of Gyrodinium impudicum occurs under high phosphate levels versus nitrogen (nitrogen-limited conditions), and to the general assumption that dinoflagellates require higher phosphorus to face their higher contents of nucleic acids (Costas and Lopez-Rodas, 1991). In a culture experiment, the phosphate critical point for the growth of G. impudicum stands between 1.35 and 4.05 µM (Chang et al, 2001).…”

“…This species closely resembles Cochlodinium polykrikoides Margalef based on morphological features (Lee et al, 2001). Originally, G. impudicum athecate autotrophic species (Yahia-Kéfi et al, 2005) was described Gyrodinium impudicum as non-toxic species of no associated harmful effects, and a red tide bloom-forming species during June and September in different Mediterranean areas with high densities between 2x10 5 -6.3x10 5 cells.L -1 (Fraga et al, 1995). However, there is a possibility that G. impudicum might cause fish deaths due to the production of a mucous exopolysaccharide (Kim et al, 1999).…”

Spatial and seasonal variability of pico-, nano- and microphytoplankton at the bottom seawater in the north coast of Sfax, Eastern Mediterranean Sea

“…and made the second most abundant cell group. These genera were reported to be present under high phosphate availability (Satsmadjis and Frigilos 1983;Costas and Lopez-Rodas 1991) and were observed in the Gulf of Tunis under high phosphate concentrations and reduced nitrogen resources, suggesting that the proliferation of dinoflagellates was mainly phosphate-driven (Daly-Yahia Kéfi et al 2005). In particular, the continuum of dinoflagellates may be explained by the cell motility allowing them to explore different depths (Drira et al 2009).…”

Winter phytoplankton blooms in the offshore south Adriatic waters (1995–2012) regulated by hydroclimatic events: Special emphasis on the exceptional bloom of 1995

“…Regarding AW's broader influence in the Mediterranean Basin in 1995, the early inter diatom bloom in the Bay of Tunis (SW Mediterranean Sea) that year had salinity <36.8 and was dominated by A. glacialis and L. annulata (Daly-Yahia Kéfi et al, 2005) at abundances in excess of 10 4 cells L -1 . The diatoms A. glacialis and L. annulata, and the coccolithophore E. huxleyi were among the most abundant species in the upwelling of the Alboran Sea (SW Mediterranean), an area strongly influenced by the Atlantic current (Mercado et al, 2005).…”