This study describes the changes in species composition of phytoplankton under different
Si:N ratios from spring to summer of 2010 and 2011. For this purpose, natural
Phytoplankton was cultured in mesocosmic experiments at two stations in the north
ern part
of Latakia coastal water. The abundance of phytoplankton was measured, and the specific
composition of phytoplankton was determined. Diatoms dominated during 2010 and 2011,
while Dinoflagellates did not compete with diatoms during this study. The enrichment experiment
affected the species composition of the diatoms themselves, where the species
Pseudo-nitzschia pseudodelicatissima Schil and Leptocylindrus danicus Cleve dominated
under different Si:N ratios.
Experiments were carried out at two stations in the northern part of Latakian coastal
water during March 2010, to investigate the influence of Si: N ratios on diatoms growth
and to determine the conditions that would generate Si limitation in diato
m growth and that
might cause a shift from diatom to din flagellate dominance. To achieve that, Natural Phytoplankton
were cultured in mesocosm experiments. At the beginning of the experiment,
the inorganic nutrients were manipulated to give different inorganic Si: N ratios (ranged
between 0, 3 and 7). The results showed that Diatoms were still dominant under these Si: N
ratios and Din flagellates remained unaffected, regardless of the above different ratios. The
experiment did not show any Silicate limitation to the diatom growth even under the lowest
N: Si ratios. Moreover, the species composition of diatoms was affected by the enrichment
experiments operated in two stations. Here, the Nitzschia closterium species dominated
under both low and high Si: N ratios although their occurrence is not common during
the spring phytoplankton bloom at both sites.
