Environmental factors and seasonal dynamics of Prorocentrum lima population in coastal waters of the Gulf of Tunis, South Mediterranean.

In the frame of a phytoplankton study, a series of samples were collected in the Punic harbors of Carthage (Gulf of Tunis, South Mediterranean) from March 2008 to March 2010. Species composition, seasonal variations of pelagic Prorocentrum populations and several physico-chemical parameters were specified, as well as the relation between Prorocentrum species dynamics and water temperature, salinity and nutrient concentrations. The main detected species are included in the benthic/epiphytic group; P. lima (Ehrenberg) Stein 1878 and P. emarginatum Fukuyo 1981. P lima was the dominant species. The highest abundance of P. lima (6.97 x 10(3) Cells L(-1)) was recorded in August 2008 where temperature and salinity values ranged from 23.1 to 30.2 degrees C and 36.1 to 40.3 psu, respectively. The dynamics of the P. lima population had significant positive correlations with both temperature and salinity, and negative correlations with both nitrogen/phosphorus ratio and ammonium concentrations. Proliferations of this species represent a serious hazard for public health in Tunis northern coasts.

Seasonal dynamic and in situ division rates of the dominant Dinophysis species in Punic harbors of Carthage (Gulf of Tunis, South Mediterranean).

This study investigates spatio-temporal variations of in situ division rate (µ) of two species of the genus Dinophysis. Based on a postmitotic index approach, estimates of µ from net-haul samples were compared during five daily cell cycles studies in three stations of the Punic harbors of Carthage (Gulf of Tunis). To study the annual cycle of Dinophysis spp., weekly sampling were carried out from March 2008 to June 2010. In addition, sampling over 24 h was conducted on three-cycle studies in late spring and two-cycle studies in autumn, seasons characterized by Dinophysis proliferations. We recorded important abundances of Dinophysis sacculus stein (2.25 × 10(4) cells/l, June 2008) and Dinophysis cf. acuminata (3 × 10(4) cells/l, June 2009). Cellular division was phased in D. sacculus stein and D. cf. acuminata, but the division time, required for the population cohorts to pass from one phase to another, and values of estimated division rates varied between seasons and stations for the same species. D. cf. acuminata exhibit moderate (0.22 day(-1)) to high (0.68 day(-1)) value of µ. In contrast, D. sacculus shows very low µ values (0.02-0.17 day(-1)) in autumn season to moderate values (0.21-0.35 day(-1)) in late spring. The results presented here confirm that the postmitotic index approach allowed estimated of µ at low field depths and concentrations (10(2)-10(3) cells/l).

Occurrence of diarrhetic shellfish poisoning (DSP) toxins in clams (Ruditapes decussatus) from Tunis north lagoon.

The main diarrhetic shellfish toxins, okadaic acid (OA) and dinophysistoxin-1, 2 (DTX-2, 2) were detected by liquid chromatography-tandem mass spectrometry (LC-MS/MS) as pyrenacyl esters in clams (Ruditapes decussatus) collected in Tunis north lagoon from January 2007 to June 2008. Sample analyses by LC-MS/MS displayed OA and related congeners (DTX-2, 2) with a highest detected level of 21 µg OA eq/kg shellfish meat for the samples of January 2007. Nevertheless, all samples were MBA negative. During the study period, potentially toxic dinoflagellate Dinophysis sacculus was recorded all year, blooming at different times. Highest concentrations were recorded during January 2007 with 4.6 × 10(4) cells per liter and 4.10(4) cells per liter in the northern and southern districts, respectively. Results show that there is no significant correlation between D. sacculus densities in water column and diarrhetic shellfish poisoning (DSP) toxins concentrations unregistered in clams. These data reveal that DSP toxicity in clams of Tunis north lagoon is low according to European regulatory limit (160 µg OA eq/kg shellfish meat). However, a potential threat, in this area, is represented by DSP toxic species as D. sacculus and provides grounds for widen and reinforcing sanitary control of the phycotoxin measures in the region.

First recorded proliferation of Coolia monotis (Meunier, 1919) in the North Lake of Tunis (Tunisia) correlation with environmental factors.

Coolia monotis is a potentially toxic epiphytic dinoflagellate widespread along the Mediterranean coasts, where it is frequently detected year round at low concentrations. However, it only proliferates recurrently in some localities. The North Lake of Tunis is one of the affected areas in the southwestern part of the Mediterranean Sea. This site is one of the most productive aquatic Tunisian areas (Recreational Fisheries and shellfish collecting). In the south part of this area of study, recurrent C. monotis proliferation (5 x10(5) cells per liter) took place in late spring and early summer of 2006. During this proliferation, the spatial distribution of C. monotis species, phytoplankton community, and abiotic factors were studied. The composition of the phytoplankton community exhibited a clear dominance of dinoflagellates over other genera. We suggest that proliferation development of C. monotis was linked to climatic conditions, water temperature (r = 0.24, p < 0.05) and high concentrations of nitrogenous nutrients, essentially NH(4)(+) (r = 0.18, p < 0.05) and NO(3)(-) (r = 0.21, p < 0.05).