What factors drive copepod community distribution in the Gulf of Gabes, Eastern Mediterranean Sea?

Abstract

The spatial and temporal variations in copepod communities were investigated during four oceanographic cruises conducted between July 2005 and March 2007 aboard the R/V Hannibal. A close relationship was observed between the temperature, salinity, hydrographic properties and water masses characterising the Gulf of Gabes. Indeed, water thermal stratification began in May-June, and a thermocline was established at a 20-m depth, but ranged from 25 m in July to more than 30 m in September. The zooplankton community is dominated by copepods representing 69 % to 83 % of total zooplankton. Spatial and temporal variation of copepods in relation to environmental factors shows their close relationship with the hydrodynamic features of the water column. Thermal stratification in the column, established in summer, supports copepod development. In fact, copepod abundance increases gradually with rising water temperature and salinity, starting from the beginning of thermal stratification (May-June 2006) and lasting until its completion (July 2005 and September 2006). When the water column is well mixed (March 2007), copepod abundance decreased. Our finding shows that temperature and salinity seem to be the most important physical factors and thus strongly influence the taxonomic diversity and distribution of the copepod population. They are characterised by the dominance of Oithona nana, representing 75-86 % of total cyclopoid abundance. The most abundant species during the stratification period were O. nana, Acartia clausi and Stephos marsalensis in July 2005 and September 2006. However, during the mixing period, Euterpina acutifrons was more abundant, representing 21 % of the total. Unlike the copepod community, which is more abundant during the period of high stratification, phytoplankton proliferates during semi-mixed conditions.

Spatial Distribution and Source Identification of Heavy Metals in Surface Waters of Three Coastal Areas of Tunisia

“…This area has been subjected to increasing pressure linked to the development of several activities on the coast and in the sea. The Gulf of Gabes (southwestern Mediterranean) is one of the most vulnerable aquatic ecosystems, contributing about 65% of national fish production in Tunisia [32][33], fauna biodiversity [34][35][36][37][38] and a wide distribution of Posidonia Oceanica, an endemic species representing a good nursery for fish eggs and larvae [39]. However, due to the increase of urbanization, industry, overfishing, tourism, and the discharge of huge amounts of phosphogypsum and other pollutants, the Gulf of Gabes has been reported to be densely polluted [40].…”

Factors driving the seasonal distribution of zooplankton in a eutrophicated Mediterranean Lagoon

“…On a seasonal scale and unlike other Mediterranean areas where two zooplankton peaks are reported per year (Kamburska and Fonda-Umani, 2009;Drira et al, 2014), GML presents one peak of zooplankton abundance per year in late summer-early autumn with means of ±sd = 2.6 ± 0.9 Â 10 5 ind m À3 and ±sd = 4.0 ± 1.3 Â 10 5 ind m À3 , respectively. The zooplankton community is characterized by the presence of large consumers such as veligers and copepods able to pray upon microalgae (Lam-Hoai et al, 2006) chiefly in summer, as phytoplankton bloomed with a dominance of diatoms and dinoflagellates, namely Prorocentrum micans and Scrippsiella trochoidea (Dhib et al, 2013(Dhib et al, , 2015, which results in maximum Chl a concentrations (Table 1).…”

“…1.4 ± 1.7 0.3 ± 0.5 0.0 ± 0.0 0.0 ± 0.0 Cladoceran density (Â10 2 ind m À3 ) 0.5 ± 0.5 2.5 ± 2.9 2.6 ± 2. waters, regardless of conditions of salinity or food abundance, but also in the open sea (Gaudy, 1985;Turner et al, 2012;Drira et al, 2014). McKinnon et al (2005) also reported greater abundances of copepods, nauplii of copepods in the coastal waters where their respective proportions presented seasonal variations.…”

“…It is therefore essential to study the seasonal succession of zooplankton communities in order to understand the main determining factors governing the biological productivity of the lagoon. We thus hypothesized that the zooplankton populations expected in a lagoonal ecosystem such as GML should exhibit a considerable overlap between estuarine, coastal and offshore zooplankton because the lagoon: (i) is especially dynamic due to its shallowness, having only a limited connection to the sea and lacking the thermal stratification known to strongly influence zooplankton distribution in such ecosystems (Reygondeau and Beaugrand, 2011;Drira et al, 2014), (ii) exhibits a specific hydrology since it is an almost stagnant area, (iii) shows strong seasonal environmental gradients with salinity up to 51 and (iv) undergoes nutrient enrichment due to GML exposure to soil washing and fresh water inflow justifying its eutrophic status. All these features combine to http://dx.doi.org/10.1016/j.marpolbul.2015.06.012 0025-326X/Ó 2015 Elsevier Ltd. All rights reserved.…”

Spatial pattern of ciliates in relation to environmental factors at Sfax south coast (Gulf of Gabes, Tunisia)

“…N/P ratio was widely used as an indicator of nitrogen or phosphorus limitation (25). The high DIP concentrations as well as their high magnitude relative to total phosphorus and the resulting low N/P ratios (< 16 Redfield ratio) in the south coast, N availability was the limiting element for phytoplankton growth and contrasting with results from the gulf of Gabes currently report phosphate depletion (26,27). These results may be explained by the continuous supply of DIP effluent from SIAPE and by the fact of a faster recycling of phosphorous than nitrogen (28).…”