Tintinnids and rotifers in a northern Mediterranean coastal lagoon. Structural diversity and function through biomass estimations

Abstract

Daily zooplankton samples were obtained from the Etang d e Thau, France, a 70 km2 coastal lagoon of the northwestern Mediterranean Sea. The survey was monitored at 2 stations inside the lagoon and at 1 station on the seaside during 4 periods in 1994. The microzooplankton, towed with a 40 pm mesh size net, included tintinnids, rotifers, anthozoan larvae, and crustacean and mollusk larvae. The tintinnids and rotifers have not been studied in the lagoon yet. Over all the sampling periods, their mean biomass represented between 26 and 4 5 YO of the net collected mlcrozooplankton biomass, which was estimated by image analysis. Their biomass in the central part of the lagoon free of anthropic activity was close to the level observed at the nearby seaside. However, at the shellfish culture area, the occurrence of oysters and of epibiotic fauna resulted in a drastic biomass reduction of these taxocoenoses by a factor of 10 compared to values measured in the middle of the lagoon. Samples collected during the fall indicated well-developed tintinnid and rotifer populations in this season. lnside the lagoon these populations seemed to be already abundant in early spring (March and June samples). An ordination of taxa biomasses showed 2 main factors which might have contributed to the organization of the tintinnid and rotifer assemblages: the geographical position and the thermal period. The geographical position integrated the lagoon-sea water exchange. The thermal period reflected both the populations' development cycles and the env~ronmental constraints. The resulting effects appeared in assemblages structured in a space and time gradient. The capacity of the tintinnids and rotifers to quickly colonise the habitat (reproduction modes, resistance forms) and to use a wide range of food resources (organic matter, bacteria, pico-and nanoplankton) likely enhances their ability to serve as trophic links between primary and secondary producers. Hence, their function in the lagoon ecosystem is not minor.

Influence of shellfish farming activities on the biogeochemical composition of the water column in Thau lagoon

“…The deficit of chl a concentrations (> 40%) in shellfish farming zones (Table 1) is higher than the 13 to 25% calculated in 1986/1987 by Jarry et al (1990), even if the distinct sampling strategies preclude a strict comparison between the 2 studies. Lam Hoai et al (1997) measured, in shellfish farms, a deficit in microzooplankton biomasses (40 to 200 µm pore size) corresponding to about 30 %. The difference in deficit between chl a and POC is probably due to the preferential grazing of filter feeders on phytoplankton.…”

“…Primary production transforms these nutrients into particulate matter. The grazing of heterotrophic communities on phytoplankton (Lam Hoai et al 1997) should explain several peak values of POC concentrations, and particularly those following peaks in chl a concentrations. The relationship between PON and POC concentrations at ZA is similar to that reported from data collected in summer 1994 at the same station (Souchu et al 1998).…”

Tintinnina (Ciliophora) and Foraminifera in plankton of hypersaline Lagoon Bardawil (Egypt): spatial and temporal variability

“…They are the crossroads of terrestrial and marine trophic chains. Unicellular organisms of different trophic levels play an important role in this system of relationships (Anderson et al, 1979;Lam-Hoai et al, 1997;Ramdani et al, 2009). Despite their obvious importance, our knowledge about the eukaryotic unicellular heterotrophic diversity of lagoons is still limited and poorly documented.…”

“…In the Mediterranean Sea, there are more than 100 lagoons with different salinity regimes (Pérez-Ruzafa et al, 2011), but few studies have been devoted to heterotrophic protists in them (Lam-Hoai et al, 1997;Collos et al, 2005;Sakka Hlaili et al, 2007;Ramdani et al, 2009). The majority of lagoons are of brackish or marine salinity and only a small portion of them are hypersaline.…”

Impact of introduced juvenile mussel cultures on the pelagic ecosystem of the western Wadden Sea, The Netherlands

“…Since smaller algal cells (< 3 µm) are less well retained compared to larger cells (> 3 µm; Riisgård & Møhlenberg 1979, but see Strohmeier et al 2012) and since the small cells are assumed to be better competitors for light and nutrients (Riegman et al 1993), an increase in small-sized phytoplankton abundance could be expected to occur under heavy filtration pressure. The few studies that included heterotrophic plankton when examining the effect of bivalves on the plankton community found a decrease in microzooplankton as a result of bivalve grazing (Lam-Hoai et al 1997, Pace et al 1998, Trottet et al 2008b, Froján et al 2014. A decrease in heterotrophic nanoflagellate predators was suggested as an explanation for the increase in picophytoplankton (< 2 µm) (Cranford et al 2009), while in other areas a decrease in nano-sized predators (2−20 µm) did not result in an increase of the picoalgae (Froján et al 2014).…”