Diel, seasonal and man-induced changes in copepod assemblages and diversity, with special emphasis on hyperbenthic calanoid species, in a Mediterranean meromictic system (Lake Faro)

Abstract

The present study focuses on variations in day and night copepod community structure in a meromictic Mediterranean ecosystem (Lake Faro). Because of the high salinity in the lake, this environment is defined as a coastal-marine rather than true-lagoon ecosystem. Copepod abundances showed wide oscillations, with marked spatial and seasonal heterogeneity. The copepod assemblage was dominated by coastal and estuarine species Paracartia latisetosa and Acartia margalefi, in late summer–autumn and spring, respectively. A remarkable change in species composition was the occurrence of the alien species Oithona brevicornis, never having been reported in this environment before. O. brevicornis is progressively replacing the congener species O. nana. The discovery of the hyperbenthic calanoid species ‘ecological group’ contributes to increased functional diversity of this ecosystem, despite their relatively low abundances. All six hyperbenthic calanoid species occurred in the plankton community only at night, with spatial distribution patterns being related to substrate more than water physico-chemical parameters. Among all hyperbenthic calanoid species, Pseudocyclops xiphophorus was the only one able to inhabit the whole lake because of its daytime habitat (fouling material, attached to submerged ropes and mooring posts, widely distributed all around the lake). In this habitat, the temporal abundance pattern resembled the night-time one in plankton community.

Fecundity and development of the bentho-pelagic copepod Pseudocyclops umbraticus: effects of temperature

“…Bentho-pelagic calanoids are only present in the zooplankton community at night (Zagami & Brugnano 2013), which confirms the hypothesis of their circadian vertical migration between the bottom and the water column (Damkaer 1970, Alldredge & King 1985, Ohtsuka 1985, Jacoby & Greenwood 1988, Campolmi et al 2002. Measurements of the lifehistory parameters of these copepods, such as development and egg production, will therefore provide useful information about energy transformation in pelagic food webs during the night.…”

“…Its spatial distribution is determined mainly by the substratum rather than by any physical parameters (Zagami & Brugnano 2013). Temperature is the only important environmental factor that affects the seasonal abundance pattern of P. umbraticus, although potentially in an indirect manner, as higher temperatures induce lower oxygen concentrations at the lake bottom, therefore restricting the available habitat (Zagami & Brugnano 2013).…”

“…Bentho-pelagic coupling of calanoids occurs mostly in autumn, resulting in increased abundance and, in some Mediterranean coastal brackish water environments such as Stagnone of Marsala and Lake Faro (Italy), a marked contribution to functional diversity (Campolmi et al 2002, Zagami & Brugnano 2013.…”

“…Measurements of the lifehistory parameters of these copepods, such as development and egg production, will therefore provide useful information about energy transformation in pelagic food webs during the night. Bentho-pelagic coupling of calanoids occurs mostly in autumn, resulting in increased abundance and, in some Mediterranean coastal brackish water environments such as Stagnone of Marsala and Lake Faro (Italy), a marked contribution to functional diversity (Campolmi et al 2002, Zagami & Brugnano 2013.…”

“…Its spatial distribution is determined mainly by the substratum rather than by any physical parameters (Zagami & Brugnano 2013). Temperature is the only important environmental factor that affects the seasonal abundance pattern of P. umbraticus, although potentially in an indirect manner, as higher temperatures induce lower oxygen concentrations at the lake bottom, therefore restricting the available habitat (Zagami & Brugnano 2013).In the present study, egg production rates (EPR), de velopment and egg-laying behaviours of P. umbraticus were studied in the laboratory at different temperatures under food-satiated conditions. The findings were then considered in relation to the natural seasonal fluctuations that occur in the population abundances of P. umbraticus in Lake Faro, and also in relation to what is known of the temperature effects and reproductive patterns of the congener species P. xiphophorus, which is present in the same environment although it lives on a different substrate (biological material on ropes suspended in the oxygenated layer, and mooring posts all around the lake).…”