M. Moraitou-Apostolopoulou

Seasonal horizontal and vertical variability in primary production and standing stocks of phytoplankton and zooplankton in the Cretan Sea and the Straits of the Cretan Arc (March 1994-January 1995)

Abstract Phytoplankton communities, production rates and chlorophyll levels, together with zooplankton communities and biomass, were studied in relation to the hydrological properties in the euphotic zone (upper 100 m) in the Cretan Sea and the Straits of the Cretan Arc. The data were collected during four seasonal cruises undertaken from March 1994 to January 1995. The area studied is characterised by low nutrient concentrations, low 14 C fixation rates, and impoverished phytoplankton and zooplankton standing stocks. Seasonal fluctuations in phytoplankton densities, chlorophyll standing stock and phytoplankton production are significant; maxima occur in spring and winter and minima in summer and autumn. Zooplankton also shows a clear seasonal pattern, with highest abundances occurring in autumn–winter, and smallest populations in spring–summer. During summer and early autumn, the phytoplankton distribution is determined by the vertical structure of the water column. Concentrations of all nutrients are very low in the surface waters, but increase at the deep chlorophyll maximum (DCM) layer, which ranges in depth from about 75–100 m. Chlorophyll- a concentrations in the DCM vary from 0.22–0.49 mg m −3 , whilst the surface values range from 0.03–0.06 mg m −3 . Maxima of phytoplankton, in terms of cell populations, are also encountered at average depths of 50–75 m, and do not always coincide with chlorophyll maxima. Primary production peaks usually occur within the upper layers of the euphotic zone. There is a seasonal succession of phytoplankton and zooplankton species. Diatoms and ‘others’ (comprising mainly cryptophytes and rhodophytes) dominate in winter and spring and are replaced by dinoflagellates in summer and coccolithophores in autumn. Copepods always dominate the mesozooplankton assemblages, contributing approximately 70% of total mesozooplankton abundance, and chaetognaths are the second most abundant group.

Differentiation of the sensitivity to copper and cadmium in different life stages of a copepod

Copper is more toxic to all life stages of the copepod Tisbe than cadmium. The most sensitive life stage of Tisbe to both copper and cadmium is the one-day-old nauplius. The resistance of larval stages of Tisbe increases with age (one-day-old nauplii 48h lc50=0.3142 mg Cu l−1. and 0.5384 mg Cd l−1, 0.3415 mg Cu l−1. and 0.645 mg Cd l−1. for five-days-old nauplii and 0.5289 mg Cu l−1. and 0.9061 mg Cd l−1. for ten-days-old nauplii. The two reproductive stages of Tisbe tested (females with ovigerous bands and females bearing the first ovigerous sac) demonstrated an increased sensitivity to metals and proved more sensitive than the ten-days-old copepodids (only females with ovigerous bands had a similar sensitivity to copper with the ten-days-old copepodids).

Acute toxicity of copper to a copepod

Abstract The acute toxicity of copper to the marine copepod Acartia clausi was determined by means of static bioassays. Natural copepod assemblages from two different locations, one from an area polluted with industrial effluents and domestic wastes and another from a relatively uncontaminated area, were compared. Results of metal toxicity tests expressed as 48 h LC50 values indicate a significant difference in the tolerance of copper between the two populations, with the LC50 of the pollution-adapted population higher than that of the population from the uncontaminated area.

Effects of sublethal concentrations of cadmium as possible indicators of cadmium pollution for two populations of Acartia clausi (Copepoda) living at two differently polluted areas.

Toxicity of heavy metals to marine organisms is a subject of interest because, due to technological development, the sea receives an increasing amount of heavy metals. Acute toxicity studies have played a major role in estimating the effects of heavy metals to marine organisms because survival is considered the best index of a pollutant stress, being in general the least variable. However, long term exposure to sublethal concentration of a pollutant may markedly alter the normal functioning of organisms and thus destroy a population as effectively as lethal doses. Therefore, the study of the effects of sublethal doses is indispensable if we want to set realistic standards of water qualtiy criteria. The purpose of this study was twofold: first to establish and characterize the sublethal effects of cadmium on different physiological processes (longevity, feeding, respiratory rates), and second to verify whether there exist differences in the effects of sublethal concentrations of cadmium between the two populations of Acartia adapted to differently polluted areas.

Individual and combined toxicity of three heavy metals, Cu, Cd and Cr for the marine copepod Tisbe holothuriae

The acute toxicity of Cu, Cd and Cr to the marine copepod Tisbe holothuriae, Humes, was estimated by static bioassays and the LCinf50su48h(in mg/l) was calculated. Copper proved to be the most toxic (LCinf50su48h= 0,08 ± 0,01 mg/l) and chromium the least toxic (LCinf50su48h= 8,14 ± 0,05 mg/l), while cadmium showed an intermediate toxicity (LCinf50su48h= 0,97 ± 0,04 mg/l).In mixtures of the two metals an obvious synergism of the effects was observed in all cases. In all three combinations with two metals (Cu + Cd, Cu + Cr, and Cd + Cr) the mortality was higher than that expected on a purely additive basis. The mixture of the three metals presented a higher toxicity than that of the individual metals acting separately, but lower than that of all two metals mixture.

Combined toxicity of four toxicants (Cu, Cr, oil, oil dispersant) to Artemia salina.

In sea waters multicontaminant pollution appears to be the rule rather than the exception. For a realistic approach to pollution effects it is essential to estimate the combined toxicity of two or more chemicals. There is a need to understand the mechanisms of quantify the effects of multiple toxicity in order to provide responsible authorities with rational estimate of the effects of chemical mixtures. Thus the potential toxic effects of mixtures of toxicants has recently become a subject of growing scientific interest. In this paper the authors have tried to estimate the joint toxicity of some pollutants commonly found in nearshore polluted waters: two metals, copper and chromium; an oil (Tunesian crude oil zarzaitine type); and an oil dispersant (Finasol OSR-2).

Influence of Life-History Adaptations on the Fidelity of Laboratory Bioassays for the Impact of Heavy Metals (Co2+ and Cr6+) on Tolerance and Population Dynamics of Tisbe holothuriae

Abstract To investigate the influence of life-history adaptations on the fidelity of laboratory bioassays, copepods Tisbe holothuriae were collected from two areas (polluted and non-polluted) and maintained in the laboratory under temperatures similar to their wild habitat. The sensitivity of Tisbe increased with increasing temperature. The wild animals from the polluted area were more tolerant to Co 2+ and Cr 6+ than those from the non-polluted area. Laboratory animals (40 generations after sampling) from the polluted area, were still more tolerant than those from the non-polluted area. These animals also exhibited a similar or increased tolerance, whereas those of the first generation showed a higher sensitivity, compared to the wild ones from the same area. Demography also varied in successive generations after sampling. Laboratory bioassays using T. holothuriae can predict most of its responses in the field, but attention should be paid to adaptations to temperature, pollution and the laboratory environment.

Toxicity of chromium to the marine planktonic copepodAcartia clausi, Giesbrecht

The toxicity of chromium to the marine planktonic copepodAcartia clausi, Giesbrecht was studied. The LC50 48 h values (concentration of chromium lethal to 50% of the test animals) vary with the experimental temperature, the form of chromium compound tested and the annual generation to which theAcartia specimens belong. The elevation of temperature resulted in a considerable increase ofAcartias sensitivity to chromium. Cr6+ in the form of Na2CrO4 was more toxic toA. clausi than in the form of CrO3 · Cr3+ in the form of Cr(NO3)3 9 H2O precipitated to the bottom and was not toxic toAcartia.Acartia specimens belonging to the summer generation were more sensitive to chromium than those belonging to the winter or autumn generation. The exposure ofAcartia to sublethal concentrations of chromium resulted in a reduction of its longevity proportional to the chromium concentrations used.Furthermore, whenA. clausi was exposed to sublethal chromium concentrations it showed a decrease of feeding capacity and increase of respiratory rates, which became more pronounced with increasing chromium concentrations.

Pollution effects on the phytoplankton-zooplankton relationships in an inshore environment

The quantitative and qualitative relationships between the phytoplankton and zooplankton populations were examined for one year in an inshore environment (Elefsis Bay) of the Aegean Sea. It was found that quantitative relationships among these populations were influenced by the trophic level of the environment and their stocks were significantly correlated only in non-polluted conditions. The quantitative relationship between the principal grazers in the zooplankton population (Acartia clausi, Oithona nana) and the phytoplankton dominant species Exuviaella baltica, upon which these copepods were believed to graze preferentially, was tested and the results were discussed.

Effects of pre-exposure on the tolerance of Artemia salina to oil and oil dispersant

Abstract Higher tolerance (acclimation phenomena, adaptation) to oil (Tunisian crude oil) and oil dispersant (Finasol OSR 2, Finasol OSR 5), can be induced in Artemia salina after pre-exposure to these toxicants. The higher tolerance includes acute toxicity (LC50) and sublethal physiological dysfunctions (respiration). High pre-exposure concentrations lead to rapid induction of acclimation phenomena but the higher resistance is partly lost after exposure of the acclimated animals to clean sea water. Exposure to low concentrations of the toxicants induce a slow appearance of adaptation phenomena, but higher tolerance does not disappear after exposure to clean sea water and is strengthened after the detoxification period.