Theodoros Kevrekidis

Seasonal and local variations of metal concentrations in the seagrass Posidonia oceanica (L.) Delile in the Antikyra Gulf, Greece

Abstract The accumulation of Fe, Pb, Zn, Cu, Cd, Na, K, Ca and Mg in the leaves of seagrass Posidonia oceanica (L.) Delile was studied in the Gulf of Antikyra. The investigated area was of interest because of the specific composition of its substrate (involving bauxite) and also because of the nearby discharge wastes from an aluminium factory. All metal concentrations in the phanerogam were evenly distributed at the seven stations where there were adequate data for analysis. Cd, K and Ca displayed significant seasonal variation with high concentrations in P. oceanica during summer and autumn and low levels in winter and spring. This variation could have been the effect of age-dependent distribution of these metals in the leaves. Significant variation was also evident in Pb concentrations, which was probably associated with the growth dynamics of Posidonia oceanica. Other factors playing a role were the biomass of calcareous epiphytes on the plant leaves (as concerns Ca) and the interactions of metals for binding by the plant tissues. The dependence of metal concentrations in the plant on their concentrations in the environment (sediment and seawater) was also relevant. A significant correlation was found between Cd concentrations in the plant and those in sediment. A comparison between metal concentrations in P. oceanica of the Antikyra Gulf and those of the species belonging to the subfamily Posidonioideae from other areas is also presented. Cu, Pb, Cd, Fe, Ca and Mg concentrations in P. oceanica in the study area were generally high.

Annual versus perennial growth cycle in Ruppia maritima L.: temporal variation in population characteristics in Mediterranean lagoons (Monolimni and Drana Lagoons, Northern Aegean Sea)

Abstract A perennial population of Ruppia maritima in a permanent lagoon in the Evros Delta grew from April to October and reproduced during summer. Numbers of rhizome and stem internodes increased in spring–summer and in late summer–autumn, revealing two successive periods of both horizontal and vertical expansion; leaf density increased continuously until October (78,210 leaves m−2). An annual population in a temporary lagoon grew and reproduced from May to August, and died afterwards leaving seeds as the habitat temporarily dried. Numbers of rhizome internodes sharply increased only in August, while numbers of stem internodes increased in June, indicating that a slow horizontal expansion was followed by a fast and brief vertical expansion; subsequently a second intense horizontal expansion occurred; leaf density peaked in August (58,080 leaves m−2). Several characteristics increased after mid-spring, attaining similar maximum values in annual and perennial populations. However, the perennial population had larger leaves and higher root biomass, but lower reproductive organ biomass. Rhizome, stem and leaf biomass increased sharply in August (113.2 g dw m−2) in the annual population and progressively up to October (167.8 g dw m−2) in the perennial population. Using principal component analysis, growth and reproduction were found to be mainly affected by temperature.

The green seaweed Ulva rigida as a bioindicator of metals (Zn, Cu, Pb and Cd) in a low-salinity coastal environment

The capacity of Ulva rigida as a bioindicator of Zn, Cu, Pb and Cd contamination in oligohaline coastal waters was investigated. Metal concentrations in U. rigida, water and sediments and several environmental variables were measured seasonally at four stations in the coastal section of the Evros River Delta, Aegean Sea. All four metals in sediments had a significant local variation; in particular, they decreased with increasing distance from the fluvial end-member of Evros River. Mean Zn, Cu, Pb and Cd concentrations in U. rigida were 61.0, 22.4, 6.1 and 1.1 m gg -1 dry weight, respectively. This macroalga, compared to other co-occurring macroalgal species, had a high metal accumulation capacity, mainly of Cu and Cd. Local patterns of Zn, Cu and Pb in U. rigida were similar to those in sediments, while that of Cd was not; moreover, Cu and Pb in U. rigida correlated positively with their sediment contents, suggesting that this seaweed satisfies the basic prerequisite for a bioindicator of these elements in oligohaline environments. No metal in U. rigida displayed a significant seasonal variation, and there was no significant variation in ambient concentrations. A negative correlation between Zn in U. rigida and water salinity was found, probably due to both a higher metal burden in the freshwater flowing in the study area and to a decrease in Zn uptake with increasing salinity; Cd in the macroalga correlated negatively with water column ammonium.

Metal content of some green and brown seaweeds from Antikyra Gulf (Greece)

An analysis was made of the levels of Fe, Cu, Zn, Cd, Pb, Na, K, Ca and Mg in three green and four brown seaweeds, abundant in the Antikyra Gulf (Viotia, Greece). After Ca and the macroelements K, Mg, Na, the higher concentrations found were of Fe and Pb, with Fe>Pb. Cadmium content was low in most species. Differences between species and taxonomic groups were also considered. Fe, Zn, Cd and Ca in the green algaDasycladus vermicularis increased from March to July and had their maxima in summer or autumn (Cd), whereas Cu, Pb and Mg showed an opposite pattern of seasonal variation with maxima in winter. Cu, Zn, Cd and K inD. vermicularis were correlated with their concentrations in the sediment and not with their dissolved levels in seawater. Iron inD. vermicularis was positively correlated with Zn and negatively with Cd.

Life history, aspects of reproductive biology and production of Corophium orientale (Crustacea: Amphipoda) in Monolimni lagoon (Evros Delta, North Aegean Sea)

Monthly samples of Corophium orientale were collected during February 1998–February 1999 in both parts of Monolimni lagoon (0.3 < Sal. < 6 psu, 2 < Temp. < 28.5 °C). Corophium orientaleshowed a semiannual life cycle. In the southern part, breeding occurred from early spring to mid autumn having three peaks, in early spring, early summer and early autumn, and three cohorts were produced, a spring cohort, a summer cohort and an overwintering one. In the shallower innermost northern part of Monolimni lagoon, breeding peaked in mid-spring and, also, in early autumn, and two discrete cohorts, a spring and an overwintering one, were produced. A lack of large individuals, attributed to a temporary size – selective predation by migrating shorebirds, was observed during summer. That lack possibly contributed to the hiatus in reproduction. Photoperiod seemed to be a more important cue than temperature in the initiation of the reproductive cycle, while extremely low salinities (<1 psu) did not deter breeding. Females attained maturity at a smaller size in late spring and, especially, in summer than in early spring at lower temperatures. Brood size was a function of females’ body size. Females, matured during summer at high temperatures, showed the lowest brood size, body length ratio. Mean brood size was small (12–13 early embryos) and embryo loss during development high (54%), possibly due to a negative effect of low salinities. A 1:1 sex ratio existed in the small body length classes, but females preponderated in the large ones. The spring cohort in the southern part, which developed at moderate temperatures, showed the highest growth rate (40 μm day−1). Secondary production of C. orientalecalculated by Hynes’s method gave a mean annual density of 4562.5 and 9327.6 ind. m−2, a mean annual crop (B) of 1.03 and 2.67 g DW m−2, an annual production (P) of 6.91 and 22.54 g DW m−2 and a P/B ratio of 6.7 and 8.4 in the northern and southern part of the lagoon, respectively.

Population Dynamics, Reproduction and Growth of Upogebia Pusilla (Decapoda, Thalassinidea) in the Evros Delta (North Aegean Sea)

[Monthly samples of Upogebia pusilla were collected from February 1983 to February 1984 in an area of the Evros Delta located close to the sea, where salinity and temperature of the water ranged from 4 to 25% and 4.3° to 24.5°C, respectively. Population density and wet weight biomass varied greatly, being higher in summer. Young shrimps appeared in August and had a maximum life span of approximately three years. Ovigerous females were found from April to August. The frequency of females among the collected individuals was 0.393. The smallest ovigerous female had a total length (TL) of 39 mm, while the maximum TL for females was 82 mm and for males 106 mm. Growth in age classes I and II was greater in the period from July to August. Mean growth of carapace length (CL) was described by the Von Bertalanffy function. A positive correlation existed between total length and CL or wet weight (W)., Monthly samples of Upogebia pusilla were collected from February 1983 to February 1984 in an area of the Evros Delta located close to the sea, where salinity and temperature of the water ranged from 4 to 25% and 4.3° to 24.5°C, respectively. Population density and wet weight biomass varied greatly, being higher in summer. Young shrimps appeared in August and had a maximum life span of approximately three years. Ovigerous females were found from April to August. The frequency of females among the collected individuals was 0.393. The smallest ovigerous female had a total length (TL) of 39 mm, while the maximum TL for females was 82 mm and for males 106 mm. Growth in age classes I and II was greater in the period from July to August. Mean growth of carapace length (CL) was described by the Von Bertalanffy function. A positive correlation existed between total length and CL or wet weight (W).]

Trace element patterns in marine macroalgae

Novel information on interspecific variation in trace element accumulation in seaweeds is provided. Concentrations and concentration factors (CFs) of a wide set of elements (As, Ba, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Se, Sr, U, V and Zn) in 26 dominant macroalgae from the Gulf of Thessaloniki, Aegean Sea were determined and compared. Uni-and multivariate data analyses were applied. Phaeophyceae showed higher concentrations and CFs of As and Sr than Rhodophyta and Chlorophyta, indicating that the accumulation of these elements is closely related to species biochemical composition. Filamentous macroalgae displayed higher concentrations and CFs of several elements, particularly Cd, Co, Cr, Cu, Mn and V than sheet-like, coarsely-branched and/or thick-leathery macroalgae, irrespective of phylogenetic relationships, indicating that the accumulation of several elements is largely related to thallus morphology and growth strategy. On a species basis, Cystoseira spp. showed both the highest concentrations and CFs of As, Padina pavonica of Sr and U, Ceramium spp. of Mn, Ceramium and Cladophora species of Co and Cu, Cladophora prolifera of Cr and Polysiphonia deusta and Ulva clathrata of Cd. Se concentration in Ulva rigida correlated positively with seawater Se concentration, and As concentration in this species with sediment As concentration. Thereby, these seaweeds could be regarded as potential biomonitors for the respective elements. A literature review was performed and global element concentrations and CFs were presented for seaweeds from genera collected during this survey. The data presented can contribute to the interpretation of biomonitoring data and the design of biomonitoring programs for the protection and management of coastal environments.

Estimating lagoonal biodiversity in Greece: comparison of rapid assessment techniques

An attempt is made to compare the results of different rapid biodiversity assessment techniques at the pan-Mediterranean, sectorial and local levels. A uniform multivariate pattern exists at the pan-Mediterranean and national (sectorial) levels: lagoons can be different when they host only a few species, but as species numbers increase, lagoons become homogenous in composition. Multivariate techniques cannot distinguish anthropogenically-impacted lagoons from those, which are naturally disturbed. In the pan-Mediterranean context it is the higher taxonomic levels, but in the national and local context it is the most abundant macrobenthic groups (polychaetes, molluscs and crustaceans) and meiobenthos which provide patterns closest to that derived from the species level. Taxonomic distinctness indices applied to polychaete and mollusc inventories provide meaningful results at most levels and scales of observation. These indices seem to be robust enough to discriminate anthropogenically impacted from naturally disturbed lagoons.

Microtubule integrity and cell viability under metal (Cu, Ni and Cr) stress in the seagrass Cymodocea nodosa

The effects of increasing Cu, Ni and Cr concentrations (0.5, 5, 10, 20 and 40 mg L(-1)) on microtubule organization and the viability of leaf cells of the seagrass Cymodocea nodosa for 13 consecutive days were investigated under laboratory conditions. Increased oblique microtubule orientation, microtubule depolymerization at the 5-40 mg L(-1) Ni treatments after 3 d of exposure, and a complete microtubule depolymerization at all Ni treatments after 5 d were observed. Cu depolymerised microtubules after three to 7 d of exposure, while Cr caused an extensive microtubule bundling after 9 or 11 d of exposure, depending on metal dosage. Fluorescence intensity measurements further consolidated the above phenomena. Cell death, occurring at later time than microtubule disturbance, was also observed at all Cu and Ni treatments and at the 10-40 mg L(-1) Cr treatments and adding to the above quantification of the number of dead cells clearly showed that only a portion of the cell population studied died. The data presented, being the first assessment of microtubule disturbance in seagrasses, indicate that microtubules in seagrass leaf cells could be used as a valuable and early marker of metal-induced stress in biomonitoring programmes.

Trace element (Al, As, B, Ba, Cr, Mo, Ni, Se, Sr, Tl, U and V) distribution and seasonality in compartments of the seagrass Cymodocea nodosa

Novel information on the biological fate of trace elements in seagrass ecosystems is provided. Al, As, B, Ba, Cr, Mo, Ni, Se, Sr, Tl, U and V concentrations in five compartments (blades, sheaths, vertical rhizomes, main axis plus additional branches, roots) of the seagrass Cymodocea nodosa, as well as in seawater and sediments from the Thessaloniki Gulf, Greece were determined monthly. Uni- and multivariate data analyses were applied. Leaf compartments and roots displayed higher Al, Mo, Ni and Se annual mean concentrations than rhizomes, B was highly accumulated in blades and Cr in sheaths; As, Ba, Sr and Tl contents did not significantly vary among plant compartments. A review summarizing reported element concentrations in seagrasses has revealed that C. nodosa sheaths display a high Cr accumulation capacity. Most element concentrations in blades increased in early mid-summer and early autumn with blade size and age, while those in sheaths peaked in late spring-early summer and autumn when sheath size was the lowest; elevated element concentrations in seawater in late spring and early-mid autumn, possibly as a result of elevated rainfall and associated run-off from the land, may have also contributed to the observed variability. Element concentrations in rhizomes and roots generally displayed a temporary increase in late autumn, which was concurrent with high rainfall, low wind speed associated with reduced hydrodynamism, and elevated sediment element levels. The bioaccumulation factor based on element concentrations in seagrass compartments and sediments was lower than 1 except for B, Ba, Mo, Se and Sr in all compartments, Cr in sheaths and U in roots. Blade V concentration positively correlated with sediment V concentration, suggesting that C. nodosa could be regarded as a bioindicator for V. Our findings can contribute to the design of biomonitoring programs and the development of predictive models for rational management of seagrass meadows.