Natural and anthropogenic influences on the diversity structure of reef fish communities in the Tuamotu Archipelago (French Polynesia)

Despite the rapid rate of human-induced species losses, the relative influence of natural and anthropogenic factors on the functional diversity of species assemblages remains unknown for most ecosystems. A model was previously developed to predict the diversity structure of coral reef fish assemblages in 10 atolls of low human pressure and contrasting morphology of the Tuamotu Archipelago (French Polynesia). This existing model predicted smoothed histograms (spectra) of species richness according to size classes, diet classes and life-history classes of fish assemblages using a combination of environmental characteristics at different spatial scales. The present study applied the model to Tikehau, another atoll of the same archipelago where commercial fishing is practiced and where the same sampling strategy was reproduced. Significant differences appeared between predicted and observed species richness in several size, diet and life-history classes of fish assemblages in Tikehau. Two parameters which were not accounted for in the initial model, i.e. fishing pressure and atoll position within the archipelago, explained together 63% of variance in model residuals, >60% being explained by fishing pressure only. The respective effects of fishing and atoll position on the diversity of coral reef fish assemblages are discussed, with the potential of such modelling approach to assess the relative importance of factors affecting functional diversity within communities.     

Influence of some coral reef communities on the calcium carbonate budget of Tiahura reef (Moorea,French Polynesia)

The calcium carbonate budget of coral reefs is the result of the interaction of the processes of calcification and biological degradation, and is reflected in the chemical properties of the seawater overlying the reefs. A series of experiments at Moorea Island (French Polynesia) in 1988 monitored the diurnal and nocturnal variations in the chemical properties of seawater under field and laboratory conditions. Our results revealed that in the study area (Tiahura barrier reef flat), the calcium carbonate budget varied over space and time as a function of location in the water current. Two in-situ sites were investigated; one was situated 100 m from the algal crest of the barrier reef, the other 300 m further downstream. As a result of cumulative upstream events, the daily net calcification was ten times higher at the downstream (5.22 gm^-2 d^-1) than at the upstream (0.45 gm^-2 d^-1) site. The carbonate uptake by in situ Porites lobata in enclosures (8 kgm^-2 yr^-1) was ten times higher than the uptake by the whole community in the surrounding water (0.8 kgm^-2 yr^-1) and five times higher than that recorded for P. lobata in laboratory experiments (1.4 kgm^-2 yr^-1), where illumination levels were 10% of in situ levels. In laboratory experiments, the planktonic fraction of the seawater had no perceptible influence on the calcium carbonate budget. In the absence of bioeroders, living coral totally depleted the carbonate content of the seawater (3.7 gm^-2d^-1). Bioerosive organisms played an important role in restoring this calcium carbonate; e.g. sea urchins grazing on algal turf covering dead coral ingested CaCO₃ and released this as a carbonate powder (1.26 gm^-2d^-1); a form of carbonate which is extremely accessible to chemical dissolution.     

Zooplankton of tikehau atoll (Tuamotu archipelago) and its relationship to particulate matter

The standing stock and taxonomic composition of zooplankton (>200 m) were monitored in the lagoon of Tikehau atoll from April 1985 to April 1986. These data were supplemented by two 10 d studies on the variability, structure and functioning of the pelagic ecosystem. The biomass of animals >200 m comprised 50% of the total biomass of all organisms from 35 to >2000 m. The zooplankton populations were characterized by successive blooms of copepods, larvaceans, pteropods and salps, probably arising from the periodic input of detritus from the reef during windy periods. As a result, the ecosystem was not in a steady state and the data for the fluxes of organic matter are presented separately for April 1985 and April 1986. Using the C:N:P ratio method, net growth efficiencies, K ₂, were calculated for total mesozooplankton, mixed copepods, and two planktonic species, Undinula vulgaris and Thalia democratica. Combined with nitrogen and phosphorus excretion rates, these K ₂ values enabled the assessment of production rates. On a 24 h basis, P:B ratios (%) were close to 100 for the total zooplankton and 54, 34 and 800 for mixed copepods, U. vulgaris and T. democratica, respectively. These ratios are 5.7 times lower than that recorded for phytoplankton. High productivity may be ascribable to the high density of seston, the high temperature (29.5°C), and the kind of organisms present. Zooplankton production equalled 38 and 30% of ¹⁴C uptake during April 1985 and April 1986, respectively. Ingestion of animals >35m was calculated by means of assimilation efficiencies and amounted to 17 and 7% of particulate organic carbon, 100 and 38% of living carbon, and 64 and 140% of primary production during the two periods, respectively. Finally, inorganic exduring was 32 and 18% of phytoplankton nitrogen and phosphorus requirements. A model based on the dimensional structure of the pelagic food-web, has been drawn to illustrate the biomass and carbon, nitrogen and phosphorus fluxes in the study area. The lagoon appears to export part of its planktonic biomass, which is 4.2 times lower one sea mile outside the main pass connecting the lagoon to the open ocean.     

Excretion of ammonia by zooplankton and its potential contribution to nitrogen requirements for primary production in the Catalan Sea (NW Mediterranean)

Excretion of ammonia by mesozooplankton (>200 m zooplankton) and its potential contribution to the nitrogen requirement for phytoplankton growth has been estimated for different hydrographical situations along a transect across the Catalan Sea (Northwestern Mediterranean). The nitrogen excreted as ammonia was estimated from mesozooplankton biomass and specific excretion rates. Nitrogen requirements of phytoplankton were estimated by means of carbon fixation rates and C:N ratios of <200 m particulate organic matter. Minimum C:N ratios and maximum primary production, zooplankton biomass, phytoplankton nitrogen requirements, and nitrogen excretion of zooplankton occurred near the Catalan density front. On average, the nitrogen regenerated by the mesozooplankton accounted for 43% of the nitrogen requirements of the phytoplankton. The specific excretion rates of ammonia and the percentage of phytoplanktonnitrogen requirements supplied by excreted nitrogen were higher at coastal stations. In some coastal and frontal stations, the ammonia excreted exceeded the phytoplanktonnitrogen demand. Bacteria competing for nutrient supply and the possible uncoupling between rate processes and standing stocks of phyto- and zooplankton could explain the apparent excess of regenerated ammonia.     

Spatial repartition and ontogenetic shifts in habitat use by coral reef fishes (Moorea,French Polynesia)

This study explores the extent to which ontogenetic habitat shifts modify spatial patterns of fish established at settlement in the Moorea Island lagoon (French Polynesia). The lagoon of Moorea Island was divided into 12 habitat zones (i.e. coral seascapes), which were distinct in terms of depth, wave exposure, and substratum composition. Eighty-two species of recently settled juveniles were recorded from March to June 2001. Visual censuses documented changes in the distribution of juveniles of each species over time among the 12 habitats. Two patterns of juvenile habitat use were found among species. Firstly, some species settled and remained in the same habitat until the adoption of the adult habitats (i.e. recruitment; e.g. Chaetodon citrinellus, Halichoeres hortulanus, Rhinecanthus aculeatus). Secondly, others settled to several habitats and then disappeared from some habitats through differential mortality and/or post-settlement movement (e.g. 65–70 mm size class for Ctenochaetus striatus, 40–45 mm size class for Epinephelus merra, 50–55 mm size class for Scarus sordidus). A comparison of the spatial distribution of juveniles to that of adults (61 species recorded at both stages) illustrated four patterns of subsequent recruitment in habitat use: (1) an increase in the number of habitats used during the adult stage (e.g. H. hortulanus, Mulloidichthys flavolineatus); (2) a decrease in the number of habitats adults used compared to recently settled juveniles (e.g. Chrysiptera leucopoma, Stethojulis bandanensis); (3) the use of different habitat types (e.g. Acanthurus triostegus, Caranx melampygus); and (4) no change in habitat use (e.g. Naso litturatus, Stegastes nigricans). Of the 20 most abundant species recorded in Moorea lagoon, 12 species modified the spatial patterns established at settlement by an ontogenetic habitat shift.Communicated by T. Ikeda, Hakodate     

Sensitivity of benthic community respiration and primary production to changes in temperature and light

In-situ measurements of benthic community respiration and primary production on an intertidal sandflat in Nova Scotia, Canada were used to test the hypothesis that community responses to light and temperature were similar within and between seasons. Multiple regression indicated that mean incubation temperature explained 57% of the variance in total sediment oxygen demand (TOD). The logarithmic relationship between TOD and temperature (Q₁₀=6.5) was not significantly different between fall and spring, suggesting no acclimation within season. Chemical oxygen demand measured in formalin-poisoned cores averaged 30% of TOD. Microalgal gross primary production (GROSS) was measured as oxygen production in light cores. Mean incubation temperature and sediment chlorophylla explained 56% of the variance. The linear relationship between GROSS and temperature had Q₁₀=2.0. When production was normalized to chlorophylla [GROSS(SP)], seasonal production-temperature curves were significantly different. The spring curve had Q₁₀=3.3; in the fall, production and temperature were not related. GROSS(SP)-light curves derived from Plexiglas shade experiments in the field were linear and not significantly different between fall and spring. Temperature alone was a better predictor of GROSS(SP) than light, even when P/I curves were adjusted for temperature. One can therefore model community respiration and photosynthesis at this site using daily averages in temperature, which are then summed over longer time scales to estimate monthly or seasonal rates.     

In situ net primary productivity and photosynthesis of Antarctic sea ice algal, phytoplankton and benthic algal communities

Primary production at Antarctic coastal sites is contributed from sea ice algae, phytoplankton and benthic algae. Oxygen microelectrodes were used to estimate sea ice and benthic primary production at several sites around Casey, a coastal area in eastern Antarctica. Maximum oxygen export from sea ice was 0.95 mmol O₂ m⁻² h⁻¹ (~11.7 mg C m⁻² h⁻¹) while from the sediment it was 6.08 mmol O₂ m⁻² h⁻¹ (~70.8 mg C m⁻² h⁻¹). When the ice was present O₂ export from the benthos was either low or negative. Sea ice algae assimilation rates were up to 3.77 mg C (mg Chl-a)⁻¹ h⁻¹ while those from the benthos were up to 1.53 mg C (mg Chl-a)⁻¹ h⁻¹. The contribution of the major components of primary productivity was assessed using fluorometric techniques. When the ice was present approximately 55–65% of total daily primary production occurred in the sea ice with the remainder unequally partitioned between the sediment and the water column. When the ice was absent, the benthos contributed nearly 90% of the primary production.     

Settlement seasonality and temporal changes in hard substrate macrozoobenthic communities of Lesina Lagoon (Apulia, Southern Adriatic Sea)

The macrofauna settling on experimental substrates was studied at two sites of the Lesina Lagoon to test its possible role in monitoring ecological variations in a brackish-water ecosystem. The community settlement was seasonally investigated on 3-month-old wooden poles; the development was monitored from 2001 to 2005. Comparisons with benthic assemblages settled on 10-yr-old poles were also performed. The main hydrological parameters were periodically measured during the study. A total of 38 species were collected. The assemblage reached the highest development in the central lagoon, showing relevant carbonate structures which supported a rich vagile fauna. Close to the sea-water inlet species richness and abundance values were lower, with the disappearance of some brackish-water species. A remarkable salinity drop during 2004 produced some faunistic changes in the assemblages, which however maintained different structures between the study sites, thus confirming macrozoobenthos as an efficient bioindicator of different environmental conditions for transition biotopes and a useful investigation tool in monitoring programmes.     

Biodegradation of shells of the black pearl oyster,Pinctada margaritifera var. cumingii,by microborers and sponges of French Polynesia

The composition, distribution and infestation sequence of organisms that destroy the commercially valuable shells of the black oyster Pinctada margaritifera var. cumingii Jameson, 1901 were studied. Three ecologically different groups of boring (euendolithic) organisms were identified: (1) phototrophic boring microorganisms (cyanobacteria, Hyella caespitosa, Hyella sp., Mastigocoleus testarum, Plectonema terebrans, and green algae, Phaeophila dendroides, Ostreobium quekettii); (2) heterotrophic boring microorganisms (fungi, Ostracoblabe implexa); (3) filter-feeding boring organisms (sponges, Cliona margaritiferae, C. vastifica). The phototrophic endoliths dominate the external pristmatic region of the shell, whereas the valuable interior nacreous region is attacked mainly by heterotrophs. Boring patterns reflect in part the shape and behaviour of the organisms and in part the structural properties of the shell, and inflict different types of damage. Infestation starts with microbial borers, which prepare the conditions for later invasion by more damaging clionid sponges. The infestation begins always at the apex, the oldest part of the shells, from which the periostracum is often removed by natural attrition or by cleaning procedure. The rate of bioerosion in 1 yr-old hatchery shells is 36 times higher than in natural populations.     

Effect on benthic communities of a major input of organic matter and other pollutants (coast off Barcelona,Western Mediterranean)

Benthic communities on soft bottoms off Barcelona, at and around two main pollution sources, the mouth of the Besòs River and the outlet of the submarine pipeline draining wastewater and organic sludges from the wastewater treatment plant of Sant Adrià del Besòs, have been studied. Samples were obtained with a Van Veen grab from 36 stations covering a 100 km² grid, between 10 and 70 m in depth. The effect of both pollution sources is clearly seen both at the species (the following macrofauna groups have been studied: Polychaeta, Mollusca, Echinodermata and Crustacea Decapoda) and community levels. The distribution of species and individuals numbers, species diversity and a pollution index, and of some selected (indicator) polychaeta species, all clearly define the degree of environmental degradation and the extent of the areas under the influence of the organic pollution.     

Seasonal abundance and toxicity of the dinoflagellate Gambierdiscus spp. (Dinophyceae), the causative agent of ciguatera in Tahiti, French Polynesia

The benthic dinoflagellate Gambierdiscus spp. is the primary causative agent of ciguatera fish poisoning in French Polynesia. However, the initiation of ciguatera outbreaks and the factors that control ciguatoxin production in this dinoflagellate are still poorly understood. In this paper, we present some original data concerning the seasonal abundance and toxicity of natural populations of Gambierdiscus spp. based on a long-term survey in a ciguateric site of the island of Tahiti. From February 1993 to December 1997, Gambierdiscus spp. population densities were monitored weekly in the Atimaono barrier reef of Papara in relation to temperature and salinity. Densities peaked at 4992 cells g⁻¹ in October 1994 and constituted ≥1000 cells g⁻¹ on several occasions. A total of 58 blooms were recorded in the area, of which 65% occurred in 1995 and 1996 alone. Our data confirmed the high endemicity of Gambierdiscus spp. in the Papara area. Refined analysis of our raw data by a principal-component analysis of processes (PCAP) revealed a seasonality in cell densities from February 1993 to May 1995. During this period, Gambierdiscus spp. populations tended to reach maximum abundance at the beginning and end of the hot season. In contrast, salinity did not appear to be a determining factor in the seasonal abundance of this dinoflagellate. The noticeable increase in both peak densities and frequency of blooms further noticed in 1995 and 1996 was preceded by unusually high water temperatures in January to April 1994, concomitant with a severe coral-bleaching episode. During the course of the study, a total of 303 × 10⁶ cells obtained from 48 successive blooms was harvested. Toxicity screening revealed that toxin production was maximum from October 1994 through December 1996. No correlation was found between toxicity of these blooms and their biomass nor the seasonal pattern of temperatures. It is suggested that the toxicity of naturally-occurring blooms of Gambierdiscus spp. and, consequently, the severity of ciguatera incidents in a given area, is mainly dependent on the clonal nature of cells which coexist within local populations of this dinoflagellate. Received: 12 October 1998 / Accepted: 15 June 1999     

Biology of Serranicotyle labracis,ectoparasite of Dicentrarchus labrax (Teleostei): contribution to the study of its populations

Serranicotyle labracis (Van Beneden and Hesse, 1863) Maillard, Euzet and Silan, 1988 (synonym: Microcotyle labracis Van Beneden and Hesse, 1863) is a monogenean Polyopisthocotylea and a gill parasite of the bass Dicentrarchus labrax (Linné, 1758). Analysis of a western Mediterranean population of this parasite (Gulf of Lions, Languedoc, France) clarified several aspects of its biology. Its location in the gill biotope (Silan et al. 1987) was not fundamentally different from that found by Oliver (1977) and Winch (1983), but its distribution in host populations differed from that reported in the earlier studies; it displayed a negative binomial distribution in the study zone. At a finer level of observation, the behaviour of the hosts, as a function of degree of maturity and sex, appeared to determine more than any other factor the extent of infestation by the parasite. Previous suggestions in the literature to account for these differences in population dynamics are discussed.     

As(V)-reduction to As(III) by arsenic-resistant Bacillus spp. bacterial strains isolated from low-contaminated sediments of the Oliveri-Tindari Lagoon,Italy

Five arsenic-resistant bacterial strains designated MT1, MT2, MT3, V1 and V2 were isolated from sediments of the Oliveri-Tindari Lagoon (Italy), which comprises six small lakes whose sediments contain low arsenic concentrations. Phylogenetic analysis of the 16S rRNA gene sequences assigned them to the genus Bacillus. Bacillus sp. strain MT3 showed higher tolerance to As(III) and As(V), as indicated by minimum inhibitory concentrations of 14 and 135 mmol^?1, respectively. Bacillus sp. strain V1 showed growth inhibition at 14 mmol^?1 in the presence of As(III) and at 68 mmol^?1 in the presence of As(V), whereas the arsenic resistance of Bacillus sp. strain MT1 was 10 and 27 mmol^?1 for As(III) and As(V), respectively. The strains Bacillus spp. MT2 and V2 showed low levels of As(III) and As(V) resistance, as it was unable to grow at concentrations>7 and 14 mmol^?1, respectively. The isolated arsenic-resistant Bacillus spp. strains were able to reduce As(V) to As(III), especially Bacillus spp. strain MT3. This study suggests that the isolated bacterial strains play a role in the arsenic biogeochemical cycle of arsenic-poor sediments in the Oliveri-Tindari Lagoon.     

Anthopleura stellula (Actiniaria,Actiniidae) and its reproduction by transverse fission

Anthopleura stellula Ehrenberg 1834, a sea anemone from Eilat, Red Sea, is redescribed in detail and shown to be synonymous with Anthopleura elatensis England 1969. Asexual reproduction by autonomous transverse fission has been observed over a period of 8 months in A. stellula maintained in Mediterranean seawater (37.0 to 37.5 S). Fission always occurs at the same level, below the pharynx, and is followed by an asynchronous regenerative process beginning at the initial point of cleavage. The distal portion of a bisected anemone regenerates a new pedal disc, while pharyngeal formation is induced by the mesenteries of the first-budding directive tentacle in the proximal half; the original oral disc pattern is restored. After regeneration has been completed, the newly formed anemone can similarly engage in transverse fission. The fission process spreads infectionsly. If Bunodactis verrucosa, a Mediterranean anemone, is maintained in the same aquarium with A. stellula then the beginnings of fission followed by dedifferentiation are observed in the Mediterranean species, which does not ordinarily reproduce asexually. A. stellula still exhibits its induced ability to divide transversly if transferred into fresh Mediterranean seawater. When these specimens are exposed to low temperatures (12° to 13°C) for 2 months, fission activity still remains, but for only one division; there is no further fission, and no regeneration of a pedal disc. Abrupt increases in salinity to the salinity level of the Red Sea (40.0 to 41.0) interrupt the fission activity and pedal disc regeneration. A. stellula incised at the level where fission usually occurs promptly undergo transverse fission if cultured with other dividing anemones. However, the other anemones merely exhibit wound healing if the salinity is high. It is thought that fission and regeneration are induced by stimulating substances produced by the anemones during low salinity conditions and that the stimulating substances accumulate in the aquarium water.     

Transmission of Pseudoterranova decipiens (Nematoda: Ascaridoidea) via benthic macrofauna to sympatric flatfishes (Hippoglossoides platessoides,Pleuronectes ferrugineus,P. americanus) on Sable Island Bank,Canada

Larval ascaridoid nematodes were surveyed in three flatfish species, Hippoglossoides platessoides, Pleuronectes ferrugineus, and P. americanus, from Sable Island Bank in February and June 1989. Pseudoterranova decipiens (sealworm) abundances differed significantly with both host species, the heaviest levels being found in H. platessoides, and host length, infections generally increasing with length, but not between February and June samples. Moderate numbers of larvae were found in P. ferrugineus while P. americanus were seldom infected. Two third-stage P. decipiens larvae (L₃), 3.2 and 7.0 mm in length, were recovered from the cephalothoraxes of two Mysis mixta in H. platessoides stomachs while five L₃'s (2.8 to 8.7 mm in length) were found among food (polychaetes, cumaceans, tanaids, amphipods) in the stomach of a P. ferrugineus. Levels of P. decipiens infection appear to be directly related to consumption of suprabenthic prey, which commonly occur in the diet of H. platessoides but are exploited less frequently by P. ferrugineus and rarely by P. americanus.     

Sexual reproduction, larval development and benthic planulae of the solitary coral Monomyces rubrum (Scleractinia: Anthozoa)

The reproductive biology of the solitary ahermatypic coral Monomyces rubrum was studied in northeastern New Zealand between January 1996 and January 1998. The period of oogenesis lasted around 11 months, from late January to December, while spermatogenesis was more rapid, starting in late August and culminating in a spawning period in early December. Reproduction commenced at a polyp size of around 1,000 mm³ (5-6 years old) and the maximum estimated fecundity of the largest corals (7,000 mm³) was no more than 200 eggs. Oocytes were probably fertilized while within the mesentery and were shed into the coelenteron where they developed, via a solid blastula stage, for approximately 1 month. Planulae were relatively large, 3-4 mm in length and 1-2 mm diameter at the time of release, and crawled or swam immediately to the substratum. Peaks of planula shedding were semi-lunar in January 1997, but only one peak was observed in January 1998. The production of a few large rapidly settling larvae by this member of the family Flabellidae is consistent with the trend for solitary short-lived corals from other families to brood larvae rather than spawn gametes.     

Geographical variability in the bioenergetic characteristics of Monoporeia/Pontoporeia spp. populations from the northern Baltic Sea,and their potential contribution to benthic nitrogen mineralization

The physiological condition, determined as the ammonia excretion rate (V NH ₄ ⁺ ), total lipid level and lipid class composition, of two deposit-feeding benthic amphipods, Monoporeia (=Pontoporeia) affinis and Pontoporeia femorata, was studied from 12 opensea stations in the northern Baltic Sea between 24 May and 11 June 1993. The M. affinis populations can be geographically grouped according to their physiological condition: (1) eastern Gulf of Finland, with moderate lipid level (mean 24.4% of dry wt) and high V NH ₄ ⁺ (45.2 mol NH ₄ ⁺ g^-1 dry wt d^-1); (2) Bothnian Sea, wigh high lipid level (34.5%) and low V NH ₄ ⁺ (24.6 mol NH ₄ ⁺ g^-1 dry wt d^-1); and (3) Bothnian Bay, with low lipid level (15.2%) and high V NH ₄ ⁺ (44.3 mol NH ₄ ⁺ dry wt d^-1). A similar pattern could be observed also in the level of triacylglycerols and the neutral-to-polar lipid ratio. P. femorata, the dominating species in the western Gulf of Finland, showed variable station-specific excretion rates (22.3 to 43.0 mol NH ₄ ⁺ g^-1 dry wt d^-1) and lipid levels (23.4 to 30.4%). The spatial variability in the weight-specific V NH ₄ ⁺ of M. affinis could not be explained by the differences in the size of individuals, lipid level or lipid class composition; this emphasizes the significance of the effects of spatially differing nutritional conditions, which manifest themselves as different modes of metabolic energy production and different intensities of energy storage. In addition, the potential contribution of the amphipod populations to benthic nitrogen mineralization was estimated; in May to June, the NH ₄ ⁺ release of different populations ranged from 12 to 237 mol NH ₄ ⁺ m^-2d^-1. In general, populations with high abundance and/or biomass release the greatest amounts of NH ₄ ⁺ , but the values are modified by the physiological condition of the individuals.     

Concentrations of cadmium,manganese, copper,zinc, and lead in the tissues of the oyster (Crassostrea iredalei) obtained from Setiu Lagoon,Terengganu, Malaysia

Heavy metals pollution in aquatic environments is a major problem contributing to human health issues. The study of these pollutants through bioindicators such as the oyster Crassostrea iredalei is important for (1) determining the levels and sources and (2) regulating the quantity of pollutants. The concentrations of cadmium (Cd), manganese (Mn), copper (Cu), zinc (Zn), and lead (Pb) in tissues of C. iredalei, sediment and surrounding water was measured, and data was analyzed to determine the relationship between sampling periods and between oyster tissue, sediment, and water. The highest concentration of metals in oyster tissue was Zn, followed by Cu, Mn, Cd, and Pb. Concentrations of Cd, Cu, and Zn exceeded the maximum level allowed according to the Malaysian Food Act of 1983, which is equivalent to the WHO recommended levels of heavy metals in organisms used for consumption. The highest metal concentration in sediment was Mn followed by Zn, Pb, Cu, and Cd. Concentrations of heavy metals in surrounding water were Zn, Pb, Cu, Mn, and Cd. There was no correlation between metal concentration in oyster tissue and in sediment for all five metals.     

Spatial and temporal variability of phytoplankton biomass,primary production and community structure in the Pontevedra Ria (NW Iberian Peninsula): oceanographic periods and possible response to environmental changes

The spatial distribution of phytoplankton assemblages, chlorophyll, primary production and physical and chemical parameters were studied in the Pontevedra Ria in Galicia (NW Iberian Peninsula) from October 1997 to October 1998. In addition to the usual oceanographic periods described for the Galician Coast, two other periods were observed: a Prebloom or winter bloom, occurring during calm, sunny days in winter and a Continental period, related to the allochthonous intrusion of low salinity water from the Miño River in late spring. The phytoplankton biomass and production in both periods reached values of up to 145 mgChl-a m^?2 and 3.6 gC m^?2 day^?1, respectively, which were similar to those found in summer upwelling blooms. Throughout the year, the phytoplankton biomass and primary production gradients along the ria’s axis were highly dependent on the balance between upwelling and runoff. When the latter prevailed, increased values were measured toward the inner ria, while the opposite pattern was observed during summer upwelling blooms. According to projections derived from climate models and the analysis of wind patterns, temperature and precipitation trends in the area, a drop in the productivity of the ria would be expected as a result of reduced upwelling intensity in summer and decreasing rainfall in spring. In any case the estuarine part of the ria would be the most seriously affected.