Alkaline phosphatase in a littoral Mediterranean marine ecosystem: role of the main plankton size classes

This work investigates the alkaline phosphatase activity in a littoral marine ecosystem (Toulon Bay and Le Niel Bay, France) in order to study its biochemical characteristics with respect to pH, sea water composition and phosphate sensitivity. We also characterise the active forms in sea water and determine the extent to which zooplankton generate phosphatase activity with respect to other plankton classes. In Toulon Bay, phosphatase was produced mostly by the microplankton fraction (>90 μm), accounting for more than 90% of total activity. In contrast, most of the phosphatase activity in Le Niel Bay was generated by the nanoplankton fraction (5–90 μm) and the picoplankton fraction (0.25–5 μm). The microplankton enzymes had non Michaelis-Menten kinetics suggesting the involvement of multiple enzyme processes with distinct kinetic constants. This activity is in major part secreted into the sea water and is stimulated by the ionic strength and the pH of the sea water. Cypris larvae of the genus Balanus played a special role in this release. For the nanoplankton and picoplankton, part of this activity was due to non-secreted enzymes, probably bound to membranes or occurring intracellularly. Moreover, nano and picoplankton phosphatase required higher pH than microplankton enzyme. For all plankton size classes, there was no activity at low pH, suggesting that acid phosphatases were not involved in reactions with substrates dissolved in water.     

Plankton dynamics due to rainfall,eutrophication, dilution,grazing and assimilation in an urbanized coastal lagoon

After a prolonged summer dry period, the effects of a distinctive and continuing rainfall on the nutrients and plankton of an urban coastal lagoon were investigated over 2 months. The lagoon filled up over 5 weeks from <10% of its maximum volume until it broke open to the sea. Nutrients (ammonia and oxidised nitrogen) significantly increased the day after initial rainfall, before returning to pre-rainfall conditions within 5 days. Phytoplankton biomass grew 10 fold within a week after initial rainfall in the 25–30 °C water and declined to near initial levels 2 weeks later. The assemblage of phytoplankton and zooplankton changed dramatically after 1 day and again by 6 days later, gradually returning to the original community by 2 weeks after the initial rainfall. Zooplankton responded within a day with a two fold increase in the adult stages of the calanoid copepod Oithona sp., followed a week later by nauplii and adult Acartia bispinosa. The influx of adult Oithona indicates resting populations that were previously under sampled by our plankton net. The plankton community returned to the initial state by 2 weeks, to being dominated by a centric diatom and A. bispinosa after 5 weeks. Dilution of the lagoon reached a maximum of 0.25 d⁻¹, while growth rates of the phytoplankton population reached a maximum of 1 d⁻¹, and A. bispinosa nauplii growth of 2.5 d⁻¹. Declines in chlorophyll biomass from the maximum 10 μg l⁻¹, at a rate of approximately 10% d⁻¹ are consistent with the modelled uptake by zooplankton. The nutrients from runoff, growth and the influx of new zooplankton into the water column, resulted in a depleted δ¹³C and δ¹⁵N stable isotope signature of A. bispinosa by 2–4 ppt within 1–2 weeks, consistent with diatom growth and the terrestrial supply of depleted nutrients. δ³⁴S of A. bispinosa was enriched by 2 ppt for 1–2 weeks after rainfall, but unlike C and N, returned to pre-rainfall levels by the end of the study period. We suggest that plankton studies in coastal lakes with variable water levels that are not tidally driven, should account for the influence of changes in water levels to help explain data variability.     

绿色海堤的沉积地貌与生态系统动力学原理: 研究综述*

绿色海堤是传统结构工程与海岸生态系统共同组合而成的新型海堤, 用以应对未来海面上升、风暴加剧给低地海岸防护带来的挑战。需解决的问题主要有海岸生态系统消浪过程及生态系统在海堤体系中的配置方式。理论分析、现场观测、物模数模所获结果表明, 海岸生态系统确有显著的消浪功能: 1) 陆架泥区消浪, 其机制以再悬浮和浮泥运动为主, 底部摩擦为次; 2) 潮滩下部的粉砂细砂滩底部摩擦和推移质运动共同造成波能耗散, 而上部的泥滩则以再悬浮和悬沙输运为主; 3) 在盐沼、红树林、海草床等由植被构成的生态系统, 植物通过形态阻力、茎秆运动来阻滞水流、耗散波能, 其效能高于沉积物床面对波能的耗散; 4) 生物礁主要有珊瑚礁和牡蛎礁, 其消能作用主要通过床面摩擦和波浪破碎, 效能较高, 尤其是在风暴期间。生态系统如何成为海堤的有机组成部分, 尤其是侵蚀型海岸的生态位修复和绿色海堤整体设计, 还需进一步研究相关的科学问题: 与硬质工程结合的盐沼-牡蛎礁的适应性生物学; 未来环境变化条件下生态系统的稳定性; 绿色海堤生态系统空间配置及其与风暴事件的时间尺度匹配; 基于均衡剖面理论的海堤形态优化。     

Plankton dynamics and carbon flux in an area of upwelling off the coast of Morocco

A carbon flux study was carried out off the coast of Morocco, at 31°N, in a region characterized by the presence of a persistent cyclonic eddy. Two short-term (4 and 3 day) deployments of free-floating sediment traps were combined with water column sampling and rate process measurements as the ship followed the traps. For a period of 36 h between trap deployments, a hydrographic section was run along 31°30'N as part of a larger scale survey being carried out simultaneously on the R.V. A. von Humboldt. The first trap deployment was near the eastern margin of the eddy and the traps moved to the north and west in a frontal jet associated with its northern boundary. After the second deployment, which was at the recovery point of the first, the traps moved to the west and then to the southwest. Throughout the study, chlorophyll concentrations varied between 27 and 125 mg m⁻² (0–100 m), with highest concentrations in the upwelled water nearest the coast and in upwelled water generated within the cyclonic eddy. Particulate organic carbon (POC) and particulate organic nitrogen (PON) concentrations were relatively uniform (13.6±1.8 and 1.63±28 g m⁻² with phytoplankton carbon accounting for 16–85% of total POC. Bacterial carbon was 5% of total POC and mesozooplankton carbon concentrations were equivalent to 9% of total POC. Microzooplankton biomass was not assessed but POC:PON ratios in the water column were often high, suggesting there was sometimes a large detrital component in the POC. Primary production rates varied between 1.0 and 2.5 g C m⁻² day⁻¹. Bacterial consumption accounted for 50% of primary production. Metabolic rates suggested that copepods were ingesting more than 0.4 g C m⁻² day⁻¹. while filtration rates suggested that ingestion of phytoplankton carbon was only 0.2 g C m⁻²day⁻¹, even when phytoplankton constituted 85% of the POC. f-ratios (based on uptake rates for ¹⁵N-nitrate and ammonia) were between 0.1 and 0.4, and excretion by mesozooplankton could account for 40% of the daily ammonium uptake by phytoplankton. HPLC pigment analysis showed that when chlorophyll biomass was high, diatoms were dominant, whereas when it was low, small prymnesiophytes, chlorophytes and diatoms were all important. The composition of the fluoresecent pigments in material in the sediment traps indicated that intact phytoplankton and copepod faecal pellets were the main sources but the relative rates of sedimentation of pigment, POC and PON for the two trapping periods did not reflect differences that were observed in the overlying water column. This was likely to be the result of spatial heterogeneity and strong horizontal currents heterogeneity and strong horizontal currents within the euphotic zone. Thus, material collected at 100 m probably did not originate in the water column immediately overlying the traps and trapping efficiencies might also have been variable.     

The Continuous Plankton Recorder: concepts and history, from Plankton Indicator to undulating recorders

Alister Hardy conceived the Continuous Plankton Recorder (CPR) survey in the 1920s as a means of mapping near-surface plankton in space and time, interpreting the changing fortunes of the fisheries and relating plankton changes to hydrometeorology and climatic change. The seed he planted has grown to become the most extensive long-term survey of marine organisms in the world and the breadth of his vision becomes ever more apparent. The survey has now run for over 70 years and its value increases with every passing decade. Operating from ‘ships of opportunity’ the machines used are robust, reliable and easy to handle. Wherever possible, all the sampling and analytical methods have not been changed to maintain the consistency of the time series. Computerisation and the development of new statistical approaches have increased our ability to handle the large quantities of information generated and enhance the sensitivity of the data analyses. This overview, based on almost 900 papers, recounts the various phases in the history of the survey. It starts with the Indicator Survey (1921–1934), the deployment of the first CPR on the Discovery Expedition (1924–1927) and the early CPR survey in the North Sea (1931–1939). The survey reopened in 1946 after the Second World War and expanded across the North Atlantic to North America from 1959. Taxonomic studies were initiated and an emphasis was placed on patterns of distribution, which were seen to reflect the varying oceanographic conditions. The years 1968–1976 saw further expansion with operations even in the American Great Lakes, publication of a Plankton Atlas and initial evidence for a downward trend in plankton biomass. At about this time electronic instrumentation was attached to CPRs to make additional measurements and work was started on the development of a new generation of undulating Continuous Plankton and Environmental Recorders (CPERs). In 1976 the survey moved to Plymouth. Scientific priorities in the UK changed in the subsequent decade and funding became more difficult to secure even though some of the CPR papers being published at the time are now regarded as classics in plankton ecology. In 1988 the UK Natural Environment Research Council (NERC) decided to close the survey. An international rescue operation led to the creation of the Sir Alister Hardy Foundation for Ocean Science (SAHFOS) in 1990, which has continued with consortium funding from a number of countries, and from 1999 again included NERC. The scientific rationale of the survey has gained credibility as concern over climate change and other anthropogenic effects has grown and as the key role that plankton plays as an indicator of large-scale environmental conditions becomes ever more apparent. Recently, the survey became an integral component of the Global Ocean Observation System (GOOS) and expanded into the North Pacific. It plays a complementary role in many large international and multidisciplinary projects and is providing inspiration, advice and support to daughter surveys elsewhere in the world. At the start of a new millennium, Hardy’s vision from the 1920s is a powerful driving force not just in international biological oceanography, but in global environmental science.     

Plankton origin of particulate dimethylsulfoniopropionate in a Mediterranean oligotrophic coastal and shallow ecosystem

We report here dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) levels as a function of plankton communities and abiotic factors over a 12-month cycle in the Mediterranean oligotrophic coastal and shallow ecosystem of Niel Bay (N.W. Mediterranean Sea, France). Total particulate DMSP (DMSP_p) and DMS concentrations were highly seasonal, peaking during a spring (April) bloom at 8.9 nM and 73.9 nM, respectively. Significant positive correlations were found between total DMSP_p concentration and the abundance or biomass of the dinoflagellate Prorocentrum compressum (Spearman's rank correlation test: r = 0.704; p = 0.011). Similarly, DMS concentrations peaked during the development of blooms of P. compressum and Gymnodinium sp. There seemed to be a positive relationship between the chlorophyll a to pheopigment ratio and DMS concentrations, suggesting that DMS was released during phytoplankton growth. High DMS levels recorded in the shallow Niel Bay may also result from the activity of benthic macroalgae, and/or macrophytes such as Posidonia spp., or the resuspension of sulfur species accumulating in sediments. The fractionation of particulate DMSP into three size classes (>90 μm, 5–90 μm and 0.2–5 μm) revealed that 5–90 μm DMSP-containing particles made the greatest contribution to the total DMSP_p pool (annual mean contribution = 62%), with a maximal contribution in April (96%). This size class consisted mainly of dinoflagellates (annual mean contribution = 68%), with P. compressum and Gymnodinium sp. the predominant species, together accounting for up to 44% of the phytoplankton present. The positive correlation between DMSP concentration in the 5–90 μm size class and the abundance of P. compressum (Spearman's rank correlation test: r = 0.648; p = 0.023) suggests that this phytoplankton species would be the major DMSP producer in Niel Bay. The DMSP collected in the >90 μm fraction was principally associated with zooplankton organisms, dominated by copepods (nauplii and copepodites). DMSP_>90, not due to a specific zooplankton production, resulted from the phytoplankton cells ingested during grazing. The concomitant peaks of DMS concentration and zooplankton abundance suggest that zooplankton may play a role in releasing DMSP and/or DMS through sloppy feeding.     

Marine ecosystem management: Fish abundance and size under exploitation

This study is targeted on policy makers and environmental scientists to illustrate the typical historical scale of depletion of our fish stocks, and what current and emerging legislation might mean for fisheries management and the metrics of fish stocks. The population demography of the Bristol Channel sole is described since 1820. Their decline in abundance, and change in length compositions, are modelled. By 2000, the mature stock had been depleted to less than 5% of its original size, and larger sole were rarely caught. The implications of maximum sustainable yield targets, and of good environmental status, are examined.     

Coastal ecosystem dynamics: Relevance of benthic processes

It is believed that the ecological balance and productivity of marine coastal environments are directly related to nutrient supplies from various sources including riverine-estuarine-coastal exchange, upwelling, precipitation, nitrogen fixation, and nutrient regeneration. In south Texas coastal waters, where phytoplankton productivity is comparable to other high productive coastal areas, many nutrient sources are suspected, but are not equally important in supplying sufficient nutrients to drive coastal production dynamics. Nitrogen regeneration from the benthos is implicated from a 2.5-y study of the nutrient cycling processes important in contributing to production levels in these waters. Sediments of the south Texas coastal habitat appear to exhibit a sensitive coupling with overlying waters, where a strong negative correlation exists between the random periodicity of external supplies of ‘new’ nitrogen to the coastal system and the rate at which nitrogen is recycled by sediments. This pattern buffers these waters against extended periods of low input of nutrients from external sources. The development of a conceptual scheme for nutrient cycling in this coastal habitat has provided a more holistic framework from which we can derive an objective assessment of the importance of mechanisms in the system. All data collected so far suggest that the primary production of organic matter and passage through the benthic habitat of these coastal waters is an important pattern responsible for the continued maintenance of productivity in the south Texas coastal ecosystem.     

Planktonic protist communities in semi-enclosed mariculture waters: temporal dynamics of functional groups and their responses to environmental conditions

The functional groups of planktonic protist communities and their responses to the changes of environmental conditions were investigated in a semi-enclosed shrimp-farming pond in Qingdao,Shandong Province,China,during a six-month study period (a complete shrimp-culture cycle) from May to October 2002.The results reveal that: (1) the protist communities represented five trophic and functional groups of the species identified,about 60% were photoautotrophs,20% algivores,12% bacterivores,5% raptors and about 3% non-selectives;(2) the photoautotrophs,algivores and bacterivores were the primary contributors to the changes in the protist communities in short temporal scales,the succession of dominance typically being bacterivores→photoautotrophs→algivores,with the raptors dominating the protist communities in a single sample (early June);(3) the photoautotrophs and non-selectives were the primary contributors to the peak of protist abundance in early October whereas the photoautotrophs,bacterivores,raptors and non-selectives mainly gave rise to two bimodal peaks of biomass in July and October respectively;(4) five functional groups of protist communities represented significant correlations with water nutrients (i.e.,NH 3-N,NO 3-N,and PO 4 ),either alone or in combination with temperature,of which algivores and raptors were strongly correlated with phosphate and the concentration of Chl a,while bacterivores were strongly related to nitrogen and the concentration of bacteria.These findings confirm that planktonic protists are potentially useful bioindicators of water quality in the semi-enclosed mariculture system.     

Interdecadal climate regime dynamics in the North Pacific Ocean: theories, observations and ecosystem impacts

Basin-scale variations in oceanic physical variables are thought to organize patterns of biological response across the Pacific Ocean over decadal time scales. Different physical mechanisms can be responsible for the diverse basin-scale patterns of sea-surface temperature (SST), mixed-layer depth, thermocline depth, and horizontal currents, although they are linked in various ways. In light of various theories and observations, we interpret observed basinwide patterns of decadal-scale variations in upper-ocean temperatures. Evidence so far indicates that large-scale perturbations of the Aleutian Low generate temperature anomalies in the central and eastern North Pacific through the combined action of net surface heat flux, turbulent mixing and Ekman advection. The surface-forced temperature anomalies in the central North Pacific subduct and propagate southwestwards in the ocean thermocline to the subtropics but apparently do not reach the equator. The large-scale Ekman pumping resulting from changes of the Aleutian Low forces western-intensified thermocline depth anomalies that are approximately consistent with Sverdrup theory. These thermocline changes are associated with SST anomalies in the Kuroshio/Oyashio Extension that are of the same sign as those in the central North Pacific, but lagged by several years. The physics of the possible feedback from the SST anomalies to the Aleutian Low, which might close a coupled ocean–atmosphere mode of decadal variability, is poorly understood and is an area of active research. The possible responses of North Pacific Ocean ecosystems to these complicated physical patterns is summarized.     

Growth and grazing rate dynamics of major phytoplankton groups in an oligotrophic coastal site

There has been more attention to phytoplankton dynamics in nutrient-rich waters than in oligotrophic ones thus requiring the need to study the dynamics and responses in oligotrophic waters. Accordingly, phytoplankton community in Blanes Bay was overall dominated by Prymnesiophyceae, remarkably constant throughout the year (31 ± 13% Total chlorophyll a, Tchl a) and Bacillariophyta with a more episodic appearance (20 ± 23% Tchl a). Prasinophyceae and Synechococcus contribution became substantial in winter (Prasinophyceae = 30% Tchl a) and summer (Synechococcus = 35% Tchl a). Phytoplankton growth and grazing mortality rates for major groups were estimated by dilution experiments in combination with high pressure liquid chromatography and flow cytometry carried out monthly over two years. Growth rates of total phytoplankton (range = 0.30–1.91 d⁻¹) were significantly higher in spring and summer (μ > 1.3 d⁻¹) than in autumn and winter (μ ∼ 0.65 d⁻¹) and showed a weak dependence on temperature but a significant positive correlation with day length. Microzooplankton grazing (range = 0.03–1.4 d⁻¹) was closely coupled to phytoplankton growth. Grazing represented the main process for loss of phytoplankton, removing 60 ± 34% (±SD) of daily primary production and 70 ± 48% of Tchl a stock. Chla synthesis was highest during the Bacillarophyceae-dominated spring bloom (Chl a_synt = 2.3 ± 1.6 μg Chl a L⁻¹ d⁻¹) and lowest during the following post-bloom conditions dominated by Prymnesiophyceae (Chl a_synt = 0.23 ± 0.08 μg Chl a L⁻¹ d⁻¹). This variability was smoothed when expressed in carbon equivalents mainly due to the opposite dynamics of C:chl a (range = 11–135) and chl a concentration (range = 0.07–2.0 μg chl a L⁻¹). Bacillariophyta and Synechococcus contribution to C fluxes was higher than to biomass because of their fast-growth rate. The opposite was true for Prymnesiophyceae.     

Use of Continuous Plankton Recorder information in support of marine management: applications in fisheries, environmental protection, and in the study of ecosystem response to environmental change

The Continuous Plankton Recorder (CPR) survey was conceived from the outset as a programme of applied research designed to assist the fishing industry. Its survival and continuing vigour after 70 years is a testament to its utility, which has been achieved in spite of great changes in our understanding of the marine environment and in our concerns over how to manage it. The CPR has been superseded in several respects by other technologies, such as acoustics and remote sensing, but it continues to provide unrivalled seasonal and geographic information about a wide range of zooplankton and phytoplankton taxa. The value of this coverage increases with time and provides the basis for placing recent observations into the context of long-term, large-scale variability and thus suggesting what the causes are likely to be. Information from the CPR is used extensively in judging environmental impacts and producing quality status reports (QSR); it has shown the distributions of fish stocks, which had not previously been exploited; it has pointed to the extent of ungrazed phytoplankton production in the North Atlantic, which was a vital element in establishing the importance of carbon sequestration by phytoplankton.The CPR continues to be the principal source of large-scale, long-term information about the plankton ecosystem of the North Atlantic. It has recently provided extensive information about the biodiversity of the plankton and about the distribution of introduced species. It serves as a valuable example for the design of future monitoring of the marine environment and it has been essential to the design and implementation of most North Atlantic plankton research.     

NPZ Models of Plankton Dynamics: Their Construction, Coupling to Physics, and Application

Nutrient-phytoplankton-zooplankton (NPZ) models have been in use in oceanography for at least three decades, and are still a common research tool. Given the discoveries of the last two decades, particularly concerning the role of bacteria in the plankton, there are questions as to whether NPZ models can still be supported as a useful tool in planktonic research. Here I review the construction of NPZ models, and some of the physical platforms they have been coupled to. I then discuss the applications of NPZ-physical models, and conclude that they still constitute an important and viable research tool, provided that the questions being explored are clearly stated. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mesozooplankton dynamics in the Benguela ecosystem,with emphasis on the herbivorous copepods

Recent research developments on the ecology, dynamics and trophic position of copepods in the Benguela ecosystem are synthesized. Attention is focused on herbivorous species of the southern Benguela and how they cope with the physical and biological variability characteristic of this upwelling region. Copepods constitute on average approximately half of the total zooplankton carbon and. are most abundant during the upwelling season. They are able to maintain large population densities within local coastal upwelling areas by combining ontogenetically based vertical migration behaviour with features of the current system. Some species have developed finely tuned strategies to overcome periods of starvation between upwelling bouts by storing lipid reserves or by entering temporary developmental arrest. In situ measurements of production rates of local species are among the highest recorded for copepods. Despite an apparent excess of food, copepods exert only limited impact on the phytoplankton, removing on average <25 per cent of that available daily. Indirect estimates of carbon flux indicate that 11–25 per cent of copepod daily ration is used for egestion of faecal pellets. Copepods are the preferred prey of a wide variety of invertebrate and vertebrate predators. Large copepods in particular are important in the diet of commercially exploited pelagic fish. Localized areas of low abundance of copepods have been found in association with high densities of anchovy during peak spawning and recruitment periods. Copepods may therefore constitute a central limiting factor for pelagic fish production in the southern Benguela.     

A modelling study of ecosystem dynamics and nutrient cycling in the Humber plume, UK

The European Regional Seas Ecosystem Model (ERSEM) has been coupled with a two-dimensional depth-averaged transport model of the Humber plume region and run to simulate 1988–1989. Simulations of the spatial and temporal variations in chlorophyll-a, nitrate, phosphate and suspended particulate matter distributions in winter, spring and summer show how the development of the spring bloom and subsequent maintenance of primary production is controlled by the physicochemical environment of the plume zone. Results are also shown for two stations, one characterised by the high nutrient and suspended matter concentrations of the plume and the other by the relatively low nutrient and sediment concentrations of the offshore waters. The modelled net primary production at the plume site was 105 g C m⁻² a⁻¹ and 127 g C m⁻² a⁻¹ offshore. Primary production was controlled by light limitation between October and March and by the availability of nutrients during the rest of the year. The phytoplankton nutrient demand is met by in-situ recycling processes during the summer. The likely effect of increasing and decreasing anthropogenic riverine inputs of nitrate and phosphate upon ecosystem function was also investigated. Modelling experiments indicate that increasing the nitrogen to silicate ratio in freshwater inputs increased the production of non-siliceous phytoplankton in the plume. The results of this model have been used to calculate the annual and quarterly mass balances describing the usage of inorganic nitrogen, phosphate and silicate within the plume zone for the period of the NERC North Sea survey (September 1988 to October 1989). The modelled Humber plume retains 3.9% of the freshwater dissolved inorganic nitrogen, 2.2% of the freshwater phosphate and 1.3% of the freshwater silicate input over the simulated seasonal cycle. The remainder is transported into the southern North Sea in either dissolved or particulate form. The reliability of these results is discussed.     

Effects of mining wastes on a seagrass ecosystem: metal accumulation and bioavailability, seagrass dynamics and associated community structure

Two different Cymodocea nodosa (Ucria) Ascherson beds growing in mining-contaminated sediments were compared with two reference beds in the Mar Menor coastal lagoon. The accumulation of Zn, Pb and Cd in different fractions of the plant, the sediment parameters that regulate the availability of metals, the seabed structure and dynamics of each seagrass bed and its associated macroinvertebrate community were studied. C. nodosa accumulates metals from the sediments and reflects their bioavailability for this seagrass. At each station, the metal content of the rhizomes was lower than that of leaves and roots. The concentration of acid-volatile sulfides does not seem to influence the availability of metals to the seagrass, possibly due to oxygen transport to underground tissues. The highest metal concentration in all the contaminated stations was found in the leaf-biofilm, due to the formation of complexes between metals and the extracellular polymeric substances that form the biofilm. All the seagrass beds were seen to be undergoing expansion, those growing in contaminated sediments accumulating great quantities of metals and showing highest photosynthetic leaf surface area and highest leaf biomass. However, these structural parameters were not seen to be responsible for the differences in the faunal composition observed between contaminated and reference beds. Moreover, the multivariate analysis identified the metal content of leaves, biofilm and sediments as important variables that may be responsible for these differences in faunal composition. In this study we have demonstrated that both the seagrass C. nodosa and the biofilm on the plant leaves may be used as environmental tools in the Mar Menor lagoon. The former is an useful indicator of sediment contamination, whereas the latter seems to be a good sentinel of water quality.     

The dynamics of the Adriatic Sea ecosystem.: An idealized model study

A biomass-based ecological model is presented here for the Adriatic Sea. The hydrodynamical part is composed of the Princeton Ocean Model, while the European Regional Seas Ecosystem Model describes the biogeochemical processes. An idealized Adriatic basin geometry has been used, with perpetual year seasonal cycle forcing the hydrodynamics and river-borne nutrient input forcing externally the biogeochemical processes. The simulation results highlight the role of the physical processes in determining and maintaining some of the nutrient and phytoplankton biomass distribution and characteristics in the basin. The characteristics of the phytoplankton seasonal cycle have been found to depend, in order of priority, on the river-borne nutrient input and physical horizontal and vertical processes.