Flux of cadmium through euphausiids

Flux of the heavy metal cadmium through the euphausiid Meganyctiphanes norvegica was examined. Radiotracer experiments showed that cadmium can be accumulated either directly from water or through the food chain. When comparing equilibrium cadmium concentration factors based on stable element measurements with those obtained from radiotracer experiments, it is evident that exchange between cadmium in the water and that in euphausiid tissue is a relatively slow process, indicating that, in the long term, ingestion of cadmium will probably be the more important route for the accumulation of this metal. Approximately 10% of cadmium ingested by euphausiids was incorporated into internal tissues when the food source was radioactive Artemia. After 1 month cadmium, accumulated directly from water, was found to be most concentrated in the viscera with lesser amounts in eyes, exoskeleton and muscle, respectively. Use of a simple model, based on the assumption that cadmium taken in by the organism must equal cadmium released plus that accumulated in tissue, allowed assessment of the relative importance of various metabolic parameters in controlling the cadmium flux through euphausiids. Fecal pellets, due to their relatively high rate of production and high cadmium content, accounted for 84% of the total cadmium flux through M. norvegica. Comparisons of stable cadmium concentrations in natural euphausiid food and the organism's resultant fecal pellets indicate that the cadmium concentration in ingested material was increased nearly 5-fold during its passage through the euphausiid. From comparisons of all routes by which cadmium can be released from M. norvegica to the water column, it is concluded that fecal pellet deposition represents the principal mechanism effecting the downward vertical transport of cadmium by this species.     

Trophic food web and ecosystem attributes of a water reservoir of the Ria Formosa (south Portugal)

Using a top-down modelling approach, a balanced trophic food web model of a water reservoir of the Ria Formosa lagoonal system was constructed. Few adjustments of input data were necessary to run the model since most of the parameters were estimated at the study site and the characteristics of the water reservoir allowed a high degree of control and precision in terms of sampling and data collection. Trophic levels of the 14 compartments included in the model varied between 1.0 for primary producers and detritus to 3.4 for carnivorous fish and the 14 groups were aggregated in a food chain with six trophic levels. The water reservoir has a detritus based food chain, with the majority of the biomass concentrated in the first two levels, the producers level and the herbivore/detritivore level (97.6%). The transfer efficiencies were low, and decreased with increasing level number, varying between 6.0 and 0.2%. The degree of “ecosystem maturity” was difficult to establish, but several parameters indicate that it could be high. The water reservoir studied, which has similar environmental and ecological characteristics as the Ria Formosa lagoon, is near its carrying capacity.     

Population dynamics and production of euphausiids

Seasonal changes in abundance, size and aspects of the population structure of Meganyctiphanes norvegica (M. Sars) and Nyctiphanes couchi (Bell) are described from samples taken with the Continuous Plankton Recorder at 10 m depth over a 2 yr period (1966 and 1967) in the North Atlantic Ocean and the North Sea. M. norvegica lived for a maximum of just over 2 yr, and adults of both year-classes spawned during a limited breeding season in the spring or summer. N. couchi spawned over a prolonged breeding season, giving rise to a complex of cohorts with overlapping size ranges. It was concluded that 3 or 4 cohorts were spawned in each year and that the maximum life span was probably greater than 1 yr, although maturity may be attained in less than a year. Estimated annual production at 10 m depth for M. norvegica ranged from 0.80 to 18.74 mg m^-3yr^-1 and for N. couchi from 0.67 to 8.23 mg m^-3yr^-1. P:B ratios ranged from 1.3:1 to 6.3:1 for M. norvegica and 4.0:1 to 5.5:1 for N. couchi.     

Resource-partitioning and predation impact of a low-latitude myctophid community

This study, based on data collected during summer 1985 in the eastern Gulf of Mexico, examined the degree of overlap in two prime niche parameters, space and food, in 17 of the most abundant myctophid species which inhabit the epipelagic zone at night. Cluster-analyses of vertical distribution information and diet characteristics revealed that while large groups of species overlapped (>60%) in either vertical distributions or diet, when both niche parameters were considered together, little interspecific or intraspecific (size class) overlap occurred. Our data suggest that for myctophids trophic competition is reduced through resource-partitioning, although with considerable overlap at niche boundaries. Niche separation presumably is the result of competition during the evolution of the ecosystem and is maintained presently as diffuse competition: the effect on a species of the combined competition from all other species at that trophic level. We suggest that the large degree of niche overlap enables the packing of over 50 myctophid species in the epipelagic zone at night. Our calculations indicate that myctophid predation nightly removes 2% of the zooplankton biomass. Myctophid predation is selective in that greatest pressure is on certain size classes and types of prey (copepods, ostracods and euphausiids). In the case of copepods, impact is greatest on the larger, more mature stages and hence on the breeding population. It is estimated that myctophids account for at least one-third of the daily production of zooplankton removed from the epipelagic zone by micronekton in the eastern Gulf.     

Trophic diversity in amphipods within a temperate eelgrass ecosystem as determined by gut contents and C and N isotope analysis

A conjoint analysis of gut contents and stable C and N isotopes was applied to determine the main food sources and feeding habits of dominant amphipods in an eelgrass bed (Zostera marina) in Gwangyang Bay, Korea. Gut content observations demonstrated that, while Gammaropsis japonicus and Jassa slatteryi are herbivorous, feeding on epiphytes and detritus, Pontogeneia rostrata and Monocorophium acherusicum are omnivorous, feeding on mesozooplankton fragments and detritus. Stable isotope data confirmed that epiphytes, detritus, and mesozooplankton fragments were major food sources for amphipods in the eelgrass bed. Isotopic mixing model calculations clearly showed an interspecific difference in diet composition. A high isotopic dissimilarity between amphipod taxa demonstrated interspecific trophic diversity, reflecting their herbivorous (G. japonicus and J. slatteryi) and omnivorous (P. rostrata and M. acherusicum) feeding habits and confirmed the detrivorous feeding habits of caprellids. Such trophic diversity at interspecific level of the amphipod species indicates that they use different food resources within their microhabitats and play species-specific functional roles as mediators in trophic pathways from producers to higher-level consumers of the eelgrass ecosystem. Finally, our findings suggest that information on the species-specific trophic ecology of amphipods is needed to better understand their potential role in the trophic dynamics and carbon flow of seagrass bed ecosystems.     

Estuarine management strategies and the predictability of ecosystem changes

The Dutch Delta Region (S-W Netherlands) originally consisted of interconnected estuaries, interfacing the rivers Rhine, Meuse and Schelde with the North Sea. The ecosystems were immature, with physical rather than biological control of population dynamics. Main functions were shipping and shellfisheries. An emergent function of the interconnected estuaries was the buffering and upgrading of river-borne substances before they entered the sea. Execution of the Delta Project in the period 1960–1986 resulted in isolation of several water systems disconnected from rivers and sea, and loss of gradients within these systems. Population dynamics were now controlled by chemical and biological rather than physical factors. Vulnerability to external perturbation increased. These changes also affected the buffering capacity, i.e. reduced the utility of the area as stabiliser of the geosystem. Recreational use and appreciation of natural values increased, potentially conflicting with shipping and shellfisheries. Retrospective analysis of the environmental policy and management revealed three consecutive strategies in the Delta Project. 1. Reactive one-issue management, focusing on safety against flooding only. This strategy aimed at complete closure of the estuaries thus transforming them into fresh water lakes. It has destroyed feed-backs and buffering between coastal and inland waters. This strategy has not promoted sustainable development and has increased the vulnerability of the area to future catastrophes. 2. Protective bio-ecological management focused on the preservation of existing values of landscape and environment, and resulted in the maintenance of saline conditions and preservation of marshes by shore protection measures. The drawback of this passive orientation to existing values ?where they are now? is the necessity of continuous intensive care because the natural adaptive ability is not being restored. 3. Constructive geo-ecological management is based on understanding functional properties within and between ecosystems as integrated elements of the landscape structure. This strategy aims at environmental protection, restoration and development of values ?where they must be?. Re-establishment of gradients by e.g. re-introducing tidal influence and by restoring salt marshes should contribute to sustainable development.     

Estuarine management strategies and the predictability of ecosystem changes

The Dutch Delta Region (S-W Netherlands) originally consisted of interconnected estuaries, interfacing the rivers Rhine, Meuse and Schelde with the North Sea. The ecosystems were immature, with physical rather than biological control of population dynamics. Main functions were shipping and shellfisheries. An emergent function of the interconnected estuaries was the buffering and upgrading of riverborne substances before they entered the sea. Execution of the Delta Project in the period 1960–1986 resulted in isolation of several water systems disconnected from rivers and sea, and loss of gradients within these systems. Population dynamics were now controlled by chemical and biological rather than physical factors. Vulnerability to external perturbation increased. These changes also affected the buffering capacity, i.e. reduced the utility of the area as stabiliser of the geosystem. Recreational use and appreciation of natural values increased, potentially conflicting with shipping and shellfisheries. Retrospective analysis of the environmental policy and management revealed three consecutive strategies in the Delta Project. 1. Reactive one-issue management, focusing on safety against flooding only. This strategy aimed at complete closure of the estuaries thus transforming them into fresh water lakes. It has destroyed feed-backs and buffering between coastal and inland waters. This strategy has not promoted sustainable development and has increased the vulnerability of the area to future catastrophes. 2. Protective bio-ecological management focused on the preservation of existing values of landscape and environment, and resulted in the maintenance of saline conditions and preservation of marshes by shore protection measures. The drawback of this passive orientation to existing values Ôwhere they are nowÕ is the necessity of continuous intensive care because the natural adaptive ability is not being restored. 3. Constructive geo-ecological management is based on understanding functional properties within and between ecosystems as integrated elements of the landscape structure. This strategy aims at environmental protection, restoration and development of values Ôwhere they must beÕ. Re-establishment of gradients by e.g. re-introducing tidal influence and by restoring salt marshes should contribute to sustainable development.     

Polonium-210 in euphausiids: A detailed study

A detailed study of ²¹⁰Po, the predominant alpha-emitting nuclide found in most marine organisms, has been undertaken in a particular zooplanktonic species, the euphausiid Meganyctiphanes norvegica. The purpose was to obtain information concerning the origin, the localization and the flux of the nuclide in and through this organism. Measurements of ²¹⁰Po were made in euphausiids of different sizes, in dissected organs and tissues, and in excretion products. The results show higher concentrations in the smaller specimens; this fact cannot be explained on the basis of surface adsorption, but is probably related to the ingestion of food. Dissection results show that the distribution of ²¹⁰Po in euphausiids is not homogeneous, but that the majority is concentrated in the internal organs, the alimentary tract and the hepatopancreas in particular. The natural radiation dose received by these organs is in consequence much higher than that received by the whole animal. Use of a dynamic model allowed the flux of ²¹⁰Po through M. norvegica to be calculated. The calculations confirm that food is the principal source of ²¹⁰Po for this species, and clearly show that fecal pellets constitute the major elimination route. Extrapolation of the data to zooplankton in general leads to the conclusion that zooplankton metabolic activity plays an important role in transporting ²¹⁰Po from the surface layers of the ocean to depth.     

Morphology of the gastric mill in ten species of euphausiids

SEM observation revealed the detailed morphology of the gastric mill in ten species of euphausiids, Bentheuphausia amblyops, Thysanopoda acutifrons, Meganyctiphanes norvegica, Pseudeuphausia latifrons, Euphausia superba, Tessarabrachion oculatum, Thysanoessa longipes, Nematoscelis microps, Nematobrachion boopis, and Stylocheiron maximum. The well-developed gastric mill of euphausiids consists of a pair of cluster spines and a pair of lateral teeth displaying great diversity in morphology. It is suggested that there are three categories of gastric mill and filterpress (gland filter) within euphausiids. One is the well-developed gastric mill with filter-press of B. amblyops; a second is the well-developed gastric mill of M. norvegica, T. oculatum, E. superba, P. latifrons and T. longipes; and the third is the gastric mill without lateral teeth of T. acutifrons, N. microps, N. boopis and S. maximum.     

Biology of euphausiids in the subarctic waters north of Iceland

The seasonal abundance, maturity, spawning, and population dynamics of Thysanoessa inermis (Krøyer, 1846), T. longicaudata (Krøyer, 1846), and Meganyctiphanes norvegica (M. Sars, 1857) were studied in the subarctic waters north of Iceland from February 1993 to February 1994. The material was sampled at approximately monthly intervals along a transect of eight stations extending from 66°16′ to 68°00′N at 18°50′W. Information on temperature and chlorophyll a concentrations is also presented. Spring warming of the water began in March to April and maximum temperatures were recorded in August (3.8?°C). The spring bloom of the phytoplankton started in late March and highest chlorophyll a concentrations were measured during middle to late April (7.0?mg chlorophyll a m^?3). T. inermis was the dominant species in the samples, constituting 77% of juvenile, male and female euphausiids present. The greatest abundance of juvenile, male and female T. inermis and M. norvegica was observed during autumn and winter, with lower abundance in spring and summer. T. longicaudata showed only limited changes in seasonal abundance. Male T. inermis had spermatophores in their ejaculatory ducts from February to May, while mature females had spermatophores attached during April and May. T. longicaudata males bore spermatophores from February to July, whereas females only bore spermatophores in April and May. M. norvegica males had spermatophores from February to April, while the single female with spermatophores was caught in February. Euphausiid eggs were first recorded during the latter part of April; the highest numbers of eggs were observed in the samples taken in late May. Maximum numbers of nauplii of both Thysanoessa spp. and M. norvegica were recorded in late May. The main spawning of the euphausiids coincided with the phytoplankton spring bloom. Most male T. inermis took part in breeding at 1 yr of age while most females appeared not to mature until 2 yr of age. T. inermis has a life span of just over 2 yr, T. longicaudata appears to live just over 1 yr. Limited data did not allow the life span of M. norvegica to be determined.     

Trophic strategies of garfish, Arrhamphus sclerolepis, in natural coastal wetlands and artificial urban waterways

We used carbon stable isotope and stomach content analyses to test whether snub-nosed garfish, Arrhamphus sclerolepis (Hemiramphidae), in the extensive artificial urban waterways of southeast Queensland, Australia, rely on autotrophic sources different to those in natural wetlands. Carbon isotope values of A. sclerolepis were similar to those in previous investigations, with enriched values in natural habitat (mean = −13.9‰, SE=0.6) and depleted values (−19.1‰, 0.1) in artificial habitat. A. sclerolepis in natural habitat consumed large amounts of seagrass during the day and night, and at night also ingested small quantities of crustacean prey. In artificial habitat, A. sclerolepis consumed macroalgae during the night and switched to invertebrates (terrestrial ants) in the day. Values of δ¹⁵ N in all the fish were 3–8‰ more enriched than sources. Mathematical modelling of feasible source mixtures showed that in natural habitat the bulk of the dietary carbon is obtained from seagrass, but the nitrogen is obtained from animal prey. In artificial habitat, carbon is obtained from a mixture of macroalgae and animals. We could not determine the nitrogen sources in artificial habitat of A. sclerolepis since, even after accounting for trophic fractionation of δ¹⁵ N, the values were outside the range of potential sources. If the types of animals ingested vary over time, perhaps one or more types of animal important in the provision of nitrogen was not sampled during the study. This study demonstrates that not only does A. sclerolepis occur in both artificial and natural habitats, but it uses the same strategy of bulk herbivory with the inclusion of smaller amounts of animal prey. This understanding of how ecological processes support fisheries production in artificial habitat improves the overall understanding of the effects of urbanisation on coastal food webs.     

Zoogeography and diversity of euphausiids around southern Africa

Published and unpublished records of euphausiid distributions around southern Africa are examined for zoogeographic pattern and the results compared with patterns generated from intertidal data sets. Two basic groups of euphausiids are discerned from cluster analysis, corresponding to neritic and oceanic assemblages. Superimposed upon these are Indian Ocean (Agulhas Current) and Atlantic Ocean (Benguela Current) groups. Patterns of diversity and zoogeography generally conform to the large-scale hydrological features in the area. Diversity is higher in the oceanic than in neritic regions. Maximum diversity is recorded off Cape Point, where Indian, Atlantic and southern Ocean waters interact. Diversity is otherwise higher along the east coast, and particularly low in the nearshore waters of the Benguela Current. While particular species of euphausiids can be associated with Agulhas Current and Angola Current waters, westcoast communities lack any distinctive species, and this is discussed. Although the patterns of zoogeography observed for euphausiids are generally similar to those observed for rocky shore communities, there are clear differences between them that reflect their respective habitats and the influence that large-scale water movement has on each.     

Mechanisms mediating plant distributions across estuarine landscapes in a low-latitude tidal estuary

Understanding of how plant communities are organized and will respond to global changes requires an understanding of how plant species respond to multiple environmental gradients. We examined the mechanisms mediating the distribution patterns of tidal marsh plants along an estuarine gradient in Georgia (USA) using a combination of field transplant experiments and monitoring. Our results could not be fully explained by the "competition-to-stress hypothesis" (the current paradigm explaining plant distributions across estuarine landscapes). This hypothesis states that the upstream limits of plant distributions are determined by competition, and the downstream limits by abiotic stress. We found that competition was generally strong in freshwater and brackish marshes, and that conditions in brackish and salt marshes were stressful to freshwater marsh plants, results consistent with the competition-to-stress hypothesis. Four other aspects of our results, however, were not explained by the competition-to-stress hypothesis. First, several halophytes found the freshwater habitat stressful and performed best (in the absence of competition) in brackish or salt marshes. Second, the upstream distribution of one species was determined by the combination of both abiotic and biotic (competition) factors. Third, marsh productivity (estimated by standing biomass) was a better predictor of relative biotic interaction intensity (RII) than was salinity or flooding, suggesting that productivity is a better indicator of plant stress than salinity or flooding gradients. Fourth, facilitation played a role in mediating the distribution patterns of some plants. Our results illustrate that even apparently simple abiotic gradients can encompass surprisingly complex processes mediating plant distributions.     

Ecomanagement of biodiversity and ecosystem functioning in the Mediterranean Sea: concerns and strategies

Marine biodiversity is generally higher in benthic than in pelagic systems, and in coastal than in open sea systems. Sediments are the most human-impacted domain and therefore represent the target zone for both the study and actions needed for the preservation of biodiversity. Losses of marine diversity, higher (or simply more evident) in coastal areas, are generally the result of conflicting uses of coastal habitats. Large difficulties arise from the analysis and evaluation of the actual biodiversity, especially when different environments are compared, as often studies on biodiversity are dependent upon the distribution of the specialists. On the other hand, losses of marine biodiversity might be underestimated, due to the limited knowledge of the ecosystems' functioning, of the species inhabiting various habitats and of the still limited capacity to assess microbial biodiversity, which represents the largest fraction of the global marine biodiversity. Finally, claimed losses of biodiversity might be just apparent, as the sea floor is a bank of resting stages of various plankton species that are likely to spend even decades in the sediment before reactivating and inducing unattended blooms in the water column. The Mediterranean Sea displays high species diversity, but might reach the highest values in terms of adaptive strategies and functional diversity. Moreover, the Mediterranean Sea represents also a key area for the study of the relative influences of the natural and anthropogenic changes on biodiversity and its consequences on ecosystem functioning. Habitat destruction, over-fishing, contaminants, eutrophication, introduction of alien species, and climate changes are producing increasingly evident changes in community structure and biodiversity of this warm and miniature ocean. We summarized the main effects of different disruptive agents on the marine biodiversity of the Mediterranean Sea, with special attention on the biodiversity relevance in ecosystem functioning and possible implications in bio-geochemical cycles. The present overview aims at focusing and synthesizing the most important factors potentially affecting the interactions between biodiversity and ecosystem functioning in the Mediterranean in order to better define possible strategies of conservation and eco-management.     

Comparing ecosystem engineering efficiency of two plant species with contrasting growth strategies

Many ecosystems are greatly affected by ecosystem engineering, such as coastal salt marshes, where macrophytes trap sediment by reducing hydrodynamic energy. Nevertheless, little is known about the costs and benefits that are imposed on engineering species by the traits that underlie their ecosystem engineering capacity. We addressed this topic by comparing ecosystem engineering efficiency defined as the benefit-cost ratio per unit of biomass investment for two species from the intertidal habitat: the stiff grass Spartina anglica and the flexible grass Puccinellia maritima. These species were selected for their ability to modify their habitat by trapping large quantities of sediment despite their contrasting growth form. On a biomass basis, dissipation of hydrodynamic energy from waves (a proxy for benefits associated with ecosystem engineering capability as it relates to the sediment trapping capability) was strikingly similar for both salt marsh species, indicating that both species are equally effective in modifying their habitat. The drag forces per unit biomass (a proxy for costs associated with ecosystem engineering ability as it relates to the requirements on tissue construction and shoot anchoring to prevent breaking and/or washing away) were slightly higher in the species with flexible shoots. As a result, stiff Spartina vegetation had slightly higher ecosystem engineering efficiency, due to lower engineering costs rather than to a higher engineering effect. Thus, Spartina is a slightly more efficient rather than a more effective ecosystem engineer. Ecosystem engineering efficiency was found to be a species-specific characteristic, independent of vegetation density and relatively constant in space. Analyzing ecosystem engineering by quantifying trade-offs offers a useful way toward developing a better understanding of different engineering strategies.     

Day/night vertical distribution of euphausiids in the eastern tropical Pacific

Between March 23 and April 4, 1981, samples were taken in the eastern tropical Pacific. The day/night vertical distribution of euphausiid species and biomass are described and contrasted in detail on two eastern tropical Pacific stations, the DOME station, in a region of continuous upwelling and the BIOSTAT station, in a nonupwelling area. The effects of various biological parameters, such as temperature, salinity and oxygen concentrations on the distributions of the species are examined. The numbers of euphausiids m^-2 on both stations were highest during the day, indicating that avoidance of the sampler was not a problem. During the day the largest concentration of adult euphausiids was between 300 and 350 m whereas the juveniles were concentrated between 170 and 80 m on both stations. Very few individuals were found within the oxygen minimum layer, but low concentrations of some species were found below the oxygen minimum down to 1 000 m. At night the euphausiid concentration migrated upward into the mixed layer (20 to 30 m) at BIOSTAT and to the base of the mixed layer at the DOME. Significant differences in the night depths of the species were found on both stations. The oxygen minimum layer appeared to act as a barrier to the vertical distribution of all species. Only two species were found in water with an oxygen concentration of <0.1 ml O₂ l^-1. Twentyone species of euphausiids were found on the two stations but the adult population was dominated by only two or three species on both stations. The reproductive state of the species suggested that some species reproduced earlier on the DOME than on BIOSTAT. Analysis of the depth distribution by cluster analysis showed that the most abundant species occupied different depths during the night and day at BIOSTAT but the two most abundant species were concentrated at the same depth at the DOME station although portions of each species population occupied different pelagic zones.     

Exploring fisheries strategies for the western English Channel using an ecosystem model

An ecosystem model of the western English Channel ecosystem in 1994 was used to explore the effects of the use of a fishing policy optimization routine on profits, number of jobs and ecosystem structure. The optimization for single objective led to the specialization of the fishing fleet, with some fleet types being almost excluded. The profits and mainly the job optimizations led to big changes in the ecosystem structure, with loss of diversity, but the overall biomass of all vertebrate groups represented in the model increased considerably. For the objective focusing on ecosystem structure, there was an increase in biodiversity, with many long-lived groups predicted to increase, although the overall vertebrate biomass suffered just a small increase. An “ideal” mixed policy configuration was found when slightly greater weight was given to ecosystem structure than was given to profits and jobs. This scenario led to an overall reduction in effort but also to increased profits and biodiversity, while keeping the number of jobs at the same level as the baseline estimates. The results of the optimizations showed that the average trophic level of the catches is quite resistant to changes in the underlying system structure. On the other hand, despite the high level of aggregation of the model structure, a biodiversity index estimated by the model presented large changes as a function of the weights placed on the single policy functions, reflecting the changes in the system structure. The output of the application of the fishing optimization presented here should be considered in qualitative rather than in quantitative terms as an aid and part contribution to the complicated discussions on future long term management actions. Nonetheless it points to an overall reduction in fishing capacity, an objective widely accepted within the scientific community, while keeping the fishery in a profitable state.     

Vertical distributions of euphausiids and fish in relation to light intensity in the Northeastern Atlantic

The relationship between the vertical distributions of euphausiids and fish and light intensity has been studied directly by using a photometer in conjunction with an acoustically controlled rectangular midwater trawl. Samples were taken at a position centered on 47°N; 17°W on 15 and 16 May 1978. Five species of euphausiid and six species of fish have been analysed, both groups contained migrant and non-migrant species. The population of each of these species occurred throughout a light regime spanning at least three orders of magnitude of intensity; none of them was restricted to, or followed, and isolume. There were no sexual or size differences in the distributions of the euphausiids, but the population of Argyropelecus hemigymnus was probably stratified during the day, with smaller individuals occurring shallower than large ones. The results are discussed in relation to previous observations and to the theories of photic regulation of distributions and migrations.     

Trophic state, ecosystem efficiency and biodiversity of transitional aquatic ecosystems: analysis of environmental quality based on different benthic indicators

Estuaries and coastal lagoons are characterized by a strong spatial and temporal variability of physicochemical characteristics and productivity patterns. In these environments, the magnitude and direction of the ecological responses to inorganic nutrient increase (i.e. eutrophication) are difficult to predict. In the framework of the project, New Indicators of Trophic state and environmental quality of marine coastal ecosystems and transitional environments (NITIDA), we analysed benthic indicators of trophic state, ecosystem efficiency, and environmental quality in four different transitional environments. The trophic state of the sediments was assessed in terms of quantity and bioavailability of sediment organic C pools; ecosystem efficiency was determined in terms of the prokaryote efficiency in exploiting enzymatycally degraded organic C; environmental quality was determined in terms of meiofaunal diversity. Here, we provide a synopsis of the results obtained and a meta-analysis of the scores assessments obtained using the different ecological indicators of environmental quality and demonstrate that trophic state, ecosystem efficiency, and biodiversity in transitional ecosystems are closely linked. We conclude that the assessment of the environmental quality of transitional ecosystems should be based upon a battery of trophic state indicators and 'sensors' of ecosystem functioning, efficiency, and quality.