Polychaete assemblages as indicators of habitat recovery in a temperate estuary under eutrophication

From 1980 to 2000, the Mondego estuary (Portugal) suffered dramatic changes due to eutrophication, leading to a decline in seagrass beds and changes in community structure, namely a decline in species richness and replacement of herbivores by detritivores. Because the conservation status of the estuary was being compromised, a restoration project was implemented in 1998 in order to restore the original natural seagrass habitat. This project included several restoration/management measures, including the protection of the remaining seagrass patches and improvement of the hydraulic conditions through modifying sluice opening regimes, thereby reducing the nutrient loading in the southern arm of the estuary. In addition, several stakeholder forums were convened to inform local people of the ecological and economic importance of the area. In this paper we evaluate the success of this management plan as judged by changes in the polychaete assemblages.http://www.sciencedirect.com/science/article/B6WDV-4KW5WMJ-2/1/bb4d7ae09864d325f549e5b779b3f58

The effect of eutrophication abatement on the bivalve Scrobicularia plana

Over the last few decades, the excessive growth of macroalgae and decline of seagrass beds, associated with increased eutrophication, has become a worldwide problem. It is known that submersed aquatic vegetation (SAV) offers stable habitats, allowing the continuous availability of food and protection against predators and contributing to biodiversity, sediment stability and water transparency when compared to areas covered by macroalgae mats. In the Mondego estuary (Portugal), several mitigation measures (nutrient-load reduction, seagrass-bed protection and freshwater-circulation enhancement) were implemented in 1998 in order to promote the recovery of the seagrass beds and the entire surrounding environment following a long period of eutrophication. Here the success of this restoration project is evaluated by comparing the water nutrient concentrations, the extent of seagrass cover and the dynamics of the bivalve Scrobicularia plana before and after the implementation of the management measures. During the period in which environmental quality declined, S. plana's adult abundance, total biomass and growth production also declined, parallel with the almost total disappearance of Zostera noltii. After the implementation of management measures, dissolved nutrients and green macroalgal blooms were much reduced, and seagrass beds started to recover. The S. plana population also responded positively, becoming more structured (including individuals of all age classes), with higher biomass and growth production.http://www.sciencedirect.com/science/article/B6WDV-4FCRFDM-1/1/d653dc6f4a1a90598f31649f450376a

Annual production of estuarine fauna in different environmental conditions: An evaluation of the estimation methods

Secondary production is one of the most comprehensive measurements of ecosystem health. Production of five estuarine species, with different life history and abundance in the ecosystem, was estimated for 2 consecutive years at a Zostera noltii bed and sand-muddy area, with contrasted environmental conditions. Calculations were performed using different estimation methods, commonly cited in secondary production studies. Annual production estimated by cohort increment summation varied between 43.3 and 209.2 g AFDW m- 2 y- 1. All the other methods were compared with the results obtained from this methodology to evaluate each method's performance. In general, satisfactory results were obtained with Brey (2001) [Brey, T., 2001. Population dynamics in benthic invertebrates. A virtual handbook. Version 01.2. http://www.awi-bremerhaven.de/Benthic/Ecosystem/FoodWeb/Handbook/main.html. Alfred Wegener Institute for Polar and Marine Research, Germany] version 4-04 (deviations that ranged between - 4 to + 10%). The responses of the other empirical methods were more variable, depending on the species characteristics. Therefore, the optimal selection of an empirical method in secondary production studies depends on the species considered and on the quality of the parameters required for the application of the method. Brey (2001) [Brey, T., 2001. Population dynamics in benthic invertebrates. A virtual handbook. Version 01.2. http://www.awi-bremerhaven.de/Benthic/Ecosystem/FoodWeb/Handbook/main.html. Alfred Wegener Institute for Polar and Marine Research, Germany] version 4-04 was considered the best methodology. For the less representative species the simple sum of biomass increments from one sampling date to the next may be an easy and valid option.http://www.sciencedirect.com/science/article/B6T8F-4GJK8KW-1/1/1c17d83eab721fd37e876b68e0e6afe

Are eulittoral assemblages suitable for detecting the effects of sewage discharges in Atlantic and Mediterranean coastal areas?

The search for cost-effective indicators able to detect anthropogenic impacts is an essential prerequisite to plan mitigation interventions, which can prevent further deterioration of coastal areas. Eulittoral assemblages are accessible for sampling, and their dominant species are easy to identify and widely distributed. This study assessed the potential of eulittoral assemblages to reflect environmental perturbations related to sewage discharge across different environmental and geographical locations. Sampling occurred in impacted (near sewage discharge) and control areas, on both Atlantic and Mediterranean shores. Multivariate analyses showed that the structure of eulittoral invertebrate assemblages differed significantly between control and impacted areas for the Mediterranean, but not for the Atlantic case study. Macroalgae responses to sewage discharge were found on the Mediterranean shore with a significantly higher abundance of Chlorophyta near the outfall. Limpet populations of the genus Patella appear to be affected by sewage discharge. The response of limpet populations differed between Atlantic and Mediterranean shores, probably due to among-species differences of ecological traits. Our results suggest that the response of eulittoral assemblages and limpets to sewage discharge might be strictly context-dependent, thus limiting their potential to serve as general indicators in monitoring the effects of this source of human impact over large spatial scales

Fatty acid profiling reveals seasonal and spatial shifts in zooplankton diet in a temperate estuary

Fatty acids composition of copepod and cladoceran species and their possible food sources was investigated in the Mondego estuary (southern Europe) in order to explain the seasonal variation of the small copepods Acartia clausi, Acartia tonsa, Copidodiaptomus numidicus, Temora longicornis and the freshwater cladoceran Daphnia longispina. A total of 12 zooplankton species (7 marine, 2 estuarine and 3 freshwater species) were studied. A multivariate analysis revealed a clear seasonal distribution of zooplankton species in terms of fatty acids composition and abundance, with winter and spring zooplankton species showing maximal concentrations and diversity of total fatty acids. These findings underline the role of lipids as storage during the colder seasons in a highly variable environment like an estuary. Estuarine and freshwater species showed a more diverse array of saturated and unsaturated fatty acids rather than marine species, except for Centropages typicus. Fatty acids markers of trophic position indicated the presence of two trophic levels: copepod species were primarily omnivorous, whereas cladocerans showed to be herbivorous. Our results suggest that feeding patterns of plankton change spatially and temporally, reflecting the shifts in dominance between diatoms and flagellates as well as between dinoflagellates/diatoms and small animals

Bulletin of the Kyushu University Farm

In this work, we analysed the latitudinal trends in the nursery habitat colonization processes of the European flounder (Platichthys flesus). This was accomplished by estimating the duration of the pelagic and metamorphic stages, as well as the duration of the spawning period, in several nursery areas across its geographical distribution range in the European Atlantic Coast: Mondego estuary (Portugal), Vilaine estuary (France), Slack estuary (France), Wadden Sea (Netherlands) and the Sørfjord (Norway). All juvenile flounders were captured with beam trawls in June/July 2010, and otolith microstructure was used to determine the duration of each stage by means of daily growth increments. The pelagic and metamorphic stages were longer at the middle of the distribution range, and lasted in total up to two months after hatching. The spawning period occurred between mid-January and early-July over the species' distribution range, with a time lapse of nearly two months between the Mondego estuary and the Sørfjord, as a consequence of warmer water temperature earlier in the season in southern areas. In general, total length of the captured fish showed a latitudinal cline between the northernmost and southernmost sampling sites, with higher values at the middle of the distribution range. The results also suggested the existence of a countergradient growth compensation mechanism in the northernmost populations. Apart from temperature, which sets the general metabolic pace of organisms, differences between sites were also related with local features, such as the extension of the continental platform and adaptations to transport and retention mechanisms

Population dynamics of Cyathura carinata (Isopoda) in a eutrophic temperate estuary

From January 1993 to September 1995, Cyathura carinata was a target species of a monitoring programme carried in the Mondego Estuary (Portugal). Being one of the key species of the intertidal mud flats, this isopod was found to be most abundant in a eutrophic area, where seasonal macroalgal blooms usually occur. Its density decreased towards downstream areas, where some Zostera noltii beds exist. At the Mondego Estuary, the present work stated that C. carinata: (a) had a 2-year life span, even though, 80-90% of the individuals died when 1 year old, revealing a strong post-reproduction mortality; (b) produced a single cohort per year; (c) showed continuous growth (with lower rates during winter); (d) evidenced protogynous hermaphroditism and (e) presented a high growth production and a low turnover ratio. A latitudinal gradient reflected in the life features of C. carinata was described. Except for the life span and the frequency of reproduction, which are generally valid for all populations, C. carinata from the Mondego Estuary fitted the characteristics of other populations from the south of Europe.http://www.sciencedirect.com/science/article/B6WDV-4DHX5FG-4/1/8852e529818474ae130b838a34deae2