Diatom ecological preferences in a shallow temperate estuary (Ria de Aveiro,Western Portugal)

The study of the diatom ecological preferences was conducted from January 2002 to June 2003 in Canal de Mira, Ria de Aveiro, Western Portugal. Three sampling stations along a salinity gradient were sampled monthly, in new moon, at high and low tide. Salinity, temperature, pH, dissolved oxygen and nutrient contents were measured for each sampling station; chlorophyll a and diatom diversity and abundance were also evaluated. Canonical correspondence analysis was used to identify the environmental variables governing the composition and structure of diatom assemblage. The variation in the species data among the different reaches was strongly determined by the salinity spatial gradient and by the temperature temporal gradient. The lower reaches were dominated by marine species (e.g. Auliscus sculptus, Chaetoceros densus, Fallacia forcipata,Licmophora flabellata, L. grandis, Surirella comis), while in the most upstream station typical freshwater species dominated (e.g. Caloneis permagna, Cymatopleura solea, Cymbella tumida, Gomphonema longiceps, Pinnularia stommatophora, Stauroneis smithii). Weighted averaging was used to estimate optima and tolerances of some diatom taxa for the most influential variables. It was possible to establish groups oftaxa with defined and distinctive salinity and temperature preferences.     

Zooplankton and ichthyoplankton communities in a temperate estuary: spatial and temporal patterns

Zooplankton and ichthyoplankton assemblages were studied fromJanuary 2003 to June 2004 in a temperate shallow estuary (Mondegoestuary, Portugal). Monthly sampling was performed at five stationsat high and low tides, with subsurface tows with 335 and 500µm mesh Bongo nets. Analysis of variance (ANOVA) showeda significant effect (P < 0.05) of the mesh size of the neton the abundance of main zooplankton groups. On average, theabundance of the 500 µm taxocenosis was 67 and 102 timeslower than the 335 µm taxocenosis at high and low tidesrespectively, especially in the south arm. More than 80 specieswere identified in the zooplankton samples. The upper reachesof northern arm are dominated by freshwater crustacean mesozooplanktonlike Acanthocyclops robustus and Diaptomus spp. and the cladoceransDaphnia, Ceriodaphnia and Bosmina, often being codominant. Inthe southern arm, the resident estuarine copepod Acartia tonsawas dominant, eventually being the most abundant taxon. Marinereaches of estuary are usually dominated by the marine calanoidcopepods Acartia clausi and Temora longicornis and the siphonophoresMuggiaea atlantica. Concerning the ichthyoplankton, this wasdominated by the larvae of estuarine resident species, mainlyPomatoschistus sp., and eggs of Engraulis encrasicolus. Theabundance of Pomatoschistus sp. larvae was positively correlatedwith water temperature. Statistical analysis (canonical correspondenceanalysis) used to determine the spatiotemporal structure ofthe zooplankton assemblages and its correlation with environmentalvariables showed that salinity and temperature were the mainfactors influencing the distribution of zooplankton. The resultsobtained also showed that abundance was strongly influencedby the hydrological circulation pattern and direct or indirecthuman impacts that occur in each arm of the estuary. This article was presented at Plankton Symposium III, held atFiguera da Foz, portugal, between 17 and 20 March 2005, underthe auspices of the University of Coimbra and the Universityof Aveiro, and coordinated by Mário Jorge Pereira andUlisses M. Azeiteiro.     

Evidence for Changes in Estuarine Zooplankton Fostered by Increased Climate Variance

Estuaries are among the most valuable aquatic systems in terms of their services to human welfare. They offer an ideal framework to assess multiscale processes linking climate and food web dynamics through the hydrological cycle. Resolving food web responses to climate change is fundamental to resilience management of these threatened ecosystems under global change scenarios. Here, we examined the temporal variability of the plankton food web in the Mondego Estuary, central Iberian Peninsula, over the period 2003 to 2012. The results pointed out a cascading effect from climate to plankton communities that follow a non-stationary behavior shaped by the climate variance envelope. Concurrent changes in hydrographic processes at the regional, that is, upwelling intensity, and local, that is, estuarine hydrology, scales were driven by climatic forcing promoted by the North Atlantic Oscillation; the influence of which permeated the physical environment in the estuary affecting both autotrophic and heterotrophic communities. The most conspicuous change arose around 2008 and consisted of an obvious decrease in freshwater taxa along with a noticeable increase in marine organisms, mainly driven by gelatinous zooplankton. The observed increase in small-sized cosmopolitan copepods, that is, Clausocalanus arcuicornis, Oithona plumifera, thermophilic species, that is, Penilia avirostris, and gelatinous zooplankton suggests a structural change in the Mondego plankton community. These results provide empirical support to the expectation that expanding climate variance changes plankton structure and functioning, likely fostering trophic interactions in pelagic food webs.     

Zooplankton distribution and dynamics in a temperate shallow estuary

The spatial, temporal and tidal dynamics of the zooplanktonic community of the Mondego estuary was studied from January 2003 to 2004. The monthly sampling procedure included the measurement of hydrological parameters (salinity, temperature, Secchi transparency, chlorophyll a and nutrients) and the collection of zooplankton with a Bongo net of 335 μm mesh size. Zooplankton composition, distribution, density, biomass and diversity were determined. The principal component analysis (PCA) revealed the existence of a spatial gradient with the upstream sampling stations, associated to high values of nutrients, in opposition to the downstream stations characterized by higher salinity and transparency values. The Copepoda was the main dominant group and Acartia tonsa revealed to be the more abundant taxon. The spatial and temporal dynamics of zooplanktonic communities analysed by non-metric MDS showed the existence of four assemblages of species-sites, reflecting differences in zooplankton composition between both branches of the estuary. The results suggest that abundance, biomass and diversity of the zooplanktonic community are strongly influenced by the hydrological circulation pattern and by direct or indirect human impacts that occur in each branch. The northern branch is dominated by the river flow suffering from regular dredging activities and the southern branch is dominated by tidal circulation suffering from an ongoing eutrophication process.     

Estimation of ecological exergy using weighing parameters determined from DNA contents of organisms – a case study

We studied the changes of exergy and specific exergy with data of benthic macrofauna communities, periodically sampled along an estuarine gradient of eutrophication in the Mondego estuary (Western Portugal). Exergy estimates were calculated from organism biomass, based on weighing factors for the relative content of exergy per unit of biomass determined from DNA contents of organisms. Results were discussed in terms of both the macrofauna biomass production and the structural organisation of the system. Estimates for the exergy indices provided useful indications for the evaluation of environmental impact due to the eutrophication process. Different average values for the indices of exergy and specific exergy were estimated relatively to areas with different levels of eutrophication, in the spatial gradient of eutrophication. Higher exergy levels and lower exergy content per unit of biomass (specific exergy) were associated to populations more stabilized or areas less perturbed. Additionally, the index of specific exergy seemed capable of providing indications for the qualitative alterations in the communities (in temporal and spatial terms) that go in the direction of the observations made in this ecosystem.     

Fishermen’s knowledge and conservation attitudes: focus on the great cormorant Phalacrocorax carbo (Linnaeus, 1758) in the Minho River,Portugal

Aquatic Ecology - Considerate the attitudes of traditional communities and their local ecological knowledge (LEK) can contribute to better policymaking and more appropriate management plans. Thus,...     

The effect of environmental parameters and cyanobacterial blooms on phytoplankton dynamics of a Portuguese temperate Lake

The increasing occurrence of cyanobacterial blooms in freshwaters is of great concern due to the ability of many cyanobacteria to produce cyanotoxins. In the present work, the eutrophied Vela Lake (Central Portugal), used for recreational purposes and as a water source for agriculture, was monitored every fortnight between 2000 and 2001. Phytoplankton diversity and densities were measured and correlated to environmental parameters. A seasonal phytoplanktonic succession was observed and it was mainly correlated with conductivity, temperature, total suspended solids and nutrients availability (particularly phosphorus). Diatoms were dominant during winter months (inferior temperatures and higher nutrients availability) followed by green algae in early spring and then cyanobacteria from late spring until early autumn (less nutrient availability and higher temperatures). A massive cyanobacterial bloom of Aphanizomenon flos-aquae occurred early in May 2001 and was preceded by the lowest nitrogen levels measured in the water during all the study period. At the time of this bloom senescence, dissolved oxygen was severely depleted and a massive death of ichthyofauna was recorded. A Microcystis aeruginosa bloom was also detected in July 2001 and it occurred following a rapid decrease in abundance of green algae and diatoms. By considering not only the environmental parameters but also the occurrence of cyanobacterial blooms as explanatory variables in a canonical correspondence analysis, the variance explained for the phytoplanktonic assemblage during the study period was increased in about 7% achieving a total of 61.0%, indicating a correlation that may be due to the known competitive advantage and/or allelopathy of the bloom-forming cyanobacteria towards microalgae.