Papers by Alexandra Baeta
Stable Isotope Ecology
Encyclopedia of Ecology, 2019
Réseaux trophiques des écosystèmes intertidaux : étude par les isotopes stables et l'analyse des réseaux
Cette thèse de Doctorat examine le réseau trophique estuarien lié aux herbiers à zostères, Zoster... more Cette thèse de Doctorat examine le réseau trophique estuarien lié aux herbiers à zostères, Zostera noltii et quantifie le rôle trophique des consommateurs de la macrofaune benthique, dans deux zones intertidales de l'estuaire du Mondego, à différentes périodes de 1993 à 2008. Elle s'intéresse spécifiquement (i) à l'incorporation de l'azote issu des activités humaines, en considérant l'assimilation d'azote comme un indicateur de l'eutrophication et (ii) au rôle des zostères dans le réseau trophique benthique. Six modèles ont été développés afin d'analyser les effets, (i) d'un enrichissement en nutriments, (ii) des mesures de mitigation, et (iii) d'une inondation centennale, sur les propriétés du réseau trophique benthique estuarien. La présence de Z. noltii change peu la structure du réseau trophique planctonique, soutenu en partie par la matière organique particulaire et supporte principalement des poissons comme prédateurs. Les autres consomm...
Journal of Experimental Marine Biology and Ecology, 2004
Over the last 20 years, the Mondego estuary, Portugal has experienced excessive growth of macroal... more Over the last 20 years, the Mondego estuary, Portugal has experienced excessive growth of macroalgae especially in the inner parts of the system, with several algal species implicated. In this study, we compare the effects of morphologically different species, the red alga Gracilaria verrucosa and the green macroalga Enteromorpha intestinalis on macrobenthic assemblages, by a field experiment whereby the biomass of algae was manipulated and the resultant changes in macrofauna abundance evaluated. The experiments were carried out in different areas (a relatively undisturbed sea grass bed and an upstream eutrophic area) experiencing different degrees of overall enrichment.
Estuarine, Coastal and Shelf Science, 2005
The biological features, population dynamics and secondary production of Carcinus maenas were stu... more The biological features, population dynamics and secondary production of Carcinus maenas were studied between June 2003 and June 2004 in four areas within the Mondego estuary, Portugal. Benthic samples were collected monthly, during the night, at high water of spring tides using a 2-m beam trawl, and plankton samples were collected monthly, during the day, at high tide with a Bongo net. Only the first zoeae stage of C. maenas larvae was found in the plankton; it was collected at all sampling stations throughout the year. A continuous pattern of benthic recruitment was observed in the upstream areas of the estuary with the highest peaks occurring in the spring 2004. Females carrying eggs were also caught through the year, although mainly in downstream areas. Juveniles' sex-ratio was favourable to males at almost all the sites sampled. Ventral carapace colour varied between green and orange-red, with the proportion of the green morphotype increasing with the increasing distance from the mouth of the estuary. The proportion of crabs in moult also increased from downstream to upstream areas. For both sexes the crab population showed a similar size structure throughout the year. The upstream areas of the estuary were characterized by the dominance of juveniles, with adults migrating to downstream areas. The average annual production of C. maenas, P (growth production), was estimated at 0.08 g m ÿ2 y ÿ1 AFDW, and the average annual biomass (B) was estimated at 0.058 g m ÿ2 , resulting in a P=B ratio of 1.4.
Ecological Modelling, 2011
Human-mediated and natural disturbances such as nutrient enrichment, habitat modification, and fl... more Human-mediated and natural disturbances such as nutrient enrichment, habitat modification, and flood events often result in significant shifts in species composition and abundance that translate into changes in the food web structure. Six mass-balanced models were developed using the "Ecopath with Ecosim" software package to assess changes in benthic food web properties in the Mondego estuarine ecosystem (Portugal). Field, laboratory and literature information were used to construct the models. The main study objective was to assess at 2 sites (a Zostera meadow and a bare sediment area) the effects of:
Feeding ecology of the green crab, Carcinus maenas (L., 1758) in a temperate estuary, Portugal
Crustaceana, 2006
... 3) Corresponding author; e-mail: [email protected] © Koninklijke Brill NV, Leiden, 2006 Crusta... more ... 3) Corresponding author; e-mail: [email protected] © Koninklijke Brill NV, Leiden, 2006 Crustaceana 79 (10): 1181-1193 Also available online: www.brill.nl/cr Page 2. 1182 ALEXANDRA BAETA ET AL. INTRODUCTION The ...
Journal of Sea Research, 2015
Seagrass patches interspersed in a sediment matrix may vary environmental conditions and affect f... more Seagrass patches interspersed in a sediment matrix may vary environmental conditions and affect feeding habits of consumers and food-web structure. This paper investigates diet shifts between bare sediments and a Zostera noltei (Hornemann, 1832) meadow for three facultative deposit-feeding macrofaunal consumers, notably the bivalve Scrobicularia plana (da Costa, 1778), the polychaete Hediste diversicolor (O.T. Müller, 1776), and the gastropod Hydrobia ulvae (Pennant, 1778). In July 2008, one eelgrass meadow and two bare sediment locations were chosen in the Mondego estuary (40°08″ N, 8°50′ W, Portugal) and sampled for stable isotope signatures (δ 13 C and δ 15 N) of macrofauna consumers and some of their potential basal food sources, such as sedimentary organic matter (SOM), microphytobenthos (MPB), seagrass shoots, leaves and seaweeds laying on the surface sediment. The δ 15 N of H. diversicolor was 3‰ higher in the eelgrass meadow than in bare sediment, indicating a change of trophic position, whereas the Bayesian stable-isotope mixing model showed that S. plana assimilated more macroalgal detritus than microphytobenthos in the eelgrass bed. Such habitat-related diet shifts have the potential to change structure and spatial dynamics of benthic food webs.
Cephalopods in the diet of nonbreeding black-browed and grey-headed albatrosses from South Georgia
Polar Biology, 2014
ABSTRACT The food and feeding ecology of albatrosses during the nonbreeding season is still poorl... more ABSTRACT The food and feeding ecology of albatrosses during the nonbreeding season is still poorly known, particularly with regard to the cephalopod component. This was studied in black-browed Thalassarche melanophris and grey-headed T. chrysostoma albatrosses by analysing boluses collected shortly after adults returned to colonies at Bird Island, South Georgia (54°S, 38°W), in 2009. Based on stable isotopic analyses of the lower beaks, we determined the habitat and trophic level (from δ13C and δ15N, respectively) of the most important cephalopods and assessed the relative importance of scavenging in terms of the albatrosses’ feeding regimes. Based on lower rostral lengths (LRLs), the main cephalopod species in the diets of both albatrosses was Kondakovia longimana, by frequency of occurrence (F > 90 %), number (N > 40 %) and mass (M > 80 %). The large estimated mass of many squid, including K. longimana, suggests that a high proportion (>80 % by mass) was scavenged, and that scavenging is much more important during the nonbreeding season than would be expected from breeding-season diets. The diversity of cephalopods consumed by nonbreeding birds in our study was similar to that recorded during previous breeding seasons, but included two new species [Moroteuthis sp. B (Imber) and ?Mastigoteuthis A (Clarke)]. Based on similarities in LRL, δ13C and δ15N, the squid consumed may have been from the same oceanic populations or region, with the exception of Taonius sp. B (Voss) and K. longimana, which, based on significant differences in δ15N values, suggest that they may have originated from different stocks, indicating differences in the albatrosses’ feeding regimes.
Seasonal and temporal variations in population dynamics of the Carcinus maenas (L.): the effect of an extreme drought event in a southern European estuary—CORRIGENDUM
Journal of the Marine Biological Association of the United Kingdom, 2011
Cambridge Journals Online (CJO) is the e-publishing service for over 270 journals published by Ca... more Cambridge Journals Online (CJO) is the e-publishing service for over 270 journals published by Cambridge University Press and is entirely developed and hosted in-house. The platform's powerful capacity and reliable performance are maintained by a combination of our own expertise and a process of consultation with the library and research communities. With the help of these stakeholders, we maintain CJO as an industry-leading e-publishing service.
Marine Environmental Research, 2009
Marine Ecology Progress Series, 2014
This study investigated the extent to which the plasticity of a generalist, opportunistic species... more This study investigated the extent to which the plasticity of a generalist, opportunistic species allows individuals to shift their feeding ecology and foraging niche, throughout the annual cycle, and between 2 years of contrasting diet and oceanographic conditions during the breeding season. The spatio-temporal variations in the foraging niche of an overpopulated gull species -the yellow-legged gull Larus michahellis population at Berlenga Island (Portugal)were assessed using blood (plasma and cells) and different feathers for stable isotope analyses (δ 13 C and δ 15 N) from 52 breeding adults in 2 consecutive years (2011 and 2012). In addition, GPS loggers were deployed on 11 individuals (and removed after several foraging trips) to infer the foraging behaviour of this species during the incubation period. Results suggest inter-annual differences in the feeding ecology and foraging behaviour of birds during the breeding season that were associated with the availability of food resources around the colony. Despite the high feeding plasticity and opportunistic behaviour of yellow-legged gulls, individual birds exhibited shortand long-term consistency in their feeding ecology, with exception of the period between winter and pre-laying. Our results support the hypothesis that individual feeding preferences throughout most of the annual cycle are an intrinsic characteristic of this population, and potentially of related opportunistic and generalist species.
Marine Biology, 2009
In estuaries, eelgrass meadows contribute to fundamental ecosystem functions of estuaries, provid... more In estuaries, eelgrass meadows contribute to fundamental ecosystem functions of estuaries, providing food to several predators and buVering the negative eVects of eutrophication. We asked whether the presence of the eelgrass Zostera noltii decreased the nitrogen concentration in the overlying water, aVected the sources of nitrogen sequestrated by primary producers and changed the benthic and pelagic food web structures. We also studied the importance of these food webs in providing food to Wsh. We compared bare sediment to sediment covered by a Z. noltii meadow, and examined nutrient concentrations in the water column and 15 N in primary producers as indicators of anthropogenic inputs of nutrients. We then measured both 13 C and 15 N in the tissues of plants and consumers to establish food web structures. There were no diVerences in the concentrations and sources of nitrogen between sites. Rather, 15 N values indicated anthropogenic inputs of N (e.g. sewage discharges, agriculture) in both sites. There were no major diVerences in the structure of the planktonic food web, which was in part sustained by particulate organic matter and supported most predator Wsh, and in the structure of the benthic food web. Nonetheless, there were diVerences in the sources of food for omnivore consumers and for the detritivore Scrobicularia plana. Overall, the benthic food web did not use food derived from the eelgrass or macroalgae deposited on the substratum. Suspension feeders used particulate and sediment organic matter, whereas the 13 C and 15 N values of the other consumers indicated a likely contribution of benthic microalgae. Furthermore, in both habitats we found large variability in the isotope signatures of benthic macrofauna consumers, which did not allow distinguishing clearly diVerent trophic groups and indicated a high level of omnivory and a mixed diet opportunistically making use of the availability of food in the surroundings.
Marine Biology, 2007
A restoration programme was introduced in the Mondego Estuary (Portugal) to recover seagrass beds... more A restoration programme was introduced in the Mondego Estuary (Portugal) to recover seagrass beds of Zostera noltii endangered by eutrophication. A long-term survey of 10 years was used to assess the development of the processes involved, focusing one of the key species (Cyathura carinata, Isopoda). The mitigation measures implemented since 1998 (nutrient loading reduction, freshwater circulation improvement and seagrass bed protection) enhanced water quality and seagrass recovery, thus preventing the development of macroalgal blooms. C. carinata was resilient to the occurrence of floods and macroalgal blooms, although both events caused dispersion of individuals. This isopod was not much influenced by the changes occurring in the estuary, showing an unalterable population structure during the entire study period. After 1998, its density and biomass became more stable at an inner unvegetated sand flat area, where this isopod was most abundant; its population slightly increased in a bare mud flat at the middle section of the estuary; but it could not establish successfully in a downstream Z. noltii bed, contrarily to other common estuarine species. Apart from other unknown reasons, the disrupted balanced between trematodes and their hosts, caused by the eutrophication processes, may have an important role in the discontinuity of C. carinata at the Z. noltii bed. If the intertidal areas become fully restored to the original seagrass coverage, high prevalence and intensity trematodes may prevent this isopod and other crustaceans from recovering within the intervened areas, by enhancing host mortality and recruitment failure. In order to avoid this kind of situation, it may be necessary to survey the levels of parasite infestation within the target hosts and safeguard areas where crustaceans present healthy populations.
Polar marine biology science in Portugal and Spain: Recent advances and future perspectives
Journal of Sea Research, 2013
Estuaries and Coasts, 2010
Anthropogenic activities are a disturbance factor of coastal systems and can be widely recognized... more Anthropogenic activities are a disturbance factor of coastal systems and can be widely recognized as a major threat to the health of coastal systems. However, natural events cannot be disregarded from management issues because of their significant influence on the communities living in these areas. Based on long-term subtidal data from the Mondego Estuary (Portugal), the effects of natural events (e.g., floods and droughts) on macrobenthic communities were compared with the anthropogenic events. Sampling stations were grouped into characteristic zones (mouth, north arm, south arm) so the community dynamics of each of these estuarine areas could be followed over time. Environmental assessment was performed for stations using the Benthic Assessment Tool (BAT), and compared with the existing pressures. Human impacts persist over a number of years and gradually reduce ecosystem health, as discussed in the European Water Framework Directive. Paradoxically, natural events cause stronger impacts but are of a shorter duration, which allows for a faster recovery of macrobenthic communities. The study showed that caution should be taken when developing and implementing water policies so as not to disregard the importance of the different events (natural and human-caused) on the ecosystem health (e.g., community degradation and water quality and ecological quality status assessment).
Niche segregation amongst sympatric species at exposed sandy shores with contrasting wrack availabilities illustrated by stable isotopic analysis
Ecological Indicators, 2014
Ecological Indicators, 2009
Ecological Indicators, 2013
The biomasses, carbon standing stocks, and exportations of three saltmarsh species -Scirpus marit... more The biomasses, carbon standing stocks, and exportations of three saltmarsh species -Scirpus maritimus, Spartina maritima and Zostera noltii -were determined and their isotopic composition analyzed to illustrate their role in carbon storage in a temperate Atlantic estuary (Mondego, Portugal). Biomass values were higher in the warmer seasons than in the cold seasons, with carbon contents following the same trend. Carbon content ranged from 27-39% in S. maritimus and S. maritima to 30-39% for Z. noltii. S. maritimus had the highest carbon production in the aboveground organs and had similar results with S. maritima in the belowground carbon production. These three species together occupied about 50% of the salt marsh area and they stored in 21 months of study 24,000 kg of carbon in their aboveground and belowground organs. Z. noltii presented highest carbon concentration in the sediment and S. maritimus the lowest. Stable carbon isotopic analysis showed that apparently, the sedimentary organic matter is composed by a mix of terrestrial sources, macro and microalgae. Regard the high carbon exportation, S. maritima and Z. noltii are constantly accumulating carbon. The studied species have both a sink and source behaviour simultaneously.
Marine Ecology Progress Series, 2014
Currently, a central demand of coastal and marine food web researchers is the search for holistic... more Currently, a central demand of coastal and marine food web researchers is the search for holistic and functional ecosystem health indicators. Based on concepts directly derived from R. L. Lindeman's work Ecology 23:399-418), 6 estuarine food web models were analysed to assess the potential impact of multiple disturbances on the trophic state of food webs. The models described a Zostera noltii meadow and a bare sediment site in the Mondego estuary, Portugal, during 3 distinct time periods corresponding to (1) nutrient enrichment, (2) the implementation of mitigation measures, and (3) after a centenary flood. We tested 4 candidate metrics, directly derived from the trophic-dynamic concepts proposed by Lindeman (1942): food chain length, the detritivory/herbivory ratio, trophic efficiency per trophic level and mean trophic efficiency. Based on this case study, none of the metrics are yet ready to be used per se as operational metrics to quantify and interpret the impact of disturbances on the ecosystem's trophic state. Trophic efficiency appeared to be sensitive to external pressures. However, the mean trophic efficiency of the system might not be sufficient to draw conclusions about the trophic efficiency of the ecosystem: trophic efficiency should be observed at the trophic level in order to better understand cascading effects within food webs.