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- Factores que influenciam a abundância e condição nutricional das larvas de peixes nos rios Mira e GuadianaPublication . Esteves, Eduardo; Andrade, José PedroA investigação sobre os mecanismos que regulam o recrutamento tem sido tema de vários estudos desde o início deste século e várias hipóteses têm sido apresentadas para explicar as flutuações no recrutamento. Entre os contributos mais recentes para a compreensão daqueles mecanismos encontra-se a análise da condição nutricional, sendo que o desenvolvimento de técnicas que possibilitem avaliar a taxa de crescimento das larvas e que permitem distinguir a sua condição nutricional tem sido tema central da investigação recente em ictioplanctonologia. De entre as várias metodologias existentes destaca-se a análise de componentes químicos, designadamente os ácidos nucleicos e proteinas, e o cálculo de índices de condição (razões RNA/DNA, PROT/DNA ou PROT/RNA, por exemplo). A aplicação destes índices ecofisiológicos de condição permitirá esclarecer, embora preliminarmente, a importância relativa de alguns factores que determinam a mortalidade larvar e o recrutamento. Assim, neste trabalho pretendeu-se, por um lado, adaptar, aplicar e comparar técnicas para a determinação de ácidos nucleicos e proteínas às larvas de peixe recolhidas nos rios Mira e Guadiana e, por outro, estudar a influência da temperatura, da salinidade e da abundância de potenciais presas e predadores sobre a distribuição espacial e nictemeral das larvas de peixe (Clupeidae, Engraulidae, Gobiidae, Blennidae e Atherinidae) e a sua condição nutricional. Entre Março e Setembro de 1997, recolheram-se amostras de micro-, meso- e ictioplâncton e registou-se a temperatura e salinidade superficiais, em 18 estações estabelecidas nos rios Mira (n=8, ~30 km do rio) e Guadiana (n=10, ~178 km do rio). Complementarmente, foram colhidas amostras durante ciclos de 24 horas de amostragem realizados em Vila Nova de Milfontes e Vila Real de Santo António em Maio, Junho, Julho e Setembro. No laboratório triaram-se as amostras formolizadas e identificaram-se os organismos recolhidos. As larvas de peixe congeladas em azoto líquido foram identificadas e os conteúdos em ácidos nucleicos determinados com duas técnicas fluorimétricas. Compararam-se os resultados obtidos com os dois protocolos e calcularam-se equações para a sua inter-calibração. As proteínas foram determinadas com um método espectrofluorimétrico. Estudaram-se as relações entre a densidade dos ovos e das larvas de peixe (ind. 100 m-3) e a condição nutricional larval (razões RNA/DNA, PROT/DNA, PROT/DNA e Gpi) e os parâmetros abióticos e bióticos considerados através de análise de correlação e regressão múltipla. Os ovos e larvas de peixe foram relativamente pouco comuns. Os estados larvares ocorreram geralmente em densidades inefriores a 100 ind. 100 m-3, excepto nos ciclos de e ocorreram de forma diferente à descrita na literatura. A distribuição espacial e nictemeral dos ictioplanctontes parece reflectir, por um lado, o comportamento reprodutivo dos adultos e, por outro, a influencia de factores hidrológicos. A anchova, os gobiídeos e os blenídeos parecem incluir-se no primeiro grupo, enquanto os clupeídeos integraram o segundo. Entre os parâmetros estudados, a temperatura e a abundância de alguns taxa de predadores potenciais explicaram parte significativa da variabilidade da densidade ictioplanctónica (R2<0,88). A temperatura constitui um factor estruturante de habitats e biologicamente limitante, enquanto a predação determina a mortalidade larvar. Os resultados da comparação de metodologias de quantificação de ácidos nucleicos confirmaram a ideia de que os valores obtidos variam com o protocolo usado. Alguns aspectos das metodologias, designadamente a interferência dos compostos utilizados para purificar os homogeneizados ou a actividade variável da ribonuclease, poderão explicar as diferenças encontradas. Por outro lado, verificou-se que os métodos se aplicam de modo diferente às populações larvares estudadas. No entanto, calcularam-se equações para inter-calibração de resultados entre técnicas. Em função dos aspectos metodológicos discutidos neste estudo, o método de Caldarone & Buckley (1991) apresentou vantagens importantes (simplicidade, rapidez e maior número de larvas analisadas por periodo de tempo) e que aconselham a sua utilização para estudos de rotina da condição nutricional larvar. A generalidade das larvas encontravam-se em boas condições nutricionais, sendo que as percentagens de larvas com RNA/DNA<1,3 ou 1,0 não ultrapassaram 14% (11 - 13% nos blenídeos e <7,1% nas restantes famílias). Os resultados da análise das percentagens de larvas em estado de inanição através de Gpi<0% dia-1 confirmaram genericamente os referidos acima. A condição nutricional larvar correlacionou-se significativamente com a temperatura e com maior número de variáveis indicadores da abudância de potenciais presas relativamente aos predadores potenciais (R2£0,95). A temperatura influencia o metabolismo das larvas e a disponibilidade de alimento condiciona a sobrevivência larvar. Apenas se obtiveram diferenças significativas entre rios nos valores médios da razão RNA/DNA para gobiídeos. O número de larvas analisadas, a aplicabilidade das metodologias e o impacte distinto dos factores abióticos e bióticos estudados poderão explicar aqueles resultados. As maiores percentagens de larvas em estado de inanição (>5,6%) verificaram-se no rio Mira, designadamente em clupeídeos e blenídeos. Pelo contrário, os gobiídeos e aterinídeos encontravam-se em piores condições no rio Guadiana (>2,9%). Tendo em consideração que a disponibilidade de alimento foi relativamente semelhante nos dois rios, a temperatura e abundância de predadores parecem ter sido os factores mais determinantes. A temperatura influencia a distribuição e a condição nutricional larvar, através do seu efeito sobre as taxas de crescimento e mortalidade, enquanto os predadores poderão remover as larvas em piores condições. Em conclusão, a distribuição das larvas de peixe parece condicionada pela temperatura e pela pressão da predação, enquanto a condição nutricional parece depender da temperatura e da disponibilidade de alimento, sendo, no entanto, controlada pela predação, através da sua acção sobre a mortalidade larvar. Os modelos empíricos obtidos para a distribuição da densidade (R2<0,88) e para análise de condição larvar (R2<0,95) parecem confirmar estas hipóteses.
- A global synthesis of ecosystem services provided and disrupted by freshwater bivalve molluscsPublication . Zieritz, Alexandra; Sousa, Ronaldo; Aldridge, David C.; Douda, Karel; Esteves, Eduardo; Ferreira-Rodriguez, Noe; Mageroy, Jon H.; Nizzoli, Daniele; Osterling, Martin; Reis, Joaquim; Riccardi, Nicoletta; Daill, Daniel; Gumpinger, Clemens; Vaz, Ana SofiaIdentification of ecosystem services, i.e. the contributions that ecosystems make to human well-being, has proven instrumental in galvanising public and political support for safeguarding biodiversity and its benefits to people. Here we synthesise the global evidence on ecosystem services provided and disrupted by freshwater bivalves, a heterogenous group of >1200 species, including some of the most threatened (in Unionida) and invasive (e.g. Dreissena polymorpha) taxa globally. Our systematic literature review resulted in a data set of 904 records from 69 countries relating to 24 classes of provisioning (N = 189), cultural (N = 491) and regulating (N = 224) services following the Common International Classification of Ecosystem Services (CICES). Prominent ecosystem services included (i) the provisioning of food, materials and medicinal products, (ii) knowledge acquisition (e.g. on water quality, past environments and historical societies), ornamental and other cultural contributions, and (iii) the filtration, sequestration, storage and/or transformation of biological and physico-chemical water properties. About 9% of records provided evidence for the disruption rather than provision of ecosystem services. Synergies and trade-offs of ecosystem services were observed. For instance, water filtration by freshwater bivalves can be beneficial for the cultural service ‘biomonitoring’, while negatively or positively affecting food consumption or human recreation. Our evidence base spanned a total of 91 genera and 191 species, dominated by Unionida (55% of records, 76% of species), Veneroida (21 and 9%, respectively; mainly Corbicula spp.) and Myoida (20 and 4%, respectively; mainly Dreissena spp.). About one third of records, predominantly from Europe and the Americas, related to species that were non-native to the country of study. The majority of records originated from Asia (35%), with available evidence for 23 CICES classes, as well as Europe (29%) and North America (23%), where research was largely focused on ‘biomonitoring’. Whilst the earliest record (from 1949) originated from North America, since 2000, annual output of records has increased rapidly in Asia and Europe. Future research should focus on filling gaps in knowledge in lesser-studied regions, including Africa and South America, and should look to provide a quantitative valuation of the socio-economic costs and benefits of ecosystem services shaped by freshwater bivalves.
- Nitrate reductase activity in green macroalgae as an environmental indicator of temperature and salinity changes and its implication for climate change projectionsPublication . Madeira, Hélder T.; Aníbal, Jaime; Carvalho, Liliana F.; Esteves, Eduardo; Veiga-Pires, C.Temperature and salinity changes can affect nutrient assimilation dynamics in primary producers. Green macroalgae use nitrate as a main source of nitrogen for their metabolism. Nitrate needs to be reduced by nitrate reductase, before amino acids synthesis. Our aims were to study the effect of temperature and salinity changes on nitrate reductase activity (NRA) in Ulva rigida and Enteromorpha clathrata, and to assess if this enzyme can be used as an environmental indicator for changes in such abiotic factors. The study of NRA was carried out using potassium nitrate as substrate and propanol as a membrane permeabilizer, letting the produced nitrite to exit the macroalgae cells into the assay medium, allowing its quantification through a colorimetric method. This procedure was carried out at five temperatures (10, 20, 30, 35 and 40 °C) and three salinities of the assay medium (0, 15 and 36 g/kg). Results show that both Ulva and Enteromorpha have maximum NRA at salinities of 36 g/kg, although nitrate reduction can occur in freshwater or brackish water, but at significantly lower rates. NRA varied significantly with temperature for both macroalgae, although Ulva showed maximum NRA at 30 °C, while NRA peaked at 35 °C in Enteromorpha. Likely adequate models were tentatively fitted to NRAtemperature data at different salinities. NRA is a suitable proxy of the effects of temperature and salinity changes on the ability of green macroalgae to uptake and metabolize nitrogen nutrients and can thus be the base for macroalgae proliferation models under climate change model scenarios.
- A importância da avaliação sensorial da qualidade do pescadoPublication . Esteves, E.; Aníbal, J.Globalmente, a pesca é uma indústria que movimenta milhares de milhões de euros por ano (as importações e exportações de produtos da pesca atingiram, em 2005, cerca 82 mil milhões de euros e 78 mil milhões de euros, respectivamente, dados da FAO – Food and Agriculture Organization das Nações Unidas).
- Regressão não-linear utilizando a ferramenta Solver® do Microsoft Excel®Publication . Esteves, EduardoEm vários domínios do conhecimento científico são usados modelos matemáticos para descrever um conjunto de dados empíricos. Se no caso dos modelos lineares, a análise de regressão para obter os parâmetros dos modelos é "simples" e vulgarizada, é mais difícil ajustar aos dados funções (matematicamente) mais "complicadas", p.ex. modelos não-lineares. Neste artigo, pretende-se 1) apresentar os conceitos fundamentais da análise de regressão não-linear, 2) descrever, usando um exemplo, a utilização da ferramenta Solver® do Microsoft Excel® para analisar problemas cujo objectivo é "descrever" relações estatísticas (não-lineares) entre variáveis, e 3) compilar os "problemas" identificados com a utilização do Excel® (incluindo o Solver®) como ferramenta de análise estatística.
- Seasonal variations in gross biochemical composition, percent edibility, and condition index of the clam Ruditapes Decussatus cultivated in the Ria Formosa (South Portugal)Publication . Aníbal, J.; Esteves, E.; Rocha, C.The grooved carpet shell clam, Ruditapes decussatus (L. 1758), is one of the most popular and profitable molluscs exploited in rearing plots in the Mediterranean. However, annual catch has been declining steadily since the early nineties. In order to understand the seasonality of its nutritional value, thus providing an improved basis for economical valuation of the resource, gross biochemical composition, percentage edibility and condition index were investigated during a year with monthly periodicity in a commercially exploited population of the clam Ruditapes decussatus in the Ria Formosa, a temperate mesotidal coastal lagoon located in the south of Portugal. Our results show that total and non-protein nitrogen co-varied during the year, resulting in a protein content that peaked in the warmest months. Although complementary in summer, carbohydrate and lipid contents showed irregular annual trends. The observed seasonality was comparable to that shown by studies elsewhere at similar latitudes, and are underpinned by the reproductive cycle of the species. Our results show the clams to be at their prime nutritional value at the beginning of summer, when protein content peaks.
- Macroalgae mitigation potential for fish aquaculture effluents: an approach coupling nitrogen uptake and metabolic pathways using Ulva rigida and Enteromorpha clathrataPublication . Aníbal, J.; Madeira, Hélder T.; Carvalho, Liliana F.; Esteves, E.; Veiga-Pires, C.; Rocha, CarlosAquaculture effluents are rich in nitrogen compounds that may enhance local primary productivity, leading to the development of algae blooms. The goal of this study was to assess the potential use of naturally occurring green macroalgae (Ulva and Enteromorpha) as bioremediators for nitrogen-rich effluents from a fish aquaculture plant, by evaluating their respective uptake dynamics under controlled conditions. Ulva and Enteromorpha were incubated separately in aquaculture effluent from a local pilot station. Algae tissue and water samples were collected periodically along 4 h. For each sample, nitrate, nitrite, and ammonia concentrations were quantified in the effluent, while internal algae reserve pools and nitrate reductase activity (NRA) were determined within the algae tissues. Both macroalgae absorbed all dissolved inorganic nitrogen compounds in less than 1 h, favoring ammonia over nitrate. Ulva stored nitrate temporarily as an internal reserve and only used it after ammonia availability decreased, whereas Enteromorpha stored and metabolized ammonia and nitrate simultaneously. These distinct dynamics of ammonia and nitrate uptake supported an increase in NRA during the experiment. This study supports the hypothesis that Ulva or Enteromorpha can be used as bioremediators in aquaculture effluents to mitigate excess of dissolved inorganic nitrogen.
- Ecology of the early life-history stages of shad Alosa fallax fallax (Lacépède, 1803) in the River Mira, with a note on Alosa spp. larvae in the River GuadianaPublication . Esteves, E.; Andrade, José PedroAllis and Twaite shad Alosa spp. are anadromous clupeid species, which still migrate into several rivers along Portugal to spawn but are regarded as Endangered or Vulnerable (using IUCN criteria). Within the framework of a countrywide research project, this dissertation reports the work carried out (from February 1998 until July 2000) to study the biology and ecology of the early life-history stages of Twaite shad, Alosa fallax fallax, in the River Mira (with a final note on Alosa spp. in the River Guadiana). Twaite shad larvae were more abundant in the surface waters during the day whereas no diel abundance pattern was observed for embryos (i.e. yolk-sac larvae). Furthermore, eggs, embryos and larvae were only found in the upstream stations of River Mira from late-March until mid- June. As expected, no habitat selection occurs at either the egg or embryonic life stages. Conversely, shad larvae abundances were related to several environmental co-variates through a complex non-linear generalised additive model (GAM). Paired translucent and opaque rings in a regularly-recurring sequence deposited around the sagittae of A. fallax fallax were readily visible. The high proportion of sagittae used suggests the usefulness of otolith microstructural analysis to estimate age and to study growth and morality of larvae. Growth and mortality rates varied seasonally (ranging from 0.36 to 0.60 mm d -1 and from 16 to 30 % d -1 , respectively). In a typical year, larvae are in better nutritional condition (RNA/DNA ratio) during two relatively short time-periods, around mid-April and mid to late?May when water temperatures average 22 ?C and levels of prey are <80 nauplii 100 m -3 . Conversely, RNA/DNA are significantly reduced when water turbidity is higher than 2 mg DW m -3 and potential prey are readily available (>20 nauplii 100 m -3 ). The few occurrences of Alosa spp. embryos and larvae in the River Guadiana and the tributary Ribeira de Odeleite precluded sensible analysis. Future topics of research to clarify some issues or directed at unanswered questions are proposed.
- Effects of alterations in fresh water supply on the abundance and distribution of Engraulis encrasicolus in the Guadiana estuary and adjacent coastal areas of south PortugalPublication . Chícharo, Luís; Chicharo, Alexandra; Esteves, E.; Andrade, José Pedro; Morais, P.A reduction of inflow to the Guadiana River on the border between Portugal and Spain may directly contribute to the degradation of fish habitats. Changes are expected to the spawning behaviour of Engraulis encrasicolus adults, to the migration patterns of larvae in the estuary, and to the catches of fisheries in the lower part of the river and adjacent coastal areas. Spawning of E. encrasicolus occurs in the lower part of the estuary and in the adjacent coastal areas. However, high abundances of larvae have been registered in the middle and upper parts of the estuary, the most productive region of the estuary, that with the estuarine turbidity maximum (ETM). In a year of normal inflow, such as the hydrologic year 1987-1988, some retention of larvae occured in this area. However, in an abnormal hydrologic year with a low inflow (1999-2000), and with an increase in freshwater inflow during the spring months, a disturbance to the migration pattern seems to have affected the survival of larvae in the estuary. High river flow, probably associated with an increased input of nutrients, appears to have important und positive effect on adult numbers, because anchovy fishery catches in the adjacent coastal area increased under these conditions.
- Age and growth in the Alfonsino, Beryx splendens (Berycidae) from the Azores (central eastern Atlantic)Publication . Aníbal, J.; Esteves, Eduardo; Krug, H.; Silva, H. M. daAge was determined in the Alfonsino, Beryx splendens, by counting the opaque rings on the anti‐sulcal surface of left sagittae obtained from specimens, 15–43.5 cm fork length (FL), caught off the Azores. Females were from 1 to 12 years old and males were 1 to 9 years old. Von Bertalanffy (VB) growth equations were fitted to data obtained from age‐length keys, back calculation, and length‐frequency analyses. Growth was compared between sexes and among methods. Growth was similar in males, whereas in females the equations derived from length‐frequency analysis overestimated length‐at‐age relative to other methods. Sex specific growth could not be confirmed.