DINÂMICA POPULACIONAL DE ENGRAULIS ENCRASICOLUS LINNAEUS, 1758 NO ESTUÁRIO DO GUADIANA E NA ZONA COSTEIRA ADJACENTE

Funder

Organizational Unit

Publications

The unexpected occurrence of late Sardina pilchardus (Walbaum, 1792) (Osteichthyes: Clupeidae) larvae in a temperate estuary

Publication . Morais, P.; Faria, Ana Margarida da Silva; Teodosio, Maria; Chícharo, Luís

The presence of sardine larval stages inside estuaries has generally been regarded as accidental and restricted to the lower part of estuaries. Sampling done with a zooplankton net in the Guadiana estuary corroborated this hypothesis. Late sardine larvae (32.8 ± 2.0 mm) were, however, unexpectedly collected with an otter trawl, 14 km upstream from the mouth of the estuary. Thus, this work intends to: (1) discriminate and compare the abiotic characteristics of the sites where maximum abundance of sardine larval stages were registered, when captured with a zooplankton net, with the characteristics of the sites where late sardine larvae were collected with an otter trawl; (2) demonstrate that the presence of the late sardine larvae inside the Guadiana estuary was not accidental. The average salinity of the site were late larvae where collected was 4.2 ± 2.3, i.e. 87.3% lower than the average salinity where maximum abundance of early larvae was registered. We suggest that the presence of the late sardine larvae inside the Guadiana estuary was not accidental. In order to migrate to that location and remain in the estuary, counteracting river inflow, these late larvae must have employed active migration and retention strategies. New methodologies need to be implemented for routine sampling of all larval stages of sardine, in order to achieve a complete understanding of their life cycle.

2009Journal article

Open Access

Effect of sex on ratios and concentrations of DNA and RNA in three marine species

Publication . Chicharo, Alexandra; Amaral, Ana Margarida Araújo; Morais, P.; Chícharo, Luís

The aim of the present study was to quantify differences in RNA:DNA ratios between male and female fish Pomatoschistus microps, crustaceans Crangon crangon, and bivalves Ruditapes decussatus. RNA:DNA ratios were greater in females than in males, especially because of a greater RNA content per unit dry weight in females. Sexual dimorphism in addition to physiological and behavioural differences between males and females may account for these results. RNA:DNA ratios of adult marine organisms should be interpreted with caution, because the effect of sex on nucleic acid concentrations may bias results if the sex ratio in the sample from which results were derived is not representative of the population.

2007Journal article

Open Access

The life cycle of Engraulis encrasicolus sensu lato in the Guadiana estuary: Ecology, Ecohydrology and Biology

Publication . Morais, P.; Chícharo, Alexandra

O estuário do Guadiana é o segundo estuário português mais bem conservado, mas também o segundo mais vulnerável aos impactes antropogénicos. As barragens são uma das principais fontes de impactes na bacia do Guadiana. Uma visão holística é então necessária para a melhor gestão deste ecossistema, a qual tem vindo a ser alcançada com uma abordagem ecohidrológica. Os objectivos principais deste trabalho foram compreender a dinâmica do estuário do Guadiana e da zona costeira adjacente, durante o primeiro ano de enchimento da barragem de Alqueva; estudar o ciclo de vida do biqueirão Engraulis encrasicolus sensu lato neste estuário e integrar a informação da abundância e distribuição dos ovos num modelo hidrodinâmico do estuário, para a criação duma ferramenta de gestão ecohidrológica. Durante o enchimento desta barragem, o caudal foi preponderante na definição das alterações abióticas e bióticas na área de estudo. As principais mudanças foram o deslocamento do máximo de turbidez do estuário para montante, a alteração da dinâmica de nutrientes nas secções médias e altas do estuário e o aumento do fornecimento de nutrientes ao estuário para níveis apenas registados durante anos hidrológicos com caudais elevados. Uma descarga não controlada da barragem de Alqueva provocou a advecção dos estados larvares de biqueirão para a zona costeira. A desova deste peixe é feita no interior do estuário por espécimens residentes. Em condições de caudal reduzido (Q< 3.2 ± 0.1 m3.s-1), a transição entre o baixo e o médio estuário constitui o local ideal para a desova. A zona de transição entre o médio e o alto estuário é o local de desenvolvimento das larvas e juvenis. Os adultos encontram-se predominantemente a jusante destes locais. Biqueirões adultos foram capturados na zona terminal do estuário e na pluma apenas durante períodos de cheia (Q> 3000 m3.s-1). O biqueirão presente no estuário do Guadiana era geneticamente idêntico ao da zona costeira adjacente, podendo ser a espécie que foi recentemente descrita- Engraulis albidus. As análises isotópicas de carbono e oxigénio aos otólitos indicaram que são duas populações. A concentração de Sr, ao longo dos otólitos de espécimens da população costeira, indicou que esta é formada maioritariamente por indivíduos provenientes de estuários. O modelo ecohidrológico permitiu avaliar os impactos sobre a permanência dos ictioplanctontes no estuário, quando o caudal é gerido de forma a prevenir ou mitigar situações de eutrofização no alto estuário do Guadiana. Dos vários perfis de caudal testados, apenas os de caudais máximos de 20 m3.s-1 e 50 m3.s-1 não comprometem a presença de ictioplanctontes no interior do estuário. Esta ferramenta tem o potencial para ser aplicada noutros ecossistemas e deve ser desenvolvida e melhorada.

2007Doctoral thesis

Open Access

MOHID as a tool to evaluate the impact of water discharge from dams on the advection of estuarine fish larval stages

Publication . Morais, P.; Martins, Flávio Augusto Bastos da Cruz; Chicharo, Maria Alexandra Teodosio; Lopes, J.; Chícharo, Luís

The impoundment of rivers by dams is the biggest direct anthropogenic impact on the hydrological cycle. The utility of dams, as providers of water for human consumption, irrigation and electrical production, is undeniable. However, the price to pay, weighting benefits versus ecological impacts caused by dams, is enormous and often questionable. The deleterious ecological impacts caused by dams are detected at the dam’s site are and at hundreds of kilometers downstream from dams, even in estuaries and coastal areas. The uncontrolled water discharge from dams, both high volumes of water and inappropriate timing, compromise fish recruitment because eggs are flushed from estuarine spawning and nursery areas. Thus, our goal was to develop an hydrodynamic modelling approach that evaluates the impact of water discharge from dams on the advection of fish larval stages off estuaries and into coastal areas. This goal was accomplished by merging the abundance of anchovy eggs along the Guadiana estuary in MOHID.

2013Book part

Open Access

An ecohydrology model of the Guadiana Estuary (South Portugal)

Publication . Wolanski, Eric; Chícharo, Luís; Teodosio, Maria; Morais, P.

A 1-D ecohydrology model is proposed that integrates physical, chemical and biological processes in the Guadiana Estuary during low flow conditions and that predicts the ecosystem health as determined by the following variables: river discharge, nutrients, suspended particulate matter, phytoplankton, zooplankton, bivalves, zooplanktivorous fish and carnivorous/omnivorous fish. Low flow conditions prevail now that the Alqueva dam has been constructed. The ecological sub-model is based on the non-linear Lotka-Volterra equation. The model is successful in capturing the observations of along-river changes in these variables. It suggests that both bottom-up and top-down ecological processes control the Guadiana Estuary ecosystem health. A number of sensitivity tests show that the model is robust and can be used to predict e within likely error bounds provided by the sensitivity tests e the consequences on the estuary ecosystem health of human activities throughout the river catchment, such as the irrigation farming downstream of the Alqueva dam, reclamation of the salt marshes by urban developments, and flow regulation by the Alqueva dam. The model suggests that the estuarine ecosystem health requires transient river floods and is compromised by flow regulation by the Alqueva dam. Remedial measures are thus necessary.

2006Journal article

Open Access