Browsing by Author "Faria, Ana Margarida da Silva"
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- Are tidal lagoons ecologically relevant to larval recruitment of small pelagic fish? An approach using nutritional condition and growth ratePublication . Chicharo, Maria Alexandra; Araújo Amaral, Ana Margarida; Faria, Ana Margarida da Silva; Morais, R.; Mendes, C.; Piló, David; Ben-Hamadou, Radhouan; Chícharo, LuísThere are numerous studies dealing with larvae of Small Pelagic Fish (SPF), but only a few have actually addressed advanced larval phases. Temperate coastal lagoons are particularly understudied, due to the absence of standard method to capture advanced larval fish in these near shore shallow habitats. Accordingly, this study aims to describe abundances, nutritional condition and in situ growth of postflexion (SPF) from the Ria Formosa, a tidal coastal lagoon in southern Portugal. The nutritional condition and in situ growth were determined through cohort analysis and standardized RNA:DNA ratio (sRD), complemented with feeding incidence (gut content) and fatty acids (FAs, trophic biomarkers) of postflexion larvae sampled sequentially with light traps, from spring 2005 to summer 2006. Simultaneously, environmental parameters such as water temperature, salinity, dissolved oxygen and chlorophyll a were measured. Post-larvae of SPF were captured through the year in important numbers. The dominant species were Sardina pilchardus (50.7%), Engraulis encrasicolus and Atherina presbyter (11.4%). These results are distinct from those based on adult/juvenile surveys or early planktonic phases in the Ria Formosa where clupeiformes were occasionally reported. Sardines were captured mainly in winter, spring and early summer and anchovies mainly during summer and autumn. Sand smelt, a resident species, was present throughout the year. In the early summer, the three species were present and during this period some diet overlapping occurred, the feeding incidence of the clupeiformes was very low, but atherinids always exhibited full guts reflecting the different gut morphology or indicating different lifecycle strategies. The bulk of the diet was mollusks, crustaceans and appendicularians, for sand smelts, sardines and anchovies, respectively. The results of FA analyses showed some contribution of phytoplankton to SPF in the area. All SPF exhibited higher condition (sRD) and growth rates in summer, which are explained by the adequate temperature and higher planktonic productivity. This is especially relevant because the successful development of postflexion larvae in these nursery areas largely determines the successful recruitment to adult fish populations.
- How to sample larval fish for taxonomical and ecophysiological studies in shallower temperate coastal ecosystems?Publication . Chícharo, Luís; Faria, Ana Margarida da Silva; Morais, P.; Araújo Amaral, Ana Margarida; Mendes, Carlos; Chicharo, Maria Alexandra TeodosioRecruitment predictions for fish are often difficult to make due to the intrinsic variability of species and the incomplete sampling procedures. The aim of this study was to analyse the fish larval catches (abundance, diversity, size and damage) from a standard 500 mm ichthyoplankton net and different light traps (structure, size and light intensity) in temperate coastal turbid waters. Catches from different gear were always made on the same date or season, same location and same tidal phase. Results showed that light traps captured significantly bigger larvae (almost post-flexion) than those captured with the ichthyoplankton net, nevertheless the diversity was lower. Clupeidae species were the most represented taxon; nevertheless, the traps also caught Atherinidae, Gobiidae, Sparidae, Soleidae and Labridae. The light traps were less stressful devices, allowing the capture of live and active larvae. This showed other possible uses for the light trap, e.g. larval behavioural and physiological studies. Light traps constitute a good complementary sampling option for post-flexion larvae, being aware of species selectivity associated with their use.
- Ichthyoplankton dynamics in the Guadiana estuary and adjacent coastal area, South-East PortugalPublication . Faria, Ana Margarida da Silva; Morais, P.; Chicharo, Maria Alexandra TeodosioThe species composition, abundance and distribution of the ichthyoplankton of the Guadiana estuary and adjacent coastal area were studied in relation to several environmental parameters. Sampling occurred during new moon Spring tides, at the ebb and flood, at nine stations, from March 2002 to February 2003. Temperature, salinity, dissolved inorganic macronutrients, seston and organic matter and chlorophyll a were determined at each station. A total of 22 and 34 fish eggs and larvae taxa were identified, respectively. The highest abundances were registered in the lower and middle part of the estuary, probably due to the presence of species that use the estuary as a preferential spawning ground, mainly Pomatoschistus spp. and Engraulis encrasicolus sensu lato. Temporal patterns of occurrence of ichthyoplankton allowed each species’ spawning season to be determined. Two taxa dominated the ichthyoplanktonic community during spring and summer (Pomatoschistus spp. and E. encrasicolus), whereas Sardina pilchardus was particularly abundant during autumn and winter. The forcing variables responsible for community structure were chlorophyll a and seston for eggs, while temperature, salinity and nitrite explained the larval component. Comparisons of the results with previous ichthyoplankton studies of the Guadiana estuary conducted before the Alqueva dam was built also indicate that river flow has an important impact on the distribution and abundance of ichthyoplankton in the estuary.
- On the edge of death: rates of decline and lower thresholds of biochemical condition in food-deprived fish larvae and juvenilesPublication . Meyer, S.; Caldarone, E. M.; Chicharo, Maria Alexandra Teodosio; Clemmesen, C.; Faria, Ana Margarida da Silva; Faulk, C.; Folkvord, A.; Holt, G. J.; Hoie, H.; Kanstinger, P.; Malzahn, A.; Moran, D.; Petereit, C.; Stottrup, J. G.; Peck, M. A.Gaining reliable estimates of how long fish early life stages can survive without feeding and how starvation rate and time until death are influenced by body size, temperature and species is critical to understanding processes controlling mortality in the sea. The present study is an across-species analysis of starvation-induced changes in biochemical condition in early life stages of ninemarine and freshwater fishes. Datawere compiled on changes in body size (dry weight, DW) and biochemical condition (standardized RNA–DNA ratio, sRD) throughout the course of starvation of yolk-sac and feeding larvae and juveniles in the laboratory. In all cases, themean biochemical condition of groups decreased exponentially with starvation time, regardless of initial condition and endogenous yolk reserves. A starvation rate for individuals was estimated from discrete 75th percentiles of sampled populations versus time (degree-days, Dd). The 10th percentile of sRD successfully approximated the lowest, life-stage-specific biochemical condition (the edge of death). Temperature could explain 59% of the variability in time to death whereas DW had no effect. Species and life-stage-specific differences in starvation parameters suggest selective adaptation to food deprivation. Previously published, interspecific functions predicting the relationship between growth rate and sRD in feeding fish larvae do not apply to individuals experiencing prolonged food deprivation. Starvation rate, edge of death, and time to death are viable proxies for the physiological processes under food deprivation of individual fish pre-recruits in the laboratory and provide useful metrics for research on the role of starvation in the sea.
- Ontogeny of behavioural abilities in temperate reef fish larvaePublication . Faria, Ana Margarida da Silva; Gonçalves, Emanuel; Chícharo, AlexandraA maior parte das espécies associadas a recifes possui uma fase larvar pelágica, seguida de uma fase juvenil e adulta demersal. A fase pelágica pode apresentar consideráveis capacidades de dispersão. A visão tradicional, baseada em estudos de um conjunto limitado de espécies de sistemas temperados, pressupunha que as capacidades natatórias das larvas no plano horizontal eram muito limitadas e, dessa forma, irrelevantes para o potencial de dispersão. Segundo esta perspectiva, a dispersão era essencialmente explicada por fenómenos de transporte passivo e a única informação necessária para modelar a dispersão seriam as correntes e a duração da fase larvar. No entanto, nas últimas duas décadas, a investigação do comportamento natatório das larvas de recifes tropicais veio provar que as larvas estão longe de serem partículas passivas, e têm capacidades comportamentais consideráveis, capazes de influenciar os seus padrões de dispersão. Apesar dos recentes avanços nos estudos de comportamento larvar em peixes de recifes tropicais, os estudos de comportamento em peixes temperados são ainda escassos. Nesse sentido, esta tese representa um significativo contributo para o estudo das capacidades natatórias de peixes de sistemas temperados. A ontogenia do comportamento natatório foi investigada em quatro espécies temperadas (2 Gobiesocidae, 1 Sparidae, 1 Soleidae) e uma espécie temperada-quente (Sciaenidae). Os resultados sugerem que a diferença de capacidades natatórias entre espécies tropicais e temperadas não é significativa quando aspectos taxonómicos, morfológicos e estados de desenvolvimento são tidos em conta. Adicionalmente, foi analisada a influência da condição nutricional no comportamento natatório e observou-se que larvas em inanição são capazes de levar a cabo comportamentos de fuga a predadores e captura de presas, mas em termos de potencial de dispersão, estas larvas são significativamente afectadas, compromentendo assim a sua sobrevivência e futuro recrutamento.
- Ontogeny of swimming behaviour in sardine Sardina pilchardus larvae and effect of larval nutritional condition on critical speedPublication . Silva, L.; Faria, Ana Margarida da Silva; Chicharo, Maria Alexandra Teodosio; Garrido, SusanaThe ontogeny of swimming behaviour in sardine Sardina pilchardus larvae was studied, from hatching to 75 days post-hatch (dph), by measuring the critical swimming speed (Ucrit) and observing locomotory behaviour. In addition, the effect of larval nutritional condition on Ucrit at the onset of their swimming abilities (20 to 25 dph) was evaluated by rearing larvae under 4 different feeding treatments. Diets consisted of different concentrations of dinoflagellates, rotifers and the copepod Acartia grani, and a wild plankton assemblage. Recently hatched larvae were mostly inactive, but from 2 dph onwards larvae started to swim freely in the rearing tank, and time spent swimming increased throughout ontogeny. Larvae younger than 20 dph (i.e. <7.90 mm TL) could not swim for the entire adjustment period at the minimum current speed, but thereafter Ucrit increased significantly with larval age and length, reaching a maximum of 9.47 cm s-1 at 19.10 mm TL and 55 dph. Growth, survival and the nutritional condition of sardine larvae, assessed by the RNA residual index, were significantly higher for larvae reared with the high-concentration diet, contrary to the other derived nucleic acids indices (RNA/DNA and DNA/DW), which showed no differences between diets. Despite differences in the survival and growth rates of sardine larvae, Ucrit at the onset of swimming did not differ significantly among diets, but was significantly related to larval nutritional condition as assessed by the RNA residual index. Overall, our results show that early larval stages of sardines have poor swimming ability and probably rely on food patches in the wild to survive; however, close to metamorphosis (especially from 45 dph onwards), larvae spend most of the time swimming and are capable of resisting the mean current speeds of their natural environment, which may strongly enhance chances for survival.
- The unexpected occurrence of late Sardina pilchardus (Walbaum, 1792) (Osteichthyes: Clupeidae) larvae in a temperate estuaryPublication . Morais, P.; Faria, Ana Margarida da Silva; Teodosio, Maria; Chícharo, LuísThe 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.