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- Linking hydrodynamics and fish larvae retention in estuarine nursery areas from an ecohydrological perspectivePublication . Teodosio, Maria; Garel, ErwanGlobal change is affecting freshwater flow into estuarine nursery areas, with effects on fish larvae retention. Until now, related studies usually considered all early phases of fishes as passive drifters. However, the swimming behaviour of temperate fish larvae in these areas with strong tides and freshwater inflow is poorly described. The goal of this study was to review the swimming abilities of temperate fish species through ontogeny, the influence of nutritional conditions and how they are able to cope with hydrodynamics changes in nursery areas (including extreme freshet events resulting from dam management), using the Guadiana Estuary as a case study. The ontogeny of the swimming behaviour of estuarine fish larvae from different taxonomic groups was analyzed using the maximum sprint or critical swimming speed (Ucrit). Those results were compared with current observations performed under various tidal and river discharge conditions. In addition, the effect of larval nutritional condition on swimming abilities was also discussed. Overall, most of the species presented skills to be retained inside nursery areas, using distinct strategies. Those involve short term directional horizontal swimming against the axial currents, vertical migration and the use of residual upstream flows, especially over shallower areas. Nevertheless, during high freshet events all the studied species larvae will be flushed out of the estuary with consequent survival threaten. Extensive investigations are needed to thoroughly explore the relation of in situ behavioural responses of fish larvae and small scale estuarine hydrodynamics, towards a sustainable ecohydrological management of nurseries in flow regulated estuaries.
- Effects of starvation on swimming performance and body condition of pre-settlement Sparus aurata larvaePublication . Faria, Ana M.; Gonçalves, Emanuel J.; Chicharo, AlexandraBody condition in larval fishes is an important determinant of survival in the natural environment. However, few studies correlate body condition with behavioural traits critical for survival, such as swimming performance. In the present study, we compared normally fed larvae of gilthead seabream Sparus aurata Linnaeus, 1758, at various intervals post-hatch with larvae which were starved for 1 to 3 d (for Ucrit) or 2 d (for swimming endurance). Feeding treatment (fed and or unfed) had no effect on the relationship between Ucrit and larval size. However, in the endurance experiment, fed individuals swam twice as far as unfed larvae (19.7 km for fed larvae and 9.5 km for unfed larvae). The RNA/DNA ratio was higher in fed larvae in the Ucrit experiment, but significant effects were only detectable after a 3 d period of starvation. Fulton’s condition factor was significantly higher in fed larvae in the endurance trial, which suggests that growth (in weight) of starved larvae was affected by long-term swimming. Taken together, these results suggest that for aging and orientation behaviours (activities in which critical speeds might be involved) are not affected by reduced feeding over a few days, but that sub-lethal effects of starvation may affect dispersal potential (for which endurance swimming is critical) and therefore compromise subsequent recruitment to the adult population.
- The DNA/RNA ratio as a useful indicator of the nutritional condition in juveniles of Ruditapes decussatusPublication . Chícharo, Luís; Teodosio, MariaCondition indices have been widely used to assess how healthy individuals are under certain circumstances. It has been shown that the RNA/DNA ratio is a good indicator of the nutritional condition of severa1 marine organisms. A very sensitive fluorometric method for RNA/DNA quantification (Clemmesen, 1990) was applied to fed and starved post-larvae laboratory-reared clam, Ruditapes decussatus. The presented study shows that the RNA/DNA ratio is a useful indicator of nutritional stress for bivalve spat. The decrease in RNA/DNA ratio recorded here, under starved conditions was lower than in similar experiments on fish. A lower metabolic rate in clams may result in a slower response with respect to RNA/DNA ratios than that observed in vertebrates.
- Nutritional condition and starvation in Sardina pilchardus (L.) larvae off southern Portugal compared with some environmental factorsPublication . Chicharo, Maria Alexandra TeodosioThe aim of this study was to determine the condition and the incidence of starvation among field-caught Sardina pilchardus larvae, using RNA/DNA ratios and to compare them with various abiotic and biotic factors. S. pilchardus larvae were collected off southern Portugal, during April and May 1992. A highly sensitive fluorometric method for quantifying larvae nucleic acid was applied. Sardine larvae were generally in good condition. The means of the RNA/DNA ratios were relatively high and low percentages of starving larvae (RNA/DNA ratio ,1.3) were recorded, ranging from 0 to 12.5%. These two results were associated with high prey availability, which contributes to enhanced condition, and with a high density of potential predators, which may result in fewer larvae in poor condition.
- Assessing the impact of environmental forcing on the condition of anchovy larvae in the Cadiz Gulf using nucleic acid and fatty acid-derived indicesPublication . Teodosio, Maria; Garrido, Susana; Peters, J.; Miguel de Sousa Leitão, Francisco; Re, P.; Peliz, A.; Santos, A.M.P.Understanding the environmental processes affecting fish larvae survival is critical for population dynamics,"conservation purposes and to ecosystem-based fishery management. Using anchovies (Engraulis encrasicolus) of the Cadiz Gulf as a study case and considering the "Ocean Triad" hypothesis, we investigate the larval ecophysiological status and potential survival in relation to oceanographic variables. Therefore, this study aims to describe the nutritional condition of anchovy larvae during spawning season (peak in summer) through nucleic acid- and fatty acid (FA)-derived indices and to analyze the effects of the major environmental parameters (Depth, Temperature, Salinity, Plankton biomass) on anchovy survival potential at early phases. Fish larvae were collected in August from 30 m to 400 m depth at 35 stations off the southern Iberian coast. A previous upwelling event influenced the oceanographic conditions of the more western stations off Cape Sao Vicente (CSV). Along the coast, the water became warmer from west to the east through Cape Santa Maria (CSM) ending at Guadiana estuary, where easterly winds originated the development of a counter current. The standardized RNA/ DNA (sRD) of anchovy larvae decreased throughout larval ontogeny, reflecting a reduction of growth during the development. Essential FA concentrations also decreased, but docosahexaenoic acid (DHA) in particular was highly conserved even after the reduction of total FA concentration in anchovy larvae related to the onset of swimming abilities (post-flexion phase). The oceanographic conditions (west upwelling, east counter current, and stratification) led to a nearshore aggregation of plankton and anchovy larvae with good ecophysiological conditions in the central area of the southern coast, where an optimal range of temperature and chlorophyll, as an indirect food proxy for anchovy larval development, were registered. The study proves that the oceanographic conditions of the study area are putative drivers of the ecophysiological condition of anchovy larvae to guarantee potential survival, supporting the "Ocean Triad" hypothesis with major repercussions for recruitment and population dynamics.
- Standard metabolism and growth dynamics of laboratory-reared larvae of Sardina pilchardusPublication . Moyano, M.; Garrido, Susana; Teodosio, Maria; Peck, M. A.This study provides the first measurements of the standard respiration rate (RS) and growth dynamics of European sardine Sardina pilchardus larvae reared in the laboratory. At 15° C, the relationship between RS (µl O2 individual−1 h−1) and larval dry mass (MD, µg) was equal to: RS = 0·0057(±0·0007, ± s.e.)·MD0·8835(±0·0268), (8–11% MD day−1). Interindividual differences in RS were not related to interindividual differences in growth rate or somatic (Fulton's condition factor) or biochemical-based condition (RNA:DNA).
- Does the nutritional condition limit survival potential of sardine Sardina pilchardus (Walbaum, 1792) larvae off the north coast of Spain? RNA/DNA ratios and their variabilityPublication . Chicharo, Maria Alexandra; Chícharo, Luís; Valdes, L.; Lopez-Jamar, E.; Re, P.The aim of this study was to determine the nutritional condition of Sardina pilchardus larvae and the percentage of larvae that were starving at the time of capture. The survey was conducted, during the spawning season, in April and May of 1991 and 1992, off the northern coast of Spain. An accepted ¯uorimetric technique was used to determine the concentrations of both RNA and DNA and to calculate RNA/DNA ratio for each larva. RNA/DNA ratios were related to the zooplankton biomass (>53 mm). Low percentages of starving larvae (RNA/DNA ratio less than 1.3) were registered, ranging from 0% to 2.5%. Results based on the mean and variance of individual larval growth rates showed that predation pressure was not increasing from 1991 to 1992. Based on the presence of sardine larvae in good condition together with low predation, a high recruitment was expected. However, the 1993 recruitment, from 1992 spring spawning, was very poor. This was associated mainly with unfavourable advection from the nursery area. Moreover, even low levels of starvation, such as registered, operating over long time periods could have considerable consequences for larval mortality.
- The distribution of estuarine fish larvae: nutritional condition and co-occurrence with predators and preyPublication . Esteves, E.; Pina, T.; Teodosio, Maria; Andrade, José PedroFish larvae were collected monthly between March and September 1997 in the Mira and Guadiana estuaries (southern Portugal). Hydrological parameters were registered and zooplankton samples were obtained simultaneously. Densities of fish larvae (ind·100 m–3) were calculated from 211 samples and larval nutritional condition measured as RNA/DNA ratios were obtained for 346 individuals, using a fluorimetric method for nucleic acid quantification. Correlating variables were further studied using multiple regression analysis in order to assess the relative importance of abiotic and biotic factors affecting within-year trends in abundance and nutritional condition of estuarine fish larvae. Results indicated that: 1) the abundance of fish larvae seems conditioned by temperature and predation; and 2) their nutritional condition is dependent on temperature and prey availability. Temperature is an important variable structuring estuaries and therefore conditions the behaviour and physiology of fish larvae. Furthermore, the co-occurrence of predators and larvae might be related to similar feeding patterns or comensalism. Whenever feeding conditions are suitable, they usually determine enhanced growth and nutritional condition. However, predation seems to control this latter relationship through its effect on larval mortality.