Browsing by Author "Flores, Augusto A. V."
Now showing 1 - 3 of 3
Results Per Page
Sort Options
- Longitudinal distribution and lateral pattern of megalopal settlement and juvenile recruitment of Carcinus maenas (L.) (Brachyura, Portunidae) in the Mira River Estuary, PortugalPublication . Silva, Inês C.; Dinis, Ana M.; Francisco, Sara Martins; Flores, Augusto A. V.; Paula, José R.Settlement is a critical process in the life history of crabs, and thus affecting the abundance, distribution and structure of estuarine communities. The spatial pattern of settlement of megalopae of the shore crab Carcinus maenas along a longitudinal estuarine gradient (Mira River Estuary, Portugal) was examined, as well as its effects on the juvenile population. To measure megalopal settlement, four replicate collectors were deployed in six equally spaced stations along the estuarine axis. Juveniles were collected on the same locations with a quadrat randomly deployed on the substrate. To assess fine-scale megalopal settlement within a curved region of the estuary, replicate collectors were deployed on both margins along Moinho da Asneira curve. Megalopae settled differently along the six longitudinal points, with a tendency to attenuate their settlement upstream. Within the curved region, megalopae preferentially settled on the left margin collectors, probably due to the weaker velocity speeds felt on this margin. Concerning the overall juvenile density, there were significant differences among the stations distributed along the estuary, but they did no reflect a longitudinal dispersion attenuation pattern. Size-frequency distribution of the juvenile population showed that the average size is higher on the left margin. Recruits (carapace length between 1.0 mm and 3.4 mm) were more abundant on the upstream stations. Density of early juveniles (3.4 mme6.5 mm) and juveniles (6.5 mme10 mm) was more stable throughout the estuary axis than that of recruits. This distribution pattern may result from tidal excursion processes or mechanisms to avoid biotic interactions, such as predation and competition.
- The use of artificial benthic collectors for assessment of spatial patterns of settlement of megalopae of Carcinus maenas (L.) (Brachyura: Portunidae) in the lower Mira Estuary, PortugalPublication . Paula, José R.; Silva, Inês C.; Francisco, Sara Martins; Flores, Augusto A. V.Artificial benthic collectors have been widely used for the assessment of settlement rates of decapod crustaceans. However, to date no consistent works have addressed spatial patterns of settlement in different estuarine habitats, and no specific studies targeted the interaction of artificial surfaces with the surrounding natural substrate. It may be expected that the artificial surface may produce a different thigmotactic response when compared to the natural substrate, which may limit the use of this technique for assessment of natural settlement rates. In this study the settlement rates of megalopae of the estuarine crab Carcinus maenas were addressed, specifically deploying artificial benthic collectors in different habitats both intertidal and subtidal in the lower Mira estuary. A number of experiments were performed concerning stratification and temporal fluctuations of settlement. Further, the interaction of collector surface with the surrounding substrate was investigated, by comparing settlement rates in natural and artificial substrates in different habitats. Results have shown significant differences in settlement between different estuarine habitats, both in spatially replicated experiments and in a high-resolution temporal experiment. However, comparison between settlement rates in artificial and natural substrates has shown that there is a strong interference between collectors and surrounding substrate, limiting interpretation of results concerning settlement rates in artificial substrate alone.
- Tide and wind control of megalopal supply to estuarine crab populations on the Portuguese west coastPublication . Queiroga, Henrique; Almeida, Maria João; Alpuim, Teresa; Flores, Augusto A. V.; Francisco, Sara Martins; Gonzàlez-Gordillo, Ignácio; Miranda, Ana Isabel; Silva, Inês C.; Paula, José R.Physical processes that force transport of planktonic larvae of invertebrates are responsible for some of the spatial and temporal variability in recruitment. We investigated the influence of tide- and winddriven circulation on intra-year variability of megalopal supply to populations of the crab Carcinus maenas in 2 estuaries on the Portuguese west coast. Daily data on physical variables and on supply and settlement of megalopae were subjected to time series analysis and multiple regression techniques in order to identify periodicity in the variables as well as time lags between larval supply and physical variables. Relaxation of northerly winds, which favor upwelling, was associated with temperature increase and subtidal sea level rise at the coast, which are indicative of coastal convergence of the surface layer. Supply of megalopae to the estuaries, as measured with passive plankton nets, followed a fortnightly cycle with maximum larval supply at the time of maximum tidal amplitude. Supply was enhanced by southerly winds, with delays of 0 to –2 d. Settlement of megalopae on artificial settlement substrates deployed on the bottom was uncoupled to supply at both estuaries. Therefore, transport of C. maenas megalopae to the nearshore is accomplished by onshore advection following downwelling winds, and supply to the estuaries occurs by selective tidal stream transport. Involvement of internal waves and internal tidal bores cannot be be ruled out, but very particular periodicities of the generating mechanisms would have to be assumed to account for the observed time lags.