Browsing by Author "Venegas, RM"

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Internal tidal bore warm fronts and settlement of invertebrates in central Chile
    (2004) Vargas, CA; Narváez, DA; Piñones, A; Venegas, RM; Navarrete, SA
    We studied the occurrence of large high frequency temperature fluctuations and their potential association with settlement of intertidal invertebrates during the spring/summer period 1999/2000 at Las Cruces, on the coast of central Chile. Our results showed the existence of internal tidal bores, characterized by sharp drops in water temperature at the surface and near the bottom, and subsequent temperature increases, which occurred with a semidiurnal periodicity. Measured currents support the hypothesis of alternating onshore and offshore movement of warm-water fronts. The frequency of the events varied through the summer and their amplitude seems to be modulated by onshore winds. The strongest events were observed when strong onshore winds occurred in late afternoon hours and the entire water column showed a semidiurnal temperature signal. Highest values of chlorophyll concentration in the intertidal zone and daily settlement of bivalves, gastropods and crustaceans were observed at times when conditions were favorable for occurrence of internal tidal bores. Results suggest that internal tidal bore warm fronts could play an important role in the transport of neustonic larval invertebrates and the delivery of phytoplankton to at least some intertidal sites along the coast of Chile. (C) 2004 Elsevier Ltd. All rights reserved.
  • No Thumbnail Available
    Item
    Larval development of the intertidal barnacles Jehlius cirratus and Notochthamalus scabrosus (Cirripedia: Chthamalidae) under laboratory conditions
    (2000) Venegas, RM; Ortíz, V; Olguín, A; Navarrete, SA
    Larvae of the common intertidal chthamalid barnacles Jehlius cirratus and Notochthamalus scabrosus were obtained from mature adults collected in central and northern Chile and cultivated in the laboratory at temperatures typical of the conditions encountered by larvae in these regions. Morphological and developmental descriptions of the six naupliar stages and the cyprid stage of both species are given. Both species clearly present the general pattern of development for chthamalids, in which the structural characters of the cephalic shield and abdominal process, in conjunction with the utilization of the alphabetical setation formula for antennae, facilitate the identification and differentiation between larval stages. The average time of naupliar larval development of J. cirratus and N. scabrosus in sea-water temperature ranging 15-18 degrees C was 31 and 37 days, while larvae cultivated in temperatures ranging 18-20 degrees C completed naupliar development after 13 and 20.2 days, respectively. This represents a 58% and 45.5% reduction in naupliar development time with a three-degree increase in mean sea water temperature for J. cirratus and N. scabrosus, respectively. The development time from cyprid until settlement and metamorphosis of N. scabrosus lasted between 9 and 11 days, depending on the temperature, while cyprid development for J. cirratus lasted 8 days at 18-20 degrees C. The average sizes of the naupliar and cyprid stages were similar between the species at both temperature ranges. Although the increased temperature reduced the time of larval development, it did not significantly affect larval sizes.