The coast of central Chile is characterized by the occurrence of coastal upwelling during the austral spring and summer seasons, which probably has important consequences for the cross‐shelf transport of larval stages of many species. Three cruises were conducted off the locality of El Quisco during upwelling‐favorable wind periods to determine the surface distribution of epineustonic competent larvae of the gastropod Concholepas concholepas during such events. Contrary to the predictions of a traditional model, where neustonic‐type larvae are transported offshore under such conditions, competent larvae of this species were exclusively found in the area between the shore and the upwelling front. Two additional cruises were conducted during calm periods to determine diel variation in the vertical distribution of C. concholepas competent larvae. The absence of competent larvae at the surface during early night hours suggests a reverse vertical migration. Thus, the retention of C. concholepas competent larvae in the upwelled waters could be the result of the interaction between their reverse diel vertical migration and the typical two‐layer upwelling dynamics.

No abstract

The abundance of competent epineustonic larvae of the gastropod Concholepas concholepas (Gastropoda: Muricidae) in nearshore waters at 2 sites along the central coast of Chile was examined through monthly plankton tows from July 1999 to June 2000. Larvae were found in plankton collections from July 1999 to February 2000 with maximum abundance in September and October. Settlement in artificial collectors deployed onshore on the lower intertidal zone showed the same unimodal pattern with a settlement peak during October and November. Variation in larval distribution among sampling dates was related to the occurrence of north-south winds. We found that C. concholepas larvae were more abundant closer to shore after moderate southerly wind periods than on calm days, probably because of the shoreward advection of the upper sea surface layer. While sampling during a strong coastal upwelling event (produced by strong southwesterly winds), C. concholepas larvae were only found in the upwelled waters between the front and the coast. This unusual pattern contrasts with what would be expected for typical epineustonic larvae, suggesting the existence of a mechanism of transport or retention by which C. concholepas larvae stay near coastal settling areas, thus avoiding offshore dispersion.

No abstract

Clusters of egg capsules deposited by some common marine Mollusca may suffer problems of a low diffusive oxygen supply to the embryos they contain, especially if the capsules are exposed to hypoxic seawater or attachment and growth of marine biofouling organisms. The present study was undertaken to determine the effects of severe biofouling by sessile Protozoa on intracapsular oxygen tension (IPO,) and the development of embryos contained in the egg capsules of the muricid snail Chorus giganteus. We also investigated the effects of ambient oxygen tension (EP02) on IPO,. The presence of sessile Protozoa attached to the outer wall of the egg capsules significantly reduced the IPO, compared to capsules not fouled by Protozoa. Clean capsules containing embryos showed an IP02 of about 105 mm Hg, compared with about 92 mm Hg for protozoan-fouled capsules when both were immersed in air-saturated seawater at 12°C. The embryos in capsules without Protozoa grew normally, hatching in about 70 d as veliconch larvae, whereas the development of larvae in protozoan-fouled capsules showed impairment of shell formation and delay in hatching for up to 5 mo. Pre-hatch embryos at 60 d measured about 922 pm and had an ash content near 18 pg embryo-'; embryos in capsules covered by micro-organisms measured only about 783 pm, with an ash content of about 3 pg embryo-' over the same time period. Our study suggested that the lack of larval calcification observed in the presence of sessile Protozoa on the outer wall of the egg capsules was probably related to reduced IPO,. Similarly, any factor reducing oxygen supply to encapsulated embryos (i.e. exposure to water masses with low oxygen content, biofouling, reduced water movement) could impair embryonic development, a significant phenomenon thus far not reported in C. giganteus. MARINE ECOLOGY PROGRESS SERIES Mar Ecol Prog Ser