Browsing by Author "Manríquez, PH"

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    Feeding by larvae of intertidal invertebrates
    (2006) Vargas, CA; Manríquez, PH; Navarrete, SA
    One of the leading determinants of the structure and dynamics of marine populations is the rate of arrival of new individuals to local sites. While physical transport processes play major roles in delivering larvae to the shore, these processes become most important after larvae have survived the perils of life in the plankton, where they usually suffer great mortality. The lack of information regarding larval feeding makes it difficult to assess the effects of food supply on larval survival, or the role larvae may play in nearshore food webs. Here, we examine the spectrum of food sizes and food types consumed by the larvae of two intertidal barnacle species and of the predatory gastropod Concholepas concholepas. We conducted replicated experiments in which larvae were exposed to the food size spectrum (phytoplankton, microprotozoan and autotrophic picoplankton) found in nearshore waters in central Chile. Results show that barnacle nauplii and gastropod veligers are omnivorous grazers, incorporating significant fractions of heterotrophs in their diets. In accordance with their feeding mechanisms and body size, barnacle nauplii were able to feed on autotrophic picoplankton (< 5 mu m) and did not consume the largest phytoplankton cells, which made the bulk of phytoplankton biomass in spring-summer blooms. Balanoid nauplii exhibited higher ingestion rates than the smaller-bodied chthamaloid larvae. Newly hatched C. concholepas larvae also consumed picoplankton cells, while competent larvae of this species ingested mostly the largest phytoplankton cells and heterotrophic protozoans. Results suggest that persistent changes in the structure of pelagic food webs can have important effects on the species-specific food availability for invertebrate larvae, which can result in large-scale differences in recruitment rates of a given species, and in the relative recruitment success of the different species that make up benthic communities.
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    Self-fertilization as an alternative mode of reproduction in the solitary tunicate Pyura chilensis
    (2005) Manríquez, PH; Castilla, JC
    The hermaphroditic broadcasting tunicate Pyura chilensis Molina, 1782 is a sessile filter-feeder organism that occurs in intertidal and subtidal habitat s along the Chilean and Peruvian coast. In natural populations, P. chilensis form dense aggregations, small patches or occur as isolated individuals. This suggests that self-fertilization could be a potential insurance against adverse conditions for cross-fertilization. In this study, P. chilensis were reared in the laboratory as isolated and paired individuals, to assess occurrence and success of fertilization, settlement and metamorphosis. Occurrence of self-fertilization was also compared between specimens forced to cross-fertilize and specimens maintained in reproductive isolation for different periods. We also manipulated cross- and self-fertilization using strip-spawned gametes. Our study shows that P. chilensis is a hermaphroditic species with adolescent gonochorism; that is, individuals first developed male function and then later male and female functions simultaneously as specimens increased in size (protandrous hermaphroditism). The results also show more frequent fertilization in paired specimens and in manipulated fertilization involving cross sperm. Moreover, no perceptible differences in fertilization, settlement, and metamorphosis success among self and outcross progeny were found. Prolonged periods of reproductive isolation resulted in more frequent self-fertilization. Occurrence of selling and highly successful settlement and metamorphosis of progeny originating from reproductively-isolated specimens suggest that even though outcrossing predominates, selling is an advantageous alternative when sources of allosperm are scarce.
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    Settlement of the gastropod Concholepas concholepas on shells of conspecific adults
    (2004) Manríquez, PH; Navarrete, SA; Rosson, A; Castilla, JC
    Competent larvae of the commercially important marine gastropod Concholepas concholepas (Gastropoda: Muricidae) 'loco', were collected in the field and exposed in the laboratory to adult conspecific shells with and without barnacle epibionts. Settlement and metamorphosis was induced by the presence of barnacles on shells of live or dead conspecifics, but not by C concholepas shells without barnacles. Results from laboratory experiments agreed well with field surveys showing the presence of recruits on conspecific shells overgrown with barnacles in shallow subtidal habitats (similar to3-30 m deep), suggesting the potential importance of barnacles inin inducing settlement and metamorphosis of locos under natural conditions. Most loco recruits were found below the C. concholepas shell apex, feeding on barnacles, inhabiting crevices among them, and inside dead barnacles. The mean size of recruits on locos' shells increased over four months from the beginning of the settlement season and no individual larger than 1.5 cm was observed, suggesting that they abandon adult loco shells at this size, roughly 5-6 months after settlement.
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    Significance of marine protected areas in central Chile as seeding grounds for the gastropod Concholepas concholepas
    (2001) Manríquez, PH; Castilla, JC
    The importance of non-harvested areas, marine protected areas, and management and exploitation areas (= harvest-controlled) as seeding areas of Concholepas concholepas (Bruguiere, 1789) larvae was quantitatively evaluated at intertidal and subtidal sites at Las Cruces, central Chile. Egg capsules of C, concholepas were sampled along both intertidal and subtidal strip-transects monthly in harvested, harvest-controlled and non-harvested areas from September 1990 to December 1993. Additionally, egg capsules of C, concholepas were sampled at subtidal sites in the 3 categories of areas during 1993 and 1994. Spawning activity of C, concholepas was consistently concentrated between February and July in both the intertidal and the subtidal zones. The total area occupied by egg capsules of C, concholepas was larger in non-harvested than in harvested areas; moreover, larger capsules were found in non-harvested areas. These differences in total surface occupied by egg capsules and their sizes have an important impact on the estimated number of C. concholepas larvae that would be released from harvested and non-harvested areas. We conclude that protected areas may play an important role in the natural replenishment of C. concholepas stocks.