Browsing by Author "Ortiz, V"

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    Does early development of the Chilean tunicate Pyura praeputialis (Heller, 1878) explain the restricted distribution of the species?
    (1999) Clarke, M; Ortiz, V; Castilla, JC
    Relationships between the rate of larval development and dispersal of a species can have a large influence on observed patterns of its distribution and abundance. Distribution patterns of the dense belt-forming rocky intertidal ascidians Pyura praeputialis and Il stolonifera (Urochordata: Ascidiacea: Pyuridae) show drastic differences. II stolonifera extends along the coast of South Africa for 1000s of kilometers and I? praeputialis shows a similar range in Australia (New South Wales, Victoria and Tasmania). On the contrary, in Chile I! praeputialis is characterized by a population which occurs along less than 70 km of coastline in and around the Bay of Antofagasta. The larval and development characteristics of the South African and Australian species have been studied while those of the population from Chile has not been described. This study describes the early embryology and larval development of the Chilean species and shows that the development times and the free-swimming larval stage of I? praeputialis in Chile and Australia are similar. Therefore, it is suggested that the differences in the extension of their range of distribution in Australia and Chile cannot be accounted for due to differences in the developmental biology, but it may be due to a recent invasion of the species to Chile. Comparison between the development biology of P. praeputialis and II chilensis are also made.
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    Invasion of a rocky intertidal shore by the tunicate Pyura praeputialis in the Bay of Antofagasta, Chile
    (2004) Castilla, JC; Guiñez, R; Caro, AU; Ortiz, V
    Invasion by marine nonindigenous species (NIS) is a spread phenomenon. The tunicate Pyura praeputialis shows pronounced disjoint geographical distribution: along thousands of kilometers in wave-swept headlands on the southeastern coast of Australia, from where it appears to have originated, and exclusively along 60-70 km inside the Bay of Antofagasta, Chile. mtDNA sequences suggested that the species invaded this rocky shore recently. We used field manipulations and juvenile A praeputialis transplant techniques to test hypotheses regarding the capacity of the tunicate to survive and grow at different sites and tidal heights inside and outside Antofagasta, and its competitive performance for primary space (inside the Bay) against the native mussel Perumytilus purpuratus. We conclude that survival and growth of A praeputialis showed no significant differences among sites inside and outside the Bay, and suggest that the restrictive distribution of the species in Chile is caused by a specific oceanographic retention mechanism and/or its brief larval dispersal. We demonstrated that, inside the Bay, P. praeputialis outcompetes Perumytilus from the Mid-Low intertidal, constraining Perumytilus to the Upper Mid-Intertidal, modifying the local pattern of intertidal zonation. We show that predation on P. praeputialis juveniles by starfish and snails constitutes a regulatory mechanism for the setting of its low intertidal limit. Major ecological impacts caused by NIS invasions to rocky shores by aggressive primary space users may result in negative aspects, but also may contribute to biodiversity enhancement. We call attention to the need for increment manipulations and testing of ecological hypotheses regarding marine NIS.