Browsing by Author "Caro, AU"

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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.
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    Predator-inducible defences and local intrapopulation variability of the intertidal mussel Semimytilus algosus in central Chile
    (2004) Caro, AU; Castilla, JC
    Predator-inducible defences have a strong influence on the expression of morphological traits of intertidal invertebrates. For instance, mussels exposed to predators often have thicker shells than non-exposed. On the intertidal rocky shores of Chile, the mussel Semimytilus algosus is a preferred prey of many carnivorous invertebrates, including the snails Nucella crassilabrum and Concholepas concholepas, and the crab Acanthocyclus gayi. Preliminary observations indicated that S. algosus exists as 2 morphotypes: a thick, smooth shell and a thinner, ringed shell. The thick-shell morphotype was found mostly on compact, rocky platforms, whereas the thin one was found on emergent rocks. We examined the role of invertebrate predators in determining the morphological differences observed in S, algosus as a process of defence induction. The density and size of mussel predators showed significant differences between habitats: A. gayi dominating the platforms and N. crassilabrum emergent rocks. C. concholepas did not show differences between habitats. Water-borne cue experiments demonstrated that the mussel shell thickness is increased by the presence of predators, especially A. gayi. Furthermore, in contrast to the other predators, A. gayi preferentially selects mussels of the thin-shell morphotype. We demonstrate the cause and effect connection between variation in mussel shell morphology in the laboratory and their associated spatial distribution in the field, as well as the ecological role played by predators. We propose that, at local scales, the distribution and abundance of predators in the field explain the inter-population morphological differences of the mussel S. algosus.