Clement P. Dumont

Predation contributes to invasion resistance of benthic communities against the non-indigenous tunicate Ciona intestinalis.

Marine anthropogenic structures offer novel niches for introduced species but their role in the subsequent invasion to natural habitats remains unknown. Upon arrival in new environments, invaders must overcome biotic resistance from native competitors and predators if they are to establish successfully in natural habitats. We tested the hypotheses that (1) artificial structures (e.g., suspended aquaculture installations) present a niche opportunity for invasive species by providing a refuge from native benthic predators, and (2) native predators in natural benthic habitats suppress successful colonization by invaders. A recruitment experiment showed that the ascidians Pyura chilensis (native) and Ciona intestinalis (invasive) could recruit to both suspended artificial structures and natural benthic habitats. Ciona, however, was only able to establish adult populations on artificial structures. In natural benthic habitats Ciona only recruited and grew in predator-exclusion cages, because without this protection predation prevented its establishment. In predation experiments, native invertebrate and fish predators removed all invasive ascidians (recruits and adults) in benthic habitats, which contrasted with the high adult survival of the native ascidian P. chilensis. The refuge from a number of benthic predators facilitates the establishment of large populations of invasive species on suspended structures. We present a conceptual model of the invasion processes that includes the anthropogenic structures as a transitional stepping-stone that facilitates invasion by enhancing and prolonging propagule supply to surrounding natural communities. Those established invaders might then overcome biotic resistance during time periods when populations of consumers or competitors are weakened by natural or anthropogenic disturbances. Our results suggest that the conservation of natural habitats with a high diversity of native predators can be an effective means to prevent the spread of invasive species growing on suspended structures.

Male Morphotypes and Mating Behavior of the Dancing Shrimp Rhynchocinetes brucei (Decapoda: Caridea)

Abstract In crustaceans, the presence of large males with highly developed prehensile appendages (chelipeds or gnathopods) generally is suggestive of female monopolization during her receptive period. While mate guarding is common among some malacostracan crustaceans (brachyuran crabs and some amphipod families) it is relatively rare in caridean shrimp. Here we explored sexual dimorphism and the presence of morphotypic differences among males of the dancing shrimp Rhynchocinetes brucei. We furthermore quantified the behavioral events during mating interactions to examine whether mate guarding extends over the entire period of female receptivity. Males and females had similar body sizes, but males developed increasingly larger third maxillipeds and first chelipeds during ontogeny. Large males with hyperdeveloped maxillipeds and very large chelipeds featured a high degree of broken appendages and eyes, which probably results from intrasexual agonistic interactions. About 30% of the non-competitive male-female interactions with post-ovigerous females resulted in successful matings. Males usually initiated body contact with the female shortly after the females parturial molt, and they frequently touched the females genital region with their anterior body parts. The first (and in most cases only) spermatophore transfer event occurred at variable times (0.2-7 h) after the females molt. Following spermatophore transfer some males guarded the female in the cage state (between their pereiopods) until the female had finished spawning and was ovigerous. Post-copulatory mate guarding could last up to 70 min, but not all males guarded the female after the copulation. We suggest that male guarding of the receptive female throughout the mating process reduces the risk of sperm competition.