M.S. - Oceanography (Marine Biology)

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    Life history and feeding ecology of a specialized nudibranch predator (Phyllodesmium poindimiei) with implications for biocontrol of an invasive octocoral (Carijoa riisei) in Hawaiʻi
    ( 2008) Wagner, Daniel
    Biocontrol has been used successfully in terrestrial agricultura1 systems for a long time (Funasaki et al. 1988; Murdoch & Briggs 1996; Simbeloff & Stiling 1996; Secord 3 2003), however, in marine systems biocontrol is still in its infancy (Simbeloff & Stiling 1996; Secord 2003). In estuary and marine systems only few proposals to identify and test potential biocontrol agents have been put forward (reviewed by Secord 2003). These include: (1) pathogenic microorganisms (viruses, bacteria and protozoa) against harmful algal blooms; (2) the predatory butterfish Peprilus triacanthus and the parasitic larval sea anemone Edwardsia lineata against the ctenophore Mnemiopsis leidyi in the Black Sea; (3) the castrating barnacle Sacculina carcini against the crab Carcinus maenas; (4) the spermiphagous ciliate Orchitophyra stellarum against the starfish Asterias amurensis; (5) sacoglossan opistobranchs against the green alga Caulerpa taxifolia in the Mediterranean Sea; and (6) the planthopper Prokelesia marginata against the saltmarsh cordgrass Spanina alterniflora. Besides the shorter history of marine biological control, as opposed to terrestrial biocontrol, there are several fundamental differences between terrestrial and marine ecosystems that directly influence organismal biology. These differences include life histories, taxonomic relationships and biodiversity, larval and adult dispersal strategies, biomechanics of the medium and relative system openness (Strathmann 1990; Lafferty and Kuris 1996; Kareiva 1996; Secord 2003). Together, the uncertainty in predicting marine systems is much greater, making it harder to identify and test potential biocontrol agents (Lafferty and Briggs; Secord 2003). Decisions on the identification of potential biocontrol agents are guided by host specificity and seek to maximize damage to the pest populations, with both of these factors being important (Murdoch and Briggs 1996; Secord 2003; Sax et al. 2005). For instance, studies with sacoglossan opistobranchs as potential biocontrol agents against the alga Caulerpa taxifolia in the Mediterranean Sea revealed that several slug species are specialized feeders of C. taxifolia; however slugs were ineffective biocontrol agents due to low feeding rates (Williams and Walker 1999; Coquillard et al. 2000; Thibaut et al. 2001). Ideally, a biocontrol agent should maximize damage to a specific pest without affecting non-target species. Additionally, the life histories of potential biocontrol agents need to be considered (Simberloff and Stiling 1996; Secord 2003). For example, the sacoglossans Oxynoe olivacea and Lobiger seradiflaci are unsuitable biocontrol agents against Caulerpa because of low feeding rates and planktotropic larval development, which typically leads to dispersal away from the biocontrol's local target pest (Lafferty and Kuris 1996; Secord 2003). The only reported predators of Carijoa outside of Hawaii are ovullids in Indonesia (Calcinai et al. 2004), and an endemic tritoniid nudibranch Tritonia sp. (Kahng 2006), the aeolid nudibranchs Phyllodesmium serratum and P. poindimiei, all from southern Australia (Rudman 1981, 1991). In Hawaii, studies on the associated microcommunity of C. riisei conducted in the 1970's failed to identify any predators of C. riisei (Thomas 1979). In 1995, the dendronotid nudibranch Tritoniopsis elegans (Audoin 1826) and the aeolid nudibranch Phyllodesmium poindimiei (Risbec 1928), were first seen in Hawaii apparently feeding on C. riisei (Wagner et al. 2007). Laboratory assays with the native Hawaiian octocorals Sinularia densa (Whitelegge 1897) and Sarcothelia edmonsoni (Verrill 1928) in the presence and absence of C. riisei, demonstrated that T. elegans is a generalist octocoral predator which preys readily on C. riisei, but also feeds on S. edmonsoni and S. densa when C. riisei is absent (Wagner et al. 2007). The generalist nature of T. elegans feeding makes it an undesirable biocontrol agent against C. riisei in Hawaii. In contrast, P. poindimiei quickly starved in the absence of C. riisei even when offered alternative octocoral prey (Wagner et al. 2007; current study). Prior to these studies, P. poindimiei had only been observed from a variety of Western Pacific locations from New Caledonia to southern Australia (Rudman 1981,1991; Burn 2006; Slack-Smith & Bryce 2004) in close association with Carijoa (Rudman 1991). Given the rapid proliferation and ecological impact of C. riisei in Hawaii (Kahng and Grigg 2005), there is interest in the potential use of P. poindimiei as a biocontrol agent. However, little is known about the basic biology of this nudibranch species. The purpose of this study was to: (1) confirm the specialized nature of P. poindimiei feeding; (2) quantity the impacts of P. poindimiei on C. riisei; and (3) answer basic life history questions of P. poindimiei including adult longevity, fecundity and larval type, by using both laboratory cultures and time-series observations of field sites.