Abstract.-In this paper we report the apparently seasonal presence of fin whales in Mejillones Bay (23°S), in northern Chile.We compiled a total of 19 sightings representing 95 whales, including 2 mother-calf pairs, between July and October 2006-2014. We observed groups of 1-10 individuals (mean 5 ± 2.7 ind.) principally in nearshore waters, 30-1000 m off the southwestern tip of Mejillones Bay in austral winter/spring. Fin whales came close to, and potentially overlapped with, the main port access routes of large cargo vessels. Information from real-time monitoring of whale presence relayed to Port Authorities is suggested as to avoid collisions.
The trophic interactions between the scyphozoan medusa Chrysaora plocamia and the palm ruff Seriolella violacea were investigated off northern Chile and showed that large numbers of hyperiid amphipods parasitizing the medusa may channel energy back to the fishes, which feed on the parasites. The biomass of hyperiids eaten by the fish was a function of the biomass of hyperiids parasitizing the medusa. This temporally available food supply may enhance fish recruitment. The large number of hyperiids parasitizing diverse jellyfish species represents a missing trophic link in current efforts to understand the effects of jellyfish blooms on marine food webs.
Jellyfish display strong population variability. Competitive interactions between fish and jellyfish have been depicted as a major mechanism controlling this variability. Biological associations involving jellyfish are, however, more diverse than predation–prey interactions and remain poorly understood. Parasitic associations in particular may have relevant effects on jellyfish host populations. We studied basic patterns (temporal patterns of parasite intensity–biomass and the distribution pattern of parasites among hosts) of the association between the parasitic anemone Peachia chilensis and its scyphozoan host, Chrysaora plocamia. The mean number of parasites per host (MI) was high (average = 465) and showed significant differences during the pelagic life phase of the medusa. The mean biomass of parasites per host was also significantly different among months but showed a different temporal pattern to that of MI, which may reflect recruitment pulses of parasitic larvae. The mean biomass of P. chilensis per host averaged 56.3 mg ash-free dry mass, which represents a trophic flow of energy probably linking pelagic and benthic food webs. The distribution of parasites among hosts was best fitted to the negative binomial distribution model, as typical for host–parasite systems. We concluded that the parasite-induced host mortality and reduction of fecundity, represented by parasitic castration, is restricted to a few hosts and is therefore under the expected levels that characterize the dynamic equilibrium of host–parasite systems.
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