Aldo S. Pacheco

The elusive life cycle of scyphozoan jellyfish – metagenesis revisited

Massive proliferations of scyphozoan jellyfish considerably affect human industries and irreversibly change food webs. Efforts to understand the role of jellyfish in marine ecosystems are based on a life cycle model described 200 years ago. According to this paradigm the pelagic medusae is considered seasonal and alternates with the benthic polyp stage from which it derives. However, we provide evidence that a) the occurrence of several species of medusae is not restricted to a season in the year, they overwinter, b) polyp- and medusa generations are neither temporally nor spatially separated, and c) “metagenesis” which is defined as the alternation between sexual and asexual generations does not always occur. Hence we recommend additions to the current model and argue that the scyphozoan life cycle should be considered multi-modal, rather than metagenetic. The implications of these findings for jellyfish proliferations, including possible consequences and associated environmental drivers, are discussed.

The role of hyperiid parasites as a trophic link between jellyfish and fishes

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.

Diet composition of the large scyphozoan jellyfish Chrysaora plocamia in a highly productive upwelling centre off northern Chile

Abstract Jellyfish are arguably one of the most important predators in the sea, and understanding their role in ecosystem functioning is critical. Modelling seems the best approach to understand and forecast their role, but these efforts are seriously hampered by the scant knowledge of the detailed diet composition of most species. We sampled a population of the largest scyphomedusa (Chrysaora plocamia) from an upwelling centre in the Humboldt Current Upwelling System. Fish eggs/larvae and holoplanktonic crustaceans represented a substantial proportion (between 52.4% and 99.3%) of the diet of C. plocamia and that of other species within the genus Chrysaora, thus highlighting their potential impact in ecosystems sustaining large fisheries. The diet composition of C. plocamia displayed a strong temporal variability pattern that seemingly reflects the control of upwelling pulses on population dynamics of the species being predated by this medusa.

Patterns of spatial and temporal distribution of humpback whales at the southern limit of the Southeast Pacific breeding area.

Understanding the patterns of spatial and temporal distribution in threshold habitats of highly migratory and endangered species is important for understanding their habitat requirements and recovery trends. Herein, we present new data about the distribution of humpback whales (Megaptera novaeangliae) in neritic waters off the northern coast of Peru: an area that constitutes a transitional path from cold, upwelling waters to warm equatorial waters where the breeding habitat is located. Data was collected during four consecutive austral winter/spring seasons from 2010 to 2013, using whale-watching boats as platforms for research. A total of 1048 whales distributed between 487 groups were sighted. The spatial distribution of humpbacks resembled the characteristic segregation of whale groups according to their size/age class and social context in breeding habitats; mother and calf pairs were present in very shallow waters close to the coast, while dyads, trios or more whales were widely distributed from shallow to moderate depths over the continental shelf break. Sea surface temperatures (range: 18.2–25.9°C) in coastal waters were slightly colder than those closer to the oceanic realm, likely due to the influence of cold upwelled waters from the Humboldt Current system. Our results provide new evidence of the southward extension of the breeding region of humpback whales in the Southeast Pacific. Integrating this information with the knowledge from the rest of the breeding region and foraging grounds would enhance our current understanding of population dynamics and recovery trends of this species.

Fast Growing, Healthy and Resident Green Turtles (Chelonia mydas) at Two Neritic Sites in the Central and Northern Coast of Peru: Implications for Conservation

In order to enhance protection and conservation strategies for endangered green turtles (Chelonia mydas), the identification of neritic habitats where this species aggregates is mandatory. Herein, we present new information about the population parameters and residence time of two neritic aggregations from 2010 to 2013; one in an upwelling dominated site (Paracas ∼14°S) and the other in an ecotone zone from upwelling to warm equatorial conditions (El Ñuro ∼4°S) in the Southeast Pacific. We predicted proportionally more adult individuals would occur in the ecotone site; whereas in the site dominated by an upwelling juvenile individuals would predominate. At El Ñuro, the population was composed by (15.3%) of juveniles, (74.9%) sub-adults, and (9.8%) adults, with an adult sex ratio of 1.16 males per female. Times of residence in the area ranged between a minimum of 121 and a maximum of 1015 days (mean 331.1 days). At Paracas the population was composed by (72%) of juveniles and (28%) sub-adults, no adults were recorded, thus supporting the development habitat hypothesis stating that throughout the neritic distribution there are sites exclusively occupied by juveniles. Residence time ranged between a minimum of 65 days and a maximum of 680 days (mean 236.1). High growth rates and body condition index values were estimated suggesting healthy individuals at both study sites. The population traits recorded at both sites suggested that conditions found in Peruvian neritic waters may contribute to the recovery of South Pacific green turtles. However, both aggregations are still at jeopardy due to pollution, bycatch and illegal catch and thus require immediate enforcing of conservation measurements.

First records of emerging benthic invertebrates at a sublittoral soft-bottom habitat in northern Chile

Some benthic invertebrates perform vertical diel migrations by swimming up from the seabed to the water column, i.e., they emerge. Although such migrations m...

Testing stress responses of the bivalve Protothaca thaca to El Niño–La Niña thermal conditions

Abstract Protothaca thaca is an important bivalve species inhabiting the upwelling ecosystem of Chile and Peru. Temperature in this ecosystem changes dramatically during El Niño (EN) events, with P. thaca showing high tolerance to increased temperatures. To understand the metabolic processes behind this adaptation we studied the effects of temperature on standard metabolism, growth and body condition index of P. thaca from Northern Chile. Oxygen consumption, daily growth rate and body condition index of animals acclimated to 12, 16 and 20°C were measured using an intermittent flow-through system. Our results show that these processes are significantly lower at 12°C compared to 16 and 20°C. No differences are observed between the higher temperatures. The relative thermal independence of routine metabolism is suggested to conserve energy, which allows the species to be more tolerant to high temperatures. Overall, the physiological responses of P. thaca at whole-animal level largely confirm that this clam is well suited to tolerate positive thermal anomalies associated with strong EN in the study area. However, results at lower temperatures show contrasting responses, which emphasizes the need to be cautious in sclerochronological studies, which tend to assume direct relationships between single environmental factors and micro-growth increment width.

Is it possible to go whale watching off the coast of Peru?: A case study of humpback whales

Whale watching is the human activity of encountering cetaceans in their natural habitat for recreational and scientific purposes. Despite the high diversity of cetaceans in Peruvian waters, this activity has yet to be developed. Herein we present data regarding the distribution of humpback whales (Megaptera novaeangliae) off northern Peru, evaluating the possibility of extending whale watching activities in this area. Data were obtained from surveys conducted from an ecotourism boat. Humpbacks were distributed in shallow waters, usually in pairs or trios throughout the study period between late July and late September. The presence of whales off northern Peru is due to winter migration for breeding and calving purposes. A high probability of encountering humpbacks within the study area could encourage the development of a whale watching industry. As this stage in the life cycle of this species is very delicate, we suggest the adoption of the precautionary principle in the management of the activity in order to minimize the risk of negative impacts on humpback populations. Whale watching in northern Peru is feasible and could be considered an alternative to fishing.

Aerial behavior of humpback whales Megaptera novaeangliae at the southern limit of the southeast Pacific breeding area

We evaluated the set of aerial displays shown by humpback whales Megaptera novaeangliae in the northern coast of Peru, a region that is considered the southern limit of the breeding area of the stock G in the Southeast Pacific. From August to October 2010, aerial displays were quantified from a whale-watching boat together with shore sightings. Our results indicated that the most frequent aerial display was breaching, followed by tail and flipper splashing. The maximum number of displays occurred in September. Groups made of pairs of whales performed the most frequent aerial behavior during the study period. Our results contrast with previous information off Ecuador suggesting that most intense aerial displays are performed when humpbacks are gathered in larger groups (more than 3 whales). These results add new information about humpback whales aerial behavior in the northern coast of Peru.

First record of hybridization between green Chelonia mydas and hawksbill Eretmochelys imbricata sea turtles in the Southeast Pacific.

Hybridization among sea turtle species has been widely reported in the Atlantic Ocean, but their detection in the Pacific Ocean is limited to just two individual hybrid turtles, in the northern hemisphere. Herein, we report, for the first time in the southeast Pacific, the presence of a sea turtle hybrid between the green turtle Chelonia mydas and the hawksbill turtle Eretmochelys imbricata. This juvenile sea turtle was captured in northern Peru (4°13′S; 81°10′W) on the 5th of January, 2014. The individual exhibited morphological characteristics of C. mydas such as dark green coloration, single pair of pre-frontal scales, four post-orbital scales, and mandibular median ridge, while the presence of two claws in each frontal flipper, and elongated snout resembled the features of E. imbricata. In addition to morphological evidence, we confirmed the hybrid status of this animal using genetic analysis of the mitochondrial gene cytochrome oxidase I, which revealed that the hybrid individual resulted from the cross between a female E. imbricata and a male C. mydas. Our report extends the geographical range of occurrence of hybrid sea turtles in the Pacific Ocean, and is a significant observation of interspecific breeding between one of the world’s most critically endangered populations of sea turtles, the east Pacific E. imbricata, and a relatively healthy population, the east Pacific C. mydas.