José M. Riascos

SUITABILITY OF THREE STAINS TO MARK SHELLS OF CONCHOLEPAS CONCHOLEPAS (GASTROPODA) AND MESODESMA DONACIUM (BIVALVIA)

Abstract Different stains are used to internally mark calcified structures of mollusc shells in growth experiments. Because of interspecific variations in marking success, an assessment of suitability for each species is necessary. The potential of calcein, alizarin red, and strontium chloride hexahydrate (strontium chloride) was investigated for the Chilean abalone Concholepas concholepasr and the surf clam Mesodesma donacium, two molluscs of commercial importance in Chile. Wild specimens from Northern Chile were marked using different concentrations and immersion periods of the three stains. Animals were reared for 20 days to allow growth, mortality, body condition index (BCI), and growth rate was measured to assess the effects of the treatments. To detect marks, individuals were culled and shell sections analyzed using scanning electron microscopy for strontium chloride and fluorescence microscopy for calcein and alizarin red, respectively. Strontium chloride produced narrow bright bands only at concentrations of 2,880 mg·l−1 and 24 h exposure. Calcein markings produced fluorescent bands detectable in all treatments (50 and 100 mg·l−1, 3 and 6 h) whereas alizarin red only yielded irregular bands with 50–100 mg·l−1 and 6 h exposure. Our results show that growth rates of C. concholepas are significantly affected by the stains factor: Strontium chloride showed the lowest growth rates whereas that of alizarin red and calcein was similar to the control group. High concentrations of strontium chloride negatively affected (P < 0.05) the body condition of the gastropod. Although no statistical differences were found, BCI of M. donacium followed the same trend as observed for C. concholepas. In conclusion, calcein was the best growth marker for both species because it produced bright, long-lasting bands even at low concentrations and immersion times without detectable lethal or sublethal effects.

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.

Recurrent, thermally-induced shifts in species distribution range in the Humboldt current upwelling system

El Niño-Southern Oscillation (ENSO) is a global climate variablility, which fundamentally influences environmental patterns of the Humboldt Current System (HCS) off Chile and Peru. The surf clams Donax obesulus and Mesodesma donacium are dominant and highly productive bivalves of exposed sandy beaches of the HCS. Existing knowledge indicates that El Niño (EN, warm phase of ENSO) and La Niña (LN, cold phase of ENSO) affect populations of both species in a different way, although understanding of the mechanisms underlying these effects is still lacking. The aim of this study was to test hypotheses attempting to explain field observations on the effect of strong EN or LN events by using controlled experimental conditions. Growth and mortality rates of both species were registered during a four-week experiment under EN temperature conditions, normal temperature conditions and LN temperature conditions. While D. obesulus exhibited reduced growth and higher mortality under LN conditions, M. donacium showed reduced growth and higher mortality under EN conditions. The results clearly indicate different temperature tolerance windows for each species, possibly reflecting the evolutionary origins of the Donacidae and Mesodesmatidae in regions with contrasting temperature regimes. These results provide experimental support for previous hypotheses suggesting that thermal tolerance is the driving factor behind observed changes in the species distributions of D. obesulus and M. donacium during the extreme phases of ENSO.

Population dynamics of the tropical bivalve Cardita affinis from Malaga Bay, Colombian Pacific related to La Nina 1999-2000

The population dynamics of the “cholga” Cardita affinis (Sowerby 1833) from Málaga Bay, Colombia, was studied from December 1999 to February 2002, which included the 1999–2000 La Niña event (LN) and the post-LN period 2001–2002. This climatic deviation caused precipitation anomalies in Málaga Bay. Salinity, precipitation, and sea surface temperature anomalies were highly correlated with the bivalve’s body mass cycle. Irregular spawning events were observed during LN by comparison with the regular period. Individual growth and mortality were found significantly higher during LN than during the post-LN period while longevity was almost twofold lower during LN. Increased mortality was probably related to environmental stress. Individual production and productivity were higher during LN, although the annual biomass was lower than during the post-LN period. These results may be related to higher food availability during LN, which agrees well with the results on growth performance. The observed changes provide a base line for future studies regarding effects of El Niño/LN events on population dynamics of tropical bivalves.

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.

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.

Long-term parasitic association between the boring polychaete Polydora bioccipitalis and Mesodesma donacium.

Polydora and related genera are common pests for molluscs. Establishing differences between native species and recent invaders provides the basis for understanding the effect of parasites and has implications for resource management. P. biocipitalis has been reported as a recently introduced species to the Chilean-Peruvian coast, raising concerns about its threat to native bivalve species. In contrast, studies on the infestation of P. bioccipitalis on the surf clam Mesodesma donacium, one of the most important species for shellfisheries, suggest a long-term parasitic relationship. The present study analyses infested (i.e. blistered) fossil shells of M. donacium deposited during the Holocene and Middle Pleistocene epochs and critically reviews evidence supporting the hypothesis of the recent introduction of P. bioccipitalis to the Chilean-Peruvian coast. The blistering pattern seen on fossil and recent shells can be considered species-specific for the infestation of M. donacium by P. bioccipitalis. No evidence was actually found on vectors, introduction pathways or distribution range to support the status of P. bioccipitalis as an introduced species. On the contrary, our findings point to a long-term association, at least for several hundred thousand years, between M. donacium and P. bioccipitalis.

Breaking out of the comfort zone: El Niño-Southern Oscillation as a driver of trophic flows in a benthic consumer of the Humboldt Current ecosystem

The trophic flow of a species is considered a characteristic trait reflecting its trophic position and function in the ecosystem and its interaction with the environment. However, climate patterns are changing and we ignore how patterns of trophic flow are being affected. In the Humboldt Current ecosystem, arguably one of the most productive marine systems, El Niño-Southern Oscillation is the main source of interannual and longer-term variability. To assess the effect of this variability on trophic flow we built a 16-year series of mass-specific somatic production rate (P/B) of the Peruvian scallop (Argopecten purpuratus), a species belonging to a former tropical fauna that thrived in this cold ecosystem. A strong increase of the P/B ratio of this species was observed during nutrient-poor, warmer water conditions typical of El Niño, owing to the massive recruitment of fast-growing juvenile scallops. Trophic ecology theory predicts that when primary production is nutrient limited, the trophic flow of organisms occupying low trophic levels should be constrained (bottom-up control). For former tropical fauna thriving in cold, productive upwelling coastal zones, a short time of low food conditions but warm waters during El Niño could be sufficient to waken their ancestral biological features and display massive proliferations.