Antonio Brante

Empirical estimates of natural mortality for the Chilean hake (Merluccius gayi) : evaluation of precision

Abstract The precision of the natural mortality rate (M) for Chilean hake (Merluccius gayi) is evaluated using empirical models in which a parametric bootstrap resampling method is incorporated. The empirical models of Pauly (Pauly, D., 1980. J. Cons. Int. Explor. Mer. 39(2), 175–192.), Rikhter and Efanov (Rikhter, V.A., Efanov, V.N., 1976. ICNAF Res. Doc. 76/VI/8:12 p.), and Hoening (Hoening, J.M., 1983. Fish. Bull. US, 82(1): 898–902.) were used to estimate M. The model estimates of M were evaluated based on the error in the estimates of the input parameters and the degree of significant differences between males and females. The average of 3000 equally probable and alternative values of M obtained using the models of Pauly and Hoening were similar for males and females. However, these models produced significant differences between sexes only when the error in the estimates of the input parameters was taken into account. There were not significant sexual differences when the prediction error was included in the variance estimation procedure. The ability to determine significant sexual differences is an important aspect which is usually overlooked in evaluating estimates of male and female M obtained from empirical models.

Seasonal changes in abundance and shifts in dominance of life history stages of the carrageenophyte Sarcothalia crispata (Rhodophyta, Gigartinales) in south central Chile

The population dynamics of the carrageenophyte Sarcothalia crispatais described from subtidal beds at two localities in south-central Chile. Seasonal fluctuations in total density and biomass were not evident. Frondswere identified to phase by the presence of reproductive structures and theresorcinol reaction. The monthly changes in abundance of each kind offrond were determined. Permanent gametophytic or sporophyticdominance was not evident: the more exposed site showed a seasonal shiftfrom sporophytic dominance in summer to gametophytic dominance inwinter, whereas the more protected site showed an interannual shift fromgametophytic to sporophytic dominance. The differences between localitiesand years suggest a very local population dynamics with large contributionof self-seeding to the maintenance of the S. crispata beds.

Non-Random Sibling Cannibalism in the Marine Gastropod Crepidula coquimbensis

Sibling cannibalism is commonly observed in marine species. For instance, intrabrood cannibalism has been documented in marine gastropods with direct development, suggesting a relationship between embryo behavior and the evolution of life history strategies. However, there has been little effort to document the factors driving sibling cannibalism in marine species. The kin selection theory suggests that the level of relatedness plays an important role in cannibalism patterns. We examined Crepidula coquimbensis, a marine gastropod that broods and encloses its brooded offspring in capsules. Encapsulated embryos show sibling cannibalism and high levels of intracapsular multiple paternity. Given these features, cannibalistic behavior may be driven by kin-relatedness. To test this hypothesis, we constructed artificial aggregations of embryos to mimic three levels of relatedness: high, medium and low. For each category of aggregation, the cannibalism rate and benefits (i.e. size at hatching of surviving offspring) were estimated. In addition, at the end of embryo development, we performed parentage analyses to determine if cannibalism was associated with the relatedness between cannibal and victim embryos. Our results show that the intensity of sibling cannibalism increased in aggregations characterized by the lowest level of relatedness. There were important benefits of cannibalism in terms of hatching cannibal size. In addition, cannibalism between embryos was not random: the variation in reproductive success between males increased over the course of the experiment and the effective number of fathers decreased. Altogether, these results suggest that polyandry may play an important role in the evolution of sibling cannibalism in C. coquimbensis and that kin selection may operate during early embryonic stages in this species.

The relationship between temperature, oxygen condition and embryo encapsulation in the marine gastropod Chorus giganteus

Intracapsular oxygen availability is one of the main factors affecting embryo development of marine gastropod species with encapsulation. This is because the low solubility and diffusion rate of O 2 in water, plus the low oxygen diffusion rate that the capsule wall presents, reduces oxygen inside capsules. In addition, temperature affects embryo development inside capsules through its effect on embryo metabolic rate and oxygen availability. In spite of both factors being highly correlated and that a synergic effect on embryo development may be expected, there are few studies evaluating temperature and intracapsular oxygen availability simultaneously. In this work we evaluated the role of the capsule wall of the marine gastropod Chorus giganteus as a barrier for oxygen diffusion and its interaction with temperature affecting intracapsular oxygen availability and embryonic development. For that, we cultivated capsules in seawater at three different temperatures, 9, 12 and 15°C, for a time to complete embryo development. Oxygen level was measured inside capsules with and without embryos, and outside capsules at all temperatures. The number of capsules successfully hatched at the end of the experiment, and early and late embryo mortality were recorded. Finally, we measured embryo metabolic rate at the three different temperatures assayed. We found that embryo mortality and abnormal morphological development were more frequent at higher temperatures. Intracapsular oxygen availability decreases at higher temperatures in capsules with and without embryos. These results may be explained by an increase in the total intracapsular embryo metabolic rate (per capsule) with temperature and an inadequate oxygen diffusion rate from seawater through the capsule wall and intracapsular fluid to the embryonic cells. Our findings suggest that encapsulation is constrained at high temperatures in C. giganetus affecting significantly its reproductive success. This may have important consequences in a scenario of global warming.

Paternity Outcomes in the Freshwater Gastropod, Chilina dombeiana in the Biobío River, Chile

Studying the mating system of obligate aquatic organisms that inhabit river ecosystems is important for understanding its evolution as well as the role of biological and environmental factors in modulating population dynamics and species distributional patterns. Here, we studied the reproductive strategy of the Chilean endemic freshwater snail, Chilina dombeiana, in the Biobío River, one of the largest rivers in Chile. This species has a low potential for dispersal given the absence of a free-swimming larval stage (benthic larval development) and given that adults have a low capacity for mobility. We hypothesized that: 1. Females would mate with different males (polyandry) resulting in intrabrood multiple paternity, 2. Individuals from closer sites would be more related than individuals from distant sites, and 3. Male parental contributions would be unevenly distributed within broods. Individuals from three different sites were sampled along the river: upper, mid, and river mouth. In the laboratory, hatching juveniles from a total of 15 broods were collected for paternity analyses. We used microsatellite markers and the programs GERUD and COLONY to determine whether multiple paternity exists and to estimate the contribution of different males to the brood. We found that multiple paternity was very common at all of the sites analyzed with as many as 8 males fertilizing a single female and a mean of 4.2 fathers per brood estimated by COLONY. Sire contribution was skewed to particular males in several broods. In addition, overall relatedness among broods for the three sites ranged from 0.17 to 0.45 with evidence of many half-siblings. Relatedness differed among the three sites. Particularly in upstream sites or in anthropogenically disturbed populations, the high levels of multiple paternity observed in C. dombeiana may be an efficient strategy to avoid inbreeding and prevent the loss of genetic diversity within populations.

A New Case of Poecilogony From South America and the Implications of Nurse Eggs, Capsule Structure, and Maternal Brooding Behavior on the Development of Different Larval Types

Poecilogony is the production of different larval types within the same species. Although rare, poecilogonous species are ideal systems for testing the evolutionary and ecological implication of different developmental modes in marine invertebrates. Here, we described a new case of poecilogony, the Southern Hemisphere spionid Boccardia wellingtonensis. We used a combination of common-garden experiments, video recordings, and in vitro manipulations of individuals from three sites to (1) document the type of poecilogony, the brooding behavior of the mother, and the hatching process; (2) experimentally measure the effect of nurse eggs on the growth and type of larvae produced; and (3) document variation in the length of the brooding period, number of capsules, larvae, and nurse eggs of mothers from three sites to explore the potential for plasticity in reproductive traits. These results were compared to the previously reported poecilogonous species B. proboscidea, which resembles B. wellingtonensis in size, morphology, ecology, and reproductive strategy but differs in capsule structure. We found that in contrast to B. proboscidea, B. wellingtonensis produced larvae that, in isolation and in the presence of nurse eggs, developed into a wide range of offspring sizes. Mothers brood and hatch the larvae with frequent partial hatching of the brood during the brooding period. Although larvae could not liberate themselves, larvae crossed to other capsules as interconnections between capsules broke during the developmental period, potentially affecting food availability, sibling competition for nurse eggs, and cannibalism. Variation in brooding time and number of capsules deposited among sites suggest local adaptations.

Diversidad de nematodos marinos de Chile continental y antártico: una evaluación morfológica y molecular

Free-living nematodes are an important component of the marine benthos. In Chile there have been few studies on this group, and the majority has focused on the morphological aspect only. In this study, ribosomal 18S RNA and mitochondrial COI genes were used as genetic markers to complement morphological analyses to study the continental and Antarctic Chilean marine nematofauna. Different protocols for fixing, extracting and amplifying DNA were also tested. Not all the possible combinations produced good results. In fact, only the 18S gene showed consistently results. Phylogenetic analyses showed some discordance between classical taxonomy (i.e., based on morphology) and molecular data. These results suggest that taxonomic classification using integrative approaches including morphological characteristics and molecular information is needed to study the diversity and evolution of this complex group.

Asociación de Crepidula coquimbensis con Pagurus edwardsi: efecto sobre el potencial de dispersión y diferenciación genético poblacional

Crepidula coquimbensis is a protandric marine gastropod with direct development and restricted mobility, which only inhabits inside of empty shells of other marine gastropods cohabiting with hermit crabs of the genus Pagurus. In this study, we report potential dispersal mechanisms of C. coquimbensis and the effect on its population genetic distance and structure, using the gene COI, in three localities of northern Chile. The results suggested that C. coquimbensis shows high levels of genetic differentiation at local scale, and the association with P. edwardsi would be its only one mechanism of dispersal.

Presence of the tunicate Asterocarpa humilis on ship hulls and aquaculture facilities in the coast of the Biobío Region, south central Chile

Non-native ascidians are important members of the fouling community associated with artificial substrata and man-made structures. Being efficient fouling species, they are easily spread by human-mediated transports (e.g., with aquaculture trade and maritime transports). This is exemplified by the ascidian Asterocarpa humilis which displays a wide distribution in the Southern Hemisphere and has been recently reported in the Northern Hemisphere (NW Europe). In continental Chile, its first report dates back from 2000 for the locality of Antofagasta (23°S). Although there was no evidence about the vectors of introduction and spread, nor the source, some authors suggested maritime transport by ship hulls and aquaculture devices as putative introduction pathways and vectors. In the present study, we report for the first time the presence of A. humilis on the hull of an international ship in a commercial port in Concepción bay (36°S), south central Chile. We also found one individual associated to a seashell farm, 70 km far from Concepción bay. Further individuals were subsequently identified within Concepción bay: one juvenile settled upon international harbor pilings and a dozen individuals along aquaculture seashell longlines. For the first specimens sampled, species identification was ascertained using both morphological criteria and molecular barcoding, using the mitochondrial gene cytochrome c oxidase subunit I (COI) and a nuclear gene (ribosomal RNA 18S). The nuclear 18S gene and the mitochondrial gene COI clearly assigned the specimens to A. humilis, confirming our morphological identification. Two haplotypes were obtained with COI corresponding to haplotypes previously obtained with European and Northern Chilean specimens. The present study thus reports for the first time the presence of A. humilis in the Araucanian ecoregion, documenting the apparent expansion of this non-native tunicate in Chile over 2,000 km, spanning over three ecoregions. In addition we reveal the potential implication of the international maritime transport as a vector of spread of this species along the Eastern Pacific coast, and the putative role of aquaculture facilities in promoting local establishments of non-native tunicates.

Non-indigenous species contribute equally to biofouling communities in international vs local ports in the Biobío region, Chile

Abstract Growing coastal urbanization together with the intensification of maritime traffic are major processes explaining the increasing rate of biological introductions in marine environments. To investigate the link between international maritime traffic and the establishment of non-indigenous species (NIS) in coastal areas, biofouling communities in three international and three nearby local ports along 100 km of coastline in south-central Chile were compared using settlement panels and rapid assessment surveys. A larger number of NIS was observed in international ports, as expected in these ‘invasion hubs’. However, despite a few environmental differences between international and local ports, the two port categories did not display significant differences regarding NIS establishment and contribution to community structure over the studied period (1.5 years). In international ports, the free space could be a limiting factor for NIS establishment. The results also suggest that local ports should be considered in NIS surveillance programs in Chile.