Centro i-mar

ABSTRACT Protandrism was confirmed in Crepidula fecunda Gallardo 1979 by histological analysis of the gonad. Individuals were classified as immature (12 mm or less in shell length), male (13–26 mm), intersex (25–28 mm), and female (over 26 mm). There was an evident loss of mobility with growth— large females became completely sessile. The presence of epithelial glands in mobile individuals was associated with the need for lubrication during crawling, whereas the proliferation of subepithelial glands in sessile females was associated with adhesion. Mobility of immature and male individuals was related to grazing activities on biofilms, and in males was also associated with copulation. Grazing activity of motile individuals was carried out so that the radula teeth did not come into direct contact with the substratum, but rather harvested the biofilm surface. Sessile females used the radula to rasp the area under their shells, thus cleaning the substratum in preparation for oviposition. Since this process required that the radula enter into direct contact with the substratum, it suffered abrasion of radular teeth and loss of radular denticles, producing important alterations in its appearance in mature females. A complex interaction was observed between size, mobility, histological changes in the foot, activity, and tooth‐wear of the radula, which have been related to the sessile habit, sex change, and the oviposition process in this species.

ABSTRACT Euphausia mucronata es un organismo del zooplancton endémico de la corriente Peru-Chile. Su abundancia aparece estrechamente asociada a zonas de surgencia costera, lo que plantea una interrogante acerca de cómo es que los individuos evitan ser arrastrados lejos de la zona de surgencia por las corrientes derivadas del proceso de surgencia. El objetivo de esta tesis fue poner a prueba en el foco de surgencia de Pta. Angamos (Península de Mejillones) dos mecanismos generales propuestos para la mantención de larvas de eufausido en zonas de surgencia costera. El primer mecanismo se basa en una migración vertical de los individuos, que de tener la amplitud suficiente, podría llevarlos a encontrar un flujo profundo en dirección inversa al que los aleja de la zona de surgencia. El segundo supone que no existe migración vertical de larvas, proponiendo que la retención de larvas puede producirse en frentes térmicos superficiales y /o remolinos producto de la interacción de la circulación inducida por la surgencia y la configuración topográfica de la costa al interior de bahías orientadas al ecuador.Los resultados mostraron que toda el área de la Península estuvo dominada desde la superficie hasta mas de 200 m por un flujo hacia el sur, sobre el que se sobrepuso la circulación derivada de la surgencia costera. En lugares donde se encontró filamentos atribuibles a la circulación de surgencia, estos no superaron los 20 m superficiales. Un filamento se dispuso en dirección norte desde la Pta. Angamos y el otro ingresó a Bahía Mejillones, girando luego hacia el norte siguiendo la línea de costa. Dentro de Bahía Mejillones y desde el filamento a la costa, se encontró una sombra de surgencia, y hacia fuera del mismo filamento se encontró un remolino apreciable desde superficie hasta más de 100 m.No se encontró evidencias de migración vertical diaria en ningún estado de desarrollo. Se observó evidencia de una migración ontogenética sobre el filamento oceánico, pero no sobre el filamento costero. El mayor porcentaje de larvas se encontró entre el límite inferior de la circulación asociada a los filamentos, en donde las velocidades netas son las más bajas de la columna de agua. Al interior de Bahía Mejillones, la abundancia de larvas fue mayor en los frentes térmicos y en el remolino comparados a la encontrada en el filamento costero y la sombra de surgencia. La composición de las larvas indica que en los frentes y remolino ellas pueden ser retenidas hasta completar su desarrollo. Euphausia mucronata is an endemic zooplanctonic organism of Peru-Chile current. Its abundance is related to coastal upwelling zones. However, coastal upwelling habitats are highly advective-diffusive environments, which impose contraints for the maintenance of local population of plankton. ¿How then is the larvae population of E mucronata retained in coastal region?The goal of this thesis was test two larval retention mechanisms in the Pta. Agamos coastal upwelling center. The first mechanism is based on diel vertical migration behaviour of larvae. If vertical migration have the correct aplitude it might bring larvae to compensatory subsurface current, transporting larvae back to the coast. The second mechanism assume no vertical migration. In this case, larvae can be retained in secondary thermal fronts and/or eddies produced by the interaction between upwelling circulation and topography whithin the equator oriented Mejillones Bay.The results shows a dominance of poleward circulation which compromise at least the measured 0 - 200 m layer. Over this circulation field could be recognized upwelling derived circulation, affecting 0 – 20 m layer. In active upwelling condition the upwelling filament develop two branches, one toward north and other toward Mejillones Bay, turning to north close to Bay’s coast. An upewlling shadow was encountered beteween the coastal filament and Bay’s coast, and in the north-west side of the filament a cyclonic eddie was encontered, comprising at least 0 – 100 m layer.No one of larval stages show diel vertical migration. Evidence of ontogenetic migration was observed in the oceanic filament, but not in coastal filament. The bulk of larvae were in the limit of 0-20 m and 20-80 m layers, where net velocities were the smallest of column water. Whithin Mejillones Bay, the larval abundance was grater in secondary thermal fronts and cyclonic eddie than coastal filament and upwelling shadow. The larval composition indicates that fronts and eddies can retain larvae enough to complete the development.

Hypoxia–temperature interactions can have major effects upon fish physiology and energetics. In estuarine species, such effects can be also modified by natural salinity gradients leading to a three-way habitat contraction under extreme conditions. In this paper we use Fry's paradigm to propose an explanatory framework and to expand traditional mass balance bioenergetic models, incorporating dissolved oxygen and salinity effects. Water temperature was modeled as the controlling factor that establishes maximum potential rates and minimum oxygen demand; dissolved oxygen was considered to constrain physiological responses whenever oxygen demands exceed oxygen delivery rates; salinity was incorporated as a masking (loading) factor, demanding both energy and oxygen for osmoregulation processes. This general framework was expressed as a set of algorithms, with a total of 30 parameters, which were estimated using results from a large set of laboratory experiments conducted on young-of-the-year and yearling Atlantic sturgeons, as well as from other published studies. Compared to an empirical quadratic fit of these laboratory data, the model was more informative (lower AIC), suggesting that measured responses followed theoretical expectations. The model was tested in mesocosm trials, where strong correlations were observed between predicted and observed monthly and seasonal growth rates but modest to poor correlations were observed for predicted daily instantaneous growth rate. Sensitivity tests showed that uncertainty in activity cost and food consumption ratio parameters contributed most to model error.

The present work reports behavioural responses by young-of-the-year (21–30 cm) Atlantic sturgeon Acipenser oxyrinchus oxyrinchus and shortnose sturgeon Acipenser brevirostrum to nine binary combinations of dissolved oxygen saturation (40, 70 and 100%), temperature (12, 20 and 28°C) and salinity (1, 8 and 15). Both species showed no acclimation effects and similar discrimination and avoidance reactions to hypoxia (40% oxygen saturation), selecting higher dissolved oxygen choices in 71% of the tests. Acipenser oxyrinchus oxyrinchus and A. brevirostrum showed a similar preference for 20°C (>64% incidence), but differed in their responses to extreme temperature choices. Acipenser brevirostrum showed a significant avoidance behaviour to the 12°C but not to the 28°C choice. In contrast, A. o. oxyrinchus showed similar preference for 12 and 20°C, but avoided the 28°C choice in 71% of the tests where this temperature was included (P < 0·01). No significant preferences were observed among salinity choices, except between salinities 1 and 8, where A. o. oxyrinchus showed a significant preference for salinity 8. Behavioural responses matched expectations from bioenergetics in both species and were also consistent with the distribution of juvenile A. o. oxyrinchus capture locations in the Chesapeake Bay.

Southern blue whiting Micromesistius australis support one of the largest industrial fisheries in South America. Two main spawning/nursery grounds are known: one in the SW Atlantic Ocean (SWA), southwest from the Falkland (Malvinas) Islands; and other in the SE Pacific Ocean (SEP), south from the Taitao Peninsula. Juveniles originating from both grounds are believed to mix during migration and/or in feeding areas in the Scotia Sea. Previous efforts to distinguish stocks in this area have yielded contradictory results between genetics and otolith microchemical analyses. In the present work we revisited the null hypothesis of a single stock occurring in the broader SWA-SEP region by comparing and integrating results from different approaches: trace metals (Ca, Sr, Ba, Mg, Mn) and stable isotopes (δ13C, δ18O) in otolith cores, and parasite assemblage compositions in adults from SWA and SEP spawning grounds. We found significant differences in Sr:Ca, δ13C and δ18O mean ratios between spawning grounds. The best trace element discriminant model classified 83% of the samples. Each stable isotope discriminated >90% of the samples, while combining them into a bivariate discriminant model led to 100% classification success. Higher δ18O levels in the SWA samples agreed with lower mean temperature and higher ambient δ18O levels in that area. Parasite assemblage compositions also showed significant differences between grounds regarding the prevalence of Chondracanthus, Contracaecum, Hepatoxylon and Grillotia and the abundance of Diclidophora, Anisakis, Contracaecum, Hysterothylacium and Hepatoxylon. Parasite-based discriminant models supported 90–100% correct assignment of samples to capture location. Although preliminary due to limited sampling coverage, our results support the existence of at least two ecologically distinct sub-populations of southern blue whiting in South America. The joint use of otolith microchemistry and parasitological techniques showed to be a promising way to test hypotheses concerning ecological stocks in marine fishes.

For rare and endangered species, bioenergetics modeling can represent a valuable approach for understanding issues of habitat value and connectivity among potential habitats within nurseries in restoration programs. We used multivariable bioenergetics and survival models for Atlantic sturgeon to generate spatially explicit maps of potential production in the Chesapeake Bay. For the period 1993 2002, spatial and temporal patterns in water quality effects (temperature, dissolved oxygen [DO] and salinity) on potential production were evaluated. In addition, two forecasted scenarios were modeled: one implementing newly revised U.S. Environmental Protection Agency (EPA) DO-criteria for the Chesapeake Bay, and the other assuming a bay-wide increase of 1 °C due to an underlying trend in regional climate. Atlantic sturgeon's low (survival/growth) tolerance to temperatures >28 °C was a critical constraint during their first 1 2 summers of life. Hatched in freshwater (spring to mid-summer), young-of-the-year were predicted to occupy cooler (deeper) areas as temperature approached sub-lethal levels. While most thermal refuges were located down-estuary, a large fraction of potential refuges were unsuitable due to persistent hypoxia and/or salinity levels beyond the limited osmoregulatory capabilities of early juvenile Atlantic sturgeon. As a result, suitable summer habitats for juvenile Atlantic sturgeons in the Chesapeake Bay were predicted to be spatially restricted and variable between years, ranging from 0 to 35% of the modeled bay surface area. In critical (drought) years, almost no summer habitat was predicted to be available for juvenile Atlantic sturgeon. Value and size of nursery habitat was highly sensitive to climatic oscillations and anthropogenic interventions affecting freshwater inflow, water temperature and/or DO. Achieving EPA DO-criteria for the Chesapeake Bay was predicted to increase total suitable habitat by 13% for an average year, while increasing water temperature by just 1 °C bay-wide would reduce suitable habitat by 65%.

Orange roughy Hoplostethus atlanticus juveniles <24 cm fork length (LF) (10–17 years old) were recorded for the first time in Chile, when 10 specimens were collected on the continental slope and seamount JF2 in Juan Fernandez Archipelago. The LF, total mass, anatomical and parasitological information are reported. Relevance to current life-cycle hypotheses is discussed.

For rare and endangered species, bioenergetics modeling can represent a valuable approach for understanding issues of habitat value and connectivity among potential habitats within nurseries in restoration programs. We used multivariable bioenergetics and survival models for Atlantic sturgeon to generate spatially explicit maps of potential production in the Chesapeake Bay. For the period 1993–2002, spatial and temporal patterns in water quality effects (temperature, dissolved oxygen [DO] and salinity) on potential production were evaluated. In addition, two forecasted scenarios were modeled: one implementing newly revised U.S. Environmental Protection Agency (EPA) DO-criteria for the Chesapeake Bay, and the other assuming a bay-wide increase of 1 °C due to an underlying trend in regional climate. Atlantic sturgeon's low (survival/growth) tolerance to temperatures >28 °C was a critical constraint during their first 1–2 summers of life. Hatched in freshwater (spring to mid-summer), young-of-the-year were predicted to occupy cooler (deeper) areas as temperature approached sub-lethal levels. While most thermal refuges were located down-estuary, a large fraction of potential refuges were unsuitable due to persistent hypoxia and/or salinity levels beyond the limited osmoregulatory capabilities of early juvenile Atlantic sturgeon. As a result, suitable summer habitats for juvenile Atlantic sturgeons in the Chesapeake Bay were predicted to be spatially restricted and variable between years, ranging from 0 to 35% of the modeled bay surface area. In critical (drought) years, almost no summer habitat was predicted to be available for juvenile Atlantic sturgeon. Value and size of nursery habitat was highly sensitive to climatic oscillations and anthropogenic interventions affecting freshwater inflow, water temperature and/or DO. Achieving EPA DO-criteria for the Chesapeake Bay was predicted to increase total suitable habitat by 13% for an average year, while increasing water temperature by just 1 °C bay-wide would reduce suitable habitat by 65%.

Dissolved oxygen and salinity are relevant structuring factors which should be incorporated into habitat and bioenergetic models for estuarine fishes. We measured growth, food consumption, routine and postprandial metabolism, egestion and survival responses of juvenile Atlantic sturgeon (young-of-the-year: YOY, 6–48 g) in an incomplete factorial array of temperature, salinity and dissolved oxygen levels. Complementary measures were also conducted on yearlings (1 year-old, 70–300 g) to evaluate size and age effects upon food consumption and growth. All three factors had a significant effect on major bioenergetic responses, as well as several of their first order interactions. Maximum growth and food consumption rates were observed above 70% dissolved oxygen saturation, at 20 °C, and between salinities of 8 and 15. Postprandial metabolism was reduced and egestion increased under hypoxia (50% DO saturation), suggesting compensatory mechanisms aimed to reduce assimilation rates. A significant shift in growth responses with age indicated higher tolerance to salinity in yearlings than in YOY. No other size dependent changes were significant, either for hypoxia or for temperature effects. Survival tended to increase with dissolved oxygen saturation, and decreased at the highest temperature and salinity levels. Our results indicated both additive and synergistic effects of tested environmental factors upon ecophysiological responses and highlighted the need to consider these in new bioenergetic models.

Deep-sea fishes have been poorly sampled globally, and overall knowledge of demersal fish distributions and the drivers of community composition and diversity remain limited. Here, we used nine comparable datasets with species-level identification of fishes from research surveys around the world to test the hypothesis that deep-sea demersal fish assemblage composition on seamounts is consistent between major oceans. Two levels of analysis were undertaken: the first combined all presence-absence data from a seamount, while a second more detailed analysis included catch weight data based on a smaller number of seamounts. Overall, there was a consistent separation of seamounts by region based on the compositions of their fish assemblages. New Zealand and SE Australian seamounts have a very similar ichthyofauna, which differs substantially from seamounts in the eastern South Pacific Ocean off Chile. In the North Atlantic, Bear Seamount appears to be distinct from all others, while seamount fish assemblages off Ireland, the Azores, and Faraday Seamount have some affinities. The Tasman Sea and New Caledonian seamounts show strong intra-regional variation. On an ocean basin scale we therefore reject the hypothesis that the composition of deep-sea demersal fish fauna is homogeneous globally. However, regional patterns of both species composition and relative abundance show some similarities between widely separated geographical locations, especially where orange roughy is a dominant species. Salinity was the main environmental factor identified in a multivariate analysis of environmental covariate data. This is likely to be a result of salinity being a key characteristic defining both Antarctic Intermediate Water and North Atlantic Deep Water, the water masses found over most seamounts examined in this study, and which may explain similarities between deep-sea fish assemblages.

The transport of marine invertebrate larvae is strongly influenced by their distribution in the water column, which could be affected by the biological features of the larvae and environmental variables. Larvae can modify their swimming behavior throughout their planktonic cycle, thereby changing the observed distributional patterns. This ability, coupled with oceanographic features, could induce landward or seaward transport. We studied the vertical distribution of C. concholepas larval stages in two differently stratified systems in Chilean inland seas; Refugio Channel (a strongly stratified channel, where previously has been described as a frontal system) and Guaitecas (a gently stratified system). Combinations of 12–24 h larval collection experiments were done simultaneously with fixed temperature and salinity profiles; meteorological data were also obtained. The results suggest that both salinity and day period influence the C. concholepas distributional patterns in the water column. Early veliger and competent larvae are concentrated in different parts of the water column, probably related to their transport capacities. The upper layer of the water column at the Refugio site, unlike the Guaitecas site, showed a stratified regime, which could affect larval density and larval length between the two sites. Finally, our results suggest that Refugio may be a sink habitat for C. concholepas.