No abstract

In Chile, management of natural resources usually starts right before its imminent collapse or after evident declination. In the northern area of the country, the fishery of brown seaweeds has an enormous social, ecological, and economical importance. More than 11,000 people depend directly or indirectly on the collection and harvesting of this resource. Ecologically, kelps constitute areas for food, reproduction, and refuge for hundreds of invertebrates and fish species. Economically, landings up to 300,000 dry tons per year represent close to US $60 million for the industry. Until 2002, the Chilean brown seaweed fishery was mainly sustained by natural mortality, where plants cast ashore were collected by artisanal fishermen. Since then, three brown seaweed species of economic importance (Lessonia nigrescens, Lessonia trabeculata, and Macrocystis pyrifera) have been intensively harvested in coastal areas between 18°and 32°S. To manage kelp populations along the northern Chilean coast, regulations have been based on the principle "how you harvest is more important than how much you harvest". This exploitation strategy has been adopted in consensus between fishermen, industries, governmental entities, and scientists. Since L. nigrescens represents more than 70% of total brown seaweed landings, this study tests the effects of L. nigrescens harvesting on the following population variables: (1) abundance, (2) distribution, (3) juvenile recruitment, (4) plant morphology, (5) frequency of reproductive plants, and (6) biodiversity of the macroinvertebrate community associated to kelp holdfasts. Our results show that, despite the enormous harvesting pressure on Lessonia density and biomass, the associated macroinvertebrate richness has been maintained, due to normal plant growth and high recruitment all year round.

For successful rearing of the flounder Paralichthys adspersus, it is important to optimize growth and survival in the early larval stages. Several authors indicate that the application of β-glucans and mannan-oligosaccharides (βG MOS) in rearing water should improve the larval health, diminishing the effects of physiological stress and physical damage that the aquaculture activities cause to the individuals. In order to evaluate the effect of βG MOS on P. adspersus incorporation on P. adspersus larval survival and growth in intensive culture, experiments were carried out with six-days post-hatch larvae, which had only just begun to feed on live prey (rotifers), and fifteen-day post-hatch larvae. Three treatments were used, applying 5 mg•L-1 , 10 mg•L-1 , and 15 mg•L-1 of βG MOS to the rearing water during the first five days of the experiment and then comparing the results with a control. The results indicate that applications of 5 mg•L-1 of βG MOS in the rearing water enhance larval survival and growth with respect to the control, whereas additions of 15 mg•L-1 of βG MOS suppressed both of these parameters. This effect increases for larvae that have recently absorbed the yolk sac. An histological analysis of the intestinal epithelium of the larvae suggests that βG MOS promotes the expression of monocytes (forerunner cells of macrophages) associated with the non-specific immune system of the fish.

Abstract.-Scurria scurra is a patelogastropod inhabiting the stipes and holdfasts cavities of Lessonia nigrescens complex species forming a herbivore-kelp association highly specialized. It has been proposed that the exploitation of kelp beds of Lessonia berteroana in northern Chile is a disturbance that affects Scurria-Lessonia association such as ENSO (El Niño-Southern Oscillation) events. Considering the above, and the important ecological role that have kelps as foundation species, this study proposes the use of Scurria-Lessonia association as an ecological indicator to monitor the integrity of kelp beds of L. berteroana. To achieve this, the abundance and size structure of S. scurra in plants of L. berteroana was evaluated under 3 different types of conservation strategies of fishing resources: open access areas and management areas (with harvest), and marine protected areas (without harvest) in the Region of Atacama and Region of Coquimbo, Chile. In addition, we monitored the time of recovery post-harvest of Scurria-Lessonia association in an experimental site (Lagunillas, 30°S). The results show that S. scurra population in open accessareas is dominated by juveniles in low abundances, a situation not detected in management areas and marine protected areas. Furthermore, the recovery of S. scurra post-harvest of Lessonia at the experimental site took more than 2 years (30 months). An indicator was proposed to validate the actions of management plan of brown algae for open access areas to fisheries. This ecological indicator is easy to observe, evaluate and disseminate among users of the productive chain of Chilean kelp resource. Key words: Kelp fisheries, ecological indicators, marine conservation, northern ChileResumen.-Scurria scurra es un patelogastrópodo que habita los estipes y cavidades de discos adhesivos del complejo de especies Lessonia nigrescens formando una asociación herbívoro-alga altamente especializada. En el norte de Chile, se ha propuesto que la explotación de praderas de Lessonia berteroana es una perturbación que afecta la asociación Scurria-Lessonia de manera similar que los eventos ENOS (El Niño-Oscilación del Sur). Considerando lo anterior, y el importante rol ecológico que cumplen las algas pardas como especies fundacionales, este estudio propone el uso de la asociación Scurria-Lessonia como un indicador ecológico para monitorear la integridad de praderas explotadas de L. berteroana.

Abstract.-This study establishes the dietary protein level for maximum growth in Paralichthys adspersus juveniles.According with this purpose, three diets based on fish meal were formulated with increasing protein levels (48, 57 and 60%), which were compared with a commercial diet (54% protein; BIOMAR S.A.). Furthermore, the optimal protein level were determined and compared through bioassays using growth indicators, fitness, and regression analysis. A total of 156 juveniles (131.3 ± 23 g), separated in 13 individuals per group, were maintained in black conical tanks with a flat base, with 5.5 kg m -2 initial densities, and with a circulation system of open water for 175 days. The fish were fed daily to satiety twice per day with diets based on fish meal and oil, starch, vitamins and minerals. Based on the results of this study, we conclude that the optimal dietary protein level was obtained in diets with 54 and 57% of protein. If production costs are prioritized in flounder culture, the 54% protein diet is optimal for juveniles. However, considering the flounder growth, then 57% protein diet contains the optimal level. This study is a precedent for further research on the nutritional requirements of P. adspersus in order to improve their growth in captivity.Key words: Aquaculture, nutrition, fish, food, indicatorsResumen.-Este estudio establece el nivel óptimo de proteína dietaria para obtener el máximo crecimiento de juveniles de Paralichthys adspersus. Con este propósito, se formularon 3 dietas con niveles crecientes de proteína en base a harina de pescado (48, 57 y 60%), las cuales fueron comparadas junto a una dieta comercial (54% de proteína; BIOMAR S.A.). El nivel óptimo de proteína fue determinado a través de bioensayos utilizando indicadores de condición, utilización del alimento y análisis de regresión. Un total de 156 juveniles (131,3 ± 23 g), divididos en grupos de 13 individuos, fueron mantenidos en estanques cónicos negros de base plana con densidad inicial de 5,5 kg m -2 , y con un sistema de circulación de agua abierto por un periodo de 175 días. Los peces fueron alimentados diariamente dos veces al día a saciedad. En base a los resultados de este estudio se concluye que el nivel óptimo de proteína dietaria fue obtenido con dietas de 54% y 57% de proteína. Si los costos productivos son priorizados en el cultivo del lenguado, entonces la dieta con 54% de proteína es óptima para alimentar a los juveniles. En cambio, si se considera el crecimiento de esta especie, entonces es la dieta con 57% de proteína la que contiene el nivel óptimo. Este estudio es un precedente para realizar nuevas investigaciones en los requerimientos nutricionales de P. adspersus con el fin de mejorar su crecimiento en cautiverio.Palabras clave: Acuicultura, nutrición, peces, alimentación, indicadores INTRODUCCIÓNEl lenguado, Paralichthys adspersus (Steindachner, 1867) es una especie promisoria para su cultivo porque tiene una alta demanda y valor comercial (Alvial & Manríquez 1999). Esta especie es un recurso sobreexplotado,...