Tamara Rubilar

Echinoderms from Argentina: Biodiversity, Distribution and Current State of Knowledge

This chapter reviews the research on echinoderms that occur in the waters of Argentina. One hundred and thirty-four echinoderm species have been recorded. Two species of Crinoidea, 58 Asteroidea, 32 Ophiuroidea, 16 Echinoidea, and 26 species of Holothuroidea. The variety of marine environments and the main oceanographic processes in the region are described. Comprehensive information regarding historical and recent echinoderm research is included. A review of the biological, ecological, and chemical research of species inhabiting the Argentine Sea is also presented. Until recently studies on echinoderms in Argentina were very limited. Further studies should be carried out to increase knowledge of the biology and ecology of the fauna. In addition, systematic and phylogenetic studies of Asteroidea, Ophiuroidea and Holothuroidea are needed. Echinoderm fisheries have been sporadic occurring only in the Beagle Channel, especially for the local market. Benthic disturbance resulting from bottom trawling fisheries at various localities seems to be a major threat to echinoderms in the Argentine Sea.

Temporal and spatial differences in the reproductive biology of the sea urchin Arbacia dufresnii

The reproductive cycle of Arbacia dufresnii was studied in two contrasting populations on the eastern coast of Patagonia (Nuevo Gulf and San Jorge Gulf) from January 2008 to August 2010. Sea urchins from San Jorge Gulf had larger test diameter and heavier gonads than did sea urchins from Nuevo Gulf. A. dufresnii showed an annual cycle in both populations, with gametogenesis occurring mainly in the autumn and the winter. An extended spawning period took place during the spring and the summer. Sea urchins from Nuevo Gulf had a strong seasonal pattern of reproduction, with presence of gonadal stages showing re-absortion and accumulation of reserves in nutritive cells at different seasons, whereas individuals from San Jorge Gulf had mature gametes during most of the year. Interannual variation of seawater temperature affected the gamete production and spawning duration in both populations. Higher temperatures during gametogenesis enhanced gonadal growth and gametes were released early. The major population differences found in gonadal cell composition highlight the plasticity in reproductive traits of A. dufresnii, and may be responsible for the wide distribution of A. dufresnii in different environments.

Ingestion, Absorption and Assimilation Efficiencies, and Production in the Sea Urchin Arbacia dufresnii Fed a Formulated Feed

ABSTRACT Sea urchins have been used as a source of food from prehistoric times and as a research animal model since the 19th century. They presently are harvested in many parts of the world. In Argentina, sea urchins have been studied only from biological perspectives. Of the 14 species of sea urchins found off the coast of Argentina, Arbacia dufresnii is the most abundant. It is an omnivorous species that exists in dense populations in Nuevo Gulf. Biomass production in sea urchins, especially gonad yield, is related to food quantity and quality. In the field, A. dufresnii has a small size and low gonad biomass and gamete production. Therefore to test the hypothesis that a high-quality formulated food would produce more biomass and gonad yield than that found in the sea urchins from a natural population, sea urchins were reared in a laboratory aquaculture system for 8 wk in autumn when gametogenesis occurs. In April, 30 sea urchins were collected and dissected to establish the initial condition (Baseline). Another 32 sea urchins were collected in April and maintained until June in aquaria at constant temperature and salinity and fed a formulated feed (Fed). At the conclusion of the experiment, 30 sea urchins were collected from the field population in June (Field) to establish the population condition in the Field and for comparison with the Fed sea urchins. Fed sea urchins had a 20% greater gain in weight resulting from an increase in both somatic and gonadal tissue beyond that of the field population. All organs increased in weight in females and all organs except the lantern in males. The absorption efficiency in Fed sea urchins was over 80%. Fed sea urchin had organic biomass production higher than Field sea urchins. Differences were found in the gonad cellular composition: Fed females had a unimodal oocyte size-frequency distribution, in contrast to a multimodal distribution in Field females. Fed males had fewer mature gametes than Field males. Both testes and ovaries had more nutritive phagocytes in Fed sea urchins than in Field sea urchins. Proximate composition of gonads, however, was similar in Fed and Field sea urchins. Fed individuals showed a remarkable increase in biomass production. The biochemical and cellular composition of the gonads reflected this. This indicates that A. dufresnii fed a highly nutritional food is able to assimilate nutrients with high efficiency and produce an increased gonad yield.

Nutrient allocation in the gonads of the sea urchin Arbacia dufresnii in different stages of gonadal development

This study reports nutrient allocation in different stages of gonadal development for two populations of the sea urchin Arbacia dufresnii off the Patagonian coast of Argentina (Nuevo Gulf and San Jorge Gulf). The biochemical composition of gonads was used to assess nutrient allocation by measuring ash, soluble protein, lipid and trichloroacetic acid-soluble carbohydrate concentrations, and absolute contents over a 24-month period. Reproductive output in terms of energy was calculated for females. Results were correlated with histological stage of the gonads. Soluble proteins were the main component for the Nuevo Gulf population while unmeasured organic material (i.e. insoluble proteins and nucleic acids, especially in testes) was prevalent in gonads from San Jorge Gulf. Soluble protein and lipid concentrations followed the gonadal cycle, while carbohydrate concentration was almost negligible, especially in the Nuevo Gulf population. The different patterns in the gonadal cycle in the two populations were reflected in the biochemical composition of gonads. Concentrations and contents of the biochemical components and reproductive output were higher in the population from San Jorge Gulf owing to the larger size of gonads and gametes. These findings contribute to the better understanding of the plasticity of the reproductive biology of A. dufresnii in different environments.

Embryonic development of Pachycheles chubutensis (Decapoda: Anomura)

The different stages of embryonic development of the porcellanid crab Pachycheles chubutensis are described, along with the chronology of each stage at 16 ± 1°C. Five different developmental stages (I-V) were recognized including: (i) early cells and 100% of the vitellum; (ii) formation of the embryonic primordium at the animal pole of the egg; (iii) presence of dark pigmentation on the posterior part of the ocular globe ; (iv) appearance of chromatophores on mouth parts and in the abdominal zone; and (v) eyepigmentation in circular-oval form, filling the entire surface. The embryonic development lasts from spawning to hatching approximately 21 days, with the second stage being the longest.