Oscar R. Chaparro

Molecular Phylogenetic and Embryological Evidence That Feeding Larvae Have Been Reacquired in a Marine Gastropod

Evolutionary transitions between different modes of development in marine invertebrates are thought to be biased toward the loss of feeding larvae. Because the morphology of feeding larvae is complex and nonfeeding larvae or encapsulated embryos with benthic development often have simplified morphologies, it is presumed to be easier to lose a larval stage than to reacquire it. Some authors have gone so far as to suggest that feeding larvae, morphologically similar to the ancestral feeding larvae, cannot be reacquired. However, the larval structures of some groups, most notably gastropods, are often retained in the encapsulated embryos of species that hatch as benthic juveniles. Therefore the re-evolution of feeding larvae using the same structures may be possible in these groups. Here we present the first well-substantiated case for the recent re-evolution of feeding larvae within a clade of direct-developers. DNA sequence data show that Crepipatella fecunda, a species of calyptraeid gastropod with planktotrophic development, is nested within a clade of species with direct development, and that Crepipatella dilatata, a species with direct development, appears to be paraphyletic with respect to C. fecunda. Observation of the embryos of C. dilatata shows that the features necessary for larval feeding and swimming are retained in the encapsulated veligers, suggesting that heterochronic shifts in hatching time and changes in nurse-egg allotment could have resulted in the re-evolution of feeding larvae in this species.

Recent developments, status, and prospects of molluscan aquaculture on the Pacific coast of South America

Abstract A detailed review is given of recent developments, status, and prospects of molluscan aquaculture on the Pacific coast of South America. A brief history of the fishery and cultivation efforts reveals that in Colombia (Pacific coast), Ecuador, and Peru the production of molluscs is entirely based on the natural resources and is chiefly restricted to mussels, scallops ( Chlamys purpurata ), and the mangrove cockles of the genus Anadara . Culture activities in these three countries are still in a preliminary experimental stage. In Chile, at least nine species of clams (such as Protothaca thaca, Ameghinomya antiqua, Mulinia spp., and Mesodesma donacium ), three species of mussels ( Mytilus chilensis. Choromytilus chorus , and Aulacomya ater ), the native oyster Ostrea chilensis , and the Chilean abalone Concholepas concholepas are of great commerical value. Large-scale aquaculture efforts, however, are restricted to M. chilensis, C. chorus, A. ater , and the Chilean oyster. First attempts to intensify the culture of scallops ( C. purpurata ) in the north of Chile have had favorable results with respect to future large-scale developments. The introduction and cultivation of Crassostrea gigas is still in an experimental stage. Potential intensification and modernization of culture methods; technical, economic, and sociopolitical problems; and new opportunities and prospects for expansion are analyzed and discussed. The discussion includes an evaluation of the fishery and cultivation products in light of the world market. Enhanced production of underutilized species and enhanced use of underutilized areas for future mariculture installations are analyzed in light of potential new markets. Finally, a detailed list of problem areas is given to form a basis for future research efforts.

The importance of broodstock nutrition on the viability of larvae and spat in the Chilean oyster Ostrea chilensis

Abstract Broodstock of the Chilean oyster Ostrea chilensis were conditioned at 17 °C and fed with monospecific cultures of Chaetoceros gracilis, Isochrysis aff. galbana or Pseudoisochrysis sp. offered daily at a ration equivalent to 1.5% of dry tissue weight of the oysters. A group of starved oysters maintained in the hatchery and a second group held under natural conditions in the estuary of the Quempillen River were used as controls. Spawning began earlier in the broodstock fed Pseudoisochrysis (mean time 23 days after the initiation of conditioning) than in the other groups held in the hatchery (32–35 days). In the estuary, however, spawning occurred much later (91 days from the beginning of the experiment). The mean diameter of the eggs released ranged from 210 μm (Pseudoisochrysis condition) to 268 μm (estuary condition). There was a positive correlation between egg diameter and the lipid, protein and carbohydrate contents, which were highest in eggs produced by females maintained in the estuary and lowest in eggs from females fed Pseudoisochrysis. Females held in the estuary released the largest pediveliger larvae (mean diameter 461 μm) at the end of the brooding period, whereas starved females released the smallest pediveligers (mean diameter 317 μm). The highest growth rates were recorded in the spat produced by females which ripened in the estuary, followed by spat from females fed I. aff. galbana. Instantaneous mortality rates were lowest in these two groups. Spat produced by starved females showed low rates of growth and survival.

Embryonic Velar Structure and Function of Two Sibling Species of Crepidula With Different Modes of Development

The structure and function of the embryonic velum of two closely related species of Crepidula with different modes of development are examined. The velum of C. dilatata, a direct developer whose embryos feed on nurse eggs, does not differ substantially from the velum of C. fecunda, a species with planktotrophic larvae. Although velar ciliation develops earlier in embryos of C. dilatata, embryos of both species were able to feed on small particles, using the opposed-band ciliary mechanism. However, the embryos of C. dilatata lose this ability as they grow. The embryos of C. dilatata were not able to swim, whereas those of C. fecunda swam consistently in vials of seawater. This difference in swimming ability is probably due to differences in velum-body size allometry between the two species.

Grazing-filtration as feeding mechanisms in motile specimens of Crepidula fecunda (Gastropoda: Calyptraeidae)

Quantification of ingestion by grazing and by filtration in Crepidula fecunda showed that during the motile phase of the life cycle (<28 mm in shell length), the species depends on both feeding strategies to supply its energetic requirements. This species improves the energetic quality of the material ingested by exercising preferential selection for organic material from all the materials that are available on the substrate, with an average organic enrichment of 13%. The ontogenetic change in the relative importance of grazing and filter feeding appear to be species-specific within the genus; some species have motile forms in earlier life stages which need to move about the substrate to obtain food and locate aggregations of conspecifics. After growing to about 28 mm in length, C. fecunda become sessile females and depend solely on filter feeding to meet their nutritional requirements.

Physiological energetics of the estuarine crab Hemigrapsus crenulatus (Crustacea: Decapoda: Varunidae): responses to different salinity levels

Hemigrapsus crenulatus is an abundant and frequent decapod crustacean inhabiting estuarine environments, where it must tolerate large shifts in salinity. The present study evaluates the effect of salinity (5, 13, 21 and 30 psu) on the adult physiological processes related to the energy balance. The growth potential (SFG) and the respired oxygen:excreted nitrogen ratio were used as indices of stress. Ingestion, excretion and respiration rates showed a significant dependence on salinity, being higher at low salinities. The assimilation efficiency remained constant along the studied salinity gradient. The assimilation and ingestion rates were inversely related with the salinity. Given this scenario, the growth potential remained constant within the studied salinity gradient, as did the oxygen:nitrogen ratio. The results suggest that the increased energy losses at low salinity due to respiration and excretion are compensated by an increment in the ingestion rate, contributing to the success of H. crenulatus in dynamic habitats such as estuaries.

Short-term feeding response of the mussel Mytilus chilensis exposed to diets containing the toxic dinoflagellate Alexandrium catenella

La respuesta inicial del bivalvo Mytilus chilensis fue medida bajo cuatro dietas que contenian diferentes proporciones del dinoflagelado toxico Alexandrium catenella. Las dietas que contenian las concentraciones mas altas de este dinoflagelado mostraron el mayor efecto durante las primeras horas de exposicion. Despues de este periodo inicial, M. chilensis demostro la capacidad para aclimatarse a estas dietas toxicas, con parametros de alimentacion que alcanzaron valores similares a aquellos de los organismos controles. No fue claro si el efecto negativo sobre la conducta de alimentacion fue causado por la presencia de la toxina paralizante o debido al gran tamano de las celulas del dinoflagelado, en comparacion al tamano de las celulas de Isochrysis galbana usadas en la dieta control. Sin embargo, estudios paralelos con dietas conteniendo el dinoflagelado no toxico Alexandrium affine, de similar tamano y forma a A. catenella, sugieren que el tamano de las celulas fue la causa principal que afecto la conducta de alimentacion. La capacidad de aclimatacion ya sea a la toxina o al tamano celular del dinoflagelado, identifica a M. chilensis como una buena especie para la deteccion temprana de eventos toxicos producidos por A. catenella, ya que debido a su relativa insensibilidad a la toxina permite una rapida recuperacion de su conducta de alimentacion y la acumulacion de toxina en sus tejidos

Regulatory aspects of the brood capacity of Crepidula fecunda, Gallardo 1979 (Gastropoda: Calyptraeidae)

Incubation is thought to increase embryonic survival in numerous groups of marine invertebrates. This paper considers whether the production of gametes and physical space involved in capsular incubation limits brooding capacity in Crepidula fecunda, a marine gastropod from the coast of Chile. C. fecunda females spawned only mature eggs, leaving immature eggs within the gonad. Average oocyte area was significantly different (P<0.05) between nonincubating females, those at terminal incubation (with advanced veligers), and those containing a pinnotherid crab, compared to females in early stages of incubation. Over the period of brooding, the area occupied by the capsules increased, and the area of the foot of the incubating female was gradually reduced. C. fecunda females that hosted a pinnotherid crab in the incubation space did not lay eggs during the 12-month study period. Addition of a pinnotherid to the incubation area completely inhibited oviposition. Addition of a crab-sized piece of parafilm inhibited the process in more than 80% of females, while none of the females from which the pinnotherid was eliminated failed to deposit egg capsules within the 5-week study period. This suggests that any material filling the brood space inhibits deposition of egg capsules.

Histological characteristics of the foot and locomotory activity of Crepidula dilatata Lamarck (Gastropoda: Calyptraeidae) in relation to sex changes

Abstract Crepidula dilatata Lamarck individuals can be categorized into one of the following sexual states: immature (up to 8.5 mm shell length), male (7.5–19.0 mm), intersex (11.5–19.9 mm) or female (over 17.3 mm). Histological analysis of the gonads shows protandry in this species. The locomotory activity of these animals diminishes from active movement in the early stages, juveniles, and males to a strong sessile condition in females. This is related to reproductive mechanisms which involve copulation, benthic capsules and parental care. Histological analysis of the foot shows prevalence of three types of epithelial mucocytes in motile animals. A fourth type of mucocyte (M4) is present in higher abundance in sessile females and is associated with a greater adhesive capacity of the foot for the substrate. Predominance of smooth muscle bundles in the foot of younger animals will also facilitate locomotion. Older, sessile animals have thick columellar muscles, possibly associated with the need to lift the shell up for ventilation and feeding.

Unusual source of food : impact of dead siblings on encapsulated embryo development of Crepipatella fecunda (Gastropoda: Calyptraeidae)

Embryonic cannibalism has been identified in directly developing calyptraeid species through observation of the ingestion of encapsulated sibling embryos. The object of the present study was to determine the effects of experimentally induced cannibalism on larval development in encapsulated larvae of Crepipatella fecunda (a species having mixed development). The effects studied included the time of intracapsular development, protoconch size and velar characteristics of the larvae. Mortality was induced during intracapsular development through mechanical disruption (‘treatment’) of embryos. A treatment and control group of embryos from the same female were compared. Encapsulated veligers actively fed on their sacrificed congeners. Larvae hatched in less than 10 days from treated capsules and had mean shell lengths and velum areas significantly lower than those from the control, but no significant differences in cilia length. In treated capsules where the embryos underwent a slow development (>20 days), the larvae produced shells, vela and cilia larger than those of the controls. In an intermediate period of intracapsular development, the differences recorded among larval characters were not statistically significant. The results showed that: (1) the encapsulated veligers were capable of feeding on exogenous food before hatching; (2) the consumption of non-living congeners decreased the time of intracapsular development; and (3) the morphometry of the larvae hatching from treated capsules varied depending on the period of intracapsular development and seems to be adaptively stabilised towards homogeneous larval morphometry.