Composición y estructura de la comunidad de moluscos de fondos blandos de la isla Santa Cruz, golfo de California, México

Background. In the marine environment of San Cruz Island, no published references exist regarding the ecology of soft-bottom mollusks. Thus, it is important to carry out research that broadens and deepens the knowledge of this marine area and contributes to proposals of management methods and alternatives for the sustainable use of insular marine resources. Goals. This study seeks to characterize the community composition and structure of soft-bottom mollusks of the infralitoral zone of Santa Cruz Island, and describe some of the characteristics associated with their habitat. Methods. During August 2010, 32 samples were collected: 16 were biological samples and 16 were sediment samples. The composition, abundance, and diversity of the malacological community were analyzed using ecological indexes. Results. 695 individuals were recorded and grouped in two classes: Gastropoda with 446 organisms (5 orders, 11 families, and 19 species); the most abundant species was Siphonaria maura (18%); the class Bivalvia included 249 organisms (8 orders, 14 families, and 25 species); the most abundant species was Tellina eburnea (10%). The Gastropoda class were more abundant than the Bivalvia, i.e., 64.17% and 35% respectively. The species with major abundances and relative frequencies were the gastropods Siphonaria maura (18%) and the bivalve Septifer seteki (69%). Four trophic categories were identified: filterers (73%), herbivores (20%), carnivores (5%), and ectoparasites, the latter of which were the rarest group (2 %). Conclusions. At this site, the specific richness (44 taxa) was lower compared to other sites from different latitudes of the western Gulf of California, likely derived from the higher energy environment of the study area that allowed only juvenile mollusks and micromollusks to be collected.  Antecedentes. Respecto al ambiente marino de la isla Santa Cruz, no existen trabajos publicados de ecología de las especies de moluscos de fondos blandos, por lo que es importante realizar investigaciones que amplíen y profundicen el conocimiento de la zona marina y contribuyan a plantear métodos de manejo y alternativas de uso sustentable de los recursos marinos insulares. Objetivos. El presente trabajo pretende caracterizar la composición y estructura de la comunidad de los moluscos de fondos blandos de la zona infralitoral de la isla Santa Cruz y describir algunas características asociadas con su hábitat. Métodos. En agosto de 2010 se recolectaron 32 muestras, 16 biológicas y 16 de sedimentos. Se analizó la composición, abundancia y diversidad de la comunidad béntica malacológica mediante indicadores ecológicos. Resultados. Se registraron 695 ejemplares agrupados en dos clases, Gastropoda: 446 organismos (cinco órdenes, 11 familias y 19 especies), entre los cuales la especie más abundante fue Siphonaria maura (18%); y Bivalvia: 249 organismos (ocho ordenes, 14 familias y 25 especies), donde la especie más abundante fue Tellina eburnea (10%). La clase Gastropoda fue mayor (64.17%) que Bivalvia (35.82%). Las especies con mayor abundancia y frecuencia relativa fueron el gastrópodo Siphonaria maura (18%) y el bivalvo Septifer zeteki (69%). Se encontraron cuatro categorías tróficas: filtradores (73%), herbívoros (20%), carnívoros (5%) y ectoparásitos (2%). Conclusiones. En este sitio, la riqueza específica (44 taxones) fue menor en comparación con otros sitios de diferente latitud en el golfo de California occidental, posiblemente debido a que la zona de estudio es un ambiente de alta energía donde sólo se encontraron juveniles de moluscos y micromoluscos

Variación espacial de ensambles de moluscos bentónicos de fondos blandos del archipiélago Espíritu Santo, golfo de California, México

Background. The Espiritu Santo archipelago is recognized for its high biodiversity as a national park. Studies carried out on soft-bottom mollusks are of the faunistic type, and little is known about the variations in their community structure. Objective. To know the composition and the spatial variation in the structure of the assemblages of soft-bottom mollusks of the archipelago and to describe the possible incidence of the type of substrate in their structuring. Methods. In the infralittoral zone, 66 sampling sites were distributed in nine locations. The mollusks were collected by autonomous diving using a 1 m-2 metal frame and a nucleator to analyze of the sediment texture. The medium-grained sand substrate presented the highest distribution. The ecological indices of abundance, species richness (S), Shannon-Wiener diversity (H´), and Pielou evenness index (J´) were estimated. Results. 23,743 individuals were quantified, belonging to 102 species distributed in three classes, 17 orders, 39 families, and 70 genera. The bivalves were represented by 48 species, 9 orders, 17 families, and 39 genera. The gastropods by 52 species, 7 orders, 21 families and 30 genera, and the scaphopods by 1 species. Significant differences were found between localities for species richness and diversity but not for species equity. Conclusions. Spatial variations were observed in the structure of the mollusks assemblages in the archipelago, which could be due to the combined effect of the sediment texture and the presence of mangroves existing in some locations.Antecedentes. El Parque Nacional Archipiélago Espíritu Santo es reconocido por su elevada biodiversidad. Los estudios realizados sobre los moluscos de fondos blandos son inventarios faunísticos, y se conoce poco sobre la variación de su estructura comunitaria. Objetivo. Conocer la composición y la variación espacial en la estructura de los ensambles de moluscos de fondos blandos de este archipiélago y describir la posible relación con el tipo de sustrato. Métodos. En la zona infralitoral se distribuyeron 66 sitios de muestreo en nueve localidades. La colecta de moluscos se realizó mediante buceo autónomo utilizando un marco metálico de 1m2 y para el análisis de la textura del sedimento un nucleador. Se estimaron los indicadores estructurales de abundancia (N), riqueza de especies (S) y los índices de diversidad de Shannon-Wiener (H´) y de Equidad de Pielou (J´). Resultados. El sustrato de arena de grano medio presentó la mayor contribución. Se cuantificaron 23 743 organismos, registrados en 102 especies distribuidas en tres clases, 17 órdenes, 39 familias y 70 géneros. Los bivalvos estuvieron representados por 48 especies, 39 géneros, 17 familias y nueve órdenes. Los gastrópodos por 52 especies, 30 géneros, 21 familias y siete órdenes y los escafópodos por una especie. Se encontraron diferencias significativas entre las localidades para la riqueza de especies y diversidad, pero no para equidad. Conclusiones. Se observaron variaciones espaciales en la estructura de los ensambles de moluscos en el archipiélago, las cuales pudieron ser debidas al efecto combinado de la textura del sedimento y a la presencia de mangles en algunas localidades

Efecto de seis dietas en el crecimiento y supervivencia de poslarvas de abulón rojo (Haliotis rufescens) y su híbrido (H. rufescens ♀ × H. fulgens ♂)

One of the main bottlenecks in abalone aquaculture is maintaining individuals during the weaning stage, when the natural diet changes from diatoms (postlarvae) to macroalgae (juvenile). During this period, abalone pass through profound morphological and physiological changes, which suitable nutrient requirements must sustain. An inadequate diet can result in adverse effects such as late metamorphosis, starvation, slow growth and even death during this phase. Two strategies have been proposed to increase the growth and survival rates of weaning abalone: (i) extending feeding with benthic diatoms and (ii) abalone hybridization via interspecific crosses. To evaluate the efficiency of the two strategies, we assessed the growth and survival rates of postlarvae of pure red abalone (Haliotis rufescens) and a hybrid obtained by crossing red abalone females with green abalone (H. fulgens) males. Both crosses were supplied with six different diets consisting of either one macroalgae mono-diet (Macrocystis pyrifera or Ulva ohnoi) or a mixture with Navicula incerta. Overall, cross-specific diets achieved better growth rates, suggesting that each cross may need specific food items (nutrients) during weaning. Moreover, pure red abalone generally showed the highest growth rates, while the hybrid abalone showed the highest survival rates with most tested diets. Hence, hybrids appear to be better at withstanding stressful conditions, and their use in aquaculture could reduce losses and increase commercial production.   Uno de los principales cuellos de botella en la acuicultura de abulón es el mantenimiento de los individuos durante la fase de destete, cuando la dieta natural cambia de diatomeas (postlarvas) a macroalgas (juveniles). Durante este período, el abulón pasa por profundos cambios morfológicos y fisiológicos, que deben ser sostenidos por una alimentación adecuada. Una dieta inadecuada puede provocar efectos adversos como: metamorfosis tardía, inanición, crecimiento lento e incluso la muerte durante esta fase. Por ello, se han propuesto dos estrategias para aumentar las tasas de crecimiento y supervivencia del abulón durante la fase de destete: (i) ampliar el período de alimentación con diatomeas bentónicas y (ii) la hibridación de abulones mediante cruces interespecíficos. Para determinar la eficacia de ambas estrategias, se evaluaron las tasas de crecimiento y supervivencia de postlarvas de abulón rojo puro (Haliotis rufescens) y de un híbrido obtenido mediante el cruce de hembras de abulón rojo y machos de abulón azul (H. fulgens). A ambos cruces se les suministraron seis dietas diferentes consistentes en una mono dieta de macroalgas (Macrocystis pyrifera, Ulva ohnoi) o en una mezcla con Navicula incerta. En general, con las dietas específicas para cada cruce se obtuvieron mejores tasas de crecimiento, lo que sugiere que cada cruce requiere alimentos (nutrientes) específicos durante el destete. Además, el abulón rojo puro mostró en general las tasas de crecimiento más altas, mientras que en el abulón híbrido se obtuvieron las mayores tasas de supervivencia con la mayoría de las dietas probadas. Por lo que los híbridos parecen soportar mejor las condiciones de estrés, y su uso en la acuicultura podría ayudar a reducir las pérdidas y aumentar su producción comercial

The food of Selene peruviana (Actinopterygii: Perciformes: Carangidae) in the southern Gulf of California

Background. The food and feeding habits of a fish are important for understanding not only the fish biology but also the role played by the species in the ecosystem. The Peruvian moonfish (known also as Pacific moonfish), Selene peruviana (Guichenot, 1866), is a relatively abundant species, with its biology poorly known along the Mexican Pacific zone. Therefore, the aim of this study was to determine the principal food items of the Peruvian moonfish by using stable isotopes and the stomach content analysis. Materials and methods. We analyzed stomachs of 204 moonfish collected by a shrimp fishing boat along the coast of Nayarit and south of Sinaloa, Mexico from September to March, within 2006–2007. We also took 11 muscle samples of moonfish and some organisms being potential prey items for stable isotope analysis. Examining the stomach contents we determined the most important prey species using the geometric index of importance. We also determined the feeding strategy of this predator using Amundsen plots and Levin’s index and finally we calculated the trophic position. We also determined the principal preys using stable isotopes analysis along with mixing models, and based on those values we calculated the trophic position. Results. The stomachs of Selene peruviana contained chiefly engraulid fishes and crustaceans. The stable isotopes analysis (SIA) helped to identify partly digested material as representing crustaceans of the family Portunidae. The trophic position found by both methods was between 3.7 and 3.9 and we also determined that this fish tended to feed near the coast. Conclusion. Selene peruviana is an opportunistic predator that consumes preys that are abundant in the zone. The stable isotopes analysis proved to be an efficient tool supplementing the stomach content analysis and helping to identify also partly digested items

Using otolith organic matter to detect diet shifts in Bardiella chrysoura, during a period of environmental changes

Accurate knowledge on fish trophic ecology and its modifications is crucial for understanding the impact of global change on ecosystems. In this context, we investigated the value of the delta C-13 and delta N-15 of otolith soluble organic matter (SOM) for identifying temporal diet shifts in American silver perch Bairdiella chrysoura over a 30-yr period characterized by strong changes in its population size and habitats within the Terminos Lagoon (Mexico). We first compared the otolith SOM isotopic signatures from present-clay adults to those of muscle and the main local prey. Our results suggest that otolith SOM can be confidently extracted and analyzed for both present and past otoliths of this species. The mean otolith SOM signatures obtained (-15.92 +/- 1.35%, for delta C-13 and 9.38 +/- 0.93%, for delta N-15) were consistent with those of the diet as 85% of the individual signatures were included within the prey isotopic niche area. Moreover, this study supports a trophic enrichment factor between diet and otolith (TEFdiet-otolith) close to 0 for delta N-15, while for delta C-13, the TEFololith-muscle of +0.02% warrants further investigation. Then, we compared past and contemporary otolith SOM signatures to investigate temporal diet shifts in B. chrysoura. This showed that 613C and delta N-15 differed significantly between the past and present period even if the temporal shift remained relatively small (respectively +1.17%, and 0.55%). The present study substantiates the use of otolith SOM delta C-13 and delta N-15 as a proxy of fish present and past trophic position, opening the possibility for major progress in studies of temporal changes in food web ecology

Energy metabolism of juvenile scallops Nodipecten subnodosus under acute increased temperature and low oxygen availability

High temperature increases energy demand in ectotherms, limiting their physiological capability to cope with hypoxic events. The present study aimed to assess the metabolic tolerance of juvenile Nodipecten subnodosus scallops to acute hyperthermia combined with moderate hypoxia. A previous study showed that juveniles exhibited a high upper temperature limit (32 • C), but the responses of juveniles to combined hyperthermia and low dissolved oxygen are unknown. Scallops were exposed to control conditions (treatment C: 22 • C, ~7.1 mg O 2 L − 1 or PO 2 156.9 mmHg), acute hyperthermia under normoxia (treatment T: 30 • C, ~6.0 mg O 2 L − 1 or PO 2 150.9 mmHg) or acute hyperthermia plus hypoxia (treatment TH: 30 • C, ~2.5 mg O 2 L − 1 or PO 2 62.5 mmHg) for 18 h. In T, juveniles exhibited an enhanced oxygen consumption, together with a decrease in adenylate energy charge (AEC) and arginine phosphate (ArgP), and with no changes in metabolic enzyme activity in the muscle. In TH, scallops maintained similar AEC and ArgP levels in muscle as those observed in T treatment. This response occurred along with the accumulation of inosine monophosphate and hypoxanthine. Besides, reduced citrate synthase and pyruvate kinase activities, enhanced hexokinase activity, and a higher octopine dehydrogenase/ lactate dehydrogenase ratio in the mantle indicated the onset of anaerobiosis in TH. These responses indicate that juvenile scallops showed tissue-specific compensatory responses regarding their energy balance under moderate hypoxia at high temperatures. Our results give an insight into the tolerance limit of this species to combined hyperthermia and hypoxia in its northern limit of distribution