Effect of acclimation temperature and substrate type on selected temperature, movement and activity of juvenile spiny softshell turtles (Apalone spinifera) in an aquatic thermal gradient.

In some turtle species, temperature selection may be influenced by environmental conditions, including acclimation temperature and substrate quality. These factors may be particularly important for softshell turtles that are highly aquatic and often thermoregulate by burying in the substrate in shallow water microhabitats. We tested for effects of acclimation temperature (22 °C or 27 °C) and substrate type (sand or gravel) on the selected temperature and movement patterns of 20 juvenile spiny softhshell turtles (Apalone spinifera; Reptilia: Trionychidae) in an aquatic thermal gradient of 14-34 °C. Among 7-11 month old juvenile softshell turtles, acclimation temperature and substrate type did not influence temperature selection, nor alter activity and movement patterns. During thermal gradient tests, both 22- and 27 °C-acclimated turtles selected the warmest temperature (34 °C) available most frequently, regardless of substrate type (sand or gravel). Similarly, acclimation temperature and substrate type did not influence movement patterns of turtles, nor the number of chambers used in the gradient tests. These results suggest that juvenile Apalone spinifera are capable of detecting small temperature increments and prefer warm temperatures that may positively influence growth and metabolism, and that thermal factors more significantly influence aquatic thermoregulation in this species than does substrate type.

Shifting elasmobranch community assemblage at Cocos Island--an isolated marine protected area.

Fishing pressure has increased the extinction risk of many elasmobranch (shark and ray) species. Although many countries have established no-take marine reserves, a paucity of monitoring data means it is still unclear if reserves are effectively protecting these species. We examined data collected by a small group of divers over the past 21 years at one of the world's oldest marine protected areas (MPAs), Cocos Island National Park, Costa Rica. We used mixed effects models to determine trends in relative abundance, or probability of occurrence, of 12 monitored elasmobranch species while accounting for variation among observers and from abiotic factors. Eight of 12 species declined significantly over the past 2 decades. We documented decreases in relative abundance for 6 species, including the iconic scalloped hammerhead shark (Sphyrna lewini) (-45%), whitetip reef shark (Triaenodon obesus) (-77%), mobula ray (Mobula spp.) (-78%), and manta ray (Manta birostris) (-89%), and decreases in the probability of occurrence for 2 other species. Several of these species have small home ranges and should be better protected by an MPA, which underscores the notion that declines of marine megafauna will continue unabated in MPAs unless there is adequate enforcement effort to control fishing. In addition, probability of occurrence at Cocos Island of tiger (Galeocerdo cuvier), Galapagos (Carcharhinus galapagensis), blacktip (Carcharhinus limbatus), and whale (Rhincodon typus) sharks increased significantly. The effectiveness of MPAs cannot be evaluated by examining single species because population responses can vary depending on life history traits and vulnerability to fishing pressure.

Modificación del Ensamble de Comunidades de Elasmobranquios en la Isla de Cocos, un Área Marina Protegida Aislada Resumen La presión de la pesca ha incrementado el riesgo de extinción de muchas especies de elasmobranquios (tiburones y rayas). Aunque muchos países han establecido áreas de no-pesca, una escasez de datos de monitoreo implica que todavía no está claro si estas reservas están protegiendo efectivamente a estas especies. Examinamos datos colectados por un pequeño grupo de buzos a lo largo de los últimos 21 años en una de las áreas marinas protegidas (AMP) más vieja del mundo: Parque Nacional Isla de Cocos, Costa Rica. Usamos modelos de efectos mixtos para determinar tendencias en la abundancia relativa, o probabilidad de caso, de doce especies monitoreadas de elasmobranquios compensando la variación entre observadores y de factores abióticos. Ocho de las doce especies declinaron significativamente a lo largo de las últimas dos décadas. Documentamos disminuciones en la abundancia relativa de seis especies, incluidos el tiburón martillo (Sphyrna lewini) (−45%), el tiburón de arrecife de punta blanca (Triaenodon obesus) (−77%), la manta (Mobula spp.) (−78%) y la mantarraya (Manta birostris) (−89%); así como disminuciones en la probabilidad de caso de otras dos especies. Muchas de estas especies tienen extensiones de hábitat pequeñas y deberían estar mejor protegidas por una AMP, lo que enfatiza la noción de que las declinaciones de megafauna marina continuarán sin cesar en las AMP a menos de que exista un esfuerzo adecuado de control de pesca. Además de esto, la probabilidad de ocurrencia en la Isla de Cocos de de los tiburones tigre (Galeocerdo cuvier), de las Galápagos (Carcharhinus galapagensis), de punta negra (Carcharhinus limbatus) y ballena (Rhincodon typus) incrementó significativamente. La efectividad de las AMP no puede ser evaluada examinando a una sola especie porque las respuestas poblacionales pueden variar dependiendo de las características de la historia de vida y de la vulnerabilidad a la presión de la pesca.

Long-term comparison of the fish community in a Costa Rican rocky shore marine reserve.

Despite their role in supporting diverse marine fish communities, tropical rocky shores and reefs have attracted less research and fewer targeted conservation efforts compared to coral reefs. We studied fish community composition in Playa Blanca Marine Reserve (9 degrees 40' N - 84 degrees 40' W), a rocky shore site on the central Pacific coast of Costa Rica. We conducted visual surveys of fishes along six strip transects soon after the area was designated a marine reserve in 1995, then again in 2006 following an eleven-year period of complete protection. We recorded a total of 31 406 sightings of 72 species from 30 families. Pomacentrids (42.5%), labrids (16.6%) and haemulids (14.8%) dominated the community, accounting for > 70% of total fish abundance. In comparison to other sites in the region, the fish community was more similar to one reported from Bahia Honda, Panama (7 degrees 50' N - 81 degrees 35 W) than from the geographically more proximate Culebra Bay, Costa Rica (10 degrees 45' N - 85 degrees 43 W). Sixty-one species from 26 families were recorded in 1995; sixty-nine species from 28 families in 2006. Our results suggest that the Playa Blanca Marine Reserve is fulfilling its conservation role. Average fish abundance, species richness and Shannon's index of community diversity were greater in 2006 than 1995, and fish community composition varied significantly within each transect among years. Much of the change in community composition among years resulted from spatial and temporal variation in the abundance of a few dominant species, including Abudefduf troschelli, Thalassoma lucasanum, Chromis atrilobata, and Stegastes flavilatus/acapulcoensis. Of the 48 species/species groups recorded in both years, 37 (77%) were more abundant in 2006 than 1995, and several species recorded as uncommon or rare in 1995 were more frequent and abundant in 2006. Fish community composition and the abundance of some species changed in the reserve over time, but further study is needed to determine the role of small-scale marine reserves in the conservation of tropical marine biodiversity.

Long-term comparison of the fish community in a Costa Rican rocky shore marine reserve

Despite their role in supporting diverse marine fish communities, tropical rocky shores and reefs have attracted less research and fewer targeted conservation efforts compared to coral reefs. We studied fish community composition in Playa Blanca Marine Reserve (9˚40’ N - 84˚40’ W), a rocky shore site on the central Pacific coast of Costa Rica. We conducted visual surveys of fishes along six strip transects soon after the area was designated a marine reserve in 1995, then again in 2006 following an eleven-year period of complete protection. We recorded a total of 31 406 sightings of 72 species from 30 families. Pomacentrids (42.5%), labrids (16.6%) and haemulids (14.8%) dominated the community, accounting for >70% of total fish abundance. In comparison to other sites in the region, the fish community was more similar to one reported from Bahia Honda, Panama (7˚50’ N - 81˚35 W) than from the geographically more proximate Culebra Bay, Costa Rica (10˚45’ N - 85˚43 W). Sixty-one species from 26 families were recorded in 1995; sixty-nine species from 28 families in 2006. Our results suggest that the Playa Blanca Marine Reserve is fulfilling its conservation role. Average fish abundance, species richness and Shannon’s index of community diversity were greater in 2006 than 1995, and fish community composition varied significantly within each transect among years. Much of the change in community composition among years resulted from spatial and temporal variation in the abundance of a few dominant species, including Abudefduf troschelli, Thalassoma lucasanum, Chromis atrilobata, and Stegastes flavilatus/acapulcoensis. Of the 48 species/species groups recorded in both years, 37 (77%) were more abundant in 2006 than 1995, and several species recorded as uncommon or rare in 1995 were more frequent and abundant in 2006. Fish community composition and the abundance of some species changed in the reserve over time, but further study is needed to determine the role of small-scale marine reserves in the conservation of tropical marine biodiversity. Rev. Biol. Trop. 59 (1): 233-246. Epub 2011 March 01.

Los corales y los bordes rocosos tropicales están compuestos por diversas comunidades de peces pero han atraído menos investigación o conservación que los arrecifes coralinos. Estudiamos la composición de una comunidad de peces en la Reserva Marina Playa Blanca, un borde rocoso en la costa del Pacífico central de Costa Rica. Realizamos muestreos visuales de peces en seis transectos inmediatamente después que el área fue designada como reserva marina en 1995, y de nuevo en 2006, después de once años de protección. Observamos un total de 31 406 avistamientos de 72 especies y 30 familias. Los pomacentridos (42.5%), labridos (16.6%) y haemulidos (14.8%) dominaron la comunidad, sumando >70% de la abundancia total de peces. Nuestros resultados sugieren que la Reserva Marina Playa Blanca está cumpliendo con su papel de conservación. El promedio de abundancia, riqueza y diversidad de peces fueron mayores en 2006 comparados con 1995, y muchas especies clasificadas como no comunes o raras en 1995 fueron más abundantes y observadas más frecuentemente en 2006. La composición de la comunidad cambió significativamente entre 1995 y 2006, la mayoría del cambio debido a la variación temporal y espacial de algunas especies dominantes de pomacentridos y labridos. Nuestros resultados sugieren una respuesta positiva a la protección de los peces de la Reserva Marina Playa Blanca, pero más estudios son necesarios para determinar el papel de las reservas marinas pequeñas en la conservación de la biodiversidad marina tropical.