Intertidal benthic macrofauna of rare rocky fragments in the Amazon region / Macrofauna bentónica intermareal de los fragmentos rocosos raros en la región Amazónica

Rock fragment fields are important habitat for biodiversity maintenance in coastal regions, particularly when located in protected areas dominated by soft sediments. Researches in this habitat have received surprisingly little attention on the Amazon Coast, despite rock fragments provide refuges, nursery grounds and food sources for a variety of benthic species. The present survey describes the mobile macroinvertebrate species composition and richness of the intertidal rocky fragments in Areuá Island within the “Mãe Grande de Curuçá” Marine Extractive Reserve (RESEX) on the Brazilian Amazon Coast. Samples were collected during the dry (August and November 2009) and rainy seasons (March and May 2010) on the upper and lower intertidal zone, using a 625cm² quadrat. At each season and intertidal zone, macroinvertebrate samples were collected along four transects (20m each) parallel to the waterline, and within each transect two quadrats were randomly sampled. Macroinvertebrates were identified, density determined, and biomass values obtained to characterize benthic diversity from the rocky fragments. The Jackknife procedure was used to estimate species richness from different intertidal zones during the dry and rainy seasons. Macrofaunal community comprised 85 taxa, with 17 “unique” taxa, 40 taxa were common to both intertidal zones and seasons, and 23 taxa have been recorded for the first time on the Brazilian Amazon Coast. Species richness was estimated at 106±9.7 taxa and results suggest that sampling effort was representative. Polychaeta was the most dominant in species number, followed by Malacostraca and Gastropoda. Regarding frequency of occurrence, Crustacean species Dynamenella tropica, Parhyale sp. and Petrolisthes armatus were the most frequent representing >75% of frequency of occurrence and 39 taxa were least frequent representing <5% of frequency of occurrence. Occurrence of crustaceans and polychaetes were particularly noteworthy in all intertidal zones and seasons, represented by 15 and 13 taxa, respectively. The most representative class in abundance and biomass was Malacostraca that represented more than half of all individuals sampled, and was dominated by Petrolisthes armatus. The latter was one of the most frequent, numerous and higher biomass species in the samples. In general, results indicated greater richness and biomass in the lower zone. Additionally, richness and density increase during the rainy season. Rock fragment fields in Areuá Island are rich in microhabitats and include a diverse array of species in a limited area. Our results underline the importance of rock fragment fields in Areuá Island for the maintenance of biodiversity in the Amazon Coast.

Los fragmentos rocosos comprenden un hábitat importante para el mantenimiento de la biodiversidad en las regiones costeras, particularmente cuando estos se encuentran en áreas protegidas dominadas por sedimentos blandos. A pesar de que los fragmentos rocosos proporcionan refugio, zonas de crianza y fuentes de alimento para una gran variedad de especies bentónicas, las investigaciones sobre este hábitat en la costa de la Amazonia han recibido poca atención. El presente estudio describe la composición de macroinvertebrados vágiles y la riqueza de especies en los fragmentos rocosos del intermareal de la isla Areuá en la Reserva Marina Extractiva (RESEX) “Mãe Grande de Curuçá”, en la costa brasileña de la Amazonia. Las muestras fueron recolectadas durante la estación seca (agosto y noviembre 2009) y de lluvias (marzo y mayo 2010) en dos zonas del intermareal (superior e inferior), con un cuadrante de 625cm². En cada zona del intermareal y por temporada se tomaron muestras de macroinvertebrados a lo largo de cuatro transectos (20m cada uno) dispuestos paralelamente a la línea de costa. Dos cuadrantes se muestrearon al azar dentro de cada transecto. Los macroinvertebrados recolectados fueron identificados y se determinó la densidad y la biomasa de organismos para caracterizar la diversidad bentónica de los fragmentos rocosos. La riqueza de especies de las dos zonas del intermareal durante las estaciones seca y de lluvias se estimó por el método de Jackknife. La comunidad de macroinvertebrados estuvo compuesta por 85 taxones, con 17 taxones “único”, 40 taxones fueron comunes para ambas zonas del intermareal y temporadas, y 23 taxones se reportaron por primera vez para la costa brasileña de la Amazonia. La riqueza de especies se estimó en 106±9.7 taxones, por lo que los resultados sugieren que el esfuerzo de muestreo fue representativo. La Clase Polychaeta dominó en número de especies, seguida por Malacostraca y Gasteropoda. Los crustaceos Dynamenella tropica, Parhyale sp. y Petrolisthes armatus fueron las más frecuentes, con una frecuencia de presencia >75% mientras que 39 taxones fueron los menos comunes, con una frecuencia de presencia <5%. La presencia de crustáceos y poliquetos fue particularmente notable en las dos zonas y temporadas, incluyeron 15 y 13 taxones, respectivamente. La Clase Malacostraca fue la más conspicua en términos de abundancia y biomasa, representó más de la mitad de todos los individuos recolectados, con dominio de Petrolisthes armatus. Esta especie fue una de las más numerosas, frecuentes y de mayor biomasa en las muestras. En general, los resultados indican que hay una mayor riqueza y biomasa en el intermareal inferior mientras que la riqueza y la densidad aumentan en la estación lluviosa. Los sectores con fragmentos rocosos en la isla Areuá son ricos en microhábitats e incluyen una gran variedad de especies en un área limitada. Nuestros resultados enfatizan la importancia de los sectores con fragmentos rocosos en la isla Areuá para el mantenimiento de la biodiversidad en la costa de la Amazonia.

Comparación temporal de la composición y zonación de organismos en el intermareal rocoso del Parque Nacional Isla del Coco, Pacífico de Costa Rica

Temporal comparison of the composition and zonation of rocky intertidal organisms at Cocos Island National Park, Pacific, Costa Rica. Several biological and physical factors change the rocky shore communities. The desiccation time and the tolerance of the intertidal species produce the vertical zonation. In many studies around the world, a temporal change in this zonation is presented. In Costa Rica, only studies that include temporal trends were carried out in Punta Mala and Montezuma, Pacific coast in 80`s. The rocky intertidal of the Cocos Island National Park, Costa Rica were surveyed photographically. The Chatham bay was sampled in three expeditions (January 2007, October 2007 and April 2008). Photos corresponding to 25x25cm quadrats were taken with the goal to determine diversity and composition differences in rocky shore organisms between sampling dates. The Wafer bay was sampled in January and October 2007. The intertidal of Chatham consists of basaltic rock, while Wafer has basaltic and ignimbrite boulders. The main difference between sites were the higher algae cover (erect-frondose forms) and number of organism bands at Chatham bay. Temporal change was not found in the total cover of sessile fauna and autotrophs. The barnacle Tetraclita stalactifera, that occurs above the algal fringe (lower intertidal), was the invertebrate with the highest coverage. The mobile fauna biodiversity presented no significant trend between sampled months. However, the identity of species, their cover and their abundance showed a moderate temporal change. In October 2007, when the sea surface temperature was 23ºC the infralittoral zone had an increase in green algae cover. The red algae (crust and erect-frondose forms) were dominant in January and April. The pulmonate limpet, Siphonaria gigas and a bacterial biofilm at mid littoral showed a negative association. The snails of the high littoral and the supralittoral zone showed a temporal change in their abundance, but with contrasting patterns between sites. The temporal variation in the assemblages increased from the supralittoral to the infralittoral possibly due to changes in the water temperature and climatic conditions, that could influence the intertidal zone during the high and low tide, respectively. Rev. Biol. Trop. 58 (4): 1387-1403. Epub 2010 December 01.

La zona entre mareas rocoso de las bahías Chatham y Wafer en la Isla del Coco, Costa Rica fueron muestreadas fotográficamente con cuadrículas de 25x25cm en enero y octubre de 2007. Bahía Chatham también se visitó en abril 2008. El intermareal de Chatham estaba constituido por roca basáltica y en Wafer por basalto y cantos rodados de ignimbrita. Las principales diferencias entre sitios fueron las algas con mayor cobetura (erectas-frondosas) y el mayor número de bandas de organismos se dio en Chatham. No se encontró cambio temporal en la cobertura total de fauna sésil y de autótrofos. La mayor cobertura de invertebrados fue la del cirripedio Tetraclita stalactifera, siempre sobre la banda en la zona inferior de las algas. La diversidad de la fauna móvil no presentó tendencia significativa entre los meses de muestreo. Sin embargo, la identidad de las especies, cobertura o abundancia mostró un cambio temporal moderado. En octubre cuando el agua superficial del mar fue baja (23ºC), el infralitoral tuvo un incremento en la cobertura de las algas verdes. La dominancia en enero y abril fue de algas rojas (incrustantes y erectas-frondosas). Las lapas pulmonadas Siphonaria gigas y las cianobacterias del litoral medio mostraron una asociación negativa. Los caracoles de litoral alto y supralittoral presentaron un cambio temporal en su abundancia pero con diferentes patrones entre los sitios. Un incremento de variación en la composición de organismos se dio desde el supralitoral al infralitoral, posiblemente causado por el cambio en las condiciones del agua y el clima, que influyen en la zona entre mareas durante el alta y bajamar, respectivamente.

Abundance of Petrolisthes armatus (Crustacea: Porcellanidae) on a tropical estuarine intertidal rocky beach, Gulf of Nicoya estuary, Costa Rica

Population of the porcellanid crab Petrolisthes armatus was studied on a rocky intertidal beach located at the Punta Morales peninsula in the mid upper Gulf of Nicoya estuary, Pacific coast of Costa Rica, from December 1997 to November 1998 (14 dates). Horizontal plankton tows (280 micron mesh net) were also made to verify the presence of P. armatus larvae. Crabs were collected every 3 m along three 18 m long transects, at two sites on the beach, by placing a bottomless bucket fringed with canvas to prevent the organisms from escaping under the rim. A total of 15,382 P. armatus were collected. Only 146 (0.95%) crabs had a carapace length longer than 10 mm, and 8995 (58.5%) were in the size range of 2 to 4.5 mm. The remaining crabs 6241 (40.5%) were in the size range of 4.6 to 10 mm. Male and female P. armatus were represented by 2777 and 3518 individuals respectively, with a sex ratio of 1:1.26. Ovigerous females were found at all dates and included 2937 individuals (83% of females). Plankton tows yielded only 73 larvae of P. armatus (Zoea 1), with a density of 1.2 larvae/m3. No statistically significant seasonal trends in the population of this species were detected. P. armatus appears to reproduce continuously the year around in Punta Morales, and some peaks of abundance were present during the dry and rainy seasons. These trends are similar to trends reported for other crustacean species in the Gulf of Nicoya.