The objective of the present study is to estimate the removal capability of the ctenophore Mnemiopsis leidyi (Ctenophora, Lobata) on cultures of the toxic dinoflagellate Alexandrium tamarense (Dinophyta, Gonyaulacales). For this purpose, observations on its clearance and survival rates were made in controlled experiments, using different A. tamarense cell concentrations. Mnemiopsis leidyi is able to remove dinoflagellates actively from the water column only at the lowest density tested (150 cells mL-1). Animals exposed to 300 cells mL-1 presented negative clearance and removal rates (survival= 67%). All ctenophores exposed at the highest concentrations of toxic dinoflagellates (600 cells mL-1) died after 4 h. Removal may occur mainly by incorporating and entangling cells in the mucus strands formed by the ctenophore, and in a lesser way by ingestion. Results indicate that higher concentrations of A. tamarense are fatally toxic to M. leidyi and that this ctenophore could control only the initial development of this dinoflagellate bloom.

In this paper we report the first finding of the hydromedusa Gonionemus vertens Agassiz, 1862 in the southern hemisphere. About 30 newly released medusae were found within an aquarium on September 2008. The aquarium contained benthic samples collected in intertidal and subtidal rocky fringe off Mar del Plata, near a commercially important harbor in Argentina. Medusae were fed with Artemia salina until sexual maturation. Possible way of species introduction is discussed.

En este trabajo registra el primer hallazgo de la hidromedusa Gonionemus vertens Agassiz, 1862 en el hemisferio sur. Alrededor de 30 medusas recientemente liberadas fueron encontradas en un acuario en septiembre de 2008. Este acuario contenía muestras bentónicas colectadas en la franja rocosa intermareal y submareal de Mar del Plata, cerca de uno de los puertos más importantes de Argentina. Las medusas fueron alimentadas con Artemia salina hasta su maduración gonadal. Se discute la posible vía de introducción de esta especie.

We report the association between the jellyfish Lychnorhiza lucerna and the crab Cyrtograpsus affinis. Numerous examples of associations between medusae and brachyurans have been observed in the field and noted in the literature. All of these cases involve medusae of the Class Scyphozoa and crabs belonging to the families Majidae and Portunidae. The presence of three individuals of C. affinis within the subgenital space of L. lucerna constitutes a striking finding since none species of this brachyuran family (Varunidae) has been previously reported associated to scyphomedusae.

Se reporta la asociación entre la medusa Lychnorhiza lucerna y el cangrejo Cyrtograpsus affinis. Existen numerosos ejemplos de asociaciones entre medusas y brachiuros mencionados en la literatura. Todos ellos involucran a las medusas de la Clase Scyphozoa y a cangrejos pertenecientes a las familias Majidae y Portunidae. La presencia de tres individuos de C. affinis dentro de la cavidad subgenital de L. lucerna es un hecho llamativo dado que, hasta el momento, no se habia reportado a ninguna especie de esta familia de brachiuros (Varunidae) asociada con medusas de la Clase Scyphozoa.

Medusa blooms are a scarcely known phenomenon. For temperate, southwestern Atlantic waters, reports of such events are almost nonexistent. This research reports the analysis of a total of 1043 plankton samples taken from 1993 to 2006 and benthic samples collected by seasonal SCUBA diving since 1997 along the Buenos Aires coast. The medusa Obelia longissima was observed in very low densities and frequen-cies, except in October 2003, when a bloom of this species was detected. Soon afterward, two consecutive massive accumulations of O. longissima and Amphisbetia operculata colonies were detected on the coast by the mhabitants of Mar del Plata (38°00'S-57°32'W) and the coastal Mar Chiquita Lagoon (37°32'S-57°19'W) between March and April 2004. The colonies of both species were collected from the shoreline at low tide at both sites. The environmental factors of that period seemed to be particularly appropriate for promoting optimum growth conditions for these hydroid species. This paper reports and describes the mentioned abnormal phe-nomena, providing baseline information on these little-understood events.

Los blooms de medusas son un fenómeno escasamente conocido. En las aguas templadas del Atlántico sudoccidental, esta clase de eventos son casi inexistentes. Un total de 1.043 muestras de plancton de 1993 a 2006 fueron analizadas como también aquellas de bentos colectadas por SCUBA estacionalmente desde 1997 en la costa de Buenos Aires. Para la medusa Obelia longissima fueron observadas muy bajas densidades y frecuencias, con excepción de octubre de 2003 cuando un bloom de esta medusa fue detectado. Seguidamente, dos acumulaciones masivas consecutivas de colonias de O. longissima y de Amphisbetia operculata fueron detectadas sobre la línea de costa por habitantes de Mar del Plata (38°00'S-57°32'W) y de la laguna costera Mar Chiquita (37°32'S-57°19'W) entre marzo y abril del 2004. Las colonias de ambas especies fueron colectadas desde la línea de costa durante marea baja en ambas localidades. Los factores ambientales en ese período mostraron ser particularmente apropiados promoviendo las condiciones óptimas para el crecimiento de los hidroides de estas especies. Este trabajo reporta y describe el mencionado anormal fenómeno, dando información de base sobre estos eventos poco conocidos.

Embora abundantes e importantes ecologicamente no meio marinho, os ctenóforos do litoral brasileiro têm sido pouco estudados. O presente estudo tem por objetivo prover informações para auxiliar na identificação desses organismos. Para tal, são descritos métodos de fixação e documentação fotográfica dos ctenóforos. A terminologia referente ao grupo, em língua portuguesa, é apresentada na forma de um glossário. Além disso, as características que distinguem as treze espécies registradas para águas brasileiras são organizadas em uma chave de identificação. A complementação da identificação pode ser feita pela literatura indicada para cada espécie.

Although ctenophores are abundant and ecologically important in the marine environment, they are poorly known in the Brazilian coast. The present study is a taxonomic key for the ctenophores from the Brazilian coast. It aims to help students and non-specialist researchers with the identification of those organisms. Collecting, preserving and photographing methods are described. Characters that distinguish the thirteen species registered in Brazilian marine territories are presented.

Blackfordia virginica is a well-known invasive medusa inhabiting estuarine areas. It was recently detected in northern Argentina, constituting the first record of invasive hydromedusa for the Argentine Sea. In this work more than 1,500 plankton samples in the southwestern Atlantic Ocean (34-55º S) from 1983 to 2000 were analyzed. More than 5,000 specimens per sample of B. virginica were found in Río de la Plata estuary for the first time in February 2000. This river is one of the large waterways of South America with an intense nautical traffic and several exotic species has been recorded here, mainly due to trans-oceanic shipping traffic. It is important to point out that we found medusae of both sexes (therefore this species could be introduced in either the medusa or the polyp stages or both), different size classes (including very small juveniles) and maturation stages, and in such high numbers that would suggest local reproduction. For this reason the recent finding of this hydromedusa could represent the starting point of an successful introduction

Blackfordia virginica es una medusa invasora reconocida por habitar áreas estuariales. Recientemente fue descubierta en el norte de Argentina, constituyendo el primer registro de una hidromedusa invasora para el mar argentino. En este trabajo se analizaron más de 1.500 muestras de plancton en el Océano Atlántico sudoccidental (34-55º S) desde 1983 hasta el año 2000. Más de 5.000 especímenes por muestra fueron encontrados por primera vez en el estuario del Río de la Plata durante febrero del año 2000. Este río es una de las mayores vías de agua de América del Sur, posee un intenso tráfico náutico y varias especies exóticas se han registrado allí, principalmente debido al tráfico marítimo transoceánico. Es importante señalar que se encontraron medusas de ambos sexos (por lo tanto esta especie podría haber sido introducida en su estadio medusa, pólipo o ambos), con diferentes clases de tallas (incluyendo juveniles muy pequeños) y estadios de maduración y en números elevados, lo que haría pensar en una reproducción local. Por esta razón el reciente encuentro de esta hidromedusa podría representar el punto de partida de una introducción exitosa

Juvenils and adults of Chrysaora lactea, Aurelia aurita and Drymonema gorgo were found in Blanca Bay during summer and efirae of the two first occurred from October to January. These species are commonly found in Brazilian waters. Their occurrence in higher latitudes may be either due to the influence of warm waters coming from north or to the heating of local waters which could main tain their populations temporarily during spring and summer. In this period C. lactea and A. aurita may reproduce as it is suggested by the occurrence of their efirae in the surveyed area.