Life history and production of Capitella capitata (Polychaeta: Capitellidae) in Río de la Plata Estuary (Argentina)

A benthic survey was carried out from November 1998 to December 1999 in the tidal flats of Bahía Samborombón (Río de la Plata estuary, Argentina), in order to study the population structure, reproductive aspects, growth and secondary production of Capitella capitata (Fabricius, 1780). Growth was analyzed using ELEFAN routine, and the secondary production was estimated by Hynes and Coleman's method (1968). C. capitata did not present periods of very important recruitments throughout the year; however, the abundance of smallest size classes was higher during summer and autumn. The summer cohort showed a growth rate (K) of 2.05 and a seasonal growth oscillation (C) of 0.6, pointing out that worms grew very slowly during winter months. The life span of this cohort was 13 months. The autumn cohort showed a lower growth rate (K= 1.5) and its growth was lowest during winter. The life span was 15 months for this cohort. C. capitata in Punta Rasa presented an extended reproductive period, with absence of activity during winter months. The type of eggs and larvae suggest that C. capitata has benthic larval development in the study area, destining its reproductive effort to the production of a low number of eggs, and assuring larvae survival through incubation in brooding tubes. The annual mean biomass in Punta Rasa was 0.117 g m-2 (AFDW), with a mean secondary production of 0.23 g m-2 y-1 and a P/B ratio of 1.96 y-1. The relatively low density, biomass production and P/B ratio of C. capitata in Punta Rasa can be considered as reference values for this species inhabiting undisturbed or moderately disturbed areas.

El alga invasora Undaria pinnatifida (Harvey) Suringar en la Ría Deseado (Patagonia austral, Argentina): ciclo del esporofito y factores ambientales determinantes de su distribución

Undaria pinnatifida was registered in Ría Deseado (47º45´S, 65º55´W _ southern Patagonia) by the first time in spring 2005, colonizing the intertidal and shallow subtidal. A seasonal survey in 2006 showed that U. pinnatifida was established in a sheltered zone inside the estuary, along a coastal fringe of 8 km between Punta Cascajo and Cañadón del Puerto. This continuous distribution was only interrupted in the mouth of canyons that flow into Ría Deseado, where the bottom is conformed by mud and sand. The sporophytes were mainly found colonizing the rocky bottom in the lower intertidal, bordering the Macrocystis pyrifera population. The highest density and biomass of sporophytes (12.13 ind. m-2; 254.60 g m-2) were registered during spring, when the population was mainly conformed by individuals of medium sizes. The lowest density and biomass (0.33 ind. m-2; 5.69 g m-2) were registered in autumn. Juvenile sporophytes recruited throughout the year, but presented the highest percentage in the population during autumn and winter. First mature sporophytes appeared in spring and attained their maximum size in summer. After this, the sprophytes decayed and disappeared. Environmental factors such as rocky bottoms availability and water transparency may be the main factors determining the sporophytes distribution in Ría Deseado. The field experiment point out that M. pyrifera population is an important factor controlling the dispersion of U. pinnatifida towards the subtidal. SPANISH: Undaria pinnatifida fue registrada en la Ría Deseado (47º45´ S, 65º55´ W _ Patagonia austral) durante la primavera de 2005, colonizando el intermareal y submareal somero. Los relevamientos estacionales realizados durante el 2006, revelaron que U. pinnatifida se encontró establecida en una zona protegida en el interior de la ría, ocupando una franja costera de aproximadamente 8 km de largo entre Punta Cascajo y el Cañadón del Puerto. Esta distribución casi continua sólo presentó algunas interrupciones en la boca de los cañadones que desembocan en la ría, donde el fondo predominante es de tipo areno-fangoso. Los esporofitos de U. pinnatifida ocuparon preferentemente el fondo rocoso del intermareal inferior, limitando con la población de Macrocystis pyrifera. La densidad y biomasa más altas de esporofitos (12,13 ind. m-2; 254,60 g m-2) fueron registradas en primavera, cuando la población se encontró compuesta principalmente por individuos de tallas intermedias. La densidad y biomasa más bajas (0,33 ind. m-2; 5,69 g m-2) fueron registradas durante el otoño. Los esporofitos juveniles se reclutaron a lo largo de todo el año, pero alcanzaron su mayor proporción en la población durante el otoño y el invierno. Los esporofitos reproductivamente maduros aparecieron durante la primavera y alcanzaron su talla máxima durante el verano, luego del cual comenzaron a deteriorarse y a desaparecer. Factores como la disponibilidad de fondos rocosos y la transparencia de las aguas podrían actuar como los principales factores determinantes de su distribución en la ría. El experimento de campo realizado revela que los bosques de M. pyrifera actúan también como un importante factor de control, limitando la dispersión de U. pinnatifida hacia el submareal.

Accumulation of Heavy Metals in Franciscanas from Buenos Aires Province, Argentina

Marine mammals accumulate heavy metals in their tissues at different concentrations according to trophic levels and environmental conditions. The franciscana (Pontoporia blainvillei) is a small coastal species inhabiting the marine and estuarine areas of the Southwestern Atlantic Ocean. Its diet includes numerous species of small fish, squid and crustaceans. The aims of this study were to (i) assess the heavy metal concentration and burden distribution in different franciscana age classes and sex, and to (ii) evaluate both the accumulation processes and the transplacental transference of zinc, cadmium, copper and total mercury. Heavy metal concentrations (wet weight) were determined in eighteen dolphins by Atomic Absorption Spectrophotometry (AAS), by the cold vapour technique (mercury) or with air/acetylene flame (cadmium, zinc and copper). Liver showed the highest concentrations of mercury (max. 8.8 mg/g), zinc (max. 29.7 mg/g) and copper (max. 19.0 mg/g), whereas the highest cadmium concentrations (max. 6.7 mg/g) were found in kidney. Adults contained the highest concentrations for all heavy metals, followed by juveniles and calves in decreasing order, suggesting an age-related accumulation. No differences (p<0.05) were found between sexes within each age class. Organ burden distribution followed the same pattern for all metals and age classes: liver tissues contained maximum burdens. Mercury concentrations were higher than those of cadmium in both foetuses and newborns; and neither metal could be detected in the foetus. The analysed data suggested differences in the placental transference between metals, being significant for mercury and almost null in the case of cadmium. We can conclude that franciscana accumulates heavy metals and, due to its coastal distribution, it may be considered as a biomonitor of its environment. SPANISH: Los mamíferos marinos acumulan metales pesados en sus tejidos cuyas concentraciones están en relación con su nivel trófico y las condiciones ambientales. La franciscana (Pontoporia blainvillei) es una especie costera que habita áreas marinas y estuariales en el Atlántico Sudoccidental. Su dieta está constituída por peces, como item alimentario principal, calamares y crustáceos. El objetivo del presente trabajo es estudiar la distribución de metales pesados en diferentes clases de edad y en ambos sexos, evaluando procesos de acumulación y cargas de cadmio, mercurio total, cinc y cobre. Las concentraciones de metales pesados (en peso húmedo) fueron determinadas en dieciocho delfines por Espectrofotometría de Absorción Atómica (EAA), usando la técnica de vapor frío (mercurio) o llama de aire/acetileno (cadmio, cinc y cobre). El hígado presentó las concentraciones más altas de mercurio (máx. 8,8 mg/g), cinc (máx. 29,7 mg/g) y cobre (máx. 19,0 mg/g), mientras que las más altas de cadmio (máx. 6,7 mg/g) fueron encontradas en el riñón. Los adultos presentaron los niveles más altos, presentando los juveniles y cachorros concentraciones menores, lo cual sugirió una acumulación con la edad. No se encontraron diferencias significativas (p < 0,05) entre sexos dentro de cada clase de edad. Las cargas de metales pesados en los órganos presentaron la misma disribución para todos los metales y clases de edad. Los valores más altos fueron encontrados en el hígado, incluyendo los correspondientes a cadmio. Las concentraciones de mercurio y cadmio fueron no detectables en el feto, mientras que las de mercurio fueron superiores a las de cadmio en los cachorros. Los datos encontrados en el feto sugieren una transferencia nula a través de la placenta. Podemos concluir que P.blainvillei acumula metales pesados en sus tejidos y debido a su distribución costera, esta especie puede ser considerada como un biomonitor de su ambiente.

Feeding Ecology of the Franciscana (Pontoporia blainvillei) In Marine And Estuarine Waters Of Argentina

Stomach contents of 110 franciscanas (Pontoporia blainvillei), from northern Argentina were analysed in order to improve our knowledge about the feeding habits of this species and to better characterise the lactation period. The samples included calves, juveniles and adults of both sexes. Evidence of predation by franciscanas is seen at a very young age (2.5-3 months), with a transition diet composed by both milk and solid food, mainly represented by crustaceans. Weaning seems to begin by April, when franciscanas are about 6-7 months old. Franciscanas inhabiting two different habitats were analysed in this study: a brackish water estuary and an adjacent marine coastal system. The diet of Pontoporia blainvillei in northern Argentina was composed by a total of 26 prey species: 20 teleosts, 4 crustaceans and 2 cephalopods. Based on the Index of Relative Importance (IRI) the main prey species were Cynoscion guatucupa, Micropogonias furnieri, Loligo sanpaulensis and Urophycis brasiliensis. Estuarine franciscanas preyed mainly on Micropogonias furnieri (dominant species), Cynoscion guatucupa, Odonthestes argentinensis and Macrodon ancylodon, while dolphins from marine areas preyed mainly on Cynoscion guatucupa (dominant species), Loligo sanpaulensis and Urophycis brasiliensis. Our results confirm that franciscanas prey mainly on juvenile fish (< 8cm) and small loliginid squids, in close agreement with previous results obtained in southern Brazil and Uruguay. Qualitative and quantitative differences observed in the diet of dolphins from each habitat emphasise the need to discriminate between samples from different habitats and environmental parameters. SPANISH: Se analizaron 110 contenidos estomacales de franciscanas (Pontoporia blainvillei) provenientes de la costa norte de Argentina, para extender en conocimiento sobre su dieta y caracterizar la lactancia. Las muestras incluyeron cachorros, juveniles y adultos de ambos sexos. Las primeras etapas de predación se inician a muy temprana edad (2,5-3 meses), presentando una dieta de transición compuesta tanto por leche como por presas sólidas, principalmente crustáceos; el destete se iniciaría a partir de abril, a una edad estimada entre 6 y 7 meses. Las franciscanas estudiadas provienen de dos habitats diferentes: un área estuarial de baja salinidad y la region marina adyacente. La dieta de Pontoporia blainvillei de Argentina estuvo compuesta por un total de 26 especies: 20 teleósteos, 4 crustáceos y 2 cefalópodos. Basados en el Indice de Importancia Relativa (IIR), las presas más importantes fueron Cynoscion guatucupa, Micropogonias furnieri, Loligo sanpaulensis y Urophycis brasiliensis. Las franciscanas provenientes del área estuarial predaron principalmente sobre Micropogonias furnieri (especie dominante), Cynoscion guatucupa, Odonthestes argentinensis y Macrodon ancylodon, mientras que los delfines marinos predaron sobre Cynoscion guatucupa (especie dominante), Loligo sanpaulensis y Urophycis brasiliensis. Nuestros resultados confirman que la franciscana preda sobre peces juveniles (< 8cm) y pequeños calamares Loliginidae, coincidiendo con resultados previos obtenidos en el sur del Brasil y Uruguay. Las diferencias cualitativas y cuantitativas observadas en la dieta de cada uno de las áreas analizadas, nos sugieren que los futuros estudios sobre ecología trófica de la franciscana deberían discriminarse de acuerdo al origen de los ejemplares y a la tipificación del ambiente.

Perspectives of marine biodiversity studies in Argentina

This paper provides an overview of the research being carried out at the moment by a group of Argentinean scientists working on the subjects of marine biodiversity and oceanography. When the idea of the Census of Marine Life (CoML)was proposed following the Symposium held during the IAPSO-IABO conference in Mar del Plata in October 2001, there was a wide response from the marine scientific community. Information about current research projects, as well as plans for future work in the context of the CoML, were then obtained from about 70 scientists (Appendix I) belonging to 12 institutions located along the Argentinean coast (Appendix II, Figure 1). This has been used to illustrate what is currently being pursued in marine biodiversity in Argentina and which subjects are considered as priority for future research in the area. This paper is, thus, not an historical update of the knowledge of marine biodiversity, but it attempts to give an idea of the current situation and what is planned for the future. The development of an extensive database of what is known on marine biodiversity in the region is considered to be a necessity, but it constitutes a complete project on its own; as such it is included in the proposals for future work (see Future Work in this paper). It is emphasised that this synthesis is not exhaustive in the content of the topics being studied or in the number of researchers working in marine biodiversity in the country. It is, though, considered to be a representative sample of the knowledge in marine science in Argentina today. This is a starting point for the CoML project in South America and it is hoped that, as it develops, it will be improved by the active participation, advice and experience of many other scientists in the region.