The diet, digestion times, and d e n s~t~e s of Chrysaora quinquecirrha medusae, and densities of their prey were quantified in order to evaluate the importance of this conspicuous scyphomedusan on zooplankton populations in Chesapeake Bay, USA, and its tributaries. Medusae consumed a variety of zooplankton prey, but copepods, mostly Acartia tonsa, averaged 55 % of the prey items in gut contents collected during July and August from 2 tr~butaries of Chesapeake Bay in 1987 and 1988, a n d 7 1 % of the prey in gut contents from the main bay in [1987][1988][1989][1990]. Medusae showed positive selection for copepods, but negative selection for copepod naupli~. Digestion tlmes of copepods by medusae averaged 3.5 h. A n~ultiple regression equatlon related digest~on times to temperature and the number of ingested copepods, but not to medusa slze. Predation rates (numbers of copepods consumed medusa-' d-') increased with increasing prey density, medusa diameter, and temperature These results p r o v~d e a means of predicting C. quinquecirrha feeding in sjtu. Greater numbers of prey in medusae at n~ghttime than during the day probably were due to greater prey densit~es at night. Daily predation effects (percentage of the copepod standing stock consumed d.') were calculated from feeding rates, and the d e n s~t~e s of medusae and copepods. Medusa densities (peaks of 11 to 16 m-3) and predation effects (peaks of 42 to 94 % d-l of the copepods consumed) were much greater in the 2 tributar~es than at a nearshore station in the bay (peaks of 2 medusae m-3 and 3 % d-' of the copepods consumed). Ingestion of zooplankton provided a n average of 145 % of the nitrogen needed to balance excretion in medusae <45 mm In diameter, but supplied only 65 % of the n~trogen needs of medusae > 4 5 mm. Other prey, including ctenophores, fish eggs and larvae, and large polychaete worms are additional contributions to the diet. Predation by C. quinquecirrha medusae may control copepod populations in some tributaries of Chesapeake Bay, as suggested by high predat~on effects and declining copepod populations throughout the summer.

We measured predation on bay anchovy Anchoa mitchilli eggs and larvae by abundant scyphomedusae Chrysaora quinquecirrha and ctenophores Mnemiopsis leidyi from gut contents, digestion rates, and densities of predators and prey during 9 d in July 1991 at 4 stations in Chesapeake Bay, USA. These predation rates were compared to egg and larval mortality rates measured concurrently in ichthyoplankton surveys. Daily predation by medusae and ctenophores was 19 * 13":) (mean + SD) of the eggs over the 20 h stage duration, with medusae responsible for 26 to 100% of the predation. These gelatinous predators accounted for 21 i 17 ":, of the total estimated daily egg-stage rnortality. On average, medusae consumed 29 + 14 O/u d -' of the larval bay anchovy, which was 41 35% of total estimated larval mortality. Predation on larvae by ctenophores was not detected. These predation effects are compared with those measured concurrently in free-drifting 3 2 m3 mesocosms. We conclude that medusae, which had high feeding rates but low abundances, and ctenophores, which had lour feeding rates but high abundances, were important predators of bay anchovy eggs and larvae in the mesohaline region of Chesapeake Bay

No abstract

The introduction of alien, or nonindigenous, animals and plants has been identified by scientists and policy makers as a major threat to biodiversity in marine ecosystems. Although government agencies have struggled to control alien species on land and freshwater for decades with mixed success, the control of alien marine species is in its infancy. Prevention of introduction and establishment must be the first priority, but many populations of alien marine species are already well established worldwide. National and international policies leave loopholes for additional invasions to occur and provide only general guidance on how to control alien species once they are established. To address this issue, a multinational group of 25 scientists and attorneys convened in 1998 to examine options for controlling established populations of alien marine species. The discussions resulted in a framework for control of alien marine species to provide decision-making guidance to policymakers, managers, scientists, and other stakeholders. The framework consists of seven basic steps: (1) establish the nature and magnitude of the problem, (2) set objectives, (3) consider the full range of alternatives, (4) determine risk, (5) reduce risk, (6) assess benefits versus risks, and (7) monitor the situation. This framework can provide guidance for control efforts under the existing patchwork of national laws and can help provide a foundation for international cooperation. El Control de Invasiones Biológicas en los Océanos del Mundo Resumen: La introducción de animales y plantas invasoras, o no indígenas ha sido identificado por los científicos y legisladores como una de las mayores amenazas a la biodiversidad de los ecosistemas marinos. A pesar de las agencias gubernamentales han luchado por décadas por controlar a las especies invasoras en tierra y en agua dulce con resultados mezclados, el control de las especies invasoras marinas se encuentra aún en su infancia. La prevención de la introducción y el establecimiento debe ser prioritaria; sin embargo, muchas poblaciones de especies invasoras marinas ya se han establecido muy bien a nivel mundial. Las políticas nacionales e internacionales dejan espacios para que ocurran invasiones adicionales y proveen una guía solo anivel general sobre como controlar especies invasoras una vez que ya se hayan establecido. Para enfrentar este tema, un grupo multinacional de 25 científicos y abogados se reunieron en 1998 para examinar opciones para controlar poblaciones de especies marinas invasoras establecidas. Las discusiones dieron como resultado un marco de trabajo para el control de especies marinas invasoras que provee guías para la toma de decisiones para los legisladores, manejadores, científicos y otros interesados. Este marco de trabajo con- Bax et al. Controlling Alien Marine Species 1235 siste en siete pasos básicos: (1) el establecimiento de la naturaleza y la magnitud del problema, (2) la delimitación de los objetivos, (3) consideración de todas las alternativas posibles, (4) determ...

The introduction of alien, or nonindigenous, animals and plants has been identified by scientists and policy makers as a major threat to biodiversity in marine ecosystems. Although government agencies have struggled to control alien species on land and freshwater for decades with mixed success, the control of alien marine species is in its infancy. Prevention of introduction and establishment must be the first priority, but many populations of alien marine species are already well established worldwide. National and international policies leave loopholes for additional invasions to occur and provide only general guidance on how to control alien species once they are established. To address this issue, a multinational group of 25 scientists and attorneys convened in 1998 to examine options for controlling established populations of alien marine species. The discussions resulted in a framework for control of alien marine species to provide decision-making guidance to policymakers, managers, scientists, and other stakeholders. The framework consists of seven basic steps: (1) establish the nature and magnitude of the problem, (2) set objectives, (3) consider the full range of alternatives, (4) determine risk, (5) reduce risk, (6) assess benefits versus risks, and (7) monitor the situation. This framework can provide guidance for control efforts under the existing patchwork of national laws and can help provide a foundation for international cooperation. El Control de Invasiones Biológicas en los Océanos del MundoResumen: La introducción de animales y plantas invasoras, o no indígenas ha sido identificado por los científicos y legisladores como una de las mayores amenazas a la biodiversidad de los ecosistemas marinos. A pesar de las agencias gubernamentales han luchado por décadas por controlar a las especies invasoras en tierra y en agua dulce con resultados mezclados, el control de las especies invasoras marinas se encuentra aún en su infancia. La prevención de la introducción y el establecimiento debe ser prioritaria; sin embargo, muchas poblaciones de especies invasoras marinas ya se han establecido muy bien a nivel mundial. Las políticas nacionales e internacionales dejan espacios para que ocurran invasiones adicionales y proveen una guía solo a nivel general sobre como controlar especies invasoras una vez que ya se hayan establecido. Para enfrentar este tema, un grupo multinacional de 25 científicos y abogados se reunieron en 1998 para examinar opciones para controlar poblaciones de especies marinas invasoras establecidas. Las discusiones dieron como resultado un marco de trabajo para el control de especies marinas invasoras que provee guías para la toma de decisiones para los legisladores, manejadores, científicos y otros interesados. Este marco de trabajo con- Bax et al. Controlling Alien Marine Species 1235 siste en siete pasos básicos: (1) el establecimiento de la naturaleza y la magnitud del problema, (2) la delimitación de los objetivos, (3) consideración de todas las alternativas posibles, (4) determ...