Current theory on the population dynamics of marine species with complex life history patterns posits that a suite of physical and biotic forces (e.g., habitat structure and density—dependent predation or emigration) control survival and abundance in early life history, particularly after settlement. We have conducted a long—term sampling effort accompanied by a series of field and laboratory experiments examining the joint effects of habitat type, body size, and population density upon abundance and survival of early juveniles of the blue crab, Callinectes sapidus. In addition, the chance occurrence of a tropical storm during one set of experiments provided an opportunity to assess the impact of a physical disturbance upon newly settled blue crab survival and abundance. In the 10—yr sampling effort, we quantified relationships between sequential life history stages (juvenile crab instars) in seagrass beds, the initial nursery habitat for blue crabs in the lower Chesapeake Bay. Inter—instar relationships were defined as the densities of larger instars as dependent on the densities of smaller instars. Inter—instar relationships for the youngest instars are described by hyperbolic functions until crabs begin to emigrate to unvegetated habitats at approximately the fifth instar. Inter—instar relationships between crabs larger than the fifth instar and smaller crabs become either parabolic or linear functions and decay as the number of instars between sequential life history stages increases. While both the hyperbolic and parabolic functions are indicative of populations regulated by density—dependent processes, either predation or emigration, the decay in the functions describing the inter—instar relationships for crabs larger than the fifth instar indicates that the suite of processes regulating this segment of the population changes qualitatively. In laboratory and field experiments, the effects of vegetated and unvegetated habitats and size—specific predation on newly settled juveniles were tested. Tethering was used to quantify relative rates of predation, and a laboratory study was conducted to determine if tethering induced treatment—specific bias. We found no statistically significant interactions between the tethering treatment and the factor treatments of crab size and habitat during the laboratory study, indicating that tethering did not produce treatment—specific bias. Thus, tethering provided a relative measure of predation that allowed comparisons between treatments of habitat and crab size on crab survival. In both laboratory and field experiments, survival was significantly higher in vegetated habitats and with increasing size until the ninth instar, when survival did not differ by habitat. This difference explains the dispersal from vegetated to unvegetated habitats that occurred between the fifth and seventh instars. In addition, survival of all crabs was significantly increased both during and after Tropical Storm Danielle compared to pre—storm conditions. A model is developed that describes juvenil...

Endemic freshwater demosponges in the littoral zone of Lake Baikal, Russia, dominate the benthic biomass, covering 44% of the benthos. We measured in situ sponge abundance and grazing and calculated sponge‐mediated fluxes of picoplankton (plankton <2 µm) for two common species, Baikalospongia intermedia and Baikalospongia bacillifera. By means of dual‐beam flow cytometry, we found retention efficiencies ranging from 58 to 99% for four types of picoplankton: heterotrophic bacteria, Synechococcus‐type cyanobacteria, autotrophic picoplankton with one chloroplast, and autotrophic picoplankton with two chloroplasts. By using a general model for organism‐mediated fluxes, we conservatively estimate that through active suspension feeding, sponges are a sink for 1.97 g C d−1 m−2, mostly from procaryotic cell types. Furthermore, grazing by these extensive sponge communities can create a layer of picoplankton‐depleted water overlying the benthic community in this unique lake.

Submersible exploration of the Samoan hotspot revealed a new, 300-m-tall, volcanic cone, named Nafanua, in the summit crater of Vailulu'u seamount. Nafanua grew from the 1,000-m-deep crater floor in <4 years and could reach the sea surface within decades. Vents fill Vailulu'u crater with a thick suspension of particulates and apparently toxic fluids that mix with seawater entering from the crater breaches. Low-temperature vents form Fe oxide chimneys in many locations and up to 1-m-thick layers of hydrothermal Fe floc on Nafanua. High-temperature (81°C) hydrothermal vents in the northern moat (945-m water depth) produce acidic fluids (pH 2.7) with rising droplets of (probably) liquid CO 2. The Nafanua summit vent area is inhabited by a thriving population of eels (Dysommina rugosa) that feed on midwater shrimp probably concentrated by anticyclonic currents at the volcano summit and rim. The moat and crater floor around the new volcano are littered with dead metazoans that apparently died from exposure to hydrothermal emissions. Acid-tolerant polychaetes (Polynoidae) live in this environment, apparently feeding on bacteria from decaying fish carcasses. Vailulu'u is an unpredictable and very active underwater volcano presenting a potential long-term volcanic hazard. Although eels thrive in hydrothermal vents at the summit of Nafanua, venting elsewhere in the crater causes mass mortality. Paradoxically, the same anticyclonic currents that deliver food to the eels may also concentrate a wide variety of nektonic animals in a death trap of toxic hydrothermal fluids.currents ͉ habitats ͉ hydrothermal ͉ vents ͉ eels S eamounts, submerged isolated mountains in the oceans, are among the most poorly understood major morphological features on Earth, offering important research targets for ocean sciences. Seamount research, which involves fields as diverse as volcanology, geology, geochemistry, geophysics, physical oceanography, and marine biology, has yielded crucial insights into the absolute motion of the tectonic plates (1), the rheology and state of stress of the underlying lithosphere (2, 3), the chemical make-up of Earth's mantle (4), and the role of hypoxia in benthic animal distributions (5). Seamounts offer unique habitats for nektonic and benthic life, including both microbes and metazoans (6, 7). The topography of seamounts can substantially enhance internal ocean tides, providing powerful ''stirring rods'' for mixing the oceans (8) and creating local currents that transport nutrients and retain larvae (9) and concentrate commercially important fishes (10).We report here the initial, integrated results from recent volcanological, biological, and oceanographic explorations of Vailulu'u Seamount (14°13ЈS; 169°04ЈW), an active submarine volcano located 45 km east of the easternmost island in the Samoan archipelago. Our data come largely from three short oceanographic cruises in March-July, 2005. A cruise on the R͞V Kilo Moana (KM) in April 2005 included 3 days of bathymetric mapping, hydrographic profiling, and geol...

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Mussels from deep‐sea methane/sulfide seeps in the Gulf of Mexico supplement their symbiotically acquired nitrogen by feeding selectively on nitrogen‐rich bacterioplankton. The previously unknown natural diet of the mussels consists of bacteria, Synechococcus‐type cyanobacteria, and protozoans. Overall retention increased with increasing mussel size, though the largest mussels did not retain bacteria. Mussels can obtain as much as 0.12 mmol N g−1 h−1 by filter feeding on natural water‐column communities. Previous calculations indicate that nitrogen acquired through the symbionts is inadequate for maximal growth, but our conservative estimates suggest that nitrogen obtained by filter feeding is similar to that acquired by symbionts and may be an important component in the nutritional requirements of seep mussels. Additionally, we conducted a series of in situ measurements of flow and food availability over an extensive mussel bed located at the Brine Pool. Our measurements indicate that biogenic flow due to mussel pumping generates near‐bottom turbulence that prevents the development of a food‐depleted layer over the mussel bed.