Abstract. In April 1990 a new species of mytilid containing bacterial endosymbionts was discovered at a deep‐water seep site within Alaminos Canyon in the Gulf of Mexico. Activities of ribulose bisphosphate carboxylase/oxygenase and ATP sulfurylase, as well as the presence of substantial levels of elemental sulfur in the gill tissues indicate the presence of chemoautotrophic sulfur‐oxidizing symbionts in the gills. Methanol dehydrogenase activity and the tissue stable carbon isotope ratios indicate the presence of methanotrophic bacteria in the gills of the same animals. Two distinct size classes and morphological types of gram negative bacteria are visible in transmission electron micrographs of the gill tissue, one of which contains the complex internal membranes typical of methanotrophs. Both general types of symbionts have been demonstrated singly in related species of deep‐sea mytilids. In this species, however, both types are found in single individuals, often within the same cell vacuole.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. In the research presented here, we examine the effects of water velocity and canopy morphology on rates of nutrient uptake by seagrass communities. Ammonium uptake rates for two types of seagrass communities, Halodule wrightii and Thalassia testudinum, are measured over a range of velocity using a field flume. The field flume allows independent measurements of uptake by communities of natural composition and condition. We compare our results with those estimated using empirically derived engineering equations that describe transport processes to rough surfaces in order to explore the possibility that uptake rates can be predicted from these equations. We also investigate the possibility that the seagrass canopy alters the characteristics of water flow within the community, which is reflected by the friction imposed by the canopy (the friction coefficient) on the moving water. Our results indicate that ammonium uptake by seagrass communities is dependent on water velocity. Further, seagrasses affect characteristics of water flow within the community that are reflected in rates of ammonium uptake. Empirically derived engineering equations used with measured friction coefficients yield expected Stanton numbers (a nondimensional ratio of flux to a surface to advection by a surface) that are within 95% of those measured in the field flume. Thus, the capacity of these communities to remove ammonium from the water column can be predicted using empirically derived engineering equations that describe the transport of chemicals between a fluid and a rough surface.

In the research presented here, we examine the effects of water velocity and canopy morphology on rates of nutrient uptake by seagrass communities. Ammonium uptake rates for two types of seagrass communities, Halodule wrightii and Thalassia testudinum, are measured over a range of velocity using a field flume. The field flume allows independent measurements of uptake by communities of natural composition and condition. We compare our results with those estimated using empirically derived engineering equations that describe transport processes to rough surfaces in order to explore the possibility that uptake rates can be predicted from these equations. We also investigate the possibility that the seagrass canopy alters the characteristics of water flow within the community, which is reflected by the friction imposed by the canopy (the friction coefficient) on the moving water. Our results indicate that ammonium uptake by seagrass communities is dependent on water velocity. Further, seagrasses affect characteristics of water flow within the community that are reflected in rates of ammonium uptake. Empirically derived engineering equations used with measured friction coefficients yield expected Stanton numbers (a nondimensional ratio of flux to a surface to advection by a surface) that are within 95% of those measured in the field flume. Thus, the capacity of these communities to remove ammonium from the water column can be predicted using empirically derived engineering equations that describe the transport of chemicals between a fluid and a rough surface.

Extracellular layers (jelly coats) on echinoderm eggs are composed of a fibrous network imbedded in a gelatinous material. This type of fibrous network has the potential to protect eggs from mechanical stress. To determine the effects of shear stress and the role of jelly coats in protecting eggs from these stresses, eggs of the sea urchin Lytechinus variegatus, both with and without intact jelly coats, were exposed to shear stresses ranging from 0.3 to 2 Pa in a cone and plate viscometer. The percentage of eggs remaining intact after exposure to the shear stress was assessed. The results indicate that shear stress can damage eggs and that jelly coats may play a role in decreasing the effects of these stresses. Eggs with jelly coats remained intact and fertilizable at greater shear stresses than those with the coats removed. This is the first evidence that extracellular layers on invertebrate eggs can provide protection from mechanical forces.

The ocean attracts and inspires thousands of students every year to pursue degrees in science, engineering, and technology. Yet, in spite of all the attention paid to the oceans, students often lack the information needed to make wise decisions about choosing an ocean-related career. The Center for Ocean Science Education Excellence ? California (COSEE California) and the Marine Advanced Technology Education (MATE) Center have responded to this problem by developing a user-friendly interactive Web site on ocean careers (www.OceanCareers.com).