Hydrothermal vents are ephemeral because of frequent volcanic and tectonic activities associated with crust formation. Although the larvae of hydrothermal vent fauna can rapidly colonize new vent sites separated by tens to hundreds of kilometres, the mechanisms by which these larvae disperse and recruit are not understood. Here we integrate physiological, developmental and hydrodynamic data to estimate the dispersal potential of larvae of the giant tubeworm Riftia pachyptila. At in situ temperatures and pressures (2 degrees C and 250 atm), we estimate that the metabolic lifespan for a larva of R. pachyptila averages 38 days. In the measured flow regime at a fast-spreading ridge axis (9 degrees 50' N; East Pacific Rise), this lifespan results in potential along-ridge dispersal distances that rarely exceed 100 km. This limited dispersal results not from the physiological performance of the embryos and larvae, but instead from transport limitations imposed by periodic reversals in along-ridge flows and sustained episodes of across-ridge flow. The lifespan presented for these larvae can now be used to predict dispersal under current regimes at other hydrothermal vent sites.

The role of food resources in regulating seasonal population dynamics was determined in a benthic community typical of mesohaline regions in Chesapeake Bay. Four macroinvettebrates dominated the community: the bivalve Mucoma balthicu, the polychaetes Streblospio benedicti and Nereis succinea. and the amphipod Leptocheirus plumulosus. Several factors seem to regulate population dynamics at different times of the year. In March, growth and reproduction rates accelerated as temperature and phytodetrital sedimentation increased. In April, invertebrate growth rates plateaued while estimated community N requirements were equivalent to estimated N availability. In May, invertebrate growth and reproduction rates rapidly declined while estimated community energy requirements were greater than sedimenting energy supplies. In June, larval recruitment was heavy for S. henedicti and L. plumulosus; however, these juveniles showed no iapparent growth during June and their densitiesrapidly declined. The sudden appearance and disappearance of these juveniles was solely responsible for the boom-and-bust dynamics of S. benedicti and L. plumulosus. Essential W3-polyunsaturated fatty acids and essential amino acids were present at high levels in spring but were present in only trace amounts during summer. Growth of juvenile S. benedicti and L. plumulosus recruits was most likely limited by food supply in June and July, especially by the availability of essential nutrients. Estimates of predation rates could not account for these population declines.

Assessing the energy costs of development in extreme environments is important for understanding how organisms can exist at the margins of the biosphere. Macromolecular turnover rates of RNA and protein were measured at -1.5 degrees C during early development of an Antarctic sea urchin. Contrary to expectations of low synthesis with low metabolism at low temperatures, protein and RNA synthesis rates exhibited temperature compensation and were equivalent to rates in temperate sea urchin embryos. High protein metabolism with a low metabolic rate is energetically possible in this Antarctic sea urchin because the energy cost of protein turnover, 0.45 joules per milligram of protein, is 1/25th the values reported for other animals.