For 3 mo, pelagic larvae of the intertidal crab Pachygrapsus crassipes were collected daily at a single site located several hundred meters from the shore. The daily abundance of the larvae fluctuated w~t h fortnightly maxima that preceded the maxima in the daily tidal range by about 5 d. These data suggest that the larvae might be carried ashore in surface slicks generated by tidally forced internal waves. Such slicks transported drogues 1 to 2 km shoreward in 2 to 3 h on 2 out of 5 dates; on the dates when transport occurred pelagic larvae of a variety of invertebrates and fishes were 6 to 40 times more concentrated near the surface in the slicks than near the surface of the water between the slicks. The reason why the slicks failed to transport drogues shoreward on 3 dates is not known; however, on these dates, the abundance of larvae near the surface was not significantly greater in the surface slicks than in the zones between the slicks. These observations suggest that concentration and transport in slicks associated with tidally driven internal waves may be an important means for the onshore transport of pelagic life history stages of marine organisms.For many marine invertebrates and fishes, the temporal and spatial distribution of pelagic developmental stages influences the subsequent population structure of later stages in the life history. For example, timing, location and intensity of recruitment for juveniles of intertidal invertebrates (Underwood, 1979) and coral fishes (Doherty, 1983) are influenced by the heterogeneous distribution of their pelagic larvae. Such heterogeneity may result not only from adult distributions and breeding periodicities, but also from some combination of the pelagic stages' survivorship, behavior and transport by physical oceanographic processes.In spite of the obvious importance of quantitative field studies of the pelagic developmental stages of marine organisms, technical difficulties have hampered work on the subject. In the present study I measured: temporal fluctuations in abundance of O Inter-Research/Printed in F. R. Germany pelagic larvae of a crab at a given location and simultaneous spatial fluctuations in the abundance of pelagic larvae of several kinds of invertebrates and fishes. For species and location studied, there was a strong correlation between larval abundance and physical oceanographic phenomena.From early August through early November 1982, pelagic megalopa larvae of the crab Pachygrapsus crassipes were collected daily at the seaward end of the pier at the Scripps Institution of Oceanography. The pier is 320 m long and projects perpendicularly from a coastline that runs north-south; water depth at the end of the pier is about 6 m, and the bottom is sandy. The crab larvae were captured in traps that consisted of bundles of hemp rope or surf grass. Each bundle was about l m long and was bound tightly around the center (the diameter at the binding was about 3 cm). These traps were at 2 depths (just beneath the sea surface and at 1.5 m) benea...

Using tetrazolium salts we tested the hypothesis that reducing microzones can form within detrital aggregates (i.e. marine snow). Even when the ambient waters were well oxygenated, patches of reduced tetrazolium salts were found in marine snow indicating that strongly reducing microzones were present in these aggregates. Further, in both laboratory-made and field-collected marine snow we found measurable amounts of sulfide. Sulfide was present in marine snow on 9 out of 10 sample dates and the sulfide concentration within marine snow ranged from 1.3 to 25 pm01 S 1-' On only 1 out of 10 dates was sulfide detected in the oxygenated waters surrounding the aggregates. The sulfide in the marine snow was probably produced by anaerobic microbes in the reducing microzones in the marine snow. Our data suggest that the paradoxical production of sulfide in aerobic water columns is probably due to production within anoxic microzones within marine snow.

ABSTMCT: The scyphozoan Stomolophus meleagris, when disturbed (held in a container), discharges a sticky mucus. Toxins released into the mucus and water kill some fish and crustaceans and can immediately alter fish behavior, but did not affect a crab predator of S. meleagris. The mucus contains discharged and undischarged nematocysts. The toxins in the mucus are probably associated with these nematocysts. In the field. S. meleagris subjected to a simulated small predator bite released clouds of nematocysts which drove off small fish (potential predators), but did not drive off the associated predacious crabs. These 2 behaviors appear to be forms of chemical defense. Two other species of scyphozoans and a ctenophore species also discharge mucus when disturbed. Chemical defenses may be common amongst gelatinous zooplankton.

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