Surface slicks associated with tidally forced internal waves may transport pelagic larvae of benthic invertebrates and fishes shoreward

Abstract

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 with 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. Observations suggest 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.