A new exposure index is described which can be derived from wind velocity, direction, duration and the effective fetch. Effective fetch is calculated from actual fetch modified by shoreline and offshore extents of shaIlow water. The index is calculated from the sum of these components for each unobstructed 22.5 degree compass sector of the shoreline. Data are presented for tests of the index as a predictor for littoral zonation phenomena in Bermuda and the Bay of Fundy, Canada. For the zones in both locations the index satisfies the majority of variance in the data. The vertical distribution of species is weIl modeIled in many cases, but not for others. In many cases significantly better fits are obtained if the basic index is modified using a component for shore slope. The index is useful as a numerical index of exposure which can be derived from standard weather data and hydrographic charts. It is also useful in pointing out littoral species that either do not respond to exposure, or respond in a different way from the majority of species.

ABSTRACT. In situ field observations of the suspension-feeding North Atlantic sea cucumber Cucumaria frondosa from the Bay of Fundy, Canada, conducted over a 3 yr period, revealed a seasonal feeding rhythm. Sea cucun~bers extended their tentacles and began feeding in March/April and ceased feeding in September/October. There were significant relationships between this feeding activity, daylength and the quality of the seston, but not its concentration. Together daylength and chloropigment concentration explained 49% of the variability in the percentage of feeding sea cucumbers. Feeding activity was not significantly correlated with the distinct temperature cycle observed in the study area. Feeding activity was influenced by the state of the tide, water temperature and by daylight during some periods of the feeding season. However, for most of the year these factors appeared not to be important. Sea cucumbers increased their rate of tentacle insertion into the mouth as the quality of the seston increased. The rate of tentacle insertions increased with increasing seston chloropigment concentration but decreased with increasing current speed. These 2 environmental variables explained about 28 % of the variability in tentacle insertion rates. Seston quality is likely the malor environmental variable influencing seasonal feeding behaviour and feeding rate in this species.

No abstract

No abstract

No abstract