This study considers four species of littorines from rocky shores (Nodilittorina australis, N. millegrana, N. trochoides, and Littoraria undulata) and four species from mangroves (L. cingulata, L. filosa, L. scabra, and L. sulculosa) between July 1989 and June 1999. We conducted periodic censuses of the same replicate areas at four rocky shore sites spread over 40 km of shoreline and at the same replicate mangrove trees in four groups at sites at the opposite ends of a bay, about 2 km apart, This design allowed us to partition the variability in abundance of each species into components associated with the sites, sampling units within sites, time of sampling, sites x times of sampling, and the residual. The littorines of the rocky shores had the greatest variability associated with differences among the four sites for the total populations and among sites and sampling times x site for recruits, whereas the littorines of the man.-roves showed the greatest variability associated with times of sampling and sites x times of sampling. We also conducted shorter-term mark and recapture studies to provide direct evidence about growth and survivorship of these snails. All three species of littorines from mangroves with sufficient recaptures showed rapid growth, reaching half their maximum size in 0.94, 0.35, and 0.75 y for L. cingulata, L. filosa, and L. scabra, respectively, and attaining maximum lengths of 22 to 27 mm, The littorines of the rocky shores all had slower growth than those from the mangroves and were all smaller in maximum size, from 10-17 mm. With the exception of N. millegrana, which took only 0.50 y to reach half maximum size, the snails on the rocky shores took much longer to reach half their maximal lengths than those in the mangroves (1.23, 2.87, and 1.28 y for N. australis, N. trochoides, and L. undulata, respectively). Patterns in survival parallel the estimates of times to reach half maximal size. We never recaptured N. millegrana over intervals as long as I y, but some N. trochoides marked in 1988 were still alive in 1995. This long-term study of eight similar species in a single geographic area highlights the variability in life histories and demographies of littorines.
|Journal of Shellfish Research
|Published - 2001