SPATIAL AND TEMPORAL VARIABILITY IN GROWTH OF RHIZOPHORA MANGLE SAPLINGS ON CORAL CAYS - LINKS WITH VARIATION IN INSOLATION, HERBIVORY, ANDLOCAL SEDIMENTATION-RATE

1 We used demographic growth analysis to quantify seasonal and annual patterns of shoot and root module production by Rhizophora mangle sapl ings growing on three coral cays in Belize, Central America. We invest igated scaling relationships among root and shoot modules, leaf life-s pan, effects of herbivores on module and whole plant growth, and diffe rences in growth under different sedimentation regimes. 2 Production o f new shoots and aerial roots occurred seasonally. Annual peaks in sol ar insolation occurred in May; relative rates of change in numbers of shoot meristems and leaves, and stem length peaked one month following . Relative rate of change in numbers of aerial roots peaked one month following this shoot flush, and roots elongated primarily during the d ry season. 3 Increased water depth was positively correlated with the ratio of root length to shoot length in saplings. Mean shoot growth ra te was significantly lower at cays exhibiting relatively low sedimenta tion rates, as well as at similar locales within cays. 4 Average leaf life-span was 9 months. During an outbreak of the mangrove skipper Pho cides pigmalion, insect herbivores shortened leaf life-span by increas ing leaf abscission rate. Insect folivores reduced above-ground net pr imary production available for export to adjacent marine ecosystems by 5-20%. Up to seven-fold increases in percentage of roots bored by iso pods occurred concomitantly with annual peaks in new root production. Relative elongation rate of roots decreased five-fold following isopod attack. However, whilst both insects and isopods tracked production o f and consumed new modules, neither consumer contributed significantly to variance in whole-plant growth. 5 Demographic growth analysis is a powerful tool with which to predict dynamic responses of module produ ction and whole-plant growth in response to local environmental condit ions. Our analyses illustrate that growth of mangroves are sensitive t o seasonal patterns of insolation, to decreasing sedimentation and to increasing water depth. Given that growth of mangrove saplings on cora l cays declines significantly with sedimentation rate, persistence of these forests is unlikely if sea level in the Caribbean increases as p redicted.