Ellison Abstract- 1996 Ellison and Farnsworth (Spatial)

Ellison, A. M. and E. J. Farnsworth. 1996. Spatial and temporal variability in growth of Rhizophora mangle saplings on coral cays: links with variation in insolation, herbivory, and local sedimentation rate. Journal of Ecology 84: 717-731.

Abstract

1. We used demographic growth analysis to quantify seasonal and annual patterns of shoot and root module production by Rhizophora mangle saplings growing on three coral cays in Belize, Central America. We investigated scaling relationships among root and shoot modules, leaf life-span, effects of herbivores on module and whole plant growth, and differences in growth under different sedimentation regimes.
2. Production of new shoots and aerial roots occurred seasonally. Annual peaks in solar 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 dry season.
3. Increased water depth was positively correlated with the ratio of root length to shoot length in saplings. Mean shoot growth rate was significantly lower at cays exhibiting relatively low sedimentation rates, as well as at similar locales within cays.
4. Average leaf life-span was 9 months. During an outbreak of the mangrove skipper Phocides pigmalion, insect herbivores shortened leaf life-span by increasing leaf abscission rate. Insect folivores reduced above-ground net primary production available for export to adjacent marine ecosystems by 5-20%. Up to seven-fold increases in percentage of roots bored by isopods 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 of 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 production and whole-plant growth in response to local environmental conditions. Our analyses illustrate that growth of mangroves are sensitive to seasonal patterns of insolation, to decreasing sedimentation and to increasing water depth. Given that growth of mangrove saplings on coral cays declines significantly with sedimentation rate, persistence of these forests is unlikely if sea level in the Caribbean increases as predicted.

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