Jaime Polanía

Mangrove dynamics in the southwestern Caribbean since the ‘Little Ice Age’: A history of human and natural disturbances

Relatively little is known about the long-term response of Caribbean mangroves to human and natural disturbances during the ‘Little Ice Age’ (LIA). We present new palynological information on the dynamics of the Bahia Honda mangrove from the eastern coast of San Andres Island in the southwestern Caribbean for the late Holocene. Major changes in the Bahia Honda pollen record show the combined effects of natural events (strong storms and sea-level rise), and human disturbances. These changes are supported by 14C dates, sedimentological and palynological information. A storm (most probably a hurricane) was recorded around AD 1600, caused sediment reworking and the subsequent loss of about 2000 years of the vegetation record. The devastation of tree vegetation by this event allowed the expansion of heliophytic vegetation (e.g. grasses and vines). Mangroves and coastal vegetation started to recover at AD 1700, reaching their maximum extent within a few decades, when microforaminifera shells became abundant at the coring site, thus suggesting a relative sea-level rise because of the geomorphic reconfiguration of the coastal plain after the storm. Furthermore, the pollen evidence indicates more humid regional climates during the late LIA (AD 1700—1850). Mangrove and coastal vegetation declined sharply as a consequence of the establishment of coconut plantations around AD 1850. The recovery of the mangroves after AD 1960 is a result of the combined effect of relative sea-level rise and drastic changes in the local economy from coconut plantations to commerce.

Mollusc fauna of the mangrove root-fouling community at the Colombian Archipelago of San Andres and Old Providence

This paper advances a qualitative and quantitative preliminarycharacterization of the mollusc fauna associated with the submerged rootsof Rhizophora mangle L. in three mangrove areas with differentdegrees of anthropogenic impact in the San Andres (Hooker and HondaBays) and Providence (Old Providence McBean Lagoon National Park)archipelago in the Western Caribbean. The study was carried out during thedry and rainy seasons (July and November, respectively) back in 1998.Samples were taken from 34 submerged roots which were not fixed to thesubstrate. Several physico-chemical parameters were also measured insitu. All molluscs were identified and counted and indexes of speciesrichness, diversity, uniformity, similarity, dominance of species and densityof individuals were calculated. All in all 5,771 individuals belonging to 21species of 17 families were counted. Most of the species were epibenthic,herbivorous and with undifferentiated planctonic larvae, but most of theindividuals were epifaunal and attached as well as filter-feeders withplanctonic larvae. Most individuals were found in juvenile stages. The threesites, under different degrees of anthropogenic impacts, showed relatedvalues of species richness, diversity and abundance, as well as densities ofmollusc taxa in oceanic communities associated with mangrove roots.Further research should be done to find similar responses in accompanyingsignificant groups, such as Crustacea and Polychaeta.

Control of Avicennia germinans recruitment and survival by Junonia evarete larvae in a disturbed mangrove forest in Colombia

In the Cienaga Grande de Santa Marta, a brackish lagoon system on the Caribbean coast of Colombia, about 60% of the mangrove forests died from hypersalinization. The die-back was first encountered in 1964 and mass mortality started in the late 1960s. Although efforts are being made to reestablish the destroyed areas, regeneration is slow, which may be partly due toJunonia evarete caterpillars defoliating Avicennia germinans seedlings. The interaction between insects and seedlings was studied. BothJ. evarete butterflies and caterpillars were abundant during the main rainy season, the time of highest fruit production in A. germinans. During the dry season the herbivore disappeared. The caterpillars fed exclusively on A. germinans propagules, seedlings, and pneumatophores. They pre- ferred young seedlings to older plants and did not feed on trees. At some sites, 100% of the A. germinans seedlings died due to the caterpillar attack. Seedlings at open, disturbed sites were attacked more than seedlings protected by small roofs and trenches or those under a closed canopy. Only seedlings protected by insect nets or seedlings germinating at the beginning of the dry season had good chances of survival. The results suggest that in the highly disturbed areas of the Cienaga Grande regeneration of A. germinanis is strongly inhibited by the feeding behaviour ofJ. evarete caterpillars.