Palaeoenvironments of Rhizophora mangle (Rhizophoraceae) in Castilletes, Alta Guajira, Venezuela according to paleoconchas of Crassostrea rhizophorae (Ostreoida: Ostreidae).

Abstract

Palaeoenvironments of Rhizophora mangle (Rhizophoraceae) in Castilletes, Alta Guajira, Venezuela according to paleoconchas of Crassostrea rhizophorae (Ostreoida: Ostreidae). Shell middens are a very characteristic feature of coastal human adaptations. Component and variability analysis offer clues to subsistence of ancient human populations, formation processes and information of environmental changes.In this study, we tested the use of paleoshells found in shell midden to infer paleoenviroment conditions of R. mangle forest. We presented data of paleoshells from shell middens, located on Castilletes-Alta Guajira, Venezuela, dated from 3 580 ± 30 años B.P years, and we included data of actual shells from mangrove forests located on Cocinetas laggon (Castilletes) and Maracas Island (Maracaibo lagoon). We examined 185 samples of fixing traces marked by mangrove roots on paleoshells (n = 109) and actual shells (n = 76) of C. rhizophorae. Subsequently, we estimated paleoroot and modern root diameter using a geometric model using shell´s trace. To validate this model, we directly measured modern roots. Furthermore, a physiognomic study was made in both sites to associate mangrove forest with roots diameter and shells information. Results showed that there were no significant differences between estimated root diameter values obtained from traces of modern shells and the ones recorded by direct measurement of roots (Castilletes P = 0.160854; Maracas P = 0.617271); allowing the use of geometric model to obtain estimated values of paleoroots. Shell measurements showed that paleoshells were larger than modern shells. Paleoroot diameters showed no significant differences with modern Castilletes's mangrove roots (exposed zone) (P = 0.303518), contrasting with Maracas´s roots (protected zone) (P = 0.017771). Physiognomic study showed that modern Castilletes forests had diameter at breast height (DBH) and tree height (11.10 m and 4.90 m, respectively) lower than Maracas (34.86 cm and 10.62 m), responding to the wind exposure and salinity. Diameters and quantity of roots per tree were higher in Castilletes (3.01 cm y 11 roots/tree) than Maracas (2.39 cm y 7 roots/tree). We determined that paleoforests and modern forests from Castilletes have similar characteristics associated to arid environment with stronger wind exposition. We concluded that paleoshells trace analysis is a low cost and novel method that allows obtaining information about paleoenvironment of R. mangle forests. Rev. Biol. Trop. 63 (4): 1223-1233. Epub 2015 December 01.