Secondary metabolites play a key role in their environment by influencing interactions among species, structuring communities, and affecting ecosystem function. While extensive research has been conducted on this topic in terrestrial and marine ecosystems, research on chemical ecology in mangrove ecosystems is relatively new. Such research in mangrove ecosystems is warranted given their considerable ecological and economic value. This study assessed ecological activity of mangrove extracts, through the use of bioassay-guided fractionation, on feeding activity by the mangrove tree crab Aratus pisonii, which is one of the most abundant crab species in mangroves in FL and the Caribbean. It is the primary herbivore of the red mangrove Rhizophora mangle but also lives sympatrically with the black and white mangroves, Avicennia germinans and Laguncularia racemosa, respectively. Preliminary studies have shown that R. mangle and L. racemosa leaves are more palatable than those of A. germinans; thus, it was hypothesized that crabs from both locations would be deterred by A. germinans extracts. Mature mangrove leaves in FL and Belize were collected. Extractions were performed producing non-polar and polar extracts which were fractionated using column chromatography. Extracts and fractions were tested against crabs from both locations in feeding assays with agar-based artificial food.
Results/Conclusions
When non-polar and polar extracts were combined, crabs from each location were deterred by A. germinans extracts from each location compared to extracts from the other species. Non-polar extracts from FL deterred feeding by FL and Belize crabs compared to other extracts from other mangrove species. Unexpectedly, non-polar extracts from Belize stimulated feeding in crabs from Belize when compared to extracts from other mangrove species. Polar extracts largely had no effect on feeding. All but one fraction of A. germinans deterred feeding by the crabs when compared to controls without extracts. The results suggest that mangrove extracts play an important role in influencing feeding activity by A. pisonii and that several different types of compounds may be responsible, especially those derived from non-polar extracts and fractions. It appears that mangrove extracts from the two locations vary in their activity and/or that the crabs vary in their sensitivity to the extracts. Further studies need to be conducted to identify specific secondary metabolites that influence feeding activity in A. pisonii and how such metabolites influence feeding by other mangrove herbivores.