LEAF DESTRUCTION BY MELAMPUS COFFEUS IN BASIN AND FRINGE MANGROVE SWAMPS, BARNES SOUND, KEY LARGO, FLORIDA: IMPLICATIONS FOR NUTRIENT-CYCLING WITHIN MANGROVE SWAMPS

In Florida mangrove swamps, the crab Aratus pisonii consumes ~6-12% of canopy leaves, preferring red mangrove (Rhizophora mangle) leaves to other species (Erickson et al. 2003). When these leaves fall to the peat surface, the snail Melampus coffeus consumes ~40% (Proffitt & Devlin). Both organisms feed by attacking the surface of the leaf. A. pisonii scrapes and consumes the leaf epidermis, but often leaves the opposite surface undamaged. M. coffeus grazes the surface of the leaf, consuming mesophyll and small veins, but seldom larger, lateral veins. Leaves occupied by M. coffeus typically have scalloped edges along the margin of the scraped area.

We studied the ichnological signal of herbivory by A. pisonii and detritivory by M. coffeus in two sites within a mangrove swamp at Barnes Sound, Key Largo, Florida: a basin site, which is generally flooded and has thick leaf mats (19-37 stacked leaves); and a fringe site, where the peat surface is generally exposed and has thin leaf mats (0-4 stacked leaves).

We hypothesize that most leaves in the surface litter reflect both herbivory by A. pisonii and detritivory by M. coffeus; however, detritivory by M. coffeus may obscure the ichnological signal of A. pisonii.

From each site, 25 leaves were targeted to analyze leaf selection and feeding behaviors of M. coffeus. The abundance of snails, leaf surface (upper/lower) preference, and percentage of consumed area of each leaf were recorded.

The abundance of snails per leaf surface from each site was non-significant. Snail consumption was higher on fringe leaves than basin leaves (30% to 23%). Snails preferred to feed on lower leaf surfaces in fringe mangroves (p=0.045). Additionally, snails in basin mangroves portray a strong preference to consume lower surface of leaves (p=0.014).

M. coffeus are pulmonates that retreat from the leaf mat when the peat surface is flooded; inundation could shield the leaf mat from detritivory, which could explain thicker leaf mats in basin mangroves than in fringe. A higher frequency of consumption on the lower leaf surface by M. coffeus may indicate that they prefer leaves that have been scraped by crabs; this would obscure the ichnological signal of crab herbivory; thus, it would be underreported. Furthermore, M. coffeus could prefer leaves that have been fungally-attacked or portray microbial decomposition.