Opuntia corallicola (Cactaceae): Population Monitoring on Swan Key, Biscayne National Park

Grahl, Emilie; Bradley, Keith

The goals of this study were to (1) continue to monitor the 0. corallicola population on Swan Key in order to observe the health of the colony and (2) to watch for poaching and C. cactorum. In November 2001, a colony of the semaphore pricklypear cactus, Opuntia corallicola, endemic to the Florida Keys, was discovered on Swan Key in Biscayne National Park. Previous to this discovery only nine plants of reproductive age were known to exist in the wild on Little Torch Key at The Nature Conservancy's Torchwood Hammock Preserve, 145 km to the south. Since 2002, monitoring of the Swan Key population continues in order to determine basic aspects of the species' life history, to monitor for the presence of the introduced moth Cactoblastis cactorum, and to monitor for poaching. Between October 2004 and October 2005, 655 plants were tagged and monitored at two sites on Swan Key of which 490 (67.68%) were adults and 234 (32.32%) were juveniles. No evidence of C cadorum or poaching was observed. Overall, the O. corallicola population on Swan Key appears relatively stable. Mortality was relatively low (9%) but was higher than mortality recorded (2%) during the previous year. Hurricane activity may explain this higher mortality. Growth and pad production was greatest between April and July. The number of vegetative pads decreased during the late summer (Jul- Oct) months, which coincided with hurricane season. In addition to mortality, high winds associated with hurricanes caused a high number of vegetative pads to fall off of O. corallicola plants. No differences between growth periods for adults and juveniles were detected, however, growth for propagules was highest during the rainy season (April to October) suggesting. a longer growth period than adults. Flower production occurred throughout the year With a noticeable peak from January through April and was at its lowest during the rainy season (April to October).