Examination of the Allee effect on postlarval recruitment and post-settlement survival in the Caribbean spiny lobster Panulirus argus.

摘要

Positive density dependence (the Allee effect) has been reported in a number of species that are attracted to conspecific cues. This effect has been shown to influence the settlement of many species of marine invertebrates. Caribbean spiny lobsters are gregarious den dwellers attracted to conspecific cues. Previous studies have suggested that the benefit of conspecific attraction is a reduced predation risk by decreasing the time to find crevice shelters (the guide effect) or by cooperative group defense once sharing shelters. I tested a third hypothesis that attraction to conspecific cues increases the settlement of lobster postlarvae into the highest quality nursery habitat (settlement cue) in Florida Bay, FL, USA. Y-maze laboratory choice test on postlarval lobsters (N = 67) found a significant preference for odor cues of large juvenile lobsters. To determine if this preference for conspecific odors could influence lobster recruitment, I established sixteen paired field sites (25 m X 25 m) and manipulated the density of large juvenile lobsters by the addition of ten artificial crevice shelter blocks. Treatment sites received unplugged shelter blocks that could house lobsters up to 45 mm CL while control sites received plugged shelter blocks that could house lobsters up to 25 mm CL. Treatment sites attracted and retained large juvenile lobsters (> 25 mm CL) during our six month study and maintained a density five fold higher than the paired control sites. Each month I censused the density of small juvenile lobsters ( 25 mm CL) along with the density of large juvenile lobsters (> 25 mm CL); crab, fish and octopus predators; and percent cover of red macroalgae. The density of small juvenile lobsters was most influenced by large juvenile lobster density. I also seeded (N = 800) and recovered (N = 18) microwire-tagged small juvenile lobsters from both control and treatment sites. I detected a significant correlation in the number of untagged lobsters with large juvenile density, but no correlation in the number of tagged lobsters with large juvenile density. These results suggest that more postlarval lobsters were settling on sites with high juvenile lobster density supporting the predictions of the Settlement Cue hypothesis.