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The Impact of Crown Conch on Intertidal Oyster
Populations in Mosquito Lagoon

By: Casey Craig, Courtney Buck, Chelsea Landau, and Jordan Filipponi
Mentor: Dr. Linda Walters

Results

Abundance

A total of 33 live M. corona were found during our surveys when all observation dates were combined. No M. corona were found in the winter, six were found during early summer, and 27 were counted in early fall. More than half (61%) of these observed individuals were located on one reef in fall 2014. Hence this location was considered to be a hotspot for M. corona. A total of 108 shells of M. corona (no live animal) were found when all surveys were combined (Figure 1). Forty-one of these shells were encountered off the reefs, but within one meter of the reef edges. Shells without M. corona were either occupied by C. vittatus (55.3%) or were extensively damaged and appeared empty (30). Six shells of the Florida horse conch, Triplofusus giganteus, were found when all reefs were combined. Four of these were apparently empty shells. Two live tulip snails, Fasciolaria tulipa, were found on natural reefs not along a boating channel. Five shells of the Atlantic moon snail, Polinices duplicatus, were also found on natural reefs, both on and not along boating channels. All five shells were occupied by C. vittatus. No egg cases were found on any reef in any season. However M. corona egg cases were found outside of the monitoring areas during the early summer and fall surveys.

There was no seasonal effect on M. corona densities (ANOVA: p = 0.107) or shell lengths (ANOVA: p = 0.930). Individuals found during the early summer surveys had a mean shell length (± S.E.) of 9.0 ± 0.4 cm compared to 8.3 ± 0.3 cm in the fall (Figure 2). During the summer, the smallest M. corona found was 4.0 cm, while the largest 12.6 cm. Live M. corona ranged in size from 3.9 cm to 13.5 cm in the fall.

Feeding

During the three feeding trials, 50% of the oysters were consumed. There was no correlation between consumed oyster shell length and shell length of M. corona (r2 = 0.1237, Figure 3). Two conch were dead at end of the 72–hour trial; one shell already housed a hermit crab. The oysters in these cages had not been consumed and were thus not included in the analyses. On one occasion, the M. corona, laid an egg case on the cage mesh.

Tracking

Individuals were found to travel fastest on reefs along boating channels, averaging 47.8 centimeters per 10–minute interval. In contrast, M. corona were slowest, at 39.5 centimeters per 10–minutes, on reefs not along boating channels. Conch averaged 45.2 centimeters per 10–minutes on restored reefs. Hence, overall, M. corona, traveled a mean of 44.1 centimeters in 10 minutes. The longest distance an individual traveled in a 10–minute interval was 184 centimeters. There were 52 instances when M. corona did not move during a 10–minute interval, but all individuals moved some distance during the 60–minute trials. M. corona were able to travel between 2.37 meters per hour and 2.87 meters per hour, with a mean of 2.64 meters per hour.

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