| dc.description.abstract | The main focus of this study was to gather more information about the diet and ecology of the Queen conch (Lobatus gigas) in the island of Curaçao and provide background knowledge for future restoration and mariculture programs. The presence of conchs in the Sea Aquarium of Curaçao, where there is practically no poaching or predation, offered a good opportunity to study the diet and length distribution of the conchs under various semi-natural conditions. For this study, samples of conchs and possible items of their diet were collected from 5 natural sites and 6 basins of the Sea Aquarium. The presence of various species of sea mammals (i.e. dolphins, sea lions) in these basins was thought to influence diet composition and therefore the growth rate of the conchs.
Stable isotope analysis of nitrogen (δ15N) and carbon (δ13C) was used to test this hypothesis and to determine the main diets of the conchs in every site. This method allows identifying the composition of consumers and estimating the contribution of the different elements of a consumer´s diet. The results showed that in the basins of the Sea Aquarium and in the natural sites where there was human influence, the δ15N of the conchs and the algae sampled were high compared to the more pristine natural sites. The reason for that might be that the sewage of resorts and the Sea Aquarium discharge close to where the conchs were found. In the Sea Aquarium, the presence of the sea mammals inhabiting the basins could also be the reason for the high levels of δ15N.
The second main goal was to assess if the maximum sizes reached in the Sea Aquarium were larger compared to the wild and, if that was the case, try to relate it to the different diets. The length of this study did not allow for growth measurements. Therefore, the maximum length of the shell and the thickness of the flared lip were used as proxies for local growth conditions. Within the basins of the Sea Aquarium, the largest specimen found had a shell length of 33cm and a lip thickness of 1.2cm. Moreover, adults with flared lips were found in all the basins of the Sea Aquarium, but juveniles were mostly lacking. At most natural sites, however, only juveniles were found and only at Playa Grandi, some specimens with a shell length of more than 28cm and complete developed flared lip were found. The presence of these large specimens suggests that the large sizes reached in the Sea Aquarium are related to the lack of predation (including fisheries) rather than to the diet.
This study underlines that adult Queen conchs in the waters surrounding Curaçao are very rare and appear to occur only in restricted places where there is no poaching of large specimens. Even though specimens of Queen conch were larger and had a different diet in the basins of the Sea Aquarium than those living within more natural waters of Curacao, a causal relationship between growth and diet could not be established. The contrasting size-frequency distributions, finding mostly adults in the Sea Aquarium and juveniles in natural sites, suggest that the high mortality of Queen conch at accessible locations strongly influences the survival and subsequent the length that can be reached. Future restoration of wild populations appears only feasible if juveniles are allowed to reach adult size at which they can reproduce. | |
