Herbivore alternatives: Tripneustes ventricosus, on coral reefs to reduce the abundance of nuisance species.

Background/Question/Methods

This project aims to refine the restoration of herbivores by developing other successful techniques (i.e., larval rearing) to increase the population and diversity of sea urchins that will be restored to the coral reefs and other vulnerable habitats impacted by nuisance species. On June 23, 2021, 15 adults of Tripneustes ventricosus (broodstock) were collected from Mario reef in La Parguera and were brought back to the laboratory at the Department of Marine Science, UPRM. Sperm and eggs were collected from two of the broodstock that spawned immediately after arriving at the laboratory. Fertilized eggs were left overnight in beakers, and after 24 hrs., the two-arm echinopluteus were transferred to a 68L conical tank. The initial stock density of the tank was 2.5 larvae mL-1. Water changes (300% of water) occurred every day, and a complete tank change occurred every two days. The temperature and salinity of the tank were maintained at 28C and 35 ppt, respectively. A mixture of Chaetoceros gracilis and Isochrysis galbana (each 30,000 cells mL-1) was added to the larval tanks every day.

Results/Conclusions

Competent larvae, i.e., defined rudiment with tube feet and pedicellaria, were observed on Day 21. On Day 22, most of the competent larvae were moved to a settlement tank. Approximately 30 competent larvae were transferred to seven 500mL beakers, which contained different substrate types (Thalassia blades, Ulva, plates with CCA/biofilm, and control). The highest settlement (24%) occurred with the Ulva and CCA/biofilm treatments. The goal of this project is to enhance herbivory and diversify herbivore assemblages by adding T. ventricosus and other sea urchins (Echinometra viridis) to reduce nuisance species, such as Ramicrusta spp. and the invasive seagrass, Halophila stipulacea, and other competitive algal species on coral reefs in Puerto Rico.