Triton Aquaculture Project

Introduction:

Other studies have attempted to breed this shell but were unable to get the larvae to settle and become juvenile shells. Some environmental stimulus was missing from the substrates that were tested, but once this settlement trigger is known then aquaculture becomes possible. The giant triton may begin its juvenile development as an ecto-parasite on one or more species of starfish and when larvae that are ready to settle encounter these species, then settlement may be induced almost immediately. Once larval settlement can be induced, reefs could be restocked to levels of abundance that existed prior to intensive collection for the shell trade. This may assist in the control of starfish outbreaks by preventing the slow build up of starfish numbers that precedes a primary outbreak.

The locations of our survey sites have been very carefully chosen to maximise the probability of locating triton specimens. It is difficult to locate significant numbers of the triton without the enormous collection effort provided by large teams of divers. The main reason for selecting our survey sites is that they are locations where very large numbers of crown-of-thorns starfish have been killed over the last few years. This killing of starfish seems to attract the giant triton and explains why this research can only be conducted at certain places.

Following the detailed surveys of these study reefs, we will be in a better position to monitor the movements and general ecology of the triton over a number of years because we will have attached ultrasonic transducers (tags) to each of the study specimens. Providing that each specimen is located once a year to replace the lithium battery in its tag, then the project can continue past the end of the starfish outbreak when the tritons disperse over the reef and are again virtually impossible to locate without these tags. We may only locate 10 specimens but even this would enable the next stage of the triton management plan to continue.

The giant triton is normally difficult to locate because of its cryptic nature but this becomes even more difficult when it buries under sand while extending the size of its shell or seeking refuge deep in caves when brooding its egg mass. We will be able to locate tagged specimens in all these locations and we will collect small quantities of a number of triton egg masses during this project. These partial egg masses will be transferred to a sea water aquarium facility for our larval settlement experiments.

We will be testing a number of species of coral reef starfish for their ability to trigger larval settlement in the triton. While previous studies managed to rear larva almost to the point of settlement, they could not produce settled larvae that crawled on the bottom. The cultured larva all died in the plankton and the missing link may well be another species of starfish.

Objectives:

  1. To determine which conditions facilitate larval settlement and juvenile survival in the giant triton (Charonia tritonis).
  2. To grow newly settled juveniles of the giant triton and establish what are the causes of natural mortality in this species of shell.
  3. To establish an age specific mortality schedule and determine what size this shell must first attain before it can survive in the wild.
  4. To implement a management program that will assure survival of the giant triton. This is vital to the conservation of the Great Barrier Reef.
  5. To breed live specimens of the giant triton that could be used to restock a number of reefs that have low abundance of giant tritons.
  6. To provide a model of operation that could be implemented on a larger scale if required.

Conservation priorities:

The giant triton shell is sold in most shell shops in Australia despite being protected under Queensland law with the specimens that are for sale allegedly coming from overseas. The giant triton is a known predator of the crown-of-thorns starfish and live tritons are very difficult to find on the Great Barrier Reef or elsewhere. Bearing in mind that it is over thirty years since we discovered that this shell is a starfish predator, it is surprising how little research has been conducted on this species.

Strategy:

  1. Establish a research facility suitable for the maintenance of coral reef starfish for use in settlement experiments with triton larvae.
  2. Examine specimens of coral reef starfish for the presence of small gastropod ecto-parasites that may be juvenile tritons.
  3. Tag and monitor populations of giant triton and extract developing larvae from their egg masses for use in settlement experiments.
  4. Test many different species of coral reef starfish for their ability to induce settlement of giant triton larvae.
  5. If larval settlement can be induced, monitor growth of the juvenile shells to maturity.

Environmental Safety:

To ensure that there are no unnecessary environmental risks taken during this research, the main research facility will need to be located on dry land. Reef pontoons can be used for field observations and the gathering of specimens for experiments in the main research facility.

This will ensure that:

  1. No fertilised starfish eggs will be released into the wild.
  2. No juvenile tritons will be accidentally released into the wild.

 

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