Crown of Thorn removal in Andulay

 In Conservation, Crown of thorns, Fieldwork

Two weeks ago MCP celebrated Earth Day by removing two predators of hard corals- Crown of Thorns (COT) sea stars and Drupella snails. These predators are generally healthy for the biodiversity of coral reefs, however, when their populations increase dramatically they pose a serious threat.

Over the prior two weeks, invertebrate surveys at Andulay (a site only ten minutes from MCP base) indicated that the COT and Drupella populations reached infestation levels. Normal COT levels are about 10 per hectare (100m by 100m), while MCP survey teams of volunteer divers found more than 60 COT in a 100m by 5m transect. While it is unclear what caused this population spike, outbreaks often occur due to removal of their natural predators, such as titan triggerfish and pufferfish.

Diver spotting a COT

To combat these outbreaks MCP and the local community gathered to remove both species. Local scuba divers, MPA officers, Philippine Navy members, and residents came together at the Andulay MPA Bantay Dagat center for a full day of COT and Drupella removal. Diving teams covered different depth zones throughout the dive site to identify and remove COT. Hard corals exhibit a few key characteristics from COT feeding on living coral tissue. These include feeding scars along the border of plate corals, strings of tissue and mucus, and feeding scars on neighboring colonies. The image on the left is an example of a branching coral seen during the COT removal dive that has clear indications of feeding scars with patches of the coral bleached, brown, and overgrown with algae. Coral such as this were often indicators of where to look, however, COT could also be spotted anywhere near coral on the reef.

Once identified, the divers used either a vinegar syringe or thongs to remove the animal. When COT is injected with vinegar their pH levels are unbalanced and they are unable to regulate their pH, resulting in death. This method is preferred because if the COT is not brought to the surface within approximately 20 minutes after being removed from their environment they release all their eggs due to stress. If this were to happen, there is a chance that the infestation could worsen.

In addition to the COT infestation, invert surveys also found increasing numbers of Drupella. The average number of Drupellas increased 4 fold from the previous monitoring season (November to January) to the current monitoring season (February to April).

MCP volunteers used tweezers to carefully remove Drupellas from corals and collect them in a bag when they found a coral with more than 50 Drupella shells.

In total the community and MCP volunteers and staff removed 177 COTs and 699 Drupellas. A successful day of conservation diving!

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