DIVERSITY, ABUNDANCE, AND THREATS OF OCTOCORALS AT MALPELO ISLAND, TROPICAL EASTERN PACIFIC, COLOMBIA.

Abstract

During three expeditions to the island (2009 and 2010), the diversity, abundance and status of octocorals were explored. Seven species of octocorals were recorded: Leptogorgia alba, Pacifigorgia cf. lacerata, Pacifigorgia sp.1 y Pacifigorgia sp.2, Muricea cf. fruticosa, Muricea sp., and the invasive species Carijoa riisei. Octocorals form dense aggregations in rocky walls and cliffs, with higher abundances between 10 and 20 m, reaching up to 20 colonies m-2. The most abundant species was Pacifigorgia cf. lacerata with a dominance of more than 60 % and a frequency of occurrence of 100 % for all visited sites. According to depth, three well-defined zones were determined for most sites. A deep zone between 25 and 40 m with an exclusive dominance of L. alba, a shallow assemblage between 7 and 20 m dominated by Pacifigorgia spp., and a transition zone between 18 and 25 m with a mixture of L. alba and P. cf. lacerata. Surprisingly, during November 2009, diseases of possible fungal origin visibly affected populations of Leptogorgia and Pacifigorgia. Subsequently, during February 2010 the same populations of octocorals were monitored and up to 66 % of the colonies were already dead in some locations. Leptogorgia had a significant reduction at El Arrecife site, while Pacifigorgia cf. lacerata had high mortality at La Nevera and El Freezer sites, and a recovery in El Arrecife. There was a notable improvement in disease prevalence by July 2010 with less than 10 % of diseased colonies. The invasive species C. riisei was observed in La Catedral and El Monstruo bank. Thus, this information increases considerably the knowledge of octocorals on Malpelo Island and is the first warning of possible threats against local octocoral populations, such as fungal diseases and the invasive octocoral C. riisei.