Coral injuries caused by Spirobranchus opercula with and without epibiotic turf algae at Curacao

Reef-dwelling Christmas tree worms (Spirobranchus spp.) are common coral associates. Their calcareous tubes are usually embedded in the coral skeleton and can be closed by an operculum. Tubes not overgrown by coral tissue either remain bare or become covered by algae. Despite their widespread distribution, high abundance and striking appearance, little is known about the impact of these worms on their hosts. We quantified visible coral damage caused by Spirobranchus in Curacao (Southern Caribbean) and found that 62.6% of worm opercula (n = 1323) caused abrasions and tissue loss in their hosts. Filamentous turf algae, known to be potentially harmful to corals, covered 76.9% of the opercula. Examination of the six most frequently inhabited host species showed a variation in the damage percentages, although this was independent of the presence of epibiotic algae on 78.4% of all opercula. Since injured corals are more susceptible to diseases, the overall negative impact of Spirobranchus worms on their hosts may be more severe than previously assumed.