Non-colonial coral macro-borers as indicators of coral reef status in the south Pacific of Costa Rica

A.C Fonseca E,H.K Dean,J Cortés

doi:10.15517/rbt.v54i1.13977

Abstract

Coral reef status was surveyed in three south Pacific coral reefs of Costa Rica, one in Caño Island and two in Golfo Dulce, and the density, richness and distribution of non-colonial macro borers (> 1 mm) was determined in dead and live coral fragments from these reefs. Based upon traditional indicators of degradation such as high particulate suspended matter and low live coral cover, the reefs at Caño Island are in better condition than those at Golfo Dulce. Reef degradation in Golfo Dulce is mainly due to high loads of terrestrial sediments as a consequence of watersheds deforestation. In this study, 36 coral boring species are reported for the eastern Pacific. At the family level, there is high endemism (10%) and greater affinity with the Indo-Pacific (34%), as compared with the eastern Atlantic and Mediterranean (29%) and western Atlantic and Caribbean (27%). The dominant non-colonial macro boring families at the study reefs are mytilid bivalves, eunicid polychaetes and aspidosiphonid sipunculans, with the bivalves considered the main internal bioeroders due to their greater body size and abundances. The level of mortality of the coral colonies and the general level of reef degradation influenced the composition of non-colonial macro-borers. Diversity and total macro-borer density, especially aspidosiphonid density, is higher in corals with greates dead than live cover. In the healthiest coral colonies (less than 50% of partial mortality), mytilids domination, macro-borer diversity and total density, is higher in Golfo Dulce, where reefs are more degraded. In the most affected coral colonies (more than 50% dead), macro-borers total density, especially aspidosiphonids density, is higher, of the healthiest reef of this study, Platanillo. Bivalve relative abundance increases and sipunculan relative abundance decreases with increasing site degradation. In conclusion bioeroder variables can also be used as reef health indicators.

Highlights

Dreaming about boring a tunnel to escape from prison? Dreaming about boring a reef and discover its formation history?
Bivalves were the dominant macro-borer group in Sándalo, while Punta Islotes and Platanillo coral colonies were dominated by sipunculans
Sipunculans were dominant in coral colonies with more than 50% mortality in Punta Islotes and Platanillo (Fig. 2)

Summary

MATERIALS AND METHODS

The non-colonial macro-borers (>1 mm) of three reefs in the south Pacific of Costa Rica were studied: Platanillo at Caño Island, and Punta Islotes and Sándalo at Golfo Dulce (Fig. 1). Punta Islotes is located in the north internal side of Golfo Dulce (8o43’41’’ N; 83o23’8’’ W), 5 to 6 km from the Esquinas River (Fig. 1) This fringing reef has an area of 12 ha, reaches a maximal depth of 12 m, and has a mean thickness of 9 m (Cortés 1991, Cortés et al 1994) which is high in comparison with other eastern Pacific reefs (Macintyre et al 1992). Sándalo is located in the south east side of Golfo Dulce (8o34’28’’ N; 83o20’15’’ W) within 0.5 and 1 km west of the Tigre River mouth (Fig. 1) This is a fringing reef with an area of 5 ha and a maximum depth of 6 m dominated by P. lobata (Cortés 1992). The Morisita similarity index and the Shannon– Wienner diversity index (H’) with logarithm in base 2 were estimated, and a student-t test was done to determine the significance of the indexes differences between sites and coral mortality categories

RESULTS

Findings

DISCUSSION