DISTRIBUTION AND ABUNDANCE OF THE ROCKY BOTTOM ASCIDIANS OF CUAJINIQUIL BAY, COSTA RICA

Abstract

The ascidians of the Central-American Pacific coast are poorly studied, although this group is one of the most important members of the benthic fauna of this region. The present study shows data of density (individuals per square meter) of the solitary ascidians Rhopalaea birkelandi (Tokioka) and Ascidia ceratodes (Huntsman), at 5, 10 and 15 m deep in three transects perpendicular to the coast. These transects were located in Isla David, Bajo Rojo and Bajo Viejón, coastal areas of Cuajiniquil Bay, northeast coast Costa Rica. Other three species of colonial ascidians, Didemnum moseleyi (Herdman), Lissoclinum caulleryi (Ritter y Forsyth) and Polyandrocarpa tincta (Van Name), are part of the benthic communities of the rocky bottoms of this bay at depths greater than 10 m. The cluster analysis (using Jaccard similarity coefficient) shows a high similarity between transects located at Bajo Viejón and Isla David. The difference between 5, 10 and 15 m deep is significant (H= 6.24, gl= 2.51, p= 0.04). In Bajo Rojo only solitary ascidians were found with an average density ten times lower than other sites. These differences could be related to lower substratum availability due to the stronger competition with brown algae which covers most of the sea bottom at Bajo Rojo and/or the higher environmental stability of the hard bottom communities that are usually found on the edges of the higher part of the bay, greatly exposed to oceanic waters and away from impacts that sediments from the Cuajiniquil river could be producing in the middle part of the bay.