Effects of physical factors on larval behavior, settlement and recruitment of four tropical demosponges

Abstract

This study investigated the effects of light, water flow and water temperature on larvae and early juveniles of 4 shallow-water Caribbean demosponges, Tedania ignis, Haliclona tubifera, Sigmadocja caerulea and Halichondria magniconulosa. Larval release was not a synchronous event, either at the individual or population level in any of these species. Parenchymella larvae were photonegative during their whole life, but their swimming speed to escape from a light source varied with species and was related to the ratio of larval body length:flagellar tuft length. The presence of a water flow faster than the larval swimming speed had no effect on the settlement success of these 4 species in experimental flumes. Larvae of all 4 species preferred shaded sites at settlement in flumes. However, microhabitat irradiance in the field was correlated with abundances of adults only in 1 species, S. caerulea. The presence of water flow was positively associated with juvenile survivorship in the field only in the caseof T ignjs. Water flow was also positively associated with the adult abundance of T ignis, but negatively associated with the abundance of H. tubifera. Recruitment varied substantially among species, being extremely low in H. tubifera and H. magniconulosa. Larval activity and settlement of 2 species were strongly affected by abnormally low temperatures: swimming speed decreased, the free-swimming phase was dramatically shortened and recruitment was virtually inhibited. Low temperatures, therefore, potentially prevent larval dispersal and recruitment into cold waters and might restrict the geographic distribution of these species to tropical areas and warm shallow waters.