Bacterial communities of oceanic sea star (Asteroidea: Echinodermata) larvae

Abstract

Planktotrophic sea star larvae of several species are abundant in oligotrophic waters of the Gulf Stream, western Sargasso Sea, and Caribbean Sea. One abundant larval morphotype at the bipinnaria stage of development is unusual in its ability to constitutively produce clones and in harboring a community of auto-fluorescent bacteria. We hypothesized that the bacterial community would be distinct in these larvae compared to those that do not consistently reproduce clonally. Three sea star larval morphotypes were collected in the Gulf Stream off the coast of Florida. We used DNA-based maximum likelihood phylogenetic analyses to taxonomically classify the larvae and 16S rDNA profiling by deep sequencing to characterize the bacterial communities harbored within. The cloning bipinnaria and non-cloning brachiolaria morphotypes were determined to be a single species of Asteroidea in the family Oreasteridae. The third morphotype, a non-cloning bipinnaria, was identified as Mithrodia clavigera. With bacterial 16S rDNA profiling, we found that the two species of larvae harbor bacterial communities distinct from each other. The Oreasteridae bacterial community at both developmental stages has a photosynthetic Cyanobacteria Synechococcus sp. as the most abundant bacteria. The M. clavigera larvae host a flora consisting primarily of Gammaproteobacteria. The identification of the larval microbiomes is a step toward understanding their host–microbe interactions. Specifically, the association of photosynthetic bacteria with cloning larvae allows for future assessments of whether the bacteria supplement the nutrition of the larvae during extended periods of development and clonal reproduction in open ocean regions where phytoplankton food for the larvae may be in limited supply.