Molecular investigation of the invasive sponge Hymeniacidon sinapium (de Laubenfels, 1930) in Elkhorn Slough, California

Abstract

A large number of invasive marine invertebrates are recognized from Elkhorn Slough (ES), California. One of these species in the slough is treated as Hymeniacidon sinapium (Family Halichondriidae) but its species identity is in doubt pending molecular confirmation. The purpose of this investigation was to confirm the presence of H. sinapium in ES, determine its distribution in the slough, and compare its genetic diversity to others in California and worldwide. To address these goals, 23 specimens of Hymeniacidon were analyzed using DNA sequences of the nuclear rDNA internal transcribed spacers (ITS1 + ITS2) and the 5.8S exon. The sequences were compared against those of H. sinapium from: San Diego and Tomales Bay in California; Japan; and South Korea. All ES sequences were found to be nearly identical to the other H. sinapium sequences, differing by only 1-3 nucleotides. ES specimens displayed five unique genotypes: three showed intragenomic polymorphisms (IGPs) in the ITS1 region (positions 155, 181, and 195). These data conclusively document the presence of H. sinapium in ES as well as define the species to a relatively narrow portion of its eastern shores (~4 km long). Since the genetic diversity of H. sinapium in ES is higher than that reported worldwide, its presence in ES is likely the result of multiple introductions. One of the IGPs in ES was found to be the most abundant and was widely distributed in the slough: an indication that it may be spreading.