PCR amplification of a middle repetitive element detects larval stone crabs (Crustacea : Decapoda : Menippidae) in estuarine plankton samples

Planktonic larval dispersal and recruitment can be major determinants of th e structure and dynamics of marine communities. However, these processes ha ve been difficult to study because of their natural variability and the lim itations of methods used to collect and analyze plankton samples. In partic ular, the use of microscopy to determine the composition of plankton sample s is time-consuming and often limited by a lack of reliable morphological c haracters for species identification. The need for methods of greater accur acy and efficiency has led to the development of molecular approaches to pl ankton analysis, including detection by DNA hybridization, amplification of DNA from plankton samples by the polymerase chain reaction (PCR) and taxon omic characterization by ribosomal DNA sequence analysis. Here we describe a PCR-based method that detects larval crabs in estuarine plankton samples. This technique is unusually expedient and relatively cost-effective. It is based on the detection of a middle repetitive sequence characteristic of t he stone crab Menippe mercenaria, as well as the closely related species M. adina. Amplification by PCR of a 585 base pair region of this sequence fro m plankton samples accurately indicates the presence of either species. Bec ause of the high abundance of this sequence in the genome of Menippe, singl e larvae can be detected in typical plankton samples. Unlike methods based on 'universal' sequences (rRNA or regions of the mitochondrial genome), the amplification of a PCR product of the expected size is a reliable indicati on of the presence of the target species, and no further characterization i s necessary. This technique is intended to facilitate the large-scale proce ssing of plankton samples that is necessary for accurate determination of t he temporal and spatial distributions of individual species in plankton com munities.