Temporal occurrence of planktotrophic bivalve larvae identified morphologically and by single step nested multiplex PCR

We report the application of a recently developed molecularmethod, single step nested multiplex PCR (SSNM-PCR) assay andmicroscopy to identify and investigate temporal patterns ofbivalve larvae in a Danish estuary, Isefjord. All samples werecollected during the SUSTAINEX program from June to November2001. Using the molecular assay, larvae could be categorizedinto six groups: the blue mussel, Mytilus edulis, Ensis spp.,species of the Myoidae superfamily (Mya spp.), the common cockle(Cardiidae family), members of the Abra and Macoma genera ofthe Tellinoidae superfamily and members of the surf clam genera,Spisula spp. A seventh group was composed of unknown larvae.Greater resolution was possible by microscopy, but only forrelatively large and intact individuals (>150–200 µm).The molecular approach was capable of differentiating betweenlarvae regardless of shell size. Where it was possible to directlycompare identifications based on both methods, concordance washigh for M. edulis, Macoma balthica/Abra alba and E. americanus,whereas identification of Myoidae spp. and Cardiids was lessconsistent. Over the course of the study, two patterns of larvaloccurrence were observed. Larvae from species known to exhibita protracted annual spawning period (M. edulis, Myoidae spp.,Mysella bidentata and Cardiids) were present in the water columnthroughout the sampling period, whereas larvae of Abra alba,Barnea candida, E. americanus, Macoma balthica, Musculus marmoratusScrobicularia plana and Tapes pullastra appeared at clearlydefined periods.