Spatial and temporal monitoring of invasive Hydroides dianthus (Verrill, 1873) (Annelida, Serpulidae) in Eel Lake, Argyle, Nova Scotia using a species-specific molecular assay

In 2012, an invasion by a serpulid tubeworm, unknown to the Atlantic Canada region, caused heavy biofouling on an oyster lease in Eel Lake, Argyle, Nova Scotia. The species was identified as Hydroides dianthus (Verrill, 1873) , and this morphological identification was confirmed by comparing a newly sequenced COI gene fragment with H. dianthus sequences available in GenBank . Heavy biofouling on the oyster lease resulted in the need to develop mitigation strategies. It was hypothesized that by understanding the spawning behaviour and spatial/temporal patterns of H. dianthus larvae in Eel Lake, biofouling could be mitigated by determining an optimal depth that oyster cages should be maintained at during its active spawning period. To monitor H. dianthus in Eel Lake, species-specific primers associated with the COI gene were developed. Specificity and sensitivity of primers were tested, and the primer set H. dianthus COI4F/R was chosen for monitoring . Water samples were collected from Eel Lake from June to August 2013, and eDNA was extracted. Spatial and temporal monitoring of H. dianthus using eDNA was completed at four sites (three fouled, one non-fouled), and at three depths (0.3 m, 1.5 m, and 3.0 m) in Eel Lake. Water samples tested positive for H. dianthus in most sites and depths on June 20 th , indicating a spawning event had occurred. Subsequently, no significant differences between sites and depths were found and H. dianthus was detected throughout the summer in all locations and depths monitored. The mean % of positive PCR results significantly increased from 18.7 to 65.0% from June to August. Results suggest that H. dianthus spawned frequently during a reproductive season ranging from at least June 20 to August 30 in Eel Lake at temperatures ~ 18–22 °C. The results of this study indicated that an optimal oyster cage depth for biofouling mitigation could not be determined and highlighted the challenges to aquaculture associated with biofouling of H. dianthus .