Abstract:Dalian is the principal farming region for the economic alga Undaria pinnatifida, producing 65% of the national annual biomass. In late October 2019, insect pests caused serious damage to seedlings of U. pinnatifida in this region. We performed field investigation excursions and analyzed pest samples through the sequencing of the mitochondrial COⅠ gene. The results showed that explosive growth of Caprella danilevskii was the major cause. Caprella spp. are considered common biofouling organisms that usually inhabit the surface of maricultural algae and maricultural facilities, such as cultural rope and oyster nets. Steadily increasing seawater temperatures and the drifting brown alga Sargassum horneri biomass also played a role in the explosion of the pests. To the best of our knowledge, this is the first description of the morphological characteristics of different Caprella spp. collected in the same area in China. Caprella spp. are commonly found on the surface of cultured seaweed and marine aquaculture facilities, which has caused enormous losses to the Sargassum fusiforme farming industry in Fujian Province and Gracilaria lemaneaformis farming industry in Shandong Province for the past few years. We conclude with a proposal for dispersing or killing Caprella species through a traditional ammonium bicarbonate fertilizer application method. Sequence analysis revealed that these COⅠ gene fragments were 479 bp in length and showed an obvious AT-skewness. The transition/transversion bias (1.130) was much higher than the critical value (0.4), which could offer effective phylogenetic information. There was no insertion or deletion that occurred in each fragment. The average inter-species genetic distance was 0.231 (0.210~0.279) and the average intra-species genetic distance was 0.014 (0~0.030). The phylogenetic relationships among Caprella species were represented. The results proved that the cloned COⅠ gene contains rich information on gene variations. This gene is conserved in intra-species and is different among species. It is a suitable DNA barcode for identifying species in the genus Caprella.
