Citation:

Darling, J., J. Martinson, K. Pagenkopp-Lohan, K. Carney, E. Pilgrim, A. Banerji, K. Holzer, AND G. Ruiz. Metabarcoding quantifies differences in accumulation of ballast water borne biodiversity among three port systems in the United States. SCIENCE OF THE TOTAL ENVIRONMENT. Elsevier BV, AMSTERDAM, Netherlands, 749:141456, (2020). https://doi.org/10.1016/j.scitotenv.2020.141456

Impact/Purpose:

This manuscript demonstrates the utility of high throughput sequencing (HTS) approaches for understanding biodiversity being transported in ballast water. That understanding is important for assessing risks of introduction of non-native aquatic species with ballast water discharge, risks that EPA is charged with regulating under the Vessel Incidental Discharges Act of 2019. Our results indicate that HTS can be a powerful tool for assessing these risks, and is therefore of interest to managers and policy-makers (including those in Office of Water and Regional offices) concerned with ballast water introductions.

Description:

Characterizing biodiversity conveyed in ships' ballast water (BW), a global driver of biological invasions, is critically important for understanding risks posed by this key vector and establishing baselines to evaluate changes associated with BW management. Here we employ high throughput sequence (HTS) metabarcoding of the 18S small subunit rRNA to test for and quantify differences in the accumulation of BW-borne biodiversity among three distinct recipient port systems in the United States. These systems were located on three different coasts (Pacific, Gulf, and Atlantic) and chosen to reflect distinct trade patterns and source port biogeography. Extensive sampling of BW tanks (n = 116) allowed detailed exploration of molecular diversity accumulation. Our results indicate that saturation of introduced zooplankton diversity may be achieved quickly, with fewer than 25 tanks needed to achieve 95% of the total extrapolated diversity, if source biogeography is relatively limited. However, as predicted, port systems with much broader source geographies require more extensive sampling to estimate diversity, which continues to accumulate after sampling >100 discharges. The ability to identify BW sources using molecular indicators was also found to depend on the breadth of source biogeography and the extent to which sources had been sampled. These findings have implications both for the effort required to fully understand introduced diversity and for projecting risks associated with future changes to maritime traffic that may increase source biogeography for many recipient ports. Our data also suggest that molecular diversity may not decline significantly with BW age, indicating either that some organisms survive longer than recognized in previous studies or that nucleic acids from dead organisms persist in BW tanks. We present evidence for detection of potentially invasive species in arriving BW but discuss important caveats that preclude strong inferences regarding the presence of living representatives of these species in BW tanks.

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