Higher-order patterns of aquatic species spread through the global shipping network

Abstract

The introduction and establishment of nonindigenous species (NIS) through global ship movements poses a significant threat to marine ecosystems and economies. While ballastvectored invasions have been partly addressed by some national policies and an international agreement regulating the concentrations of organisms in ballast water, biofouling-vectored invasions remain largely unaddressed. Development of additional efficient and costeffective ship-borne NIS policies requires an accurate estimation of NIS spread risk from both ballast water and biofouling. We demonstrate that the first-order Markovian assumption limits accurate modeling of NIS spread risks through the global shipping network. In contrast, we show that higher-order patterns provide more accurate NIS spread risk estimates by revealing indirect pathways of NIS transfer using Species Flow Higher-Order Networks (SF-HON). Using the largest available datasets of non-indigenous species for Europe and the United States, we then compare SF-HON model predictions against those from networks that consider only first-order connections and those that consider all possible indirect connections without consideration of their significance. We show that not only SF-HONs yield more accurate NIS spread risk predictions, but there are important differences in NIS spread via the ballast and biofouling vectors. Our work provides information that policymakers can use to develop more efficient and targeted prevention strategies for ship-borne NIS spread management, especially as management of biofouling is of increasing concern.

A Framework for Compiling Quantifications of Marine Biosecurity Risk Factors Associated With Common Vessel Types

“…A virtue of our framework is that it requires very little computational effort compared to more sophisticated modeling approaches (e.g., Saebi et al, 2020;Hatami et al, 2021), and is easy to implement by simple arithmetic application of the final vessel type risk scores. The risk factors we included are broad, with readily available data that do not require extensive effort to collect, as would be the case for risk assessments that investigate and summarize patterns of individual ship transits (David and Gollasch, 2019).…”

“…We had also hoped to assess whether NBIC data, which is specific to vessel arrivals in the United States, can be extrapolated to apply globally. A number of studies that have created global models use ballast data from NBIC and extrapolate it to apply to the rest of the globe (e.g., Xu et al, 2014;Wang et al, 2018;Sardain et al, 2019;Saebi et al, 2020) because NBIC data are readily available, reliable, and plentiful. However, ballast discharge frequency and volume would depend on the type and quantity of cargo being imported and exported, which differs by nation and often also ports within a nation.…”

An example for transatlantic hitchhiking by macrozoobenthic organisms with a research vessel

“…aquaculture, ship traffic, pet trade and tourism (e.g. [1][2][3][4][5][6][7][8]). One of the most important is certainly unintentional transport by ship.…”

“…Apparently Namibia has not been one of the hotspots of worldwide species introduction [3]. However after a very recent study even the temperate zone of southern Africa has a high risk of introduction of nonindigenous species (NIS) especially from eastern Indo-Pacific and temperate northern and tropical eastern Pacific [7]. In 2016 Alexander et al [11] published a review paper on South African marine invasion literature and in 2020 Robinson et al [12] listed 95 marine alien species (of which 56 have spread to become invasive) known from South African coast.…”

Ship traffic connects Antarctica’s fragile coasts to worldwide ecosystems

“…The absence of established nonnative marine species in Antarctica is a boon for conservation, but it restricts the methods available to predict species flow into the region. For example, methods used for global or regional risk assessments of nonnative marine introductions via ballast water and hull fouling ( 51 – 54 ) are not possible for Antarctica, for which data are insufficient on propagule pressure, species introductions, or species spread to validate models. Nevertheless, the potential source of nonnative biofouling species, where they might be introduced to, and the introduction risk from different activities (e.g., research, tourism, and fishing) are all functions of the traffic network of ship operations.…”