Geographic variation in marine invasions among large estuaries: effects of ships and time.

Coastal regions exhibit strong geographic patterns of nonnative species richness. Most invasions in marine ecosystems are known from bays and estuaries, where ship-mediated transfers (on hulls or in ballasted materials) have been a dominant vector of species introductions. Conspicuous spatial differences in nonnative species richness exist among bays, but the quantitative relationship between invasion magnitude and shipping activity across sites is largely unexplored. Using data on marine invasions (for invertebrates and algae) and commercial shipping across 16 large bays in the United States, we estimated (1) geographic variation in nonnative species richness attributed to ships, controlling for effects of salinity and other vectors, (2) changes through time in geographic variation of these ship-mediated invasions, and (3) effects of commercial ship traffic and ballast water discharge magnitude on nonnative species richness. For all nonnative species together (regardless of vector, salinity, or time period), species richness differed among U.S. coasts, being significantly greater for Pacific Coast bays than Atlantic or Gulf Coast bays. This difference also existed when considering only species attributed to shipping (or ballast water), controlling for time and salinity. Variation in nonnative species richness among Pacific Coast bays was strongly affected by these same criteria. San Francisco Bay, California, had over 200 documented nonnative species, more than twice that reported for other bays, but many species were associated with other (non-shipping) vectors or the extensive low-salinity habitats (unavailable in some bays). When considering only ship- or ballast-mediated introductions in high-salinity waters, the rate of newly detected invasions in San Francisco Bay has converged increasingly through time on that for other Pacific Coast bays, appearing no different since 1982. Considering all 16 bays together, there was no relationship between either (1) number of ship arrivals (from foreign ports) and number of introductions attributed to ships since 1982 or (2) volume of foreign ballast water discharge and number of species attributed to ballast water since 1982. These shipping measures are likely poor proxies for propagule supply, although they are sometimes used as such, highlighting a fundamental gap in data needed to evaluate invasion dynamics and management strategies.

Per capita invasion probabilities: an empirical model to predict rates of invasion via ballast water.

Ballast water discharges are a major source of species introductions into marine and estuarine ecosystems. To mitigate the introduction of new invaders into these ecosystems, many agencies are proposing standards that establish upper concentration limits for organisms in ballast discharge. Ideally, ballast discharge standards will be biologically defensible and adequately protective of the marine environment. We propose a new technique, the per capita invasion probability (PCIP), for managers to quantitatively evaluate the relative risk of different concentration-based ballast water discharge standards. PCIP represents the likelihood that a single discharged organism will become established as a new nonindigenous species. This value is calculated by dividing the total number of ballast water invaders per year by the total number of organisms discharged from ballast. Analysis was done at the coast-wide scale for the Atlantic, Gulf, and Pacific coasts, as well as the Great Lakes, to reduce uncertainty due to secondary invasions between estuaries on a single coast. The PCIP metric is then used to predict the rate of new ballast-associated invasions given various regulatory scenarios. Depending upon the assumptions used in the risk analysis, this approach predicts that approximately one new species will invade every 10-100 years with the International Maritime Organization (IMO) discharge standard of < 10 organisms with body size > 50 microm per m3 of ballast. This approach resolves many of the limitations associated with other methods of establishing ecologically sound discharge standards, and it allows policy makers to use risk-based methodologies to establish biologically defensible discharge standards.

Global marine biosecurity and ship lay-ups: intensifying effects of trade disruptions.

Recent global trade disruptions, due to blockage of the Suez Canal and cascading effects of COVID-19, have altered the movement patterns of commercial ships and may increase worldwide invasions of marine non-indigenous species. Organisms settle on the hulls and underwater surfaces of vessels and can accumulate rapidly, especially when vessels remain stationary during lay-ups and delays. Once present, organisms can persist on vessels for long-periods (months to years), with the potential to release propagules and seed invasions as ships visit ports across the global transportation network. Shipborne propagules also may be released in increasing numbers during extended vessel residence times at port or anchor. Thus, the large scale of shipping disruptions, impacting thousands of vessels and geographic locations and still on-going for over two years, may elevate invasion rates in coastal ecosystems in the absence of policy and management efforts to prevent this outcome. Concerted international and national biosecurity actions, mobilizing existing frameworks and tools with due diligence, are urgently needed to address a critical gap and abate the associated invasion risks.

Considering Commercial Vessels as Potential Vectors of Stony Coral Tissue Loss Disease.

Stony coral tissue loss disease (SCTLD) is a troubling new disease that is spreading rapidly across the greater Caribbean region, but the etiological agent(s) and the mechanisms(s) of spread are both unknown. First detected off the coast of Miami, Florida, major ocean currents alone do not explain the pattern of spread, with outbreaks occurring across geographically disjunct and distant locations. This has raised concerns by researchers and resource managers that commercial vessels may contribute as vectors to spread of the disease. Despite existing regulatory and management strategies intended to limit coastal marine invasion risks, the efficacy of these measures is still unresolved for ship-borne microorganisms, and disease transport via ballast water and hull biofouling are under examination given the high ship traffic in the region. Here, to help inform the discussion of ships as possible vectors of SCTLD, we provide an overview of the current state of knowledge about ships and their potential to transfer organisms in the greater Caribbean, focusing in particular on ballast water, and outline a set of recommendations for future research.

Naturalization of plant populations: the role of cultivation and population size and density.

Field experimentation is required to assess the effects of environmental stochasticity on small immigrant plant populations-a widely understood but largely unexplored aspect of predicting any species' likelihood of naturalization and potential invasion. Cultivation can mitigate this stochasticity, although the outcome for a population under cultivation nevertheless varies enormously from extinction to persistence. Using factorial experiments, we investigated the effects of population size, density, and cultivation (irrigation) on the fate of founder populations for four alien species with different life history characteristics (Echinochloa frumentacea, Fagopyrum esculentum, Helianthus annuus, and Trifolium incarnatum) in eastern Washington, USA. The fate of founder populations was highly variable within and among the 3 years of experimentation and illustrates the often precarious environment encountered by plant immigrants. Larger founder populations produced more seeds (P < 0.001); the role of founder population size, however, differed among years. Irrigation resulted in higher percent survival (P < 0.001) and correspondingly larger net reproductive rate (R(0); P < 0.001). But the minimum level of irrigation for establishment, R(0) > 1, differed among years and species. Sowing density did not affect the likelihood of establishment for any species. Our results underscore the importance of environmental stochasticity in determining the fate of founder populations and the potential of cultivation and large population size in countering the long odds against naturalization. Any implementation of often proposed post-immigration field trials to assess the risk of an alien species becoming naturalized, a requisite step toward invasion, will need to assess different sizes of founder populations and the extent and character of cultivation (intentional or unintentional) that the immigrants might receive.

A spherical falling film gas-liquid equilibrator for rapid and continuous measurements of CO2 and other trace gases.

Use of gas-liquid equilibrators to measure trace gases such as CO2, methane, and radon in water bodies is widespread. Such measurements are critical for understanding a variety of water quality issues such as acidification due to elevated CO2 or other processes related ecosystem metabolism and function. However, because gas-liquid equilibrators rely on generating sufficient surface area for gas exchange between liquid and gas phases, most traditional equilibrators pass water through small orifices or interstitial spaces that rapidly clog in highly productive or turbid waters, conditions that are common in estuaries, coastal bays, and riverine systems. Likewise, in cold temperatures, such equilibrators are subject to freezing. Both situations lead to failure and limit utility, especially for long term, continuous environmental monitoring. Here we describe and test a gas-liquid equilibrator that relies on a continuous falling film of water over a spherical surface to drive gas exchange. Our results demonstrate that this design is accurate in its ability to equilibrate fully to aqueous CO2 concentrations, is functional across a wide range of gas concentrations, and has a response time that is comparable with other equilibrator designs. Because this equilibrator uses free flowing, falling water to produce a surface for gas exchange, our field trials have shown it to be very resistant to clogging and freezing, and therefore well suited to long term deployment in highly productive waters like estuaries where CO2 concentrations fluctuate hourly, daily, and seasonally. When generated across a spherical surface, the falling film is not adversely affected by tilting off vertical, conditions that are common on a ship, small vessel, or buoy.

Potential effects of LNG trade shift on transfer of ballast water and biota by ships.

As the US natural gas surplus grows, so does the prospect of establishing new trade partnerships with buyers abroad, a process that has major consequences for global ship movement and ballast water delivery. Since US annual imports of liquefied natural gas (LNG) peaked in 2004-2007, the country is rapidly transitioning from net importer to net exporter of LNG. Combining multiple datasets, we estimated changes in the associated flux of ships' ballast water to the US during 2015-2040, using existing scenarios for projected exports of domestic LNG by ships. Our analysis of the current market (2015) scenario predicts an approximate 90-fold annual increase in LNG-related ballast water discharge to the US by 2040 (42millionm3), with the potential to be even greater under high oil prices. We also described changes in geographic connectivity related to trade direction. These findings highlight how 21st century global energy markets could dramatically alter opportunities for seaborne introductions and invasions by nonnative species.

Evaluating the combined effects of ballast water management and trade dynamics on transfers of marine organisms by ships.

Global trade by merchant ships is a leading mechanism for the unintentional transfer of marine organisms, including non-indigenous species, to bays and estuaries worldwide. To reduce the likelihood of new invasions, ships are increasingly being required to manage their ballast water (BW) prior to discharge in coastal waters. In the United States, most overseas arrivals have been required to manage BW discharge since 2004, primarily through ballast water exchange (BWE), which flushes out ballast tanks in the open ocean (>200 miles from shore). Studies have found BWE to generally reduce the abundance of organisms, and the amount of water exchanged has been estimated at 96-100%. Despite its widespread use, the overall effect of this management strategy on net propagule supply through time has not been explored. Here, temporal changes in zooplankton concentrations and the volume of BW discharged in Chesapeake Bay, U.S. were evaluated, comparing pre-management era and post-management era time periods. Chesapeake Bay is a large port system that receives extensive BW discharge, especially from bulk cargo vessels (bulkers) that export coal overseas. For bulkers arriving from overseas, mean zooplankton concentrations of total and coastal indicator taxa in BW did not decline between pre- (1993-2000) and post management (2012-2013) eras, when controlling for season and sampling method. Moreover, bulkers discharged 21 million tonnes (82% of total for Chesapeake Bay) of overseas BW in 2013, representing a 374% increase in volume when compared to 2005. The combination of BW discharge volume and zooplankton concentration data indicates that (a) net propagule supply by bulkers has increased since BWE began in Chesapeake Bay; and (b) changes in vessel behaviour and trade have contributed strongly to this outcome. Specifically, the coal-driven increase in BW discharge volume from 2005-2013, concurrent with the onset of BWE regulations, worked to counteract intended results from BW management. A long-term analysis of bulker arrivals (1994-2013) reveals a 20-year minimum in arrival numbers in 2000, just when the implementation of BWE began. This study underscores the need to consider shifts in trade patterns, in order to advance and evaluate effective management strategies for biological invasions.