Informed stakeholder support for managing invasive <i>Hydrilla verticillata</i> linked to wildlife deaths in a Southeastern reservoir

<p>Fouts KL, Poudyal, NC, Moore R, Herrin J, Wilde, SB. 2017. Informed stakeholder support for managing invasive <i>Hydrilla verticillata</i> linked to wildlife deaths in a Southeastern reservoir. Lake Reserve Manage. 00:1–10.</p> <p>Public opinion surveys prior to implementing management actions provide managing agencies with a detailed understanding of stakeholders' attitudes and help inform the general public on the complexity of potential management actions. Like many other Southeastern U.S. reservoirs, J. Strom Thurmond (JST), on the border of Georgia and South Carolina, has been infested with nonnative hydrilla (<i>Hydrilla verticillata</i>). Avian Vacuolar Myelinopathy (AVM), a fatal wildlife disease linked to a neurotoxic cyanobacterial species growing on hydrilla, has been documented on this 28,733-ha reservoir since 1998, when the hydrilla acreage first exceeded 350 ha. As of 2016, 90 bald eagle (<i>Haliaeetus leucocephalus</i>) mortalities and hundreds of waterfowl deaths have been attributed to AVM disease on JST. To assess and compare the diverse stakeholders' attitudes toward aquatic vegetation, knowledge of AVM, and support for management actions to remove hydrilla, a mail survey was conducted targeting various JST user groups (anglers, boaters, campers, waterfowl hunters, and shoreline property owners). Generally, respondents were overwhelmingly in favor of reducing hydrilla density on JST, but shoreline permit holders (homeowners) were significantly more supportive of hydrilla management than boaters. Similarly, all user groups supported management actions to remove aquatic vegetation, including stocking triploid sterile grass carp (<i>Ctenopharyngodon idella</i>). Support for removing hydrilla was found to be significantly higher among users knowledgeable of AVM, suggesting that outreach activities educating the public on the effects and prevention of the disease would help enhance stakeholder support for hydrilla removal and management in public reservoirs.</p

Climate and pH Predict the Potential Range of the Invasive Apple Snail (<em>Pomacea insularum</em>) in the Southeastern United States

<div><p>Predicting the potential range of invasive species is essential for risk assessment, monitoring, and management, and it can also inform us about a species’ overall potential invasiveness. However, modeling the distribution of invasive species that have not reached their equilibrium distribution can be problematic for many predictive approaches. We apply the modeling approach of maximum entropy (MaxEnt) that is effective with incomplete, presence-only datasets to predict the distribution of the invasive island apple snail, <i>Pomacea insularum</i>. This freshwater snail is native to South America and has been spreading in the USA over the last decade from its initial introductions in Texas and Florida. It has now been documented throughout eight southeastern states. The snail’s extensive consumption of aquatic vegetation and ability to accumulate and transmit algal toxins through the food web heighten concerns about its spread. Our model shows that under current climate conditions the snail should remain mostly confined to the coastal plain of the southeastern USA where it is limited by minimum temperature in the coldest month and precipitation in the warmest quarter. Furthermore, low pH waters (pH <5.5) are detrimental to the snail’s survival and persistence. Of particular note are low-pH blackwater swamps, especially Okefenokee Swamp in southern Georgia (with a pH below 4 in many areas), which are predicted to preclude the snail’s establishment even though many of these areas are well matched climatically. Our results elucidate the factors that affect the regional distribution of <i>P. insularum</i>, while simultaneously presenting a spatial basis for the prediction of its future spread. Furthermore, the model for this species exemplifies that combining climatic and habitat variables is a powerful way to model distributions of invasive species.</p> </div

Present populations of the island apple snail, <i>Pomacea insularum,</i> and its occupiable area.

<p>Map shows the southeastern United States. As predicted by the maximum entropy model, red represents areas with the highest climatic compatibility for the snail as determined by using an inclusion threshold that correctly classifies all sites above the minimum 10% training omission threshold. Pink represents areas determined to be suitable by using the less stringent threshold calculated by correctly classifying all known <i>P. insularum</i> points above the minimum training presence.</p

The average receiver operating curve from the ten model runs showing relative specificity and sensitivity.

<p>One standard deviation above and below the average curve is shown in blue. Area Under the Curve (AUC) is calculated from this curve.</p

<i>Pomacea insularum</i> adult (6.1 cm) and an egg mass (7.6×2.5 cm).

<p><i>P. insularum</i> has a channeled suture and often exceeds 10 cm in height and lays conspicuous large pink egg masses. Photo credits: (left)–Freshwater Gastropods of North America website; (right)–J. Morgan.</p

Experimentally determined incipient physiological tolerance limits under laboratory conditions for adult and juvenile <i>Pomacea insularum</i> collected in Texas (from Ramakrishnan [31]).

<p>For salinity and pH the ranges of values bracket the median lethal values at 28 days exposure (LD₅₀/28). Temperature limits were statistically calculated from experimental data to yield the temperatures at which 99% mortality occurred in 28 days (LTp₉₉). Emersion values are the maximum observed survival time of the snail out of water at the stated temperature and humidity.</p

Experimental Feeding of <i>Hydrilla verticillata</i> Colonized by Stigonematales Cyanobacteria Induces Vacuolar Myelinopathy in Painted Turtles (<i>Chrysemys picta</i>)

<div><p>Vacuolar myelinopathy (VM) is a neurologic disease primarily found in birds that occurs when wildlife ingest submerged aquatic vegetation colonized by an uncharacterized toxin-producing cyanobacterium (hereafter “UCB” for “uncharacterized cyanobacterium”). Turtles are among the closest extant relatives of birds and many species directly and/or indirectly consume aquatic vegetation. However, it is unknown whether turtles can develop VM. We conducted a feeding trial to determine whether painted turtles (<i>Chrysemys picta</i>) would develop VM after feeding on <i>Hydrilla</i> (<i>Hydrilla verticillata</i>), colonized by the UCB (<i>Hydrilla</i> is the most common “host” of UCB). We hypothesized turtles fed <i>Hydrilla</i> colonized by the UCB would exhibit neurologic impairment and vacuolation of nervous tissues, whereas turtles fed <i>Hydrilla</i> free of the UCB would not. The ability of <i>Hydrilla</i> colonized by the UCB to cause VM (hereafter, “toxicity”) was verified by feeding it to domestic chickens (<i>Gallus gallus domesticus</i>) or necropsy of field collected American coots (<i>Fulica americana</i>) captured at the site of <i>Hydrilla</i> collections. We randomly assigned ten wild-caught turtles into toxic or non-toxic <i>Hydrilla</i> feeding groups and delivered the diets for up to 97 days. Between days 82 and 89, all turtles fed toxic <i>Hydrilla</i> displayed physical and/or neurologic impairment. Histologic examination of the brain and spinal cord revealed vacuolations in all treatment turtles. None of the control turtles exhibited neurologic impairment or had detectable brain or spinal cord vacuolations. This is the first evidence that freshwater turtles can become neurologically impaired and develop vacuolations after consuming toxic <i>Hydrilla</i> colonized with the UCB. The southeastern United States, where outbreaks of VM occur regularly and where vegetation colonized by the UCB is common, is also a global hotspot of freshwater turtle diversity. Our results suggest that further investigations into the effect of the putative UCB toxin on wild turtles <i>in situ</i> are warranted.</p></div

Clinical signs observed in the treatment group turtles after the first observed deficits on day 82 of the experiment.

<p>Clinical signs observed in the treatment group turtles after the first observed deficits on day 82 of the experiment.</p

Electron Micrograph of central nervous tissue of a painted turtle fed toxic <i>Hydrilla</i> material.

<p>Electron Microscopy, painted turtle (<i>Chrysemys picta</i>), brain: Axons are swollen and degenerate and myelin sheaths are frequently disrupted by large, clear, intramyelinic vacuoles (orange stars). In less severely affected axons, splitting can be seen to occur at the intraperiod lines (blue arrow). Scale bar is 2 μm.</p

Histopathological slide of the optic tectum of a painted turtle fed toxic <i>Hydrilla</i> material.

<p>Painted turtle (<i>Chrysemys picta</i>), brain: Numerous clear vacuoles (black arrows) representing myelin degeneration and dilation of axonal sheaths are present in the white matter of a turtle treated with toxic hydrilla. H&E, 100X. Scale bar is 100 μm.</p