Dispatches - Frontiers in Ecology and the Environment

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DISPATCHES DISPATCHES DISPATCHES Fake seagrass makes the case for conservation Claire Miller Scientists in New Zealand are using plastic seagrass beds to study how juvenile fish respond to changes in a vital but shrinking habitat. While meadows teeming with fish survive in remote areas, sediment in runoff from adjacent land development has killed much of New Zealand’s subtidal seagrass and degraded what little remains. Fisheries ecologist Mark Morrison (National Institute of Water and Atmospheric Research, Auckland, New Zealand) says that creating fake mats allows researchers to control the density and length of fronds, and then measure the effect of increasingly dense seagrass on fish abundance. The mats (24 in all, each 3 m 2 ) used in the experiment covered a range of six densities, from sparse to very thick, and were spread over 2000 m 2 in the Whangapoua Plastic seagrass is a haven for juvenile fish. Estuary, near Auckland, just before the fish recruitment period over the southern summer. The study found that the denser the seagrass, the more abundant and diverse the fish. Maximum abundance for some species was reached at the highest grass-blade densities, with food limitation then probably kicking in as fish consumed all the zooplankton passing over the mats. “There is only one seagrass species in New Zealand, and it grows in both the intertidal and subtidal zones”, Morrison explains. “Subtidal seagrass NIWA beds are thought of as being rare, but I don’t think it was always so. I think we have just lost a lot of it over the past 100 years. When the system is stressed, the subtidal beds are the first to thin out and disappear. But if only the intertidal beds are left, then much of its habitat value disappears, because the fish may have to move out into bare seafloor areas, where they are susceptible to predation when the tide goes out.” While seagrass is making a tentative comeback in some areas, threats continue from land-based activities. One problem is that people view recovering seagrass as a weed to be removed, to keep beaches sandy. “Coastal managers need to protect dense seagrass beds in the subtidal zone”, says Morrison. “Restoration of seagrass is very expensive, so the take-home message is to look after what you’ve got and create the right conditions, by controlling degrading activities, so seagrass can restore itself.” n 203 Re-examining invasive indicators Virginia Gewin In a recently published paper, ecologists Ken Thompson (University of Sheffield, Sheffield, UK) and Mark Davis (Macalester College, St Paul, MN) assert that global changes in nutrient deposition, climate, and landscape disturbance are making the distinction between native and nonnative species less ecologically meaningful (Trends Ecol Evol 2011; doi: 10.1016/j.tree.2011.01.007). “Species are simply winners – plants able to thrive in these conditions – or losers, those that can’t”, says Thompson. “There’s nothing special about being alien or nonnative.” A number of invasive species experts agree with the essence of Davis and Thompson’s claims. “There is nothing really fundamental about a species status as ‘native’ or ‘alien’ that explains how they ‘work’”, agrees Dave Richardson, Deputy Director of Science Strategy at the University of Stellenbosch’s Center of Excellence for Invasion Biology (Stellenbosch, South Africa). At issue is whether or not country of origin matters. Many ecologists believe that distinguishing plants into native or nonnative does still has value. “Plant traits are only one aspect of invasions”, points out Thomas Stohlgren, a research ecologist at the US Geological Survey’s Fort Collins Science Center (Fort Collins, CO); other factors – eg the pathways responsible for moving species, as well as their current and potential distribution – also play a role in determining whether a plant has the potential to become invasive when introduced. “The best, most consistent predictor of species invasion is whether they have successfully invaded another habitat”, says Doria Gordon, Director of Conservation Science for The Nature Conservancy (Gainesville, FL). While Thompson says this is consistent with the view that winners will be winners anywhere, Gordon suggests that predictive tools based on traits, history of invasiveness, and biogeography avoid the import of “winners” with high economic and environmental costs. While Thompson and Davis split species into winners and losers, alternative ways to classify species are appearing in the literature. For example, Richardson characterizes invasiveness as inherent or induced. He hypothesizes that in some plant groups invasiveness has a strong inherent component (species are either likely or unlikely to become invasive), whereas in others, invasiveness is induced, influenced more by humans moving species or modifying the environment. Philip Hulme, a plant ecologist at the Bio-Protection Research Centre in Christchurch, New Zealand, suggests splitting species into “passengers” or “drivers” of environmental change. “Unfortunately, we can’t yet predict impact-based traits”, he says. As researchers explore these new paradigms, it seems unlikely that relying on native or non-native status alone will prove sufficient to identifying invaders. n © The Ecological Society of America www.frontiersinecology.org
DISPATCHES DISPATCHES DISPATCHES 204 Shark clean-up services Madeline McCurry-Schmidt For the past 20 years, divers have observed sharks visiting the Monad Shoal, a seamount off Malapascua Island in the Philippines, but couldn’t figure out why the flat-topped, relatively barren area was such a popular shark hang-out. The answer came in 2005, when researchers from the Philippines, the UK, and Canada used remote video cameras to monitor shark behavior. The sharks were enlisting the assistance of small cleaner fish (eg the yellownose goby, Elacatinus randalli) that inhabit the shoal to remove various parasites. The study was published this March (PLoS ONE 2011; doi:10.1371/journal. pone.0014755). “Interactions with cleaner fish are the principal method by which sharks remove parasites, but little information on shark–cleaner interactions has been documented”, A pelagic thresher shark (Alopias pelagicus). explains Nigel Hussey, a post-doctoral fellow at the University of Windsor’s Great Lakes Institute for Environmental Research (Windsor, Canada), and a coauthor of the study. “The Monad Shoal seamount – in the case of pelagic thresher sharks [Alopias pelagicus] – is therefore extremely important for facilitating this interaction to maintain shark fitness.” The migration of sharks to the shoal is more than just a beauty routine. The study shows that parasites, such as monogenean flatworms, N Hussey commonly infest pelagic thresher sharks’ pelvic and gill areas, the region most favored by cleaner fish. To prevent infection, sharks that usually live in deep, open water periodically venture into shallow-water shoals for cleaning. Having parasites removed is so important that visiting sharks of different species “can be observed together at the same cleaning station”, says Hussey. Pelagic thresher sharks are joined at the Monad Shoal by grey reef sharks (Carcharhinus amblyrhynchos), manta rays (Manta birostris), and devil rays (Mobula spp), and the various species have adopted different strategies for getting cleaned. While thresher sharks swim in a circular path around the “cleaning stations”, grey reef sharks “pose in a near-vertical, [head-down] position with their mouths open during the cleaning interactions”. This odd pose may help the cleaner fish to access parasites around the sharks’ gills and mouth. n Infectious disease: from wetland to farm and back Chelsea L Wood Midnight meeting: peccaries and cattle forage together for fruit. As the UK’s National [Animal] Vaccination Month gets underway this May, veterinarians are encouraging pet owners – particularly those in rural areas – to vaccinate their animals against infectious disease, and ecological research is demonstrating that the vets have a point. Wherever human development encroaches on intact ecosystems, diseases can be exchanged between domestic and wild animals. This sort of transmission appears to be occurring in the Brazilian Pantanal, where a recent publication reports that leptospirosis may be carried from wetland to farm (and back) by wild white-lipped peccaries (Tayassu pecari) (Trop Anim Health Prod 2010; doi:10.1007/s11250-010-9622-2). Caused by Leptospira, a genus of spirochaete bacteria, leptospirosis affects a variety of vertebrates – including humans and other mammals. The disease is especially devastating for livestock operations, causing miscarriages in cattle, as well as reductions in milk production and body mass, and even death. In Brazil, leptospirosis is a major concern for the extensive livestock industry in the Pantanal. Whitelipped peccaries – wild ungulates related to pigs and native to the region – are particularly bold and nomadic, and are therefore likely to cross into agricultural land where they can come into contact with domestic animals, creating the opportunity for disease transmission. To investigate the potential for such contact to facilitate leptospirosis, the researchers trapped peccaries and tested their blood for antibodies to A Keuroghlian Leptospira interrogans. They found that 70% of the peccaries sampled had a high prevalence of Leptospira antibodies, representing a potentially large reservoir of disease. Alexine Keuroghlian (Wildlife Conservation Society, Rio de Janeiro, Brazil), a coauthor of the study, explains, “The high percentage of seropositive animals that we observed…is probably related both to favorable environmental conditions and to the coexistence of wild and domestic animals.” The authors note that there is insufficient information to assess whether Leptospira flows primarily from wild to domestic animals or vice versa. Tatiana Tavares de Freitas (Federal University of Mato Grosso, Cuiaba, Brazil), the primary author of the paper, suggests that “Further studies will be required to understand the effects of leptospirosis on the population dynamics and reproduction of wild white-lipped peccaries and other wildlife species. Forest fragmentation and increased exposure to exotic animals may cause diseases to emerge that threaten the persistence of wildlife populations.” n www.frontiersinecology.org © The Ecological Society of America
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