Filipe Banha

The role of waterfowl and fishing gear on zebra mussel larvae dispersal

The zebra mussel, Dreissena polymorpha (Pallas 1771), is an invasive freshwater species with major negative impacts, promoting changes in ecosystem structure and function and also contributing to economic losses. Navigation has been considered the primary vector of dispersion and little importance has been given to alternative natural (waterbirds) and other human vectors. Using an experimental approach under field conditions, we evaluated and compared zebra mussel dispersal potential by fishing gear (waders and keepnets) versus mallard ducks (Anas platyrhynchos), by examining the adherence and survival rate of zebra mussel larvae on each vector. In addition, we evaluated the survival of zebra mussel larvae under desiccating conditions (i.e., a set of controlled temperatures and relative humidities). Larvae adhered to all types of vectors and survived desiccation under both laboratory and field conditions and thus appear able to be dispersed long distances overland by both ducks and fishing gear. Specifically, on a per-event basis, fishing gear has a higher potential to spread zebra mussel larvae than ducks. Survival was three times higher on human vectors and the number of larvae attached to human vectors was over double of that on the ducks. However, our findings demonstrate that natural vectors, like ducks, can contribute to the transport of zebra mussel larvae at a local scale. Nevertheless, since vectors related to human activity presented a higher potential for transport, it is imperative to continue campaigns to raise the awareness of anglers and boaters as well as continue the implementation of legislation to reduce the risk of zebra mussel dispersal.

Waterbird-mediated passive dispersal is a viable process for crayfish (Procambarus clarkii)

Human transport and active dispersal of the red swamp crayfish (Procambarus clarkii) contribute to its rapid spread. However, some small aquatic organisms can be transported by birds. We made two hypotheses related to waterbird-mediated passive dispersal of juvenile crayfish. The first is that, depending on water depth, recently hatched crayfish can attach to ducks, initiating passive external transport (i.e., ectozoochory). The second is that recently hatched crayfish can survive bird flight, being affected by crayfish features, flight distance, and environmental conditions. A first experiment tested the attachment of juvenile crayfish to ducks at different water depths by using a freshly dead duck and tanks with crayfish. Another set of three experiments tested crayfish survival during air transportation. To simulate bird flight, we first used a vehicle moving at bird flight speed, and we then used trained pigeons. Several flight distances, environmental conditions, and crayfish sizes were tested. Our results showed that juvenile crayfish were capable of clinging to duck feathers and were transported when ducks were removed from the water. Furthermore, some juveniles of P. clarkii were able to survive long-distance transport when suspended outside a moving vehicle or when transported by birds. The probability of success was affected by water depth, crayfish size, distance travelled, and relative humidity. Our results support the occurrence of passive transportation of this invader by means of attachment to birds. These findings indicate that waterbird-mediated passive dispersal should be taken into account to explain P. clarkii’s rapid spread and should be considered when managing its invasions.

Environmental cues during overland dispersal by three freshwater invaders: Eriocheir sinensis, Pacifastacus leniusculus, and Procambarus clarkii (Crustacea, Decapoda)

Freshwater crustaceans are known to disperse overland, aiding the invasion of new environments. To analyze the effect of environmental variables (humidity, temperature, illuminance, vegetation, and slope) on the movement direction of Eriocheir sinensis (H. Milne Edwards, 1853), Pacifastacus leniusculus (Dana, 1852) and Procambarus clarkii (Girard, 1852) in land, the animals were placed at the centre of a metal gutter and given a choice between two values of each variable. Chi-squared tests revealed significant preferences for E. sinensis to move downhill, P. leniusculus to move toward cooler areas and P. clarkii to move downhill and toward cooler areas. To test the ability of P. leniusculus and P. clarkii (E. sinensis was not present at the testing site) to return to water, they were placed in a circular arena near the river bank and their direction of movement was recorded. Chi-squared tests revealed that P. leniusculus, when isolated and in groups of 6, showed a significant tendency to move downstream, but not directly toward the water. P. clarkii showed no significant preference in movement direction. Since movement direction and overland dispersal are influenced by environmental gradients of temperature and elevation, these variables are fundamental for predicting autonomous overland dispersal and colonization patterns.

Non-native freshwater fauna in Portugal: A review

We present the most updated list of non-native freshwater fauna established in Portugal, including the Azores and Madeira archipelagos. This list includes 67 species at national level but corresponds to 84 species records, of which 53 are in the mainland, 23 in the Azores and 8 in Madeira archipelagos. We also discuss the progression of the cumulative number of introductions since 1800 and identify the most probable vectors of introduction, main taxonomic groups and their regions of origin. Furthermore, we review the existing knowledge about ecological and economic impacts, invasion risk and potential distribution of invaders, under present and future climatic conditions, and the applied management actions, including the production of legislation. Along the 20th century the number of successful introductions increased at an approximate rate of two new species per decade until the beginning of 1970s. Since then, this rate increased to about 14 new species per decade. These introductions were mainly a result of fisheries, as contaminants or for ornamental purposes. Fish and mollusks are the taxonomic groups with more established species, representing more than half of the total. Most species (>70%) are native from other regions of Europe and North America. Studies about ecological or socioeconomic impacts are more common for fish, crustaceans and mollusks. Impacts for most amphibians, reptiles and mammals are not thoroughly studied. A few studies on the impacts and management actions of health-threatening mosquitoes are also available. The potential distribution in the Portuguese territory was modelled for 26 species. Only a minority of these models provides projections of distributions under scenarios of future climate change. A comparison of the Portuguese and EU legislation shows large discrepancies in the invasive species lists. Using the EU list and a ranking procedure for the national context, we identify freshwater species of high national concern for which actions are urgently needed.