Comparison of methods for estimating the spread of a non-indigenous species

Aim  To compare different quantitative approaches for estimating rates of spread in the exotic species gypsy moth, Lymantria dispar L., using county-level presence/absence data and spatially extensive trapping grids.
Location  USA
Methods  We used county-level presence/absence records of the gypsy moth's distribution in the USA, which are available beginning in 1900, and extensive grids of pheromone-baited traps, which are available in selected areas beginning in 1981. We compared a regression approach and a boundary displacement approach for estimating gypsy moth spread based on these sources of data.
Results  We observed relative congruence between methods and data sources in estimating overall rates of gypsy moth spread through time, and among regions.
Main conclusions  The ability to estimate spread in exotic invasive species is a primary concern in management programmes and one for which there is a lack of information on the reliability of methods. Also, in most invading species, there is generally a lack of data to explore methods of estimating spread. Extensive data available on gypsy moth in the USA allowed for such a comparison. We show that, even with spatially crude records of presence/absence, overall rates of spread do not differ substantially from estimates obtained from the more costly deployment of extensive trapping grids. Moreover, these methods can also be applied to the general study of species distributional changes, such as range expansion or retraction, in response to climate change or other environmental effects.     

Biological control of marine invasive species: cautionary tales and land-based lessons

Biological control (biocontrol) has successfully regulated pest populations in terrestrial agroecosystems, but it has also caused negative unintended consequences for native species. Marine biologists and resource managers have recently published a growing number of proposals to include biocontrol in integrated pest management programs in oceans, seas and estuaries. Here, I review six ecologically and taxonomically diverse case studies of marine biocontrol programs at various stages of planning and implementation. Proposals include viral or microbial control of harmful algal blooms, predatory control of the ctenophore Mnemiopsis leidyi in the Black Sea, parasitic regulation of the European green crab Carcinus maenas, castration by ciliates of the seastar Asterias amurensis in Australia, herbivory of the toxic green alga Caulerpa taxifolia in the Mediterranean by sacoglossan sea slugs, and insect biocontrol by the planthopper Prokelesia marginata to ameliorate ecological impacts of the saltmarsh cordgrass Spartina alterniflora. Where data exist, I evaluate these examples in terms of lessons marine invasion biologists can glean from the rich history of terrestrial biocontrol, and explicitly contrast agroecosystems with invaded marine habitats. Host specificity cannot be guaranteed in the marine biocontrol proposals examined. Feasible alternatives to classical biocontrol in the marine realm should be emphasized, including more investment in invasion prevention tools, early detection and eradication while invasions are small, and increased attention to native natural enemies to control exotic pests. Biocontrol in marine habitats is risky: it poses many more uncertainties and has a much sparser history than its counterpart on land.     

Blitzkrieg in a Marine Invasion: Caulerpa racemosa var. cylindracea (Bryopsidales, Chlorophyta) Reaches the Canary Islands (North-East Atlantic)

On the basis of morphological and genetic studies (rDNA ITS1, 5.8S, ITS2, and a 18S rDNA intron), we confirm here that Caulerpa racemosa var. cylindracea (Sonder) Verlaque, Huisman et Boudouresque, a southwestern Australian taxon recently introduced into the Mediterranean Sea also occurs in the Canary Islands. This is the first report of C. racemosa var. cylindracea in the Atlantic. It was observed for the first time in the Canary Archipelago in 1997–1998. The speed and regional scale of expansion (north Atlantic Ocean and the Mediterranean Sea) of this invasive species appear to be among the most dramatic ever recorded. The possible outcome of this introduction in the Atlantic is discussed.