Coastal invertebrates and climate change: evidence for risks & opportunities

Whichever group of terrestrial invertebrates grabs your attention in Britain, it’s hard not to notice, and read about, changes in species‘ distribution with warming temperatures. Mainstream books (e.g. Smallshire & Walsh 2004) give suggestions for future vagrants and colonists to look out for, while even a cursory look at the topic gives any number of anecdotal references to invertebrates moving further north into or within Britain, including coastal species spreading inland. However, what systematic evidence is there for such range expansions?

With funding limited, many British species are recorded somewhat fragmentarily and although new locations may be noted, it can be difficult to find rigorous monitoring of northward or inland spreads. However, an excellent example is the work undertaken by Musolin (2010), looking at expansion in Japan of the southern green stink bug Nezara viridula (a species which, in 2003, also colonised Britain where it is known as the southern green shieldbug or the green vegetable bug.) Along with Tougou et al. (2009), this showed a clear northward range expansion with warming temperatures, especially along the warmer coasts and via urban areas which form ‘heat islands’. The species is native to Japan which is at the northern edge of its Asian range, but as in Britain, its spread does depend on its ability to overwinter and possibly the need to adapt its diapause period. In Britain, although there have been specimens imported with vegetables or pot-plants prior to 2003, it is only recently that the species has been able to overwinter, and although its status is not entirely clear, it has already spread from its initial locations in north London as well as appearing on the south coast.

NBN distribution map of Nezara viridula (as of 16/12/2010)

Looking at another Hemipteran species reported to be spreading in Britain, the striking red and black rhopalid Corizus hyoscyami, a similar pattern is seen. Generally considered to be a species of sandy coasts in southern Britain, it has recently spread further north (especially the west coast) and has been seen much more often at inland locations, including on mint in my partly-sandy back garden this summer, about 10km inland. I am unaware of any systematic work on this species, but a quick look at the data held by the National Biodiversity Network (NBN) for this species shows that the northernmost records (grid square SH, covering NW Wales) all occur since 1993 with one in each of 1993, 1995, 1997 and 1998, two in 2000, one in 2001 and 3 in 2005. Although this doesn’t form a pattern in itself, it does suggest a northward movement as there are numerous earlier records from previous decades (and indeed centuries), but none so far north, with most along the south coast. Although the NBN database isn’t complete (my record isn’t there yet, but it will be...), the map does show a few inland records including what appears to be spread upstream along the Severn valley.

NBN distribution map of Corizus hyoscyami (as of 16/12/2010)

C. hyoscyami on mint in my garden, summer 2010.

This clearly isn’t rigorous, but does suggest that, like some other species, C. hyoscyami may be benefitting from warming temperatures allowing it to spread both inland and northward. However, this is of course only one aspect of the story: not only does it imply that northern and/or upland specialists may be squeezed with nowhere to go, but also begs the question about what happens in the longer term? Well, for soft cliff habitats, this has been looked at in broad terms by Whitehouse (2007). Here, the conclusion is that, given the expected rise in sea level, changes to precipitation patterns and increased storm frequency and storm ferocity, most impacts on soft cliff invertebrate assemblages will be negative. These effects will increase erosion rates and so may alter the morphology of many important sites, including through damage associated with destabilisation of slopes - changes in precipitation patterns put assemblages associated with hydrological features such as seepages at particular risk. Some warmth-loving species may be able to spread into other habitats, along with colonisation by species from continental Europe, but the responses of individual invertebrate species to climate change are largely unknown and understudied. However, all likely scenarios seem to suggest that although there will be some winners for whom climate change is a genuine opportunity, this may only be in the short- to medium-term, and that most such assemblages, without appropriate conservation measures (e.g. ensuring suitable habitat areas remain even if not in exactly the same location), are at risk from negative impacts. Saying that, I strongly suspect that some species will surprise us with their adaptability, though I would prefer to see carbon emissions falling so as to minimise such impacts and the subsequent need to ‘hope for the best’...

References

Musolin, D.L. (2010). Range expansion of the southern green stink bug Nezara viridula (Heteroptera: Pentatomidae)
in response to the rapid climate change in Japan. Het News, 15, 4-6

Smallshire, D. & Swash, A. (2004). Britain’s Dragonflies. WILDGuides, Old Basing.

Tougou, D., Musolin, D.L., & Fujisaki, K. (2009). Some like it hot! Rapid climate
change promotes shifts in distribution ranges of Nezara viridula
and N. antennata in Japan. Entomologia Experimentalis et Applicata, 130 (3), 249-258 : 10.1111/j.1570-7458.2008.00818.x

Whitehouse, A.T. (2007). Managing Coastal Soft Cliffs for Invertebrates: Summary Report. Buglife - The Invertebrate Conservation Trust, Peterborough.