Proceedings of the Third International Conference on Invasive ...

<strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> <strong>Third</strong> <strong>International</strong> <strong>Conference</strong> on Invasive SpartinaChapter 2: Spartina Distribution and SpreadWILL SPARTINA ANGLICA INVADE NORTHWARDS WITH CHANGING CLIMATE?A.J. GRAY 1,2 AND R.J. MOGG 11 Centre for Ecology and Hydrology, CEH Dorset, Winfrith Technology Centre, Dorchester, Dorset, DT2 8ZD, UK2 email: ajg@ceh.ac.ukSpartina anglica’s successful invasion has depended on its ability to occupy mudflats atlower elevations than existing saltmarsh vegetation but has slowed, with dieback in <strong>the</strong>south and successional replacement in <strong>the</strong> north. The elevational niche <strong>of</strong> S. anglica in <strong>the</strong>UK was shown to extend below that <strong>of</strong> its main competitor Puccinellia maritima by 68centimeters (cms). The niche <strong>of</strong> <strong>the</strong> two species overlapped by 20 cms and within thiszone <strong>the</strong>ir distribution depends on <strong>the</strong> outcome <strong>of</strong> <strong>the</strong>ir competitive interaction. Thisinteraction was investigated in <strong>the</strong> light <strong>of</strong> projected climate changes and <strong>the</strong> fact that <strong>the</strong>two species utilize different photosyn<strong>the</strong>tic pathways. A competition experiment underelevated levels <strong>of</strong> temperature and carbon dioxide is described and its implications for <strong>the</strong>future development <strong>of</strong> Spartina-dominated marshes is discussed.Keywords: Spartina anglica, elevational niche, Puccinellia maritima, climate change,competition, C3 and C4 grassesTHE ORIGIN AND SPREAD OF S. ANGLICASpartina anglica CE Hubbard is arguably <strong>the</strong> bestknown example worldwide <strong>of</strong> an invasive allopolyploidspecies. It originated on <strong>the</strong> south coast <strong>of</strong> England sometime between 1870, when <strong>the</strong> sterile F1 hybrid S. townsendiiwas first noticed, and 1892 when <strong>the</strong> first fertile specimenwas collected. The allopolyploid was subsequently named asSpartina anglica and its spread both naturally and bydeliberate planting, has been extremely well documented —Gray et al. (1991) provide a summary. The parental species,S. maritima, a native <strong>of</strong> <strong>the</strong> old world, and S. alterniflora,accidentally introduced from North America intoSouthampton Water, probably in ships’ ballast, were incontact for a relatively short period (30-40 years?).Never<strong>the</strong>less <strong>the</strong> patterns <strong>of</strong> isoenzyme variation haveunambiguously established <strong>the</strong> hybrid origin <strong>of</strong> S. anglica(Raybould et al. 1991a), and analysis <strong>of</strong> <strong>the</strong> DNA sequence<strong>of</strong> <strong>the</strong> chloroplast leucine tRNA gene intron has shown thatS. alterniflora was <strong>the</strong> female parent in <strong>the</strong> original cross(cpDNA is maternally inherited in most grass species)(Ferris et al. 1997). This is not surprising in view <strong>of</strong> <strong>the</strong>relative frequency <strong>of</strong> <strong>the</strong> two species in <strong>the</strong> area <strong>of</strong>hybridization during <strong>the</strong> middle <strong>of</strong> <strong>the</strong> last century.Following hybridization and chromosome doubling(nei<strong>the</strong>r <strong>of</strong> which events have been repeated experimentally)<strong>the</strong> hybrids and <strong>the</strong>ir parents appear to have been quiterapidly isolated both genetically and ecologically. Spartinamaritima is found in <strong>the</strong> mid-level and high marsh zones <strong>of</strong>well established salt marshes and is today largely confined to<strong>the</strong> east coast <strong>of</strong> England in <strong>the</strong> counties <strong>of</strong> Essex andSuffolk (Raybould et al. 1991b). The nearest extantpopulation to <strong>the</strong> site <strong>of</strong> origin is on <strong>the</strong> Isle <strong>of</strong> Wight, about10 miles away. Spartina alterniflora has been reduced to asingle clonal population in Southampton Water and israpidly being lost as <strong>the</strong> lower zones <strong>of</strong> <strong>the</strong> salt marshes areeroded along this coast. (There are a small number <strong>of</strong> o<strong>the</strong>rclones <strong>of</strong> <strong>the</strong> species elsewhere but <strong>the</strong>se have beendeliberately introduced from known sources since <strong>the</strong> date <strong>of</strong><strong>the</strong> original hybridization.) Thus, somewhat ironically inview <strong>of</strong> <strong>the</strong> main <strong>the</strong>me <strong>of</strong> this conference, S. alterniflora in<strong>the</strong> UK is regarded as a rare and threatened species <strong>of</strong>conservation interest, and its presence was recentlyinstrumental in <strong>the</strong> refusal for permission to extend anddevelop <strong>the</strong> nearby port. The sterile hybrid S. townsendii isalso largely confined to <strong>the</strong> original hybridization site,although its distribution is uncertain because it wasintroduced to many estuaries along with <strong>the</strong> fertile form.By contrast S. anglica has colonized, or been planted in,almost all English and Welsh estuaries, is found in Scotland,and occurs in suitable habitats around <strong>the</strong> coast <strong>of</strong> Europefrom 48 to 57.5° N. It has famously been introduced to manyo<strong>the</strong>r parts <strong>of</strong> <strong>the</strong> world and in several areas has become aserious invader <strong>of</strong> native biotopes. As detailed below, S.anglica mostly occurs in <strong>the</strong> lowest zones <strong>of</strong> salt marshes,and at its peak occupied almost 25% <strong>of</strong> <strong>the</strong> total saltmarsharea in Britain (10,000 hectares (ha) <strong>of</strong> <strong>the</strong> 44,000 hasurveyed by Charman (1990)).The initial rapid genetic isolation, and current ecologicalisolation, <strong>of</strong> <strong>the</strong> species involved in <strong>the</strong> evolution <strong>of</strong> S.anglica makes a fascinating contrast to <strong>the</strong> situation in SanFrancisco Bay, where hybridization between <strong>the</strong> native plantS. foliosa, and its ecological replacement, are a feature <strong>of</strong> <strong>the</strong>invasion <strong>of</strong> <strong>the</strong> non-native S. alterniflora.- 103 -