The Spread ofElminius ModestusDarwin In North-West Europe

Abstract

Material collected prior to 1940 indicates that Elminius modestus was not present on British coasts at that time.Elminius increased in abundance in south-east England from 1946 to 1950 and extended its range as far as the Humber, where it halted.Its advance westwards along the south coast was similarly halted at Portland, but by 1948 independent colonies had been established in several of the river systems of Devon and Cornwall, in Milford Haven, and in the Bristol Channel.The first populations in the Irish Sea were in Morecambe Bay. From there Elminius spread rapidly south and west along the north coast of Wales, and more slowly north and west towards Galloway, eventually bridging the sea to the Isle of Man.Detailed observations showed that Elminius advanced along the uniformly favourable north coast of Wales as a definite front moving at a rate of approximately 20–30 km per year. Around Anglesey where tidal currents were stronger it appeared simultaneously in many scattered centres.A distinction is drawn between marginal dispersal taking place under the influence of normal agencies at the boundary of an existing population, and remote dispersal due to an artificial or freak transport over a long distance. In the case of Elminius the maximum distance that is likely to be bridged by marginal dispersal in the absence of strong residual drifts is about 30 miles.Elminius probably first appeared near Southampton, and was introduced into the Thames estuary area probably by remote dispersal. Thence it spread along the east coast and was transported to Holland. Its extension into south Devon, the Bristol Channel, the Irish Sea, and to the French coast must also be attributed to remote dispersal.The main ecological effects of Elminius result from competition for space with Balanus balanoides. Since Elminius breeds in summer, its dominance has a profound effect on the composition of the summer plankton, greatly increasing the number of barnacle nauplii, presumably at the expense of other larvae.

Pelagic Larval Duration and Dispersal Distance Revisited

“…In these studies, dispersal distance was the annual distance the species spread, but obviously, individuals disperse to distances less than the distance to the annual spreading front. This can be clearly seen in Crisp's data on the spread of Elminius modestus (Crisp, 1958). The spread of the species was about 25 km per year, but large numbers of recruits were present from the previous year's spreading front out to 25 km; in other words, settlement adequate to sustain the population was observed from 0 to 25 km from the spreading front.…”

Scale of dispersal in varying environments and its implications for life histories of marine invertebrates

“…Studies of passive diffusion from a point source (Okubo 1971) suggest spread in the range of ten to one hundred kilometers associated with pelagic periods on the order of a week to a month. Expansion of species ranges provide similar estimates (Crisp 1958;Gerdes 1977;Quayle 1964). Consider two types of invertebrates: one with feeding larvae which spread over 100 km and one with non-feeding larvae which spread over 10 km.…”

“…We are particularly interested in patterns of temporal and spatial variation in environmental favorability which offer a substantial advantage to spread of offspring over very large regions (circa 50 km or more) as compared to more moderate scales of dispersal. A spread of about 50 km is the usual result of development with a feeding larva as opposed to the smaller spread experienced by a nonfeeding but swimming larva in the life cycles of benthic invertebrates, an estimate supported both by diffusion studies (Okubo 1971) and rates of expansion of species' ranges (Crisp 1958;Gerdes 1977;Quayle 1964). Environmental favorability, as we use the term in this paper, may be interpreted as local environmental attributes influencing either: 1) per individual reproductive output of arriving propagules (a component of fitness) or 2) the final number of reproducing adults (carrying capacity) at a given site.…”

Long-term changes in the macrozoobenthos around the rocky island of Helgoland (German Bight, North Sea)

“…The species was introduced to the southern British coast during the 1940s, probably as a fouling organism on ships from Australia, then rapidly spread over north-west European coasts and was first recorded at Helgoland in 1954 (Crisp 1958;Den Hartog 1959;Ku¨hl 1963). Here, E. modestus has become a prominent member of the intertidal community, at least partly at the expense of the native Semibalanus balanoides (L.).…”