June 18th, 2010
Mytilus galloprovincialis shell.
An invasive mussel has contracted significantly southward along the Californian coast despite expectations that it would move poleward under climate change.
In what is one of the largest and most rapid range changes recorded for any species, Thomas Hilbish and co-researchers found that in less than 10 years the Mediterranean mussel (Mytilus galloprovincialis) declined over about one-third (540 km) of its former range and was rare or absent from the northern 200 km of its former range.
They propose that the movement is due to smalle-scale climate cycles that have brought cooler temperatures to coastal habitats in California during the past decade compared to the preceding 15 years.
Decade-scale variations in climate are typically greater than that expected over the same period due to global warming.
Listed as one of the world’s 100 worst invasive species, the Mediterranean mussel originates from warm-temperate areas in the Mediterranean Sea and Atlantic Ocean and was introduced to Southern California in the first half of the 20th century.
It hybridises with an endemic species, Mytilus trossulus, in a zone over 500 km long. The hybrid zone also shifted south during the cooler decade, but the distribution of the native species did not change.
The difference in sea surface temperatures between the warmer and cooler decadal phases averaged only about 1 °C, but could have greatly influenced the survival of larvae of the invasive mussel.
The authors explain that a drop in average sea surface temperature from 13 to 12 °C could increase the duration of the larval phase by as much as 50%.
With about 15% mortality per day of larvae, the increased duration may result in a 10-fold increase in cumulative larval mortality at 12 °C compared with 13 °C. In this way, decadal-level climate variation can cause rapid ecological change.
Hilbish TJ, Brannock PM, Jones KR, Smith AB, Bullock BN and Wethey DS. 2010. Historical changes in the distributions of invasive and endemic marine invertebrates are contrary to global warming predictions: the effects of decadal climate oscillations. Journal of Biogeography 37(3): 423-431.