Abstract
To elucidate how the population dynamics of the acorn barnacle Balanus glandula transitioned after its invasion in 2000 along the Pacific coast of Japan, a population census was conducted from 2004 to 2014 at five shores along 49 km of coastline 144–193 km east outside of the invasion front. Survey areas at each shore consisted of five paired plots (cleared recruitment plots and control plots). Larval recruitment was first detected in 2004 but benthic individuals were not detected until 2 years later. The abundance and occurrence of B. glandula increased until around 2010; abundance then decreased but occurrence remained high (70%) until 2014, suggesting that the metapopulation of this barnacle approached a maximum around 2011. From 2011, the population dynamics of B. glandula changed considerably at two contrasting spatial scales: at a regional scale, the dependency of the number of larvae on stock size decreased, whereas at a local scale, the relative contribution of larval supply as a determinant of local population dynamics decreased. These findings suggest that the major driving force of population dynamics of the introduced barnacle changed in just a few years after invasion; therefore, population census data from just after an invasion, including larval recruitment monitoring just outside the invasion front, is essential to understanding invasion dynamics by sessile marine organisms.
Highlights
During the early phase of a biological invasion, both the range size and population density of the invading species increase with time [1,2,3], because an invasion event is usually initiated by the arrival of few propagules beyond their native range [4,5,6]
At local scales, population dynamics are often strongly affected by recruitment variability, which reflects external larval supply at the locality, especially at low levels of larval supply [19,20,21]
The invading barnacle B. glandula increased in coverage and occurrence from 2004 until around 2010, and declined in coverage but with a high level of occurrence (e.g., 70%) until 2014, suggesting that the metapopulation of B. glandula in the region approached its peak around 2011
Summary
During the early phase of a biological invasion, both the range size and population density of the invading species increase with time [1,2,3], because an invasion event is usually initiated by the arrival of few propagules (i.e., introduced individuals) beyond their native range [4,5,6] Such temporal trends in distribution and abundance weaken with time after the invasion and are lost after population equilibrium has been reached [7,8]. Most of them have complex life histories that include pelagic and benthic phases linked by larval recruitment [11,12] The transition between these two contrasting life phases can be crucial in determining the population dynamics of marine sessile organisms [13,14]. At local scales, population dynamics are often strongly affected by recruitment variability, which reflects external larval supply at the locality, especially at low levels of larval supply [19,20,21]
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