Lower thermal limits to larval development do not predict poleward range limits of the introduced tropical barnacle Megabalanus coccopoma

Abstract

As the earth's climate has warmed, many tropical species have expanded their ranges poleward and encountered high-latitude seasonal temperature regimes, in which further permanent expansion is limited by physiological vulnerability to cold temperatures. The barnacle Megabalanus coccopoma is native to shorelines from Baja California to Peru and has been introduced to many locations worldwide, including the southeastern USA. The ability of larvae to develop successfully at local temperatures can be an important factor limiting the spread of invasive species. To determine if cold temperatures limited larval success near the northern range limit of M. coccopoma along the Atlantic southeastern USA coast, we measured lower temperature limits to larval development, examined the effects of temperature on larval growth and energy accumulation, and calculated a larval energy budget to estimate the extent of potential larval dispersal in this region. Larvae were able to develop through metamorphosis at 16°C, which is much colder than sea surface temperatures during the spawning season in their invasive range, making it unlikely northern range limits are set by a lower temperature limit to larval development. Energy budgets suggest that for larvae produced at the northern end of the invasive range, long distance dispersal to sites far poleward of the current range limit is possible. Similar to the findings of the handful of other studies on cold tolerances of tropical marine invertebrate larvae, larvae should be successful far poleward of current adult distributions.