Living on the edge: reproductive cycle of a boreal barnacle at its southernmost distribution limit

摘要

Environmental controls on the biogeographic distribution of species are becoming increasingly relevant under the present climate change conditions. The reproductive cycle of the acorn barnacle Semibalanus balanoides at its southernmost European distribution limit in Galicia (Northwest Iberian Peninsula) was studied in two locations (42.57 degrees N 8.96 degrees W, 42.61 degrees N 8.89 degrees W) with different temperatures during a 4-year time series (2012-2016), where an isolated population breeds even though the temperature thresholds documented for northern populations of the species are exceeded. Ovary production, total number of embryos and pre-hatching developmental stage were significantly higher in the colder location than in the warmer one. Fecundity was higher in colder reproductive seasons mediated by upwelling regime and food supply 3 months prior to fertilization. Investment in ovary tissue was favored by high temperatures and food availability, whereas suspended sediment was negatively correlated with investment in ovary tissue. Larvae release was associated with high temperatures and suspended sediment. Phenology of reproductive events was similar to what was described in farther north populations. Results indicated that reproductive output of the species at its southernmost European distribution limit is comparable to that reported in northern latitudes and suggest adaptation or acclimatization to local environmental conditions as maturation of gonads and fertilization was successfully carried out at higher temperatures than documented in northern European populations.