Interactive effect of elevated pCO₂ and temperature on the larval development of an inter-tidal organism, Balanus amphitrite Darwin (Cirripedia: Thoracica)

Abstract

The projected increase in the pCO2 and temperature level by the end of the 21st century, is expected to influence the life cycle of marine invertebrates. Experiments were carried out with an acorn barnacle, Balanus amphitrite a dominant inter-tidal organism, to investigate the effect of these variables on its larval development and metamorphosis. Four alternate combinations of temperature and pCO₂: (1) control (~ 30 °C and ~ 400 μatm); (2) elevated pCO₂ (~ 30 °C and ~ 750 μatm); (3) elevated temperature (~ 34 °C and ~ 400 μatm); and (4) synergistic (~ 34 °C and ~ 750 μatm) were tested. Apart from their direct effect, the diet-mediated influence was also evaluated by providing a diatom feed (Chaetoceros calcitrans) that was grown under similar conditions as that of nauplii. In both the direct and diet-mediated effects, irrespective of pCO₂ levels, elevated temperature favoured faster naupliar development. However, in the direct effect, the synergistic condition yielded poor quality cyprids (non-feeding, pre settlement larval stage) as evidenced by lower RNA:DNA ratio, that resulted in lower metamorphosis. On the contrary, in the diet-mediated evaluation, the feed grown in the synergistic condition had higher protein content that facilitated faster naupliar development, better quality of cyprids (higher RNA:DNA ratio) and yielded a higher percentage of metamorphosis. The results suggest that future climatic conditions will affect the quality of food consumed by invertebrate larvae, thus influencing their development and metamorphosis. Therefore, future studies evaluating the climate change scenarios to depict the changes in settlement and recruitment of marine invertebrates should be advocated to integrate the changes in the food chain.