Ocean acidification affects calcareous tube growth in adults and reared offspring of serpulid polychaetes

Abstract

The energetically costly transition from free-swimming larvae to benthic life stage and maintenance of a calcareous structure can make calcifying marine invertebrates vulnerable to ocean acidification. The first goal of this study was to evaluate the impacts of ocean acidification on calcified tube growth for two Serpulidae polychaete worms. Spirorbis sp. and Spirobranchus triqueter were collected at 11 m depth from the Northwest Mediterranean Sea and maintained for 30 and 90 d, at three mean pHT levels (total scale) of 8.1 (ambient), 7.7, and 7.4. Moderately decreased tube elongation rates were observed in both species at a pHT of 7.7 while severe reductions occurred at pHT 7.4. There was visual evidence of dissolution and tubes were more fragile at lower pH but, fragility was not attributed to changes in fracture toughness. Instead, it appeared to be due to the presence of larger alveoli covered in a thinner calcareous layer. The second objective of the study was to test for effects in offspring development of the species S. triqueter. Spawning was induced, and offspring were reared in the same pH conditions the parents experienced. Trochophore size was reduced at the lowest pH level but settlement success was similar across pH conditions. Post-settlement tube growth was most affected. At 38 d post-settlement, juvenile tubes at pHT of 7.7 and 7.4 were half the size of those at pHT 8.1. Results suggest future carbonate chemistry will negatively affect initiation and persistence of both biofouling and epiphytic polychaete tube worms.