Reproduction in a changing ocean :the effects of ocean acidification and other environmental stressors on the sea urchin Paracentrotus lividus and the Polychaete Ficopomatus enigmaticus

Abstract

Atmospheric CO enrichment is a key factor contributing to global climate 2 change. Major consequences of climate change include increasing sea surface temperature and decreasing seawater pH (ocean acidification) – both of which are predicted to lead to an increase in ocean hypoxic events. Early ontogenetic stages of invertebrates have shown sensitivity to these environmental changes. Previous research has focused on short-term exposure to these environmental factors; however, the long- term and multi-generational effects of ocean acidification on organismal reproduction and development have received little attention. The aim of this thesis is to address this shortcoming for reproduction and early embryonic development of the economically- and ecologically-important sea urchin, Paracentrotus lividus (Lamark, 1816) and the reef-forming invasive polychaete, Ficopomatus enigmaticus (Fauvel, 1923). Fertilisation success and early embryogenesis of P. lividus were negatively impacted under conditions of increased pCO, at ambient temperature and ambient 2 +2°C after 12 months exposure. Sperm motility – determined by computer assisted sperm analysis (CASA) – showed a significant increase in average swimming speed measured as curvilinear velocity (VCL) at increased pCO levels after 6 months but by 2 12 months VCL values had decreased. There was no overall significant effect of pCO 2 on VCL but there was a significant reduction in fertilisation success under hypoxic conditions. Increasing pCO levels appeared to buffer the effects of hypoxia, however, 2 with significantly lower fertilisation success observed only under hypoxic conditions at ambient pCO. Multi-generational experiments examined the effects of increased pCO on 2 F.enigmaticus. Both percentage sperm motility and sperm VCL were similar between experimental treatments, but there was a significant difference between generations 0 and 2. In contrast, fertilisation success was negatively affected by both pH and generation, with a significant reduction seen with pH at all generations and a significant reduction seen between generation 0 and generation 2. Oocyte diameter was also significantly affected by pH and generation, with a significant increase in egg diameter seen at generation 1 in all pH treatments except pH 7.95, which shows a significant increase and generation 2, which suggests differing levels of maternal investment. This research suggests that in the long term, ocean acidification, temperature and hypoxia may seriously impact the reproduction and development of two important marine invertebrate species. This research highlights the need for further long-term investigation involving multiple stressors to provide a more comprehensive understanding of the long-term effects arising from changing oceanic chemistry.