Abstract
The impact of global climate change on coral reefs is expected to be most profound at the sea surface, where fertilization and embryonic development of broadcast-spawning corals takes place. We examined the effect of increased temperature and elevated CO2 levels on the in vitro fertilization success and initial embryonic development of broadcast-spawning corals using a single male:female cross of three different species from mid- and high-latitude locations: Lyudao, Taiwan (22° N) and Kochi, Japan (32° N). Eggs were fertilized under ambient conditions (27 °C and 500 μatm CO2) and under conditions predicted for 2100 (IPCC worst case scenario, 31 °C and 1000 μatm CO2). Fertilization success, abnormal development and early developmental success were determined for each sample. Increased temperature had a more profound influence than elevated CO2. In most cases, near-future warming caused a significant drop in early developmental success as a result of decreased fertilization success and/or increased abnormal development. The embryonic development of the male:female cross of A. hyacinthus from the high-latitude location was more sensitive to the increased temperature (+4 °C) than the male:female cross of A. hyacinthus from the mid-latitude location. The response to the elevated CO2 level was small and highly variable, ranging from positive to negative responses. These results suggest that global warming is a more significant and universal stressor than ocean acidification on the early embryonic development of corals from mid- and high-latitude locations.
Highlights
Ocean acidification and increased seawater temperatures will continue to have an impact on coral reefs in the near future [1]
In our first experiment, with A. hyacinthus, much larger changes in CO2 were measured between the vials containing eggs and sperm and the control vials
The data presented here on fertilization success, abnormal development and early developmental success demonstrate that the response to elevated temperature and CO2 levels varies between different species and latitudinal location
Summary
Ocean acidification and increased seawater temperatures will continue to have an impact on coral reefs in the near future [1]. The effects are expected to be most profound at the sea surface, where fertilization and subsequent embryonic development of broadcast-spawning reef coral species takes place (reviewed in [2,3]). Broadcast-spawning is a reproductive mode whereby gametes are released into the water column and fertilization and embryonic development occurs externally. More than 80% of all reef coral species practice this mode of sexual reproduction, as opposed to brooding coral species, which produce larvae through internal fertilization [4]. Most broadcast-spawners release egg-sperm bundles that float to the water surface, where fertilization occurs and embryonic development proceeds for several days after the bundles are broken up. Since fertilization is the fundamental first step in the life cycle of corals, information about the influence of climate change on reproductive success is essential to predict the dynamics of reef coral assemblages in the future
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