Sesoko Ocean Acidification Project | AICAL Project

Morita M, Suwa R, Iguchi A, Nakamura M, Shimada K, Sakai K, Suzuki A.
Ocean acidification reduces sperm flagellar motility in broadcast spawning reef invertebrates. Zygote 18:103-107

In this paper, we report that near-future ocean acidification may disrupt the sexual reproduction of broadcast spawning reef invertebrates. Our finding that sperm motility in reef invertebrates (coral and sea cucumber) decreases at pH levels just below ambient pH (-0.2 to -0.4 pH units, changes predicted to occur in the ocean within 100 years) strongly indicates that ocean acidification is likely to threaten its inhabitants in the not too distant future. Moreover, our findings in Acropora, which are among the most ecologically important reef- building corals, are particularly noteworthy because of the economic importance of reefs as sites of fisheries and tourism.

Acropora digitifera and its sperm. Bar = 50μm. Photo by M. Morita.

Suwa R, Nakamura M, Morita M, Shimada K, Iguchi A, Sakai K, Suzuki A.
Effects of acidified seawater on early life stages of scleractinian corals (Genus Acropora). Fisheries Science in press

In this paper, we investigated the effects of increased CO2 on early life stages (larval and polyp stages) of Acropora spp. with the aim of estimating CO2 tolerance thresholds at these stages. Larval survival rates did not differ significantly between the reduced pH and control conditions. In contrast, polyp growth and algal infection rates were significantly decreased at reduced pH levels compared to control conditions. These results suggest that future ocean acidification may lead to reduced primary polyp growth and delayed establishment of symbiosis.

Photo: A planula larvae of Acropora digitifera. Bar = 100μm. Photo by M. Nakamura.

Photo: A primary polyp of Acropora digitifera. A white part is a skeleton of the coral polyp. Bar = 200μm. Photo by R. Suwa.

Kuroyanagi A, Kawahata H, Suzuki A, Fujita K, Irie T.
Impacts of ocean acidification on large benthic foraminifers: Results from laboratory experiments. Marine Micropaleontology 2009, 73:190-195

In this study, we cultured asexually-produced individuals of Marginopora kudakajimensis under four different pH conditions to examine the effects of lowering pH on their growth rates. These results suggest that 1) they already may have experienced a reduction in growth in natural environments since preindustrial times and 2) although the seawater CO2 system of reef water shows great variation, the calcification rate of these large foraminifers should remain at the present level at pH 7.9–8.2 (NBS scale). However, at around pH 7.7, their calcification rate would decline steeply, which would probably preclude their survival.

Figure: SEM photos of Marginopora kudakajimensis measured after 10 weeks of culture at (A) pH 7.7, (B) pH 7.9, (C) control, and (D) pH 8.3.