The effects of in-vitro pH decrease on the gametogenesis of the red tree coral, Primnoa pacifica

Primnoa pacifica is the most ecologically important coral species in the North Pacific Ocean and provides important habitat for commercially important fish and invertebrates. Ocean acidification (OA) is more rapidly increasing in high-latitude seas because anthropogenic CO2 uptake is greater in these regions. This is due to the solubility of CO2 in cold water and the reduced buffering capacity and low alkalinity of colder waters. Primnoa pacifica colonies were cultured for six to nine months in either pH 7.55 (predicted Year 2100 pH levels) or pH 7.75 (Control). Oocyte development and fecundity in females, and spermatocyst stages in males were measured to assess the effects of pH on gametogenesis. Oocyte diameters were 13.6% smaller and fecundities were 30.9% lower in the Year 2100 samples. A higher proportion of vitellogenic oocytes (65%) were also reabsorbed (oosorption) in the Year 2100 treatment. Lower pH appeared to advance the process of spermatogenesis with a higher percentage of later stage sperm compared to Control. There was a laboratory effect observed in all measurement types, however this only significantly affected the analyses of spermatogenesis. Based on the negative effect of acidification on oogenesis and increased rate of oosorption, successful spawning could be unlikely in an acidified ocean. If female gametes were spawned, they are likely to be insufficiently equipped to develop normally, based on the decreased overall size and therefore subsequent limited amount of lipids necessary for successful larval development.