Ocean acidification and kelp development: reduced pH has no negative effects on meiospore germination and gametophyte development of Macrocystis pyrifera and Undaria pinnatifida
Leal, PP and Hurd, CL and Fernandez, PA, Ocean acidification and kelp development: reduced pH has no negative effects on meiospore germination and gametophyte development of Macrocystis pyrifera and Undaria pinnatifida, Journal of Phycology pp. 1-36. ISSN 0022-3646 (In Press) [Refereed Article]
The absorption of anthropogenic CO2 by the oceans is causing a reduction in the pH
of the surface waters termed ocean acidification (OA). This could have substantial effects on
marine coastal environments where fleshy (non-calcareous) macroalgae are dominant
primary producers and ecosystem engineers. Few OA studies have focused on the early life
stages of large macroalgae such as kelps. This study evaluated the effects of seawater pH on
the ontogenic development of meiospores of the native kelp Macrocystis pyrifera and the
invasive kelp Undaria pinnatifida, in south-eastern New Zealand. Meiospores of both kelps
were released into four seawater pH treatments (pHT 7.20, extreme OA predicted for 2300;
pHT 7.65, OA predicted for 2100; pHT 8.01, ambient pH; and pHT 8.40, pre-industrial pH)
and cultured for 15 d. Meiospore germination, germling growth rate, and gametophyte size
and sex ratio were monitored and measured. Exposure to reduced pHT (7.20 and 7.65) had
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positive effects on germling growth rate and gametophyte size in both M. pyrifera and U.
pinnatifida, whereas, higher pHT (8.01 and 8.40) reduced the gametophyte size in both kelps.
Sex ratio of gametophytes of both kelps was biased towards females under all pHT
treatments, except for U. pinnatifida at pHT 7.65. Germling growth rate under OA was
significantly higher in M. pyrifera compared to U. pinnatifida but gametophyte development
was equal for both kelps under all seawater pHT treatments, indicating that the microscopic
stages of the native M. pyrifera and the invasive U. pinnatifida will respond similarly to OA.