How does rising atmospheric CO2 affect marine organisms?

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The Virtues of Promiscuity in Coral Larvae
Cumbo, V.R., Baird, A.J. and van Oppen, M.J.H. 2013. The promiscuous larvae: flexibility in the establishment of symbiosis in corals. Coral Reefs 32: 111-120.

The authors write that "coral reefs thrive in part because of the symbiotic partnership between corals and Symbiodinium," but they say that "the point at which symbiosis is established (i.e., larva vs. juvenile) remains uncertain, as does the source of free-living Symbiodinium in the environment."

What was done
In the words of Cumbo et al., they "compared the types of symbionts taken up by Acropora larvae exposed to sediments collected from three different locations on the Great Barrier Reef, and compared this to the Symbiodinium types within adult cnidarians for each location." In addition, they "tested whether the Symbiodinium types changed during ontogeny by comparing types within the larvae, juvenile and adults of the same species at each location."

What was learned
The three researchers report that (1) "Symbiodinium clearly reside in the sediments of shallow reef communities and are capable of initiating symbiosis with aposymbiotic coral larvae," and that (2) "the larvae of many species of corals are promiscuous, associating with multiple Symbiodinium types independent of coral species or location." As for what these findings imply ...

What it means
... Cumbo et al. say they suggest that "as sea surface temperatures rise, the promiscuity of larvae could benefit corals by allowing them to acquire symbionts with the greatest heat tolerance in each new generation (LaJeunesse et al., 2004; Baird et al., 2007)." In addition, while they say that "this mechanism of acclimatization will most likely be restricted to species that show horizontal transmission of symbionts," they remark that such species account for approximately 85% of all species.

Baird, A.H., Cumbo, V.R., Leggat, W., Rodriguez-Lanetty, M. 2007. Fidelity and flexibility in coral symbioses. Marine Ecology Progress Series 347: 307-309.

LaJeunesse, T.C., Bhagooli, R., Hidaka, M., DeVantier, L., Done, T., Schmidt, G.W., Fitt, W.K. and Hoegh-Guldberg, O. 2004. Closely related Symbiodinium spp. differ in relative dominance in coral reef host communities across environmental, latitudinal and biogeographic gradients. Marine Ecology Progress Series 284: 147-161.

Reviewed 28 August 2013