How does rising atmospheric CO2 affect marine organisms?

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It Lives! Return of the Giant Kelp
Ladah, L.B., Zertuche-Gonzalez, J.A. and Hernandez-Carmona, G.  1999.  Giant kelp (Macrocystis pyrifera, Phaeophyceae) recruitment near its southern limit in Baja California after mass disappearance during ENSO 1997-1998. Journal of Phycology 35: 1106-1112.

What was done
During the El Niņo event of 1997-1998, density and population structure of giant kelp "forests" - located near Bahia Tortugas, Baja California, Mexico - were evaluated quarterly from January 1997 to September 1998 via diving surveys, while aerial surveys were conducted along most of the Baja California coast.

What was learned
From August 1997 to January 1998, sea surface temperature anomalies in Bahia Tortugas were greater than +3°C compared to the previous 10-year average; and from the fall of 1997 to the spring of 1998, not a single giant kelp could be found where extensive forests of these plants had lived previously.  "Unexpectedly," however, according to the authors, "plants were found in Bahia Tortugas again in July 1998, in spite of the widespread disappearance of the species less than a year earlier," which was presumably caused by the record-breaking sea surface temperatures.

What it means
From evidence derived from population structure data and the rapidity with which the giant kelp plants reestablished themselves nearly everywhere they had been before, the authors suggest that "a microscopic stage that was not visible during dive surveys survived the stressful conditions of ENSO and caused the recruitment event, supporting the hypothesis that a bank of microscopic forms can survive conditions stressful to macroscopic algae."  Indeed, they state there is independent evidence to suggest that "microscopic stages may subsist in nature under low light intensities in a semi-dormant state until conditions become favorable."

It is interesting to note that this is the second type of "unexpected" recovery of marine biota from the unusually high water temperatures that occurred during the 1997-1998 El Niņo event - the other being the coral reef recovery discussed in our editorial Back from the Dead: Coral Recovery Signals Resiliency of Reef Ecosystems - and since tiny algae likely played a major role in both events, we wonder if there might not be a common denominator that may explain both of these biological "resurrections."  Something is clearly responsible; for in both cases the unexpected did indeed happen.  Hence, it would seem only logical that this question serve as a point of departure for future research.  The more we can learn about these mysterious happenings, the better foundation we will have for assessing the implications of potential global change.  As things stand now, pessimism based on ignorance is fueling the fires of irrationality, leading to calls for draconian actions to combat speculative consequences of phenomena of unproven reality.

Reviewed 6 September 2000