The story correlates red tides in Florida with Saharan dust storms. The cover story of the same issue (“Dust, the thermostat,” p. 200: Dust, the Thermostat) dealt, in part, with dust blowing across the Mediterranean Sea and the Atlantic Ocean. Are there “red tides” in these areas? Are they correlated with Saharan dust? David D. Jones
St. Paul, Minn.

The reason the red tides correlated with algal blooms in Florida is that they oversupplied a nutrient–iron–at a critical time. Elsewhere, the extra iron might not be needed or might arrive at times when the appropriate bacteria are not present. So, effects can be very specific to time and geography.–J. Raloff