Consequences of solar radiation on bacterial secondary production and growth rates in subtropical coastal water (Atlantic Coral Reef off Belize, Central America)

Abstract

This study reports the effects of natural solar radiation on production and growth rates of bacterial assemblages in coastal surface water of the Atlantic Barrier Coral Reef off Belize, Central America. Bacterial production rates measured in the late afternoon were significantly lower than rates measured in the morning. There were also significant differences in the specific growth rates of bacterial assemblages between water samples: bacteria grew faster, i.e. displayed shorter doubling times, in the early morning. Bioassay experiments showed a significant increase in rates of bacterial secondary production in water samples exposed in situ to ambient solar radiation at the water surface. There was also a pronounced increase in the growth rates and cell volumes of bacteria grown in sunlight-irradiated water samples. We suggest that enhanced metabolism of bacteria grown in water samples that were previously exposed to solar radiation was due mainly to photodegradation of dissolved organic matter and subsequent enrichment of water with easily utilizable substrates. The results of these studies indicate that solar radiation can directly alter bacterial production and growth over diel cycles in subtropical waters. These physico-chemical and biological interactions between solar radiation and heterotrophic bacteria in subtropical coastal water may have important biogeochemical implications at both the ecosystem and global levels.