Abundance and Photosynthetic Characteristics of Trichodesmium spp. Along the Atlantic Barrier Reef at Carrie Bow Cay, Belize

Abstract

Abstract. Trichodesmium abundance and photosynthetic rates were determined across a transect of the Atlantic Barrier Reef at Carrie Bow Cay, Belize in May 1993 and May‐June 1994. A fore reef station receiving oceanic water had a Trichodesmium abundance characteristic of the open Caribbean Sea (≤ 102 colonies m‐3 and 104‐‐105 trichomes m‐3). Several species were present; however, in all cases a sharp decrease in abundance occurred across the reef to the coastal lagoon. At this latter site, virtually no Trichodesmium was present, although a substantial bloom of the diatom Proboscia alata occurred in 1994.Maximum photosynthetic rates and the initial light‐limited slope a were significantly lower in offshore stations than in reef top populations. The increased photosynthetic rates and light‐harvesting ability in reef‐top populations, as well as the lack of significant photoinhibition, indicated that the Trichodesmium abundance decrease was probably not due to a decline in photosynthetic capacity. Grazing and physical removal rather than a physiological decline were likely mechanisms operating to reduce Trichodesmium abundance in these regions. These data suggest that the Belizean barrier reef is a sink for Trichodesmium transported in from offshore regions.