Orcutt, Karen M. ¹, and Kjell Gundersen²

¹Darling Marine Center, 193 Clark’s Cove Rd, Walpole, ME 04573, USA, Tel: 207-563-3146, Fax: 207-563-3119, E-mail: Karen.Orcutt@maine.edu and ²Bigelow Laboratory for Ocean Sciences, McKown Point Road, PO Box 475, West Boothbay Harbor, ME 04575, USA

Seasonal patterns and spatial distribution of Trichodesmium spp. at the Bermuda Atlantic Time-series Study (BATS) site

Seasonal patterns of Trichodesmium colony and species distribution were investigated over three year period at the BATS site. Colony abundance estimates using surface net tows showed a strong seasonal pattern with maximum peak abundance in late summer each year. The magnitude of the annual peak abundance appeared to be regulated by sea surface temperature, the strength of the seasonal thermocline and apparent wind speed in the area. A peak of Trichodesmium trichomes was found at the base of the euphotic zone in August 1996 at BATS and preceded a maximal colony abundance peak in surface waters two months later. This peak in trichome abundance coincided with a deepening of the phosphocline relative to the nitracline. We observed an inverse relationship between colony abundance and free trichomes suggesting that Trichodesmium grows as filamentous trichomes at depth providing a seed population for the colonies aggregating in surface waters. Data from the literature and the two transect studies reported here, shows that colony abundance estimates of Trichodesmium are predominantly higher off the SE coast of the USA, in the central Sargasso Sea gyre and in the Caribbean Sea than at the BATS site. This study concurs with recent literature emphasizing the importance of the diazotroph Trichodesmium spp. in new production in the world’s tropical and sub-tropical oceans.