Trichodesmium. single-celled phytoplankton Trichodesmium, Sea Sawdust , Black Water Dive 6-20-15 with Pura Vida Divers on the Siren out of Riviera Beach, over 400' depth Gulfstream current,Species of the single-celled phytoplankton Trichodesmium form colonies with distinctive shapes. Individual colonies, shown here, are visible to the naked eye; where currents and winds gather many colonies together, the aggregation