An illustrated marine flora of the Pelican Cays, Belize

-The Pelican Cays, Belize, Central America, represent a benign and biologically diverse environment dominated by sessile photosynthetic and filter-feeding populations. Most are delicate and particularly susceptible to physical damage and eutrophication. Pelican Cays has a rich marine flora, totaling 190 taxa, with 86 Rhodophyta (red algae), 23 Phaeophyta (brown algae), 72 Chlorophyta (green algae), 5 Cyanophyta (blue-green algae) and 4 Magnoliophyta (flowering plants). Each species description includes the author citation, original reference, basionym and synonyms when appropriate. The detailed descriptions are accompanied by line drawings of anatomical and morphological features to aid in identification. Distributions are listed for the Caribbean Basin, along with the habitat where each taxon is typically found, and 73 new seaweed records are added for Belize. The cause of the exceptionally high biodiversity in such a small area is the unusual convergence of complex mangrove, coral, seagrass and algal biomes under stable oligotrophic conditions. Nearly one-fourth of the macrophyte flora are rare or uncommon species. The long-lived coarse, leathery and calcareous form groups dominate with 67% of the taxa, indicative of constant, low-nutrient conditions. Few of the ephemeral filamentous and sheet-like green algae that predominate under elevated nutrient regimes are present. The preponderance of long-lived red algal taxa (86 of 190 total macrophyte taxa) is a further indication of a relatively pristine environment. Botanical survey and inventory information on the spectacular Pelican Cays ecosystem is provided in the hope of contributing toward a timely conservation plan and responsible management of the resource. The atoll-like Pelican Cays, located in the Central Province of the Belize Barrier Reef (Maps 1-3), comprise a pristine, low-energy, mangrove-island ecosystem dominated by sessile photosynthetic and filter-feeding populations. Most are morphologically delicate and vulnerable to damage from boat wakes, physical disturbance and sedimentation, as well as natural (Lapointe et al. 1993) and anthropogenic (Littler et al. 1993) eutrophication. The predominant algal form groups (67% of taxa are coarsely-branched thickleathery or calcareous forms) indicate constant, low-nutrient conditions with a paucity of the filamentous and sheet-like green algal forms that characterize nearby eutrophic mangrove cays (e.g., Man-of-War Cay, Channel Cay, Douglas Cay). The macrophyte biodiversity of the Pelican Cays area (190 taxa) is greater than any comparable system studied in the Caribbean. In comparison, the treatment "Marine Plants of the Caribbean and Adjacent Seas" (Littler et al. 1989) contained only 209 taxa obtained over an8-year period. In the past, we have recorded rich floras of important undocumented macrophytes in Belizean mangrove systems such as Twin Cays (Littler et al. 1985) and Tobacco Range (Littler et al. 1995). However, the Pelican Cays' macrophytic diversity far exceeds that of Twin Cays and Tobacco Range combined. The cause of this unusually high marine plant biodiversity in such a small geographic area is the unique juxtaposition of mangrove, coral, seagrass and algal biomes under stable oligotrophic conditions (e.g., indicated by consistently "ginclear" waters). The preponderance of longlived red algal taxa (86 out of 190 total macrophyte taxa) is a further indication of a relatively benign, pristine environment (Littler et al. 1987). 2 BULLETIN OF THE BIOLOGICAL SOCIETY OF WASHINGTON