C. Edward Proffitt

Postglacial expansion pathways of red mangrove, Rhizophora mangle, in the Caribbean Basin and Florida

PREMISE OF THE STUDYnThe Last Glacial Maximum (LGM) was a period of massive range contraction. Post-LGM, water-dispersed coastal species, including the red mangrove (Rhizophora mangle), expanded poleward as propagules were transported by ocean currents. We assessed postglacial marine expansion pathways for R. mangle within the Caribbean Basin and Florida.nnnMETHODSnSix microsatellite loci were used to genotype 237 individuals from nine R. mangle populations in the Caribbean, Florida, and Northwest Africa. We evaluated genetic variation, population structure, gene flow along alternative post-LGM expansion pathways to Florida, and potential long-distance dispersal (LDD) from West Africa to Caribbean islands.nnnKEY RESULTSnThese R. mangle populations had substantial genetic structure (FST = 0.37, P < 0.0001) with three discrete population clusters (Caribbean mainland, Caribbean islands, and Florida). Genetic connectivity along the mainland pathway (Caribbean mainland to Florida) vs. limited gene dispersal along the Antilles Island pathway (Caribbean islands to Florida) supported Florida recolonization from Caribbean mainland sources. Genetic similarity of Northwest Africa and two Caribbean islands provided evidence for trans-Atlantic LDD. We did not find a pattern of decreasing genetic diversity with latitude.nnnCONCLUSIONSnWe outline a complex expansion history for R. mangle, with discrete pathways of recolonization for Florida and Caribbean islands. Contrary to expectation, connectivity to putative Caribbean mainland refugial populations via ocean currents, and not latitude, appears to dictate genetic diversity within Caribbean island and Florida R. mangle. These findings provide a framework for further investigation of additional water-dispersed neotropical species, and insights for management initiatives.

Effects of Lyngbya majuscula blooms on the seagrass Halodule wrightii and resident invertebrates

Cyanobacterial blooms have been increasing worldwide due to increased nutrients associated with urban, industrial, and agricultural development. Blooms that occur in the Indian River Lagoon (IRL), Florida may be increased by nutrient-laden runoff from storm water and non-point sewage pollution due to alterations to the watershed. In the IRL, during the summer of 2006, extensive blooms of the marine cyanobacterium, Lyngbya majuscula, were observed forming mats throughout beds of the seagrass Halodule wrightii in Fort Pierce, Florida. The effects of cyanobacterial blooms were compared to artificial shading of H. wrightii to assess the shading potential of L. majuscula. The combined effects of L. majuscula removal and artificial shading showed increases in the below ground biomass of H. wrightii. However, leaf length increased in the presence of L. majuscula. In response to artificial shading, H. wrightii decreased in density, but showed similar leaf elongation. A common bivalve in our study area, Macoma constricta, increased in density when L. majuscula was removed. Therefore, when L. majuscula blooms occur, light limitation is one of the mechanisms altering H. wrightii density and leaf lengths in the IRL. Loss of H. wrightii biomass due to shading from cyanobacterial mats may further damage the diversity and habitat value of the IRL.