A COMPARATIVE-STUDY OF TEMPERATURE RESPONSES OF CARIBBEAN SEAWEEDS FROM DIFFERENT BIOGEOGRAPHIC GROUPS

Temperature tolerances were determined for Caribbean isolates (total 3 1) of seaweeds belonging to three distributional groups: 1) species co nfined to the tropical western Atlantic (Botryocladia spinulifera, Cha maedoris peniculum, Cladophoropsis sundanensis, Dictyopteris justii, D ictyurus occidentalis, Haloplegma duperreyi, and Heterosiphonia gibbes ii); 2) amphi-Atlantic species with a (sub)tropical distribution that have their northern boundary in the eastern Atlantic at the tropical C ape Verde Islands (Bryothamnion triquetrum and Ceramium nitens) or the subtropical Canary Islands (Ceratodictyon intricatum, Coelothrix irre gularis, Dictyopteris delicatula, Ernodesmis verticillata, and Lophocl adia trichoclados; and 3 species with an amphi-Atlantic tropical to wa rm-temperate distribution also occurring in the Mediterranean (Cladoph oropsis membranacea, Digenea simplex, Microdictyon boergesenii, and Wu rdemannia miniata). For some isolates, growth response curves and temp erature requirements for reproduction were also determined. Growth occ urred in the range (18)20 degrees-30 degrees C with optimum growth rat es at 25 degrees-30 degrees C, irrespective of distribution group. Rep roduction generally occurred at (20)25 degrees-30 degrees C although t here were some exceptions. Species were extremely stenothermal, with t hose restricted to the western Atlantic surviving a total range of onl y 10 / 13 degrees C (between 18 / 20 degrees and 30 / 33 degrees C). T olerance to high temperatures was correlated with vertical position in the intertidal/subtidal zone rather than biogeographic grouping. Spec ies restricted to the subtidal were the beast tolerant, with permanent survival at 30 degrees C but not at 33 degrees C. Tolerance to low te mperatures was not different in subtidal and intertidal species but wa s significantly better in amphi-Atlantic than in western Atlantic spec ies. In the former group, damage occurred at 15 degrees-18 degrees C b ut in the latter group at 18 degrees-20 degrees C. We propose that the se differences in low-temperature tolerances in Caribbean populations of species from different distribution groups reflect adaptations to g lacial cold-stress in the tropical eastern Atlantic and subsequent tra ns-Atlantic dispersal.