A COMPARATIVE STUDY OF TEMPERATURE RESPONSES OF CARIBBEAN SEAWEEDS FROM DIFFERENT BIOGEOGRAPHIC GROUPS¹

Abstract

Temperature tolerances were determined for Caribbean isolates (total 31) of seaureds belonging to three distributional groups: 1) species confined to the tropical western Atlantic (Botryocladia spinulifera, Chamaedoris peniculum, Cladophoropsis sundanensis, Dictyopteris justii, Dictyurus occidentalis, Haloplegma duperreyi, and Heterosiphonia gibbesii); 2) amphi‐Atlantic species with a (sub)tropical distribution that have their northern boundary in the eastern Atlantic at the tropical Cape Verde Islands (Bryothamnion triquetrum and Ceramium nitens) or the subtropical Canary Islands (Ceratodictyon intricatum, Coelothrix irregularis, Dictyopteris delicatula, Ernodesmis verticillata, and Lophocladia trichoclados; and 3) species with an am‐phi‐Atlantic tropical to warm‐temperate distribution also occurring in the Mediterranean (Cladophoropsis membranacea, Digenea simplex, Microdictyon boergesenii, and Wurdemannia miniata). For some isolates, growth response curves and temperature requirements for reproduction were also determined. Growth occurred in the range (18)20–30° C with optimum growth rates at 25°–30°C, irrespective of distribution group. Reproduction generally occurred at (20)25°–30° C although there were some exceptions. Species were extremely stenothermal, with those restricted to the western Atlantic surviving a total range of only 10/13° C (between 18/20° and 30/33° C). Tolerance to high temperatures was correlated with vertical position in the iniertidal/subtidal zone rather than biogeography grouping. Species restricted to the subtidal were the least tolerant, with permanent survival at 30° C but not at 33°C. Tolerance to low temperatures was not different in subtidal and intertidal species but was significantly better in am phi‐Atlantic than in western Atlantic species. In the former group, damage occurred at 15°–18° C but in the latter group at 18°‐20° C. We propose that these differences in low‐temperature tolerances in Caribbean populations of species from different distribution groups reflect adaptations to glacial cold‐stress in the tropical eastern Atlantic and subsequent trans‐Atlantic dispersal.

Temperature responses of tropical to warm-temperate Atlantic seaweeds. I. Absence of ecotypic differentiation in amphi-Atlantic tropical-Canary Islands species

“…In the north-and south-western Atlantic, the geographical distribution is probably delimited by low lethal (I8-20°C) winter temperatures, as summer temperatures at the distribution boundaries (24-28°C) are high enough for sufficient growth (Pakker et al, 1995). The nature of Lophodadia trichoctados.…”

“…The regression equation was used to find approximate tolerance limits (in °C) from the tolerance index of each isolate. In the calculations no distinction was made between the criteria 'severely damaged' and 'dead', because most cladophoralean species could regenerate from tiny plasma fragments at temperatures more than 10°C below those at which severe damage starts to occur (Pakker et al, 1995). We do not believe that marginal survival capacities at these low temperatures have a biogeographical meaning because in the field these severely damaged plants will not be able to regenerate due to factors such as grazing and competition, which are absent in culture experiments.…”

“…General methods and equipment used in tolerance experiments are described by Pakker et al (1995) Taylor (1928Taylor ( , 1960, Cheney & Dyer (i974), Richardson (1975), Oliveira Filho (1977, Cordeiro-Marino (i978), van den Hoek et al (1978), Price & John (1979), Norris & Bucher (1982), Hanisak & Blair (1988), Schneider & Searles (199I), Falcao et al (1992); eastern Atlantic, Levring (I974), Lawson & John (1977), Gil-Rodriguez & Afonso-Carrillo (I980), Price & John (1980), Lawson & John (1982), Audiffred & Weisscher (1984), Audiffred & Prud'homme van Reine (1985), Price et al (i986, 1988) Three plants were incubated in a 200 ml Erlenmeyer flask, containing IS0ml of medium, and placed in culture cabinets (i0"2°C) at 5, 8, 10, 12, 15, 18, and 20°C. Plants were transferred to the experimental low temperatures in steps of no more than 3°C per 3 days. After 2, 4 and 8 weeks one plant was removed and gradually brought back to the optimal growth temperature.…”

Life on the boundary: Environmental factors as drivers of habitat distribution in the littoral zone

“…Temperature has long been recognized as a key factor governing seaweed biogeography (e.g. Stephenson, 1944;Lewis, 1964;Lünning, 1984;Pakker et Anderson et al, 2012;Wernberg et al, 2013) and reproduction (Lüning, 1990;Ballesteros, 1991) and since it varies with latitude (Mieszkowska et al, 2006;Martínez et al 2012), it is often responsible for the distribution of northern/southern geographic boundaries of seaweeds (Breeman, 1988). Some mediolittoral habitats show a strong relationship with the seawater mean temperature gradient (17º-18.6º) from northern to southern Catalan waters.…”

How different is Mediterranean Caulerpa taxifolia (Caulerpales: Chlorophyta) to other populations of the species?

“…Strictly tropical macroalgal species are stenothermal, having a lower temperature tolerance limit of 18 to 20°C, which corresponds to the 20°C winter seawater isotherm (Pakker et al 1995(Pakker et al , 1996. This isotherm occurs on the Australian east coast near 23°S latitude (Middleton 1995), approximately 550 km north of Southport, the pre-2000 southern distribution limit of Caulerpa taxifolia on this coast.…”