ABSTRACT
Mid-latitude marine macroalgae are exposed to a number of environmental stress factors in their habitat mainly on temperate rocky shores. Pulse amplitude modulation (PAM) fluorometers have been used and in the water to determine the effects of environmental stress parameters on photosynthesis at mid-latitudes. Most PAM measurements on algae were made by exposing the thalli at the surface, on a research vessel or on the beach. Many phytoplankton (including cyanobacteria) and macroalgae are capable of synthesizing ultraviolet (UV)-absorbing pigments which protect them from damaging solar radiation. Scytonemin is restricted to some cyanobacteria. In addition to attenuating solar UV, scytonemin has been shown to have the capability of scavenging oxygen radicals. Cyanobacteria, eukaryotic phytoplankton and macroalgae use mycosporine-like amino acids as absorbers for ultraviolet radiation. Even though many macroalgae are adapted to wide thermal windows they may be endangered in extreme habitats, such as cold-water algae or reef algae for which the water temperatures exceed their limits.
