Macroalgae in Tropical Marine Coastal Systems - Seaweed Biology - page 320

tropical coastal areas, macroalgae are essential to the productivity, structure, and
function of each of these communities. Throughout this chapter, the role of
macroalgae in regime shifts from systems dominated by the aforementioned habitat
providers to ones dominated by algae as well as the factors that bring about these
changes will be discussed.
16.2 Abiotic Conditions
Compared to the extreme seasonal changes in temperate regions, the variability of
abiotic conditions in the tropical zone is limited, aside from the influence of the
rainy season which can reduce salinity, increase water velocity, and decrease PAR.
16.2.1 Temperature
Three types of physiological responses to temperatures determine a species' bio-
geographical boundaries (Breeman 1988 ): growth, reproduction, and mortality
(see Chap. 3 by Eggert). Pakker et al. ( 1995 ) suggested that tropical macroalgae are
the most stenothermal macroalgae of any biogeographical region; their growth gener-
ally reaching a peak between 25 and 30 C, with those restricted to the tropical western
Atlantic surviving a total variation of only 10/13 C. In comparison, macroalgae from
colder regions are tolerant of a much wider range of temperatures (see Chap. 3 by
Eggert and Chap. 18 by Bartsch et al.). Macroalgae of the tropical to warm-temperate
Eastern Atlantic Ocean andMediterranean Sea show the same temperature limitations
as those of the Western tropical Atlantic Ocean and Caribbean Sea. Unsurprisingly,
species restricted to the subtidal regions, and thus rarely exposed to extreme variations
in abiotic conditions, are least tolerant of high temperatures, generally succumbing to
temperatures exceeding 33 C. Furthermore, both subtidal and intertidal species
appear to be limited by temperatures lower than 18/20 C.
16.2.2 Nutrients
Seawater in tropical regions is generally low in nutrients due to strong stratification
of the water column that prevents vertical mixing of nutrients. Tropical marine
habitats that are not exposed to terrestrial effluents are particularly nutrient poor,
thereby preventing the proliferation of phytoplankton and macroalgae and increas-
ing the light availability for benthic organisms. Occasionally nutrients become
temporarily available through terrestrial runoff during the rainy season or upwelling
events, encouraging strong seasonal responses (see also Chap. 21 by Teichberg
et al.). After several decades of scientific research it has become clear that nutrients