Disturbance and organization of macroalgal assemblages in the Northwest Atlantic

Abstract

Large seaweeds are often structurally dominant in subtidal and intertidal rocky shore benthic communities of the N.W. Atlantic. The mechanisms by which these algal assemblages are maintained are surprisingly different in the two habitats. In the subtidal community, kelps are dominant space competitors in the absence of strong grazing interactions. In contrast, the large perennial seaweeds of intertidal zones (fucoids and Chondrus crispus) are competitively inferior to both sessile filter feeders and ephemeral, pioneer algal species. Intertidal seaweed beds are maintained by carnivory of whelks, which reduces filter feeder populations, and by herbivorous periwinkles which reduce ephemeral algal populations. Through most of the intertidal zone, disturbance, both biological and physical, dictates which species shall compete and equilibrium conditions obtain subsequently.The roles of subtidal consumers are quite different. Sea urchins are the major algal herbivores and these voracious animals maintain an equilibrium state in which large tracts of subtidal coralline pavement are kept free of kelp forests. Urchins do not seem to play a successional facilitative role for kelps in the way that periwinkles do for fucoids in the intertidal. Control of herbivore populations is thus a key to the maintenance of subtidal foliose algal beds. It is clear that parasitic amoebas can decimate sea urchin populations so that kelp forest dominance is assured. However, the importance of carnivory in limiting urchins in the subtidal community is unclear in the absence of appropriate manipulation experiments. It is possible that carnivorous decapods and fin fish control sea urchin populations and hence foliose algal abundance, but this must remain speculative. The seaweed-dominated state of the subtidal system is an alternative equilibrium condition to the urchin/coralline alga configuration. The structure of the kelp beds is relatively uniform in responding to frequent small-scale, infrequent large-scale, or no, disturbance.

Ecology of marine algae on rocky shores and subtidal reefs in temperate Australia

“…Overall, we need to recognize that algal assemblages in Australian marine habitats provide a unique opportunity to evaluate the paradigms emerging from temperate systems elsewhere (e.g. Chapman & Johnson, 1990;Santelices, 1990;Schiel & Foster, 1986).…”

“…These were first to provide some geographic comparisons from one part of Australia to another, which might have provided insights into the generality of patterns and processes. Second, we believed that comparison of Australian algal assemblages with those in other temperate regions of the world would provide tests of some of the generalizations that have emerged elsewhere (see Underwood & Denley, 1984;Chapman & Johnson, 1990;Foster, 1990).…”

Addition of species abundance and performance predicts community primary production of macroalgae

“…Subtidal assemblages of benthic macroalgae vary substantially in time and space due to physical disturbance (Dayton and Tegner 1984;Airoldi and Cinelli 1997;Mumby et al 2005), grazing Chapman and Johnson 1990;Gagnon et al 2005), and competition for light and space (Reed and Foster 1984;Santelices and Ojeda 1984). To better understand the patterns and controls of primary production by macroalgae and their ecological consequences, we developed a simple physiologically based model of benthic macroalgal production using three components: (1) taxon-specific foliar standing crop, (2) bottom irradiance, and (3) taxon-specific macroalgal photosynthesis versus irradiance (P vs. E) parameters.…”

Exposure-driven macroalgal phase shift following catastrophic disturbance on coral reefs

“…A broad range of factors can influence succession and recovery of terrestrial and marine ecosystems following disturbance, such as competition (Dayton 1971), herbivory (Chapman and Johnson 1990), recurrent disturbance events (Connell et al 1997), and environmental stress (Menge and Sutherland 1987). Favourable environmental conditions can modulate patterns of recovery by increasing Liagora cover (%) Fig.…”