Graduate Thesis Or Dissertation
 

Early succession in beds of the red alga, Iridaea cornucopiae Post. & Rupr. (Gigartinaceae) : alternate pathways

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  • Multiple successional sequences have been observed following disturbance in communities on marine hard substrata. Observations of the turf-forming alga, Iridaea cornucopiae Post. & Rupr. (Gigartinaceae), suggest that I. cornucopiae may assume its dominance by its ability to vegetatively pre-empt space. High limpet densities in the natural community, suggest that I. cornucopiae may be a grazer-resistant and, perhaps, grazer-dependent alga. Succession would be expected to take different trajectories if conditions affecting vegetative recovery or levels of herbivory were varied. Observational and experimental studies indicate that established beds of I. cornucopiae resist both invasion by ephemeral algae (in the presence of limpet grazers) and physical disturbances. The community can rapidly adjust, by vegetative regeneration of dominant perennial algae, to disturbances which remove only the canopy. Recovery from disturbances which remove perennating structures, however, is slow. Effects of herbivores and season of initial disturbance on primary succession were experimentally investigated, using copper paint barriers for limpet exclosures. Effects of copper paint on subsequent colonization were quantified for the first time. Most groups of organisms were not affected by the presence of the paint. Densities of barnacles and limpets were reduced, while abundances of some early successional algae were enhanced (possibly due to reduced limpet densities). Removal of limpets resulted in qualitatively different early successional pathways. In the presence of limpets, the successional pathway was characterized by high levels of free space and persistence of perennial algae. In the absence of limpets, the early successional assemblages were dominated by ephemeral algae. Season of initial disturbance affected successional trajectories mainly because of seasonal patterns in the establishment of perennial algae. Different species of ephemeral algae were able to recruit in both seasons of disturbance tested (fall and spring), but perennial algal establishment was highly seasonal. The removal of ephemeral species by grazers may be a necessary condition for early establishment of perennial algae, but it clearly is not sufficient. Space made available by grazers during physiologically stressful periods may be effectively unavailable for colonization by perennial algae.
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