Chapter

Competition Among Sessile Organisms on Coral Reefs

DOI: 10.1007/978-94-007-0114-4_20 In book: Coral Reefs: An Ecosystem in Transition, pp.347-371

ABSTRACT

Competition among sessile organisms is a major process on coral reefs, and is becoming more important as anthropogenic disturbances
cause shifts in dominance to non-reef builders such as macroalgae, soft corals, ascidians, and corallimorpharians. Long-term
monitoring and field experiments have demonstrated that competition for limited space can exert major impacts on reef biodiversity
and community composition across habitats and regions. Recent experiments also reveal increasingly important roles of allelopathic
chemicals and the alteration of associated microbes in shaping competitive outcomes among benthic space occupiers. Competition
impacts the recruitment, growth, and mortality of sessile reef organisms and alters their population dynamics. Co-settlement
and aggregation of conspecific coral colonies may lead to intense intraspecific competition, including chimera formation and
potential somatic and germ cell parasitism. The complexity of competitive outcomes and their alteration by a wide variety
of factors, including irradiance, water motion, and nutrient levels, results in mostly circular networks of interaction, often
enhancing species diversity on coral reefs. Competition is a model process for revealing impacts of human activities on coral
reefs, and will become increasingly important as alternate dominants gain space at the expense of reef-building corals.

KeywordsInterference competition-exploitation competition-competition-cnidarian-macroalgae-cyanobacteria-scleractinian-corallimorpharian-actinarian-sea anemone-ascidian-zoanthid-fungiid-hydrocoral-octocoral-soft coral-stony coral-coral-sponge-climate change-chimera-growth-mortality-reproduction-competitive network-coral–algal interaction-phase shift-feedback loop-model-allelopathy-herbivory-recruitment-antibiotic-microorganism-bacteria-abrasion-palytoxin-bleaching-disease-natural products-nematocyst-mucus-diversity-community structure-aggression-population-alternate dominant

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    • "The model also includes three groups of algae: (a) cropped turf algae, a functional group of algae that undertake weak competitive interactions and facilitate the growth and recruitment of other benthic species (Box and Mumby 2007; González-Rivero et al. 2012; Mumby 1999); (b) seasonally constrained macroalgae, a group of upright fleshy algae represented by the genus Dictyota that exhibit seasonal mortality in winter (Ferrari et al. 2012b; Renken et al. 2010) and dominate the macroalgal composition at Glover's Atoll (Online Resource 1); and (c) Lobo‑ phora variegata, a common competitor with corals and sponges (Box and Mumby 2007; González-Rivero et al. 2012), and the second most dominant species at Glover's Atoll (Online Resource 1). Both groups of macroalgae have been reported to be major competitors of corals and sponges (Chadwick and Morrow 2011; González-Rivero et al. 2012). Lastly, the model incorporates the dominant bioeroding sponge C. tenuis. "
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    ABSTRACT: Disturbance releases space and allows the growth of opportunistic species, excluded by the old stands, with a potential to alter community dynamics. In coral reefs, abundances of fast-growing, and disturbance-tolerant sponges are expected to increase and dominate as space becomes available following acute coral mortality events. Yet, an increase in abundance of these opportunistic species has been reported in only a few studies, suggesting certain mechanisms may be acting to regulate sponge populations. To gain insights into mechanisms of population control, we simulated the dynamics of the common reef-excavating sponge Cliona tenuis in the Caribbean using an individual-based model. An orthogonal hypothesis testing approach was used, where four candidate mechanisms—algal competition, stock-recruitment limitation, whole and partial mortality—were incorporated sequentially into the model and the results were tested against independent field observations taken over a decade in Belize, Central America. We found that releasing space after coral mortality can promote C. tenuis outbreaks, but such outbreaks can be curtailed by macroalgal competition. The asymmetrical competitive superiority of macroalgae, given by their capacity to pre-empt space and outcompete with the sponge in a size-dependant fashion, supports their capacity to steal the opportunity from other opportunists. While multiple system stages can be expected in coral reefs following intense perturbation macroalgae may prevent the growth of other space-occupiers, such as bioeroding sponges, under low grazing pressure.
    Full-text · Article · Jan 2016 · Oecologia
    • "The latter are dominated by the spaghetti sponge Callyspongia samarensis (Wilson, 19 25), w hos e l oo sely arra nge d br anch es m a y successfully compete for space with corals by means of overshadowing (Fig. 1a). More importantly, it might also potentially hinder the settlement and survival of coral recruits as some sponges have been observed to be aggressive towards adult corals (Chadwick and Morrow 2011). "

    No preview · Article · Oct 2015 · Marine Biodiversity
    • "The acquisition of a suitable substratum is necessary for proper development and growth of the sessile organisms such as sponges and corals (Wulff, 2006a, b; Chadwick & Morrow, 2011). The interacting organisms adopt various offensive and defensive strategies to obtain a suitable substratum and protect the acquired space from other encroaching neighbours (Chadwick & Morrow, 2011). The sponge maintains its living space either by overgrowing (especially in case of encrusting sponges) and/or by producing toxic chemicals (allelochemicals ) (Wulff, 2006b). "
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    ABSTRACT: Abstract Availability of suitable substratum is often a limiting factor for sessile organisms. We studied growth and regeneration of golf ball sponge Cinachyrella cf. cavernosa with and without its aggressive neighbour, soft coral (Zoanthus sansibaricus) in rocky intertidal area of Anjuna (Goa), India to understand impact of spatial competition on these life-history processes. Specific growth rate of C. cf. cavernosa ranged from 3.38 ± 0.47 to 24.57 ± 1.99% year−1. A wound-healing experiment demonstrated 50–100 times faster regeneration, compared to their average growth rate. Both growth and regeneration decreased as sponge size increased. The sponges exhibited 36–69% higher growth and 30–76% faster regeneration rate in the absence of the competitor species, Z. sansibaricus. The protein synthesis ability (RNA to DNA ratio), which is an index for physiological activity was adversely affected by sponge size and competitor abundance. Results suggest that in a space-limited region, the presence of an aggressive neighbour acts as one of the crucial factors affecting the primary functions (such as growth and regeneration) of the sponge. This study also highlights the remarkable regenerative ability of the slow growing sponge C. cf. cavernosa which aids in maintaining its abundance under stressful conditions of rocky intertidal region.
    No preview · Article · Oct 2015 · Hydrobiologia
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