Chapter

Competition Among Sessile Organisms on Coral Reefs

DOI: 10.1007/978-94-007-0114-4_20

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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    • "Although sponges are an important component of coral reef biodiversity , and together with stony and soft corals form complex three-dimensional structures that provide shelter to numerous marine organisms, they are also very successful competitors for space on reefs, at the expense of corals (Aerts & van Soest, 1997; de Voogd et al., 2004; Wulff, 2012). Generally, sponges have a competitive advantage over corals because they can successfully resist coral defences and persevere in environments that are unfavourable to corals (Chadwick & Morrow, 2011). Additionally, the sponge T. hoshinota can actively kill and overgrow live coral tissue. "
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    ABSTRACT: The cyanobacteriosponge Terpios hoshinota is expanding its range across the Indo-Pacific. This species can have massive outbreaks on coral reefs, actively kill corals it overgrows and affect the entire benthic community. Although it has received much attention on the post-outbreak follow-up, little is known about its ecology, habitat preferences, and the possible environmental triggers that cause its outbreaks. We present a baseline study in the Spermonde Archipelago, Indonesia, where T. hoshinota was first observed in 2012. We surveyed 27 reefs and recorded patches between 14 and 217 cm 2 , at four reef sites (~15% cover). The sponge was found on both mid-shelf and outer shelf reefs but not close to the coast and the city of Makassar. Differences in benthic community structure, as well as spatial variables relating to the on-to-offshore gradient in the Spermonde archipelago, neither constrained nor promoted its expansion. Patches of the sponge were mostly overgrowing branching corals, belonging to Acroporidae species. Genetic variation within T. hoshinota was studied by sequencing partitions of the mitochondrial CO1 and nuclear ribosomal 28S gene. Two haplotypes were found within the Spermonde archipelago, which differed from the CO1 sequence in GenBank. The present study provides an indication of habitat preferences of T. hoshinota in non-outbreak conditions, although it is still unclear which environmental conditions may lead to the onset of its outbreaks.
    Journal of the Marine Biological Association of the UK 05/2015; DOI:10.1017/S002531541500034X · 1.13 Impact Factor
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    • "A further bottleneck may occur if settled coral larvae do not survive to the juvenile stage. For example, high macrobenthic cover may lead to intense competition for space (Chadwick and Morrow 2011), reducing growth or survivorship (Hughes et al. 2007). Even if corals survive to become juveniles, a mobile substrate (e.g., unconsolidated rubble) may increase mortality rates via periodic abrasion and/or "
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    ABSTRACT: Processes that affect recovery of coral assemblages require investigation because coral reefs are experiencing a diverse array of more frequent disturbances. Potential bottlenecks to coral recovery include limited larval supply, low rates of settlement, and high mortality of new recruits or juvenile corals. We investigated spatial variation in local abundance of scleractinian corals in the Seychelles at three distinct life history stages (recruits, juveniles, and adults) on reefs with differing benthic conditions. Following widespread coral loss due to the 1998 bleaching event, some reefs are recovering (i.e., relatively high scleractinian coral cover: 'coral-dominated'), some reefs have low cover of living macrobenthos and unconsolidated rubble substrates ('rubble-dominated'), and some reefs have high cover of macroalgae ('macroalgal-dominated'). Rates of coral recruitment to artificial settlement tiles were similar across all reef conditions, suggesting that larval supply does not explain differential coral recovery across the three reef types. However, acroporid recruits were absent on macroalgal-dominated reefs (0.0 +/- A 0.0 recruits tile(-1)) in comparison to coral-dominated reefs (5.2 +/- A 1.6 recruits tile(-1)). Juvenile coral colony density was significantly lower on macroalgal-dominated reefs (2.4 +/- A 1.1 colonies m(-2)), compared to coral-dominated reefs (16.8 +/- A 2.4 m(-2)) and rubble-dominated reefs (33.1 +/- A 7.3 m(-2)), suggesting that macroalgal-dominated reefs have either a bottleneck to successful settlement on the natural substrates or a high post-settlement mortality bottleneck. Rubble-dominated reefs had very low cover of adult corals (10.0 +/- A 1.7 %) compared to coral-dominated reefs (33.4 +/- A 3.6 %) despite no statistical difference in their juvenile coral densities. A bottleneck caused by low juvenile colony survivorship on unconsolidated rubble-dominated reefs is possible, or alternatively, recruitment to rubble-dominated reefs has only recently begun. This study identified bottlenecks to recovery of coral assemblages that varied depending on post-disturbance habitat condition.
    Coral Reefs 06/2014; 33(2-2):449-461. DOI:10.1007/s00338-014-1137-2 · 3.62 Impact Factor
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    • "Physical encounters between individuals of sit-and-wait predator species, such as sea anemones and hydras, appear to be the most common mode of interference competition . Even when conspecifics do not exhibit aggressive behaviour, neighbouring individuals in a dense aggregation are often forced to fight for a prey item (Chadwick & Morrow, 2011). This type of encounter between sessile predatory cnidarians, armed with tentacles, is usually a slow process in which foraging success can depend on individual traits. "
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    ABSTRACT: Contrary to a generalisation arising from many studies, a larger body size is not always the key to competitive superiority amongst animals. An analysis of competition between pairs of Hydra oligactis, Hydra vulgaris and Hydra circumcincta, that simultaneously encountered a single prey item, showed that competitive success in these sessile predators depended on species and clone in inter- and intraspecific competition, respectively. H. oligactis appeared to be competitively superior, even to the larger H. vulgaris individuals. Phenotypic traits important for prey capture, such as the fraction of the nematocyst that penetrates the prey (penetrants), were positively related to success in intraspecific competition. Body size appeared to be a positive key factor in determining foraging success in the competition between pairs of conspecifics from single or different clones. In contrast to the results of the intraspecific competition, body size was not significantly related to the foraging success of competing heterospecifics.
    Hydrobiologia 09/2013; 714(1). DOI:10.1007/s10750-013-1527-4 · 2.21 Impact Factor
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