Negligible effect of competition on coral colony growth

Abstract

Competition is an important determinant of assemblage structure and population regulation, often resulting in decreased growth, fecundity or survival. In corals, most studies testing for an effect of competition on demographic traits, such as growth, have been experimental and often impose very high levels of competition upon colonies. To more realistically assess the role of competition on coral traits, multispecies studies in the wild are required. Here, we use 5 yr of data that includes 11 coral species on the reef crest at Lizard Island on the Great Barrier Reef to quantify the effect of competition on growth. Additionally, we test whether species differ in their susceptibility to direct-contact (overgrowth and digestion) and overtopping competition, and whether species from some morphological groups are more likely to compete with one another than with species from other morphological groups. We also investigate the relationships between competitive ability and three key traits: growth rate, mechanical stability and fecundity. In contrast to most previous work using field manipulations of competition, we found a negligible effect of competition on growth. Acropora species consistently won overtopping encounters but lost in direct-contact encounters, and these results were consistent among the four Acropora morphological groups. In contrast, the massive Goniastrea spp. were poor at overtopping but generally won direct-contact encounters. Only tabular colonies were disproportionally more likely to compete against one another than with other morphologies. This propensity increases intraspecific relative to interspecific competition, a phenomenon that can promote coexistence when it is present among dominant competitors. Good competitors grew more quickly and had higher fecundity but were less mechanically stable, implying a tradeoff between performance during disturbance vs. performance in the absence of disturbance. We conclude that competition among adults is less likely to influence community dynamics than previously thought. If competition does have an effect, it is more likely to occur at life-stages other than adults.

Resolving the depth zonation paradox in reef‐building corals

“…) or changes in competitive interactions (Álvarez‐Noriega et al. ), suitable data are rarely available. Ultimately the abundance of colonies over depth does not necessarily indicate a refuge for the population, which must produce larvae capable of reaching and successfully colonizing shallow habitats.…”

Coral Morphology Portrays the Spatial Distribution and Population Size-Structure Along a 5–100 m Depth Gradient

“…Nevertheless, we found that light explains only 10% of the variation, suggesting that biotic factors might have a greater contribution. For example, a lack of suitable competitors that can also withstand the unique mesophotic conditions, particularly during their earlylife stages (Álvarez-Noriega et al, 2018), allows corals to grow without suppression from such neighboring competitors. Additionally, demographic traits (such as growth rate) that are linked to a species' life-history strategies may affect its size-distribution.…”

Metabarcoding reveals distinct microbiotypes in the giant clam Tridacna maxima

“…Since all aquariums were filled with seawater from the same pipe and some healthy giant clams in T assemblages harbored the Vibrionaceae species at a lower proportion, the prevalent hypothesis is an increased susceptibility of infection due to the presence of corals. Benthic species, particularly corals, are highly competitive [60] and have been classified based on their aggressiveness [61][62][63][64]. Corals compete either by direct physical contact or via the production and secretion of secondary metabolites that can weaken or kill neighboring organisms [65][66][67][68][69][70].…”