Competition mechanisms of the common soft coral Clavularia koellikeri for benthic space domination

Full description

Background: Hard corals are often thought to be outcompeted for benthic space with other taxa, particularly fast-growing and chemically rich organisms, such as soft corals. The soft coral Clavularia koellikeri is often described as a dominant competitor due to its occupation of large areas on Indo-Pacific reefs, but its competitive ability and mechanisms toward different hard corals remain unknown. Here we investigated competition between C. koellikeri and two common branching hard corals Acropora cf. kenti and Porites cf. cylindrica using a combination of field assessments and aquaria experiments.

Methods: First, in the field, in shallow reefs of Orpheus Island (central GBR), we quantified and compared damaged areas on all hard coral taxa contacted by Clavularia koellikeri. We selected the branching hard corals Acropora cf. kenti and Porites cf. cylindrica after the contact observations during the field assessments, as they were the most common corals recorded in contact with C. koellikeri and apparently showed different responses to those contacts. Then, we conducted a 17-day aquaria experiment to investigate the effects of physical contact of C. koellikeri in both hard corals. We assessed the effects measuring the photosynthetic efficiency (PE) and visual tissue damage on hard corals and tentacle expansion of the soft coral. Lastly, we conducted a 24h experiment using crude chemical extracts of C. koellikeri and another common soft coral, Sarcophyton sp., embedded in gel pads to assess responses of hard corals to chemical competition, and assessed the effects through PE measurements and visual damaged tissue areas on hard corals.

Dataset: Data used to run analyzes refer to percent damaged area on hard corals contacted by Clavularia koellikeri in the field; photosynthetic efficiency (PE) measurements and tissue damage of hard corals from both experiments (contact and chemical experiments), and tentacle expansion of C. koellikeri in the contact experiment. Details on responses, treatments, and data collection are reported in the READ ME file.

Software/equipment used to create/collect the data: Subaquatic camera Underwater fluorometer Diving PAM II Walz

Software/equipment used to manipulate/analyse the data: Quantitative data analysed using statistical software R in RStudio (R Core Team v. 4.2.3) (operated in Mac OS X).