The role of morphological variation in breaking stress and reproductive investment in the drifting macroalgae turbinaria ornata ( phaeophyta ) in the lagoon system of mo ’ orea

Turbinaria ornata is a brown macroalgae, distributed across subtropical and tropical waters, commonly found in the reef system of French Polynesia that uses detachment of propagules as a dispersal mechanism. This study explores the biomechanical survivorship of T. ornata, as a function of morphology and flow environment. Variations in the hydrodynamic regime at different geomorphic features in the lagoon pass system, was assessed by clod cards used as a proxy for an integrated index of hydrodynamic forces experienced by T. ornata fronds. Morphology, breaking strength, and reproductive investment were measured for each frond. Morphological measurements allowed for phenotypic comparisons of fronds from different flow environments. Breaking strength was measured by progressively adding weight to suspended fronds until breakage, allowing quantification of how easily fronds are dislodged from the substrate. Reproductive investment was quantified by determining relative number of reproductive receptacles found per frond. Differences in both morphology and breaking strength between fringing reef and back reef populations suggest that morphotypes of T. ornata exist as an adaptive measure in response to hydrodynamic regime found at each habitat. Additionally, examination into morphology and breaking strength reveals that stipe dimensions, specifically length is the strongest driver of breaking strength. Further investigation in reproductive investment revealed no significant correlation between breaking strength and reproductive output. The combination of differences in breaking strength and lack of correlation with reproductive investment suggests that the probability of dislodgement for each morphotype is uniform, ensuring the continual reproductive success of T. ornata in propagating fronds ecomorphologically adapted to a wide range of flow habitats.