The Effects of Three Species of Macroalgae on Acropora Aspera Physiology

The recent decline of coral reef cover has been associated in many cases with an increase in algal biomass. Macroalgal blooms are common in nutrient enriched waters, and can often outcompete coral. This experiment considered the effects of three species of macroalgae on the physiology of the branching coral Acropora aspera on a reef flat in the southern Great Barrier Reef. Samples of A. aspera that were in direct contact with the macroalgae Hypnea sp., Padina sp., or Colpomenia sp. were collected and studied. The effects of the macroalgae on A. aspera physiology were analyzed using measurements of protein concentration, dinoflagellate density, and chlorophyll a concentration. The experiment revealed that direct contact with any of the three species of macroalgae resulted in reduced protein concentration in A. aspera. Contact with macroalgae also impacted the density of dinoflagellates and chlorophyll a concentration in A. aspera, but the effects varied between each of the three species of macroalgae. These changes in coral physiology may suggest that A. aspera has the ability to adapt to competition and abrasion by macroalgae. Furthermore, these results suggest that the effects of macroalgae on coral physiology is variable and dependent on the species involved. Physiological changes could potentially lead to a decline in the coral reef’s structure and functioning, which represents a significant loss of biodiversity and economic value.