Positive associations between macroalgal species in a rocky intertidal zone and their effects on the physiological performance ofUlva lactuca

• Published in: Marine ecology. Progress series (Halstenbek) 2005-05, Vol.292, p.173-180
• Main Authors: Molina-Montenegro, Marco A., Muñoz, Alejandro A., Badano, Ernesto I., Morales, Billy W., Fuentes, Katia M., Cavieres, Lohengrin A.
• Format: Article
• Language: English
• Subjects: Habitats; Intertidal zones; Macroalgae; Marine ecology; Photosynthetically active radiation; Plant ecology; Plant interaction; Species; Vegetation canopies; Water loss
• ISSN: 0171-8630; 1616-1599

Positive interactions become more important as physical stress increases. Rocky intertidal habitats display marked desiccation and heat stress gradients, increasing from low- to high-tidal levels. The presence of some macroalgae has been shown to facilitate several intertidal organisms by ameliorating stressful conditions. However, few studies have reported positive interactions among 2 or more macroalgal species, and none has addressed how seaweed canopies could modify the physiological performance of other associated algae along intertidal gradients. Here we report on spatial association patterns of 2 macroalgae (the kelpMacrocystis pyriferaand the green algaUlva lactuca) occurring along a rocky intertidal vertical gradient in southern Chile. We conducted an evaporative water loss experiment and compared temperature and photosynthetic active radiation beneath the canopy ofM. pyriferaand on exposed substrates. We compared maximum quantum-yield (F v/F mratio = (F m–F₀)/F m, whereF₀ andF mare the minimum and maximum chlorophyll fluorescence yields, respectively) and photochemical efficiency in Photosystem II (ΦPSII) ofU. lactucabeneath and away from kelp canopies along the intertidal gradient. Positive association patterns betweenM. pyriferaandU. lactucawere detected at high-tidal areas, while neutral patterns were evident at low-tidal heights. Evaporation, temperature, and PAR were lower beneath kelp canopies. The photosynthetic performance ofU. lactucawas lower in individuals on exposed substrates compared to those associated withM. pyrifera, with this effect being more pronounced in the upper intertidal zone. Our results support the prediction that the importance of positive interactions increases with stress. We suggest thatM. pyriferacould be acting as a ‘nurse species’ forU. lactuca, possibly extending the vertical distribution of this green alga to high intertidal zones.