Response of the zooxanthellae of Palythoa caribaeorum (Cnidaria: Zoanthidea) to different environmental conditions in coastal and oceanic ecosystems of the Tropical Atlantic

• Published in: Helgoland marine research 2016-01, Vol.70 (1), p.1, Article 2
• Main Authors: Santos, Gleice S., Amaral, Fernanda D., Sassi, Cristiane F. C., Schwamborn, Ralf
• Format: Article
• Language: English
• Subjects: Adaptation; Archipelagoes; Cell density; Cell size; Coasts; Colonies; Coral reefs; Distribution patterns; Ecosystems; Endosymbionts; Environmental conditions; Environmental stress; Marine ecosystems; Marine invertebrates; Palythoa caribaeorum; Photosynthesis; Polyps; Population density; Population growth; Reefs; Temperature effects; Tropical climate; Water depth; Zooxanthellae
• ISSN: 1438-387X; 1438-3888
• DOI: 10.1186/s10152-016-0454-y

The present study tested the hypothesis that endosymbionts of the zoanthid Palythoa caribaeorum show specific responses in cell density, size, and mitotic index (as proxy for cell population growth) under different environmental conditions (water depth, position within the reef and within the colony). Colony fragments were sampled at the nearshore coastal reefs of Porto de Galinhas and at the oceanic St. Peter and St. Paul’s archipelago (SPSP), Brazil. At the coastal reefs, zooxanthellae showed higher density on the reef flat (mean: 2.99 × 10⁶ cm⁻²) than at the back reef (mean: 2.07 × 10⁶ cm⁻²). Zooxanthellae were larger at the center of the colonies (mean: 10.61 µm) than at the edges (mean: 10.11 µm), where younger polyps were found. At SPSP, zooxanthellae showed smaller cell diameters at 3 m depth, than at 5–15 m. Cell size increased with depth, thus enhancing the photosynthetic efficiency of colonies in deeper environments. Strategies and adaptations of these endosymbionts to environmental stressors are discussed. Symbiont distribution patterns shown in this study have fundamental implications for the monitoring of the health of tropical reef ecosystems.