The Roles of Secondary Calcifiers in Reef Construction and Maintenance in Coral and Rocky Reefs of the Mexican Pacific

Carbonate production by sclerobionts was quantified with calcification-accretion units (CAUs) to evaluate the roles of different taxonomic groups in the construction and maintenance of coral reef structures in two sites in the Mexican Pacific with contrasting environmental characteristics: Yelapa and Isla Espíritu Santo (IES). Five CAUs were collected every 6 months for 2 years. The average calcification rate in Yelapa and IES was 1.04 ± 0.11 kg m⁻² year⁻¹ and 1.01 ± 0.82 kg m⁻² year⁻¹; no difference in calcification was found between sites (H = 0.13, df = 1, p = 0.71), although significant differences in calcification were found over time (H = 9.13, df = 3, p = 0.03). Barnacles exhibited the highest calcification rate (Yelapa: 0.63 ± 0.8 kg CaCO₃ m⁻² year⁻¹; IES: 0.54 ± 0.6 kg CaCO₃ m⁻² year⁻¹), followed by mollusks (Yelapa: 0.27 ± 0.35, IES: 0.18 ± 0.26 kg CaCO₃ m⁻² year⁻¹), crustose coralline algae (CCA) (Yelapa: 0.025 ± 0.029 kg CaCO₃ m⁻² year⁻¹; IES: 0.08 ± 0.11 kg CaCO₃ m⁻² year⁻¹), and bryozoans (Yelapa: 0.04 ± 0.06 kg CaCO₃ m⁻² year⁻¹; IES: 0.11 ± 0.11 kg CaCO₃ m⁻² year⁻¹). Cover was dominated by barnacles (27.7%), CCA (16.5%), and mollusks (13.7%) in Yelapa and by bryozoans (27.9%), CCA (20.4%), and barnacles (17.4%) in IES. The coverage of all groups (except CCA) was different between sites, and all taxonomic groups (except foraminifera) exhibited differences over time. The role of each taxonomic group was attributed according to their substrate preference (exposed or cryptic). In Yelapa, bryozoans and polychaetes filled cavities, while CCAs and bryozoans contributed to vertical reef accretion in IES.