Differential abundance of haploid and diploid phases of Gracilaria tikvahiae (Gracilariales, Rhodophyta) along a temperature, nutrient, and geographic gradient in Florida, EUA.

• Grant number: 24/14924-4
• Support Opportunities: Scholarships abroad - Research Internship - Post-doctor
• Start date: May 01, 2025
• End date: April 30, 2026
• Field of knowledge: Biological Sciences - Botany - Applied Botany
• Principal Investigator: Mutue Toyota Fujii
• Grantee: Fabiana Marchi dos Santos
• Supervisor: Claudia Maria Ligia Collado Vides
• Host Institution: Instituto de Pesquisas Ambientais (IPA). Secretaria de Meio Ambiente, Infraestrutura e Logística (São Paulo - Estado). São Paulo , SP, Brazil
• Institution abroad: Florida International University (FIU), United States
• Associated to the scholarship: 23/01804-8 - Understanding the reproductive biology of red algae (Rhodophyta) using physiological and molecular tools, BP.PD

Abstract

Rising ocean temperatures resulting from global climate change will have a major impact on coastal ecosystems dominated by seaweeds, since it is an important factor controlling the metabolic, growth and reproduction of macroalgae. Interactions between global (increasing ocean temperatures) and local (eutrophication) stressors on marine ecosystems are predicted and can lead to community shifts towards dominance by opportunistic species or influencing transitions to new habitats, and consequently leading to changes in the structure, function and services that these ecosystems provide. Gracilaria tikvahiae is a primary producer red algae (Gracilariales, Rhodophyta), which grows in the intertidal region, where it also acts as a habitat structurer. The species has a triphasic life history with alternation of generations. The gametophytic phase (n) is dioecious, free-living and isomorphic to the tetrasporophytic phase (2n), while the carposporophytic phase (2n) is microscopic and dependent on the female gametophyte. Moreover, it is an economically important species because it produces the phycocolloid agar, which has several applications in the food, cosmetic, and medicinal industries. G. tikvahiae can be found along a broad latitudinal gradient on the coast of Florida USA, whether in estuaries, beaches and even in eutrophic bays, being considered as opportunistic by some researchers since it is resistant to a wide range of temperatures (0-30 °C) and salinity (8-60 ps¿). Lagoons and bays on the east coast of Florida are adjacent to large urban centers that are highly susceptible to anthropogenic impacts caused by direct nutrient discharge from agricultural waste, pharmaceuticals, surface water and groundwater. Eutrophication has been considered a causal factor in the alteration of the structure and composition of aquatic vegetation in Florida, however, little is known about the effects of eutrophication on the reproductive aspects of marine macroalgae. Considering that nutrient patterns can be impacted by water management practices, it is important to examine the combined effect of this variable with seasonal temperature variations on the diversity, distribution, abundance and sexuality of G. tikvahiae. Conducting a taxonomic study using molecular barcode markers in parallel with abundance studies allows the identification of species to be verified. This helps to determine whether the populations analyzed actually belong to the same species. A phylogeographic approach based on these molecular data allows for mapping and understanding patterns of genetic diversity within and between populations of a species. This enables the comprehension of how biological diversity is distributed geographically and which factors have influenced or impeded its distribution (barriers). Such information is essential for the conservation and management of natural populations, as well as for the improvement and selection of more productive strains for mariculture. This work hypothesizes that the distribution and abundance of the different reproductive phases of the life cycle of G. tikvahiae are directly associated with nutrient availability and seasonal temperature patterns, making the species highly susceptible to the impacts of local (eutrophication) and global (increasing ocean temperatures) stressors. The specific goals of this study include: (1) to evaluate the seasonal and spatial patterns of abundance and nutrient content in the tissues of the gametophytic (female and male) and tetrasporophytic phases of G. tikvahiae along a latitudinal gradient on the east coast of Florida (USA); (2) to correlate seasonal and spatial patterns of abundance and internal nutrient content with salinity, temperature, dissolved oxygen, and nutrient availability in the water column; and (3) to explore the relationships between the taxonomic divergences and water quality parameters (salinity, temperature, dissolved oxygen, and nutrients).