Ecology of aquatic macrophytes in coastal rivers of São Paulo: diversity, interspecific competition and spatial distribution in environmental gradients

Author(s)

Lais Samira Correia Nunes

• Document type: Doctoral Thesis
• Press: Rio Claro. 2020-10-16.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Biociências. Rio Claro
• Defense date: 2020-09-03
• Advisor: Antonio Fernando Monteiro Camargo

Abstract

This Ph.D. thesis aimed to study the diversity, interspecific competition and spatial distribution of aquatic macrophytes in coastal rivers in the São Paulo State, through field studies (eight coastal rivers) and greenhouse experiments. We elaborated an inventory of macrophyte species and life forms in the coastal rivers and found a total of 45 taxa, 24 families and 6 life forms. The emergent macrophytes were the most frequent ones and they were found in all rivers, but the floating and submerged macrophytes were recorded in only two rivers. We observed a gradient of species distribution in the north-south gradient of the coast, with only 4 species occurring in a large part of the studied coastal length and 43.5% of the taxa occurring in only one of the sampled rivers. We observed that the differences in the characteristics of the coastal plains (width and slope) influence the characteristics of the coastal rivers, especially their environmental heterogeneity (EH), lengths and longitudinal salinity gradients. We found that EH positively influences life form richness and species composition variation among the rivers; however, it does not drive species richness. The coastal rivers with similar EH were those with the greatest similarity in species composition regardless of their geographical distances. We observed great beta diversity of macrophyte species and life forms at local and regional scales. At the local scale, the species turnover and life form nestedness were explained by the rivers’ longitudinal environmental gradients. At the regional scale, the life form beta diversity was explained by rivers’ length; however, species composition variation was probably related to biotic and historical factors in dispersion and colonization. From the field studies, we conclude that the differences in the characteristics of the coastal plains promote different environmental characteristics of the coastal rivers and lead to different communities and patterns of diversity and spatial distribution of aquatic macrophytes along the São Paulo coastal region. In relation to the experimental studies, we found that the competition between the emergent macrophytes Spartina alterniflora and Crinum americanum in natural sediment of the lower and middle Itanhaém River Estuary is not density-dependent of young individuals, as S. alterniflora had greater ability than C. americanum in any density in both sediment types. We also found that the distribution and stand organization of these species in the Itanhaém River Estuary may be influenced by their arrival order in colonization and priority effects, as young individuals did not establish themselves in heterospecific cultures of adult individuals. In an experiment using artificial substrate, we found that salinity was not limiting for the S. alterniflora and C. americanum growth in monoculture and it did not influence the S. alterniflora total nitrogen content. However, in higher salinity (30), C. americanum had higher total nitrogen content in relation to the treatment with no salt addition (0), possibly as a strategy of salt tolerance. In the higher salinity treatment, asymmetric interspecific competition occurred with greater competitive ability of S. alterniflora. The results of our experiments suggest that, possibly, in the lower Itanhaém River Estuary C. americanum was competitively excluded by S. alterniflora regardless of their colonization densities, and that in the middle estuary the arrival order was important for the organization of their mixed stands. (AU)

• FAPESP's process: 16/01416-4 - Spatial distribution and competitive interaction among aquatic macrophytes in tropical estuaries
• Grantee: Lais Samira Correia Nunes
• Support Opportunities: Scholarships in Brazil - Doctorate