Banca de QUALIFICAÇÃO: BRUNA SANTANA DA SILVA

Uma banca de QUALIFICAÇÃO de MESTRADO foi cadastrada pelo programa.
STUDENT : BRUNA SANTANA DA SILVA
DATE: 29/10/2025
TIME: 14:00
LOCAL: Sala Crustáceo, Departamento de Oceanografia e Limnologia (DOL) e Google Meet (https://meet.google.)
TITLE:

ntegrated evaluation of the carbonate system in a reef environment and the metabolic responses of Siderastrea stellata to heat stress

KEY WORDS:

CO2 flux; Acidification; Climate change; Coral reefs.

PAGES: 41
BIG AREA: Ciências Biológicas
AREA: Ecologia
SUMMARY:

Coral reefs are among the most vulnerable ecosystems to global climate change, especially due to ocean acidification, which alters the carbonate system and impairs coral calcification. The increase in CO₂ emissions intensifies the dissolution of this gas in the oceans, promoting imbalances in pH and biogeochemical processes. Additionally, rising temperatures cause thermal stress and bleaching, affecting the symbiosis between corals and zooxanthellae. This study aimed to evaluate the carbonate system and CO₂ fluxes in the Parrachos of Rio do Fogo (RN), as well as to investigate the effects of thermal stress on the metabolism of the coral Siderastrea stellata. Six field campaigns were carried out between May 2024 and May 2025, with sampling at two reefs (Garças and Rastro) during dry and rainy seasons. Surface and bottom water samples were analyzed for physicochemical parameters, nutrients, and carbonate system variables. In parallel, ex situ thermal stress experiments were conducted on colonies of S. stellata, exposed to controlled temperatures (27–32 °C) under light and dark conditions to measure metabolic and calcification rates. Results showed no significant differences between the Garças and Rastro reefs, but marked seasonal variations were observed. During the rainy period, lower pH and salinity values and higher temperature, nutrient, and dissolved CO₂ levels were recorded, indicating greater continental input and intensified respiration and decomposition. In contrast, during the dry period, internal reef processes predominated, with higher calcification. Principal Component Analysis (PCA) explained 70% of the variability, clearly separating dry and rainy periods. The %NCP of 66,3% revealed the predominance of organic carbon metabolism, with the reef acting as a CO₂ sink during the dry season (net autotrophy) and as a CO₂ source during the rainy season (net heterotrophy). During the rainy season, aragonite saturation frequently fell below the optimal level for calcification (<3), which may compromise calcium carbonate formation.In the current context, with the increase in anthropogenic CO2 emissions and temperature due to climate change, the CO2 sink potential of the oceans and reefs is being undermined, with a possible reversal of these as a CO2 source in the long term. It is concluded that the Parrachos of Rio do Fogo exhibit strong seasonal variation in reef metabolism, modulated by physical and biogeochemical processes. The increase in temperature and continental input tends to favor net heterotrophy and reduce the CO₂ sink potential, highlighting the vulnerability of these reefs to global climate change.

COMMITTEE MEMBERS:
Presidente - 3257898 - Cybelle Menolli Longhini
Interno - ***.984.064-** - HENRIQUE DOUGLAS DOS SANTOS BORBUREMA - null
Externa ao Programa - ***.007.366-** - KELLY YUMI INAGAKI - UFRN