Banca de DEFESA: ANITA GOMES OLIVEIRA

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : ANITA GOMES OLIVEIRA
DATE: 11/12/2023
TIME: 14:00
LOCAL: Instituto de Geociências, Auditório Yeda Ferreira
TITLE:

Use of multiphase echosounder to identify and differentiate reef-building and non-reef-building phases
in Todos os Santos Bay

KEY WORDS:

multiphase echo sounder; backscatter; reefs; phase shift

PAGES: 58
BIG AREA: Ciências Exatas e da Terra
AREA: Oceanografia
SUBÁREA: Oceanografia Geológica
SPECIALTY: Geomorfologia Submarina
SUMMARY:

Coral reefs are highly relevant ecosystems due to their role from biogeochemical cycles to the
protection of the coastline and their tourist value. One of the most impactful threats to the building capacity of a reef is phase shift, a phenomenon in which hermatypic corals are largely replaced by non-calcifying organisms, mainly macroalgae and soft corals. Geophysical mapping was carried out in 3 reef areas of Todos os Santos Bay, namely Pedra Alva, Poste IV and Mangueira. Bathymetric, sonographic and acoustic backscatter level maps were generated. The reef outcrops vary from 3m deep in the shallowest reef (Poste IV) to 10m at the top of the deepest reef (Pedra Alva), where depths in the sedimentary surroundings reach up to 34m. The elevation profile of the Poste IV reef was the one with the least topographic irregularity and also where the greatest coverage of non-building organisms such as algae and soft corals was calculated. Through sonographic imaging it was possible to delimit the reef formations and detect textural changes in the sedimentary areas due to the difference in reflectivity in the mosaic. From the Backscatter mosaic it was possible to segment the areas into different acoustic classes, from which validation points were carried out, including underwater photos, video transects and sediment collection. With this ground truthing it was possible to calculate the percentage of coverage of building and non-building organisms, as well as determining the predominant grain size classes in the sedimentary areas. Despite all reefs having high percentages of coverage of non-building organisms (above 70%), the Pedra Alva reef still has a significant coverage of hermatypic corals, which may be indicative of a construction phase. The levels of acoustic backscatter in the reef areas did not show greater intensity than some sedimentary points in their surroundings, most likely due to the large coverage of non-building organisms, which directly affects the roughness and hardness of the bottom.

COMMITTEE MEMBERS:
Presidente - 1348177 - RUY KENJI PAPA DE KIKUCHI
Interno - 1140224 - ARTHUR ANTONIO MACHADO
Externo à Instituição - LUIZ ANTONIO PEREIRA DE SOUZA