By Carolina D. Teixeira
English edit by Carla Elliff
Many here may have already heard that reefs are ecosystems with rich biodiversity and that they provide highly relevant ecosystem services, such as the mineralization of calcium carbonate, the provision of fishing resources and the protection of coastlines. Not to mention their immense tourist potential! The largest and richest reefs in the South Atlantic, the Abrolhos reefs, are located in southern Bahia and northern Espírito Santo. They are the only ones, in the whole world, that form the so-called “chapeirões”, which consist of mushroom-shaped reef structures with steep shaded walls and laterally expanded and well-lit tops. These huge reef columns are built by coralline algae, bryozoans and corals, reaching more than 20 meters deep and 50 meters in diameter.
Aiming to conserve part of this unique ecosystem, the Abrolhos National Marine Park was created in 1983, and was the first of its kind in Brazil. However, the region as a whole constantly suffers from misuse of the coastal zone, including dredging near reefs, deforestation and uncontrolled urbanization. The Abrolhos reefs have also been deeply impacted by climate change, as I showed in my scientific initiation work, and suffer from poor fishing management. The National Park, despite being very important, is not enough to control this flood of threats!
Given this context, long-term studies are essential to guide managers and other actors responsible for managing sea resources. Since 2006, scientists from different universities in Brazil, gathered in a network called Rede Abrolhos and have been monitoring the region through sampling inside and outside the National Park, and in places more or less impacted by activities in the coastal zone. My master's work involved analyzing data from the effort undertaken between 2006 and 2018, as part of CNPq's Long-Term Ecological Research Program. Using this database, I sought to answer three central questions: 1) how has benthic cover changed over the years?; 2) was there a change in dominance in any specific site and/or habitat?; 3) how do the life histories of the most abundant species influence community dynamics?
To answer these questions, we chose five reefs, three of them close to the coast (coastal reefs) and two further away (external reefs). The coastal sites included the Pedra de Leste and Sebastião Gomes reefs, where the waters are naturally more turbid, with Sebastião Gomes also receiving sediment from a dredging operation from a navigation channel used to transport logs. Recife das Timbebas, also coastal, occurs in a coastal area less subjected to sedimentation and partially protected by the National Park. The two reefs monitored in Parcel dos Abrolhos, more than 60 km away from the coast (see the map below to locate the area), are located in the least turbid and most emblematic and protected area of the National Park.
A: Map of the study area and the sampling points located on the different reefs (TIMB = Timbebas, PLES = Pedra de Leste, SGOM = Sebastião Gomes, PAB = Parcel dos Abrolhos). Turbidity values (Kd490) refer to 2018 winter averages; B and C: aerial view of the outer and coastal reefs, respectively. The boat present in B and C measures 15 meters. Source: Rede Abrolhos, CC BY SA 4.0 license.
In the first year of the project (2006) - when I was still in the 6th year of elementary school and my advisor was a young PhD - metal pins were placed in the reefs, in order to allow the exact same plots to be re-sampled throughout time. And, 15 years later, they are still there! PVC structures with 15 subdivisions are fitted to these pins, which are photographed individually. This method is known as photo-square, and each reef has 20 fixed points that allow us to generate 300 standardized photos each year. At the end of the work, I analyzed around 16 thousand images!
Photo-square divided into subplots (A); quantification of benthos using the photo-square method at the top (B); quantification of benthos using the photo-square method on the wall (C). Source: Rede Abrolhos, CC BY SA 4.0 license.
In general, the Abrolhos reefs maintained a relatively stable coral cover, without a regional decline that could characterize the process known as “phase shift”, that is, without the massive replacement of corals by other organisms that do not build reefs, such as macroalgae. Fluctuations in coral cover were mainly linked to positive thermal anomaly events, when the measured temperature is higher than the region's average temperature over the years. However, in Sebastião Gomes, the site closest to the dredging disposal area, fast-growing non-building organisms overcame the corals, with emphasis on the zoanthid Palythoa caribaeorum, popularly known as “baba-de-boi” in Brazil. The smallest temporal variation was observed on the tops of the National Park's chapeirões and on the walls of the coastal reefs, a trend that may be related to the life history of the dominant organisms in these locations, which include corals known to be more tolerant to environmental fluctuations, such as the Montastraea cavernosa.
Montastrea cavernosa, the most abundant coral on the Abrolhos reefs. Source: Rede Abrolhos, CC BY SA 4.0 license.
Although we have not identified a decline in coral cover on a regional scale, we have enough evidence to assume that reef cover will not remain stable for much longer. Stressors continue to intensify and thermal anomalies are becoming increasingly frequent. Our work, carried out by many hands (there are 14 co-authors from 5 different universities), clearly shows that controlling local stressors that contribute to reef deterioration must be prioritized, especially since reversal and restoration tend to become increasingly difficult and expensive as degradation increases.
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About the author
Carolina D’Ornellas Teixeira is from Rio, with a degree in Marine Biology from UFRJ and a master’s degree in Ecology, also from UFRJ. She became interested in the world of corals as an undergraduate when she studied the mass bleaching caused by thermal anomalies from 2015-2017. She currently works at the Biodiversity Assessment and Monitoring Laboratory (SAGE-COPPE), at UFRJ, where she works within the scope of PELD Abrolhos.
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Suggested reading
Our research has already been published and can be accessed at: https://doi.org/10.1371/journal.pone.0247111.
The history of degradation in the Abrolhos region can be found at: https://doi.org/10.1371/journal.pone.0247111.s002.
To learn about the other work of the Abrolhos Network, follow us on social media or visit our website: http://abrolhos.org/.
#BatePapoComNetuno #RedeAbrolhos #MarineScience #Reefs #Coral #Abrolhos #EnvironmentalMonitoring #Oceanography #MarineBiology