183-8 Post-Collapse Reef Dynamics at Coral Gardens, Belize: Assessing pH, Algal and Survivor shifts.

Session: Recent Advances and New Voices in Marine and Coastal Geoscience (Posters)

Poster Booth No.: 39

Presenting Author:

Alessandra Baz-Aguilar

Authors:

Baz-Aguilar, Alessandra Angelica¹, Schurr, Astrid C.², Lujan, Daymon T.³, Greer, Lisa⁴, Rose, Emmie⁵, Wirth, Karl R.⁶

(1) Earth and Environmental Geoscience Department, Washington and Lee University, Lexington, VA, USA, (2) Earth and Environmental Geoscience Department, Washington and Lee University, Lexington, VA, USA, (3) Environmental Studies Department, Washington and Lee University, Lexington, VA, USA, (4) Earth and Environmental Geoscience, Washington and Lee University, Lexington, VA, USA, (5) Earth and Environmental Geoscience Department, Washington and Lee University, Lexington, VA, USA, (6) Geology Department, Macalester College, St. Paul, MN, USA,

Abstract:

Coral Gardens, Belize served as an ecological refugium for endangered Acropora cervicornis (Staghorn) coral, providing a stable habitat for this species despite a regional decline in Acropora spp. Between June and December 2023, the reef experienced a mass mortality event coincident with a severe marine heatwave. This study aimed to assess the state of Coral Gardens following the death of the living A. cervicornis framework. Using the same methods used to quantify live A. cervicornis abundance in past years, we assessed the survival of non-acroporid corals and opportunistic algae. Two long-term monitoring sites at Coral Gardens, T1 and T5, were surveyed annually by photographing 1-meter quadrats along established transects. Live coral was identified and quantified using Adobe Illustrator, Adobe Lightroom, and MATLAB to determine percentage of each species and total abundance. pH was measured using a Meter HOBO MX2500 at hourly intervals from June 2019 to June 2025, with calibration and redeployment every 6 months. Temperature data was collected using Onset UA-002-64 and UA-001-64 pendant loggers at hourly intervals. The average live A. cervicornis cover across five monitoring sites was over 30% in 2012. Live cover dipped to ~15% by 2017 but rebounded slightly to almost 20% in June 2023. By June 2025, non-acroporid survivors averaged only 2.96% per m² across 34 quadrats at T1, while at T5 this dropped to <1% across 41 quadrats. Primary survivors include Porites porites, Porites astreoides, Dichocoenia stokesii, Millepora sp., and Orbicella sp. At T5, once dominated by ~60% live A. cervicornis coverage in 2012, Dictyota sp. and an unidentified orange encruster (likely red algae) have now taken over. As of June 2025, algal coverage ranges from 14% to 74% per m² with an average of 48%. We explored the “CO₂ double threat,” a term that describes temperature rise and ocean acidification as the combined impacts of increasing atmospheric CO₂. Thermal stress remains the primary driver of coral mortality, as preliminary pH data suggests no clear declining trend since June 2019, and as of Spring 2025 pH ranged from 8.12 to 8.15 ± 0.1 units. This rapid ecological shift following the period of high coral mortality raises concerns about the long-term stability of the reef, as its future structure remains uncertain.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7727

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