15 years of Bocas del Toro Coral
Corals are sessile (non-moving) organisms with calcium carbonate structures inside which live small algal creatures called zooxanthellae. Forming a symbiotic relationship, these organisms provide a basis for reef life and one of the most biologically diverse habitats in the world. Bocas Del Torro is lucky enough to still be a prime example of the species richness that can occur in these regions.
A recent study by Briand et al collated coral health data over 15 years (1999-2013), encapsulating 3 bleaching events (1999, 2005, 2010) and a rapid alteration in the face of coral systems within the archipelago.
Reefing habitats in Bocas can be split into two major categories, the first being Lagoon environments, the second are forereefs. Lagoons are small areas of water separated from a larger body of water by sandbars, barrier reefs or other types of natural barriers (1). A forereef is the outer section of a reef, located on the outside part of a reef edge and facing the open sea (2). Both are integral to the geomorphology of the Archipelago they protect.
Both reefs converged towards traits associated with opportunistic and disturbance-tolerant or generalist coral species. E.g. Orbicella faveolata increasingly dominated forereefs can acclimate to novel environmental conditions created by high sea surface temperatures and demonstrated a positive acclimatise response during the 2010 bleaching event due to prior thermal stress in the 2005 event. Strong survivorship in this species could support reef-building processes in reefs that would otherwise rapidly degrade. Further conservation should be directed towards preventing further shifts in dominance towards low-relief, opportunistic coral species, as expanding evidence suggests that these simplified of homogenous communities cannot maintain key ecosystem function and services.
Reefs more resilient than lagoons
This paper found that whilst convergence towards similar coral traits did occur, lagoonal reefs experienced greater decline in coverage of key coral species and diversity (5x greater) than forereefs. Forereefs were less impacted by long term local anthropogenic disturbances and are thus more resilient to the effects of anthropogenic disturbances.
Nutrient enrichment (documented by high chlorophyll a concentration and therefore eutrophication), from natural runoff from mountains surrounding Almirante Bay. Whilst forereefs were associated with high exposure and low chlorophyll a, could mean higher exposure areas are flushed and so less nutrient buildup, alongside greater distance to areas of effluent input means more protection and less eutrophication. Acropora palmata is more present in forereefs, a feature of unaltered environment, Whilst the lagoonal reefs are consistent with findings of decreases in A. palmata in sheltered reefs since the 1960s, meaning that these reefs cannot maintain reef-building processes upheld by large structurally complex species like A. palmata. Therefore, more erosion and regime-shifts than forereefs. This was shown, there were regime-shifts in lagoonal reefs, away from all coral species and into rubble and algae. But was relatively consistent in forereefs. Density driven temperature inversion was recorded during the 2005 bleaching event, augmenting stress and bleaching at greater depths, so even depth is not a refuge from thermal stress = more death. Runoff from agrochemicals have created hypoxic or “dead” zones in lagoonal areas with low circulation in Almirante Bay, most recently coinciding with the 2010 bleaching event.
The rapid decrease in quality of Bocas Del Toro demonstrates how quickly degradation can occur. This archipelago is an incredibly special place, one that should be protected and conserved for future generations.
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- NOAA. ‘What is a lagoon?’. NOAA Ocean Facts. Available at: What is a lagoon? (noaa.gov) . [Date Accessed: 25/01/2024].
- Cabioch, G. (2011) Forereef/Reef Front. Hopley, D (eds) Encyclopedia of Modern Coral Reefs. Encyclopaedia of Earth Sciences Series. DOI: https://doi.org/10.1007/978-90-481-2639-2_216
- Briand, J. Guzman, H. Sunday, J. (2023) Spatio-temporal patterns in coral reef composition and function across an altered environmental gradient: A 15-year study in the Caribbean. Frontiers of Marine Science. DOI: https://doi.org/10.3389/fmars.2022.977551