Kathryn’s Coral Chronicles #1

Hi everyone, it’s Kathryn again! 👋 If you missed my first chapter, you can catch up here over on our Marine Savers site. 💙

This month, I will be providing an update on a coral frame site at Kuda Huraa known as “The Channel”. Positioned along the sunrise side of the Resort, this designated area features a shallow beach environment. The Channel underwent dredging and now boasts a sandy bottom, varying in depth from 1 to 4 meters. Historically, it has been an optimal location for deploying coral frames due to abundant sunlight for coral growth, strong currents, and ample water flow. Moreover, its proximity to the shore allows for easy accessibility for snorkelling and frame maintenance.

Both the 2016 and 2024 mass coral bleaching events severely impacted coral reefs around the world. Elevated water temperatures recorded at our Channel site surpassed the thermal thresholds of the corals, causing coral bleaching and mortality, followed by algal overgrowth. Additionally, land reclamation work at the neighbouring local island of Huraa has obstructed water flow into The Channel. Compounding the environmental stressors, growth of Montipora digitata has proliferated, further limiting water flow and currents, thereby affecting the health of our coral frames. Despite these challenges, a select few coral species have shown resilience and continued to thrive, so we will delve into these resilient species and examine the factors contributing to their survival in the face of adversity.

Coral Species Resilient to Bleaching (Maldives): our Channel Site

Coral species: Montipora

Let’s discuss Montipora, particularly Montipora digitata, which currently dominates The Channel at Kuda Huraa. These colonies exhibit digitate morphology with upright branching and small corallites. Known for their rapid growth and ability to settle quickly on substrates, Montipora digitata is a relatively common species found in shallow reef environments (Corals of the World). While we have observed instances of Montipora mortality due to algal overgrowth, overall, this species has become predominant over others in Kuda Huraa.

Our research into Montipora outbreaks revealed that such occurrences are not unprecedented. A study conducted in Micronesia documented a coral-to-coral phase shift akin to what is now unfolding in the Kuda Huraa channel. In an area once characterized by diverse stony corals, an invasion of Montipora species took hold. The study suggested that specific environmental conditions—such as elevated temperatures, nutrient availability, and limited water mixing—favor certain genotypes of Montipora, enabling them to thrive while diminishing other coral species, thereby altering species composition (Micronesia Study).

This situation prompts us to question whether the prevalence of Montipora is preferable to having no corals at all in the affected area, given that environmental stressors are expected to persist. While we currently lack a definitive answer to this question, we are mindful of preventing the spread of Montipora to other areas, such as the house reef, where a diverse coral community still thrives. It is clear that ongoing monitoring of Montipora and its impact on The Channel is crucial. Future studies could include a comparative analysis of fish biomass and diversity between The Channel and house reef to better comprehend the repercussions of this phase shift.

Coral species: Pavona

We have observed encrusting corals on frames and natural substrate in The Channel. We have identified one of them as Pavona varians, a common species that appears in most reef environments. We believe we also have encrusting Leptoseris species in The Channel, but today we will focus on the Pavona. Mesmerising in its gold colour and complex patterns, Pavona varians is no doubt a stunning coral. While the colonies in The Channel are encrusting, Pavona varians can appear in different forms such as laminar and submassive (Corals of the World). Their corallites are unevenly distributed, appearing in valleys or aligned between ridges.

Currently, we lack precise information regarding the potential size and phenotypic variability of Pavona varians colonies in The Channel. However, ongoing monitoring efforts will continue to track their presence and growth on our frames.

Coral species: Pocillopora

Pocillopora damicornis can even settle in wharf piles and mangrove swamps, reflecting their high tolerance to different water conditions. They are definitely strong corals which makes it no surprise that they are doing rather well in The Channel.

Pocillopora verrucosa colonies are composed of uniform upright branches. These branches are thick and sturdy to ensure stability in their preferred environments of high wave action. However, in more protected habitats their branches will appear thinner and less compact. We tend to see more of the latter in The Channel due to the calm conditions of the area. This is just one example of the amazing plasticity exhibited by this family.

Pocillopora meandrina are commonly referred to as bush corals and exist on exposed reef front. The branches are upright and radiate from the initial point of growth (Corals of the World). In shallow water, the branches are flattened and look curved from above. The verrucae tend to be neat and uniform. The surface may have irregular bumps or ridges, and the corallites are often distributed in valleys or aligned along the ridges.

Our observations reveal notable species diversity within Pocillopora colonies, encompassing not only various growth forms but also a wide array of marine organisms. These colonies serve as habitats for a diverse community, accommodating juvenile damselfish, colorful chromis, and trapezia crabs among other species. Against the backdrop of the ongoing 2024 coral bleaching event and the decline of Acroporid corals, the ecological significance of Pocillopora cannot be understated.

PHOTOS (below): species of Pocillopora create an important refuge for marine life in The Channel

Coral species: Psammacora

Several colonies of Psammacora haimiana have been identified as surviving within The Channel. Psammacora haimiana is recognized as a relatively uncommon coral species. These colonies typically exhibit encrusting or submassive growth forms, with polyps that extend notably during daylight hours, imparting a fuzzy appearance. Colonies are characterized by blunt-ended columns and a distinctive corallite arrangement (Lizard Island Field Guide).

Remarkably, despite the bleaching event, the Psammacora colonies in The Channel resisted paling and maintained their characteristic dark brown pigmentation throughout the event.

In summary, the mass coral bleaching event of 2024 compounded with several other stressors, with devastating consequences for The Channel’s coral population.

The shallow, tranquil waters proved particularly vulnerable to the elevated temperatures, leading to significant coral mortality. Amidst the coral losses, the bleaching event provided valuable insights into the resilience of certain coral species to environmental stressors.

Many of the coral species highlighted in this report are inadequately researched, presenting opportunities for further exploration and discovery. We eagerly anticipate documenting the resilience of these coral species that have demonstrated resistance to bleaching, and will continue to monitor their ongoing growth within The Channel environment.

Continued in Part 2