Kathryn’s Coral Chronicles #2

Kuda Huraa Channel Project (Continued)

Hi everyone, it’s Kathryn again! If you missed them, catch my first Chapter (at Marine Savers) and my Coral Chronicles #1.

In my previous update, I discussed the challenges faced by the Kuda Huraa channel site, where a combination of natural and anthropogenic stressors has significantly impacted coral survival. The 2024 mass bleaching event, sediment flux, algae overgrowth, corallivorous predators, restricted water flow, and the invasion of Montipora digitata have all contributed to the decline of Acropora species at this site. Despite these challenges, several coral families have shown surprising adaptability.

In the past few months, the Kuda Huraa team has been working tirelessly to support the surviving coral populations. We have shifted our approach from propagating fast growing Acroporas to focusing on the corals that have typically not been the focus of the restoration project. This includes slower-growing species like Porites, which can rely on stored energy reserves during stressful conditions, and faster-growing corals such as Montipora foliosa, showcasing a diversity of genera and growth forms.

Having a restoration site like the channel will give us a unique opportunity to gather information about these more understudied species, especially in regards to spawning. Currently, the Maldives has very little information about spawning of corals outside the Acropora genus. The channel would be an ideal place to learn and observe, given its accessibility to shore and species diversity. Given the limited knowledge about these species, continuous monitoring of their growth and survival, particularly regarding coral frame structures, is essential.

The purpose of these updates is to document our ongoing efforts at the channel to guide future restoration projects in the Maldives and beyond. Many of the corals currently being studied are unconventional choices for restoration, and documenting their performance provides valuable insights for restoration practitioners. With minimal records on the survivorship and growth rates of these species on coral frames, this project represents a significant exploration into uncharted territory.

The channel’s future remains uncertain due to escalating environmental stressors. The potential for beach nourishment could lead to sand movement that might smother corals, further complicating the situation. It is crucial to document these developments, as understanding what survives under such conditions, why, and whether restoration strategies should pivot towards these less-studied species will be invaluable.

Surviving Corals of the Channel, Part 2

Coral species: Montipora foliosa

Montipora foliosa is one of our primary target species for the channel restoration project. This coral, belonging to the family Acroporidae, is known for its broad, flat plates that spread across reef substrates. Native to the Indo-Pacific region, including the Great Barrier Reef and Indonesia. Montipora foliosa grows relatively quickly and thrives in shallow reef environments. We have identified a large patch of this species near the channel, which has fragmented during storms and heavy currents and subsequently settled on coral frames. We have repopulated many frames with this species as our observations suggest that M. foliosa is acclimating well (accretion within four weeks), with promising results also noted at the water villas.

Coral species: Goniopora tenuidens

Goniopora tenuidens, a coral from the family Poritidae, features slender, branching or columnar growth and feather-like polyps. Found in the Indo-Pacific region, including the Philippines, Indonesia, and Australia, this species thrives in shallow reef environments with moderate to high light and strong water flow. Currently, a large, healthy colony of G. tenuidens is established on a coral frame, and we have opted not to fragment it to avoid unnecessary stress.

Coral species: Porites rus

Porites rus is a hardy coral species known for its encrusting or mound-like growth and densely packed polyps. Native to the Indo-Pacific, including the Great Barrier Reef and the Philippines, it thrives in shallow waters with moderate to high light and water flow. Porites rus has been growing on several coral frames in the channel and shows a slow to moderate growth rate.

Coral species: Porites cylindrica

Porites cylindrica, another resilient species from the family Poritidae, is distinguished by its robust, cylindrical growth form and numerous small polyps. This coral, also found in the Indo-Pacific, shows a range of colors and has been successfully colonizing frames in the channel, alongside Montipora digitata.

Coral species: Acropora

Despite a 99% mortality rate of Acropora species in the channel over the past year, we have two surviving species. One is Acropora gemmifera, known for its intricate, branching structure. While other colonies have perished due to bleaching, predation, or algal overgrowth, one colony remains in the channel and is being monitored closely.
Additionally, Acropora secale, another species with dense, branching colonies, was found in poor condition but has been fragmented and repopulated on coral frames. These fragments are still pale, and their response to transplantation remains uncertain.

Coral Rubble & The Future of the Channel

The future of the Kuda Huraa channel remains highly uncertain due to a variety of environmental and anthropogenic factors. However, I think it is important to note that the channel faces unique challenges that distinguish it from other reef sites, particularly due to the extensive overgrowth of Montipora digitata and the resulting accumulation of coral rubble. This issue is pivotal because it influences both the current state and future potential of the channel’s coral ecosystem.

As I described in Part 1, the channel has undergone a potential phase-shift from a diverse stony coral ecosystem on coral frames to a predominance of Montipora digitata. This species has not only overgrown numerous coral frames but has also spread extensively across the sandy beach floor. Although much of the M. digitata is still alive, the species’ fragile structure has resulted in significant fragmentation and mortality. The accumulation of dead coral and M. digitata rubble is becoming a pressing concern, as this debris can exacerbate existing ecological problems.

Coral rubble, which forms from the skeletons of deceased corals, is subject to bioerosion—a process accelerated by ocean acidification and rising sea temperatures. When coral colonies die, their calcium carbonate skeletons are exposed and can be broken down by bioeroders over time. If this rubble remains stable, organisms such as crustose coralline algae (CCA) and sponges can bind and cement the material, aiding in the reef’s natural recovery. However, in the Kuda Huraa channel, the rapid accumulation and mobility of rubble are disrupting these processes. Increased rubble cover and mobility can smother potential coral recruits and fragments, impeding their growth and stabilization.

Excellent reference: Kenyon et al (2022) “Coral rubble dynamics in the Anthropocene and implications for reef recovery.” Limnology and Oceanography

The ongoing movement of rubble is compounded by the channel’s relatively low hydrodynamic conditions, which, although not as turbulent as other reef environments, still contribute to fragment displacement. Additionally, corallivorous predators like Drupella snails and crown-of-thorns starfish, along with herbivorous fish, further disrupt coral colonies and disperse fragments. These factors result in smaller, more unstable rubble pieces that are challenging to stabilize compared to larger reef fragments. The continual movement and buildup of rubble hinder the natural binding and cementation processes, stalling reef recovery.

To address these challenges, several stabilisation methods are currently under investigation. These include various forms of netting, baskets, rock piles, and cement structures designed to stabilize loose rubble and support coral growth. Each method has its advantages and limitations, and their effectiveness will depend on future environmental conditions in the channel. Reefscapers and other stakeholders may need to explore and implement these strategies to enhance coral recruitment and reef resilience.

In conclusion, the channel presents an uphill battle for restoration efforts. The environmental stressors and shifting coral dynamics highlight the need for innovative and adaptive restoration strategies. Despite the challenges, the channel remains a crucial habitat supporting a diverse array of marine life, including cryptic coral species and various fish, octopuses, eels, turtles, and rays. Restoration efforts, while difficult, are vital for preserving this biodiversity and understanding how future coral restoration might adapt to changing environmental conditions.

The information gathered from this project will be invaluable for guiding future restoration initiatives in Kuda Huraa and throughout the Maldives, ensuring that strategies evolve in response to both climate change and anthropogenic pressures.