Coral reefs are among the most biodiverse and productive ecosystems on Earth, providing critical ecological, economic, and cultural benefits. However, they are increasingly threatened by climate change, ocean acidification, and anthropogenic pressures, including overfishing, pollution, and habitat destruction. One of the lesser-studied but significant threats to coral reefs is the predation by corallivorous gastropods of Drupella rugosa (Born, 1778), which can cause extensive damage to coral colonies, particularly those of Acropora cervicornis (Lamarck, 1816). This thesis investigates the ecological impact of Drupella outbreaks on coral reefs, with a focus on Koh Tao Island, Thailand, a region heavily impacted by both natural and anthropogenic stressors. The study was conducted from April to September 2024 across three sites on Koh Tao Island: Chalok Bay, Taa Cha Bay, and Laem Thian Bay. The research aimed to (1) study the behavior of Drupella during outbreaks, (2) to monitor the grazed corals and (3) to compare short- and long-term effects of culling by analyzing data from previous removal campaigns. Fieldwork involved the use of transects, quadrats, and underwater photography to monitor coral health, Drupella density, and the effects of predation. Additionally, experiments were conducted to compare the recovery of Acropora colonies with and without Drupella removal, as well as the role of damselfish (Plectroglyphidodon lacrymatus) in the colonization of coral scars by macroalgae. The results revealed significant spatial variability in coral health and Drupella density across the study sites. Chalok Bay exhibited the highest percentage of healthy Acropora colonies (36.1%), but also the highest density of Drupella predation. In contrast, Laem Thian Bay showed the lowest coral health, with 56.9% of colonies dead or covered by macroalgae. The feeding rate of Drupella was highest in Laem Thian (4.65 cm²/day in colonies without removal), followed by Chalok (2.53 cm²/day) and Taa Cha (1.17 cm²/day). Manual removal of Drupella reduced coral consumption rates, but the practice was found to accelerate algal colonization by damselfish, leading to long-term coral degradation. Colonies where Drupella were removed showed initial recovery, but scars were quickly colonized by macroalgae, hindering coral regrowth. The study highlights the complex interactions between Drupella predation, damselfish behavior, and coral health. While manual removal of Drupella can provide short-term relief for coral colonies, it may inadvertently exacerbate long-term reef degradation by facilitating algal overgrowth. The findings suggest that effective management of Drupella outbreaks requires a holistic approach, including the monitoring and control of damselfish populations, as well as broader efforts to improve reef resilience through reduced anthropogenic pressures and enhanced ecosystem management. In conclusion, this research underscores the need for integrated conservation strategies that address both direct and indirect impacts of Drupella predation on coral reefs. By understanding the ecological dynamics of Drupella outbreaks and their interactions with other reef organisms, this study provides valuable insights for the sustainable management of coral reef ecosystems in the face of increasing environmental and anthropogenic challenges.
Le barriere coralline sono tra gli ecosistemi più ricchi di biodiversità e produttivi della Terra, offrendo benefici ecologici, economici e culturali essenziali. Tuttavia, sono sempre più minacciate dai cambiamenti climatici, dall'acidificazione degli oceani e dalle pressioni antropiche, tra cui la pesca eccessiva, l'inquinamento e la distruzione dell'habitat. Una delle minacce meno studiate ma significative per le barriere coralline è la predazione da parte dei gasteropodi corallivori di Drupella spp., capace di cause danni estesi alle colonie di corallo, in particolare quelle di Acropora cervicornis (Lamarck, 1816). Questa tesi indaga l'impatto ecologico delle epidemie di Drupella sulle barriere coralline, con un focus sull'isola di Koh Tao, in Thailandia, una regione fortemente colpita da fattori di stress sia naturali che antropici. Lo studio è stato condotto da aprile a settembre 2024 in tre siti sull'isola di Koh Tao: Chalok Bay, Taa Cha Bay e Laem Thian Bay. La ricerca mirava a (1) studiare il comportamento di Drupella durante le epidemie, (2) monitorare i coralli colpiti e (3) confrontare gli effetti a breve e lungo termine della rimozione analizzando i dati delle precedenti campagne di rimozione. Il lavoro sul campo ha comportato l'uso di transetti, quadrati e fotografia subacquea per monitorare la salute dei coralli, la densità di Drupella e gli effetti della predazione. Inoltre, sono stati condotti esperimenti per confrontare il recupero delle colonie di Acropora con e senza rimozione di Drupella, nonché il ruolo del pesce damigella (Plectroglyphidodon lacrymatus) nella colonizzazione delle cicatrici dei coralli da parte delle macroalghe. I risultati hanno rivelato una significativa variabilità spaziale nella salute dei coralli e nella densità di Drupella nei siti di studio. Chalok Bay ha mostrato la percentuale più alta di colonie di Acropora sane (36,1%), ma anche la più alta densità di predazione di Drupella. Al contrario, Laem Thian Bay ha mostrato la salute dei coralli più bassa, con il 56,9% di colonie morte o ricoperte da macroalghe. Il tasso di alimentazione di Drupella è stato più alto a Laem Thian (4,65 cm²/giorno in colonie senza rimozione), seguito da Chalok (2,53 cm²/giorno) e Taa Cha (1,17 cm²/giorno). La rimozione manuale di Drupella ha ridotto i tassi di consumo dei coralli, ma si è scoperto che la pratica accelera la colonizzazione delle alghe da parte dei pesci damigella, portando alla degradazione dei coralli a lungo termine. Le colonie in cui Drupella è stata rimossa hanno mostrato un recupero iniziale, ma le cicatrici sono state rapidamente colonizzate da macroalghe, ostacolando la ricrescita dei coralli. Lo studio evidenzia le complesse interazioni tra la predazione di Drupella, il comportamento dei pesci damigella e la salute dei coralli. Mentre la rimozione manuale di Drupella può fornire un sollievo a breve termine per le colonie di coralli, può inavvertitamente esacerbare la degradazione della barriera corallina a lungo termine facilitando la crescita eccessiva delle alghe. I risultati suggeriscono che una gestione efficace delle epidemie di Drupella richiede un approccio olistico, che includa il monitoraggio e il controllo delle popolazioni di damigelle, nonché sforzi più ampi per migliorare la resilienza della barriera corallina attraverso pressioni antropogeniche ridotte e una migliore gestione dell'ecosistema. In conclusione, questa ricerca sottolinea la necessità di strategie di conservazione integrate che affrontino sia gli impatti diretti che indiretti della predazione di Drupella sulle barriere coralline. Grazie alla comprensione delle dinamiche ecologiche delle epidemie di Drupella e delle loro interazioni con altri organismi della barriera corallina, questo studio fornisce preziose informazioni per la gestione sostenibile degli ecosistemi delle barriere coralline di fronte alle crescenti sfide ambientali e antropogeniche.
Gestione delle epidemie di Drupella spp. (Mollusca, Gastropoda): conseguenze ecologiche nella barriera corallina di Koh Tao (Thailandia)
TONOLINI, ROSITA
2023/2024
Abstract
Coral reefs are among the most biodiverse and productive ecosystems on Earth, providing critical ecological, economic, and cultural benefits. However, they are increasingly threatened by climate change, ocean acidification, and anthropogenic pressures, including overfishing, pollution, and habitat destruction. One of the lesser-studied but significant threats to coral reefs is the predation by corallivorous gastropods of Drupella rugosa (Born, 1778), which can cause extensive damage to coral colonies, particularly those of Acropora cervicornis (Lamarck, 1816). This thesis investigates the ecological impact of Drupella outbreaks on coral reefs, with a focus on Koh Tao Island, Thailand, a region heavily impacted by both natural and anthropogenic stressors. The study was conducted from April to September 2024 across three sites on Koh Tao Island: Chalok Bay, Taa Cha Bay, and Laem Thian Bay. The research aimed to (1) study the behavior of Drupella during outbreaks, (2) to monitor the grazed corals and (3) to compare short- and long-term effects of culling by analyzing data from previous removal campaigns. Fieldwork involved the use of transects, quadrats, and underwater photography to monitor coral health, Drupella density, and the effects of predation. Additionally, experiments were conducted to compare the recovery of Acropora colonies with and without Drupella removal, as well as the role of damselfish (Plectroglyphidodon lacrymatus) in the colonization of coral scars by macroalgae. The results revealed significant spatial variability in coral health and Drupella density across the study sites. Chalok Bay exhibited the highest percentage of healthy Acropora colonies (36.1%), but also the highest density of Drupella predation. In contrast, Laem Thian Bay showed the lowest coral health, with 56.9% of colonies dead or covered by macroalgae. The feeding rate of Drupella was highest in Laem Thian (4.65 cm²/day in colonies without removal), followed by Chalok (2.53 cm²/day) and Taa Cha (1.17 cm²/day). Manual removal of Drupella reduced coral consumption rates, but the practice was found to accelerate algal colonization by damselfish, leading to long-term coral degradation. Colonies where Drupella were removed showed initial recovery, but scars were quickly colonized by macroalgae, hindering coral regrowth. The study highlights the complex interactions between Drupella predation, damselfish behavior, and coral health. While manual removal of Drupella can provide short-term relief for coral colonies, it may inadvertently exacerbate long-term reef degradation by facilitating algal overgrowth. The findings suggest that effective management of Drupella outbreaks requires a holistic approach, including the monitoring and control of damselfish populations, as well as broader efforts to improve reef resilience through reduced anthropogenic pressures and enhanced ecosystem management. In conclusion, this research underscores the need for integrated conservation strategies that address both direct and indirect impacts of Drupella predation on coral reefs. By understanding the ecological dynamics of Drupella outbreaks and their interactions with other reef organisms, this study provides valuable insights for the sustainable management of coral reef ecosystems in the face of increasing environmental and anthropogenic challenges.| File | Dimensione | Formato | |
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https://hdl.handle.net/20.500.12075/21217