食草動物，海藻和珊瑚之間的關係：探索台灣膽 diadematids 在台灣珊瑚礁復原力中的作用
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2020
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The interaction between herbivores, algae, and corals is a key to understand coral reef resilience. However, most previous studies have focused on herbivorous fishes and have conducted in the Caribbean and the Great Barrier Reef. Therefore, information on other herbivores and/or outside the regions is scarce, causing a serious information deficiency. In this PhD study, we examined the interaction between herbivores, algae, and corals in southern Taiwan through field surveys and an in situ cage experiment. In the first study (Chapter 2), we examined herbivore assemblages in southern Taiwan and determinants of juvenile coral abundance (proxy of coral recovery) thereby considering eight factors. We found that diadematid sea urchins were dominant herbivores in many reef sites, compared with herbivorous fishes and gastropods, and diadematid abundance was the best (positive) predictor of juvenile coral abundance in generalized linear mixed models (GLMMs). In the second study (Chapter 3), we conducted an in situ cage experiment using three density conditions (0, 8, 16 indiv./m2) of the locally dominant diadematid, Diadema savignyi. Results demonstrated a strong algal control by D. savignyi: algal cover (biomass) declined rapidly from 95% (1.5 g/100cm2) in 0 indiv./m2 to 47% (0.5) in 8 indiv./m2 and 5–16% (0.02) in 16 indiv./m2. On the other hand, coral recruitment process, examined in coral recruit density and growth/survival of small coral fragments (proxy of coral juveniles) significantly declined in 16 indiv./m2, whereas those were similar between 0 and 8 indiv./m2. In the third study (Chapter 4), we examined the assemblage structure and determinants of abundance in diadematid sea urchins in southern Taiwan, as their ecological information was virtually lacking. We identified five species and one species complex from two genera based on morphology and colour patterns: Diadema savignyi, D. paucispinum, D. setosum, Diadema spp., Echinothrix calamaris, and E. diadema. Of these, D. savignyi was the dominant species (32.1% of total), and D. savignyi, Diadema spp., E. calamaris, and E. diadema were commonly observed at most study sites. Among seven factors considered, macroalgal cover was the only significant (positive) predictor of diadematid abundance in the GLMM. Results of this PhD study elucidated the increasingly important role of diadematid sea urchins in coral recovery, via controlling algae and enhancing coral recruitment process. This phenomenon is most likely occurred by a probable shift in dominant herbivores from herbivorous fishes to non-fishery species, diadematid sea urchins under chronic overfishing in southern Taiwan. We suggest to consider the remnant, but often ignored herbivores, diadematid sea urchins in management and conservation planning of coral reefs, along with recovery efforts for other key macro-herbivores, herbivorous fishes and gastropods.
The interaction between herbivores, algae, and corals is a key to understand coral reef resilience. However, most previous studies have focused on herbivorous fishes and have conducted in the Caribbean and the Great Barrier Reef. Therefore, information on other herbivores and/or outside the regions is scarce, causing a serious information deficiency. In this PhD study, we examined the interaction between herbivores, algae, and corals in southern Taiwan through field surveys and an in situ cage experiment. In the first study (Chapter 2), we examined herbivore assemblages in southern Taiwan and determinants of juvenile coral abundance (proxy of coral recovery) thereby considering eight factors. We found that diadematid sea urchins were dominant herbivores in many reef sites, compared with herbivorous fishes and gastropods, and diadematid abundance was the best (positive) predictor of juvenile coral abundance in generalized linear mixed models (GLMMs). In the second study (Chapter 3), we conducted an in situ cage experiment using three density conditions (0, 8, 16 indiv./m2) of the locally dominant diadematid, Diadema savignyi. Results demonstrated a strong algal control by D. savignyi: algal cover (biomass) declined rapidly from 95% (1.5 g/100cm2) in 0 indiv./m2 to 47% (0.5) in 8 indiv./m2 and 5–16% (0.02) in 16 indiv./m2. On the other hand, coral recruitment process, examined in coral recruit density and growth/survival of small coral fragments (proxy of coral juveniles) significantly declined in 16 indiv./m2, whereas those were similar between 0 and 8 indiv./m2. In the third study (Chapter 4), we examined the assemblage structure and determinants of abundance in diadematid sea urchins in southern Taiwan, as their ecological information was virtually lacking. We identified five species and one species complex from two genera based on morphology and colour patterns: Diadema savignyi, D. paucispinum, D. setosum, Diadema spp., Echinothrix calamaris, and E. diadema. Of these, D. savignyi was the dominant species (32.1% of total), and D. savignyi, Diadema spp., E. calamaris, and E. diadema were commonly observed at most study sites. Among seven factors considered, macroalgal cover was the only significant (positive) predictor of diadematid abundance in the GLMM. Results of this PhD study elucidated the increasingly important role of diadematid sea urchins in coral recovery, via controlling algae and enhancing coral recruitment process. This phenomenon is most likely occurred by a probable shift in dominant herbivores from herbivorous fishes to non-fishery species, diadematid sea urchins under chronic overfishing in southern Taiwan. We suggest to consider the remnant, but often ignored herbivores, diadematid sea urchins in management and conservation planning of coral reefs, along with recovery efforts for other key macro-herbivores, herbivorous fishes and gastropods.
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none, sea urchins, coral reefs, algae, coral reef resilience, Taiwan, Southeast Asia