Marine Reserves Substantially Enhanced Herbivorous Fish Abundance and Thereby Increased Macroalgae Removal

27 Mar Marine Reserves Substantially Enhanced Herbivorous Fish Abundance and Thereby Increased Macroalgae Removal

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Abstract

珊瑚礁中，藻食性魚類在藻類移除上扮演關鍵性角色。但隨著環境變遷與人為干擾，導致藻食性魚類數量逐年下降，影響珊瑚與藻類間的平衡。相關研究提出，藻食性魚類的攝食量會隨著珊瑚礁棲地有所不同，其結果指出攝食頻度較高的棲地魚類的豐度也較高，但魚類豐度與攝食相關原因還不清楚。目前海洋保護區在有效的管制下，魚類豐度在保護區內較高，但仍沒有資料顯示這樣的高豐度是否會反應在攝食上。一般研究指出生物族群數增加能幫助減低個體的警戒時間，並能更專注在攝食。但是珊瑚礁藻食性魚類是否具此行為，進而改善移除藻類效率尚待求證。最後我們也想驗證保護區的高豐度藻食性魚類是否會造成有較低的藻類覆蓋。此研究目的想探討高豐度的藻食性魚類是否會：(1) 互相合作警戒掠食者，使攝食頻度提高；(2) 高攝食頻度下消耗更多藻類，並降低藻類覆蓋度。我們透過水下觀察法量化優勢藻食性魚類 (鸚哥魚科Scaridae, 刺尾鯛科Acanthuridae, 臭肚魚科Siganidae)，並且比較在墾丁保護示範區和一般使用區中不同棲地 (珊瑚礁平台、珊瑚礁冠、珊瑚礁坡)的攝食頻度。結果顯示鸚哥魚科和刺尾鯛科魚類的群游行為會提高其攝食頻度。而這兩科的攝食頻度在保護示範區內的珊瑚礁平台較高，在一般使用區則是珊瑚礁冠較高。保護示範區因高豐度的鸚哥魚而能更有效率地移除藻類，使藻類覆蓋率較低。此研究說明保護區有效地增加藻食性魚類豐度後，高豐度鸚哥魚能較一般使用區的更有效地移除藻類，維持珊瑚與藻類的平衡。

English Abstract

Herbivorous fishes play an essential role in regulating algal growth on coral reefs. Nowadays, human disturbances and habitat degradation have caused herbivorous fish populations to decline, resulting in macroalgae overgrowth in coral reefs. Some studies indicate that the feeding rate and abundance of herbivorous fishes vary with depths and habitats in coral reefs. However, the relationship between feeding rate and fish abundance has yet to be examined. Fish abundance increased significantly in marine protected areas (MPAs) with effective management when compared to areas of general usage. Increased group size allows individuals to reduce time of vigilance and focus more on feeding. However, whether herbivorous fishes show foraging behavior in shoal and if such behavior affects algal coverage remain unknown. Moreover, previous studies indicate that algal coverage is lower in depths where higher feeding rates occur, but how fish abundance affect algal coverage is still unclear. Therefore, we investigated whether high abundance of herbivorous fish would (1) increase feeding rate through shoaling and thus (2) more algae is consumed and algae coverage is reduced. We quantified the feeding rate of herbivorous fish (Scaridae, Acanthuridae, and Siganidae) across reef profiles (flat, crest and slope) in MPAs and areas for general utilization in Kenting National Park by underwater visual census. We found herbivorous fishes of Scaridae and Acanthuridae increased feeding rate in larger shoals. In addition, Acanthuridae had the highest feeding rate on crests while Scaridae had higher feeding rate on flats in MPAs. MPAs with higher Scaridae abundance had lower algal coverage. Overall, this study illustrated that high Scaridae abundance in MPAs proved more efficient in algae removal, especially when shoaling in a larger group.