海下灣一向都有很多刺冠海膽，但牠們如何突然成為珊瑚殺手呢？
那首先了解一下刺冠海膽的食性。
海下的刺冠海膽是Diadema setosum，棲息在0.5-6米水深礁岩區，在日間，牠們會藏身於各半遮蔽的礁石隙之中，偶爾露出長長的刺。
到夜間，牠們會走到附近的礁岩及沙面活動及攝食。
食性方面：
“Diadema setosum is commonly associated with coral reefs, but is also found on sand flats and in seagrass beds. Along with the other members of the family, D. setosum is a prolific grazer. They are known to feed on a variety of algal species common on tropical coral reefs. The ecological importance of the taxon as a whole has been stressed because of its herbivorous habits.”(1)
Ecology of Diadema setosum
“Occurs in assemblages in reef areas with high percentage of dead corals. Feeds on algae and grows on dead corals or rubble areas.”(2)
即是牠們是以藻類為食，特別是生長在死去的珊瑚上面及礫石上的藻類。
2006年，更有研究指出刺冠海膽對最偏愛食那種藻：
“Both Diadema savignyi and D. setosum selected Codium geppiorum (杰氏松藻)as their most preferred species, followed by Hydroclathrus clathratus(網胰藻).”(3)
而海膽數目高峰又和海膽偏愛的藻類覆蓋率有關：
“Peak abundances of diadematid sea urchins coincided with many of their grazing preferences at their maximum percentage cover.”(3)
一般資料都沒有提到刺冠海膽會食珊瑚。
不過也有例外，但只是提到是偶然地攝食珊瑚。
“Regular echinoids of the genus Diadema are coral-reef inhabitants that feeds one macroalgae but also,occasionally, on living corals and all sorts of encrusting organisms. ”(4)
而且有報告指出小核果螺的大量出現可能是季節性現象：
“Thus, reported feeding clusters of D. rugosa are probably not ‘plague’ outbreaks but examples of seasonally fostered ‘aggregations’ of feeding (and probably reproducing) individuals. Indeed, no ‘plague-like’ outbreak of any species of Drupella has been reported upon in the literature since 1999.”(6)
I have to say after the Lung Mei and all the other event and news concerning AFCD, police as well most government departments, I've lost all the hope to expect they'll do their job properlly-even if they will speak the truth.作者:
nyagolily 時間: 2015-11-11 10:23
Abstract
Sea urchins are common herbivores and bioeroders of coral ecosystems, but rarely have they been reported as corallivores. We determined the spatial pattern of hard coral damage due to corallivory and bioerosion by the sea urchin Diadema setosum Leske in Hong Kong waters. Coral damage was common at the northeastern sites, with 23.7 – 90.3% colonies being either collapsed or severely damaged with >25% tissue loss. Many genera of corals were impacted by the sea urchin but the damage was most obvious for the structure forming genus Platygyra. The percentage of severely damaged and collapsed coral had significant positive correlation with the abundance of D. setosum, which ranged from 0.01 to 5.2 individuals per coral head or 0.1 – 21.1 individuals m−2 across the study sites. Remedial management actions such as sea urchin removal are urgently needed to save these fringing coral communities.
