The Lagoon at Caroline/Millennium Atoll, Republic of Kiribati: Natural History of a Nearly Pristine Ecosystem

A series of surveys were carried out to characterize the physical and biological parameters of the Millennium Atoll lagoon during a research expedition in April of 2009. Millennium is a remote coral atoll in the Central Pacific belonging to the Republic of Kiribati, and a member of the Southern Line Islands chain. The atoll is among the few remaining coral reef ecosystems that are relatively pristine. The lagoon is highly enclosed, and was characterized by reticulate patch and line reefs throughout the center of the lagoon as well as perimeter reefs around the rim of the atoll. The depth reached a maximum of 33.3 m in the central region of the lagoon, and averaged between 8.8 and 13.7 m in most of the pools. The deepest areas were found to harbor large platforms of Favia matthaii, which presumably provided a base upon which the dominant corals (Acropora spp.) grew to form the reticulate reef structure. The benthic algal communities consisted mainly of crustose coralline algae (CCA), microfilamentous turf algae and isolated patches of Halimeda spp. and Caulerpa spp. Fish species richness in the lagoon was half of that observed on the adjacent fore reef. The lagoon is likely an important nursery habitat for a number of important fisheries species including the blacktip reef shark and Napoleon wrasse, which are heavily exploited elsewhere around the world but were common in the lagoon at Millennium. The lagoon also supports an abundance of giant clams (Tridacna maxima). Millennium lagoon provides an excellent reference of a relatively undisturbed coral atoll. As with most coral reefs around the world, the lagoon communities of Millennium may be threatened by climate change and associated warming, acidification and sea level rise, as well as sporadic local resource exploitation which is difficult to monitor and enforce because of the atoll's remote location. While the remote nature of Millennium has allowed it to remain one of the few nearly pristine coral reef ecosystems in the world, it is imperative that this ecosystem receives protection so that it may survive for future generations.

2009年4月的科考航次中，研究团队开展了一系列调查，以表征千禧环礁（Millennium Atoll）潟湖的物理与生物参数。千禧环礁是坐落于中太平洋的偏远珊瑚环礁，隶属于基里巴斯共和国（Republic of Kiribati），属于南莱恩群岛链（Southern Line Islands chain）的组成部分，是全球现存为数不多的相对原始的珊瑚礁生态系统之一。该潟湖封闭性极强，潟湖中部广泛分布网状斑块礁与线状礁，环礁边缘则环绕着岸礁；潟湖中部最大水深达33.3米，多数池区的平均水深介于8.8至13.7米之间。最深区域栖息有大面积的盾形陀螺珊瑚（Favia matthaii）平台，推测其为优势种鹿角珊瑚属（Acropora spp.）提供了附着基底，二者共同形成了网状礁体结构。底栖藻类群落主要由结壳珊瑚藻（crustose coralline algae, CCA）、微丝状藻垫以及零星分布的仙掌藻属（Halimeda spp.）和蕨藻属（Caulerpa spp.）斑块构成。该潟湖的鱼类物种丰富度仅为相邻礁前礁的一半，同时是诸多重要渔业物种的关键育幼栖息地，其中包括黑鳍礁鲨（blacktip reef shark）与波纹唇鱼（Napoleon wrasse）——这两类物种在全球其他海域均遭受过度捕捞，但在千禧环礁潟湖中却较为常见；此外，潟湖还栖息有大量的大砗磲（Tridacna maxima）。千禧环礁潟湖为相对未受干扰的珊瑚环礁生态系统提供了优质的参照样本。与全球多数珊瑚礁一样，千禧环礁的潟湖群落可能面临气候变化及其伴随的海水升温、海洋酸化与海平面上升的威胁，同时还受到零星的本地资源开发压力，而由于环礁地处偏远，这类开发难以监测与管控。尽管千禧环礁的偏远性使其得以跻身全球为数不多的近乎原始的珊瑚礁生态系统之列，但亟需对该生态系统加以保护，使其能够存续至后世。