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

University of Hull, United Kingdom
PLoS ONE (Impact Factor: 3.23). 06/2010; 5(6):e10950. DOI: 10.1371/journal.pone.0010950
Source: PubMed


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.

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Available from: Katie Barott, Oct 05, 2015
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    • "We have not classified the previously-mentioned Millenium Atoll with the cellular reefs listed above because the scale of the cellular morphology at Millenium and in many other Pacific atoll lagoons is up to an order of magnitude larger than the Abrolhos. While the large-scale cellular reefs also seem to consist predominantly of branching Acropora (Roy & Smith, 1971; Grovhoug & Henderson, 1976; Valencia, 1977; Barott et al., 2010), we do not believe our model applies directly to them because it cannot produce cells of their horizontal dimensions unless it is scaled up massively, to unrealistic depths of at least 100 m. We are currently investigating the large-scale cellular morphology. "
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    ABSTRACT: The three-dimensional form of a coral reef develops through interactions and feedbacks between its constituent organisms and their environment. Reef morphology therefore contains a potential wealth of ecological information, accessible if the relationships between morphology and ecology can be decoded. Traditionally, reef morphology has been attributed to external controls such as substrate topography or hydrodynamic influences. Little is known about inherent reef morphology in the absence of external control. Here we use reef growth simulations, based on observations in the cellular reefs of Western Australia's Houtman Abrolhos Islands, to show that reef morphology is fundamentally determined by the mechanical behaviour of the reef-building organisms themselves-specifically their tendency to either remain in place or to collapse. Reef-building organisms that tend to remain in place, such as massive and encrusting corals or coralline algae, produce nodular reefs, whereas those that tend to collapse, such as branching Acropora, produce cellular reefs. The purest reef growth forms arise in sheltered lagoons dominated by a single type of reef builder, as in the branching Acropora-dominated lagoons of the Abrolhos. In these situations reef morphology can be considered a phenotype of the predominant reef building organism. The capacity to infer coral type from reef morphology can potentially be used to identify and map specific coral habitat in remotely sensed images. More generally, identifying ecological mechanisms underlying other examples of self-generated reef morphology can potentially improve our understanding of present-day reef ecology, because any ecological process capable of shaping a reef will almost invariably be an important process in real time on the living reef.
    PeerJ 07/2015; 3(5):e935. DOI:10.7717/peerj.935 · 2.11 Impact Factor
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    • "comm. Jim Maragos), which is dominated by Acropora spp., but also characterised by abundant cover of crustose coralline algae , turfing algae and the giant clam Tridacna maxima (Barott et al., 2010). A large number of T. maxima shells and many dead coral microatolls remain in Palmyra's lagoon supporting this suggestion . "
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    ABSTRACT: The lagoon at Palmyra Atoll in the central Pacific was subject to major military modifications during WWII and now the dominant fauna on the lagoon's hard substrate are sponges, not corals. In this study, we quantified the physical and biological factors explaining the variation in sponge distribution patterns across 11 sites to determine the potential for the sponges in the lagoon at Palmyra to invade the surrounding reef systems. Significant differences in sponge assemblages were found among all but three sites. For all the models we examined the strongest environmental relationships were found for variables related to sedimentation/turbidity and food/habitat availability. Our findings suggest that the sponges in Palmyra's lagoon are likely to be restricted to this habitat type where they are associated with conditions resulting from the earlier heavy disturbance and are unlikely to spread to the outer reef environments unless there is a dramatic decline in environmental quality.
    Marine Pollution Bulletin 11/2012; 66(1-2). DOI:10.1016/j.marpolbul.2012.08.017 · 2.99 Impact Factor
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    • "For the special case of atoll environments, it has been demonstrated that human habitation can have significantly deleterious effects on their ecological integrity [5],[7],[8],[11] and one might therefore surmise that uninhabitated atolls would lend themselves best for conservation and could potentially serve as refuges for healthy coral reefs [15]. Exactly why this should be so, and what processes would be important, thus merits closer inspection. "
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    ABSTRACT: We explore impacts on pristine atolls subjected to anthropogenic near-field (human habitation) and far-field (climate and environmental change) pressure. Using literature data of human impacts on reefs, we parameterize forecast models to evaluate trajectories in coral cover under impact scenarios that primarily act via recruitment and increased mortality of larger corals. From surveys across the Chagos, we investigate the regeneration dynamics of coral populations distant from human habitation after natural disturbances. Using a size-based mathematical model based on a time-series of coral community and population data from 1999-2006, we provide hind- and forecast data for coral population dynamics within lagoons and on ocean-facing reefs verified against monitoring from 1979-2009. Environmental data (currents, temperatures) were used for calibration. The coral community was simplified into growth typologies: branching and encrusting, arboresent and massive corals. Community patterns observed in the field were influenced by bleaching-related mortality, most notably in 1998. Survival had been highest in deep lagoonal settings, which suggests a refuge. Recruitment levels were higher in lagoons than on ocean-facing reefs. When adding stress by direct human pressure, climate and environmental change as increased disturbance frequency and modified recruitment and mortality levels (due to eutrophication, overfishing, pollution, heat, acidification, etc), models suggest steep declines in coral populations and loss of community diversification among habitats. We found it likely that degradation of lagoonal coral populations would impact regeneration potential of all coral populations, also on ocean-facing reefs, thus decreasing reef resilience on the entire atoll.
    PLoS ONE 06/2012; 7(6):e36921. DOI:10.1371/journal.pone.0036921 · 3.23 Impact Factor
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