Reconnaissance geomorphology of Rangiroa Atoll, Tuamotu Archipelago. With List of Vascular Flora of Rangiroa

Stoddart, D. R.; Sachet, Marie-Hélène

doi:10.5479/si.00775630.125.1

Cited by 33 publications

(31 citation statements)

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“…For example, at the northeastern narrow rim section, our evidence indicates that sediment is moving along the narrow section of the eastern side of the atoll to accumulate on the northern side of Cust Point. Similarly, there is a broad trend of sediment movement in a northerly direction along the south-western narrow rim between Pointe Marianne and Barachois Sylvain, which agrees with Stoddart's observations and lends support to our study [4]. Rather than implying erosion, alongshore fluxes of reef island material dominate under a transport regime in which the site-specific relationship between wave energy and sediment calibre prevent stable deposition [9].…”

Section: Received: 13 March 2014 / Accepted: 17 March 2014 / Publishesupporting

confidence: 80%

“…These alter shoreline configuration and elevation, resulting in spatially heterogeneous atoll rims [7]. Such heterogeneity is evident around the lagoon rim in the distinction between "narrow" and "normal" atoll rim types [2,4]. Narrow rims (45-250 m wide) represent geomorphologically recent and unstable links between older land areas that are often subject to along shore sediment transport and common breaching.…”

Section: Received: 13 March 2014 / Accepted: 17 March 2014 / Publishementioning

confidence: 99%

“…We acknowledge the accuracy limitations of the comparison between the Stoddart (1967) map [4] and the recent satellite image. Unfortunately it is often the case that historical maps and aerial photographs represent the only available record of past reef island shorelines and, while these are of differing scales and quality [5] they offer the best opportunity available for determining reef island change over time [6].…”

Section: Received: 13 March 2014 / Accepted: 17 March 2014 / Publishementioning

confidence: 99%

“…We calculate the additional margin of error associated with the small scale (1:125,000) of the historic map to be 20m, not the "more than 30 metres" claimed. This disparity may arise because Sheppard has cited a different map (Figure 31 from [4]) as the source of the baseline map: we used the map that was independently georeferenced by David Stoddart, on which shorelines are sketched with finer cartographic pens ( Figure 2 from [4]). We make no judgment on the accuracy of Stoddart's maps because very little detail is provided on how these were made, other than that Stoddart's surveys were undertaken by tape and compass traverse with errors in measurement distances of <1%.…”

Section: Received: 13 March 2014 / Accepted: 17 March 2014 / Publishementioning

confidence: 99%

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Response to Sheppard, C. Atoll Rim Expansion or Erosion in Diego Garcia Atoll, Indian Ocean? Comment on Hamylton, S.; East, H. A Geospatial Appraisal of Ecological and Geomorphic Change on Diego Garcia Atoll, Chagos Islands (British Indian Ocean Territory). Remote Sens. 2012, 4, 3444–3461

Hamylton

East

2014

Remote Sensing

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We welcome Sheppard's comments on our recent assessment of both ecological and geomorphic change at Diego Garcia Atoll in the central Indian Ocean [1]. Whilst our assessment incorporated numerous aspects of change, including movements of the lagoon rim shorelines, changes in the terrestrial vegetation on the lagoon rim and amendments to the bathymetry of the lagoon basin through dredging activities [2], this comment solely addresses the estimates of shoreline change. Here we make some brief remarks relating to this shoreline assessment of Diego Garcia and elaborate on some of the complexities of the geomorphic processes that underpin shoreline dynamics. These complexities have important implications for understanding reef island shoreline dynamics, both at this site and globally.The contrast between our estimations of shoreline change at Diego Garcia and Sheppard's in situ observations appears to be overstated. Sheppard provided eight independent photorecords of his inter-annual observations for inclusion in our study ([3]) with which moderate correspondence was found when compared to our findings [2]. Four photographs exhibiting erosion were also associated with erosion in analysis of rim width transects. The remaining four photo records suggested no shoreline change, but our measurements suggested that rim widths had eroded over the longer 38-year period. Thus, our study [2] appears to indicate a greater amount of erosion than Sheppard's photographic evidence. Indeed, the wider study reported both erosion and accretion across 26 and 43 OPEN ACCESS

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Section: Received: 13 March 2014 / Accepted: 17 March 2014 / Publishesupporting

confidence: 80%

Section: Received: 13 March 2014 / Accepted: 17 March 2014 / Publishementioning

confidence: 99%

Section: Received: 13 March 2014 / Accepted: 17 March 2014 / Publishementioning

confidence: 99%

Section: Received: 13 March 2014 / Accepted: 17 March 2014 / Publishementioning

confidence: 99%

See 2 more Smart Citations

Response to Sheppard, C. Atoll Rim Expansion or Erosion in Diego Garcia Atoll, Indian Ocean? Comment on Hamylton, S.; East, H. A Geospatial Appraisal of Ecological and Geomorphic Change on Diego Garcia Atoll, Chagos Islands (British Indian Ocean Territory). Remote Sens. 2012, 4, 3444–3461

Hamylton

East

2014

Remote Sensing

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“…These islands are subject to a combination of regional oceanographic factors including the Indian Ocean Dipole, reversing annual monsoons, the Southern Equatorial Current and seasonal Tropical Cyclones [3]. For approximately eight months of the year the prevailing winds blow from the southeast, with remaining seasons fluctuating between westerly winds and transitional conditions [12]. This regime is reflected in the local wave climate and the islands therefore have a natural history of geomorphic mobility due to seasonal shifts in sediment supply, storm and wave activity.…”

Section: Introductionmentioning

confidence: 99%

A Geospatial Appraisal of Ecological and Geomorphic Change on Diego Garcia Atoll, Chagos Islands (British Indian OceanTerritory)

Hamylton

East

2012

Remote Sensing

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This study compiled a wide range of modern and historic geospatial datasets to examine ecological and geomorphic change at Diego Garcia Atoll across a 38-year period . This remarkable collection of spatially referenced information offered an opportunity to advance our understanding of the nature and extent of environmental change that has taken place with the construction of the military airbase at Diego Garcia. Changes assessed included movements of the lagoon rim shorelines, changes in the terrestrial vegetation on the lagoon rim and amendments to the bathymetry of the lagoon basin through dredging activities. Data compiled included detailed shoreline and vegetation maps produced as part of the H.M.S. Vidal Indian Ocean Expedition (1967), three Ikonos satellite images acquired in 2005 that collectively covered the complete Atoll area, a ground truthing field dataset collected in the northern section of the lagoon for the purpose of seafloor mapping (2005), observational evidence of shoreline erosion including photographs and descriptions of seawater inundations and bathymetric soundings from five independent surveys of the lagoon floor (1967, 1985, 1987, 1988 and 1997). Results indicated that much of the change along the lagoon rim is associated with the expansion of the inner lagoon shoreline as a result of the construction of the military airbase, with an estimated increase in land area of 3.01 km 2 in this portion of the atoll rim. the lagoon, particularly in the vicinity of the Main Passage. As no previous record of benthic character exists, a complete benthic habitat map of the atoll was derived through classification of the three IKONOS satellite images. Management implications arising from this overall appraisal of geomorphic and ecological change at Diego Garcia included the need for ongoing monitoring of shoreline change at a representative set of sites around the atoll rim, monitoring of the water flow regime through the northern channels between the open ocean and the lagoon basin and an ongoing mapping campaign to record periodic changes in the character of the benthic surface ecology.

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Persistence at the final stage of volcanic island ontogeny: Abiotic predictors explain native plant species richness on 111 remote Pacific atolls

Larrue

Butaud

Daehler

et al. 2018

Ecology and Evolution

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AimThe final island ontogeny of the general dynamic model (GDM) (i.e., before island submergence) in tropical oceans corresponds to the coral atoll stage. Here, we examined whether the species richness of native vascular plants (indigenous and endemic species) on atolls is controlled by spatial and/or physical processes. We also predicted that atolls strongly affected by anthropogenic disturbance would have lower native species richness than predicted by spatial and physical processes.LocationMarshall Islands, Kiribati Islands, Nauru, Niue, Johnston, Cook Islands, French Polynesia and Pitcairn Islands (Pacific Ocean).TaxonNative vascular plants.MethodsWe used stepwise regression to test the relative influence of five biogeographic variables on native species richness. Relationships were assessed for the full set of 111 Pacific coral atolls, as well as for atoll subsets ranging from 9 to 45 atolls. An index of human impact was then estimated, and residuals in the regression model predicting species richness from biogeographic variables were compared with the level of human impact.ResultsA regression model including atoll area, highest atoll elevation, the stepping stone distances from the nearest raised atoll and volcanic island explained native species richness on the 111 Pacific coral atolls. Regression models for different archipelagos and atoll subsets were also significant. Endemic species richness was significantly linked with highest atoll elevation and the stepping stone distances from the nearest raised atoll. Residuals in the biogeographic regression model were barely related to human impact across the 111 atolls but were significantly related to human impact in the Kiribati atolls.Main conclusionsNative species richness on atolls is mainly controlled by physical and spatial characteristics. However, anthropogenic disturbances have altered the predicted pattern of native species richness leading to a lower model fit in some atoll subsets.

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Reconnaissance geomorphology of Rangiroa Atoll, Tuamotu Archipelago. With List of Vascular Flora of Rangiroa

Cited by 33 publications

References 0 publications

Response to Sheppard, C. Atoll Rim Expansion or Erosion in Diego Garcia Atoll, Indian Ocean? Comment on Hamylton, S.; East, H. A Geospatial Appraisal of Ecological and Geomorphic Change on Diego Garcia Atoll, Chagos Islands (British Indian Ocean Territory). Remote Sens. 2012, 4, 3444–3461

Response to Sheppard, C. Atoll Rim Expansion or Erosion in Diego Garcia Atoll, Indian Ocean? Comment on Hamylton, S.; East, H. A Geospatial Appraisal of Ecological and Geomorphic Change on Diego Garcia Atoll, Chagos Islands (British Indian Ocean Territory). Remote Sens. 2012, 4, 3444–3461

A Geospatial Appraisal of Ecological and Geomorphic Change on Diego Garcia Atoll, Chagos Islands (British Indian OceanTerritory)

Persistence at the final stage of volcanic island ontogeny: Abiotic predictors explain native plant species richness on 111 remote Pacific atolls

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