This article examines reactions to the South China Sea and Chagos Marine Protection Area arbitrations under the United Nations Convention on the Law of the Sea (UNCLOS), in particular concerns about the potential widening of Part XV jurisdiction and its impact on the dispute resolution system's consent basis. It argues that assessing the impact of such cases involves a characterization of both the function of Part XV and of international judges. Ultimately, it suggests that the best test of whether UNCLOS case law has gone too far is the reaction of States in designing dispute settlement under the new Agreement under UNCLOS on the Conservation and Sustainable Use of Marine Biological Diversity of Areas Beyond National Jurisdiction.

Standardised methodologies for assessing reef-derived sediment generation rates do not presently exist. This represents a major knowledge gap relevant to better predicting reef-derived shoreline sediment supply. The census-based SedBudget method introduced here generates estimates of sediment composition and grain-size production as a function of the abundance and productivity of the major sediment-generating taxa at a reef site. Initial application of the method to several reefs in the northern Chagos Archipelago, Indian Ocean, generated total sediment generation estimates ranging from (mean ± SE) 0.7 ± 0.1 to 4.3 ± 1.3 kg CaCO3 m−2 yr−1. Sediment production was dominated by parrotfishes (>90% at most sites), with site-variable secondary contributions from sea urchins (up to 20%), endolithic sponges (~1–7%) and benthic foraminifera (~0.5–3.5%). These taxa-level contributions are predicted to generate sediments that at all sites are coral- (83–94%) and crustose coralline algae-dominated (range ~ 5–12%). Comparisons between these estimates and sedimentary data from proximal reef and island beach samples generally show a high degree of consistency, suggesting promise in the SedBudget approach. We conclude by outlining areas where additional datasets and revised methodologies are most needed to improve rate estimates and hope that the methodology will stimulate research on questions around sediment production, transport and shoreline maintenance.

Perpetuating Britain’s controversial administration of the Chagos Archipelago (BIOT – British Indian Ocean Territory) raises questions about the UK’s commitment to the rules-based order and international law. This interdisciplinary article examines British administration of the Chagos Archipelago by taking a legal-international relations perspective. It provides an overview to the rules-based order concept and its relation with international law, briefly examines the Territory’s history, and outlines how BIOT violates the principles enshrined in the rules-based order concept, specifically promotion of self-determination, prohibition of forced displacement and respect for international institutions. This study is significant due to its timing – set in a period of increased international pressure on the United Kingdom to cede sovereignty of the Chagos Archipelago to Mauritius – and also significant in a period of increased rules-based order strain throughout the Indo-Pacific. This article argues that, despite Britain’s assertion that it is a champion of the rules-based order, of which international law is a component, continued British administration of the Chagos Archipelago is in contravention of both. In an era of rules-based order strain, British BIOT policy provides fertile ground to criticisms of its foreign policy and international law selectivity and double standards.

Global marine turtle population assessments highlight the importance of the south-west Indian Ocean region, despite data gaps for the Chagos Archipelago. The archipelago hosts nesting hawksbill Eretmochelys imbricata and green turtles Chelonia mydas, both heavily exploited for 2 centuries until protection in 1968–1970. We assessed available nesting habitat and spatial distribution of nesting activity during rapid surveys of 90% of the archipelago's coastline in 1996, 1999, 2006 and 2016. We quantified seasonality and mean annual egg clutch production from monthly track counts during 2006–2018 along a 2.8 km index beach on Diego Garcia island. An estimated 56% (132 km) of coastline provided suitable nesting habitat. Diego Garcia and Peros Banhos atolls accounted for 90.4% of hawksbill and 70.4% of green turtle nesting. Hawksbill turtles showed distinct nesting peaks during October–February, and green turtles nested year-round with elevated activity during June–October. Estimates of 6,300 hawksbill and 20,500 green turtle clutches laid annually during 2011–2018 indicate that nesting on the Chagos Archipelago has increased 2–5 times for hawksbill turtles and 4–9 times for green turtles since 1996. Regional estimates indicate green turtles produce 10 times more egg clutches than hawksbill turtles, and the Chagos Archipelago accounts for 39–51% of an estimated 12,500–16,000 hawksbill and 14–20% of an estimated 104,000–143,500 green turtle clutches laid in the south-west Indian Ocean. The improved status may reflect > 40 years without significant exploitation. Long-term monitoring is needed to captureinterannual variation in nesting numbers and minimize uncertainty in population estimates.