Small-scale or artisanal production of mab & eacute; pearls from the winged pearl oyster, Pteria penguin, is supporting novel livelihood opportunities in coastal areas throughout the Indo-Pacific region. For the island nation of the Kingdom of Tonga, this activity is now well established and has led to a use of mab & eacute; pearls and mother-of-pearl from locally cultured P. penguin to produce items targeting domestic market channels linked to cruise tourism. The extent to which these items adequately service demand, however, has not been assessed. This study evaluated market penetration, competitiveness, and favorable characteristics of mab & eacute; pearl and mother-of-pearl products by surveying cruise passengers while ashore in Tonga. Data were generated by identifying cruise passengers who had purchased pearl- or mother-of-pearl products, examining the items purchased, and then determining how certain choice criteria influenced purchase behaviors. The cruise passengers surveyed (n = 268) collectively purchased 99 mother-of-pearl, 49 mab & eacute; pearl, and 19 imported pearl items, with 40.4% of them having spent $70.57 +/- 96.16 Tongan pa'anga (TOP) ($31.09 +/- 42.36 United States dollar (USD)] on 1.6 +/- 0.8 items per person. Nearly all items were purchased as souvenirs (94.6%, n = 159), either for oneself (54.7%, n = 87) or as a gift for others (45.3%, n = 72). A synthesis of results confirmed that cruise tourism is an emerging domestic market channel for mab & eacute; pearls and mother-of-pearl from Pteria penguin in Tonga, with the available items adequately servicing current demand for souvenirs from cruise passengers. Avenues to increase market penetration and competitiveness are suggested, but efforts to increase the number of cruise passenger arrivals will likely have the greatest impact on sales and local livelihoods.

Remote underwater videos (RUVs) are valuable for studying fish assemblages and behaviors, but analyzing them is time-consuming. To effectively extract data from RUVs while minimizing sampling errors, this study developed optimal subsampling strategies for assessing relative abundance, richness, and bite rates of corallivorous fish across eight geographically dispersed reef sites on the Great Barrier Reef and in the Torres Strait. Analyzing 40 frames per 60-min video yielded precise and accurate estimates of the mean number of individuals per frame (i.e., MeanCount), with systematic sampling (one frame every 90 s) proved as effective as or better than random sampling, depending on the survey sites. However, this approach underestimated species richness by 40

Understanding how bleaching severity varies across space and among and within taxa helps predict changes in community composition due to climate change and informs conservation efforts. Photogrammetry offers a non-invasive and time effective method for quantifying attributes of thousands of coral colonies across large, environmentally diverse reef areas. This approach circumvents the limitations of traditional survey methods, where detailed tracking of individual colonies comes at the expense of large sampling areas and sample sizes. Using photogrammetry, we measured colony size and scored bleaching severity of > 5000 colonies of 13 taxa across 26 sites (> 7400 m2 of reef) during a mild bleaching event in the central Great Barrier Reef (GBR) in 2022. We quantified the relationship between bleaching severity and key biological and environmental factors: colony size, taxonomic identity, degree-heating weeks (DHWs), water velocity, various measures of reef structural complexity, depth, and distance to coast. Our results show that bleaching probability decreased with increasing colony size for most taxa, contradicting the current understanding of size-dependent bleaching. Counter to conventional thinking, tabular Acropora spp. presented very low levels of bleaching in 2022 despite being among the most severely bleached taxa during the bleaching event in 1998, suggesting possible adaptation in the last two decades. Our results show a high level of idiosyncrasy in environmental gradients of bleaching severity. For instance, the effect of depth on was taxon-dependent and the effect of wave velocity differed between inshore and offshore reefs. Our results challenge prevailing paradigms around the role of colony size and environment in regulating bleaching susceptibility, suggesting that refugia are not universal but instead depend on specific environment-taxonomic combinations and taxon-specific colony sizes.

Abstract Underwater photogrammetry is routinely used to monitor large areas of complex and heterogeneous ecosystems, such as coral reefs. However, deriving data on benthic components (i.e. sand, rubble, coral and algae) from photogrammetry products has remained challenging due to the highly time‐consuming process of manual data extraction. We developed a machine learning approach to quantify benthic community composition in coral reefs from orthomosaics, which requires no manual delineation of benthic components for training or implementation. The current study presents RapidBenthos, an automated workflow that segments and classifies large‐area images. Our pipeline (1) uses a pre‐trained segmentation model, eliminating the need for manually generated fine‐scale segmented training data, and (2) classifies the resulting segments from multiple views using the underlying survey images, allowing for classification to fine taxonomic levels. Within a test photomosaic built from a coral reef area of 40 m−2, the model automatically detected 43 different benthic classes. Validation resulted in an overall classification accuracy of 0.96 and a segmentation accuracy of 0.87, when compared to a manually digitised replica. The RapidBenthos workflow was 195 times faster than manual segmentation and classification. Additional validation of 524 Acropora coral colonies from 11 additional test plots resulted in a segmentation accuracy of 0.92 and classification accuracy of 0.88 to the coarser ‘Acropora’ group. RapidBenthos has the capability to extract an unprecedented level of data from photomosaics of coral reefs or other complex environments, allowing to sustainably scale photogrammetric monitoring technique both in replicate and survey extent, which consequently can lead to new research questions and more informed ecosystem management.

Tonga’s Special Management Areas (SMAs) have been widely supported by the people of Tonga as a successful approach to the comanagement of their fisheries and marine resources. However, due to the dominant focus on expansion of the program over recent years, challenges remain for the effective and consistent monitoring and evaluation needed to understand program impacts. This review compiles all known ecological, fisheries, and socio-economic monitoring and evaluation reports related to Tonga’s Special Management Areas from 2010 onwards. A total of 25 projects with available reports were identified, with most examining ecological (42%) and socio-economic (42%) aspects of SMAs, whereas reporting on SMA fisheries data (e.g. catch) was limited to five available projects. Most studies also represented ‘baseline’ ecological and socio-economic surveys of SMAs during implementation. Only three studies have assessed the ecological impact of SMAs post intervention, and only one of these incorporated ‘follow-up’ surveys at a second time point. Among these, impacts remain mixed, with some SMAs resulting in larger and more abundant fish, but others showing no impact. Other monitoring challenges include no gender disaggregation of data, no monitoring of gleaning, haphazard monitoring by communities, and general concerns of cost, fit for purpose, and overinvestment. Although the limited available ecological data indicates that SMAs can increase fish size and abundance in some cases, rationalised, more efficient, and targeted monitoring is required to better understand and strengthen the functioning of SMAs and inform community and government management decisions.

Change detection is an essential and widely used approach for investigating ecosystem dynamics. Multi-temporal 3D models increasingly underpin photogrammetry-based analyses of change for many ecologically relevant attributes. To detect change, it is necessary to accurately align 3D models collected at different times using a process referred to as co-registration. However, achieving precise co-registration is difficult in underwater habitats due to practical challenges intrinsic to surveying them. These include a lack of accurate georeferencing information, variable light, turbidity and weather conditions, and diving restrictions dictated by the diver's pressure exposure over time. Here we present an efficient co-registration workflow for 3D models that directly addresses these challenges, derived from underwater structure-from-motion methods. To test our approach, we used 3D models from across a wide range of coral reef habitats covering all those that one may encounter in shallow reefs (15 m depth and above). We then identified and empirically estimated four key sources of error: coregistration, 3D processing, image acquisition, and reference and scaling features (RSF) placement, and quantified their relative contributions to the overall error. Our proposed co-registration workflow had a mean precision of 1.37 +/- 16.55 mm. Image acquisition and RSF placement errors contributed the most to the total workflow error (37% and 53%, respectively), while the contribution of co-registration and 3D processing errors was minimal (3% and 7%, respectively). As a result of our analysis, we provide 'good practice' guidelines to reduce errors associated with photogrammetric workflows and to facilitate efficient and reliable detection of 3D change in complex underwater ecosystems.

Close-range underwater photogrammetry, hereafter referred to as photogrammetry, is rapidly emerging as a new standard in measuring and monitoring coral reefs due to its potential to record colony- and habitat-scale metrics in two and three dimensions at sub-centimetre scales. Despite the recent popularisation of photogrammetry, a comprehensive assessment of its applications to coral reefs seascape ecology has not yet been conducted. We systematically reviewed 125 publications on coral reef photogrammetry to assess: 1) its global trends and use; 2) how benthic community data is extracted from imagery; 3) the range of metrics derived and their ecological applications; and 4) key limitations of the approach. Results indicate that development and application of photogrammetry to coral reef ecology has accelerated rapidly in the last 15 years. In total, 55 metrics derived from photogrammetry, grouped in 10 categories, have been used to inform ecological studies on benthic assemblage, habitat structural complexity, and ecosystem condition and trajectory. The high level of effort required to quantify benthic assemblages was identified as a primary workflow bottleneck. We highlight the versatility of photogrammetry to study and monitor coral reef ecosystems and its capacity to quantify benthic community dynamics, habitat, and trajectories, which are vital to inform coral reef conservation and restoration.

Mabe ' pearl culture has become a significant addition to traditional rural livelihood activities in Tonga and in other south Pacific countries. Mabe ' pearl culture is a low-cost, low-tech alternative to round pearl culture, can be undertaken by local people with minimal training, and has considerable potential for value adding through production of jewellery and handicraft items. Mabe ' pearls are produced by attaching hemispherical nuclei to the inner shell surface of pearl oysters where subsequent coverage with nacre (mother of pearl) produces commercial pearls after a culture period of around 12 months. Traditionally, local mabe ' pearl farmers attempt to maximise pearl output by implanting four high-profile nuclei into each oyster. Recent research has indicated that fewer nuclei, and those with lower profile, may improve the overall quality of resulting mabe ' pearls and this has been adopted as best-practice by Tongan mabe ' pearl farmers. This study reports an economic comparison of these two nucleus implanting arrangements. Results showed that annual returns were not dissimilar with the traditional implanting method (four high-profile nuclei) generating USD 6977 per annum, while the recommended bestpractice method (two low-profile, one high-profile nuclei) generated USD 6795 per annum. While the traditional method may generate potentially higher annual returns, there are two key considerations that favour the best-practice method: (1) reduced labour commitment that provides opportunity to engage in other livelihood activities; and (2) the production of a higher grade of pearls is more supportive of developing high value export markets for Tongan mabe ' pearls.

Environmental conditions can strongly influence the growth performance of pearl oysters and affect pearl farm production schedules. Growth and condition index (CI) of two age cohorts of Pteria penguin were measured for 13 months to investigate differences in growth performance between four culture sites within the northern (Vava’u) and southern (Tongatapu) island groups of the Kingdom of Tonga. Environmental conditions were also measured at culture sites and used to explore potential effects on oyster growth and condition. Between island groups, growth performance of P. penguin was superior at northern sites and was most strongly related to higher water temperatures at these sites. Within the southern island group, growth performance varied significantly between sites and may be driven by differences in wave energy. Monthly growth rates (GM) of P. penguin also showed significant temporal variation related to age and environmental conditions. This study demonstrated significant variation in the growth performance of P. penguin at latitudinal and local scales and suggests that in oligotrophic marine environments with minimal terrestrial inputs, such as Tonga, water temperature and wave exposure may be the primary environmental conditions influencing the growth performance of P. penguin. This study therefore recommends that optimal culture sites for P. penguin in Tonga are characterized primarily by warmer water temperatures (25–30°C) and low wave exposure (<15 joules m2 day–1). Culture of P. penguin at sites with more suitable environmental conditions enables pearl production to begin up to 34.2 % (6.5 months) earlier than at less-suitable sites and this may greatly influence mabé pearl farm profitability and feasibility.

Environmental conditions and anthropogenic impacts are key influences on ecological processes and associated ecosystem services. Effective management of Tonga's marine ecosystems therefore depends on accurate and up-to-date knowledge of environmental and anthropogenic variables. Although many types of environmental and anthropogenic data are now available in global layers, they are often inaccessible to end users, particularly in developing countries with limited accessibility and analytical training. Furthermore, the resolution of many global layers might not be sufficient to make informed local decisions. Although the near-shore marine ecosystem of Tonga is extensive, the resources available for its management are limited, and little is known about its current ecological state. Here we provide a marine socio-environmental dataset covering Tonga's near-shore marine ecosystem as compiled from various global layers, remote sensing projects, local ministries, and the 2016 national census. The dataset consists of 11 environmental and 6 anthropogenic variables summarised in ecologically relevant ways, spatially overlaid across the near-shore marine ecosystem of Tonga. The environmental variables selected include bathymetry, coral reef density, distance from deep water, distance from land, distance from major terrestrial inputs, habitat, land area, net primary productivity, salinity, sea surface temperature and wave energy. The anthropogenic variables selected include fishing pressure, management status, distance to fish markets, distance from villages, population pressure and a socioeconomic development index based on population density, growth, mean age, mean education level and unemployment. We hope this extensive and accessible dataset will be a useful tool for future assessment and management of marine ecosystems in Tonga.

Despite increasing threats to Tonga's coral reefs from stressors that are both local (e.g. overfishing and pollution) and global (e.g. climate change), there is yet to be a systematic assessment of the status of the country's coral reef ecosystem and reef fish fishery stocks. Here, we provide a national ecological assessment of Tonga's coral reefs and reef fish fishery using ecological survey data from 375 sites throughout Tonga's three main island groups (Ha'apai, Tongatapu and Vava'u), represented by seven key metrics of reef health and fish resource status. Boosted regression tree analysis was used to assess and describe the relative importance of 11 socio-environmental variables associated with these key metrics of reef condition. Mean live coral cover across Tonga was 18%, and showed a strong increase from north to south correlated with declining sea surface temperature, as well as with increasing distance from each provincial capital. Tongatapu, the southernmost island group, had 2.5 times greater coral cover than the northernmost group, Vava'u (24.9% and 10.4% respectively). Reef fish species richness and density were comparable throughout Tongatapu and the middle island group, Ha'apai (~35 species/transect and ~2500 fish/km2), but were significantly lower in Vava'u (~24 species/transect and ~1700 fish/km2). Spatial patterns in the reef fish assemblage were primarily influenced by habitat-associated variables (slope, structural complexity, and hard coral cover). The biomass of target reef fish was greatest in Ha'apai (~820 kg/ha) and lowest in Vava'u (~340 kg/ha), and was negatively associated with higher human influence and fishing activity. Overall mean reef fish biomass values suggest that Tonga's reef fish fishery can be classified as moderately to heavily exploited, with 64% of sites having less than 500 kg/ha. This study provides critical baseline ecological information for Tonga's coral reefs that will: (1) facilitate ongoing management and research; and (2) enable accurate reporting on conservation targets locally and internationally.

Mabe pearl (half-pearl) culture provides rural livelihood opportunities in the South Pacific and is a low-tech alternative to capital and labor-intensive round pearl culture. The Kingdom of Tonga is unique among the pearl-producing countries of the South Pacific in focusing on mabe pearl culture using the winged pearl oyster Pteria penguin. The Tongan mabe pearl sector is developing rapidly and stimulated by routine supply of spat to mabe pearl farmers, from the government hatchery at no cost. It is likely that some level of cost recovery for spat supply will be considered as the sector strengthens, but information on hatchery production costs is limited. This study determined the costs of operating the government pearl oyster hatchery in Tonga and developed an economic model to assess the production cost of juvenile oysters. Modeling was based on a single annual hatchery run generating 6,600 oysters from the ocean-based nursery for delivery to commercial pearl farms. Estimated capital cost was USD 19,079 (excluding government buildings and chattels), and the major production costs were hatchery labor (37%), capital purchase and replacement (20%), and nursery labor (10%). Total annual costs for the pearl oyster hatchery were USD 13,263, equating to a cost of USD 2.01 per oyster supplied to farmers in Tonga. Given significant annual profits of around USD 9,338 that can be generated from 100 harvested oysters, there is justification for cost recovery. Results will be valuable to key stakeholders and have regional relevance for hatchery production of high-value aquaculture commodities.

The structure and function of coral reef ecosystems is increasingly compromised by multiple stressors, even in the most remote locations. Severe, acute disturbances such as volcanic eruptions represent extreme events that can annihilate entire reef ecosystems, but also provide unique opportunities to examine ecosystem resilience and recovery. Here, we examine the destruction, persistence and initial recovery of reefs associated with the hydro-magmatic eruption that created Earth’s newest landmass, the Hunga Tonga–Hunga Ha’apai volcanic island. Despite extreme conditions associated with the eruption, impacts on nearby reefs were spatially variable. Importantly, even heavily affected reefs showed signs of rapid recovery driven by high recruitment, likely from local refuges. The remote location and corresponding lack of additional stressors likely contribute to the resilience of Hunga’s reefs, suggesting that in the absence of chronic anthropogenic stressors, coral reefs can be resilient to one of the largest physical disturbances on Earth.

This study assessed the use of novel, locally made, protective culture cylinders as a means of improving pearl oyster Pieria penguin performance and standardizing culture methods used by mabe pearl farmers in Tonga. Cylinders were constructed from locally sourced wire mesh, for a cost of USD 12.1 each and were used to protect oysters grown on chaplets. Growth and survival of two age cohorts of oysters-"young" (0.7-y-old and 33.1 +/- 0.7-mm dorsoventral height (DVH)) and "old" (2.7-y-old and 86.9 = 0.8 mm DVH)-cultured using this system were determined every 3-5 wk over an 11-mo period. The DVH of "young" oysters increased by 74.6 mm, wet weight (WW) by 161.2 g, and shell thickness (ST) by 23.4 mm, whereas for "old" oysters, DVH, WW, and ST increased by 55.2 mm. 271.4 g, and 14.7 mm, respectively, over the same period. "Young" oysters held in culture cylinders reached the starting size of the "old" oyster cohort within seven months of growth and at less than half their age (1.2 and 2.7 y old, respectively). "Young" oysters held in culture cylinders also showed a 3-fold greater monthly growth rate than oysters cultured in trays (6.8 and 2.1 mm month(-1), respectively). Survival of oysters in culture cylinders over the 11-mo culture period was 91.7% and 97.6% for "young" and "old" oysters, respectively, compared with 25% for oysters cultured in trays. The use of protective cylinders for P. penguin culture increases oyster survival and reduces the culture period required for P. penguin to reach minimum pearl production size by >50% relative to the current tray-based culture method, supporting improved mabe pearl farm profitability.

•Capital cost (US dollars; USD) of a Tongan mabé pearl farm was USD 2,027 with a 4-year payback period•Labour input of <10 hours per week supported annual production of 231 mabé pearls•Annual profitability of USD 9,338 generated a benefit-cost ratio of 4.86•Subsistence mabé pearl farming is profitable•Subsistence mabé pearl farming is compatible with other subsistence activities

The position and arrangement of nuclei is the most important technical aspect of mabe pearl (half-pearl) production. This study examined the effects of nucleus arrangement, profile (height) and position, on quality, nacre thickness and shape of mabe pearls produced by Pteria penguin. Oysters implanted with three nuclei produced a greater proportion of saleable mabe pearls with more regular shapes than oysters implanted with five nuclei. Use of low profile nuclei resulted in mabe pearls with increased nacre thickness and produced mabe pearls of significantly higher quality, with more regular shapes than high profile nuclei. Nucleus position significantly influenced mabe pearl quality, nacre thickness and shape. The posterior-ventral position of the left shell valve produced mabe pearls of the highest quality with the thickest nacre and was the best location for mabe pearl culture. Based on the results of this study, it is recommended that P. penguin is implanted with a maximum of three nuclei to increase the production of regular-shaped mabe pearls, and that low profile nuclei are used to improve quality and nacre thickness of mabe pearls produced in less favourable nucleus positions. An optimal nucleus arrangement for P. penguin of 130-150 mm dorso-ventral height would include one high profile nucleus in the posterior-ventral position of the left shell plus additional low profile nuclei in both the anterior-ventral position of the left shell valve and, the center of the right shell. Based on the quality grading system used in this study, a minimum commercial nacre thickness of 0.25 mm is recommended for mabe pearl production using P. penguin.

Nacre thickness is a major factor influencing the quality and value of half-pearls ('mabe'), yet accurate determination of nacre thickness, in a non-destructive manner, is problematic. Microradiography is commonly used to measure the nacre thickness of round pearls, however the suitability of this technique for mabe has not previously been assessed. Mabe were cultured in winged pearl oysters (Pteria penguin) for periods of 200 to 380 days to produce pearls with a range of nacre thicknesses. The nacre thickness of each pearl was quantified using microradiography and standard micrometer techniques. A strong, significant relationship was observed between measurements obtained using both techniques (R-2 = 0.88, P <= 0.001). Microradiography produced defined, measureable images, with a resolution of +/- 0.04 mm, for mabe pearls with nacre thicknesses between 0.1 and 1.3 mm. Mabe nacre thickness and pearl quality were significantly influenced by the position of the pearl nucleus within the shell (T-(95)= 7.14, P < 0.001, Fisher's exact test, P < 0.001, respectively). Nuclei in a posterior ventral position on the left shell valve produced the highest percentage of good quality mabe pearls (83% A grade or higher) and had a mean nacre thickness nearly twice that of mabe pearls produced at other positions in the shell (0.78 +/- 0.04 mm). A significant influence of culture duration on nacre thickness or pearl quality was not detected. Our results demonstrate that microradiography is an accurate and non-destructive technique that is appropriate to determine nacre thickness in mabe pearls. Future research should further examine the relationship between nucleus position and pearl quality to develop optimum culture protocols for mabe pearl production.

Shell dimensions of 588 hatchery-produced Pteria penguin (Roding, 1798) were measured and analyzed to describe morphometric changes in shell form of this species over its life cycle. Oysters ranged from 9.4 to 202.2 mm in dorsoventral height (DVH), 0.1-1,526.9 g in weight and spanned 0.5-5 y of age. Significant positive curvilinear relationships were observed between shell width (SW) and DVH (R-2 = 0.99, P < 0.001), diagonal length (DL) and DVH (R-2 = 0.99, P < 0.001), shell thickness (ST) and DVH (R-2 = 0.98, P < 0.001), and wet weight (WW) and DVH (R-2 = 0.99, P < 0.001). Trends in the morphometric ratios of P. penguin indicated a proportional decrease in SW and DL with increasing DVH, resulting in a shift from a horizontally elongate to a vertically elongate shell form. The ST of P. penguin remained proportionally stable over its life cycle, whereas its WW increased proportionally by more than two orders of magnitude. Based on the results of this study, future research should examine (1) the relationship between the external shell dimensions and internal nacreous area, (2) changes in nacre deposition rate in different shell locations, and (3) the relationship between soft tissue weight, shell weight, nacre thickness, and DVH of P. penguin. The description of the growth form of P. penguin represents an important first step toward determining optimum half-pearl (mabe) culture procedures for P. penguin in Tonga.

Elevated sediment loads in the epilithic algal matrix (EAM) deter grazing by herbivorous fishes and may compromise their critical roles on coral reefs. However, the properties of sediments that drive herbivore deterrence are unknown. Binary choice trials in aquaria were used to examine the effects of three sediment attributes-sediment source, grain size and organic load-on grazing by the abundant inner-shelf parrotfish, Scarus rivulatus. Fish were presented with a choice between EAM-covered rocks treated with (a) terrigenous or reefal sediments, (b) fine or coarse sediments or (c) sediments with high or low organic loads. Scarus rivulatus did not show a preference for sediments from different sources (terrigenous vs. reefal); however, a clear preference was evident for fine-grained sediments over coarse (109 % more bites) and sediments with high organic loads over low (147 % more bites). The avoidance of coarse sediments is likely to be a key factor driving the inhibition of grazing on mid-shelf reefs, which are dominated by coarse sediments. In contrast, on inner-shelf reefs, grazing by parrotfishes may be deterred primarily by high sediment loads, which reduce the proportional organic content in EAM sediments. Our study highlights the potential impact of sediments on critical ecological processes and the threats posed by changing sediment loads on inner-shelf reefs.