Biology subjects

Roelfsema, C. M.

Publications and source records attributed to Roelfsema, C. M..

4 recordsLinked to original sources

bioRxiv2024

Broadscale reconnaissance of coral reefs from citizen science and deep learning

Coral reef managers require various forms of data. While monitoring is typically the preserve of scientists, larger scale reconnaissance data that can be used to inform spatial decisions does not usually require such precise measurement. There is an increasing need to collect such broadscale, up-to-date environmental data at massive scale to prioritise limited conservation resources in the face of global disturbances. Citizen science combined with novel technology presents an opportunity to achieve data collection at the required scale, but the accuracy and feasibility of new tools must be assessed. Here we show that a citizen science program that collects seascape images and analyses them using a combination of deep learning and online citizen scientists can produce accurate benthic cover estimates of key coral groups. The deep learning and citizen scientist analysis methods had different but complementary strengths depending on coral category. When the best performing analysis method was used for each category in all images, mean estimates from 8086 images of percent benthic cover of branching Acropora, plating Acropora, and massive-form coral were [~]99% accurate compared to expert assessment of the same images, and >95% accurate at all coral cover ranges tested. The effort to achieve 95% accuracy at a site - our ecologically relevant target based on the accuracy of other tools - was attainable based on citizen scientist involvement in pilot years of the program, with 18-80 images needed depending on coral type and reef state. Power analyses showed that sampling up to 114 images per site was needed to detect a 10% absolute difference in coral cover per category (power = 0.8), accounting for natural heterogeneity. However, the benthic cover of all other coral groups as a single category could only be estimated with 95% accuracy at 60% of survey sites and for images with 10-30% coral cover. Disaggregating this other coral group into more distinct coral categories may improve accuracy. Overall, citizen science can provide an accuracy that is acceptable for many end-users for select coral morphologies. Such a combination of emerging technology and citizen science presents an attainable tool for collecting inexpensive, widespread reconnaissance data of coral reefs that can complement higher resolution survey programs or be an accessible tool for resource-poor locations.

ecology↗

bioRxiv2024

Reproducing within-reef variability in coral dynamics with a metacommunity modelling framework

Reef systems span spatial scales from 10s to 100s and even 1000s of kilometres, with substantial spatial variability across these scales. Managing and predicting the future of coral reefs requires insights into reef functioning at all spatial scales. However, investigations of reef functioning often consider individual reefs as the smallest unit (10s of kilometres), despite substantial spatiotemporal variability occurring within-reefs (100s of meters). We developed C[~]scape, a coral metacommunity modelling framework that integrates the demography of corals with population-level responses to physical and environmental spatial layers, to simulate a mosaic of interacting coral communities across a heterogenous seascape. Coral communities are linked using biophysical connectivity modelling. Coral community growth is modelled with a logistic growth model, with the intrinsic growth parameter determined from taxa-specific Integral Projection Models to incorporate demographic mechanisms. Site-specific coral habitat parameters, derived from satellite-based geomorphic and benthic habitat maps, define the maximum coral cover and are used to modulate community growth spatially and temporally as a function of the available space suitable for corals. These parameters are a proxy for the many interacting physical and environmental factors -- e.g., depth, light, wave exposure, temperature, and substrate type -- that drive within-reef variability in coral demography. Using a case study from the Great Barrier Reef, we show that modulating community growth using site-specific habitat parameters enables more accurate hindcasts of coral cover dynamics, while overlooking within-reef variability may lead to misleading conclusions about metacommunity dynamics. More generally, C[~]scape provides a valuable framework for predicting spatiotemporal dynamics of coral communities within and between reefs, offering a mechanistic approach to test a range of management and restoration options.

ecology↗

bioRxiv2020

The condition of coral reefs in Timor-Leste before and after the 2016-2017 marine heatwave.

El Nino Southern Oscillation global coral bleaching events are increasing in frequency; however, the severity of bleaching is not geographically uniform. There were two major objectives of the present project: 1) assess the state of reefs and coral health at several sites and 2) explore water quality and climate change impacts on Timorese reefs. The impacts of climate change (principally by following coral mortality) were surveyed on coral reefs before and after the 2016-2017 underwater heatwave, using temperature loggers deployed between surveys which were compared to Coral Reef Watch (CRW) experimental virtual station sea surface temperature (SST). CRW is an important and widely used tool; however, we found the SST was significantly warmer (> 1{degrees}C) than in situ temperature during the austral summer accruing 5.79 degree heating weeks. In situ temperature showed no accumulation. Change in coral cover between surveys was attributed to reef heterogeneity. There were significant differences in coral cover, coral diversity, and nutrient concentrations between site and depth and a low prevalence of disease recorded in both years. The comparison of temperature and SST indicate that bleaching stress in Timor-Leste is potentially mitigated by seasonal and oceanographic dynamics. This is corroborated by Timor-Lestes location within the Indonesian ThroughFlow. Timor-Leste is a climate refugium and the immediate conservation work lies in the management of localized anthropogenic impacts on coral reefs such as sedimentation and fishing.

ecology↗

bioRxiv2019

Citizen scientists highlight conservation value of a small subtropical reef, Flinders Reef, southeast Queensland, Australia.

Subtropical reefs are unique ecosystems that require effective management - informed by regular ecological monitoring - to foster resilience to environmental changes. Resources to conduct monitoring are limited, and citizen science can complement data from local management agencies. Here, citizen science efforts document the ecological status of a subtropical reef, Flinders Reef, Moreton Bay Marine Park, Australia. Ecological surveys, following Reef Check Australia and CoralWatch protocols, were conducted by 44 trained volunteers. Ten sites at Flinders Reef were surveyed at 5-10 m depth in autumn and spring. Additionally, underwater photos and depth surveys were integrated with satellite imagery to create a detailed habitat map. Coral cover across sites ranged between 14% and 67%. Branching corals dominated the site with 67% cover and showed 89% dissimilarity in coral community composition compared to other sites. Coral community composition was mostly explained by spatial variation, of which 16% was influenced by wave exposure. Observed reef impacts including physical damage, unknown scars and coral disease were three times lower than studies on more accessible reefs in Moreton Bay Marine Park. Invertebrate abundance was relatively low (6.65 individuals per 100 m2), with the most abundant groups observed being sea urchins (Diadema spp.), gastropods (Drupella spp.) and anemones. Butterflyfish were recorded at every site and were the most abundant fish group surveyed. Findings highlight the healthy condition of Flinders Reef, likely influenced by its offshore location and protection status as a no-take zone. This study demonstrates that increasing the current 500m radius protection zone by a further 500m could double the protected area of coral, offering potential further conservation benefits. The findings resulting from the ecological data analysis and created benthic habitat map, provide an example of how citizen science based projects can assist marine park authorities and the public in ongoing conservation efforts.

ecology↗