Annual Reef Report
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ANNUAL 2018 REEF REPORT Angsana Velavaru, Dhaalu Atoll, Authors: Nicholas Hardman, Hassan Maldives Nishan, Steph Skermer, Samantha Gallimore, Steve Newman FINDINGS AT A GLANCE 2018 The majority of sites surveyed in the atoll displayed an increase in coral cover, suggesting recovery from the bleaching event. Bare rock and rubble have declined while coral cover has increased across all depths. All sites apart from Lhohi and Velavaru had low recruit density per metre squared. Biomass of fish families Butterflyfish, Parrotfish and Groupers declined at the majority of sites from 2016 to 2018. 2 AT A AT REEF MONITORING What? Long term data is required to understand natural and human induced change in ecosystems, including impact, recovery and resilience assessments needed for effective conservation. Implemented in 2016, the Banyan Tree Long Term Monitoring Program (BTLMP) collects baseline data from coral reefs using robust methods based on ReefCheck [detailed methods on the BTGF website]. Why? Establishing baselines and understanding long-term change: Understand the state of reefs Identify changes in reef composition Identify coral bleaching patterns Monitor progress on reef recovery Support targeted reef restoration efforts Identify changes in abundance and biomass of important fish groups 2016 Global Bleaching Event This was the longest global coral bleaching event in history since the 1980s. Corals in every major reef region were bleached – dead. One quarter of the Great Barrier Reef was declared dead. 3 REEF CONDITION LEGEND LIVE CORAL TURF ALGAE ROCK RUBBLE OTHER Km Benthic categories from 8 sights surveyed in Dhaalu Atoll; 1 Velavaru, 2 Vilu Reef, 3 Bandidhoo, 4, Meedhoo, 5 Lhohi, 6 Udhoo, 7 Fandhoo and 8 Potato. Over the 8 sites surveyed in the Dhaalu atoll live coral and other were the most dominant benthic categories (35.7% and 35.6% respectively). Typically, all reefs surveyed excluding Lhohi had high coral cover, reef 5 located within the atoll had the lowest coral cover (5.7%) while reef 2 located on the outskirts of the atoll had the highest coral cover (44.4%). The majority of the reefs had a higher percentage of bare rock and rubble than turf algae cover indicating substantial grazing from herbivorous fish and invertebrates. 4 CHANGE IN CORAL COVER 70 60 (%) 50 40 30 20 Mean Percent Live Coral Cover Coral Percent Live Mean 10 0 Fandhoo Bandidhoo Udhoo Lhohi Meedhoo Vilu Reef Potato Velavaru 2016 2017 2018 Half of the reefs in Dhaalu Atoll are recovering from the bleaching event in 2016, evidenced by an increase in live coral cover from 2016 (post bleaching) to 2018 at 5m depth across 8 sites within the atoll. After a decline in 2017, Udhoo had the largest increase of coral cover (+107%). Both of the islands inhabited by local communities (Bandidhoo and Meedhoo), increased in coral cover over the three year period (+106.81%, +319.23% respectively). Potato Island’s reef decreased in coral cover (-43.9%) from 2016 to 2018. In 2016 coral cover was the highest in the atoll (+51.25%) however recent development with extensive sand pumping may have caused a decline in coral cover. 5 HOUSE REEF STATUS At all three depths coral cover increased (+22%, +56%, +33% respectively) from post bleaching to 2018. Top Reef (1m) 100 Coral cover at depths 5m, 10m were high and 1m 90 relatively low in comparison. Middle and upper slope 80 70 will in theory attract more corals recruits and help 60 improve live coral cover over time. 50 40 30 In 2016 and 2017 rock dominated at all three 20 10 depths, but in 2018 live coral dominated at 5m and 0 10m, suggesting the reef is recovering. Benthic Cover(%) Upper Slope (5m) t 70 Due to a different mythological approaches, turf 60 50 algae and bare rock have unique results for 2017. 40 However, these categories sill provide colonisable 30 Mean Percen space for coral recruits. 20 10 0 70 Middle Slope (10m) 60 50 40 30 20 10 0 Coral Live Turf Rock Rubble Other 6 2016 2017 2018 CORAL RECRUITMENT 9 8 ) 2 7 6 5 4 3 Mean RecruitMean Density(n/m 2 1 0 Fandhoo Bandidhoo Udhoo Lhohi Meedhoo Vilu Reef Potato Velavaru 2018 Recruit density is referred to as the number of recruits found per metre squared. Velavaru had the highest density of recruits and Potato had the lowest number of recruits per metre squared due to anthropogenic activities occurring on the island. Lhohi displayed the lowest percentage of coral cover but had the second highest number of recruits, however mainly dominated by Proties rus, a fast-growing species of coral. 7 FISH COMMUNITIES Generally, butterflyfish, 6000 1000 parrotfish and grouper biomass declined. 900 5000 800 Surgeonfish biomass 700 increased at 5 sites, but 4000 600 decreased at Villa Reef, Potato and Velavaru from 3000 500 2017 to 2018. This could be 400 an indicator of improved coral 2000 300 ) cover and a reduction in food 2 200 availability (turf algae). 1000 100 Biomass of butterflyfish 0 0 across the majority of sites 12000 2000 1800 declined, contradicting 10000 1600 Mean Biomass (g/200m benthic data which displays 1400 8000 increased food availability 1200 6000 1000 (coral). 800 4000 600 Grouper biomass 400 declined at all sites excluding 2000 200 Lhohi, suggestive of an 0 0 increase in overexploitation of the species due to local Lhohi Lhohi fishing pressure. Udhoo Udhoo Potato Potato Fandhoo Velavaru Vilu Reef Vilu Fandhoo Meedhoo Velavaru Vilu Reef Vilu Meedhoo Bandidhoo Bandidhoo 2016 2017 2018 8 HOUSE REEF After the bleaching 1600 800 event in 2016, butterflyfish biomass increased on the top 1400 700 reef due to improved food 1200 600 source (coral). However, 1000 500 biomass declined on upper and middle reef slope in the past 800 400 three years, contradicting 600 300 increased coral cover. 400 200 Parrot fish biomass ) 2 200 100 increased at 1m and 5m due to increased food availability. In 0 0 (g/200m contrast, the top reef 2500 1400 abundance declined. Biomass 1200 2000 There was a noticeable 1000 decline in grouper biomass at Mean Mean 1500 all depths and years suggesting 800 continued fishing from local 1000 600 communities. 400 Surgeonfish biomass 500 200 increased over the 3 years at 5m and 10m but remained low 0 0 at 1m. 1m 5m 10m 1m 5m 10m 2016 2017 2018 9 .