Calcium carbonate productivity by Halimeda macroloba in the tropical intertidal ecosystem: The significant contributor to global carbonate budgets

Abstract

Halimeda is a potential carbon sink species and an important player in the global carbonate budget. The objectives of this study were to: (i) examine the CaCO 3 and sediment productions of H. macroloba by measuring the density, growth rate, and recruitment; (ii) quantify the numbers of aragonite crystals; (iii) document reproductive events; and (iv) determine the lifespan. This study was carried out at Lidee Lek Island, Satun, Thailand during July 2015 to April 2016. The density was measured using quadrats (0.25 m 2 ) and three 50 m line transects. Alizarin Red-S marking technique was used for the growth rate and CaCO 3 accumulation rate assessments. The recruitment, reproduction and life-span were measured by tagging 500 individuals. Tagged individuals and new plants were counted. In this study, mean and the highest density of Halimeda were 44.42 AE 13.95 and 138.22 AE 11.68 thalli m −2 , respectively, and Halimeda produced 1-2 new segments.thallus −1 day −1 or 0.021 AE 0.001 g dry weight.thallus −1 .day −1 . The annual biomass production was 1910-5950 g m −2 year. −1 . There was a low rate of occurrence of sexual reproduction, observed in late July to September, ranging from 0.17% to 1.92%. For the mortality and recruitment rates, approximately 70-80% of individuals were lost during July to September 2015, probably from sexual reproduction and the recruitment rate varied from 5.36 AE 0.79% to 21.03 AE 2.33%. The highest density of new recruits was found in September 2015 right after the sexual reproductive event occurred. New recruits have been found up to April 2016 without any reproductive events, suggesting that both sexual and asexual reproduction helped maintain the population. The life span of Halimeda was 8-12 months. In addition, Halimeda accumulated CaCO 3 at approximately 0.018 g CaCO 3 thallus −1 day −1 and produced CaCO 3 at approximately 291.94-908.11 g m −2 year −1 , indicating that Halimeda contributes to CaCO 3 and helps to sink carbon through calcification. The results in terms of the density, growth rate, and CaCO 3 accumulation rate can be used to calculate the mass of carbonate sediment contributed by Halimeda.

The contributions of allochthonous and autochthonous materials to organic carbon in coastal sediment: A case study from Tangkhen Bay, Phuket, Thailand

“…Tropical calcifying macroalgae, such as Halimeda spp., are already known for their potential role in climate change mitigation, as these macroalgae continue to exhibit high growth rates in reduced pH conditions (Kaewsrikhaw, Prathep, Darakrai, & Beer, ). Moreover, these macroalgae have the ability to contribute high amounts of carbonate to the ocean budgets, with annual production of 291.94–908.11 g/m 2 of CaCO 3 (Mayakun & Prathep, ), which supports the carbon sink via calcification. On the other hand, the high canopy complexity of Halimeda spp.…”

The standing stock and CaCO3 contribution of Halimeda macroloba in the tropical seagrass-dominated ecosystem in Dongsha Island, the main island of Dongsha Atoll, South China Sea

“…These two physical disturbances could explain the unexpectedly low growth and carbonate accumulation in Halimeda. Without seagrass competition, high sedimentation, and strong waves, Mayakun et al (2014) and Mayakun & Prathep (2019) showed much higher density, growth rate and CaCO 3 production of H. macroloba at Ko Mat Sum, in the Gulf of Thailand (with mean density of 11.70 ± 1.77 thalli m −2 ) and Lidee Island in the Andaman Sea (with mean density of 44.42 ± 13.95 thalli m −2 ), respectively.…”

“…In this study, four developmental stages were categorically defined in our H. macroloba samples as follows: stage 1: newly recruited plant; stage 2: young plant with 3-4 new segments and 1-2 levels of segment; stage 3: partially calcified plant with 3-4 levels of segment; and stage 4: mature calcified plant. We followed such developmental categorization according to the definition of Mayakun & Prathep (2019). Unfortunately, stage 5: fertile plant with reproductive cells and stage 6: dead plant, were rarely found and could not be collected.…”

“…Producing one to two new segments daily, thalli grew by 0.021 g dry weight thallus −1 day −1 . Total CaCO 3 production by H. macroloba was 291.94-908.11 g m −2 y −1 and the CaCO 3 content increased with age (Mayakun & Prathep, 2019). Due to its fast growth, and high CaCO 3 productivity, this alga is a significant contributor to carbonate budgets (Mayakun et al, 2012a(Mayakun et al, , 2012b(Mayakun et al, , 2014Mayakun & Prathep, 2019).…”

“…It can utilize bicarbonate (HCO 3 − ) for calcification and precipitates aragonite crystals in its intercellular spaces (Borowitzka & Larkum, 1976). It is one of the main calcium carbonate (CaCO 3 ) producers that contribute to the marine carbonate budget in tropical reefs and lagoons (Ree et al ., 2007; Mayakun et al ., 2014; Carneiro & Morais, 2016; Kaewsrikhaw et al ., 2016; McNeil et al ., 2016; Perry et al ., 2016; Carneiro et al ., 2018; Prathep et al ., 2018; Mayakun & Prathep, 2019). For instance, global estimates showed that Halimeda species contributed around 2 kg CaCO 3 m −2 year −1 (Drew & Abel, 1985; van Tussenbroek & van Dijk, 2007; Perry et al ., 2016) or accumulated around 0.15 Gt CaCO 3 year −1 (Milliman, 1993), resulting in ~8% of total world carbonate production (Hillis, 1997).…”