Variation in seagrass community structure and its effects on blue carbon storage in tropical seagrass beds

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Devi N. Choesin, Amelia Setya Nur Kumala and Dian Rosleine, School of Life Sciences and Technology, Institut Teknologi Bandung, Bandung, Indonesia

Background/Question/Methods
Seagrass beds are considered as one of the most effective ecosystem types in storing coastal blue carbon, and thus play an important role in the mitigation of global climate change. However, coastal ecosystems continue to be degraded and threatened by anthropogenic activity. The urgency for coastal ecosystem conservation and sustainable management calls for research on the potential of blue carbon storage in seagrass ecosystems. Carbon storage in a particular ecosystem may be affected by factors such as species diversity and habitat type. In this study, we investigated the relationship between plant community structure and carbon storage in tropical seagrass ecosystems by using a case study of six coastal sites in the Karimunjawa Marine National Park in Central Java, Indonesia. This relationship was determined based on the comparison and correlation between vegetation analysis data and carbon stock estimation. Community structure was described through the measurement of seagrass density, frequency and cover, then compared through several indices, i.e., importance value, diversity, evenness, dominance, and similarity. Carbon stock at each site was calculated for three carbon pools, i.e., aboveground living biomass, belowground living biomass, and sediment by measuring organic carbon content (OCC). Biomass carbon stock was obtained using the correlation between seagrass density for each species, seagrass individual dry weight for each species, and seagrass OCC, while sediment carbon stock was obtained by multiplying dry bulk density, sediment dry weight per sampling volume, and sediment OCC.
Results/Conclusions
Eight seagrass species were recorded, i.e., Enhalus acoroides, Thalassia hemprichii, Cymodocea rotundata, Halodule pinifolia, Halophila ovalis, Halophila minor, Syringodium isoetifolium, and Cymodocea serrulata. Carbon stocks in the six sites studied ranged from 127.4 Mg C ha-1 to 426.2 Mg C ha-1. Lowest carbon stock was found in a site dominated by T. hemprichii, while highest stock was associated with the dominance of E. acoroides. The density of E. acoroides was positively correlated with total biomass carbon stocks (r=0.97; p<0.01), while its dominance was positively correlated with sediment carbon stocks (r=0.92; p<0.05) and total ecosystem carbon stocks (r=0.92; p<0.05). Overall results show that seagrass beds with different community structure differ in carbon storage capacity. Seagrass beds dominated by large-sized species such as E. acoroides showed higher estimated carbon stocks, thus suggesting the importance of considering the variability of community structure in managing seagrass ecosystems for carbon sequestration and storage.