The green seaweed Caulerpa can be found in almost every coastal area of Indonesia, and it is one of the seaweeds with immense potential to be developed in the future. The chemical factors, especially water nutrients (nitrate, nitrite, phosphate, and ammonia), play an essential role in the distribution and diversity of seaweed. This study aimed to identify the abundance, ecological index, and relationship between the water column nutrients concentration and the biodiversity of Caulerpa from three different locations (Bintan Island, Jepara, and Osi Island). There were 12 points of observation at each site. The result showed a correlation between the nutrient levels and the abundance and diversity of Caulerpa in three locations. The nitrate, ammonia, and DIN:P ratio values were significantly different between areas. In contrast, there were insignificant differences in nitrite and phosphate concentrations between sites. The highest nitrate and phosphate concentrations were observed on Osi Island. The nitrite and ammonia values were identical for the condition on Bintan Island. The nitrate value was the main characteristic that distinguished the water nutrient at all sites. The Caulerpa species found in this research were Caulerpa racemosa, Caulerpa lentilifera, Caulerpa serrulata, Caulerpa sertularoides, and Caulerpa cupresoides. The nitrate and phosphate values influenced the growth factor of the green seaweed Caulerpa lentilifera. Caulerpa racemosa and Caulerpa serrulata, on the other hand, grew in response to ammonia levels. Caulerpa cupresoides diversity and abundance were impacted by the nitrite value. The results of the canonical correspondence analysis revealed that nitrate, phosphate, and ammonia were the most important factors influencing Caulerpa distribution in three locations.
The green seaweed Caulerpa racemosa is a seaweed of high prospect that is being given emphasis by the Indonesian government. However, C. racemosa in Indonesia may include multiple species level-entity exhibiting morphological overlap and require molecular analysis for species identification. Molecular documentation of species richness of indigenous populations of C. racemosa is essential to underpin cultivar development and conservation of the species to avoid overharvesting. The present study aimed to determine the genetic diversity of C. racemosa and document the haplotype network of the specimens from four different locations (Bintan Island, Jepara, Takalar and Osi Island) using the chloroplast tufA gene. Twenty individuals from four areas were collected and amplified with the chloroplast-encoded gene tufA for species identification against publicly available data. The identification of C. racemosa based on the tufA gene showed that the species found in four locations were C. cylindracea (previously C. racemosa var. cylindracea), C. macra (previously C. racemosa var. macra), C. racemosa, and C. oligophylla (previously C. racemosa var. lamourouxii). This study records the existence of C. cylindracea in Takalar and Jepara, Indonesia for the first time. The most diverse C. racemosa species was in Osi Island, where the exploitation of this seaweed is very low. In contrast, the lowest number of C. racemosa varieties were found in Takalar, where exploitation is very high. There were only minor light variations of Caulerpa species in the tufA gene in four different sites with only four haplotypes found, and each haplotype corresponded to another species.
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