The Christmas tree worm (Spirobranchus spp.) is a biota that lives in association with hermatypic corals. This bioeroder damages the structural integrity of corals, making them susceptible to breakage. Therefore, further investigation is required to determine the distribution, diversity, uniformity, and predominance of CTW on hard corals in the Sempu Island Nature Reserve’s waters. The method used is the belt transect method, which refers to the reef check. CTW species will be identified based on their operculum, and corals will be identified based on their growth form, genus, and species. The data gathered were processed, and the abundance value and ecological index were obtained. The CTW species found at the five stations were Spirobranchus gardineri, Spirobranchus cruciger, and Spirobranchus spp., associated with massive corals of the genus Porites and genus Goniastrea. Water quality factors such as currents, sedimentation, and nitrates affect CTW’s presence. Medium-to-fast currents circulate around Sempu Island, where high sedimentation rates of 73.73 mg/ cm2/day decrease light penetration into the waterways. Additionally, elevated nitrate levels contribute to the growth of CTW operculum-covering turf algae. CTW abundance values ranged from 0.018 to 0.084 individuals/m2, diversity index (H’) ranged from 0.403 to 0.760 (low), and uniformity index (E) ranged from 0.582 to 0.966 (unstable to stable). The dominance index (C) values ranged from 0.513 to 0.705 (medium). Based on the index value, it was found that the CTW in Sempu Island was in the unstable category, so there was moderate dominance.
Marine debris significantly impacts coral ecosystems, especially in regions with high biodiversity like the Sempu Island Nature Reserve in Malang, Indonesia. According to the guidelines of ReefCheck and KLHK 2020, this indepth study looked at the types, amounts, and impacts of marine debris on coral health at five different sites close to the Pondokdadap Coastal Fishing Port. This study employs a belt transect method measuring 100×5 meters to systematically collect data. The obtained results indicate that cloth refuse is the most substantial form of waste, accounting for 84.65% of the weight of marine waste. The primary locations for this form of waste are areas with high human activity, particularly those near fishing ports. The impact of marine debris on coral reefs depends on its proximity to human activity, as it exhibits a wide range of density and composition. Millepora, a coral species characterized by its branching structure, was the most severely impacted, with damage levels spanning from 12.07% to 48.65%. This indicates its vulnerability to debris accumulation. The study determined the prevalence of a variety of waste categories, with plastic being the most prevalent. The study also focused on other types of inorganic waste, such as packaging, fishing lines, raffia ropes, rubber (flip-flops and tires), fabric, metal (cans and metal cutlery), glass bottles, and other items, primarily in the port area. The density of debris is an important indicator of the environmental pressure exerted on coral ecosystems. Among the examined locations, the Jetty station displayed the highest concentration of inorganic debris, with a density of 0.100 items/m2. In contrast, Watu Meja Station had the lowest density of inorganic waste at 0.008 items/m2, but the highest concentration of organic waste at 0.066 items/m2. This indicates that there is less human impact but more accumulation of natural refuse. This study highlights the pressing necessity for effective marine waste management strategies, particularly near active ports like Pondokdadap, to mitigate the detrimental effects on coral reefs. The health and sustainability of this critical marine ecosystem can be ensured by reducing refuse accumulation through enhanced waste management protocols and community engagement.
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