📄 earth_science

Uncovering the Vital Role of Sea urchins: A Captivating Exploration of their Abundance as Bioindicators in the Inner Ambon Bay, Maluku

This study demonstrates that sea urchins in Inner Ambon Bay, Maluku, serve as effective bioindicators for environmental health, with their abundance and diversity varying across different beaches and showing significant correlations with key water quality parameters.

Original authors: Vanela Chatrin Lekatompessy

Published 2026-08-11

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: Vanela Chatrin Lekatompessy

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine the ocean as a giant, bustling city where millions of creatures live, work, and play. Just like in any city, this underwater metropolis faces pollution from factories, boats, and runoff from the land. To know if the city is healthy or sick, scientists need a way to check the "vital signs" of the environment. They often look for specific creatures that act like living canaries in a coal mine. If these sensitive creatures are thriving, the water is likely clean; if they are struggling or disappearing, something is wrong. One such group of underwater detectives is the sea urchin. These spiky, round animals aren't just snacks for sea otters; they are crucial gardeners of the reef, eating algae and keeping the ecosystem balanced. Because they live right on the ocean floor and react quickly to changes in water temperature, saltiness, and cleanliness, scientists believe they can tell us a lot about the health of their home.

This research paper takes a closer look at a specific underwater neighborhood: the Inner Ambon Bay in Maluku, Indonesia. The author, led by Vanela Chatrin Lekatompessy, wanted to see how many sea urchins were living there, what kinds they were, and whether the number of urchins could tell them something about the quality of the water. They treated the sea urchins like bioindicators—living sensors that reflect the state of their environment. By counting the urchins and measuring the water's temperature, salt levels, oxygen, and acidity (pH), the team hoped to uncover a secret link between the animals and the water's health.

The study took place between January and February 2024 across three distinct beaches in the bay: Galala, Rumah Tiga, and Poka. Each beach was a different world. Galala was mostly muddy with seagrass; Rumah Tiga was a mix of sand and mud with some algae; and Poka was rocky with scattered sand and seagrass. The researchers waded out during the lowest tides, setting up square grids (5x5 meters) to count every sea urchin they found. They didn't just count them; they identified the species, noting that six different types were present, including the spiky Diadema setosum and the striped Echinothrix calamaris.

The results painted a fascinating picture of three very different neighborhoods. At Poka Beach, the rocky shore was absolutely packed with sea urchins—2,390 individuals were counted! It was a sea of spines. However, while Poka had the most urchins, it didn't have the most variety. In contrast, Rumah Tiga Beach had fewer total urchins (391), but it was the most diverse, hosting four different species. Galala Beach had the fewest urchins (181) and only three species. Interestingly, the researchers noticed that in the muddy parts of Galala where a specific type of seagrass grew thick, no sea urchins were found at all, suggesting these animals have very specific preferences for where they call home.

The team also looked at how evenly the different species were spread out. At Galala, the few urchins that were there were shared fairly evenly among the three species. But at Poka and Rumah Tiga, one or two types of urchins seemed to dominate the party, making the community less balanced. The researchers used a special mathematical tool called Principal Component Analysis (PCA) to see how the water quality and the urchin populations were related. The analysis suggested that Galala and Rumah Tiga were quite similar in their environmental conditions, while Poka stood apart as a unique environment.

Crucially, the study found that the water quality at all three sites was actually quite good. The temperature was between 29 and 30°C, the saltiness was between 27 and 28, the oxygen was high (7.9 to 8.9 mg/L), and the pH was between 7.8 and 8. These numbers are all within the "comfort zone" for sea urchins. The author found a significant correlation between sea urchin abundance and these key water quality variables, suggesting that the two are closely linked. This leads to a hopeful conclusion: sea urchins in Inner Ambon Bay could serve as excellent bioindicators. If their numbers drop or their diversity changes in the future, it might be an early warning sign that the water quality is declining. While the paper doesn't claim to have solved all the mysteries of the ocean, it strongly suggests that keeping an eye on these spiky creatures is a smart way to monitor the health of the bay.

Technical Summary: Uncovering the Vital Role of Sea Urchins as Bioindicators in Inner Ambon Bay

Problem Statement
Marine ecosystems are increasingly threatened by anthropogenic pollutants driven by urbanization, industrialization, and agricultural intensification. These multi-source contaminants pose significant risks to biodiversity, particularly affecting sensitive benthic macrofauna. Inner Ambon Bay, Maluku, faces specific pressures from diverse activities including fisheries, aquaculture, naval operations, commercial shipping, coastal construction (e.g., the Merah Putih Bridge), and freshwater inputs from rivers. While the ecological impacts of these stressors are understood to be detrimental, there is a need for integrated assessment tools to monitor environmental health. Sea urchins (Echinoidea), as benthic invertebrates with widespread distribution in seagrass and coral reef ecosystems, are increasingly recognized as potential bioindicators due to their sensitivity to environmental stressors and their critical role in structuring benthic communities.

Methodology
The study was conducted in Inner Ambon Bay between January and February 2024. Three distinct intertidal sites were selected based on substrate heterogeneity:

Galala Beach: Predominantly muddy substrate with Enhalus acroides seagrass.
Rumah Tiga Beach: Sandy substrate with patchy Thalassia hemprichii and brown algae (Padina australis), featuring floating aquaculture cages (karamba).
Poka Beach: Rocky substrate with fragmented coral rubble, sandy patches, and sparse Thalassia hemprichii, located near a diesel power generation facility.

Sampling Protocol:

Sea Urchin Collection: Sampling occurred during the lowest tide periods. Three stations were established per beach, stratified by substrate type. Within each station, three 5x5 meter transects were deployed, creating a total of nine plots with 27 repetitions. Specimens were counted, recorded, and identified to the species level.
Water Quality Analysis: Physicochemical parameters (temperature, salinity, dissolved oxygen, and pH) were measured in situ on each plot using a portable universal multi-parameter device.
Data Analysis:
- Diversity Metrics: Species diversity was calculated using the Shannon-Wiener Index ( $H'$ ), with ranges interpreted for community stability. Evenness was measured using the Pielou index ( $E$ ).
- Dominance and Richness: The Simpson Dominance Index ( $D$ ) and Margalef Species Richness Index ( $R_1$ ) were employed to assess community structure.
- Multivariate Analysis: Principal Component Analysis (PCA) using Past4.0 software was utilized to examine relationships between abiotic factors, water quality parameters, and sea urchin abundance.

Key Results

Species Identification: Six sea urchin taxa were identified across the three sites: Diadema setosum, Diadema savignyi, Diadema antillarum, and three color morphs of Echinothrix calamaris (white-spined, brown-striped, and green-striped).
Abundance and Distribution:
- Poka Beach exhibited the highest total abundance (2,390 individuals), dominated by the genus Diadema, which formed small aggregations.
- Rumah Tiga Beach recorded the second highest abundance (391 individuals) but displayed the highest species richness (four species).
- Galala Beach had the lowest abundance (181 individuals) and only three species; notably, no sea urchins were observed in areas of dense Enhalus acroides seagrass.
Community Structure Indices:
- Diversity ( $H'$ ): Rumah Tiga (1.45) and Galala (1.56) showed moderate diversity, while Poka had lower diversity (0.97).
- Richness ( $R_1$ ): Rumah Tiga (1.93) demonstrated higher species richness compared to Galala (0.89) and Poka (0.59).
- Evenness ( $E$ ): Galala Beach showed high evenness (0.98), whereas Rumah Tiga (0.56) and Poka (0.61) showed less even distributions, indicating higher dominance by specific Diadema species.
Environmental Correlations: Water quality parameters (Temperature: 29–30°C; Salinity: 27–28; DO: 7.9–8.9 mg/L; pH: 7.8–8.0) were within acceptable ranges for tropical sea urchins. PCA results indicated that Galala and Rumah Tiga beaches shared similar environmental characteristics and species assemblages, while Poka Beach was distinct, likely driven by its specific substrate and lower pollution levels.

Significance and Claims
The paper posits that sea urchins serve as effective bioindicators for assessing environmental health in Inner Ambon Bay. The study claims a significant correlation between sea urchin abundance and key water quality variables, suggesting that these invertebrates are sensitive to environmental changes. The distinct community structures observed across the three sites—ranging from the high abundance of Diadema in the rocky, clearer waters of Poka to the higher diversity in the mixed-substrate Rumah Tiga—reflect the influence of local anthropogenic pressures and habitat characteristics.

The author concludes that the presence, absence, and community structure of sea urchins provide valuable insights into the biological effects of anthropogenic activities. By demonstrating that sea urchin populations respond to specific environmental drivers (such as substrate type and water quality), the study supports the utility of these organisms in monitoring the resilience and health of tropical coastal ecosystems. The findings underscore the necessity of preserving diverse beach environments to maintain healthy marine ecosystems and highlight the role of sea urchins in future environmental monitoring programs.

Technical Summary: Uncovering the Vital Role of Sea Urchins as Bioindicators in Inner Ambon Bay

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