The Ecology of Sea Cucumber Bioturbation: Why Removing Them Changes the Ocean Floor

In 2024, a study published in Nature Communications delivered a finding that reframed the commercial sea cucumber trade in terms that go well beyond fisheries management. Researchers working in the Florida Keys had conducted a long-term field experiment in which sea cucumbers were removed from reef plots while control plots retained their natural populations. The result, tracked over an extended monitoring period, was unambiguous: removal of detritivore sea cucumbers from reefs increases coral disease.

This finding — that the commercial harvest of sea cucumbers affects coral survival through a mechanism entirely separate from the animals' direct value as food or medicine — places the sea cucumber trade in an ecological context that most commercial operators have not fully considered. The species whose dried body wall commands premium prices in Hong Kong, whose bioactive compounds are studied in pharmaceutical laboratories, and whose harvest drives the livelihoods of coastal fishing communities across the Indo-Pacific is simultaneously an ecosystem engineer whose absence measurably degrades the reef systems that support the very fisheries it is harvested from. Understanding how this works is not peripheral to the commercial story of sea cucumber. It is the foundation of the sustainability argument that increasingly shapes how responsible supply chains justify their sourcing practices.

What Bioturbation Is and Why It Matters

Bioturbation refers to the physical disturbance and reworking of sediments by the feeding, burrowing, and movement of living organisms. In marine sediments, bioturbation is one of the primary mechanisms by which oxygen, nutrients, and organic matter are mixed and redistributed through the sediment column. Without bioturbation, marine sediments stratify: organic matter accumulates at the surface, oxygen is rapidly depleted below a few millimeters, and anaerobic conditions develop that reduce the productivity and biological diversity of the benthic community.

Sea cucumbers are among the most significant bioturbators in tropical reef and lagoon environments globally. As deposit feeders, they ingest sediment continuously as they move across the seafloor, extracting the organic material and microbial biomass contained within it, and expelling the processed sediment behind them. A single large Holothuria scabra individual processes approximately 60-260 grams of dry sediment per day, depending on body size and environmental conditions. Multiplied across the population densities that characterized undepleted reef environments — which research has documented at densities up to several individuals per 100 square meters in historically productive areas — the cumulative sediment processing by sea cucumber populations represents a biogeochemical force of significant scale.

Research published in ScienceDirect (The World of Sea Cucumbers, Elsevier, 2024) synthesizing the ecological roles of tropical sea cucumbers documented that bioturbation and deposit-feeding activity by tropical holothuroids are among their primary ecological roles on coral reefs, with the turnover of vast quantities of sediment through their feeding activities influencing sedimentary properties including grain size, microalgal productivity, nutrient cycling, oxygen profiles, and biogeochemistry, with benefits to ecosystem functioning.

The Nutrient Cycling Function: Closing the Loop

The ecological importance of sea cucumber bioturbation is not simply the physical mixing of sediments. It is the biogeochemical transformation of organic matter that this mixing enables. Research published in PLOS ONE (2012) by MacTavish, Stenton-Dozey, Vopel, and Savage demonstrated experimentally that deposit-feeding sea cucumbers enhance mineralization and nutrient cycling in organically enriched coastal sediments. The study found that sea cucumbers significantly increased the flux of dissolved inorganic nitrogen and phosphorus from sediments into the overlying water column, accelerating the conversion of organic matter into the dissolved inorganic nutrients that are available for uptake by phytoplankton, seagrass, and coral-associated algae.

This nutrient cycling function has a specific relevance for the Indonesian coastal environments that support sea cucumber populations and the coral reef systems associated with them. Seagrass beds, which are the primary habitat of Holothuria scabra, depend on dissolved inorganic nutrients for productivity. The bioturbation activity of sandfish populations within these beds maintains the nutrient availability that sustains seagrass growth. A seagrass bed depleted of its sea cucumber population loses a significant component of its nutrient cycling infrastructure. The resulting change in sediment biogeochemistry proceeds slowly but persistently, over months to years, contributing to the gradual degradation of habitat quality that has been observed alongside sea cucumber population decline in multiple Indonesian coastal environments.

The Carbonate Chemistry Function: Sea Cucumbers and Ocean Acidification

Research on Stichopus herrmanni at One Tree Reef in the Great Barrier Reef, discussed in article 25 of this series, identified a capacity that distinguishes sea cucumbers from most other commercially traded marine species: the ability to influence the carbonate chemistry of the water column through sediment dissolution during feeding. Sea cucumbers dissolve calcium carbonate from the sediments they process, releasing dissolved inorganic carbon in a form that affects local seawater pH.

At the population densities that existed in undepleted reef environments, this carbonate dissolution function represented a measurable contribution to the buffering capacity of reef waters against ocean acidification at the local scale. Reef organisms, including coral, are sensitive to the carbonate saturation state of the water they build their skeletons in. Local buffering by sea cucumber bioturbation does not counteract global ocean acidification, but it modifies the microenvironmental conditions that coral experiences on a day-to-day basis, potentially providing a margin of resilience against episodic acidification events that depleted reef systems do not have.

A 2025 study published in ISME Communications (Oxford Academic), discussed in article 30 of this series on climate change, documented that sea cucumber gut microbial community plasticity functions as a climate shield, with implications for how sea cucumber populations in warming and acidifying oceans maintain their ecological functions. The same research noted that ocean acidification and ocean warming pose escalating threats to benthic organisms such as sea cucumbers that play pivotal roles in nutrient cycling and sediment health.

The Coral Disease Connection: The 2024 Finding and Its Implications

The Nature Communications (2024) finding that sea cucumber removal increases coral disease operates through a specific mechanism that has been progressively elucidated through a series of studies culminating in the 2025 ISME Journal (Oxford Academic) publication.

Sea cucumber grazing resulted in a 75% reduction in 16S rRNA gene abundances in reef sediments and reshaped microbiome composition, causing a significant decrease of cyanobacteria and other phototrophs relative to ungrazed sediments. Grazing also resulted in a depletion of genes associated with cyanotoxin synthesis. The depletion of cyanotoxin-associated genes is the mechanistic link to coral health: cyanotoxins produced by sediment-dwelling cyanobacteria have been implicated in coral disease and bleaching, and the removal of these cyanobacteria from reef sediments through sea cucumber grazing represents a form of disease suppression that benefits adjacent coral colonies.

The causal chain is now documented across multiple studies: sea cucumbers graze cyanobacteria from reef sediments, reducing the abundance of cyanotoxin-producing organisms; in their absence, cyanobacterial populations expand, cyanotoxin concentrations increase, and the disease susceptibility of coral in the surrounding reef increases. The Nature Communications paper provides the direct experimental evidence that this mechanism operates at the reef scale: plots from which sea cucumbers were removed showed measurably higher coral disease rates than control plots that retained their sea cucumber populations.

For supply chain operators, this finding has a specific implication that is distinct from the conservation concern it raises. The ecological function of sea cucumbers in disease suppression on coral reefs means that their removal has consequences that extend beyond the population of the harvested species itself. Overexploitation of sea cucumber populations contributes, through this mechanism, to the degradation of the coral reef ecosystem that supports both the fishery and the coastal communities dependent on it. This is not a theoretical connection. It is an experimentally demonstrated causal relationship published in one of the highest-impact multidisciplinary journals in science.

The Seagrass Connection: Bioturbation and Habitat Maintenance

Research on the interaction between sea cucumber bioturbation and seagrass health has documented a positive feedback loop that has direct implications for sandfish population management in Indonesian waters. Research cited in the Aquaculture Environment Interactions literature confirmed that Holothuria scabra increases the growth rate of seagrass in co-culture environments, through bioturbation effects on sediment nutrient availability and through the stimulation of microbial activity in the rhizosphere of seagrass roots.

This positive interaction between sandfish bioturbation and seagrass productivity creates an ecological coupling that management models treating sea cucumber populations as independent of their habitat have historically failed to capture. Removing sandfish from a seagrass-dominated lagoon does not simply reduce the sea cucumber population. It reduces the bioturbation activity that maintains the nutrient cycling infrastructure that sustains seagrass productivity. The seagrass, responding to reduced nutrient availability, shows lower productivity. Reduced seagrass productivity reduces the habitat quality available for juvenile sandfish recruitment. The population decline becomes self-reinforcing through ecological pathways that operate entirely below the threshold of detection in conventional population surveys.

Quantifying the Sediment Processing Rate: What the Numbers Show

The scale of sea cucumber bioturbation in historically undepleted reef environments is quantitatively significant. Research published in Oceanography and Marine Biology: An Annual Review (Purcell et al., 2016) synthesized sediment processing rates from multiple field studies, documenting that tropical sea cucumber populations at undepleted densities turn over the entire surface sediment layer of their habitat area on timescales ranging from months to a few years. This turnover rate is ecologically comparable to the bioturbation contribution of polychaete worms in temperate marine systems, which are recognized as the primary bioturbators of temperate marine sediments.

In Indonesian reef and seagrass environments where sea cucumber populations have been heavily depleted by commercial harvesting, the reduction in sediment processing represents a measurable loss of biogeochemical function. Research has not yet quantified this loss specifically for Indonesian coastal systems at the spatial scales relevant to fisheries management, but the underlying mechanistic relationships are sufficiently well-established in the scientific literature to support the inference that population depletion has biogeochemical consequences proportional to the magnitude of the depletion.

What This Means for Sustainable Sourcing

The bioturbation ecology of sea cucumbers adds a dimension to sustainable sourcing arguments that the conventional fisheries sustainability framework, focused on maintaining harvestable populations of the target species, does not capture. Even if a sea cucumber harvest is conducted within the population limits that allow the target species to sustain itself over time, the harvest may be removing a sufficient proportion of the bioturbating population to reduce the ecosystem functions — nutrient cycling, coral disease suppression, seagrass productivity support — that the remaining population provides.

This is not a counsel of zero harvest. It is an argument for a more comprehensive understanding of what sustainable harvest means in the context of a species with documented ecosystem engineer functions. Sourcing from suppliers who demonstrate traceability to harvest locations, who can document harvest rates relative to known population densities, and whose operations allow populations to maintain functional ecological densities rather than merely commercial recovery thresholds, is the practical expression of this understanding.

Sepanjang's direct operational engagement with Indonesian coastal environments across multiple producing regions reflects an understanding of sea cucumber that extends beyond the dried product it yields. We welcome conversations with organizations seeking to understand the full ecological context of Indonesian sea cucumber sourcing.

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Sepanjang — Indonesia's Specialty Ocean Products Co. Sourcing high-quality sea cucumber directly from Indonesian waters for over 20 years.

PT Sepanjang Laut Nusantara is an Indonesia's Specialty Ocean Products Co. specializing in Sea Cucumber, Seaweed, Abalone, and Seashell from Indonesia — for domestic and international B2B markets.

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