By Schannel van Dijken
June 6, 2017
Editor’s note: Last month, a team of conservationists set sail from the island of Fiji. Their mission: to survey marine life in the Lau Islands, an unheralded group of islets scattered over thousands of square miles of the South Pacific.
They were seeking out species — but also clues to the health of these little-explored waters. With warming seas wreaking havoc on coral reefs and upending fish migrations throughout the Pacific, managing this area will be crucial for ensuring its resilience to climate change — and ensuring that it can continue to provide food and livelihoods for the thousands who call the Lau Islands home. Read the first story in this series.
In this report, Schannel van Dijken, Pacific Islands marine program director at Conservation International, shares his findings from the expedition. While the survey painted a mostly healthy picture of reef fish populations, the situation was grim for a different type of marine species.
The Lau Islands have a serious invertebrate problem.
During our survey, we recorded 15 of the 27 species of sea cucumbers found in Fiji waters, but what was more striking was that these sea cucumbers — close relatives to starfish and sea urchins — are in dangerously low densities, with values well below the threshold densities of 10-50 individuals per hectare required to avoid reproductive failure — meaning there are not enough, nor in sufficient proximity to each other, to effectively reproduce.
A Thelenota ananas, commonly known as the prickly redfish, scours a reef bed in the Lau Islands. This species is worth around $US 90 per kilogram (US$ 200 per pound) for export.© CI/Schannel van Dijken
Overall, clams are in a marginally better state, but also in low densities, with mainly smaller individuals being recorded; we found four of the seven species of clams found in Fiji. Clam densities were patchy and generally low — and no surprise. As Fiji’s deputy secretary for fisheries told a local newspaper earlier this year, an increase in market demand for the clams has led to their being overfished. Already, two species of giant clams have already been fished to extinction locally since the 1950s and 1960s: the giant clam (Tridacna gigas) and the horse-hoof clam (Hippopus hippopus).
Similar surveys of these invertebrates in the region were conducted in 2011 and 2013, which resulted in strong recommendations to curb their decline. The results of our survey have shown, unfortunately, that things have not improved.
Why should we care about invertebrates?
Sea cucumbers and clams play crucial ecological functions in healthy reefs — if they disappear or fall below certain numbers, the health of an entire reef system can be jeopardized.
Clams siphon and filter water and contribute to reef systems as food, as shelter for other animals, and in helping to build and shape the structures of reefs themselves, as coral does.
The small giant clam, Tridacna maxima. Large clams are vital to the structures and shapes of coral reefs.© CI/Schannel van Dijken
Sea cucumbers, meanwhile, filter sediments and recycle nutrients back into the food web, breaking down organic material and redistributing these nutrients; their eggs are a crucial food source for other marine species.
Remarkably, sea cucumbers can also influence the acidity of the water in the reef. Their digestive processes contribute calcium carbonate to a coral reef’s chemical “budget,” acting as a natural antacid in local waters and helping maintain a healthy pH balance in the reef — all the more important given that climate change is causing seawater to become more acidic.
Clams and sea cucumbers are also economically important to Fiji, serving as food sources and livelihoods. They are both highly regarded as a cultural resource, with sea cucumbers being highly sought after in Asian markets.
Cyanobacteria smothering Acropora coral — a potential effect of overfishing of sea cucumbers.© CI/Schannel van Dijken
For these reasons alone, the significance of these unassuming creatures cannot be understated. Unfortunately, the low densities of sea cucumbers we observed are already having an impact on the health of the reef habitats surveyed. Alexandra Dempsey, a coral reef ecologist with the Khaled bin Sultan Living Oceans Foundation who accompanied the expedition, noted that over the period of four years from her last surveys in the Lau Islands, she observed a high increase in cyanobacteria, an indicator of poor reef health, and postulated that the over-harvesting or poaching of sea cucumbers and giant clams may have contributed to the rise in cyanobacteria observed during our survey.
Four years later, a reef in decline
In 2013, I participated in a marine species assessment in the Lau Islands with the Khaled bin Sultan Living Oceans Foundation (KSLOF). As a member of the Conservation International expedition, I explored reefs at three islands that KSLOF had previously visited. Of the three — Totoya, Vanua Vatu and Moala — the first two were still in healthy condition.
Moala, however, was not in good shape. Moala was already showing signs of poor health in 2013, when we found that cyanobacteria amounted to over 10 percent of live cover of its reefs, with ominous implications for their future health: Cyanobacteria on the seafloor can smother corals, blocking their availability to sunlight and nutrients.
Why so much cyanobacteria on Moala’s reefs? It could be made that overharvesting or poaching of sea cucumbers and other invertebrates, such as giant clams, contributed: Sea cucumbers and other echinoderms feed on algae and cyanobacteria, and so help to keep the coral reef in balance. In 2017, at Moala we recorded even fewer sea cucumbers and higher density of cyanobacteria (around 40 percent). This drastic change underscores how critical it is to protect and conserve sea cucumbers: By removing most sea cucumbers off the reef, the cyanobacteria can grow unchecked.
— Alexandra Dempsey, coral reef ecologist, Khaled bin Sultan Living Oceans Foundation
Furthermore, the long-term sustainability of the entire sea cucumber fishery in Fiji is at stake. The Lau Islands are critical for Fiji to take care of — studies suggest that gene flow of these species appears to be in an east-to-west direction, so conservation of populations in the eastern islands of Fiji (Lau Islands) will benefit genetic diversity, health and resilience across the fishery.
A lucrative species
There is a long history of trade in clams and sea cucumbers in the Pacific; the sea cucumber trade in the Pacific is now valued at US$ 50 million, second in value only to the tuna industry. But as the world has focused on protecting tuna populations, the lowly sea cucumber has suffered. While many other Pacific Island countries have severely restricted sea cucumber harvesting, Fiji has not, making it the fourth-largest exporter in the Indo-Pacific region.
The scale of harvesting of sea cucumbers in Fiji by small-scale fishers is “vast,” according to a government report, and small wonder given the value of these creatures in Asian markets. No festive occasion in China is without sea cucumbers on the menu, and they are in the top five luxury items at weddings, major celebrations, or business meals where hosts aim to impress. Because of this, they can sell for nearly US$ 3,000 per kilogram (more than US$ 6,000 a pound) in Chinese markets. This is a lucrative business to be in.
What can we do?
The long-term sustainability of the clam and sea cucumber fishery in Fiji is of great importance to coastal communities, from socioeconomic and ecological perspectives, and conservation is a fine line between maximizing sustainable resource use that supports human well-being but that doesn’t threaten the existence of the resource. Unfortunately, when economic drivers are high, this can skew this balance heavily, and we end up in a situation where an important fishery is at stake.
This is what we have in Fiji. The sea cucumber fishery is facing collapse. The most effective thing we can do right now is implement a complete and temporary halt in harvesting to enable stocks to rebuild, so that a fishery can exist in the future. This is no easy task, and will require effective, culturally relevant outreach and education with communities so that the level of understanding of these resources are well understood, and where the development, enforcement and ownership of its management is driven from the community level.
The future for Lau is in good hands — they have leaders such as Roko Sau, who understands these problems and who is working with his people to make the necessary changes. These are forward-thinking islands; they are taking the right actions to protect nature in order to thrive.
Schannel van Dijken, Pacific Islands marine program director at Conservation International, is based in Samoa.