Updated: Jun 8
"You see their tracks along the coastline...they reach the blockades, realise they cannot pass, but they keep trying to nest every few metres until they finally exhaust themselves on the beach" - Yuzi Tanaka (wildlife conservationist)
Long before the line of concrete tetrapods landed on Omotehama Beach (Miyagi, Japan), this precious dune vegetation was a rare habitat for endangered Loggerhead Turtles hatchlings.
Mothering turtles arrive on the beach every year, returning to their place of birth to reproduce, after impossibly long migrations across the planet. This cyclical event crucially relies on these tiny patches of dune vegetation for the survival of their species. The land is so essential precisely because it is so close to the shore, and the shrubs protect the turtle eggs from predation during incubation.
After thousands of kilometres making their way home, these concrete tetrapods effectively block them 2 metres from their territory. Yuzi explains "you see their tracks along the coastline...they reach the blockades, realise they cannot pass, but they keep trying every few metres until they exhaust themselves on the beach".
The inter-locking tetrapods are scattered across the entire length of the dune vegetation habitat, stretching 11 kilometres across Omotehama beach. Yuzi and his wife Mina spearheaded a campaign to relocate the blockades, and in 2008 the government tentatively agreed to set some of them back behind the dunes. But unfortunately, Yuzi notes that his campaign was a complete failure, as the government only removed 1 kilometer of blockades, and do not plan to take any further action. Every year, mothering turtles return home to find that their precious patch of vegetation is just beyond their reach. And every year, Yuzi maps their tracks with increasing dismay, and warns of their plummeting hatchling population.
Sharing Yuzi's concern, fellow conservationists in the area have taken to building designated hatchling houses on the shoreline, in front of the tetrapods. This kind of affirmative action is well-intended, but, like the implementation of the tetrapods, it is not without disagreements over correct locations, quantity, and form. Yuzi tells me,
"[turtle conservationists] go out and dig up eggs laid in the sand, because the mothers cannot reach the dune vegetation...then they relocate them all in these fenced hatchling houses".
Unfortunately these make-shift hatchling houses are designed and built using basic construction methods and materials, and the predators simply burrow under the chicken-wire fencing. Mina exclaims, "they're like food banks!".
Despite this, the hatchling houses are still being used, and conservationists disagree over their next move. The hatchling houses are closely monitored, and have seen some success in recent years according to those running the hatchling network. But, Yuzi explains that their affirmative efforts to manage and protect this species are misguided. The temperature of the ground that incubates the mother's nest eggs determines the gender of the hatchlings. So when female turtles create numerous nests along the beach - a mix of genders will hatch depending on their immediate location, due to slight fluctuations in sand temperature. But when the eggs are collected and artificially stored in designated hatchling houses, the immediate location and sand temperature will be the same for all new hatchlings. Signs of hatchling tracks leading to the tideline are therefore a misleading marker of success, as the demography of the species is neglected.
Yuzi agrees that human intervention is necessary if the loggerhead population is to recover on Omotehama beach. But this intervention does not need to be intensive or invasive. His research and mapping data suggest that the turtles do not require heavily controlled management, or a ring-fenced habitat, to protect hatchlings. The turtles simply need a viable route to a very sustainable habitat that lies just beyond the tetrapods. Relocating these giant concrete blocks appears to be the only sustainable solution to stemming the sharp decline in nesting populations.
Yet, conservationists are being forced to experiment with crude hatchling houses because the removal project is evidently deemed to be too economically inconveniently in relation to current political unrest. And while debate rages on about what course of action to take with no funding. Ultimately, the returning loggerhead population is paying the price.
In 1950, in the laboratory of two engineers in Grenoble, France. Pierre Danel and Paul Anglès d'Auriac were developing a new technology that could be used to alleviate coastal erosion, by dispersing wave forces on sub-aqueous walls. The invention was called the Tetrapod - a reinforced concrete blockade named after the biological super classification of four-limbed vertebrates, 'Tetrapoda'. The concrete tetrapod was designed to be a modular inter-locking structure, that could be used to disperse wave forces whilst remaining collectively stable due to their inter-locking design. Pierre and Paul filed a successful patent for their tetrapod design, and the first concrete blockade of its kind was soon introduced to the perimeter of a thermal power station in Roches Noires, Morocco.
The technology was deemed a success in the field of marine construction, and soon inspired a wave of concrete blockade designs and coastline conservation research, all inspired by Pierre and Paul's original design. The USA designed the Modified Cube (1959); the United Kingdom gave us the Stabit (1961); the Netherlands introduced the Akmon (1962); South Africa began moulding the Dolos (1963); and Romania implemented the Stabilopod (1969). These early technologies later gave rise to more experimental coastline reinforcement designs such as the Seabee (Australia, 1978), the Accropode (France, 1981), and the Xbloc (The Netherlands, 2001). The invention of the tetrapod was undoubtedly a benchmark in coastline conservation, but its legacy has become the centre point of an intense debate in recent years, between wildlife conservationists, marine biologists, and environmental disaster consultants.
The Japanese Government were unsurprisingly an early proponent of the tetrapod design following its success in Morocco. As Japan is so highly prone to earthquakes, typhoons and tsunamis that devastate the landscape, an entire industry of tetrapod manufacturing and dispersal has grown in response to these threats to human settlement. But whilst the concrete blockade is now a popular and widely accepted feature of the Japanese coastline, its early implementations were often marred with disagreements over their correct location, quantity, and form. One of the earliest implementations of the concrete tetrapod in Japan was on Omotehama beach, in the Shizuoka Prefecture of Honshu. The devastating effects of their introduction to the area is now a poignant example of what is at stake, and what happens when economy eclipses ecology.
According to Yuzi Tanaka, a leading wildlife conservationist based in Omotehama, the Japanese government originally wanted to introduce a series of inter-locking tetrapods to a small portion of land set back approximately 50 metres from the dune vegetation that lined the edge of Omotehama beach. This location would have been very effective for wave breaking. But the local fishermen issued numerous complaints, and persuaded the government to relocate the concrete blockades closer to the tideline. They agreed that the blockades would still be effective if positioned between the dune vegetation and the sea.
Unfortunately, whilst the complaints of the fishermen were met with sympathy - the animals that thrived on the beach were not taken into consideration. Now, after years of lobbying to remove the tetrapods with little success - perhaps a speculative alternative could be to re-imagine these concrete blocks as architectural monuments to the lost loggerhead territories. By giving the tetrapods new life as a monument, these concrete blocks could be re-homed across coastal prefectures of Japan, as a reminder of the more-than-human agents that thrive and falter within our anthropogenic landscapes. The image below imagines a literal carving of the concrete - though hundreds of artistic works could proliferate.
[ Concrete tetrapod re-imagined as a creative monument ]
Written by Steven Hutt
Special thanks to Yuzi Tanaka