Five of the seven-member research team led by Huang Wen-san (center) that made the discovery pose together for a photo. CNA photo Feb. 5, 2024
Taichung, Feb. 6 (CNA) A recent local study found that exposing some conserved sea turtle eggs to predators could help stabilize Orchid Island's ecosystem, Taiwan's National Museum of Natural Science said in a statement released Monday.
While efforts have been made to help sea turtles reproduce on the island off Taiwan's eastern coast since the 1990s, research conducted in a period spanning 23 years has found that the ecosystem is now in jeopardy because of a strategy to protect sea turtle eggs from predator reptiles, the museum said.
The discovery was made by a seven-member research team led by Huang Wen-san (黃文山), deputy director of the museum, located in Taichung, highlighting the crucial role sea turtles play in Orchid Island's trophic relationship.
"Sea turtles provide essential links between marine and terrestrial ecosystems, transporting nutrients and energy from the ocean to the land by nesting in beach habitats," the team wrote in the report titled "Loss of sea turtle eggs drives the collapse of an insular reptile community."
However, marine eggs have become less accessible to predators due to two anthropogenic factors.
Firstly, sea turtles now have fewer nesting sites due to the increasing number of people living on the island and the impacts of climate change, including rising sea levels and more frequent storms, which have led to beach erosion.
Secondly, "predator exclusion," a common management strategy deployed in sea turtle conservation, has also played a role.
Effective as this strategy is in sheltering turtle nests from egg predators, the team observed that "this practice also prevents native predators that have coevolved with sea turtles from accessing eggs and thereby stops the input of oceanic nutrients into the terrestrial community."
Taking Badai Beach, a smaller beach on Orchid Island, as an example, the research team said in its report that since 1997 different exclusion fences have been used to keep snakes away from sea turtle nests on beaches.
That measure has led to the almost complete exclusion of sea turtle eggs from the island's food web since 2001, regardless of the species' historical link to its ecosystem.
With no more sea turtle eggs to feed on, predators like kukri snakes and stink rat snakes were forced to prey on the eggs of local lizards, consuming a total of 5,000-18,000 eggs, depending on the lizard species, annually, the team wrote.
The fact that snakes are preying on lizard eggs is corroborated by the relatively stable populations of the same lizard species on nearby Green Island and in Pingtung County, where sea turtle eggs were never present, the team added.
The presence of the long-tailed sun skink declined significantly after 2002, with models estimating a population decline ranging from 27-36 percent a year, while the fall in population on Green Island and in Pingtung never exceeded 5 percent a year.
The outcome led the team to reflect on how appropriate the sea turtle conservation strategy was, given that during 1997-2000, the estimated number of lizard eggs consumed by kukri snakes was equal to around 120 sea turtle eggs a year, a relatively small portion of the total number of eggs laid.
Huang said annually there were around 20 sea turtle nests with more than 100 eggs in each.
Therefore, instead of keeping sea turtle eggs completely out of the reach of snakes, Huang's team called for a "more comprehensive approach that considers how conservation actions will affect interspecific relationships, particularly in cases involving cross-ecosystem interactions."
Making some sea turtle eggs accessible to predators could help maintain the stability of the ecosystem of Orchid Island, it said.
The research was detailed in a journal article published in Science Advances in December 2023.
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