Dan Ishibashi (an undergraduate student at the time of the research) of the Graduate School of Engineering and Science, the University of the Ryukyus, and Professor James Davis Reimer of the Tropical Biosphere Research Center, the University of the Ryukyus, in collaboration with Okinawa Institute of Science and Technology, have announced the development of a new microscale survey method called the "micro-quadrat method," using a frame of just 5 cm × 5 cm, as an alternative to conventional survey methods that work at scales of several meters.
By surveying shallow coastal waters around Okinawa Island, they detected a community of benthic organisms around reclaimed land that differed from those in other sea areas and revealed the impact of coastal reclamation. The study showed that different results can be obtained by changing the scale of observation, and that reclamation is affecting coral reefs. The results were published in Marine Biodiversity on March 10.
Photo by Takuma Masui
Field environmental and biological surveys have traditionally used the quadrat method, in which organisms within a square frame are counted, and the transect method, in which a rope is laid out and organisms appearing along it are counted. In surveys of small benthic organisms in coral reef ecosystems, 10-meter transects and 3-meter-square quadrats have been the standard approach.
However, these methods target large organisms that inhabit a relatively large area, and it is difficult to evaluate small organisms measuring just a few millimeters to a few centimeters. Benthic organisms are creatures that live attached to or on the seafloor, rocks, sand, and dead coral surfaces, and are used as indicators of environmental conditions.
In response the research team developed a new microscale survey standard called the "micro-quadrat method," using a frame of 5 cm × 5 cm. This method records and compares substrate surfaces, which conventional methods tend to group simply as "sand," "rock," or "dead coral," at a microscale.
In the survey, a 10-meter transect line was set up on the seafloor at each survey site. The coverage of benthic organisms was recorded using the conventional method, and the micro-quadrat method was also applied. Within the micro-quadrat frame, the coverage of diverse benthic organisms on the substrate surface, including crustose coralline algae (CCA), sea squirts, and small algae, as well as sand coverage, were examined.
The results showed that in the sea areas around reclaimed land, coverage by soft corals (octocorals) was relatively high under the transect method, while coverage by sand tended to be high under the micro-quadrat method.
Along natural and seawall coastlines, relatively small organisms that had been difficult to assess with conventional surveys, such as CCA and sea squirts, were found in large numbers. Statistical analysis confirmed that community composition differed greatly between coasts.
These results indicate that different survey methods and spatial scales may perceive communities differently in coastal environments. There may be diverse small benthic organisms even in places that conventional surveys would judge to have no organisms.
Using the micro-quadrat method alongside conventional methods is thought to make it possible to capture, in a complementary way, the characteristics of biological communities in microscale habitats that had previously been hard to assess.
Reimer commented: "Through the method tried in this study, we confirmed that diverse small benthic organisms live even on the surfaces of bedrock and dead coral that might appear to have few organisms at first glance. The results also suggest that coastal reclamation may be affecting the microscale habitats of coral reef seafloors. I would be grateful if people could, through this research, turn their eyes towards small creatures that are usually hard to see."
Journal Information
Publication: Marine Biodiversity
Title: Does land reclamation affect small-scale benthic communities? Micro-quadrats on coral reefs around Okinawa Island, southern Japan
DOI: 10.1007/s12526-026-01631-7
This article has been translated by JST with permission from The Science News Ltd. (https://sci-news.co.jp/). Unauthorized reproduction of the article and photographs is prohibited.