Artificial coastlines, which include engineered dikes and constructions, serve to limit erosion and guard against storms and flooding. Nevertheless, many of these structures do not safeguard ecological functions. In response, researchers in China have explored the development of unique types of cement. The research team initiated their work with a cement made from limestone and clay that solidifies underwater and subsequently incorporated polyacrylamide and chitosan. These two components were mixed into the cement to create a solid substrate, and they were also applied as a surface treatment on existing hardened cement. Within two days, biofilm was observed thriving and actively growing on the samples that had received the surface treatment.
Coastlines play a crucial role in our global ecosystem and economy. Coastal habitats are essential for preserving biodiversity, acting as natural shields against erosion, storms, and flooding while also serving as significant carbon sinks that help mitigate greenhouse gases. Local economies benefit from sustainable fisheries and tourist hotspots along the coast.
Natural coastlines, such as coral reefs, marshes, and mangroves, are fully developed and stable, capable of self-regulation and recovery. However, human activities—like urban development, overexploitative practices, and pollution—can leave these areas open to devastation.
Artificial coastlines, including human-made dikes and various engineered infrastructures, can assist in preventing erosion and offering protection from storms and flooding. Yet, many of these structures fail to provide vital ecological functions.
In the journal Biointerphases, published by AIP Publishing, a group of researchers from Southeast University and the University of Chinese Academy of Science examined how specialized cement types can contribute to the ecological protection of coastlines.
“We need to create new substrate materials that lessen biological toxicity risks for marine life,” stated author Xiaolin Lu.
Traditional artificial reef blocks are constructed using cement with a high alkaline pH of +12, which adversely affects the biofilm on reef surfaces. This biofilm, composed of various microorganisms including bacteria, algae, and fungi, serves as food for grazers and facilitates larval settlement.
The researchers began with a limestone and clay cement that sets while submerged. They introduced two treatment substances into the cement: polyacrylamide, a synthetic resin commonly used in water purification, and chitosan, a sugar derived from the shells of shrimp and similar crustaceans. Both treatments were incorporated into the cement to create a hardened substrate and were also applied as a coating on existing hardened cement.
The samples, both treated in bulk and with surface applications, were evaluated for their mechanical strength, biofilm development, and coral growth. These samples, along with a control group of plain cement, were placed in a marine tank and subjected to biofilm cultures and transplanted coral.
After just two days, biofilm was seen actively growing on the samples treated on the surface. After 30 days, the largest biofilm growth occurred on these surface-treated samples, with somewhat less growth on the bulk-treated samples, and significantly lower growth on the plain cement control. The diminished biofilm growth on the control was linked to the high alkalinity of the cement, which lacked measures to mitigate its effects. The transplanted coral also thrived better on the surface-treated samples.
Even though the bulk-treated samples showed a decrease in both biofilm and coral survival and growth, their mechanical properties appeared weakened compared to the control and the surface-treated samples.
“These new treatments demonstrated essential biocompatibility in a simulated marine ecosystem, potentially promoting biofilm growth without hampering the long-term habitation of coral samples,” Lu remarked.
The team plans to focus future research on assessing long-term surface wear and biocompatibility in practical applications.
