Healthy coastal forests are important for sea kraits

Leleuvia Island is a small (9.7 ha), flat (less than 2 m elevation) coral atoll  (Fig. 1) of the Fiji archipelago in the Pacific Ocean. It hosts an eco-resort and is unique in having protected, old-growth coastal forest on the northern half of the island. Unfortunately, untouched coastal vegetation is relatively rare because humans have cut down or damaged much coastal vegetation and an increasing proportion of the human population is concentrated in coastal regions. Rising sea level because of climate change are not helping matters.

Fig. 1: The island of Leleuvia. Photo: Gunnar Keppel

What (beside plants) do we lose when coastal vegetation is degraded or removed?  Christopher Lowe investigated the importance of coastal forest in creating unique microhabitats and suitable conditions for the survival of yellow-lipped sea kraits, Laticauda colubrina, for his Honours project. Sea Kraits are truly amphibious snakes that spend days hunting for prey in the ocean before returning to land to digest (Fig. 2). The project was supported by a team of researchers from the University of South Australia, NatureFiji-MareqetiViti, the University of the South Pacific, and the U.S. Geological Service.

Fig. 2: The yellow-lipped sea krait, Laticauda colubrina, returning to land after hunting in the adjacent coral reefs. Photo: Gunnar Keppel

The study found that sea kraits were much less frequent on the side of the island with the resort than on the side with little disturbed coastal forest. Sea kraits were often associated with microhabitats found only in old-growth coastal forest. Of particular interest was the use of crevices and hollows in the bark and stems of trees for shedding skin. The shedding of old skin is important for sea snakes to reduce drag from the presence of organisms. Furthermore, canopy cover and leaf litter were seemingly important to create suitable conditions to digest prey (Fig. 3), suggesting that heterogeneity in microclimate may be important to facilitate certain behaviours. Temperature is important for sea kraits because they are cold-blooded.

Fig. 3: Sea krait resting in the leaf litter to digest its prey. Photo: Christopher Lowe.

The high diversity of microhabitats provided by old-growth coastal forest was possibly the most exciting finding. Canopy provided important shelter and shade, reducing temperatures by up to 7°C during the day. The amount of local leaf litter differed greatly within the coastal forest, being up to 12 cm deep under trees of the deciduous beach almond, Terminalia catappa. Canopy cover, leaf litter depth and distance from the shore combined to create large variation in absolute humidity, ranging from 10.5-21.7 g.m3.

Therefore, old-growth coastal forests create diverse microhabitats that are likely to be important for many organisms. Sea kraits utilized crevices in trees to shed their skins, rested and digested their prey in locations protected by canopy, and avoided the open habitats of the developed side of the island. Protecting sea kraits, and other biodiversity of coastal ecosystems, will therefore require maintaining the environmental heterogeneity created by healthy ecosystems.

Further Reading: Lowe C, Keppel G, Waqa K, Peters S, Fisher RN, Scanlon A, Osborne-Naikatini T, Thomas-Moko N. 2022. Fijian sea krait behavior relates to fine-scale environmental heterogeneity in old-growth coastal forest: The importance of integrated land–sea management for protecting amphibious animals. Ecology and Evolution, 12: e8817. https://onlinelibrary.wiley.com/doi/full/10.1002/ece3.8817

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