Ecological Assessment of Aquatic Life Shelters under Community-Based Management in Songkhla Lagoon

Abstract

Background and Objectives: Songkhla Lagoon is the only lagoon ecosystem in Thailand. The lagoon supports high biodiversity and serves as an important natural resource for surrounding coastal communities, particularly in fisheries, aquaculture, and local cultural livelihoods. However, long-term resource exploitation and environmental changes have resulted in declines in fish abundance and ecosystem productivity. In response to these problems, local fishing communities have developed various conservation activities, particularly the construction of Aquatic Life Shelter (ALS), locally known as “Ban Pla”, to enhance ecosystem productivity. Despite their widespread use, systematic ecological assessments and empirical evidence regarding their effectiveness remain limited. Therefore, this study aimed to investigate the structural types and evaluate the ecological outcomes of ALS  in communities surrounding Songkhla Lagoon, with particular emphasis on designs adapted to local ecological conditions and community-based management processes.

Methodology: The study was conducted in eight fishing communities located across the upper, middle, and lower zones of Songkhla Lagoon. Aquatic Life Shelter types and baseline environmental characteristics, including water depth, bottom substrate, wave and current conditions, locally available materials, and biological conditions, were surveyed in collaboration with local fishers and community leaders. This information was used for site selection and the development of ALS  designs appropriate to the ecological context of each area. Ecological assessment was subsequently conducted at five sites by comparing fish diversity and biomass before and six months after ALS installation. Local fishing gears appropriate to each site were used, with three replicates per site. Fish species and biomass were recorded, and fish diversity was evaluated using the Shannon–Wiener diversity index (H′). Differences in diversity before and after ALS installation were analyzed using a paired t-test at a significance level of p < 0.05.

Main Results: Five major types of ALS  were identified in Songkhla Lagoon, including cage-type, concrete-based cluster, linear branch arrangement, aquatic life shelter, and traditional branch pile models. Each design differed according to local ecological conditions such as water depth, wave exposure, current conditions and available local materials. Ecological assessment revealed that the average Shannon–Wiener diversity index increased from 0.19 to 1.16 within six months after ALS  installation, indicating changes in fish community structure and increased fish diversity in the study areas. Fish species richness increased at all five assessment sites: from 1 to 14 species at Ban Chai Khlong, 2 to 17 species at Ban Pak Pra, 1 to 5 species at Ban Lam Kula, 2 to 4 species at Ban Klang, and 1 to 4 species at Ban Mai. A total of 26 aquatic species, comprising 25 fish species and one shrimp species, were recorded during the study period. Fish biomass also showed an increasing trend across the study sites. For example, mean fish biomass at Ban Chai Khlong increased from 21.27 ± 0.67 to 46.33 ± 0.87 kg, while that at Ban Pak Pra increased from 2.45 ± 0.32 to 8.60 ± 0.65 kg. The reappearance of indigenous fish species and several less frequently encountered species, as reported by local fishers, including Batrachocephalus mino, Megalops cyprinoides, Barbonymus schwanenfeldii, and Osteochilus melanopleurus, was also observed following ALS  installation. The findings demonstrated a relationship between ALS installation and increased fish diversity in the study areas. The ALS designs reflected adaptation to site-specific ecological conditions. Cage-type ALS  were suited to shallow-to-moderately deep waters with low wave exposure, whereas concrete-based cluster ALS were used in deeper waters with stronger currents. The Mangrove-Integrated Aquatic Life Shelter integrates ALS structures with mangrove planting to increase habitat complexity.

Conclusions: The construction of ALS in Songkhla Lagoon was associated with increased fish diversity and the reappearance of indigenous fish species in the study areas. The findings suggest that ALS may contribute to habitat restoration in brackish coastal ecosystems. Rather than functioning solely as structures for aggregating fish, appropriately designed ALS have the potential to serve as habitat restoration tools, particularly when their designs are adapted to local ecological conditions and implemented through community participation. Selection of an appropriate ALS design should therefore consider physical environmental conditions, locally available materials, local ecological knowledge, and patterns of community resource use.