Environmental linkages between the Salini salt pans and the marine system

Abstract

The Salini saltworks, Malta's most extensive salt production facility, originally a natural wetland, now serves as a nature reserve. Oriented along a northeast-southwest axis, the salina spans 740 meters in length and 140 meters in width, covering an area of 90,000 m2. It consists of two large seaward-facing reservoirs, each with an area of 12,000 m2, and 33 smaller inland pans, whose areas range between 900 and 2,000 m2. Prior research has often focused on specific taxa, predominantly birds, or examined the salina in isolation, neglecting the influence of surrounding marine conditions. This study seeks to bridge this gap by examining the salina's abiotic and biological trends and their connection to marine environments. Through monthly visits from July 2022 to July 2023, measurements were taken of water temperature, pH, electrical conductivity, and nitrate and phosphate levels from the sea to the pans. The diversity of macroalgae, spermatophytes, and macroscopic fauna was assessed via direct observations, collections, and automated photography. Findings revealed that water quality within the salina varied both spatially and temporally, displaying a pronounced abiotic gradient from the sea toward the landward pans, indicating significant shifts in water characteristics during its transit. Electrical conductivity, for example, increased from approximately 50 mS cm-1 in the marine environment to about 60 mS cm-1 in the reservoirs, and up to 200 mS cm-1 in the most inland pans. This pattern was statistically significant and more pronounced during the dry season when conductivity, nitrate, and phosphate concentrations peaked. Variations in water pH, nitrate, and phosphate levels exhibited no clear spatial trends but were influenced by seasonal changes. The extreme conditions in the innermost pans during the dry season included hypersaline waters and water temperatures sometimes exceeding 40°C. An ecological gradient was also observed, with species richness escalating in the reservoirs compared to the marine environment and decreasing significantly in the inner pans. The enhanced biodiversity in the reservoirs can be attributed to their relative stability in mechanical energy and physico-chemical conditions compared to the fluctuating marine environment and the extreme conditions in the pans. These reservoirs harboured a diverse array of life forms, including four spermatophyte species, numerous macroalgae taxa, and a wide variety of macroscopic fauna, while the more distal pans showed a stark decline in biodiversity, hosting only a few adapted species such as the Dunaliella salina. Environmental linkages between the Salini salt pans and the marine system Additionally, this research identified the Atlantic Blue Crab's presence and noted the colonisation of the reservoirs by the Upside-Down Jellyfish. Ultimately, this study accentuates the necessity of integrating internal and external environmental factors in managing the habitat, especially focusing on preserving the biodiversity-rich reservoirs within the Salini saltworks complex.