Temporal and spatial variation in microbial extracellular enzyme activity in a nearshore Gulf coast system

Microbial extracellular enzymes are critical for the degradation of organic matter and mineralization of nutrients in marine systems, yet few studies have examined how enzyme activity varies over short-and long-term timescales in nearshore coastal environments. This study assessed the day-to-day, week-to-week, and month-to-month variation in the activity of three hydrolases (phosphatase, β-glucosidase, N-acetylglucosaminidase) in seawater and sand at five beaches along the Mississippi coast, as well as the activity of two oxidases (phenol oxidase, peroxidase) in sand. Hydrolase activity in seawater and sand showed more temporal than spatial variation, with seawater enzyme activity characterized by greater variation over longer timescales with brief blooms in activity over finer spatial and temporal scales. Sand hydrolase activity showed fewer of these short-term blooms. Phenol oxidase activity in sand consistently showed variation between beaches and over time, while peroxidase activity was erratic with no consistent pattern. Prevailing environmental conditions did not strongly correlate with seawater enzyme activity, and while enzyme activity in sand was weakly negatively correlated with salinity and sand moisture content, there were few consistent patterns across timescales. Enzyme stoichiometry suggested that microbial communities in sand and seawater at beaches along the Mississippi coast were potentially limited by phosphorus and carbon. This study highlights the temporal and spatial variation of microbial activity in nearshore coastal environments even in the same broader ecosystem.