Fine-scale temporal variation in marine extracellular enzymes of coastal southern california

Abstract

Extracellular enzymes are functional components of marine microbial communities that contribute to nutrient remineralization by catalyzing the degradation of organic substrates. Particularly in coastal environments, the magnitude of variation in enzyme activities across timescales is not well characterized. Therefore, we established the MICRO time series at Newport Pier, California, to assess enzyme activities and other ocean parameters at high temporal resolution in a coastal environment. We hypothesized that enzyme activities would vary most on daily to weekly timescales, but would also show repeatable seasonal patterns. In addition, we expected that activities would correlate with nutrient and chlorophyll concentrations, and that most enzyme activity would be bound to particles. We found that 34-48% of the variation in enzyme activity occurred at timescales <30 days. About 28-56% of the variance in seawater nutrient concentrations, chlorophyll concentrations, and ocean currents also occurred on this timescale. Only the enzyme β-glucosidase showed evidence of a repeatable seasonal pattern, with elevated activities in the spring months that correlated with spring phytoplankton blooms in the Southern California Bight. Most enzyme activities were weakly but positively correlated with nutrient concentrations (r = 0.24-0.31) and upwelling (r = 0.29-0.35). For the enzymes β-glucosidase and leucine aminopeptidase, most activity was bound to particles. However, 81.2% of alkaline phosphatase and 42.8% of N-acetyl-glucosaminidase activity was freely dissolved. These results suggest that enzyme-producing bacterial communities and nutrient dynamics in coastal environments vary substantially on short timescales (<30 days). Furthermore, the enzymes that degrade carbohydrates and proteins likely depend on microbial communities attached to particles, whereas phosphorus release may occur throughout the water column.

Keywords: coastal ocean; extracellular enzyme; marine microbes; particles; phytoplankton; southern California; temporal variation; time series.

Figure 1

Time series plots for bulk seawater extracellular enzyme activities (A–D) and seawater nutrient concentrations (E,G,I,K) in surface water at Newport Pier. Chlorophyll a data (F) are derived from MODIS satellite data for a ∼3600-km² region surrounding Newport Pier (black line) or from surface water samples taken weekly at the pier (gray line). Sea surface temperatures (J) are from an automated sensor at Newport Pier (squares), MODIS satellite data from the 3600-km² region (black line), and ROMS model output from the 3600-km² region. The Bakun upwelling index (H) is shown for the Southern California Bight at 33°N, 119°W. Across shore (L) currents were derived from ROMS model outputs (surface 50 m) for the 3600-km² region. AP, alkaline phosphatase; BG, β-glucosidase; LAP, leucine aminopeptidase; NAG, N-acetyl-glucosaminidase.

Figure 2

Autocorrelation functions for (A) bulk seawater β-glucosidase activities at Newport Pier and (B) chlorophyll a concentrations derived from MODIS satellite data for a ∼3600-km² region surrounding Newport Pier. Dashed lines represent the 95% confidence interval.

Figure 3

Variance at different timescales for bulk seawater extracellular enzyme activities, seawater nutrient concentrations, chlorophyll a concentrations, and sea surface temperature. The total variance for each variable was normalized to 1.0 to facilitate comparison. AP, alkaline phosphatase; BG, β-glucosidase; NAG, N-acetyl-glucosaminidase; LAP, leucine aminopeptidase. Alongshore and across-shore refer to surface current directions.