Intertidal clams exhibit population synchrony across spatial and temporal scales

Area of Science:

• Marine Ecology
• Population Dynamics
• Bivalve Molluscs

Background:

• Long-term datasets are crucial for understanding population drivers.
• Continuous data for bivalve mollusc population dynamics are scarce.
• Intertidal clam populations face complex environmental influences.

Purpose of the Study:

• To assess synchrony in native intertidal clam populations using a 28-year dataset.
• To identify environmental covariates correlated with clam population trends.
• To analyze multidecadal changes in clam biomass across five regions.

Main Methods:

• Dynamic Factor Analysis (DFA) applied to a 28-year clam biomass dataset.
• Evaluation of seven environmental covariates, including the North Pacific Gyre Oscillation.
• Statistical modeling to identify predominant trends and significant correlations.

Main Results:

• Three predominant trends described multidecadal clam biomass changes.
• Intraspecific synchrony was highest in Saxidomus gigantea and Leukoma staminea.
• Leukoma staminea showed a decadal decline, while Saxidomus gigantea biomass increased.
• Clinocardium nuttallii populations lacked clear covariance.
• Species-specific trends were more prevalent than beach-specific synchrony.
• North Pacific Gyre Oscillation, lagged by 4 years, was the most supported covariate.

Conclusions:

• Density-independent, large-scale oceanographic factors significantly influence venerid clam populations.
• Oceanographic conditions affecting larval stages are key drivers of biomass.
• Local factors likely contribute to unexplained variability in clam population dynamics.