Comparison of two benthic assemblage sampling gears for use on intertidal oyster reefs in Louisiana

Background

Estuarine biodiversity plays a vital role in supporting ecosystem functions yet remains threatened by climate change and anthropogenic activity. Tracking and identifying estuarine biodiversity trends helps management ensure long-term provisions of human and environmental benefits by contributing to the estimation of habitat loss and the monitoring of restoration and conservation progress. However, the sampling gear and biodiversity metric used may indicate different conclusions, which can lead to uncertainty in the actual state of the ecosystem-level biodiversity. Sampling benthic biodiversity in complex estuarine habitats, such as oyster reefs, is particularly challenging because no one gear type captures entire target assemblages, and differences in gear efficiency on these complex habitats make comparisons across gear types challenging.

Methods

We investigated how estimates of oyster reef-associated benthic taxa abundance, richness, Pielou’s evenness, and Shannon-Wiener diversity differed across three Crassostrea virginica reefs in Louisiana between suction sampler and substrate tray sampling gears (n = 6), and how gear influenced comparisons across reefs (3 reefs × 6 replicates × 2 gears).

Results

Abundance and richness were higher, and Pielou’s evenness was lower, in trays compared to suction samples at all reefs. Shannon-Wiener diversity was similar in suction samples and trays at two out of three reefs. Amphipod taxa were numerically dominant in trays, skewing the distribution of abundances and driving the reef assemblage differences between gears. Abundance and Shannon-Wiener diversity were similar across reefs within each gear. However, there were significant differences in richness across reefs in tray samples only, while evenness differed across reefs only in suction samples. Our results highlight that gear choices, along with biodiversity metrics tracked, can result in different conclusions in biodiversity trends, ultimately affecting conservation decisions and management.