Publication Summary

The Marine Sediment Monitoring Program (MSMP) monitors sediment quality at sampling locations throughout Puget Sound. Objectives of the benthic component are to collect baseline data in contaminated and uncontaminated stations, as well as evaluate the condition of benthic macro-invertebrates in relation to concentrations of toxic chemicals in sediments. To address these objectives, this report documents spatial and temporal patterns of variation in species abundance and composition, and assesses effects from contamination at MSMP stations. In addition, the report identifies potential natural stresses that may structure benthic communities in Puget Sound and may constitute confounding factors in pollution monitoring studies.

The Marine Sediment Monitoring Program (MSMP) monitors sediment quality at sampling locations throughout Puget Sound. Objectives of the benthic component are to collect baseline data in contaminated and uncontaminated stations, as well as evaluate the condition of benthic macro-invertebrates in relation to concentrations of toxic chemicals in sediments. To address these objectives, this report documents spatial and temporal patterns of variation in species abundance and composition, and assesses effects from contamination at MSMP stations. In addition, the report identifies potential natural stresses that may structure benthic communities in Puget Sound and may constitute confounding factors in pollution monitoring studies.

Samples were collected March-April 1989-1993 from 76 monitoring stations located throughout Puget Sound, Hood Canal, and the Straits of Georgia and Juan de Fuca. Two types of stations were established: core stations, sampled once every year, and rotating stations, sampled once every three years in a rotating cycle alternating between the north, central, and south Puget Sound regions. Five van Veen grabs were collected at each station, and the organisms (1.0-mm sieve fraction) were identified to species. Sediment contaminants (not presented here), total organic carbon, total sulfide, and grain size were measured from the top 2 cm of paired samples.

Multivariate analysis techniques showed that infaunal assemblages in Puget Sound are primarily related to sediment composition and water depth, and secondarily to geographical location. Assemblages of numerically dominant species were characterized using rank analysis. The majority of the species in Puget Sound were not restricted to one substrate, but were broadly distributed in different types of substrates with peaks of abundance in sand, mixed sediment, or mud. Diversity measures identified some stations as consistently having low species richness. These stations were distinctly separated in cluster analysis, and consisted of upper reaches of inlets in south Puget Sound, semi-enclosed bays, and some depositional locations associated with river plumes. These locations have the potential for the development of low DO episodes in bottom waters and the accumulation of sulfide in sediments. Abundance also was low at many of these locations.

In general, spatial patterns in species abundance and composition appeared to be unrelated to contaminant concentrations at sampling locations. However, the polychaete Aphelochaeta sp. was distinctly associated with sediment contamination and/or organic enrichment. This species may be useful as an indicator of pollution. In addition, large fluctuations in abundance were associated with the numerical dominance of typically 20 species of benthic organisms plus the Phoronida. Temporal patterns in species abundance at some stations differing in sediment quality were homogeneous basin-wide and unrelated to contamination.

This study represents the first system-wide effort to characterize benthic assemblages in the Puget Sound region. The study evaluates the benthic component of the MSMP, suggests improvements to the design, and provides recommendations.