Towards Predicting Basin-Wide Invertebrate Organic Biomass and Production in Marine Sediments from a Coastal Sea

Abstract

Detailed knowledge of environmental conditions is required to understand faunal production in coastal seas with topographic and hydrographic complexity. We test the hypothesis that organic biomass and production of subtidal sediment invertebrates throughout the Strait of Georgia, west coast of Canada, can be predicted by depth, substrate type and organic flux modified to reflect lability and age of material. A basin-wide database of biological, geochemical and flux data was analysed using an empirical production/biomass (P/B) model to test this hypothesis. This analysis is unique in the spatial extent and detail of P/B and concurrent environmental measurements over a temperate coastal region. Modified organic flux was the most important predictor of organic biomass and production. Depth and substrate type were secondary modifiers. Between 69–74% of variability in biomass and production could be explained by the combined environmental factors. Organisms <1 mm were important contributors to biomass and production primarily in shallow, sandy sediments, where high P/B values were found despite low organic flux. Low biomass, production, and P/B values were found in the deep, northern basin and mainland fjords, which had silty sediments, low organic flux, low biomass of organisms <1 mm, and dominance by large, slow-growing macrofauna. In the highest organic flux and biomass areas near the Fraser River discharge, production did not increase beyond moderate flux levels. Although highly productive, this area had low P/B. Clearly, food input is insufficient to explain the complex patterns in faunal production revealed here. Additional environmental factors (depth, substrate type and unmeasured factors) are important modifiers of these patterns. Potential reasons for the above patterns are explored, along with a discussion of unmeasured factors possibly responsible for unexplained (30%) variance in biomass and production. We now have the tools for basin-wide first-order estimates of sediment invertebrate production.

Responses of infaunal composition, biomass and production to discharges from a marine outfall over the past decade

“…In this study, we used all available samples with reasonable estimates of organic flux from nearby core data (N = 987 samples) of which 88% were collected since the year 2000. A thorough description of these data is given in Burd et al (2012).…”

“…Field and laboratory methods and general sampling locations for all data are described and referenced in Burd et al (2008aBurd et al ( , 2009Burd et al ( , 2012. Background samples were collected using the same field and laboratory methods as for the Iona surveys, using 0.1 m 2 grab samples (Van Veen or Smith-MacIntyre), screened on 1 mm sieves, separated into size groups, with wet-weight biomass measurements obtained from representative size ranges for each species in a given reference collection.…”

“…The method used to determine organic biomass and production was the same for both the Strait of Georgia background samples (as described in Burd et al, 2012) and the Iona receiving environment samples. Production/biomass estimates were made for macrofauna using the empirical model of Brey (2001), which provides reasonable estimates for multi-species communities of fauna >0.5 mm.…”

“…2b), was superimposed on plots showing similar data for all of the background Strait of Georgia samples (N = 987; Fig. 12 and see Burd et al 2012). Biomass and production values for the Iona receiving environment were high relative to values found in the rest of the Strait of Georgia.…”

“…In other words, the increasing amount of organic flux from the north to the south end of the Iona monitoring gradient results in increasing faunal biomass, but not production. Burd et al (2012) hypothesized that this was related to the high burial rate of organic material near the south arm of the river, which makes much of the organic flux unavailable to near-surface organisms. This may explain the observation over the years that large, deepburrowing holothurians are much more abundant at the south end of the Iona monitoring gradient than at the north end (Lynch et al, 2011), and that biomass tends to accumulate in larger organisms in this region as organic flux increases .…”