Resale or republication not permitted without written consent of the publisher Biomarker signatures in intertidal and subtidal macroalgae and seagrasses may vary considerably in space and time.

We used a remotely operated vehicle to investigate landscape-scale patterns of subtidal drift material and invertebrates within a 60-km 2 marine basin in Washington State. Specifically, we quantified the distribution and abundance of drift macrophytes (seaweed and seagrass) and four macroinvertebrate species across depth and habitat type to depths of 170 m. Drift macrophytes were present on 97% of all video segments deeper than 30 m, with large drift piles particularly associated with low-angle habitats at depths exceeding 70 m. Two commercially harvested species (Strongylocentrotus franciscanus and Pandalus platyceros) that feed directly on drift material appear to be distributed in space (depth and substrate type) so as to maximize access to drift macrophyte food resources, according to their respective feeding modes. Basin shape and depth drive the landscape-scale distribution of drift material and indirectly the consumers that feed on it. The export of large amounts of detritus derived from nearshore macrophyte production into deep-water habitats likely fuels extensive secondary production in these aphotic zones.Nearshore macrophyte production contributes a substantial amount of carbon to high-latitude marine ecosystems. Much of this production is exported as macroscopic detritus (i.e., drift) to adjacent deeper, aphotic habitats (Mann 1988;Okey 2003). Despite the absence of endogenous carbon sources, these deep subtidal environments (DSE) often support considerable secondary productivity (Vetter 1995;Vetter and Dayton 1999;Britton-Simmons et al. 2009) and are a key source of commercial fisheries worldwide (Food and Agriculture Organization 2007). However, subtidal population and process-focused studies are typically constrained to depths accessible by divers and to relatively small spatial scales. In the present study, we examined the landscape-scale distribution and abundance of drift macrophytes and select invertebrates within the San Juan Archipelago (SJA), a 60-km 2 marine basin, in Washington State.Subtidal drift macrophytes in our system are produced by a diverse assemblage of nearshore seaweeds and seagrasses that diminish in abundance below 18 m and become rare by 23-m depth (Britton-Simmons et al. 2009) due to light limitation. Most subtidal drift biomass is contributed by kelps (order Laminariales) with substantial contributions also made by orders Fucales and Desmarestiales. Seagrasses (mostly Zostera marina) are present in the drift but contribute relatively little to biomass (BrittonSimmons et al. 2009). Drift material is an excellent food resource since it tends to have elevated levels of nitrogen (Mann 1988) and diminished levels of defensive chemicals (Duggins and Eckman 1997). This resource could be important for driving marine secondary productivity in DSE, but we know little about its distribution among depths and habitat types within DSE. Moreover, we need key information about where this material is distributed relative to the taxa that could be using it (Suchanek et al. 1985;Ve...

No abstract

Benthic marine consumers inhabiting the subphotic zone rely on subsidies of energy synthesized by macrophytes and phytoplankton in the photic zone. The effects of this energy subsidy on the trophic ecology of deep invertebrates are generally unknown. We used fatty acids (FA) and multiple stable isotopes (MSI) as trophic biomarkers to compare tissues from conspecifics of primary and secondary consumers in photic and subphotic habitats (15 and 100 m depth) at three sites in the San Juan Archipelago, Washington. FA composition differed across depths for all five species and MSI differed across depths for six of seven species. We found a general pattern of enrichment in d 13 C from shallow to deep for all consumers. d 15 N was consistently enriched in deep herbivores and suspension feeders, but did not differ in predators. Total v-3 FA were lower in deep primary consumers, whereas predator v-3 FA did not differ between depths. Total bacterial marker FA were lower in deep suspension feeders but higher in deep predators. The results suggest a possible mechanism for the differences in FA and enrichment between habitats: deep consumers potentially ingest detritus that has been biochemically altered by microbes during transport. We found support for this hypothetical mechanism in an algal aging experiment. Aged algae colonized by microbes responded with increases in bacterial FA, and decreases in v-3 FA. This study highlights the power of combining FA and MSI biomarkers, and provides evidence for the importance of organic matter degradation to food web studies.

Deep subtidal coastal food webs are increasingly a focus among coastal researchers, largely due to the reliance of these systems on subsidies of organic detritus donated from allochthonous sources. To better understand the dynamics of these food webs, researchers have frequently employed multiple stable isotope (MSI; δ 13 C, δ 15 N, δ 34 S) analysis to gain insights into the relative importance and origins of various sources of detritus. However, the role of microbial decomposition in these detritus-based food webs has been poorly quantified and frequently overlooked in MSI food web mixing models. In this study, we explicitly examined the ecological and MSI methodological effects of microbial decomposition of algal detritus. We found a relationship between δ 15 N enrichment and microbial abundance on decomposing kelp blades, and evidence that this pattern is influenced by the underlying biochemistry of the kelp. C:N ratios supported the hypothesis that microbial biofilms utilize nitrogen from kelp detritus, rather than augment the detrital nitrogen content. The results also showed that microbial effects can introduce a nonnegligible amount of error to MSI mixing models if left unquantified.KEY WORDS: Detritus · δ 15 N · Microbes · Isotopes · Kelp · Food webs · δ 13 C · δ 34 S Resale or republication not permitted without written consent of the publisher Editorial responsibility: Just Cebrian,