Energy flow and the stability of coastal ecosystems.
The stability and resilience of ecological systems is strongly influenced by the degree of “multichanneling” within local food webs. That is, animal communities that utilize energy from different primary producer functional groups – such as benthic vs. pelagic production – tend to be more stable than those which rely on a single energy channel. However, for many ecosystems, particularly marine habitats, we lack a basic understanding of which species of plants, algae, and microbes provide energy for local food webs, and the spatiotemporal dynamics of these exchanges. I study these issues in kelp forest food webs across the Americas using carbon isotope analysis (δ13C) of individual amino acids (Figure 1). Iconic and important nearshore habitats distributed across the globe, kelp forests remain understudied relative to other coastal ecosystems (Elliott Smith and Fox 2021). I have explored how energy flows through kelp forest food webs, and how pelagic vs benthic energy is partitioned within populations, communities, and across broad geographic and environmental gradients. By focusing on molecules that are minimally isotopically modified during assimilation – essential amino acids – my work provides a unique window into ecological processes and allows quantification of the importance of different basal energetic resource to animal communities. Through a combination of essential amino acid δ13C data and multivariate statistics (Figure 1), I can distinguish kelp-derived nutrients from those synthesized by phytoplankton, red, and green algae with >85% accuracy (Elliott Smith et al. 2018, 2021). Furthermore, my recent work demonstrates that these patterns are maintained across broad spatial gradients, and over centennial time scales (Elliott Smith et al. 2022). This technique represents a significant methodological advance for studies of coastal environments. Through the application of essential amino acid δ13C analysis in Alaskan and Chilean kelp forests, my research is providing new insights into the structure and function of kelp forest ecosystems. I am finding that kelps are important to coastal food webs beyond their role as a foundation species, and that kelp-derived energy indirectly subsidizes animals living in adjacent habitats (Elliott Smith et al. 2018). The importance of kelp-derived nutrients also varies among individuals of the same species, which has implications for the stability of local populations and food webs (Elliott Smith et al. 2021). More broadly, multichanneling appears commonplace in kelp forest communities, with resident species relying on energetic subsides from both kelp- and phytoplankton-derived energy, which may buffer these ecosystems from future global change. |
Historical ecology and human-ecosystem interaction.
To fully understand the processes governing ecological dynamics, we need to also consider the environmental conditions experienced by animal communities in the past, and the changing role of humans within food webs. Historical studies of human-ecosystem dynamics are particularly topical for marine habitats, which are under considerable threat from global change, and suffer from a shifting baseline syndrome owing to species declines prior to the advent of modern monitoring programs. A historical perspective can fill this gap by providing local-level ecological data prior to intensive modern human impacts. Historical studies also offer important insights into the long-term relationship of Indigenous communities with coastal ecosystems, a critical consideration in ensuring effectively and equitably managed natural resources.
As part of my NSF funded postdoctoral research, I have been exploring the ecology of kelp forest food webs prior to EuroAmerican arrival. In collaboration with my advisor Dr. Torben Rick, and Dr. Todd Braje at San Diego State University, I conduct isotopic analyses on faunal remains (fish and mammalian) from late Holocene coastal archaeological sites from Alaska to California. We are also collaborating with Dr. Courtney Hofman at the University of Oklahoma to conduct aDNA analyses on the same specimens. With these data we can reconstruct pre-industrial food web structure and the energetic underpinnings of nearshore habitats.
Our results provide a unique picture of coastal Pacific food webs, prior to modern ecological degradation. Bulk tissue and essential amino acid δ13C values of fish bones recovered from archaeological sites on the northern Channel Islands of California suggest that marine food webs were highly resilient prior to industrial era exploitation due to energetic interconnections, or multichanneling, among pelagic and benthic habitats (Figure 2). Furthermore, we find that Indigenous communities in the region were focused on middle trophic level fishes and were thus ‘fishing across’ rather than ‘fishing down’ their local food webs (Elliott Smith et al. 2023). This practice likely contributed to sustaining diverse marine food webs and human populations in the region for millennia. Our recent findings compliment previous research on the California sheephead, Semicossyphus pulcher, (Braje et al. 2017), and California sea otter, Enhydra lutris nereis (Elliott Smith et al. 2020), species which thrived for millennia in the region despite being hunted by local people. This sets historical Channel Islands fisheries apart from modern industrial and commercial practices and strongly suggests that local Indigenous peoples maintained sustainable marine harvesting practices.