Stable isotopes reveal that bottom-up omnivory drives food chain length and trophic position in eutrophic coastal ecosystems
Bibliographic record
Abstract
Abstract In coastal marine food webs, food chain length and the distribution of trophic levels mediate the impacts of emerging threats such as overfishing, pollution, and climate change, through their effect on essential properties such as productivity, connectivity, and energy transfer efficiency. These two components of food web structure are therefore an essential element of ecosystem-based management; however, what drives them remains poorly understood. It has been hypothesized that high primary production drives lower trophic levels and shorter food chain length in coastal regions. Here, we evaluate this hypothesis on the British Columbia (BC) coast as this coastal marine ecosystem is comprised of regions with contrasting levels of primary production. We measured nitrogen stable isotopes from zooplankton, micronekton, and nekton collected from four of the main water bodies of southern BC during a survey completed in August of 2019. We used Sentinel-3 satellite data to determine overall production in each region across a 5-year climatology and during the 2019 season. Results showed that primary production varied significantly between the four regions and that increases in phytoplankton biomass were driven by increases in microphytoplankton. Nitrogen isotope data demonstrated a significant inverse relationship between a region’s primary production and both total food chain length and trophic level in species sampled in multiple regions, but no change in the trophic structure of the zooplankton community across regions. Changes in species’ trophic levels were therefore driven by shifts in the level of zooplanktivory. These results support a model of bottom-up omnivory driving coastal food web structure, where levels of primary production, specifically biomass of microphytoplankton, determine food chain length and the distribution of trophic levels. High microphytoplankton biomass supports a large biomass of large grazing zooplankton, which drive increases in omnivorous feeding behaviour among the micronekton and nekton.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".