The 1989–2020 L4 record did not establish a link between temperature anomalies and the small-to-large copepod ratio

We tested whether warm months had a higher numerical ratio of small to large copepods at Plymouth L4 in the western English Channel. We used the March 2023 Western Channel Observatory data release. The main sample had 380 months in 1989–2020. We fit the log ratio against surface temperature, with separate means and linear trends for each calendar month. A 1°C temperature increase was linked to a 6.7% lower ratio. The nominal 95% range was 21.3% lower to 12.1% higher, from 9,999 paired three-year block resamples. Thus the test did not establish a link and did not show the expected shift toward small copepods. Two-year and five-year blocks, a zero-count check, past temperature, chlorophyll, water-column temperature, and seasonal checks also left the direction uncertain. The ratio uses taxon groups defined by adult species length below or at least 2 mm. It does not measure changes in individual body size. The result applies to monthly net counts at one site after month-specific trends are removed. The package has unchanged source data, provenance, a local plan, all results, figures, code, and independent checks.

copepods · Western Channel Observatory · temperature · community composition · seasonality · time series · null result · open data