Marine heatwaves did not increase year-to-year turnover, abundance change or richness change in 93 BioTIME marine assemblage studies in 1983-2023 (monthly 1-degree SST)

We tested if marine heatwaves cause more year-to-year assemblage change in marine taxa other than trawl-surveyed fish. Fredston et al. (2023) found that heatwaves were not a dominant driver of change in demersal fish. We used 93 marine studies from BioTIME 2.0 (fish, invertebrates, seabirds, algae, plankton). We split the studies into 1,236 one-degree units and rarefied each year to equal samples. This gave 12,907 consecutive-year pairs (1983-2023). A heatwave window was 2 or more consecutive months above the monthly 90th percentile of HadISST anomalies (1982-2011 baseline) between the two surveys. Two-way fixed-effects models with equal study weight and study-clustered errors gave no heatwave effect on Jaccard turnover (-0.005, 95% CI -0.021 to 0.011), Bray-Curtis on relative abundance (-0.002, -0.020 to 0.017), log abundance ratio (-0.018, -0.125 to 0.089) or log richness ratio (-0.043, -0.099 to 0.012). Within-unit permutation tests, ERSST v5, severe and persistent heatwave definitions, a mean-anomaly control, standard-protocol studies and a placebo (heatwave after the survey) gave the same result. Sampling effort did not change in heatwave years. The data exclude general effects larger than about 0.15-0.25 within-unit SD. The community temperature index increased slightly after heatwaves in per-study estimates (+0.048 degC, 95% CI 0.017 to 0.079), but not in the primary pooled model, and the increase in 1982-2002 did not occur again in 2003-2023. Limitations: 1-degree monthly surface SST is a coarse proxy for habitat temperature and cannot detect short events; there are only 8 tropical studies and few pairs after 2019.

marine heatwave · BioTIME · biodiversity time series · community turnover · community temperature index · HadISST · ERSST · rarefaction · fixed effects · replication · climate extremes · null result