Plankton distribution patterns across fine-scale fronts in the Tīkapa Moana Te Moana Nui a Toi Hauraki Gulf, Aotearoa New Zealand

Context The patchiness of chlorophyll-a in the ocean is a well-known fact, particularly in coastal areas. However, how this patchiness is reflected in plankton community composition is still poorly understood. Aims Here, we document how fine-scale fronts affect plankton community composition and diversity in coastal temperate waters (Tīkapa Moana Te Moana Nui a Toi Hauraki Gulf, Aotearoa New Zealand). Methods We collected water samples and observations of environmental descriptors at scales of <1 km, guided by a front detection algorithm based on high-resolution chlorophyll-a measurements from remote sensing. We classified plankton in three size classes (20–200 μm, 200–500 μm and ≥500 μm), by using a combination of traditional and semi-automated microscopy, into taxonomic groups, characterising the community composition across physical gradients. Key results Our results indicated localised changes in taxa either at front locations or within chlorophyll-a filaments. These gradients can be seen for three size fractions of plankton, 20–200, 200–500 and ≥500 μm. Conclusion Our results suggest that, in line with modelling studies, fine-scale features can bring together water masses hosting different communities, enriching the planktonic diversity of an area. Implications Fine-scale variability should be considered when monitoring plankton community composition for the prevention of harmful algal blooms, when interpreting time series of plankton community composition, and when assessing marine megafauna distribution.