Community-level phenological patterns of tintinnids in a coastal site with the largest annual temperature range

Surface seawater temperature varies seasonally across latitudes, shaping the temporal organization of plankton communities. However, the phenology of microzooplankton at the community level remains poorly understood, largely due to insufficient temporal resolution in most monitoring programs. In this study, we conducted a high-frequency (three times per week) year-round survey of tintinnids in Qingdao coastal waters, a site characterized by the largest annual temperature range among global coastal systems. Thirty tintinnid species were identified, all of which were neritic taxa. Based on their annual occurrence patterns, the community was classified into four phenological types: cold-water type, temperate type I, temperate type II, and warm-water type, each exhibiting distinct seasonal peaks and thermal performance ranges. These four phenological types constitute the community-level phenological pattern of tintinnids in Qingdao coastal waters. The effective breadths of thermal performance range for each type was 5–8 °C, and the number of phenological types increased with the site’s annual temperature range, from two in Hong Kong to three in Ningbo and four in Qingdao. Cold-adapted types exhibited positively skewed thermal performance curves, indicating higher sensitivity to temperature fluctuations at low temperatures, whereas warm-adapted types followed the generalized negatively skewed pattern. These results demonstrate that high-frequency observations provide a powerful framework for resolving community-level phenology and highlight the role of local thermal regimes in structuring tintinnid seasonal dynamics under a warming ocean.