Diel Changes in Habitat Use by Two Tidepool Fishes

Abstract

Abstract I examined the effects of low-tide timing on tidepool use by two southern California fishes, Clinocottus analis and Girella nigricans. Abundance of these fishes in middle and upper intertidal pools was higher when low tides occurred at night or in the early morning (4.4–9.7 fish per pool) than in the afternoon (1.3–3.4 fish per pool). Mean fish size was also higher during nighttime low tides than daytime low tides. Tidepools higher in the intertidal zone generally displayed greater differences in fish abundance between early morning and afternoon low tides than lower pools. In addition, these upper tidepools reached higher temperatures during afternoon low tides (up to 30 C) than lower tidepools, often exceeding or nearing the preferred and lethal maximum temperatures reported for the two study species. Diel vertical habitat shifts by middle and upper tidepool fishes indicate that their partitioning of rocky intertidal habitat occurs on short-term temporal as well as spatial scales.