Diel Changes in Habitat Use by Two Tidepool Fishes
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.Abstract
Number of total fish, Clinocottus analis, and Girella nigricans in middle and upper intertidal pools when low tide was in early morning (AM) versus afternoon (PM). Results of paired t-tests are presented for three comparisons made at False Point (FP1, FP2, and FP3). Number of tidepools censused (n) and P-values (P) are listed
Number of Girella nigricans trapped at Dike Rock relative to the time of day of low tide in (A) late July to early August, and (B) September. Mean hourly air temperature at Dike Rock for the sampling periods is also plotted. Fish abundance was correlated with mean air temperature at the time of pool isolation in July/August (n = 21, r2 = 0.45, P < 0.001) but not in September (n = 17, r2 = 0.01, P = 0.69)
Mean size (± 1 SE) of Clinocottus analis and Girella nigricans collected in all tidepools at low tide in early morning (AM) versus afternoon (PM). Five comparisons between morning and afternoon censuses were made, three at False Point (FP2, FP3, FP4) and two at Ocean Beach (OB1, OB2), San Diego, using paired t-tests. P-values (P) and the number of tidepools containing fish in both the morning and afternoon (n) are given
Mean size of Girella nigricans trapped at Dike Rock in (A) late July to early August, and (B) September relative to the time of day of low tide. Mean hourly air temperature at Dike Rock for the sampling periods is also plotted. Mean fish size was correlated with mean air temperature at the time of pool isolation in July/August (n = 21, r2 = 0.060, P < 0.001) and September (n = 17, r2 = 0.36, P = 0.011)