Effects of within-season temperature variations on the early life history of two estuarine demersal fishes

Cultured naked goby ( Gobiosoma bosc ) and striped blenny ( Chasmodes bosquianus ) larvae were used to compare life history parameters for early and late periods within a long spawning season during which temperature increased by approximately 10 °C. Hatch lengths, growth rates, larval period duration, settlement length, survivorship, and other metrics of these serial spawners were determined for larvae hatched during early and late time periods with ambient average weekly water temperatures of 20.8 (standard deviation ±2.1 °C) and 29.0 (±1.0), respectively. Cultured fishes provided parameter estimates in the absence of predation mortality and with constant prey availability. Four hypotheses were tested for each species: 1) total length at hatch is not related to temperature, 2) pelagic larval period (PLD) is negatively related to temperature, 3) growth rates and survivorship are positively related to temperature, and 4) flexion and settlement lengths are negatively related to temperature. For both gobies and blennies, hatch length decreased with increasing temperature, but was not significantly related to survivorship. Larval blennies retained the yolk-sac longer than gobies. At higher temperatures, striped blenny flexion length, settlement length, PLD, and instantaneous mortality significantly decreased while instantaneous growth in length increased. Naked goby flexion lengths, settlement lengths, PLD, and mortality rates also declined with increasing water temperatures while instantaneous growth rates increased with increasing water temperatures. Average growth in length did not change significantly with temperature for either species. Survivorship in both fishes was lowest during 0 to 6 days post hatch (dph) coincident with the yolk-sac and first feeding stages. Survivorship significantly increased with larval fish total length and age (dph) for both species and time periods. Average estimated striped blenny percentage survival increased by an order of magnitude (~3 to ~32 %) with increasing temperature while average naked goby percentage survival increased from ~3 % (early) to ~11 % (late) over the 8.3 °C temperature range examined. The observed life history parameter variation with seasonal temperature changes likely function to ensure survival to settlement for at least some cohorts within a year class as part of a bet-hedging life history strategy. Data from cultured fishes provide a baseline for future evaluation of demographics and rates from field collections.