Egg capsule hatch rate and incubation duration of the California market squid, Doryteuthis (= Loligo) opalescens: insights from laboratory manipulations

摘要

Egg capsules of the squid Doryteuthis (= Loligo) opalescens were reared in the laboratory to assess the dependence of time-to-hatching (incubation time) and hatching success rate on temperature and light regime. Both incubation time and hatch duration were found to be inversely related to temperature. More than 96% of paralarvae hatch from eggs reared at temperatures between 9 and 14 ℃. Hatch rate drops below 90% in warmer and colder water. No eggs hatch below 7 ℃, and the upper limit of viability is near 25 ℃. The vast majority (91%) of hatchlings emerged during the dark phase of the photoperiod. Egg capsules reared at 13.4 ℃ with a supposedly commensal polychaete, Capitella ovincola, had a slightly higher hatch rate than those without the annelid. Because eggs are naturally laid closely together, crowding was hypothesized to cause decreased ventilation and a lower hatch rate. Crowding was tested by placing two capsules (rather than one) into the small incubation chambers (50 ml). This treatment did not result in a lower hatch rate at 13.4 ℃, but at 21.4 ℃ it decreased the hatch rate by 20%. Brood incubation duration is related to temperature by the equation: Incubation (days) = 14.97 + 177.40 × exp(-0.119 x Temperature -℃) (x~2 = 282.5, P = 0.001). Stable isotope analysis confirmed that C. ovincola worms eat the capsule matrix, not the paralarvae. These polychaetes had a δ~(15)N value of 12.79‰ versus 12.06‰ for squid paralarvae, and 10.54‰ for the gelatinous matrix of egg capsules. This fractionation factor ε of 2.25‰ is consistent with marine food webs. Provision of nutrients and shelter for the annelids and increased hatch rate for the squid embryos suggests a symbiotic relationship between these organisms.