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

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 degrees C. Hatch rate drops below 90% in warmer and colder water. No eggs hatch below 7 degrees C, and the upper limit of viability is near 25 degrees C. The vast majority (91%) of hatchlings emerged during the dark phase of the photoperiod. Egg capsules reared at 13.4 degrees C 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 degrees C, but at 21.4 degrees C it decreased the hatch rate by 20%. Brood incubation duration is related to temperature by the equation: Incubation (days) = 14.97 + 177.40 x exp(-0.119 x Temperature - degrees C) (chi(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 delta N-15 value of 12.79 parts per thousand versus 12.06 parts per thousand for squid paralarvae, and 10.54 parts per thousand for the gelatinous matrix of egg capsules. This fractionation factor epsilon of 2.25 parts per thousand 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.