Description
The market squid (Doryteuthis opalescens) is an ecologically and economically valuable species in nearshore ecosystems throughout the California Current system that displays large interannual population fluctuations. Despite the importance of the fishery, the mechanisms controlling the boom and bust cycle of market squid populations remain unknown. Variability in recruitment may be driven by the abundance of prey for newly hatched paralarvae, which are especially susceptible to starvation. I determined which zooplankton are preferred prey of paralarvae by conducting a series of laboratory experiments in which D. opalescens paralarvae 0-30 days post hatching (dph) were fed single-taxon and mixed-taxa diets of relatively abundant zooplankton taxa collected from natural plankton. Paralarvae successfully captured and consumed a total of 14 zooplankton taxa ranging in size from 105 - 585 µm in the single-taxon trials. Paralarvae were then presented with assemblages of multiple prey taxa to determine the preferences of paralarvae during the first 3 weeks after hatching. In mixed-taxa trials paralarvae 7 days post hatching demonstrated strong preferences for trochophores and rotifers. Paralarvae reared on Artemia salina nauplii and field-collected zooplankton for 14 and 21 dph exhibited different preferences. Paralarvae reared on A. salina for 14 and 21 days, continued to demonstrate preferences for trochophores and rotifers, while paralarvae reared on field-collected zooplankton fed less selectively on those taxa. To determine the effects of various prey on the condition of newly hatched paralarvae, paralarvae were reared on one of four single-taxon diets for 15 dph. The body condition and survival of paralarvae differed among the diet treatments. The RNA:DNA ratios, mantle lengths, and wet weights of paralarvae reared on a diet of large nauplii were greater than those reared on all other prey taxa, followed by paralarvae reared on the copepod Oithona nana, which also yielded the greatest survival. The discovery of the preferred prey of D. opalescens paralarvae and the effects of prey taxa on the condition of paralarvae less than 30 dph provide a basis for future research on the population dynamics, management, and aquaculture of this valuable species.
