Growth and behavior during the settlement period of the American lobster, Homarus americanus
Little attention has been paid to the consequences of variation in size, and timing of ontogenetic habitat shifts marine crustaceans. The postlarval American lobster, Homarus americanus, exhibits characteristics that make this species an excellent candidate to investigate the effects of size and timing of the habitat transition in a crustacean. The objective of this research was to investigate the consequences of variability in the size and the timing of the ontogenetic habitat shift on post-settlement growth in the American lobster.
A field growth experiment gave estimates of mean size and duration of benthic instars (IV to XI). The influence of size and delayed settlement (within the instar) were evaluated by the recapture rate of micro-wire tagged postlarvae and fifth instars. Growth rates, estimated RNA:DNA ratios, of newly settled postlarvae, wild and recaptured early benthic phase lobsters were determined. Behavioral interactions among postlarval and fifth instar lobsters in a simulated cobble environment were recorded.
Lobsters settling in early- and mid-season were larger at each subsequent instar and had different growth profiles from late settlers. Time to reach the IX instar was shorter for early settling lobsters. Postlarvae present early in the season were 30-50% larger and two or three instars older than late settlers by the end of the growing season. Larger postlarvae and fifth instars were recaptured more frequently than smaller ones. No difference in recapture rate with developmental timing of settlement was observed. These observations suggest that size and time of settlement may influence settlement success and, by inference, survival.
Differences in growth rates were observed. Planktonic postlarvae had higher growth rates than benthic lobsters. Recaptured lobsters originating from wild stock had higher growth rates than those originating from laboratory stock. Differences in growth rates between planktonic and benthic lobsters may be evidence of a trade off between mortality and growth.
Behavioral patterns between settled postlarvae and fifth instar lobsters were different. Postlarval behaviors centered around shelter seeking, whereas fifth instar behaviors were within the burrow. Dominance, burrow invasion, eviction and potential territory establishment were observed in both instars.
0792: Fish production