DENSITY-DEPENDENT GROWTH INHIBITION IN LOBSTERS, HOMARUS (DECAPODA, NEPHROPIDAE)

¹ University of California, Bodega Marine Laboratory, Bodega Bay, California 94923

1. A density-dependent inhibitory effect upon the growth of juvenile lobsters was studied in two semi-recirculating seawater-table systems in which controlled metabolite gradients were established by varying rate of makeup flow. Each system contained eight columns of 45 compartments each. Homarus americanus fifth-stage juveniles were placed in the compartments in rows 5-10, 20-25, and 35-40, numbering from the incurrent end of each system, and fourth-stage H. americanus x H. gammarus F₁ hybrids were placed in all other compartments.

2. At the end of 93 days hybrids immediately downstream from the older animals were an average of 15% shorter than those five rows downstream. No effect of metabolite accumulation could be demonstrated.

3. Analysis by a compartmental model indicated that the growth-inhibitory effect was chemical and was due either to a rapidly decaying, continuously produced inhibitor with a half-life of about 1 min, or to an inhibitor pulsed in production or release.

4. Decreased growth in the middle of the blocks of older animals demonstrated that the effect was neither species- nor age-specfic. The effect is substantially different from other growth-inhibitory phenomena previously described in Crustacea.