Crab Growth

Like all crustaceans crabs grow discontinuously - periods of stasis during which size does not change alternative with periods of molting during which size increases markedly. Many approaches to representing crab growth have ignored this feature. Over the past decade my students and I have been working on refining our understanding of crab growth. In all of this work we have adopted a molt-process approach in which we specifically measure and model the two phases of growth - the intermolt period and molting itself separately.

Most of the work has used both lab and field studies. In the laboratory we have maintained and tracked the status of individual crabs over multiple molts - each individual crab must be followed through at least two molts to provide an estimate of growth per molt and intermolt period. In these experiments we have varied ration, salinity and temperature to provide a range of different growth rates. Although such lab based studies are artificial and often animals grow faster in the wild than in captivity - such lab-based studies allow us to document patterns in the growth response to environmental to different environmental forcing. We can for instance ask whether growth varies as a result in variation in growth per molt, or intermolt period. Our results clearly show that growth per molt is relatviely invariant in blue crabs - it is in fact highly constrained because of the geometric challenge of forming a new carapace within the old - whereas the intermolt period is highly plastic. Our results indicate that nearly all the variation in grab growth results from variation in the inter molt period.

Paralleling the laboratory work, we have also studied growth in the field using caging studies. We have monitored crab growth in different locations in the Chesapeake Bay and in the Hudson River. The results of these studies parallel our finding from the lab - growth per molt is constant, regardless of where in the Chesapeake Bay or Hudson River we measured it. Intermolt period was variable as a function of temperature and food availability - but did not vary between systems and regions for a constant temperature.

The growth results from these studies now play a central role in our population modeling to address fundamental ecological questions, and the more applied application to assess the status of the stock.

Last revised: 2/16/2010