Nursery role of seagrass beds: enhanced growth of juvenile blue crabs ( Callinectes sapidus Rathbun)

Abstract

The role of submerged aquatic vegetation in supporting enhanced growth of Callinectes sapidus was investigated through field and laboratory experiments. In predator-free enclosures (1 m 2) in the lower York River, Virginia, juvenile blue crabs within Zostera marina (L.) beds grew faster than crabs in enclosures deployed outside the beds. First stage crabs were introduced into vegetated or un vegetated enclosures at either 10 or 50 crabs m −2. After the 6 wk experimental period, both survival and growth were significantly higher in vegetated treatments (growth was estimated by change in “volume,” the product of carapace width, length and depth). In fiberglass mesocosms (2.67 m × 1.33 m × 0.67 m) divided into vegetated and unvegetated halves, juvenile blue crabs grew faster in the vegetation, consistent with field findings. Where differences existed between density treatments in field enclosures, juvenile crabs grew faster in high density than in low density treatments. Aggregate crab growth (summed “volumes” of all recaptured individuals) for vegetated enclosures was greater than for unvegetated enclosures. Potential contribution of cannibalism was sufficient to explain some within-habitat density effects, but was not sufficient to account for the entire aggregate differences, suggesting that food may not be limiting within the seagrass beds even at 50 crabs m −2. These results show that early stage blue crabs receive a substantial growth advantage, in addition to the refuge function shown in other studies, from their association with seagrass beds. This trophic advantage may be experienced by juveniles of other species that utilize vegetated nursery areas and may help explain the ontogenetic habitat shifts that characterize many life histories.