Passage II

Juvenile Callinectes sapidus (a species of crab) typically hide among Zostera marina (a species of sea grass) to avoid detection by aquatic predators. Two experiments examined how Z. marina population density and C. sapidus body size affect the ability of juvenile C. sapidus to avoid predation in a particular coastal area.

Experiment 1

Each of 200 small (4.5 mm wide) juvenile C. sapidus was prepared for testing as follows: One end of a 1.0 m piece of nylon fishing line was tied around the middle of the C. sapidus, and the knot was then securely attached to the C. sapidus with cyanoacrylate(a strong waterproof glue). The other end of the line was tied to its own metal rod. After being prepared, the 200 C. sapidus were equally divided into 4 groups (Groups 1-4).

Each rod associated with a Group 1 C. sapidus was randomly placed within a 100 m² plot having a Z. marina population density of 0 shoots/m² (sand only, no plants). Twenty-four hours later, the number of surviving Group 1 C. sapidus was determined.

The procedure for Group 1 was repeated for Group 2-4, except that Group 2, Group 3, and Group 4 were placed in plots having a Z.marina population density of 380 shoots/m², 760 shoots/m², and 1, 600 shoots/m², respectively.

The results are shown in Table 1.

Experiment 2

Each of 200 large (23.3 mm wide) juvenile C. sapidus was prepared as in Experiment 1 After being prepared the C. sapidus were equally divided into 4 groups (Groups 5-8 ) . The procedures for Groups 1-4 were repeated for Groups 5-8 (see Table 2).

Tables adapted from J. L. Schulman. “Habitat Complexity as a Determinant of Juvenile Blue Crab Survival.” ©1996 by The College of William and Mary.