Marine research at CNR
Substrate inclination 60
54
Percentage
50 40 30
23
20
14 7
10 2
0 0
45
75
90
135
Figure 3: Number of juveniles associated with different substrate inclinations. ment along the other surfaces was restricted. For each test two lobsters of similar size were chosen (± 1.0 mm CL), randomly assigned and tethered to one of the two structures. One hour after the lobsters were tethered to the artificial structures one octopus was released in the centre of the arena. A total of 30 lobsters and 6 octopus of similar size were used. Lobsters ranged from 28 to 63 mm CL (mean 41.3 ± 5.1 SD) and octopuses from 524 to 879 g total wet weight (mean 743.20 ± 110.67 SD). Thus, after each trial, the octopus used were put back into the storage tank from where twenty-four others were then randomly selected for further trials until the end of the experiment. These procedure reduced the chance of using the same predator in the same treatment more than once. The proportion of surviving lobsters between the treatments was determined using G-test [5] with Williams’ correc-
tion assuming that the octopus had the same probability of choosing the prey (0.5).
4
Results
Field Studies - Evaluation of habitat characteristics and settlement period for P. elephas. A total of 54 sampling replicates were conducted over the whole study period: 162 P. elephas individuals were collected, 119 were juveniles (LC < 44.5 mm) and 43 were sub-adults and/or adults. Both in 2006 and 2007, recruitment began between June and August, reaching a peak between the second half of July and the beginning of August. A higher number of individuals was collected in Isola delle Femmine (74) compared to Barcarello (45). Figures 1a, b, c, d illustrate recruitment data over depth ranges. The figures do not include the shallow depth range (5-10m) as individuals were not found at this depth. The temporal trend of recruitment appears 225