´ L
.M.Z. Chıcharo, M.A. Chicharo J. Exp. Mar. Biol. Ecol. 243 2000 81 –94 85
By solving the Laird–Gompertz equation it is possible to calculate the length, corresponding to the inflexion point of the sigmoid curve, at which the growth rate is
maximal L :
i
L 5 L e
i `
as well as the maximal growth rate G :
CM
G 5 G L
CM i
and the maximum length for the species L :
` K
c
L 5 L e
`
3. Results
3.1. Environmental factors and Mytilus galloprovincialis larval abundance During the sampling period, between May 4 and August 31, 1990, spring tides
occurred on May 23–25, June 23–25, July 23–26 and August 22–24 Fig. 2a. Wind
21
velocity ranged between 2 and 6.7 m s Fig. 2b. The highest values were registered in
July. The wind direction was variable Fig. 3. A seasonal pattern of Chlorophyll a was
21
observed Fig. 2b, with the highest value during spring 11 June, 5 mg l and lowest
21
during late summer 27 August, 1.8 mg l . Water temperature and salinity ranged from
19 to 27.58C, and from 35.1 to 36.5 PSU, respectively Fig. 2c. Mytilus galloprovincialis larvae were present in the plankton throughout the entire
sampling period Fig. 2a. The abundance began to increase the first day of May, when
23
the maximal value was recorded, 4721 individuals m . The lowest value was observed
23
by the middle of June with 37 individuals m , however an important variation in the
abundance was observed between successive samples. A great reduction was noted during spring tides.
3.2. Growth rate Ten larval cohorts of M
. galloprovincialis were identified. The progression of the modal classes considered for each cohort is plotted in Fig. 4. Fine growth lines in larval
shells Fig. 5 were assumed to be deposited daily and suggested development of an age–length relationship. Fitted parameters for all the growth models are given in Table
1. Growth curves Fig. 6 for larval shell length were significant at P , 0.05. The Laird–Gompertz model yielded the best fit to length data, as shown by the correlation
coefficients and P values for the overall growth parameters Table 1. Based on the Laird–Gompertz equation, the maximum length for the larvae of M
. galloprovincialis
21
was estimated as 209.8 mm and the maximal growth rate was 4.5 mm d , occurring at a
shell length of 97.7 mm.
´ 86
L .M.Z. Chıcharo, M.A. Chicharo J. Exp. Mar. Biol. Ecol. 243 2000 81 –94
Fig. 2. M . galloprovincialis larval abundance related to environmental parameters: a tidal amplitude; b
wind velocity and chlorophyll a; c water temperature and salinity.
´ L
.M.Z. Chıcharo, M.A. Chicharo J. Exp. Mar. Biol. Ecol. 243 2000 81 –94 87
Fig. 3. Wind direction registered near the sampling station Airport — see Fig. 1. Frequency distribution over the entire study period 4 May–31 August 1990.
4. Discussion
