4.2.4 SETTLEMENT
Diet and Diet + Water treatments and controls were placed in settlement containers after 26 days of larval development. Larvae in the Water treatment appeared to be delayed and were therefore given three additional days (29 d post-fertilisation) to achieve similar development as in the other treatments (i.e. > 50% of 8-armed plutei having a rudiment) before being transferred to the settlement containers. Details of the settlement procedure are described in section 3.2.4. Larvae were given eight days to settle, after which any remaining larvae were removed from the containers. Time post-settlement was counted from the first day larvae were placed in settlement containers, as many larvae settled within a day.
The total number of settlers per container was counted under a dissecting microscope(40x magnification) at 8 and 38 d post-settlement. All juveniles in each container were rated for normal development and were deemed as ‘abnormal’ when body shape was strongly irregular, or lacked spines or pigmentation (Table 3.3) when observed under a dissecting microscope (40x magnification). The first 20 settlers encountered were photographed under a dissecting microscope (25x magnification). Body diameter (radial length) and three spines were measured using the software ImageJ.
4.2.5 STATISTICS
All data analyses were conducted using the software R (version 3.1) with package multcomp (Hothorn et al. 2008) for pairwise comparisons and package nlme(Pinheiro et al. 2015) for mixed effects models.
4.2.5.1 Larval performance
Direct effects of copper treatments on larvae were evaluated by: (1) larval mortality rate; (2) larval normal development; (3) delayed development; (4) larval growth; and(5) larval size at the latest sampling.
Larval mortality rate was the difference in larval density divided by the initial number of larvae and time interval, to obtain the daily probability of mortality per capita early(from 4 to 15 or 16 d post-fertilisation) and late (from 15 or 16 to 23 or 24 d postfertilisation)in development. Normal larval development was the proportion of 6- and 8-armed pluteus larvae midway through development (i.e. 15 or 16 d postfertilisation)and the proportion of 8-armed pluteus larvae late in development (i.e. 23 or 24 d post-fertilisation). Mortality and normal development were analysed using repeated measures ANOVA with copper level and source of copper (Diet, Water or Diet + Water) as ‘between’ factors and larval stage (early, mid or late) as the ‘within’ factor. Both variables were square-root arcsin transformed.