Analyses of changes in size, shell-weight and body-weight of small limpets.^*

*<p>Macroalgae (Ma) was fixed with 2 levels (+/−); Treatment (Tr) was fixed and orthogonal with 3 levels; Plots (Pl) was nested in Ma x Tr with 2 levels. The replicates were the limpets (<i>n</i> = 2). Cochran's test (C) was used to test assumptions of homogeneity. Non-significant interactions (^x) were pooled when ns with <i>P</i><0.25. *, <i>P</i><0.05; ns, <i>P</i>>0.05.</p

Changes in shell-weight of small limpets.

<p>Mean changes in shell-weight (± SE; <i>n</i> = 4) of small <i>P. vulgata</i> for each treatment at the end of the experiment. S, small limpets; L, large limpets. Black bars, without macroalgae; white bars, with macroalgae.</p

Summary of the effects of macroalgae (Ma) and competition (Co) on small (S, 15 mm) and large (L, 30 mm) limpets.^*

*<p>TL, total length. **, <i>P</i><0.01; *, <i>P</i><0.05; ns, <i>P</i>>0.05.</p

Changes in size of small limpets.

<p>Mean (± SE) changes in size of small <i>P. vulgata</i> in absence (black bars) or presence (white bars) of macroalgae (<i>n</i> = 12; a), for each treatment (<i>n</i> = 8; b) or for both (<i>n</i> = 4; c) at the end of the experiment. S, small limpets; L, large limpets.</p

Analysis of mean densities of chlorophyll-<i>a</i> for caged and uncaged treatments with limpets at natural densities (10S +3L) at the end of the experiment.^*

*<p>Treatment (Tr) was a fixed factor with 2 levels (caged <i>vs</i> uncaged); Macroalgae (Ma) was fixed and orthogonal with 2 levels (+/−); Plots (Pl) was nested in Tr x Ma with 3 levels (<i>n</i> = 10). Cochran's test (C) was used to test assumptions of homogeneity. **, <i>P</i><0.01; ns, <i>P</i>>0.05.</p

Analyses of mean densities of chlorophyll-<i>a</i> for each treatment 14 or 42 days after the start of the experiment.^*

*<p>Macroalgae (Ma) was fixed with 2 levels (+/−); Treatment (Tr) was fixed and orthogonal with 5 levels; Plots (Pl) was nested in Ma x Tr with 3 levels (<i>n</i> = 10). Plots had 2 levels for analysis at 42 days because 1 plot was lost during a storm; so, 1 plot was excluded at random from all other treatments to balance the design. Cochran's test (C) was used to test assumptions of homogeneity. Non-significant interactions were pooled when ns with <i>P</i><0.25. **, <i>P</i><0.01; ns, <i>P</i>>0.05.</p

Survival of large limpets.

<p>Mean (± SE; <i>n</i> = 3) proportion of survival of large <i>P. vulgata</i> for each week (wk; a) or at the end of the experiment (b). Treatments are: 3L (circles), 3L +10L (triangles), 3L +10S (squares). S, small limpets; L, large limpets. Black symbols and bars, without macroalgae; white symbols and bars, with macroalgae.</p

Analyses of changes in size, shell-weight and body-weight of large limpets.^*

*<p>Treatment (Tr) was fixed with 5 levels (3L, + macroalgae; 3L +10S, +/− macroalgae; 13L, +/− macroalgae); Plots (Pl) was nested in Tr with 2 levels. The replicates were the limpets (<i>n</i> = 2). Only 1 tagged individual remained from the 3L treatment without macroalgae. So, this treatment was not included in the analysis and the factor Macroalgae was removed. Cochran's test (C) was used to test assumptions of homogeneity. Non-significant interactions (^x) were pooled when ns with <i>P</i><0.25. *, <i>P</i><0.05; ns, <i>P</i>>0.05.</p

Chlorophyll-<i>a</i> densities for each treatment.

<p>Mean (± SE; <i>n</i> = 10) density of chlorophyll-<i>a</i> (mug/cm²) in plots with (white bars) or without (black bars) macroalgae 14 days (a) or 42 days (b) after the start of the experiment. S, small limpets; L, large limpets.</p

How Much Is Too Little to Detect Impacts? A Case Study of a Nuclear Power Plant

<div><p>Several approaches have been proposed to assess impacts on natural assemblages. Ideally, the potentially impacted site and multiple reference sites are sampled through time, before and after the impact. Often, however, the lack of information regarding the potential overall impact, the lack of knowledge about the environment in many regions worldwide, budgets constraints and the increasing dimensions of human activities compromise the reliability of the impact assessment. We evaluated the impact, if any, and its extent of a nuclear power plant effluent on sessile epibiota assemblages using a suitable and feasible sampling design with no ‘before’ data and budget and logistic constraints. Assemblages were sampled at multiple times and at increasing distances from the point of the discharge of the effluent. There was a clear and localized effect of the power plant effluent (up to 100 m from the point of the discharge). However, depending on the time of the year, the impact reaches up to 600 m. We found a significantly lower richness of taxa in the Effluent site when compared to other sites. Furthermore, at all times, the variability of assemblages near the discharge was also smaller than in other sites. Although the sampling design used here (in particular the number of replicates) did not allow an unambiguously evaluation of the full extent of the impact in relation to its intensity and temporal variability, the multiple temporal and spatial scales used allowed the detection of some differences in the intensity of the impact, depending on the time of sampling. Our findings greatly contribute to increase the knowledge on the effects of multiple stressors caused by the effluent of a power plant and also have important implications for management strategies and conservation ecology, in general.</p> </div