Ecological Archives E088-147-A1

David Balata, Luigi Piazzi, and Lisandro Benedetti-Cecchi. 2007. Sediment disturbance and loss of beta diversity on subtidal rocky reefs. Ecology 88:2455–2461.

Appendix A. Differences in ambient levels of water turbidity and amount of sediment between study areas.

Water turbidity

Differences in water turbidity between the two study areas were quantified using a multiparametric probe (Ocean Seven 316) every two months, from January to December 2002. Three replicate readings (100s of meters apart) were made in each area at a depth of 29 m at each date of sampling and turbidity was expressed as NTU (Nephelometric Turbidity Unit). Data were analysed with a two-way factorial analysis of variance with Date (seven levels) as a random effect and Area (two levels) as a fixed factor. Cochran’s C-test was used to assess homogeneity of variances (Underwood 1997). Results (Fig. A1, Table A1) showed clear differences in water turbidity between the two areas. Although the analysis detected a significant Date × Area interaction, turbidity was significantly larger in one area consistently over the entire duration of the study (SNK tests).

Amount and characterization of sediment

Differences in the amount of sediment entrapped by organisms in the two areas were quantified by sampling plots of 25 × 20 cm with a suction pump for 30 seconds. In each area, sediment was collected on horizontal substrata from three random quadrats at each of seven sampling dates in 2002. The material was pumped into nylon stockings and preserved in 4% sea-water diluted formalin. In the laboratory, collected material was filtered on ignited and pre-weighed GF/F glass microfiber filters (70μ) and rinsed in distilled water to remove salts. Sediment was then dried to constant weight (60° for 24 h) before weighing on an Ohaus balance to a precision of 10– 4 g in the presence of silica gel (Airoldi and Virgilio 1998). Final values were expressed as g/m2. Data were analyzed as described for the analysis of water turbidity. Results (Fig. A2, Table A2) highlighted significant differences between areas in the amount of sediment deposited on horizontal surfaces. Although the analysis detected a significant Date × Area interaction, sediment was significantly more abundant in one area consistently over the course of the study (SNK tests).

Grain size distributions of sediment were examined in each area in March and June 2002. Grain size classes followed Wentworth Classification and were obtained through classical wet sieving techniques. The largest fraction of sediment was constituted by particles ranging from 125 to 250 μm (Fig. A3).

TABLE A1. Results of two-way ANOVA comparing water turbidity in each study area at different dates.

Source

df

MS

F

P

Denominator for F

Date = Da

6

2.73

99.76

<0.001

Residual

Area = A

1

12.93

11.71

<0.01

Da × A

Da × A

6

1.10

40.31

<0.001

Residual

Residual

28

0.03

     

Cochran’s test

 

C = 0.3391, P > 0.05

 

Transformation 

 

None

 

 

 TABLE A2. Results of two-way ANOVA comparing the amount of entrapped sediment in each study area at different dates.

Source

df

MS

F

P

Denominator for F

Date = Da

6

1458.63

18.41

<0.001

Residual

Area = A

1

42152.14

175.12

<0.001

Da × A

Da × A

6

240.70

3.04

<0.01

Residual

Residual

28

79.22

     

Cochran’s test

 

C = 0.3156, P > 0.05

 

Transformation

 

None

 

 

FigA1
 
   FIG. A1. Turbidity levels (mean + SE, n = 3) in the two study areas (indicated by white and black bars, respectively) from January to November 2002.

 

FigA2
 
   FIG. A2. Dry mass of sediment deposited in the two study areas (indicated by white and black bars, respectively) in 2002 (mean + SE, n = 3).

 

FigA3
 
   FIG. A3. Grain size distribution of sediment (μm) deposited in the two study areas (indicated by white and black bars, respectively) in March (A) and June (B) 2002 (mean + SE, n = 3).

 

LITERATURE CITED

Airoldi, L., and M. Virgilio. 1998. Responses of turf-forming algae to spatial variations in the deposition of sediments. Marine Ecology Progress Series 165:271–282.

Underwood, A. J. 1997. Experiments in ecology. Their logical design and interpretation using analysis of variance, Cambridge University Press, Cambridge, UK.



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