Ecological Archives E096-124-A5

Maya C. Pfaff, George M. Branch, Jennifer L. Fisher, Vera Hoffmann, Allan G. Ellis, and John L. Largier . 2015. Delivery of marine larvae to shore requires multiple sequential transport mechanisms. Ecology 96:13991410. http://dx.doi.org/10.1890/14-0229.1

Appendix E. A summary of differences in physical oceanographic variables between sites (Table E).

Time series of daily mussel and barnacle settlement (Figs. 2a-b and 3a-b) showed that settlement of both taxa was on average substantially greater – by at least a factor of 5 – at Elands Bay compared to Columbine, and nearshore settlement consistently exceeded intertidal settlement by an order of magnitude at both sites. For mussels, the mean (± SE) values at Elands Bay were 25.55 (± 1.83) and 186.06 (± 21.95) settlers.collector-1.day-1 for intertidal and nearshore collectors respectively, and at Columbine the values were 2.64 (± 0.22) and 47.06 (± 10.78). For barnacles, Elands Bay values were 7.15 (± 0.84) and 11.66 (± 2.12), and at Columbine, 0.02 (± 0.01) and 0.30 (± 0.08).

Differences in physical conditions between sites (Table E) were reflected in a lower and more variable average upwelling index for Elands Bay than Cape Columbine. Stratification was on average greater and less variable at Elands Bay, and cross-shore winds were predominantly onshore at Elands Bay but offshore at Cape Columbine. Contrary to expectations, average temperature was remarkably similar between the sites, since Cape Columbine had cooler surface water, but slightly warmer bottom water than Elands Bay. Also unexpected was the fact that swell height was lower at the seemingly more exposed Cape Columbine than at Elands Bay, which may be a reflection of the effect of shoaling in the shallower waters at Elands Bay.

Table E1. Averages (± SE) of physical variables over the 2006–2007 sampling period at Elands Bay and Cape Columbine. Wind and current speed were decomposed into along-shore (equatorward) and cross-shore (onshore) components; negative speeds indicate the reverse direction. Temperature (T) was recorded in the intertidal, and at various depths on nearshore moorings, from which a water column average and stratification index (Brünt-Väisälä frequency) were derived.

Physical variable

Elands Bay

Cape Columbine

Wind - equatorward (m. s-1)

0.80

±1.42

6.20

±2.17

Wind - onshore (m. s-1)

1.62

±0.43

-0.52

±2.70

T intertidal (°C)

12.22

±1.63

11.02

±0.95

T 5m (°C)

11.51

±1.44

11.06

±0.98

T 8m (°C)

10.96

±1.38

10.90

±0.85

T 12m (°C)

10.29

±1.13

10.75

±0.77

T 17m (°C)

9.81

±0.66

9.95

±0.65

T average (°C)

10.64

±1.14

10.67

±0.80

T stratification

3.0E-04

±1.5E-04

1.9E-04

±8.4E-05

Current - equatorward (m. s-1)

0.06

±0.12

0.03

±0.03

Current - onshore (m. s-1)

-0.02

±0.02

-0.03

±0.03

Upwelling index

0.74

±0.14

0.79

±0.07

Tidal range (m)

1.16

±0.28

1.16

±0.28

Swell height (m)

2.42

±0.97

1.14

±0.64


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