Material and methods 321 Tested Seaweeds

For flume experiments, a total of eight individual specimens of D. antarctica and two individual specimens of D. willana were haphazardly collected from Brighton Beach, New Zealand (46° S, 170° E), during low tide on June 25, 2002 and July 26, 2002. They were transported to a nearby laboratory in Dunedin, New Zealand, and tested within 24 hr. Prior to the tests in a flume, the morphometrical parameters of length, mass, volume, and planform area of the blade of the harvested seaweeds were recorded (Table 3.1). The overall length was measured with a tape measure to the nearest centimeter. The mass was measured to the nearest 0.1 kg by placing the seaweeds in a basket and attaching a spring balance. The volume was determined by immersing the seaweeds in a barrel of seawater and weighing the displaced

TABLE 3.1

Morphometrical Data of the Eight Individuals of Durvillaea antarctica (Specimens I to VIII) and the Two Individuals of D. willana (Specimens IX and X) Tested in the Flume

TABLE 3.1

Morphometrical Data of the Eight Individuals of Durvillaea antarctica (Specimens I to VIII) and the Two Individuals of D. willana (Specimens IX and X) Tested in the Flume

Volume

Individual

Morphology

Length (m)

Area (m2)

Mass (kg)

(103 m3)

I

Exposed

4.97

1.70

23.5

38.0

II

Exposed

7.15

1.52

17.5

38.0

III

Exposed

3.10

1.25

8.5

22.5

IV

Exposed

4.25

1.65

22.0

23.3

V

Intermediate

7.49

2.52

51.0

92.8

VI

Intermediate

2.18

1.07

2.5

7.0

VII

Intermediate

3.80

1.26

9.0

13.5

VIII

Sheltered

6.40

1.46

15.5

27.0

IX

Intermediate

6.03

1.55

18.5

17.8

X

Intermediate

0.35

1.01

0.4

0.4

amount of water to the closest 0.1 kg. The mass of the displaced water was then divided by the density of seawater (1024 kg m-3), giving the volume. The planform area of the seaweeds was determined by photographing the fully extended blade. Because there was no suitable point of elevation for taking an orthographic image from exactly above the spread out individuals, photographs were taken at an angle. The images were then photogrammatically rectified with a vector-based program routine (MatLab version 12, The Mathworks) to account for and correct the distortions introduced by photographing at an angle. Subsequently, the planform area was analyzed with an image analysis program (Optimas version 6.5, Media Cybernetics). The recorded morphometrical parameters were then correlated with the drag forces on the seaweeds.

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