Untreated Plexiglas panels (medical grade PMMA, size 110 × 110 × 2 mm) were deployed in the field at different stations, depths, and time intervals to cover the major settlement period of B. improvisus on the Swedish west coast. Suspended panels at least 30 m away from the shore ensured exposure to bulk flow. Duplicate test panels were fixed vertically to a rope with a buoy and a moored to the bottom. Fig. B1 shows the general arrangement of the moorings with attached panels. The panels were mounted to the rope with two plastic loops at one end making a semi-flexible joint, allowing the panels to orient in the direction of the flow. SCUBA inspection revealed no flapping of panels and orientation near parallel to main flow at speeds above approximately 2 cm/s. However, in the field where multi-spectral wave orbitals are advected past the panels, the instantaneous flow may deviate from being parallel to the panels. Close to the panel surface, on the spatial scale of larval contact, the flow will be more or less parallel due to the constraining effect of the panel. The hydrodynamic regime will vary across a settlement panel. To avoid the steepest flow gradients (Mullineaux and Garland 1993), individuals attached within 1 cm from the panel edge were not counted.
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| FIG. B1. Schematic drawing of the arrangement used to moor settlement panels in the water column. |
Initial surface adhesion
of cyprid larvae was studied using panels coated with silicon grease (Hoch-vakuumfett
mittel, Wacker, Germany). Panels were coated by immersion in 40 mL n-Hexane
with 5 g of silicon grease and then left to dry for 24 h. The grease coating
was thin (<0.2 mm), and the surface was almost as smooth as the underlying
PMMA. A pilot test was performed to investigate the risk of underestimating
initial adhesion by loss of cyprids caught in the grease or by becoming unrecognizable
during the time of the 5-d exposure. Cyprids were first allowed to make contact
with panels in the laboratory for 24 h. Trapped cyprids (on average 275 individuals
per panel) were marked with a pen on the backside of the panel and deployed
in the field at a depth of 1 m. The number of trapped cyprids on five replicate
greased panels were then counted after 2, 5, and 8 d of immersion in the
field. The flow conditions were intermediate compared to the experimental sites.
The results are shown in Table A1. No significant decline in cyprid numbers
was observed.
Table B1. The percentage loss of cyprids after immersion for 2, 5, and 8 days in the field.
Immersion time (days)
Percentage loss of attached cyprids (mean ± 1 SE)
2
0 ± 0
5
0 ±0
8
0.58 ± 0.27
LITERATURE CITED
Mullineaux, L. S., and
E. D. Garland. 1993. Larval recruitment in response to manipulated field flows.
Marine Biology 116:667–683.