Deployment of Experiments 



Five replicates of the four types of plates (thick-elevated, 

 thin-elevated, thick-benthic and thick-elevated-manganese) were 

 deployed by the submersible Pisces V at the study site in an array 

 of five linear transects, each containing all four plate 

 treatments. The transects were intended to be set out in a 

 rectangular randomized block array, but the irregular shape of the 

 sand flat constrained their deployment. In order to keep the 

 plates at least 2 m from each other and 5 m from the edges of the 

 site, some transects were laid out parallel, and others 

 perpendicular, to the long axis of the site. Despite this lack of 

 symmetry in the blocks, the arrangement of transects ensured that 

 replicates of a treatment were spread out over the sand flat, and 

 were not subject to potential biases from their positions in the 

 site. Plates were suspended with fine nylon line (<1 mm in 

 diameter) to polypropylene loops for deployment and recovery. The 

 line created very little flow disturbance near the plate and the 

 polypropylene loop floated at least 30 cm above the plate. 



All plates were deployed within two days of each other, 

 remained on the site for 46 to 50 days and were recovered within 

 two days of each other. An average deployment duration of 48 days 

 is used in the following analyses. The maximum error from this 

 approximation is < 5%, and since plates were deployed and recovered 

 in blocks (transects), the error in duration time does not bias the 

 treatments systematically. A total of 14 plates were recovered 

 intact, including three sets complete with all four treatments. 



The plates were preserved in 10% buffered formalin in seawater 

 and were later transferred to 80% ethanol for inspection. All 

 eukaryotic organisms visible under a dissecting microscope were 

 counted and identified to the lowest taxonomic group possible. 

 Individuals were counted in each of 144 subareas on a plate (which 

 was divided into 12 radial sectors, and 12 1-cm wide concentric 

 rings) for future analyses. 



Flow Measurements 



Flow patterns at the Cross Seamount study site were measured 

 at three scales. Transects of XBT (expendable bathythermograph) 

 profiles were taken over the summit of the seamount on both the 

 deployment and recovery cruises, and CTD (conductivity, 

 temperature, density) profiles were measured over the study site 

 during the recovery cruise. These measurements were collected in 

 order to infer mesoscale flow patterns over the entire seamount. 

 Current velocities in the benthic boundary layer at the study site 

 were measured (using a 300 s averaging interval) for 48 days with a 

 Neil Brown SACM (Smart Acoustic Current Meter) moored 1.8 m off the 

 seaf loor . 



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