High-Frequency Sound Interaction in Ocean Sediments
2 July 1999

Macrofaunal Distributions and Effects on Backscatter in Subtidal Sands

Peter A. Jumars
University of Washington
Oceanography Box 357940
Seattle, WA 98195-7940
(206) 543-7615, -0275 (fax), jumars@ocean.washington.edu

Robert F.L. Self
Friday Harbor Laboratories
University of Washington
620 University Road
San Juan Island, WA 98250
(460) 378-2702, (206) 543-1273 (fax), lself@u.washington.edu

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Macrofauna likely influence the propagation of sound via their effects on microtopography and on volume heterogeneity. We plan several efforts to help understand their roles at the Panama City site.

Near the beginning of the experiment, we plan to take five sets of five grab samples for archival. They will be taken roughly at the four corners of the 600-ft. square study area plus outboard of the BAMS-XBAMS site. We plan to work up the large macrofauna (> 5 mm) but to retain the rest in case anomalies arise in the acoustic data that warrant the effort of working up (counting and identifying) the smaller fauna.

A second effort will be to collaborate with Van Holliday of Marconi in quantifying volume reverberation in the vicinity of the XBAMS deployment and in particular to assess the contribution of emergent fauna. We will help to deploy the TAPS instruments and will help analyze their data. In addition, we will deploy two emergence traps several times to obtain samples of emergent fauna. In addition, in the BAMS field of view we will also attempt to clear a 4-m2 area of emergent fauna for monitoring with the Marconi tower and BAMS during recolonization. We plan to help analyze the BAMS and XBAMS data for biological signatures.

Our other major effort will be manipulation of macrofaunal abundances. During the first two weeks of the experiment, we will collect sand dollars from surrounding regions. We plan to deploy them in triplicate 1-m2 pens within the fields of view of both BAMS and XBAMS (6 treatments total). We anticipate that their calcium carbonate tests when raised in suspension feeding will have strong, directional effects on backscatter at both 300 and 40 kHz. The animals will "be" the anisotropic microtopography. We also will attempt to obtain sufficient burrowing holothuroids or thallasinid shrimp to manipulate their abundances as well. We expect their burrows to constitute significant volume heterogeneity in the background sand. The idea for all the manipulations is to compare the backscatter record before (2 wk.) and after (2 wk.) the manipulations. We will do other manipulations opportunistically if other macrofauna are evident that might have effects on backscatter.

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