1-millimeter mesh collecting hag from the dredge and replacing it with 

 a larger fine meshbag that will retain the sand hut allow water to pass 

 through. Make several uniformly timed digs to a depth of 4 inches or 

 more, the depth depending on the animals sought. Keep the air pressure 

 and water depth constant; a change in air pressure or water depth will 

 require recalibration. Measure the volume or material excavated. Aim 

 for a uniform volume to be excavated at all sample depths by keeping the 

 air pressure constant and varying the length of time of the dig according 

 to water depth. 



To collect the sample, attach the 1-millimeter mesh collecting bag 

 to the dredge. The meshbag should allow about 95 percent of the sedi- 

 ment to pass through, retaining only the organisms and a small amount of 

 sediment. Excavate to a given sediment depth (at least 4 inches, 8 inches 

 is preferable) for the calibrated length of time. Remove the meshbag from 

 the dredge, tie it closed, and put in a labeled plastic bag. 



b. Coring Devices . Benthic fauna can also be sampled at sta- 

 tions along the transect by coring. Corers may be made from sections 

 of round or square tubing or fabricated from sheet material (Fig. 6). 

 Either plastic, steel, or aluminum may be used. Push the coring device 

 at least 4 inches (8 inches is preferable) into the sediment. If the 

 diameter of the corer is appropriate in relation to the type of sediment, 

 the sample will be retained by friction, but the bottom of the corer 

 should be covered with the hand, a plate or cap, or held against the body 

 to prevent loss of the extracted sample. If the corer has a top venthole, 

 cover it with a thumb to prevent the loss of the sample. The sampler may 

 be inverted to retain organisms if necessary. 



Empty the cores with the contained organisms into labeled plastic 

 bags and close the bags with plastic-coated twist-ties. Collect sample 

 bags in a diver's "bug" bag with snap closure and haul several bags at 

 a time to the beach. 



If away from the shore, bagged samples should be temporarily stored 

 in a rubber raft, a large inner tube with a net or tub insert, or a boat 

 anchored outside the surf zone. The samples should be secured to pre- 

 vent loss in case of upset in the surf. Waves breaking on outer sandbars 

 influence the positioning of a support boat or a raft in the nearshore 

 zone. The "surf beat," the pattern of oscillations of breaking waves 

 caused by the interaction of two or more wave trains, must be considered. 

 An unexpected large wave or series of waves can be dangerous to a sam- 

 pling crew. 



VI. SAMPLE TREATMENT 



Samples should be taken to the beach, placed in a sieve (mesh size 

 of 0.5 to 1 millimeter) and sieved. If practical, it is desirable to use 

 a 0.5-millimeter sieve, particularly for the core samples for small 

 organisms; 1.0 millimeter is generally more cost-effective. If a large 

 number of samples are taken in coarse sediments, use a larger mesh sieve 



22 



