Benthic samples were taken quarterly in January, April, 

 July and October of each year. This sampling regimen 

 was chosen to compliment the timing of previous and 

 current benthic monitoring programs (Kalke and 

 Montagna 1991; Montagna and Kalke 1992; 1995; 

 Montagna et al. 1993; Martin and Montagna 1995; 

 Mannino and Montagna 1997; Ritter and Montagna 

 1999). During the initial programs, samples were taken 

 monthly (Kalke and Montagna 1991) or bimonthly 

 (Montagna and KaUce 1992). It was discovered that 

 there were roughly four seasonal events each year, 

 including winter and summer lows, and fall and 

 summer highs. Based on the cyclical nature of benthic 

 recruitment, growth and population losses, it was 

 determined that seasonal sampling was sufficient to 

 identify annual trends in long-term sampling programs. 

 Sampling began (October 28, 1994) one year before the 

 Nueces Overflow Channel was excavated (October 29, 

 1995), and continued for five additional years (through 

 October 28, 1999). Because the first sample of the 

 second year was taken early (October 3, 1995), there 

 were five pre-treatment samples and sixteen treatment 

 samples. 



Measurements 



Hydtography 



The physical hydrographic conditions of the water 

 column overlying sediments was measured at each 

 station during each sampling period. Measurements 

 were collected at the surface and near the bottom and 

 recorded on the field log sheet. Conditions recorded 

 during sampling included location, date, time, water 

 depth and weather conditions. Water quality was 

 measured with a multi-parameter instrument (Hydrolab 

 Surveyor II). A sonde unit was also lowered to just 

 beneath the surface and to the bottom. The 

 instruments allowed collection of a variety of water 

 quality parameters rapidly. The following parameters 

 were read firom the instrument's digital display unit 

 (accuracy and units): temperature (± 0.15 degrees 

 centigrade (°C)), pH (± 0.1 units), dissolved oxygen 

 (+ 0.2 milligrams per liter (mg/1)), specific conductivity 

 (± 0.015 to 1.5 (millimhos per centimeter (mmho/cm), 

 depending on range), redox potential (± 0.05 millivolts 



(mV)), depth (± 1 meter (m)) and salinity (reported in 

 ppt, automatically corrected to 25 °C). 



Benthos 



Sediment was sampled by hand with core tubes to 

 measure both meiofauna and macrofauna abundances. 

 Macrofauna were sampled with a 6.7-cm diameter tube 

 and sectioned at depth intervals of to 3 cm and 3 

 to 10 cm; meiofauna were sampled with a 1.8-cm 

 diameter tube and sectioned at depth intervals of to 

 3 cm only. Samples were presented with 5% buffered 

 formalin. In the laboratory, meiofauna were sorted 

 on 0.063 mm sieves, macrofauna on 0.5 mm sieves. 

 Macrofauna were identified to the lowest taxonomic 

 level possible (usually the species level), counted and 

 weighed to the nearest 0.01 mg for biomass. Meio- 

 fauna were identified to higher taxonomic levels 

 (usually phylum, class or order) and counted. 



Biomass of macrofauna was measured by combining 

 individuals into higher taxa categories {i.e., Crustacea, 

 Mollusca, Polychaeta and others). Samples were dried 

 for 24 hours at 55 °C, and weighed. Mollusks were 

 placed in 1 N HCl for 1 minute to 8 hours to dissolve 

 carbonate shells and washed before drying. 



AH meiofauna and macrofauna data were digitized and 

 proof-read. For macrofauna, species diversity was 

 calculated by replicate and by pooling aU replicate cores 

 for each site. Diversity was calculated using Hill's 

 diversity number one (Nl) (Hill 1973). It indicates the 

 number of abundant species in a sample and is a 

 measure of the effective number of species (Ludwig 

 and Reynolds 1988). The effective number of species 

 is a measure of the degree to which proportional 

 abundances are distributed among species (Hill 1973). 

 It is calculated as the exponentiated form of the 

 Sharmon diversity index: 



Nl- 



H' 



As diversity decreases, Nl will tend toward 1. The 

 Sharmon index is the average uncertainty per species in 

 an infinite community made up of species with known 

 proportional abundances (Shannon and Weaver 1 949; 

 Hutcheson 1970). It is calculated by: 



5-4 



Benthic Communities 



