1. Flow Influences on Particulate Organic Matter Settlement Within Tidal Creek Mudflat and Oyster Reef Habitats Young, Ginger, Mauldin, Ashley and Walters, Keith, Department of Marine Science, Coastal Carolina University, Conway, SC 29528 Objective Materials and Methods Map shows an aerial view of the tidal creek study site The small-scale (m) effects of tidal flow on particulate organic matter (POM) settlement within intertidal mudflat and natural oyster reef habitats were examined as part of a long-term study focusing on oyster reef restoration in South Carolina. POM settlement was considered an indirect measure of total water column food availability that affects growth and survival of oysters on developing reefs. The study was conducted within a Waites Island, SC tidal creek at mudflat and adjacent natural oyster reef sites. Sites were located in close proximity to ongoing experiments examining the suitability and spatial arrangement of different hard substrate types (e.g., shell clutch, cement-covered stakes) for oyster reef restoration. POM settlement data were collected over 24 h periods for 5 d during spring tides using replicate settlement traps. Tidal flow was determined indirectly over the 5 d period with dental plaster clod cylinders. Ash-free dry weight values were determined from settlement trap samples. Mudflat and oyster reef habitat settlement differences resulted from different amounts of suspended POM in the water column and not different rates of flow between sites. Abstract Waites Island tidal creek study site with ongoing clutch bag and stake reef restoration treatments shown The analysis of flow within the study site was measured using the clod card protocol (see Judge pers. com.) -Clods (2 ea.) were mounted on 5 platforms positioned flush with the sediment in mud and reef sites -Clods were collected after 5 d -The difference in clod mass was used as an indirect measure of flow POM settlement was measured using 50 ml tubes placed w/ mud and reef sites -5 tubes haphazardly placed and recovered at low tide w/ each site every day for a total of 5 d -Tubes were pushed into the sediment at each site leaving ca. 2 mm above the surface -Each tube was filled with seawater -Samples were frozen @ -20 ºC until processed -Sediments were divided into > and <63μm fractions -Fractions were dried @ 60 ºC, weighed, and ashed @ 500 ºC, reweighed to determine total dry and POM mass of the settled material All results were analyzed using SAS Results There was no significant difference in the daily loss of plaster from clods between mud and reef sites (F 1,17 = 2.1, p > 0.05) - no difference in flow between sites (Fig1). Tidal Creek Figure 1: The mean (+SE) daily erosion of plaster (hydrodynamic flow) at mud and reef sites. Figure 2: Total settlement dry mass per day (mean + SE) for the >63µm fraction. Figure 4: Total POM carbon collected (mean + SE) in settlement samplers for the >63µm fraction. Close-up of Settlement Traps w/ the Mud Site Clods, Platforms & Settlement Traps w/ the Reef Site Figure 5: Total POM carbon collected (mean + SE) in settlement samplers for the < 63µm fraction. Conclusions To determine if there are significant flow and POM settlement differences between mudflat and oyster reef habitats. There were no significant habitat by day (F 3,30 = 0.06, p > 0.05), habitat (F 1,30 = 0.31, p > 0.05) or day (F 3,30 = 2.20, p > 0.05) effects on the total settlement of material > 63 µm (Fig 2). There was a significant habitat by day interaction (F 3,30 = 3.05, p < 0.045) in the settlement of the total material < 63 µm (Fig 3). Figure 3: Total settlement dry mass per day (mean + SE) for the <63µm fraction There were no significant habitat by day (F 3,30 = 2.87, p > 0.05), habitat (F 1,30 = 0.11, p > 0.05) or day (F 3,30 = 1.53, p > 0.05) effects on the settlement of POM total carbon > 63 µm (Fig 4). There was a significant habitat by day interaction (F 3,30 = 4.66, p < 0.01) in the settlement of < 63 µm total POM carbon (Fig 5). Mud and reef differences in the settlement of POMl could not be explained by differences in flow characteristics between the sites. Settlement of <63 µm POM, both total and organic carbon amounts, was effected by habitat and date. These results could represent the effects of daily or tidal differences in flow and/or could represent actual differences in the amount of POM passing over each site. Our results suggest, but do not confirm, that oyster reef restoration success may depend on the initial habitat in which the reef is being established because of habitat effects on POM availability.