REUfest

Nitrogen in the San Antonio Bay Watershed

–Allison James

The San Antonio Bay has been found to contain much higher levels of nitrogen-15, nitrogen’s stable isotope, than other Texas bays. This is of interest because it is indicative of high levels of nitrogen pollution from waste water, which is a contributing factor to eutrophication in our bays. My project this summer is attempting to determine where along the San Antonio Bay watershed the majority of this nitrogen pollution is entering the system by looking at the nitrogen-15 isotope levels in algae, riparian and aquatic plants, and small invertebrates. I am taking my samples mostly from the two chief rivers in the San Antonio Bay system, the Guadalupe River and the San Antonio River.

Marsh Trudging

We’re now into the fourth week here and we’re all underway working on our projects. For me, I’m venturing out into a nearby marsh everyday, twice a day to collect water and sediment samples.

I filter the water samples and run tests to determine DOC and CDOM, then use the sediment in a sediment resuspension test here in the lab by recreating solar conditions. Already my results are showing that this marsh is highly productive.

Sadly, due to the Texas heat and lack of significant rainfall, my marsh is drying up and I’ve lost two sites already along with the first site’s resident blue crab Sanchez. Despite these losses, I’m still trudging out to find out what’s happening in this marsh.

Blue Crab Larval Recruitment

–Caitlin McKimmy

For my research, I’m planning on looking at Blue Crab larval recruitment around Mustang Island and the Mission-Aransas Estuary. The Blue Crab, an essential component of coastal ecosystems and a valuable economic commodity, spawns and hatches in the open ocean—larval crabs must then make their way into estuarine environments of lower salinity to develop into fully fledged adults. Larval recruitment patterns of the Blue Crab have been studied extensively in the coastal waters of the Northern and Mid-Atlantic states, and, although it is assumed that similar patterns occur on the gulf coast, relatively little research substantiates this assumption.

The coastal habitats surrounding the Marine Science institute are unique in that there are only two main points of entry through which larval crabs can enter the Mission-Aransas Estuary: Aransas Pass and Cedar Bayou. Cedar Bayou, however, is currently barely staying open, so the flow of water (and presumably Blue Crab larvae) between the Gulf of Mexico and Mesquite Bay is limited. Through my research I plan to conduct a preliminary assessment of the recruitment patterns that occur in this area. Hopefully, the data I collect will serve as a starting point for further research that might determine what effect the re-opening of Cedar Bayou would have on local Blue Crab populations.

Specifically, I plan to collect Blue Crab megalopae using artificial collectors and plankton tows at varying locations, depths, and tidal phases. I will consider hydrographic and meteorological conditions when looking at larval settlement rates. In terms of location, I am limited mostly to areas around Aransas Pass, but I also hope to gather some tentative data from other points around the Mission-Aransas National Estuarine Research Reserve. I also plan to look at data from the Texas Parks and Wildlife archive to see if there is any historical correlation between the condition of Cedar Bayou and the Blue Crab population.

Green Water Aquaculture

Rynnie Henderson

The intent of my experiment is to determine the effectiveness of using an alternative to live algae when raising red drum larvae. I set red drum eggs in my 150 liter cone tanks Thursday night, and the larvae are still looking healthy and, most importantly, alive. I will allow them to grow for three days before starting their feeding regime. On the day I start feeding, I will also begin the four treatments.

We are attempting to determine whether or not using live algae with larval fish can be replaced with a green dye or another cheaper, faster substitute. Past studies have shown that when live algae is grown in the tanks with the larvae, the growth rate and survivability of the larvae are greatly improved. As of now, it is unclear exactly why the algae is so beneficial. The algae most likely help maintain rotifer enrichment in the water column (rotifers are tiny organisms often fed to larval fish), but there appears to be little nutritional contribution from the algae directly to the fish. Some researchers speculate that the algae provide contrast for the larvae so they can more easily locate and retrieve prey. If this is the case, a green dye would have similar beneficial results to algae.

This experiment will compare the results of using Isochrysis galbana (a live algae), Chroma (a green dye), Sanolife (a manufactured algae substitute), and clear seawater (as a control) in the water with the red drum larvae. We will examine the growth rates, survival, and trypsin levels to monitor the effectiveness of each treatment. If the alternatives to live algae prove to be just as beneficial, tremendous time and money can be saved in red drum aquaculture and could possibly be used with many other fishery raised fish.