10.04.2010: Plankton Sampling Cruise
For this lab exercise, we had this opportunity to go on a sampling cruise to perform some net tows targeting plankton (animals that can’t swim fast enough to swim against water currents). A plankton tow is a very common method of capturing smaller planktonic life forms; oceanographers use this method often in studying the open oceans. Plankton tows use conical nets which are towed at low speed. Plankton is captured in the cod end; a cup at the end of the net which has three small openings covered in 500 µm mesh, the mesh allows water to flow all the way through the net and partially into the cup to prevent specimens from escaping.
Our journey began on Savannah State’s R/V Sea Otter, once the two large motors were fired up, we were off, slowly. On this beautiful day we were able to perform two different types of tows with the time we had. We used a bongo net, which has two separate nets that are attached at the ring openings. The first tow performed was a surface tow in which the net is pulled just below the surface of the water targeting organisms which stay or migrate near the surface. The location of the tow was near the SSU docks, but quite a ways down the Herb River in a long, straight, 30 ft deep area which allowed us to run the trawls with no impediments. The primary issue in using the bongo net is to get the nets even on the horizontal plane; once the nets are placed correctly the tow may begin. We ran our surface tow at .77 knots for 5 minutes, the collection cups were rinsed into our sample holders and samples were preserved in 70% ethanol. The second tow for the afternoon was an oblique tow, where the net is lowered to the bottom for the beginning of the tow and slowly pulled up sampling the entire water column from bottom to surface. For this second tow, the Sea Otter was run at 1.6 knots for 2 minutes. When the nets came up they contained a large amount of bottom sediment, our nets must have hit the bottom of the river at the beginning of the trawl. The samples were stored in ethanol and the Sea Otter and crew headed back for SSU docks. We viewed part of our sediment sample in a Plexiglas chamber, the only obvious specimen was a crab larvae with a very long spine. In the lab on campus, we observed several stages of crab larvae and phytoplankton was clearly visible.
For this lab exercise, we had this opportunity to go on a sampling cruise to perform some net tows targeting plankton (animals that can’t swim fast enough to swim against water currents). A plankton tow is a very common method of capturing smaller planktonic life forms; oceanographers use this method often in studying the open oceans. Plankton tows use conical nets which are towed at low speed. Plankton is captured in the cod end; a cup at the end of the net which has three small openings covered in 500 µm mesh, the mesh allows water to flow all the way through the net and partially into the cup to prevent specimens from escaping. 
Our journey began on Savannah State’s R/V Sea Otter, once the two large motors were fired up, we were off, slowly. On this beautiful day we were able to perform two different types of tows with the time we had. We used a bongo net, which has two separate nets that are attached at the ring openings. The first tow performed was a surface tow in which the net is pulled just below the surface of the water targeting organisms which stay or migrate near the surface. The location of the tow was near the SSU docks, but quite a ways down the Herb River in a long, straight, 30 ft deep area which allowed us to run the trawls with no impediments. The primary issue in using the bongo net is to get the nets even on the horizontal plane; once the nets are placed correctly the tow may begin. We ran our surface tow at .77 knots for 5 minutes, the collection cups were rinsed into our sample holders and samples were preserved in 70% ethanol. The second tow for the afternoon was an oblique tow, where the net is lowered to the bottom for the beginning of the tow and slowly pulled up sampling the entire water column from bottom to surface. For this second tow, the Sea Otter was run at 1.6 knots for 2 minutes. When the nets came up they contained a large amount of bottom sediment, our nets must have hit the bottom of the river at the beginning of the trawl. The samples were stored in ethanol and the Sea Otter and crew headed back for SSU docks. We viewed part of our sediment sample in a Plexiglas chamber, the only obvious specimen was a crab larvae with a very long spine. In the lab on campus, we observed several stages of crab larvae and phytoplankton was clearly visible.
