Thursday, May 12, 2005

Hello once again from the R/V Nancy Foster.

We are now in the full swing of surveying as we have successfully completed two dive trips so far and it is only 1530 hours…that’s 3:30 PM for you landlubbers. Each day there are two dive trips planned, one in the morning and the other in the afternoon. During each trip, two boats are deployed, each containing two to three divers.

Deploying divers is no easy task. It takes a coordinated effort among the ship’s crew and the scientific staff. When it is time to dive, the small boats located on the ship’s aft deck are lifted and placed into the water. Once in the water, the divers board the boats and are taken to specific locations of interest within GRNMS. Each dive location is identified as being one of the four habitats to be explored throughout the expedition (e.g., rippled sand, flat sand, densely colonized hard bottom, and sparsely colonized hard bottom).

Safety is a huge issue for the dive team and all steps are taken to make sure that the divers are safe. Since visibility is low and the divers are working in depths of 60 feet or more, it is important that the individuals remaining in the boat can identify the position of the dive team at all times. A weighted buoy is deployed directly over the habitat of interest to orient both the diver, as well as those in the boat. From this position two divers prepare to collect data on the seafloor along a 25 meter transect.

Before leaving the boat, divers double check to make sure that they have all of the gear that they need to collect data. Materials include measuring tape, clipboards with ruler, 1 m2 quadrat, camera, pencil, and waterproof datasheets. Once on the bottom, responsibilities are shared among the teams of two divers. One diver is responsible for identifying the different species of fish, their relative sizes in increments of 10 cm (i.e., <10, 10-20, 20-30, and so on until >70), and their abundance. The second diver characterizes the habitat and fishing gear impacts in five randomly placed 1.0m2 quadrats along the transect. During the survey, marine debris is counted and collected. (Today, Chris identified and collected fishing line and aluminum cans in GRNMS.)

Limited visibility in this northwest part of the sanctuary is a result of high input of organic matter from the Altamaha River which makes the diving surveys more complicated. Daniela says that this is due to the unusually high input of fluvial discharge from the Altamaha. The entire Southeastern region has experienced higher than normal averages of precipitation this season. Under normal conditions, the Altamaha’s discharge is 1500-1800 m3/second in the spring; however, this spring the river discharge has been over 2000 m3/second! Due to all of the recent rain, organic matter and sediments are carried by the runoff, into the watershed, and out to sea…and even to Gray’s Reef.

(It is not hard to imagine the impact that humans have on environments like GRNMS. After a thunderstorm, for example, think of the runoff that storm water carries to our creeks, streams, and rivers. This water combines with pesticides, herbicides, motor oil, etc. and is carried out into our estuaries…the same places that serve as nurseries for many fish which our region’s economy depends upon.)

While the divers collect data, Daniela and Kate are working diligently in the Wet Lab monitoring the echo sounder platform. Meanwhile, they collect CTD (Conductivity, Temperature, and Depth) profiles of the area. Let’s check out the first CTD profile of the trip.

On this CTD profile, you’ll notice two lines, one in red (temperature) and the other in blue (salinity). Salinity and temperature are key factors in identifying and characterizing water masses.

Let’s take a look at the temperature profile. Observe how the temperature of the column is not the same throughout. During this time of year, when the river discharge is high and when heat from the sun increases, the surface water is warm. Alternatively, the water below the surface remains quite cold. The layer of rapidly changing temperatures is referred to as the thermocline. (As the divers, such as Jenny can attest, the water below the thermocline can be quite a surprise, even when wearing a wet suit!)(Picture to right)

Now take look at the salinity profile within the water column. The water mass is not well-mixed seeing that there are stratified layers of dissolved salts (measured as salinity) in the ocean. Since fresh warmer water is less dense than salty cold water, we find the fresh water at the top of the water column with the more dense salt water at the bottom. This layer of rapidly changing salinity is referred to as the halocline.

As you’ve noticed by looking at the profiles, the halocline and the thermocline have inverse relationships. This means that as you increase in depth of the water column, the temperature decreases while the salinity increases. Though the relationship among salinity and temperature will remain the same as we explore the farther reaches of GRNMS, I wonder how the temperature and salinity profiles will vary.

The more I learn, the more questions I have; lucky for me I have a fantastic resource base…the scientists I am working among. This week I will attempt to uncover the answers to these questions and more.

If you have a research question related to the activities here in Gray’s Reef, don’t hesitate to email me. My email is

Until tomorrow,



Gray’s Reef National Marine Sanctuary:
Daily Connections to Scientific Inquiry & Nature of Science

Organizing Data:

Scientists must plan their methods for data collection and documentation well in advance of boarding the R/V Nancy Foster. Chartering a ship like this one costs exorbitant amounts of money and resources, so it is nearly impossible to go back and collect data if we were unsuccessful the first time. Therefore, the scientists must think ahead about the kinds of data they are looking to gather, their methods, available resources, schedules, etc. and use all of these factors to organize their surveys.


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