The Stinging Sea

Student Worksheet - Ecological Forecasting of Sea Nettle Abundance Worksheet

Part I – Subject Review

Answer the following questions after reading “Jellyfish in Chesapeake Bay and Nearby Waters” by Dr. Jennifer E. Purcell:

  1. Where are the greatest numbers of sea nettles found?
  2. The moon jelly, Aurelia aurita, is also common in the Chesapeake Bay during the summer. Does this species poses a stinging threat to humans similar to that of the sea nettle?
  3. How can sea nettle stings be prevented? How should they be treated?
  4. Where do sea nettles go during the winter?
  5. What do sea nettles eat?
  6. How do sea nettles capture their food?
  7. Can sea nettles feed at night?
  8. Sea nettles can grow rapidly with very little food. Why?
  9. What are three aspects of sea nettles’ life history that makes this species “geared for high reproduction”?
  10. What ecological preference of sea nettles is unusual when compared to most other jellyfishes?
  11. How do sea nettles deal with competition and predation from other species?
  12. How may human activities have increased the numbers of sea nettles in the Chesapeake Bay?
  13. Review examples of ecological forecasting projects at http://oceanservice.noaa.gov/topics/coasts/ecoforecasting, and describe three of these projects.

Part II – The Foundation for Ecological Forecasts of Sea Nettle Abundance

The mathematical model that is used to make ecological forecasts of sea nettle abundance in Chesapeake Bay was developed from data collected during 1987-2000 on Chrysaora quinquecirrha abundance, temperature, salinity, and depth. Forecasters use satellite data to obtain real-time estimates of sea surface temperature. Another mathematical model that describes water circulation in the Chesapeake Bay is used to estimate salinity distribution in various parts of the Bay. Because salinity is strongly influenced by freshwater input from major rivers, variations in the discharge rates of these rivers correlate closely with salinity changes in the Bay. In this exercise, you will use online databases to obtain information on sea surface temperature and river discharge for comparison with data on abundance in samples collected during summer months from 1987-2000.

Abundance data were obtained by towing plankton nets (1 m diameter, 1.6 mm mesh) equipped with a flowmeter. The volume of water filtered by the nets ranged from 60 m3 to 160 m3. Captured jellyfish were separated and counted by hand. Table 1 summarizes Chrysaora quinquecirrha abundances determined by this method.

Table 1. Chrysaora quinquecirrha Abundance in Chesapeake Bay 1987 – 2000

Date Chrysaora quinquecirrha
Abundance
(Individuals/m3)
Average Temperature
for Sample Month
(°C)
Susquehanna River
Average Monthly
(ft33/sec)

7 Jul,1987
28 Jul, 1988
28 Jun, 1989
15 Aug, 1990
27 Jul, 1995
20 Jul, 1996
11-13 Jul, 1997
11 Aug, 1998
29 Jun, 1999
28 Jul, 2000

0.10
0.05
0.04
0.13
0.045
0.005
0.02
0.01
0.007
0.000

27
27
26.5
27
29.0
25.6
25.8
26.6
24.8
24.4

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Sea surface temperature (SST) is measured by satellites carrying the Advanced Very High Resolution Radiometer (AVHRR), which measures infrared radiation from Earth’s surface in six spectral ranges. AVHRR data have been provided in Table 1.

The U.S. Geological Survey provides access to water data from approximately 1.5 million sites throughout the United States through the National Water Information System (NWIS). To obtain water discharge data for the Susquehanna River:

  1. Point your internet browser to NWIS Web page at http://nwis.waterdata.usgs.gov/nwis to open the “NWISWeb Data for the Nation” page. Click on the “Surface water” button under “Data Category” to open the “Surface-Water Data for the Nation” page.
  2. Under “Statistics,” click on “Monthly” which will open the Monthly Stream-flow Statistics page. There are many ways to specify sites for which data are to be retrieved, but in this case it is simplest to use the number of the USGS monitoring station on the Susquehanna River at Conowingo, MD. Under “Site Selection Criteria,” locate the “Site Identifier: column and click on the box next to “Site Number.” Click “Submit.” This will open the “Surface-Water Monthly Statistics for the Nation” page.
  3. Enter “01578310” in the box under “Site Number,” then scroll down to the bottom of the page and click “Submit.” Click on “01578310” in the table. A new page will open listing data that are available for USGS  Station 01578310, Susquehanna River at Conowingo, MD. Click on the station number and another page will open. Click the box next to “Discharge, cubic feet per second,” then scroll down to the bottom of the page and click “Submit.” A new page will open with a table listing the mean monthly discharge in cubic feet per second beginning in October, 1967.

Compute the average monthly discharges from January through June for each of the sample years (1987-1990 and 1995-2000). Use these data to fill in the stream-flow discharge column in Table 1. Plot the data in Table 1. You will have to use three different scales for the y-axis since values for abundance, temperature, and river discharge differ by several orders of magnitude. What conditions appear to correlate with higher abundance of Chrysaora quinquecirrha?

 

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