Feeding Strategies of Gelatinous Zooplankton Collected at Wallops Island

Jennifer L. Cole and Dr. Jessica Nolan

Department of Biological Sciences, York College of Pennsylvania

INTRODUCTIONWhat phylum of gelatinous zooplankton were prevalent in the plankton tows conducted at Wallops Island during the research cruises?

Cnidaria and Chaetognatha!

• Jellyfish (Phylum Cnidaria) and chaetognaths (Phylum Chaetognatha) are both classified as carnivorous gelatinous zooplankton. Jellyfish obtain their prey through the use of their tentacles via stinging cells, whereas chaetognaths detect the presence of their prey by signals and use the spines positioned around their head to aid in capture (Levington 2001).

• Jellyfish have been found to consume primarily copepods (Stibor and Tokle 2003). Similarly, the chaetognath diet consists largely of copepods and copepod nauplii. Chaetognaths are limited to the size of prey they are able to consume by the size of their mouth (Tonnesson and Tiselius 2005).

• The objective of this study was to classify the plankton available to the jellyfish and chaetognaths for consumption, as well as determine any selectivity in their diets.

METHODSJellyfish:• Jellyfish were collected during a plankton tow on April 16, 2005 in the Chincoteague Bay salt marsh. • Water for the feeding experiment was obtained from the surface at the site of jellyfish collection.

• 100mL initial control samples of the sea water were taken at the beginning of the experiment and preserved in 2% Lugol’s.

• Six glass dishes were filled with 1000mL of sea water. Of the six dishes only three contained jellyfish (treatments), specifically 3 per dish.

• The dishes were incubated in a dark room for 5 ½ hrs. Every 15 minutes each dish was stirred, and the temperature was monitored.

• After the 5 ½ hrs 100mL samples of the 3 final controls and the 3 treatments were preserved in 2% Lugol’s.

• Samples were counted using the Nikon Y-FL compound microscope.

Chaetognaths:

• Chaetognaths were collected on October 28, 2005 at an offshore station in the Mid-Atlantic Bight during a plankton tow.

• The chaetognaths were pipetted into a jar of sea water.

• 100mL of concentrated food was added to 6, 125mL plastic containers. Of the six containers 3 had chaetognaths (treatments) and there were approximately 4-8 in each container.

• These containers were placed in the dark and gently shaken every ½hr for 22hrs. The samples were then preserved in 2% formalin.

• The entire sample was counted using the Nikon SMZ-U dissecting microscope.

http://depts.washington.edu/fhl/zoo432/plankton/plcnidaria_ctenophore/sarsia

RESULTSJellyfish Study

Chaetognath Study

•Jellyfish did not consume available food during 5 1/2 hr incubation period, (p=0.9626, Figure 1).

• There were significantly more small copepods (p=0.0245) and copepod nauplii (p= 0.0138) in the treatments than in the final controls (Figure 2).

LITERATURE CITED•Levinton, J. 2001. Marine Biology: FunctionLevinton, J. 2001. Marine Biology: Function, Biodiversity, Ecology. , Biodiversity, Ecology. 2nd ed. Oxford University Press, Oxford, NY.2nd ed. Oxford University Press, Oxford, NY. •Ohman, M.D, Frost, B.W.and Cohen, E.B. 1983. Reverse Vertical Migration: An Escape From Invertebrate Predators. Science 220:1414-1406•Stibor, H. and Tokle, N. 2003. Feeding and asexual reproduction of Stibor, H. and Tokle, N. 2003. Feeding and asexual reproduction of the jellyfish the jellyfish Sarsia gemmiferaSarsia gemmifera in response to resource enrichment. in response to resource enrichment. Oecologia Oecologia 135:202-208.135:202-208.•Tonnesson, K., and Tiselius, P. 2005. Diet of the chaetognaths Tonnesson, K., and Tiselius, P. 2005. Diet of the chaetognaths Sagitta setosaSagitta setosa and and S. elegansS. elegans in relation to prey abundance and in relation to prey abundance and vertical distribution. vertical distribution. Marine Ecology Progress Series Marine Ecology Progress Series 289:177-190.289:177-190.

ACKNOWLEDGEMENTS• I would like to thank Dr. Nolan for her guidance and support throughout this entire research project. Also, a special thanks to NASA and NOAA for ship time and the Marine Science Consortium for the use of their lab facilities.

HYPOTHESES• Jellyfish will show no preference between the types of plankton available for consumption in the Chincoteague Bay salt marsh.

• Chaetognaths will show no preference between the types of plankton available for consumption at an offshore station in the Mid-Atlantic Bight.

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Figure 1 represents the diatoms found in the final controlsand treatments in relation to the number of each diatom permL. Error bars represent one standard deviation of themean. Unpaired t-test ( p > 0.05). Means not significantlydifferent (ns).

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Figure 2 represents the types of plankton found in the finalcontrols and treatments in relation the the number of eachplankton found per replicate. Astericks indicate a significantdifference between the number of plankton found in the finalcontrols and treatments. Unpaired t-test (p < 0.05).

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CONCLUSIONS• The results of the jellyfish feeding study indicated the jellyfish did not consume the prevalent chain diatoms even under bloom conditions. These jellyfish may feed upon larger plankton which could account for these findings.

• Contrary to expectations there were significantly more small copepods and copepod nauplii in the treatments than in the final controls.

• From these unexpected results I hypothesize that the large copepods were the only other zooplankton large enough to consume the small copepods and copepod nauplii. In the final controls the large copepods could swim freely and feed upon the small copepods and nauplii. However, in the treatments it appears the large copepods changed their behavior and did not consume the copepods and nauplii in order to avoid being eaten by the chaetognaths.

• Changes in copepod behavior in the presence of chaetognaths has been observed previously (Ohman et al 19xx Reverse Vertical Migration: An Escape from Invertebrate Predators).