Transcript Bergenti - York College of Pennsylvania

An Investigation of the Effect of Turbidity on the Diel Vertical Migration of Zooplankton
in the Chincoteague Bay, VA.
James Bergenti, Department of Biology, York College of Pennsylvania
Results
Methods
http://www.madrimasd.org/blogs/ciencia_marina/2009/11/30/129464
Samples collected via a
horizontal or vertical
zooplankton tow
Introduction
• Sedimentation in marine ecosystems plays a role in water
clarity. Most species of fish rely heavily on vision for
predation. Therefore, increased turbidity can reduce
predation efficiency by obscuring prey detection (Cezilly
1992).
A
D
Discussion
V= 0.01
V= 0.05
E
B
• Vertical excursions on a diel cycle are exhibited in most
species of pelagic dwelling zooplankton. This is commonly
known as diel vertical migration (DVM). This vertical
movement is primarily dictated by light (Haney 1993) and
generally occurs at dawn and dusk.
• The degree to which these vertical movements are
performed may be influenced by turbidity. Increased
turbidity may allow species of zooplankton to persist at
certain depths and reduce the need of vertical migration
(Roman 2001).
• Chincoteague Bay, located in between Assateague Island
and the eastern shore, is the largest coastal lagoon on the
eastern shore of Maryland, and has an average depth of
less than 3m. Zooplankton located here can be collected
from the surface during daylight, a trend not consistent
with typical migration behavior. The purpose of this study
was to investigate the relationship between turbidity and
migration behavior in zooplankton from this estuary.
Hypotheses
http://sites.wff.nasa.gov/code250/story31.html
3 replicates for each turbidity
level: Low (~1NTU), Medium
(~25NTU), High (~40 NTU)
Surface
C
V= 0.1
The samples were dominated by a single
species: Acartia tonsa.
•
The dominant predators in the Chincoteague
Bay could be nonvisual feeders. Oysters and
mussels, for example, are common in the bay.
•
The amount of fish, and thus the risk of
predation, may vary between seasons. Bollens
and Frost (1989) showed that the extent of
DVM is directly related to the amount of the
dominant species of zooplanktivorous fish at
the time.
•
The Chincoteague Bay is a highly productive
estuary. Food may be available throughout the
entire water column, not just at the top or
bottom.
F
High
High
Medium
Medium
Low
Low
V= 0.06
V= 0.16
Fig. 1. A-C: Percentage of total surface population found at each depth between day and night
samples in low, medium, and high turbidities. D-F: Percentage of total water column population
found at each depth between day and night samples at low, medium, and high turbidities. V
represents the strength of diel vertical migration behavior. The error bars represent a 95%
confidence interval.
12hr. day/night cycle for
approximately 48 hours in lab
to acclimate
Future Research
• Sampling at various times of the year may produce a
more diverse sample of zooplankton.
Day and night samples collected
from top, middle, and bottom
of cylinders
• This experiment was isolated in a lab. Performing this
experiment in the field may produce different results,
as the zooplankton would be exposed to natural
conditions.
Preserved with 2 mL of buffered
formalin
Identified and counted under a
microscope
Fig. 7. Percentage of total surface sample population found at the top of the water column in
low, medium, and high turbidities. A non-parametric and Kruskal-Wallis analysis were run.
There was no significant difference among the populations between each turbidity level. (P=
0.3012) The error bars represent the standard error of the mean
• It is known that this migratory behavior of zooplankton
is heavily influenced by the type of predator. Examining
the relationship of DVM and various predators may
help in the understanding of the mechanisms behind
this behavior.
Literature Cited
1. Bollens, S. M., Frost, B.W., (1989) Zooplanktivorous Fish and Variable Diel
Vertical Migration in the Marine Planktonic Copepod Calanus pacificus. Limnology
and Oceanography, Vol. 34, No. 6, pp. 1072-1093
2. Cezilly, F. 1992. Turbidity as an ecological solution to reduce the impact of fisheating colonial waterbirds on fish farms. Colonial Waterbirds 15:249–252.
3. Haney, J.F. 1993, Environmental control of diel vertical migration behavior.
Limnology and Oceanography, 39: 1-17
4. Roman, M.R., Holliday, D.V., Stanford, L.P. 2001, Temporal and spatial patterns
of zooplankton in the Chesapeake Bay turbidity maximum. Mar Ecol Prog Ser,
213: 215-227
Top
Middle
Acknowledgements
Bottom
I would like to thank Dr. Nolan for the time and expert advice she dedicated to
this study.
http://ian.umces.edu/imagelibrary/displayimage-6163.html
http://landsat.gsfc.nasa.gov/images/archive/f0015.html
•
Water Column
H0: There will be no difference in diel vertical migration
behavior with varying levels of turbidity.
H0: There will be no difference in diel vertical migration
behavior between zooplankton samples collected at
varying depths in the water column.
• Although some movement was observed, there was
no significant difference in the percentage of
zooplankton found at the top between turbidities or
between surface and water column copepods.
• Factors that may have influenced the results:
V= 0.07
• A central hypothesis explaining diel vertical migration is
the predator avoidance hypothesis. This hypothesis
suggests that zooplankton migrate into deeper water
during the day to avoid being eaten by visual predators
searching for food in shallow water, while moving to
shallower, food rich waters at night (Bollens and Frost
1989).
http://earthobservatory.nasa.gov/Features/OceanProductivity/printall.php
Fig. 8. Percentage of zooplankton found at the top depth in low turbidity from surface and
water column samples. A nonparametric Mann-Whitney test was run on the data. There was
no significant difference between the two populations. (P= 0.7) The error bars represent the
standard error of the mean.