1. Abstract
Feeding Dynamics of Callinectes sapidus
Erin Plachy and Michelle Poulopoulos
University of Tampa, Department of Biology
Introduction Results
There was no significant linear relationship between the
growth difference and feeding time (r2=0.59, n=6, F1,5= 5.68,
p=0.08).
It was shown that there was no significant difference
between the number of times the crabs ate in the morning and
the number of times they ate at night (χ2=0.28, 1 df, p>0.05).
However, there was a significant correlation between
feeding time and carapace size in blue crabs indicating that
larger crabs take less time to consume the piece of fish
(r2=0.82, n=6, F1,5= 18.08, p=0.013).
See Figure 1
Methods
Crabs collected by pushnet in Tampa Bay
Crabs were measured before and after the experiment in mm
Set up 5 tanks in Marine Ecology lab
Separate bowl setup was used for feeding time
0.05 g piece of silverside fish was provided per feeding
Consumption time was recorded per crab in seconds
Feeding time for each crab was recorded approximately every 12
hours, once in the morning and once at night
Fig 1: Carapace area in mm2 effect on average feeding time in seconds in Callinectes
sapidus. Each point on the graph represents the average feeding time of an individual crab.
y = -0.1101x + 152.57, r2=0.82, F= 18.08, p=0.013.
Juvenile Callinectes sapidus commonly known as
blue crabs, were taken from the Florida gulf waters to
explore some factors involved in feeding time.
Six blue crabs were fed a piece of silverside fish
every 12 hours.
Statistical tests:
Time of day does not affect the feeding frequency.
Growth rate of the crab was not significantly
associated with feeding time.
There was a relationship between carapace area
and feeding time.
This suggests that the dynamics of a blue crab
population will not be affected by a food source’s
change in time of activity, but could be altered by
intraspecific competition due to body size.
The blue crab, or Callinectes sapidus (Rathburn), is
a formidable predator that plays a key role in
maintaining species diversity and community structure
in many benthic communities (Hines et al., 1987).
Range: along the Atlantic coast of the United States
and Gulf region, juveniles residing mainly in seagrass
beds (Seitz et al., 2011; Seitz et al., 2005).
Diet: plants, detritus, invertebrates, fish, and
cannibalism (Hughes and Seed, 1997; Marshall et al.,
2005).
Factors that could potentially affect the feeding
dynamics of the blue crab:
Carapace size: competition is likely to favor larger
male crabs, which raises the potential for detrimental
effects on female and smaller crabs (Beattie, 2012).
Growth rate: growth rate related to ecdysis could
affect the foraging behavior of the blue crab.
Molting time (Marshall et al., 2005).
Time of day blue crabs are most actively feeding
During the postlarval stage of their life cycle,
they are more active at night (Forward et al.,
2005).
There is a lack of studies on juvenile blue crab
activity including what time of day they feed.
References
Beattie, C., K. A. Pitt, R. M. Connolly. 2012. Both size and gender of mud crabs influence the outcomes of interference interactions. Journal of Experimental Marine Biology and Ecology1-6: 434-435.
Forward, R. B. Jr., N. B. Reyns, H. Diaz, J. H. Cohen, and D. B. Eggleston. 2005. Endogenous swimming rhythms underlying secondary dispersal of early juvenile blue crabs, Callinectes sapidus. Journal of Experimental
Marine Biology and Ecology316: 91–100.
Hines, A. H., R. N. Lipcius, and A. M. Haddon. 1987. Population dynamics and habitat partitioning by size, sex, and molt stage of blue crabs Callinectes sapidus in a subestuary of central Chesapeake Bay. Marine Ecology36:
55-64.
Marshall, S., K. Warburton, B. Paterson, and D. Mann. 2005. Cannibalism in juvenile blue-swimmer crabs Portunus pelagicus (Linnaeus, 1766): effects of body size, moult stage and refuge availability. Applied Animal
Behaviour Science90: 65-82.
Seed, R. and R.N. Hughes. 1997. Chelal Characteristics and Foraging Behaviour of the Blue Crab Callinectes sapidus Rathbun. Estuarine, Coastal and Shelf Science44: 221–229.
Seitz, R. D., K. E. Knick, and M. Westphal. 2011. Diet Selectivity of Juvenile Blue Crabs (Callinectes sapidus) in Chesapeake Bay. Integrative and Comparative Biology51: 598-607.
Seitz, R. D., R. N. Lipcius, and M. S. Seebo. 2005. Food availability and growth of the blue crab in seagrass and unvegetated nurseries of Chesapeake Bay. Journal of Experimental Marine Biology and Ecology319: 57–68.
Tagatz, M. E. 1968. Growth of juvenile blue crabs, Callinectes sapidus Rathbun, in the St. Johns River, Florida. Fishery Bulletin67: 281-288.
Background image from http://www.coastalmobile.com
A close view of a
juvenile Callinectes
sapidus. Juveniles
become adults at about
100 cm (Tagatz, 1968).
Discussion
Larger blue crabs take less time to consume an equally weighted piece of fish than the smaller crabs.
Intraspecific competition between larger and smaller crabs.
Faster feeding rate on larger crabs may not necessarily put smaller crabs at a disadvantage.
Actual amount of food needed for survival was not tested.
The faster a blue crab eats does not affect the amount of growth in a given time.
A faster consumption time means a crab can consume more food in less time. However, we did not
measure how much food an individual juvenile blue crab could eat.
Study: the amount of times a blue crab molts does not necessarily result in different final sizes while
the amount of food stays constant (Tagatz, 1968).
Quantity of food may have an effect on growth rate rather than consumption time.
Juvenile blue crabs did not show any preference to what time of day they prefer to feed.
The data goes to show that if either a strictly diurnal or nocturnal food source for the blue crab
changes behavior in terms of when it is available, the blue crab population will be able to survive due to
their active feeding behavior throughout the day and night.
The ability to feed at any time during the day or night and their flexibility in prey item choice shows
they are hardy crustaceans able to withstand changes in foraging due to disturbances.
y = -0.1101x + 152.57
R² = 0.8192
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AverageFeedingTime(s)
Carapace Area (mm2)
The smaller bowl contains water from crab’s
original tank. The outer bowl is for
containing the crab if it crawls out.
Top: Tank setup
Bottom: Silverside fish with 0.05 g portion used for feeding
Acknowledgements
We would like to thank Dr. Masonjones and UT research students for collecting our crabs.