Abstract

Feeding Dynamics of Callinectes sapidus

Erin Plachy and Michelle PoulopoulosUniversity 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

MethodsCrabs 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.

ReferencesBeattie, 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.

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f(x) = − 0.110145271057079 x + 152.566921322598R² = 0.819216042117744

Carapace Area (mm2)

Av

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The smaller bowl contains water from crab’s original tank. The outer bowl is for containing the crab if it crawls out.

Top: Tank setupBottom: Silverside fish with 0.05 g portion used for feeding

AcknowledgementsWe would like to thank Dr. Masonjones and UT research students for collecting our crabs.