Transect and Data Analysis: Fiddler Crab Field Survey

Fiddler crabs (Uca spp.) are semi-earthly species that may have an effect on the residue structure and other living classes mostly by burrowing and feeding. Fiddler crabs build successful burrows in the intertidal zone, ranging from gritty shoreline sand to fine earth-covered mucky mud at low tide. Burrow digging begins when the crabs are young. Various species have depicted the burrowing behavior of fiddler crabs. These crabs are known to change their burrowing exercises due to an assortment of conditions, for example, root tangle thickness, substratum, water, ground temperature, tidal periodicity, regenerative movement, danger by potential predators, seasons, and mate show exercises.

Burrows are critical to fiddler crabs for various capacities, permitting them to embrace a semi-earthbound presence and maintain a strategic distance from ecological worries by behavioral means. Fiddler crabs unearth burrows in the residue, to stay away from over the top wave activity and get help from hot and frosty encompassing temperatures and drying up. These burrows profoundly affect the residue in these swamp regions since they diminish the dregs’ natural matter (fiddle crabs are detritovores), and circulate air through more profound silt that is typically anoxic. Thus, nonetheless, fiddler crabs likely want to make burrows in regions with particular natural parameters (silt measure, temperature, compaction, and so on.). Since these natural parameters likely change as one continues from the water’s edge upslope, it appears to be sensible that there will be more burrows in that piece of the slant with favored ecological components.

Objective

The purpose of this experiment is to apply numerous ecological fields methodologies to determine how fiddler (Uca spp) burrows alternate along the intertidal marsh zone. Secondly, measure other experimental factors to aid in the discussion of observed patterns.

Methods and Materials

Materials:

100m transect tape

Quadrat squares large

Small rulers

Penetrometers

PH pens

Site

To assess the distribution of fiddler crabs (Uca spp) in intertidal marshy regions, a field survey was piloted in Jacksonville Timucuan Trail Waterway. The survey was conducted by three groups as divided in class before the experiment. All participants were students. Identification of Uca fiddler crab species was completed by collecting qualitative results for surrounding environmental factors such as temperature, pH, compaction, etc.

Field Procedure

In the experiment burrow identification along the zone of the study was the major point of the survey. First step, we used 100m transect tape measure 100m and separate 3 sections. ( 0 meter, 50 meters, 100 meters) then used quadrat squares large from beginning which 0 meter to testing. Second section is 50 meters, Third Section. Every section we need to count 10 crab burrows and used small rule to measure how many inch for each burrows. After used penetrometers and PH pen to get data from the marsh. Various species are distributed within the region though it is hard to determine which burrow belongs to which fiddler crab species.

In this experiment burrow data were assembled from three different quadrats within a transect secured using a tape measure. Quadrats are labeled respectively starting from the edge of water upslope. The diameter of the burrows was determined using a Vernier caliper. At the chosen sites, open burrows in every quadrat were counted and recorded in addition to burrows’ diameter. The density of the burrow opening was estimated. Crabs emerging from the burrows were collected and placed in a petri dish. Results for temperature, pH, compaction, the number of holes and diameters were recorded in table 1.

Results

Air Temperature: 72〫F

Sea water Temperature: 65〫F

Cloud Cover ： 30%

Wind Speed: NW 11 Miles / Hour

Table 1

Quadrat 1

Quadrat 2

Quad3

0m

50m

100m

0m

50m

100m

0m

50m

100m

0.5

0.5

1

1

1

0.5

1.5

1.5

0.75

1

1

0.5

1

1

0.7

1

0.5

1

1.25

1

2

1.5

0.5

0.3

0.5

1

0.5

1

0.5

1

1.5

0.5

1.5

1

0.5

1

1.25

0.5

0.25

0.8

0.7

1.5

0.5

1

1

1

0.25

2

1

1

1.7

0.5

1

1.5

0.75

0.5

2

1.4

0.5

1

1

0.3

0.7

0.5

0.5

0.25

1

0.5

1.7

2

0.5

0.3

0.5

1

1

0.4

1

1

1.5

0.5

0.5

0.25

1

0.5

1

1.5

0.5

6

0.5

1

0.5

1.8

pH

6.6

6.91

6.87

7.1

6.95

6.96

6.95

7.42

6.87

Temp

24.9

65.5

69.1

75.2

71.2

71.2

24.4

22.2

22.4

Compaction

150

100

100

40

58

42

45

32

30

Holes

85

25

20

460

400

1140

260

540

960

Discussion and Analysis

From the graph of mean number of fiddler crab burrows on each quadrat, the number of holes in the first quadrat decreases from 0m-100m. There are few holes in the first quadrat because the temperatures are too high. Crabs tend to build less burrows here. As we go further up the slope the number of burrows increase due to more conducive environments. From the results I think they are accurate because animals will always to establish their homes/habitats in areas which are appropriate for them. In this case, the density of burrows shows an increase upslope. On the other hand, burrows are more upslope for the crabs to evade tidal forces that may cause water to sweep them into the ocean.

Percentage cloud cover and wind speed and direction do not affect the distribution of crab burrows in the area. The factors that hugely affect the burrows distribution include sediment temperature, compaction, and pH. Compaction affects burrows distribution because the harder the ground the tougher it becomes for fiddler crabs to construct burrows. pH also affects the burrows because near the water edge the water is salty and might not suit the body pH of crabs as we go further from the coast the pH reduces to an average of about 6.5.

Conclusion

Based on the experiment it was concluded that many environmental factors affect the distribution of burrows in the region of study. For example, sediment compaction, sediment temperature, pH and tidal forces. Other factors such as cloud cover and wind direction have least to no impact in burrows density upslope because burrows are dug into the surface.

Part 2

1. The most common Uca species of fiddler crabs in the area are sand fiddler crab (Uca pugnax), marsh fiddler crab (Uca pugilator), and mud fiddler crab (Uca minar).

Fiddler crabs (Uca spp) taxonomy: Kingdom (Animalia), Phylum (Arthropoda),Class (Malacostra), Order (Decapoda), Family (Ocypodidae), Genus (Uca), and specices (Uca pugilator, Uca minar, Uca pugnax)

2. Fiddler crabs are called so because of the extreme dissimilarities in claws size of the male, having larger claws similar to a fiddle. A similar type of fiddler crab is the marsh crab (Sesarma spp). The taxonomy of marsh crab is Kingdom (Animalia), Phylum (Arthropoda), Class (Malacostraca), Order (Decapoda), Family (Sesarmidae), Genus (Sesarma), and species (sesarma crassipes). Uca spp and Sesarma spp are not closely related because Sesarma spp are herbivores while Uca spp are detritovores, however, both species burrow together.

4. Claws of male fiddler crabs are single, large and brighter is appearance (color) than females, with a purple-grey carapace with brown or black irregular marks. The claws of the females are generally equal shaped and carapaces coloration is subdued. For other crab species, sexes are distinguished by determining the color, anatomical behaviors, and claws. For instance, males of blue crabs have blue claws while females possess red-tipped claws.

5. The level of aggression reduces since the major claw acts as a defense weapon and feeding becomes easy. Additionally, if a male loses the claw it will be mistaken for a female by other crabs.

Appendix