The Ichnological Features of the Hermit Crabs and the Physical Characteristics of the Area
Our results reveal differences between the three closely spaced micro-habitats of the study areas with respect to both the ichnological features of the Hermit Crab and the physical characteristics of the area. Three tropical ecosystems were reviewed at FIU Biscayne Campus to conduct the research project.
The first one was the pond by the Marine Science Building at 42o NE, North Miami, FL. The other two points of study included the southern beaches and the Arch Creek East Environmental Preserve. Variations in distribution of Hermit Crabs have been related to biotic and abiotic environmental factors, such as salinity, temperature, pH of soil, pH of water, luminescence, and vegetation cover.
On the first week vegetation was successfully analyzed at the pond with latitude 25o54’34’’N and longitude 80 o8’23” W. It was noticed that as proximity to water increased the grass percentage magnified and flower presence was reduced, moreover, no crab burrows were found.
Low animal life presence and no indicators of crab presence was due to lack of food supply and shelter to protect themselves from predators. In the coastal beaches sediment was primarily composed of rocks, so this parameter does have a real influence on burrow characteristics and distribution patterns for Hermit Crabs since the ground composition makes it difficult for these organism to excavate and create burrows where they can settle and find shelter.
The wetland habitat area at Arch Creek has a stand of more diverse vegetation with mangroves by the high tides, and vascular land plants from the Coniferophyta division; locally with less saline water over the saline freshwater at the pond. This micro-habitat is characterized by the greatest density of burrows, widest range of diameters, middle values in burrow depth and length, and clear increase in burrow diameter as you move far from the humidity of the soil in the mangroves to the dry land in the forest.
A significant number of Hermit Crab were observed in different sizes in the mangroves zone. Smaller Hermit Crab approximately 1cm large were spotted from two different species, fiddler crabs and mangrove crabs, near the mangroves. Larger crabs were found on the branches of the mangroves, identified as Scylla serrata, and a fossil of a crab claw, approximately 6cm, belonging to a Hermit Crab was detected.
The substrate characteristics appear to favor colonization mainly by juveniles, as revealed by the high number of burrows, smallest burrows diameters, and shallowest and shortest burrow depths and lengths. The soft substrate here impedes construction of large and deep burrows by adult fiddlers. In sum, this area presents the best conditions for endobenthic colonization and population development, including individuals of different sizes/ages.
Less favorable conditions for burrowing for Hermit Crab were manifested in the dryland of the forest at the Arch Creek, with its subaerial location under fair-weather conditions, sparse vegetation, and highest firmness values.
The lowest number of burrows occurred here, but these burrows are deeper and have longer range of diameters. These characteristics. indicate limitations on colonization, affecting mainly the smaller juvenile members of the population; only adult crabs can colonize this area, where they form deep and large burrows.
Our results confirm the importance of substrate features, including soil temperature and pH, depth of burrows, and vegetation density, in controlling the construction and characteristics of the burrows of Hermit Crabs. These environmental parameters also exert an important influence on population structure within broader areas occupied by the population.