We rejected our null hypothesis. All four crabs seem to actively choose shell type unequal to availability. Overall, the main shell occupied was Ilynassa. This is probably due to the large abundance of this shell, compared to other shell types, in the sample area. The biology of the crabs plays a part in their shell type selection. While some species overlap in shell selection, others need specific lengths, or opening size to house their body and claws.
Longicarpus prefers fuzzy llynassa, to other available shells. They actively choose any form of llynassa over other shells. P. longicarpus, also known as the long-wristed hermit crab, needs a shell long enough to hold it but also wide enough to fit their claws. In general, they choose long shells with wide openings such as, Terebra or llynassa, over all others. These crabs also seem to prefer shells with snail fur.
Pollicaris do not select shell type in proportion to availability. These crabs choose fuzzy shells over their non-fuzzy counterparts when available. Furthermore P. pollicaris chooses large shells with very wide openings over all other types. The flat-clawed hermit crab choose fuzzy llynassa, fuzzy Eupleura, or Polinices over other shells because the opening allows the crab to pull its claws over the opening, acting as a pseudo-operculum.
Carolinensis was by far the most abundant crab caught, and they do not select shell type in proportion to availability. They seem to avoid shells with snail fur. These crabs, unlike P. pollicaris, choose the non-fuzzy counterpart of llynassa, Anachis, and Terebra. Due to the abundance of P. carolinensis, they inhabited almost every shell type. The only shells they did not inhabit were Polinices and fuzzy Polinices, due to the shells large opening.
brevidactylus did not select shell type in proportion to availability, much like P. carolinensis, these crabs avoid fuzzy shells. They exhibit a clear preference to llynassa, Anachis, and Terebra. They avoid shells with large, wide openings such as Polinices, and choose shells with narrow openings and spiral tops such as Urosalpinx or littorina.
Overall wave action and shell architecture are the most significant factors to hermit crab shell selection in our sample area. According to Alcaraz and Arce, wave action plays a significant role in the distribution of shells and hermit crab shell selection. Areas with low wave velocity elicit lighter and more conical shells while areas of higher wave velocity elicit heavy, fat shells. Our data supports this hypothesis. Our study area is a subtidal zone with very little wave action. Therefore, light conical shells such as Terebra or llynassa dominated the shell abundance in our habitat and were the most inhabited shells. Hermit crabs inhabit theses light shells because it allows for increased growth and clutch sizes (Contreras-Garduno 2009). The durability of a heavy shell is not needed because the waves do not erode or break down the shells very fast (Arguelles, Araceli et al. 2009)
Snail fur is a colonial hydroid, Hydractinia echinata, commonly found on gastropod shells (Mercando 1980). Mercando and Lytle found that snail fur was a common occurrence on shells inhabited by P. longicarpus and P.
Pollicaris, but it did not colonize on shells inhabited by P. brevidactylus or P. annipules. However, it was not found to colonize on the same type of shells inhabited by other hermit crab species such as P. brevidactylus.
It is hypothesized that the living hydroid could be a means of shell partitioning within a hermit crab community, thus reducing competition for shells (Mercando 1980). A living Hydractinia colony seems to be a stimuli for differential shell selection, and not the rough textured surface of a dead Hydractinia colony (Jensen 1970, Mercando 1980).
It can be concluded that many environmental pressures contribute to the clear shell preference of sympatric hermit crab species in Beaufort, N.C. The main factors of shell selection include shell architecture and presence of snail fur. Further research should be conducted on the selection mechanism behind the preference of shells with snail fur over shells without.
