Coexistence of two sympatric hermit crab species from South Brazil: the effect of the shell adequacy index and circadian movement patterns

• Published in: Aquatic ecology 2023-06, Vol.57 (2), p.459-469
• Main Authors: da Silva, Alexandre R., Santos, Renan A. P., Rodrigues, Gabriel F. B., Vieira, Neida R., Baroni, Bruna K., Gregati, Rafael A.
• Format: Article
• Language: English
• Subjects: Adequacy; Animals; Apertures; Biomedical and Life Sciences; Circadian rhythm; Circadian rhythms; Coexistence; Competition; Crustaceans; Decapoda; Dimensions; Ecosystems; Freshwater & Marine Ecology; Life Sciences; Marine crustaceans; Marine molluscs; Pagurus brevidactylus; Shells; Sympatric populations; Width
• ISSN: 1386-2588; 1573-5125
• DOI: 10.1007/s10452-023-10022-0

Gastropod shells play an important role in the life story of hermit crabs, influencing biological characteristics directly. The adequacy of shells for hermit crabs can be evaluated through the Shell Adequacy Index, which calculates the shell's ideal size/weight compared to the actual dimensions of the occupied shells. To avoid competition for shells, animals can display a variety of strategies including alterations in their circadian rhythms. This study aimed to evaluate if two sympatric species of hermit crabs— Pagurus brevidactylus and Pagurus criniticornis— are competing for the best fitting shells and if they present differences in their circadian rhythms. Their shells were identified and measured regarding the aperture length and width. The shell adequacy was calculated using linear models of the Shell Aperture Length and Width, and the period of activity of the animals was filmed for 24 h and later analyzed. The period between 10 am and 2 pm represented daytime, while 10 pm to 2 am represented nighttime. Pagurus brevidactylus occupied mainly Cerithium atratum and Claremontiella nodulosa shells, while P. criniticornis occupied mainly C. atratum shells. Our results showed that the two species are inhabiting shells with similar traits, which may indicate competition. The species do not present distinct activity periods; however, the shell occupation pattern suggests a competition at the functional level.