MEPS 504:109-118 (2014)  -  DOI: https://doi.org/10.3354/meps10780

ABSTRACT: Life history characteristics of long-lived organisms make them particularly vulnerable to disturbances. Demographic studies of such populations are essential for evaluating susceptibility to disturbance and recovery potential, especially for ecosystem engineers supporting many dependent species. This type of demographic information, including population structure and mortality risk, is limited for long-lived rhodoliths (unattached non-geniculate coralline algae), which harbor a high biodiversity of cryptofaunal organisms. Population structure, in situ seasonal growth rates, age, and mortality estimates were determined in 2003-2004 for the subtidal rhodolith Lithothamnion muelleri in the Gulf of California, México. Individuals ranged in size from 0.5 to 16 cm diameter and the population was dominated by those <4 cm. Average annual growth (mean ± SE) was slow (0.71 ± 0.04 mm yr^-1), but faster in summer (March-October). Age projections suggest that large individuals could live for 100-300 yr. In 2003, numerous rhodoliths ≥8 cm diameter died after being cast on shore by Hurricane Marty. Slow growth and increased mortality of larger individuals suggests that recovery from disturbances is slow and that smaller (younger) individuals are more resilient. Larger, older rhodoliths support a more diverse cryptofauna and thus not only are they more vulnerable to disturbances, but their mortality contributes disproportionately to the loss of community structure.

KEY WORDS: Lithothamnion muelleri · Hurricane disturbance · Population persistence · Age and growth · Mortality · Gulf of California