Microhabitat Resource Use, Activity Patterns, and Episodic Catastrophe: Conus on Tropical Intertidal Reef Rock Benches

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<jats:p>Low species richness (five to nine species) and high population density (means of 0.2—8.6 individuals per square metre) characterize Conus assemblages on intertidal benches throughout the tropical Indo—West Pacific region. Data from 16 such habitats in Hawaii, Marshall Islands, Australia, Maldives, and Seychelles indicate that similarity of microhabitats between species is equal to or greater than random expectation. Significant between—species differences in zonation pattern occur across benches at a given time and place. The peak of C. ebraeus abundance typically occurs closest to shore; C. chaldaeus and C. sponsalis are usually most distant from shore. However, we found about as man significant within—species differences between censuses made at different times on the same bench as between—species differences within censuses. Co—occurring species thus tend not to use microhabitat resources differentially. Physical environmental variables including tide level, strength of water flow and time of day determine refuging and foraging activity patterns, and all species appear to respond similarly to these factors. The data thus do not support the hypothesis of temporal resource partitioning. We found evidence neither for homing, as mark—recapture results suggested that individuals occupy any convenient refuge after foraging, nor for interference competition for protected sites among Conus. species diversity is significantly correlated with (1) substrate topographic diversity measured either independently or as the diversity of microhabitats utilized by all species together, and (2) the proportion of individuals occupying protected sites. Where refuges (potholes and crevices) comprise only 2—9% of bench surface area, an average of 63% of Conus individuals occupy them, indicating strong selection for protected microhabitats. The presence and quality of these physical refuges are less important on benches with thick mats of algal turf binding sand. The gastropods burrow in these mats during periods of stress. A catastrophic rainstorm coinciding with low tide caused high mortality in an inner bench population at Enewetak, but more C. ebraeus survived (30%) than other species (8%). Tolerance to such unpredictable physical stress may explain the observed patterns of zonation of Conus of different species and sizes across benches.</jats:p>

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