Evidences of habitat structure-generated bottleneck in the recruitment process of the SW Atlantic mud crab Cyrtograpsus angulatus

MENDEZ-CASARIEGO, A.; EVANGELINA SCHWINDT; IRIBARNE, O. O.

Marine Biology

Springer

Año: 2004 vol. 145 p. 259 - 264

Shelters generated by the introduced reefbuilding polychaete Ficopomatus enigmaticus (Serpulidae) significantly enhance settlement of the crab Cyrtograpsus angulatus (Grapsidae) in a SW Atlantic coastal lagoon (Mar Chiquita, 37_32¢S; 57_26¢W; Argentina). However, their ultimate role in recruitment does not appear to be very important, suggesting a habitat-generated bottleneck that occurs between settlement and recruitment. Laboratory and field experiments show that newly settled crabs actively select refuges similar in size. Inside the reefs, decreases in crab density of each newly settled cohort mirror the ratio of decreases in the number of reef refuges of similar sizes, suggesting that habitat fractal structure determines the mortality rate after settlement. Field experiments using artificial shelters show that as crabs increase in size, they move outside reefs. Field tethering of juvenile- and adult-sized crabs without access to refuges showed that juvenile crabs suffer a much higher risk of mortality than adults. Our results show that the availability of small refuges provided by polychaete reefs enhances crab settlement, but, then, due to a decrease in the number of refuges as size increases, produces a demographic bottleneck during recruitment. Thus, independent of settlement intensity, enhanced survivorship in the smallest size classes due to refuge is not transmitted to larger size classes. This is likely one reason why stock-recruitment relationships may not hold in species that use shelters during both recently settled and juvenile life stages. These results provide a good example of why habitat enhancement programs need to incorporate a comprehensive evaluation of the species’ ontogenic ecology to avoid class size-specific bottlenecks.