Latin american journal of aquatic research
On-line version ISSN 0718-560X
PARDO, Luis Miguel; MORA-VASQUEZ, Paulo and GARCES-VARGAS, José. Daily settlement of Cancer crab megalopae in a microtidal estuary. Lat. Am. J. Aquat. Res. [online]. 2012, vol.40, n.1, pp. 142-152. ISSN 0718-560X.
The settlement of decapod crustaceans in estuarine environments is the last stage in a complex process in which meroplanktonic species close the pelagic life phase. This process has successive stages, beginning with the formation of larval patches offshore, their transport to nursery areas, the exploration of suitable substrates for settlement, and the metamorphosis into juveniles. The interactions between physical factors and the behavior of competent larvae regulate the diverse stages of this process, finally determining the rates of local settlement. This study analyzes the relative importance of physical forcings that act on the meso-scale (i.e. wind stress, sea level, river runoff) and micro-scale (local temperature conditions, salinity, substrate type) on the settlement of megalopae of the brachyurans Cancer edwardsii and C. coronatus, the principal species of the commercial crab fishery in Chile. Passive larval collectors were installed on the sea bottom for 73 consecutive days during the period of maximum recruitment (i.e. abundance of juvenile I) at the mouth of the Valdivia River estuary; the substrate consisted of coarse sand and something similar to an algal mat. The results showed that: a) the settlement was characterized by extended periods of a few settlers alternating with peaks that did not necessarily coincide for the studied species, b) the settlement of C. edwardsii was related to multiple forcings generated by the advection of warm waters toward the coast, c) the settlement of C. coronatus was related to forcings generated by coastal upwelling, d) the larvae of both species did not differ in the magnitude of settlement on heterogeneous substrates. This study shows that larval settlement patterns are species-specific, even in sympatric and closely related species. Thus, any generalization by taxa should be well supported by comparative studies on the same spatiotemporal scale.
Keywords : estuary; Valdivia River; Metacarcinus; Brachyura; recruitment; flow; wind stress; Chile.