MEGALOPAE AND JUVENILE CRAB SETTLEMENT ON ARTIFICIAL SUBSTRATA IN NORTHERN PATAGONIA: SEASONAL AND INTERANNUAL VARIABILITY

DELLATORRE, FERNANDO G.; FIGUEROA, N.D.; ROJAS, L.; BARÓN, PEDRO J.

La Serena, Chile

Congreso; The Crustacean Society Mid Year Meeting 2007; 2007

The Crustacean Society and Universidad Católica del Norte

Most crab populations are demographically open, depending largely on larval or juvenile settlement from the plankton. In mid latitudes, reproduction is markedly seasonal, restricting the presence of larvae in the plankton and the settlement of megalopae to the bottom to periods of weeks or a few months. The aim of this work was to determine the seasonality of settlement of different crab species in Northern Patagonia and compare the strength of settlement and its duration for each species between two consecutive years. Megalopae collectors were built with a metal frame supporting a square 0.16-m2 piece of NomadTM mat (3M, Nomad Terra 8100). Three collectors were placed on the muddy bottom at a depth of 18 m and replaced every two days from mid September 2005 to late April 2006 and from late September 2006 to late March 2007. In the laboratory, collector material was rinsed thoroughly with fresh water, filtered through a 500-?Êm sieve, and the sample was fixed in 4% formaline seawater. Early live stages of each species were identified and counted under dissecting microscope. Mean number of megalopae/juvenile of each species settled per collector every 2-day was compared between years using Student?Ls ?gt?h test. A total of 1126 megalopae and 2464 juvenile crabs were captured. Megalopae settlement of Peltarion spinosulum and Munida gregaria (= M. subrugosa) occurred during spring, being significantly higher for P. spinosulum in 2005 than in 2006 (p = 3.10-6). Cyrtograpsus altimanus and Pachycheles chubutensis settlement occurred during summer, and was  ignificantly higher in 2007 than in 2006 (p = 2.10-5 and 0.01 respectively). Megalopae and juvenile settlement of Halicarcinus planatus was detected during all of the sampling period. 2 piece of NomadTM mat (3M, Nomad Terra 8100). Three collectors were placed on the muddy bottom at a depth of 18 m and replaced every two days from mid September 2005 to late April 2006 and from late September 2006 to late March 2007. In the laboratory, collector material was rinsed thoroughly with fresh water, filtered through a 500-?Êm sieve, and the sample was fixed in 4% formaline seawater. Early live stages of each species were identified and counted under dissecting microscope. Mean number of megalopae/juvenile of each species settled per collector every 2-day was compared between years using Student?Ls ?gt?h test. A total of 1126 megalopae and 2464 juvenile crabs were captured. Megalopae settlement of Peltarion spinosulum and Munida gregaria (= M. subrugosa) occurred during spring, being significantly higher for P. spinosulum in 2005 than in 2006 (p = 3.10-6). Cyrtograpsus altimanus and Pachycheles chubutensis settlement occurred during summer, and was  ignificantly higher in 2007 than in 2006 (p = 2.10-5 and 0.01 respectively). Megalopae and juvenile settlement of Halicarcinus planatus was detected during all of the sampling period. 2 piece of NomadTM mat (3M, Nomad Terra 8100). Three collectors were placed on the muddy bottom at a depth of 18 m and replaced every two days from mid September 2005 to late April 2006 and from late September 2006 to late March 2007. In the laboratory, collector material was rinsed thoroughly with fresh water, filtered through a 500-?Êm sieve, and the sample was fixed in 4% formaline seawater. Early live stages of each species were identified and counted under dissecting microscope. Mean number of megalopae/juvenile of each species settled per collector every 2-day was compared between years using Student?Ls ?gt?h test. A total of 1126 megalopae and 2464 juvenile crabs were captured. Megalopae settlement of Peltarion spinosulum and Munida gregaria (= M. subrugosa) occurred during spring, being significantly higher for P. spinosulum in 2005 than in 2006 (p = 3.10-6). Cyrtograpsus altimanus and Pachycheles chubutensis settlement occurred during summer, and was  ignificantly higher in 2007 than in 2006 (p = 2.10-5 and 0.01 respectively). Megalopae and juvenile settlement of Halicarcinus planatus was detected during all of the sampling period.