Browsing by Author "Wehrtmann, IS"

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    Breeding biology and population structure of the intertidal crab Petrolisthes laevigatus (Anomura: Porcellanidae) in central-southern Chile
    (2004) Lardies, MA; Rojas, JM; Wehrtmann, IS
    The present study describes the seasonal reproductive cycle and population structure of the porcellanid crab Petrolisthes laevigatus , a typical inhabitant of the rocky intertidal. A total of 960 individuals (including 372 females) was collected in monthly samples from October 1993 to December 1994 in central-southern Chile. Ovigerous females were present between August and December, and were absent between January and July. The breeding season started during late winter (August), and females with embryos close to hatching occurred between October and end of spring (December). Considering the gonadosomatic index and the duration of the incubation period, it is concluded that P. laevigatus has a markedly seasonal breeding period with probably two successive spawnings per female per season. Our results compared with previous studies in temperate intertidal porcellanids suggest a lower structural variability of the population during the sampling period, but a pronounced seasonal variation in both sex ratio and abundance. The influence of environmental habitat conditions (i.e. temperature) is suggested to be responsible for the lower variation in the crab population size structure in ovigerous females, and the almost constant size distribution observed in males.
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    Egg production of Austropandalus grayi (Decapoda, Caridea, Pandalidae) from the Magellan region, South America
    (1999) Wehrtmann, IS; Lardies, MA
    Austropandalus grayi is one of three pandalid shrimp species reported from Chilean waters. Here we describe fecundity, reproductive output, and chemical composition of the incubated embryos of A. grayi, providing the first account of such information for a pandalid species inhabiting the southern hemisphere. Ovigerous females (n = 96) were collected during October - November 1994 with an Agassiz trawl in waters off Patagonia and Tierra del Fuego, South America. Both egg production (between 50 and 1858 embryos) and early egg volume ((x) over bar = 0.069 mm(3)) of A. grayi were low when compared to values reported from other pandalids. Clutch size increased with maternal size, however, the size of recently spawned eggs was not linked to female size. Although the egg mass volume remained almost stable during the incubation period, females lost on average 51.1% of their initially-laid embryos; however, this loss was more than compensated by an 88.4% increase of the egg volume during embryogenesis. Mean reproductive output was relatively low (0.133) and not related to maternal size. The RO-data of A. grayi and other pandalids seem to indicate an increasing energy allocation for reproduction towards higher latitudes, a trend which would be contrary to the results of studies with other crustaceans. Water was the predominant constituent of the chemical composition of developing embryos and increased from 62.2% to 70.2% during the incubation period. At the same time, organic matter declined and mineral content augmented. Generally, our results are in agreement with previous findings with regard to the chemical composition of developing decapod embryos.