Mariano J. Diez

Reproductive biology of the crab Halicarcinus planatus (Brachyura, Hymenosomatidae) in sub-Antarctic waters

Halicarcinus planatus is the only member of the family Hymenosomatidae that occurs in the southern tip of South America. The aim of this study is to determine both the reproductive cycle and reproductive traits of the population of H. planatus nearest to southern limit of its geographical distribution. Results of this work allow us to determine two consecutive reproductive periods in this species. Maximum values of gonadosomatic index, oocyte diameter and ovarian development in March and August indicate that spawning takes place in May and September. The simultaneous ovarian maturity and the embryonic development show that female H. planatus can re-mature its ovary. The capability of H. planatus to develop their ovaries while females are ovigerous is a unique feature among the sub-Antarctic decapods and probably an adaptative advantage to extreme environments. Based on the different biological features and recent environmental changes along the Western Antarctic Peninsula, our hypothesis is that H. planatus possesses the potential to invade shallow waters and intertidal zones in this region.

Pelagic swarms and beach strandings of the squat lobster Munida gregaria (Anomura: Munididae) in the Beagle Channel, Tierra del Fuego

The present article is the first formal record of pelagic swarms and beach strandings of the squat lobster Munida gregaria in the Beagle Channel, southern South America. To describe size composition and natural diet of beach strandings and swarms, samples from strandings were taken in April 2007, March 2008 and March 2010. Samples from swarms were taken in May 2007 and April 2010. Also, during November 2008 and January 2009, two acoustic surveys were carried out to describe both, horizontal distribution and school metrics of swarms. Pelagic swarms and beach strandings were composed of 100% individuals of the morph gregaria of M. gregaria. Mean size of males and females in both, beach strandings and swarms, were similar. The diet of pelagic M. gregaria was composed mainly of crustaceans, unicellular algae and small macroalgae, sediment and particulate organic matter. Swarms of pelagic Munida took the shape of extended layers of varying density and height. Their positions in the water column were also variable: swarms were found at different depths, from the subsurface layer to near the sea bottom. Occasionally, some large swarms occupied most of the water column. In the Beagle Channel, SW winds during spring tides could be a forcing factor for M. gregaria strandings. The absence of shoaling animals in the Beagle Channel between 1997 and 2002 and the recent occurrence of swarms are coincident with their appearance in other locations in Patagonia. In consequence, we hypothesize that the factor influencing the formation of swarms must be acting at a regional scale.

Invertebrate bycatch in Patagonian scallop fishing grounds: a study case with data obtained by the On Board Observers Program

Desde el inicio de la pesqueria de vieira patagonica, Zygochlamys patagonica, en el Mar Argentino, en 1996, el Instituto Nacional de Investigacion y Desarrollo Pesquero (INIDEP) establecio un Programa de Observadores a Bordo (OBOP). Se analizaron las tendencias generales en la composicion de la captura incidental a partir de informacion provista por OBOP, de capturas y esfuerzo pesquero (219 viajes, 575 muestras), recolectada en cinco bancos de vieira entre 39o y 44oS, durante el periodo 1997-2002. Se encontraron grandes variaciones en la densidad promedio de la captura incidental y la presencia de ocho grupos taxonomicos durante el periodo estudiado. Echinodermata fue el taxon dominante en la mayoria de los bancos de vieira relevados. Se registraron aumentos en la densidad de equinodermos y gasteropodos, y escasos organismos sesiles en el banco SWSAO, sujeto a esfuerzo pesquero elevado y continuo. En el banco SWTB, menos explotado, se observaron organismos sesiles, cuya densidad disminuyo en el periodo estudiado, y no se registraron cambios en las densidades de equinodermos y gasteropodos. Estos dos ultimos grupos, en su mayoria carroneros y depredadores, se verian favorecidos por un aumento en la disponibilidad de alimento producto de la actividad pesquera (descarte y organismos danados). Contrariamente los organismos sesiles, sustrato de asentamiento potencial, disminuyeron en densidad en areas con intensa actividad pesquera. Tambien resaltamos la importancia de esta fuente de datos, que amplia la ventana espacio-temporal de la evaluacion anual y optimiza la produccion de bases de datos a mayor escala

Distribution of Lithodes confundens Macpherson, 1988 (Decapoda, Anomura) along the Atlantic continental shelf of southern South America

Fil: Sotelano, Maria Paula. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Austral de Investigaciones Cientificas; Argentina

Moult cycle and growth of the crab Halicarcinus planatus (Brachyura, Hymenosomatidae) in the Beagle Channel, southern tip of South America

The crab Halicarcinus planatus is the only hymenosomatid crab that inhabits the southern tip of South America and is the only decapod species that reproduces twice a year in the Beagle Channel. In this article, we study the moult cycle in the field (moult frequency, analysis of size frequency distribution) and linked it with growth studied in the laboratory (absolute and per cent growth increment, Hiatt function). Hiatt functions were similar for males and females. Moult frequency was seasonal: in early austral spring and in austral summer. In females, the pubertal moult is the terminal moult, whereas males continue moulting after attaining the size of morphometric maturity. Moult increment was highly variable. The relationship between absolute moult increment and crab size was described by a quadratic function. Per cent growth increment decreased with size, and relationships were different for each sex: linear for females and quadratic for males. Seven and eight modal groups explained the size frequency distributions for females and males from the field, respectively, and revealed the existence of two cohorts of recruits per year. Further modal analysis was mainly hampered by the high variability of size increment that could make any moulting individual fall in its own or one of two following modal groups. The antagonism between growth and reproduction was evident in small males. We hypothesize that the terminal pubertal moult is an advantageous feature that allows females to maximize their investment in reproduction after their terminal moult, which allows this species to have two spawnings per year.

Gregaria to "Subrugosa," that is the question: Shape changes under laboratory conditions in the pelagic morphotype of the squat lobster Munida gregaria (Fabricius, 1793) (Decapoda: Anomura: Munididae)

Fil: Diez, Mariano Javier. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Austral de Investigaciones Cientificas; Argentina

Antioxidant defenses and lipid peroxidation in two Lithodes species from South Atlantic during summer

In Southern South America Lithodes santolla and L. confundens are the most valuable king crabs species, specially due to their high yields and their high acc...

Distribución y estructura poblacional del cangrejo Halicarcinus planatus (Brachyura, Hymenosomatidae) en el Canal Beagle, Tierra del Fuego

The crab Halicarcinus planatus is the only hymenosomatid that inhabits the southern tip of South America and has a sub-Antarctic distribution, including the ...

Winter is cool: spatio-temporal patterns of the squat lobster Munida gregaria and the Fuegian sprat Sprattus fuegensis in a sub-Antarctic estuarine environment

In the sub-Antarctic waters of southern South America, two species that form conspicuous pelagic aggregations are considered both potential fishery resources and ecologically important: the Fuegian sprat Sprattus fuegensis and the squat lobster Munida gregaria. Here, we estimate spatio-temporal patterns of the relative abundance, distribution and potential areas of overlapping of M. gregaria and S. fuegensis in the Beagle Channel. Acoustic data were collected from 18 surveys conducted between 2009 and 2016 in the Beagle Channel. Our observations on the pelagic aggregations revealed that M. gregaria swarms and S. fuegensis schools occurred along the channel throughout the year. However, the occurrence of S. fuegensis was more evident in the inner part of the channel during the winter. There was a negative relationship between the relative abundance of squat lobsters and Fuegian sprats throughout the year. This interaction may result from spatial competition associated with resources, particularly in summer. The vertical distribution and morphology of aggregations of both species showed seasonal differences. Specifically, schools of Fuegian sprats were typically pelagic in summer, whereas in winter they were bigger and associated with the bottom layer. This change could be associated with a seasonal change in the oceanographic regime of the Beagle Channel. The information presented here is necessary to understand processes in a context of possible opening of fisheries targeting these two species that have key ecological roles in this sub-Antarctic ecosystem.