Federico Tapella

Reproductive biology of the crab Munida subrugosa (Decapoda: Anomura: Galatheidae) in the Beagle Channel, Argentina

Munida subrugosa is the most abundant galatheid crab species in the Beagle Channel (558 S6 88W) oi Tierra del Fuego, Argentina. Samples of crabs and the epibenthic community were taken on a monthly basis at two diierent depth strata (540 m and 470 m), by means of epibenthic trawling from 1998 to 1999. Stomach contents from 1582 crabs were analysed, out of which only 2% had empty stomachs. The quantity of food in the stomach contents was clearly seasonal and similar at both depths. The organic matter varied throughout the year and between both depths, being signi¢cantly higher in summer/spring than in autumn/winter. Munida subrugosa shows two diierent and simultaneous feeding habits: (1) as a predator M. subrugosa feeds on crustaceans, algae, and polychaetes; and (2) as a deposit feeder M. subrugosa consumes particulate organic matter and organisms associated with the super¢cial layer of the sediment. The composition of the diet of Munida subrugosa was similar for both years, and independent of depth, sex or season. Munida subrugosa selected crustaceans only in autumn and winter, whereas most food items were found according to their availability in the habitat.

Morphological differences between ‘ subrugosa ’ and ‘ gregaria ’ morphs of adult Munida (Decapoda: Anomura: Galatheidae) from the Beagle Channel, southern South America

Munida subrugosa and M. gregaria are very abundant in the southern hemisphere, especially oi New Zealand and South America. The speci¢c identity of both species is still controversial and accurate identi¢cation is needed for conservation or ecological purposes. In this study we used univariate and multivariate methods to determine the morphological diierences between both species/morphs. Analyses of covariance of ten morphological variables regressed individually on the carapace length demonstrated that the carapace (including rostrum) and eyestalks (EL) were longer, and the anterior carapace (ACW), the rostrum basis (RBW), and dactylus (DaW) and propodus (PW) of the third maxilliped were wider in M. gregaria than in M. subrugosa. In contrast, the carapace, mandible and eyestalk were wider and the rostrum was longer in M. subrugosa compared to M. gregaria. A stepwise discriminant analysis found that ¢ve body measurements namely DaW, EL, PW, RBW and ACW, were useful to discriminate between both species/morphs. The diierence between the two discriminant functions provides an objective decision rule for the classi¢cation of both species/morphs. We also present the linear relationships of wet and dry masses on size, for use in biomass estimations of Munida spp. as prey.

SEASONAL CHANGES IN DRY MASS AND ENERGETIC CONTENT OF MUNIDA SUBRUGOSA (CRUSTACEA: DECAPODA) IN THE BEAGLE CHANNEL, ARGENTINA

Abstract Munida subrugosa is the most abundant benthic species in the Beagle Channel (55°S, 68°W), Tierra del Fuego. Moreover, this species has two simultaneous but different feeding habits: predator and deposit feeder. Because of its high abundance (100 ind·100 m−2) and trophic position, this species plays a key role in the subantarctic benthic ecosystems. However, little is known about its energetic content and changes in dry mass during its reproductive cycle. Samples of M. subrugosa were obtained in 2000 to 2001 by means of an epibenthic trawl. The relative water content (WC) and the energetic content (EC) (kJ·g−1 ash free dry mass [AFDM]) of whole adult animals, and the relative dry mass (RDM) and EC of tissues and organs of females were measured throughout one year. The EC investment of adults at the time of maximum gonadal development was evaluated. The EC was measured using a bomb calorimeter. The mean WC and EC for M. subrugosa was 59% ± 7% and 19 ± 2 kJ·g−1 AFDM, respectively. WC and EC for whole adult animals varied significantly throughout the year, attaining maximum values in autumn or summer respectively, after the pattern of seasonal reproduction and feeding. Moreover, the EC of M. subrugosa varied by 30% annually. The RDM and EC investment in gonadal development was significant higher in females. The hepatopancreas in M. subrugosa is used as an energetic storage organ, because RDM and EC increased before vitellogenesis and moulting.

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.

Daily variations of the antioxidant defense system of the lithodid crab Lithodes santolla

Several physiological processes can induce daily variations in aerobic metabolism. Lithodes santolla is a decapod crustacean of special concern since it is a sub-Antarctic species of commercial interest. The aim of this work was to study in L. santolla the daily variations in levels of enzymatic and non-enzymatic antioxidants, lipid peroxidation and protein oxidation, and haemolymphatic pH. Males of L. santolla of commercial size were randomly dissected every 4 h during a period of 24 h. Enzymatic activities of superoxide dismutase (SOD), catalase (CAT), glutathione-S-transferase and glutathione peroxidase were determined in samples of gills, muscle, hepatopancreas and haemolymph. Ascorbic acid, total glutathione, lipid peroxidation and protein oxidation were also determined in all tissues. Gills showed the highest enzymatic activity and hepatopancreas the highest concentration of non-enzymatic antioxidants. Maximum antioxidant activity was during the dark phase in gills and during the photophase in the haemolymph. Muscle showed significant daily variations, with peaks during the photophase and scotophase. Overall, an antioxidant protective mechanism is present in all tissues, where SOD and CAT represent the first line of defense. The defense mechanism in L. santolla seems to be more active during the dark phase, with slight differences among the analyzed tissues, indicating a higher metabolic rate.

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...