Gustavo A. Lovrich

CHALLENGING THE COLD: CRABS RECONQUER THE ANTARCTIC

Recent records of lithodid crabs in deeper waters off the Antarctic continental slope raised the question of the return of crabs to Antarctic waters, following their extinction in the lower Miocene ;15 million years ago. Antarctic cooling may be responsible for the impoverishment of the marine high Antarctic decapod fauna, presently comprising only five benthic shrimp species. Effects of polar conditions on marine life, including lowered metabolic rates and short seasonal food availability, are discussed as main evolutionary driving forces shaping Antarctic diversity. In particular, planktotrophic larval stages should be vulnerable to the mismatch of prolonged development and short periods of food avail- ability, selecting against complex life cycles. We hypothesize that larval lecithotrophy and cold tolerance, as recently observed in Subantarctic lithodids, represent, together with other adaptations in the adults, key features among the life-history adaptations of lithodids, potentially enabling them to conquer polar ecosystems. The return of benthic top predators to high Antarctic waters under conditions of climate change would considerably alter the benthic communities.

Cannibalism in the snow crab, Chionoecetes opilio (O. Fabricius) (Brachyura: Majidae), and its potential importance to recruitment

Abstract Density-dependent cannibalism, either on early benthic instars or on late prerecruits, has been hypothesized to regulate recruitment in the snow crab Chionoecetes opilio (O. Fabricius). However, there is little direct empirical or experimental evidence to support these hypotheses. We examined the stomach contents of 1218 C. opilio of 12–135 mm carapace width (CW) for evidence of cannibalism. Crabs were collected by beam trawl in 1993 and 1994 in the estuary and northwest gulf of the Saint Lawrence River (Canada). Complementary laboratory experiments served to constitute a library of digested crab body parts for reference in the identification of stomach contents, and to evaluate the possibility and size-specificity of cannibalism on C. opilio instar I (settlers: 3 mm CW). The natural diet of C. opilio changed with increasing body size, with smallest crabs feeding mainly on amphipods and ophiuroids, while the largest crabs fed mainly on annelids, crustacean decapods and fish. Overall, conspecifics other than exuviae occurred in the stomachs of 7.2% of wild caught C. opilio and were probably derived through predation rather than scavenged. Non-exuvial conspecifics were found most frequently in the stomachs of adult males (sperm-producing, chelae differentiated), with occurrence declining significantly from 22% to 6% of adult males by 10 mm CW size class over the range of 50–120 mm CW. Conspecific prey ranged in size from 3.9–48.8 mm CW, but most were immature crabs belonging to molt instars V (≈ 15 mm CW), VI (≈ 20 mm CW) and VII (≈ 28 mm CW). In the laboratory, instar I crabs were cannibalized by males of 8–50 mm CW, but not by males of 51–130 mm CW. Based on laboratory and field results, there are relative lower and upper size thresholds for vulnerability of intermolt crabs to cannibalism, which vary with predator size. We conclude that intraspecific predation may reduce cohort strength mainly over the first 4 years following settlement.

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.

Lipid, fatty acid and protein utilization during lecithotrophic larval development of Lithodes santolla (Molina) and Paralomis granulosa (Jacquinot)

During the larval development of the subantarctic king crab, Lithodes santolla, and stone crab, Paralomis granulosa, we compared changes in the carbon, fatty acid and protein contents of larvae reared under constant conditions from hatching to metamorphosis, either in presence or absence of food (Artemia spp. nauplii). In both species the feeding condition had no influence on any of the chemical parameters studied, indicating a fully lecithotrophic (i.e. non-feeding) mode of development from hatching of the first zoea to metamorphosis of the late megalopa. Dry mass and carbon contents at hatching were similar in the larvae of both species, but L. santolla contained initially higher total amounts of fatty acids and protein than P. granulosa. Both species utilized considerable portions of their total fatty acid pool which decreased logarithmically throughout the time of development. At metamorphosis, it was almost exhausted in P. granulosa, while L. santolla had consumed only about 60%. Protein utilization, in contrast, was higher in L. santolla (40%) than in P. granulosa (20%). Triacylglycerol was the principal storage lipid in both species, accounting initially for about 75% of the lipid fraction; it was strongly utilized during larval development. Phospholipid constituted the second largest lipid class; it also decreased in P. granulosa, but to a lesser extent in L. santolla. The major fatty acids of both species were 18:1(n9), 20:5(n3) and

Delivery and Storage of Sperm at First Mating of Female Chionoecetes opilio (Brachyura: Majidae) in Relation to Size and Morphometric Maturity of Male Parent

ABSTRACT Virgin female Chionoecetes opilio were paired with males, in a noncompetitive laboratory setting, less than 12 h after molting to maturity. The quantity of sperm that females received and stored was measured as ejaculate weight and number of sperm cells. Females copulated 1-4 times prior to spawning; the first and second intromissions lasted an average of 34.4 and 37.7 min, respectively. On the whole, the weight of ejaculate and number of sperm cells did not differ between the left and right spermathecae. The number of sperm cells received or stored in spermathecae was independent of male and female carapace widths. Morphometrically mature (large claw) males transmitted an estimated 10.8 x 106 sperm cells to each spermatheca, and an estimated 2.1 x 106 sperm cells from each spermatheca were used to fertilize the first egg clutch (≈ 70 sperm cells per oocyte). Females did not extrude eggs when fewer than 1.9 x 105 sperm cells were delivered to at least one spermatheca, resulting in a ratio of <7 sperm cells per oocyte. A median of 10.2 x 106 and 8.7 x 106 sperm cells were stored per spermatheca by females that extruded eggs after mating with morphometrically immature (small claw) and morphometrically mature males, respectively. The ratio of number of sperm cells to ejaculate weight was significantly greater in stored ejaculates from morphometrically immature males than in those from morphometrically mature males. Both male morphs mated successively with 5 different females over a period of 14-33 days, with no significant change in the weight of ejaculate or the number of sperm cells stored by females after spawning.

Changes in biomass and chemical composition during lecithotrophic larval development of the southern king crab, Lithodes santolla (Molina)

Changes in biomass and elemental composition (dry mass, W; carbon, C; nitrogen, N; hydrogen, H) were studied in the laboratory during complete larval and early juvenile development of the southern king crab, Lithodes santolla (Molina), formerly known as Lithodes antarcticus (Jacquinot). At 6±0.5 °C, total larval development from hatching to metamorphosis lasted about 10 weeks, comprising three demersal zoeal stages and a benthic megalopa, with mean stage durations of 4, 7, 11 and 47 days, respectively. No differences in development duration or mortality were observed in larvae either fed with Artemia sp. nauplii or unfed, indicating that all larval stages of L. santolla are lecithotrophic. First feeding and growth were consistently observed immediately after metamorphosis to the first juvenile crab stage. Regardless of the presence or absence of food, W, C, N and H decreased throughout larval development. Also the C:N mass ratio decreased significantly, from 7.7 at hatching to 4.1 at metamorphosis, indicating that a large initial lipid store remaining from the egg yolk was gradually utilized as an internal energy source, while proteins played a minor role as a metabolic substrate. In total, 56–58% of the initial quantities of C and H present at hatching, and 20% of N were lost during nonfeeding larval development to metamorphosis. Nine to ten percent of the initially present C, N and H were lost with larval exuviae, half of these losses occurring in the three zoeal stages combined and another half in the megalopa stage alone. Metabolic biomass degradation accounted for losses of about 47–50% in C and H but for only 10% in N. Hence, most of the losses in C and H reflected metabolic energy consumption (primarily lipid degradation), while about half of the losses in N and two thirds of those in W were due to larval exuviation. Complete independence from food throughout larval development is based on an enhanced maternal energy investment per offspring and on energy-saving mechanisms such as low larval locomotory activity and low exuvial losses. These traits are interpreted as bioenergetic adaptations to food-limited conditions in Subantarctic regions, where a pronounced seasonality of day length limits the period of primary production, while low temperatures enforce a long duration of pelagic development.

Extended hatching periods in the subantarctic lithodid crabs Lithodes santolla and Paralomis granulosa (Crustacea: Decapoda: Lithodidae)

Temporal pattern of hatching was studied in the subantarctic lithodid crabs Lithodes santolla (Molina) and Paralomis granulosa (Jaquinot) from the Argentine Beagle Channel. In both species, larval hatching occurred in low daily numbers over an extended period of up to several weeks, depending on hatch size. Low daily hatching activity and low oxygen-consumption rates in freshly hatched P. granulosa larvae are discussed as life history adaptations to, and/or physiological constraints by, the environmental conditions of high latitudes.

Larval and early juvenile development in Paralomis granulosa (Jacquinot) (Decapoda: Anomura: Paguroidea: Lithodidae), with emphasis on abdominal changes in megalopal and crab stages

Morphological variations in the two zoeal stages and megalopa of a lecithotrophic population of Paralomis granulosa (Jacquinot) reared under laboratory conditions are reviewed. Attention is also directed to certain aspects of their development not previously considered. More importantly, the first three juvenile stages are described and illustrated for the first time. Specific consideration is given to the structural changes in the abdominal tergites during the transformation from megalopa to third crab, and ancillary information on abdominal plate development in juvenile stages four and five is provided. Total pleopod loss in both sexes and subsequent reappearance in females is discussed.

Megalopal and early juvenile development in Lithodes santolla (Molina, 1782) (Decapoda: Anomura: Paguroidea: Lithodidae), with notes on zoeal variations

Summary The megalopal and first three juvenile stages of Lithodes santolla (Molina, 1782) are described in detail and illustrated, and ancillary information on carapacial spines and abdominal plate development in juvenile stages four and five are provided. Particular emphasis has been placed on the morphological changes occurring in the abdominal tergites and to the reduction and loss of uropods andpleopods. Additionally, variations in zoeal morphology from that described in an earlier study are noted. Simplification of the mandible, retarded development in the maxillule, and setal reduction on the maxilla during the three zoeal stages may be a function of the lecithotrophy of these larvae.

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.