Elba Morriconi

Biomonitoring of TBT contamination and imposex incidence along 4700 km of Argentinean shoreline (SW Atlantic: From 38S to 54S)

The imposex incidence and TBT pollution were investigated along 4,700km of Argentinean coast, including city harbors and proximal zones without marine traffic. We analyzed 1805 individuals from 12 gastropod species, including families Volutidae, Muricidae, Nassariidea, Calyptraidae, Marginellidae, and Buccinidae, and found the imposex phenomenon for the first time in six species. In high marine traffic zones, TBT pollution was registered and the percentage of imposex was high, while these occurrences were null in areas without boat traffic. The species that best reflect the degree of imposex were those inhabiting sandy/muddy or mixed bottoms. TBT determination and imposex incidence indicate that pollution was focused only in ports with high marine traffic or in areas where ship hulls are painted. This is the first report of an imposex-sediment approach to evaluate organotin contamination along the coast of a South American country.

Growth and production of the venerid bivalve Eurhomalea exalbida in the Beagle Channel, Tierra del Fuego

Growth, mortality and productivity of the hard clam Eurhomalea exalbida from Ushuaia Bay, Beagle Channel, were investigated. The parameters of the von Bertalanffy growth function were estimated to be Hl = 74 mm, K = 0.18 y � 1 ,t 0 = 0.15 y. Maximum individual production amounted to 2.74 g shell-free wet mass (SFWM) at 49.5 mm shell height. Animals between 40 mm and 70 mm shell height contributed most to overall population somatic production P of 134 g SFWM m � 2 y � 1 . Mean annual biomass B amounted to 1123 g SFWM m � 2 y � 1 . Annual P/B ratio and mortality rate Z were estimated to be 0.12 y � 1 and 0.14 y � 1 , respectively. Slow growth and low turnover make this population less suitable for sustainable commercial exploitation. D 2002 Elsevier Science B.V. All rights reserved.

Individual age and connective tissue lipofuscin in the hard clam Eurhomalea exalbida

In the hard clam Eurhomalea exalbida, autofluorescent granules were detected in high concentrations in the connective tissue around the intestine and in other tissues. Autofluorescence combined with Sudan black B and PAS positive reactions suggested that these granules were lipofuscin-like. The concentration of this material in the connective tissue (CT) around the intestine was quantified by image analysis and expressed as total area fraction occupied by lipofuscin granules. Lipofuscin concentration was distinctly better related with individual age as determined from stable isotope-validated shell growth bands than with any morphometric parameter. This relationship was described best by a Gompertz model: Lipofuscint=24.79e−e−0.029(Age t−58.578) (N=38; rnl2=0.882). Age was predicted from lipofuscinCT concentration by a von Bertalanffy model: Age t=68.00(1−e−0.146(Lipofuscint+0.028))0.664 (N=38; rnl2=0.933). Our findings suggest that lipofuscinCT concentration in E. exalbida is a function of individual age. If this holds true for bivalves in general, lipofuscin may be a suitable proxy for age in species with less clear shell growth band patterns.

Reproductive biology of the icefish Champsocephalus esox (Günther, 1861) (Channichthyidae)

Champsocephalus esox is the only icefish species found outside Antarctica. In a population from the Beagle Channel, the complete annual reproductive cycle has been determined. Gonad maturity stages have been established for males and females by histological analysis. Males are sexually mature from January–September with a maximum gonadosomatic index (GSI) of 3.63%. Histologically, testes are very homogeneous and the degree of maturation of the testicular cysts is similar among different tubules at the same maturation stage. Running ripe testes have mature sperm and a few spermatogoniae arranged near the blind end of the tubules. In sexually active females that are found from February–November, ovaries contain only ripe oocytes or postovulatory follicles, together with a batch of previtellogenic oocytes. During hydration, oocyte diameter reaches 2.7 mm, and oocyte dry weight increases due to material intake, the maximum GSI in ovulated ovaries is 21.89 and hepatosomatic index (HSI) decreases. These facts suggest a transfer of matter from liver to the gonads. Absolute fecundity ranges from 3303–8600 oocytes. Relative fecundity ranges from 22.5–43.5 oocytes per gram total weight. In C. esox , relative fecundity has a similar range to those quoted for the different C. gunnari populations, whilst mature oocyte diameter is small and reproductive season extended compared to the same parameters in other Channichthyidae.

Spawning aggregations of Merluccius hubbsi, in Patagonian waters: evidence for a single stock?

Abstract From 1971, a small scale bottom trawl fishery has developed in the San Matias Gulf (41°–42° S; 64°–65°W) of the Argentinean Sea, targeting the hake (Merluccius hubbsi Marini). The dynamics of a spawning aggregation of hake in the gulf were analyzed based on changes in sex ratio and the proportions of different stages of sexual maturity. It was concluded that the northern part of the gulf is the main spawning zone. While males are concentrated there, mature females come to the area, spawn, and then move back to the west zone. The presence of a spawning aggregation and the occurrence of all stages of the life cycle in the San Matśas Gulf, suggests that the hake population in the Gulf constitutes a stock unit separate from the continental shelf stocks. Further support for this hypothesis is provided by the oceanographic characteristics of the Gulf.

The reproductive cycle of Eurhomalea exalbida (Chemnitz, 1795) (Bivalvia: Veneridae) in Ushuaia Bay (54° 50' S), beagle channel (Argentina)

Summary The reproductive cycle of Eurhomalea exalbida (Chemnitz, 1795) in Ushuaia Bay, Beagle Channel, was studied from October 1998 to December 1999. Clams were collected monthly by SCUBA diving at 3–5 m water depth. The degree of sexual maturity was determined histologically (n=338). The sex ratio was 1:1 (Chi-squared p>0.05). First sexual maturity occurred at 39 mm shell height in males and 40 mm in females (i.e., 4 years of age). Five distinct histological stages of sexual maturity could be established in males: (1) early active, (2) late active, (3) ripe, (4) partially spawned with recovery and (5) spent. Females had oocytes ranging from small and immature to large and fully developed in their ovaries throughout the year. Since we could not classify reproductive stages based on a qualitative histological scale of sexual maturity, quantitative measures using an image analyser were used. In males a high percentage of mature individuals were present between January and August. The percentage of early active and partially spawned individuals was highest in November 1998 (70%) and 1999 (60%). In females, the mean number of developed oocytes per unit of gonadal area in a cross section, the mean diameter (minor axis) of oocytes, and the percentage of gonadal area occupied by oocytes were lowest in November, indicating a spawning peak. These results indicate synchronous gonadal development and spawning in males and females. The more intensive spawning activity in November coincides with the higher biomass and production of phytoplankton in spring.

REPRODUCTIVE CYCLE AND ENERGY CONTENT OF TAWERA GAYI (HUPÉ 1854) (BIVALVIA: VENERIDAE) AT THE SOUTHERNMOST LIMIT OF THEIR DISTRIBUTION RANGE

Abstract The reproductive cycle and the energy content of soft parts of Tawera gayi were studied monthly from August 2001 to July 2002 in Ushuaia Bay, Beagle Channel. The degree of sexual maturity was determined histologically. The sex ratio was significantly different of 1:1 (896 females, 796 males, χ2-test, P < 0.05). First sexual maturity occurred at 12 mm shell height in both sexes. In males the reproductive cycle was determined analyzing the monthly percentage of gonadal stages. High percentages (85%–100%) were mature (ripe stage) during a large part of the year (March to September) and in October the 100% of individuals were partially spawned with recovery. An image analyzer was used to determine quantitatively female reproductive cycle. The percentage of gonadal area covered by oocytes was lower in December. The mean number of mature oocytes (diameter >40 μm) by gonadal area and the mean diameter of oocytes reached the lower values during October, November, and December, indicating a spawning peak. This more intensive spawning activity coincides with the phytoplankton bloom in spring. The energy content of soft parts was measured using a microbomb calorimeter in monthly samples during a year. The mean energy content in both sexes was significantly different reaching 20.95 kJ/g AFDW for females and 21.39 kJ/g AFDW for males. The relative condition index attained the lower values in August, September, and October. The monthly values of the energy content did not show significant differences in both sexes. Results of this study indicate that notwithstanding T. gayi lives in a markedly seasonal environment as Subantarctic waters of Beagle Channel shows a protracted gamete production with a principal spawning episode and small pulses of evacuation during the rest of the year.

Alternative reproductive strategies of Ostrea puelchana

Three reproductive strategies of Ostrea puelchana from the San Matias Gulf (Rio Negro, Argentina) are described and discussed. These relate to the degree of grouping shown by the oysters; i.e., (a) Carriage (this strategie is unique to the Ostreidae); (b) clusters and (c) isolation. Incidence of these strategies differed among three study sites (Banco Reparo, Las Grutas and Bajo Oliveira). Carriage incidence was maximal at Bajo Oliveira (69.4 % of the individuals), intermediate at Banco Reparo (49.7 %), and minimal at Las Grutas (19.7%), where clusters and isolated individuals predominate. Clusters constituted only a small fraction at Bajo Oliveira (1.1 %) and Banco Reparo (3.5%). The percentage of males larger than 50 mm was notedly lower at Banco Reparo (8.0 %) than at Las Grutas (39.3 %). The Las Grutas oysters associated in clusters have a higher percentage of males (57.9%) than at other locations and in any other type of association.Sex ratio and the particular dominant reproductive strategy are characteristic of each area, indicating a balance between the different strategies to improve fertilization efficiency.