Pablo E. Penchaszadeh

No longer the pristine confines of the world ocean: a survey of exotic marine species in the southwestern Atlantic

We conducted a comprehensive survey of existing knowledge about exotic marine organisms introduced to the southwestern Atlantic Ocean, including coastal and shelf areas of Uruguay and Argentina. This domain is equivalent to the so-called Patagonian Shelf Large Marine Ecosystem, and corresponds to two biogeographic provinces: warm-temperate (Argentine Province) and cold temperate (Magellanic Province). The search included species that can be confidently categorized as introduced (31) and cryptogenic species (46). We present a comprehensive picture of recorded introductions (the first for this region) and some prominent ecological consequences. Most coastal ecosystems between the La Plata River estuary and central Patagonia have already been modified, or are expected to be so in the short term. Five recent, human-mediated biological invasions have already had a significant ecological impact. A barnacle (Balanus glandula) belt has developed on all rocky shores where none was present 30 years ago, a macro-fouler (Limnoperna fortunei) and a reef-builder (Ficopomatus enigmaticus) have strongly modified estuarine ecosystems, Pacific oyster (Crassostrea gigas) reefs are expanding in shallow bays at a fast rate, and kelp (Undaria pinnatifida) is rapidly modifying nearshore benthic communities along the coasts of central Patagonia. At this point, it is uncertain how many of the cordgrasses (Spartina spp.) found in coastal salt marshes correspond to exotic forms. Only exposed sandy beaches appear to be free from the pervasive ecological impact of invasion by exotic species. Poor knowledge of the regional biota makes it difficult to track invasions.

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.

On the reproductive biology and impact of imposex in a population of Buccinanops monilifer from Mar del Plata, Argentina

The populations of Buccinanops monilifer (Gastropoda: Nassariidae) from two different sites, Mar del Plata (Buenos Aires province) and a close non-polluted locality (Mar Chiquita), are compared in their imposex indices and reproductive parameters. In Mar del Plata, a beach nourishment (sand filling) remobilized sediment from the harbour area during 1999; our results show high imposex percentage and an increase in relative penis size index during and after this beach filling event, in contrast with the Mar Chiquita population that showed nil values during this study. Comparisons of reproductive parameters between both populations showed significantly higher frequency of spawning females and number of egg capsules per female in Mar Chiquita, while female size and number of eggs per capsule did not differ. Females from Mar del Plata that did not succeed in spawning showed higher imposex values than spawning ones. Sex-ratio was not significantly different from 1:1 in any of the sites (although male-biased in Mar del Plata and the opposite in Mar Chiquita). We found no malformations or abnormalities during intracapsular development in the imposexed population. Alternatively, we found evidence that suggests that B. monilifer intracapsular development includes the occurrence of intracapsular embryonic cannibalism of other smaller embryos, which was not previously known in this genus, and that complements adelphophagy (feeding on nurse eggs feeding).

Age and Growth of Olivancillaria deshayesiana (Gastropoda: Olividae) in the Southwestern Atlantic Ocean

ABSTRACT The population structure, particularly growth, age, mortality and somatic production of the olivid snail Olivancillaria deshayesiana were investigated. Annual formation of internal shell growth marks was confirmed by the record of stable oxygen isotopes in the shell, which reflects seasonal patterns of water temperature. A von Bertalanffy growth model fitted to 81 size-at-age data pairs, indicating that O. deshayesiana may attain 31 mm SL in about 10 years. The estimated total mortality Z and natural mortality M were 0.651 y-1 and 0.361 y-1, respectively. Fishing mortality F was 0.290 y-1, and the exploitation rate E was 0.445, indicating that this population was not overexploited at the time of the study. However, this situation may well change in the future, since the important prawn and shrimp fisheries (in intensity and scale) in the Mar del Plata area (38°20′S, 57°37′W) may indirectly affect the exploitation status of the studied population.

siphon nipping of the bivalve amiantis purpurata by the electric ray discopyge tschudii in mar del plata, argentina

A total of 67 Discopyge Ischudii was captured. Individuals were sexed, measured and their stomach content analysed. Siphon tips of the bivalve Amiantis purpurata from each stomach were individually counted, weighed and their length and width measured. The size-frequency distribution of the local population of A. purpurata was surveyed for two years. Siphons of A. purpurata were the main food item in 90% of individuals having stomach contents. The clam population was markedly bimodal, with 24 mm and 46 mm mean shell length for the younger and older size-classes, respectively. Grazing by D. tschudii on A. purpurata varied with size and sex of the fish. Small rays mainly ingested small siphons and large rays large siphons. Nipped siphon tips were longer in male than in female rays.

ON THE EGG MASSES, EGGS AND EMBRYOS OF NOTOCOCHLIS ISABELLEANA (D'ORBIGNY, 1840) (GASTROPODA: NATICIDAE) FROM NORTHERN PATAGONIA

Naticids are common predators in sandy bottoms of shallow waters around the world. Probably due to their infaunal habitat, they are hard to find alive, particularly in the Patagonian waters of Argentina. Nevertheless, their presence is confirmed by the typical predation boreholes that can be seen on their bivalve prey along the coast (e.g., Bromley, 1981; Carriker, 1981; Pastorino & Ivanov, 1996; Signorelli et al., 2006). These boreholes record information on predators without actually seeing them. Paleontologists have exploited this field, analyzing the behavior and producing models of predator-prey relationships in ancient and recent communities (Kabat, 1990, and citations herein). Studies on the spawn of naticids are scarce in modern literature, despite its common presence in sandy bottoms. The typical sand collars were recognized several decades ago as belonging to this family. Ankel (1930) and Thorson (1935, 1940, 1946), among others, described these characteristic egg masses from different areas around the world. An accurate account of the morphology of the collar and capsules, including the way the gastropod builds them, was described by Giglioli (1955) and Ziegelmeier (1961). An interesting approach was recently published by Huelsken et al. (2008), who reviewed the naticids from Giglio, an Italian island off the coast of Tuscany. They compared mitochondrial and nuclear gene fragments (COI, 16S, H3, 18S) from adults and embryos from the egg masses, leaving no doubt about the mother species of each egg mass. During the past few years, several papers were published in which egg capsules of various gastropods from the southwestern Atlantic were described (Pastorino & Penchaszadeh, 1999, 2002; Pastorino et al., 2007; reviewed in Gallardo & Penchaszadeh, 2001). However, there is no published information about naticids MALACOLOGIA, 2009, 51(2): 395−402

Macrobenthos―sediment relationships in a sandy bottom community off Mar del Plata, Argentina

The aim of this study is to characterize the different macrozoobenthos communities in Mar del Plata waters (south-western Atlantic) on the basis of their abundance and habitat, and to determine how sediment characteristics, like the grain-size composition, affect macrobenthic community structure. Multivariate techniques indicated that benthic communities and sediments in the surveyed area were included into the following five well-defined groups: (1) a medium sand assemblage dominated by the bivalve Crassinella marplatensis and Diplodonta patagonica, the echinoderm Encope emarginata, the tanaidacean Bacescapseudes sp. and the polychaete Armandia loboi; (2) a medium to very fine sand assemblage dominated by ostracods, the tanaidacean Bacescapseudes sp., amphipods and polychaetes of the family Nephtyidae; (3) a fine to very fine sand assemblage dominated by the tanaidacean Bacescapseudes sp.; (4) a silt and fine sand assemblage dominated by polychaetes particularly Scolelepis sp. and individuals of the family Nephtyidae; and (5) a fine sand assemblage dominated by amphipods and the tanaidacean Bacescapseudes sp. These results revealed the patchy distribution of macrobenthic assemblages as a result of sediment characteristics and serve as baseline information for this area strongly subjected to trawling perturbations.

Diet, prey narcotization and biochemical composition of salivary glands secretions of the volutid snail Odontocymbiola magellanica

Odontocymbiola magellanica is a neogastropod very common in Patagonian shallow waters. It feeds exclusively on molluscs inhabiting the same benthic community. Field studies showed that prey preferences are live gastropods (54%) and bivalves (46%). When no living prey are available they change their trophic behaviour to carrion or cannibalism. Feeding mechanisms observations showed that prey are not asphyxiated by the snails foot as suggested before for the Volutidae family; they are narcotized by saliva introduced in a cavity made by the foot where prey are immobilized. Saliva is produced by the salivary (SG) and accessory salivary glands (AG) and has a pH around 10, relaxing prey muscles, which are consumed alive. Secretions from AG and aqueous extracts of SG and AG were mainly composed of proteins and glycoproteins, though SDS-PAGE gels revealed that salivary proteins were richer in higher molecular weight bands. Fractionation of secretions from AG on Bio-Gel P-100 yielded only one peak. SDS-PAGE showed that it consisted of only one band (MW 51.3 kDa). Microanalysis of cations showed a higher concentration of calcium and magnesium in the accessory salivarygland. Hypotheses of function of different glands are given in relation to feeding behaviour and anatomy of O. magellanica.

The genus Buccinanops: A model for eye loss in caenogastropods*

Abstract: The genus Buccinanops (dOrbigny, 1841) (Caenogastropoda, Nassarriidae) is endemic to the SW Atlantic Ocean, and the name implies no eyes, due to the lack of visible eyes in adults. We recognize for the first time the occurrence of eyes during several developmental stages within Buccinanops. Eye spots in Buccinanops cochlidium (Dillwyn, 1817) were observed during intracapsular development and in hatchlings and juveniles. Eyes were histologically confirmed in embryonic cephalic tentacles; they were comprised of sensory cells, supportive cells, a lens, and an optic nerve cord. The ontogenetic history of the eyes of B. cochlidium is discussed.