Sandra Obenat

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.

Life cycle and population structure of the polychaeteFicopomatus enigmaticus (Serpulidae) in Mar Chiquita coastal lagoon, Argentina

Ficopomatus enigmaticus, a polychaete inhabiting the subtidal zone in the Mar Chiquita coastal lagoon, builds reef-like aggregates that facilitate silt accumulation. To describe the life cycle, samples were take monthly from September 1984 to September 1985. In contrast with other polychaetes, it has two oocyte generations per year; maturation of the oocytes takes approximately 4 mo. Temperature level and day length regime do not appear as environmental signals to the onset of oogenesis, although they possibly affect oogenesis growth. Two periods of spawning and recruitment were observed in November–December and April–May, when water temperature is above 18°C. Hermaphroditic individuals were not found. Sex ratio was male-biased in all months, significantly in November, February, and August (p<0.001). Monthly size-frequency distributions show distinct year-classes with early (November–December) and late (April–May) recruitment. Early recruited cohorts have two spawning periods during a 24-mo lifespan. Late cohorts have one spawning period during their 20-mo lifespan. The life cycle of this species can be summarized as follows: annual iteroparous—1 to 2 batches of small eggs per female during each lifespan, free spawning, planktotrophic larvae, sedentary suspension-feeder worms.

Macrobenthos and multi-molecular markers as indicators of environmental contamination in a South American port (Mar del Plata, Southwest Atlantic).

We evaluated benthic habitat quality along a presumed contamination gradient in the Mar del Plata port (Southwestern Atlantic) by coupling biological and chemical proxies in a multidisciplinary approach. Organic matter and photosynthetic pigment contents were higher in silty-clay bottoms of the inner port sites. Levels of all fecal steroids decreased from the inner sites to the port inlet. High concentrations of coprostanol in the inner sites seemed to derive from a permanent population of sea lions rather than from sewage outfalls due to coprostanol/epicoprostanol ratio (IV) values <2.5. PAHs levels were also higher in the inner sector, related to both biomass combustion and petroleum combustion associated to local marine traffic. High disturbance and low ecological status were reflected in low benthic diversity and high AMBI values in the inner sites.

Life history and reproductive biology of the invasive amphipod Melita palmata (Amphipoda: Melitidae) in the Mar Chiquita coastal lagoon, Argentina

The life history and reproductive biology of the gammaridean amphipod Melita palmata was studied in the Mar Chiquita coastal lagoon (Argentina). The animals were collected fortnightly or monthly from Ficopomatus enigmaticus reefs from December 2000 to March 2002. The population density reached a maximum of 1556.67 ±1560 ind/m 3 (mean±SD) in March 2001, decreased dramatically after intense rainfalls in winter 2001, and had a minimum value of 141.67 ±27.54 ind/m 3 (mean ±SD) in March 2002. Size differed significantly between sexes. The maximum size of males was 11.5 mm and this was 1.4 times longer than the length of females. The average sex ratio (0.44) did not differ significantly from an expected 1:1 value. Ovigerous females were present from December to March, when the temperature was above 18°C. The body size of ovigerous females ranged from 2.9 to 6.81 mm. There was a positive correlation between the brood size and body length of ovigerous females, and the maximum number of eggs per female was ten. Recruitment took place during the whole breeding season; juveniles recruited at the beginning of the season matured at the end of the same season, those recruited late would probably reach maturity in the following season.

Life history of Tanais dulongii (Tanaidacea: Tanaidae) in an intertidal flat in the southwestern Atlantic

We studied the life history, reproductive biology and spatial distribution of Tanais dulongii on an intertidal flat near Mar del Plata, Argentina. The animals were obtained by systematic sampling in three intertidal zones (high, mid and low), from October 2008 to September 2009. The population density was low during most of spring and summer, increased during autumn and reached its maximum values at the end of this season (35 000 individuals/m2); a second, but lower, density peak occurred at the end of winter (15 000 individuals/m2). Male density remained below 1000 individuals/m2 during most of the year in the three zones, although in September it was higher than 1800 individuals/m2 in the high and mid intertidal zones. Female and juvenile density was below 5000 individuals/m2 in spring and summer, with little variation between areas, but it differed among areas during autumn and winter, when both groups reached their maximum densities (20 000-40 000 individuals/m2) in the low and mid intertidal zones. Ovigerous females were always present; their maximum occurred in spring and summer but earlier in the low and later in the high intertidal zone. Recruitment was higher in autumn and early winter. The sex ratio was strongly female biased (0.08 ± 0.01). Individual life time was estimated to be 8-9 months and females developed through more instars than males. This study suggests that the different environmental conditions that T. dulongii faced in the 3 intertidal zones caused an important effect on the population dynamics.

Outbreak of a neurotoxic side-gilled sea slug (Pleurobranchaea sp.) in Argentinian coasts

Since 2009 we have been registering the outbreak of an unknown side-gilled sea slug of the genus Pleurobranchaea in coastal waters of Argentina, southwestern Atlantic Ocean. Examination of both external macroscopic features and internal structures via electron microscopy did not allow us to conclusively identify the species. Nevertheless, since Argentinian specimens closely resemble Pleurobranchaea maculata (a species native from Australia and New Zealand known to contain a potent neurotoxin) we performed a bioassay in our specimens, which was positive for neurotoxins. The presence of this pleurobranch in Argentinian waters is of concern beyond the ecological effects of the outbreak of a marine predator and requires urgent attention. This work provides a guide to distinguish between this unidentified species and the sympatric cryptogenic Pleurobranchaea inconspicua, based on features that are readily observable in fresh and preserved specimens. We discuss the potential effects of this outbreak on local communities.

Macrozoobentos asociado a los agregados de Phyllochaetopterus socialis Claparède, 1870 en el puerto de Mar del Plata, Argentina

Aggregates of the polychaete Phyllochaetopterus socialis were recorded for the first time in Mar del Plata Harbour, in December 2003. These were found at about 6 m depth, on the border between the break-water rocks and soft sediments. Three random samples (monthly or bimonthly), were taken each season by SCUBA diving. We recorded 56 species belonging to 11 phyla: Porifera, Cnidaria, Nematoda, Plathyhelminta, Arthropoda, Sipuncula, Bryozoa, Annelida, Mollusca, Echinodermata, and Chordata. The highest numbers of organisms were found in summer. The most abundant taxa were crustaceans (amphipods and tanaidaceans), molluscs, polychaetes, and bryozoans. In summer, crustaceans were dominant, whereas the rest of the groups (molluscs, polychaetes and others) showed no significant differences in density along the sampling seasons. Bryozoans were the sessile organisms with the highest relative frequency. This study extends the distribution range for some species, including Hydroides plateni and Elysia patagonica, which had never been cited in Mar del Plata harbour before. The associated macrofauna aggregate was diverse.

Morphological and genetic confirmation of Jassa slatteryi (Crustacea: Amphipoda) in a harbour of Argentina

Jassa slatteryi is reported for the first time in Mar del Plata harbour, Argentina. A morphological comparison with the original description and a genetic analysis are made to corroborate the identification of specimens. The report of range expansion along the South-western Atlantic coast is discussed.

Morphometry and Relative Growth of Populations of Tanais dulongii (Audoin, 1826) (Tanaidacea: Tanaidae) in Pristine and Impacted Marine Environments of the Southwestern Atlantic

Fil: Rumbold, Carlos Enrique. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina

First record of Phyllochaetopterus socialis Claparède, 1870 (Annelida: Polychaeta) in Mar del Plata Harbor, Buenos Aires, Argentina

Agregados del poliqueto tubicola Phyllochaetopterus socialis Claparede, 1870 fueron registrados por primera vez en el Puerto de Mar del Plata (38°02?S; 57°31?30?W), Buenos Aires, Argentina, en diciembre de 2003 mediante buceo autonomo a 6 m de profundidad. Los agregados fueron observados sobre sustrato duro, en el limite inferior del submareal. El presente trabajo amplia el rango de distribucion de dicha especie para Sudamerica, de la cual se tienen registros confirmados unicamente para el sur de Brasil y el Rio de la Plata (Argentina).