Demetrio Boltovskoy

Changes in global economies and trade: the potential spread of exotic freshwater bivalves.

The globalization of economies and trade have facilitated the spread of exotic species including the five most important freshwater suspension feeding invaders Dreissena polymorpha, D. bugensis, Corbicula fluminea, C. fluminalis, and Limnoperna fortunei. We suggest that the spread of these exotic species has not been a continuous process, but rather punctuated by periods of rapid long distance spread (jump), during which species greatly expanded their geographic ranges. Each jump has been associated with changes in the tempo of some human activity, such as the construction of shipping canals for trade, building of reservoirs for water storage and power production, political boundary changes or changes in political systems, which affected the position or permeability of national borders, human migration, changes in the mode and volume of international trade, or recent industrial practices and environmental laws. We hypothesize that the rate of spread of exotic species depends on the spatial scale of spread and may be accelerated or slowed by various human activities. In general, aquatic exotic species may quickly spread along connected waterways in a new continent they invade and soon reach their maximum range (continental scale). However, it will take much longer to colonize all isolated regions (regional scale) and longer still to spread to all isolated lakes and river systems (local scale). The difference in the rate of colonization across scales may be several orders of magnitude.

Dispersion and Ecological Impact of the Invasive Freshwater Bivalve Limnoperna fortunei in the Río de la Plata Watershed and Beyond

Limnoperna fortunei is a freshwater bivalve that invaded South America through Río de la Plata estuary in 1989 and has since become a major macrofouling pest. Along the Paraná-Paraguay waterway, which hosts intense boat traffic, L. fortunei has moved upstream at an average rate of of 250 km per year. In contrast, along the Uruguay river, where boat traffic is restricted to the lowermost 200 km section, upstream colonization is almost 10-times slower. This suggests that attachment to vessels is by far the most important dispersion mechanism. It is suggested that the Amazon, Orinoco and Magdalena basins are under high risk of invasion by this mussel, especially through their estuarine gateways. All South American basins host innumerable water bodies with favorable conditions for L. fortunei’s colonization. Known ecological tolerance limits of the mussel also suggest that it may colonize much of the area from Central America to Canada, including waters that due to their low calcium contents, high temperature and pollution levels, and low oxygen are inadequate for the survival of Dreissena polymorpha. Despite it’s remarkable geographic expansion and its extremely high population densities, L. fortunei’s ecological effects have received very little attention so far. It is suggested that the 2.4-fold increase in Argentine landings of freshwater fish between 1992–1993 and 2000–2001 may be associated with the introduction of this prey species.

THE INVASIVE BIVALVES DREISSENA POLYMORPHA AND LIMNOPERNA FORTUNEI: PARALLELS, CONTRASTS, POTENTIAL SPREAD AND INVASION IMPACTS

Abstract We contrast ecological and life history traits of the well studied freshwater invader, the zebra mussel (Dreissena polymorpha), with the lesser known invasive golden mussel (Limnoperna fortunei) to compare salient biological traits and environmental limits, and to predict the potential spread and ecosystem impacts of L. fortunei in areas where it is introduced. Both species are sessile, byssate bivalves with a planktonic larval stage and extremely high reproductive capacity. For both species adults attain much higher biomass in waterbodies they invade than all of the native invertebrates combined, and they create substrate complexity otherwise not found in freshwater systems. Both are very active suspension feeders, greatly enhance benthic-pelagic coupling, and act as effective ecosystem engineers. Although taxonomically unrelated, their ecosystem impacts are surprisingly similar and follow from the novel ecological niche they share, rather than being species specific. The golden mussel has broader environmental tolerances and therefore may be a much more successful invader than D. polymorpha in regions dominated by acidic, soft and contaminated waters. In the near future L. fortunei may colonize the southern and central parts of North America, much farther north than has been previously predicted. Although to date the zebra mussel is considered the most aggressive freshwater invader, soon many waterbodies may receive another, even more aggressive invader.

Temperature:δ18O relationships of planktonic foraminifera collected from surface waters

Abstract Most of the isotopic paleotemperature equations used for paleoceanographic reconstructions have been derived from culture experiments or inorganic precipitates of calcium carbonate. To test these equations in the modern ocean, we measured the oxygen isotope composition of planktonic foraminifera (Globigerinoides ruber, Globigerinoides sacculifer, Globigerina bulloides and Neogloboquadrina pachyderma) collected from Atlantic and Southern Ocean surface waters, and added published plankton tow data from the Pacific, Indian and Arctic Oceans. The resulting species-specific regression equations of the temperature:δ18O relationships for G. ruber, G. sacculifer and G. bulloides are statistically indistinguishable. The equations derived for G. sacculifer and G. bulloides agree with relationships obtained from laboratory experiments, in which these species were cultured at pH values close to modern surface waters. The equation derived from N. pachyderma has a significantly lower slope and offset than the other three species but produces a regression equation that is nearly identical to the one for the epifaunal benthic foraminifer Cibicides sp. Our work on plankton tow and pumped samples indicates that culture-derived equations appear to be more appropriate for predicting the absolute δ18O of the species examined compared to equations derived from inorganic precipitates. However, over the oceanic temperature range, the slopes of the equations we derive for living species agree with the slopes obtained from inorganic precipitates.

Filtration rates of the invasive pest bivalve Limnoperna fortunei as a function of size and temperature

Clearance rates of Limnoperna fortunei (Bivalvia) were investigated in laboratory experiments using monocultures of the alga Chlorella vulgaris. Experimental conditions included two mollusc sizes (15 and 23 mm), and three water temperatures (15, 20 and 25 °C) covering the normal seasonal range in the lower Paraná river and Río de la Plata estuary. Filtration rates obtained were, for the larger mussels: 9.9, 13.1 and 17.7 ml mg tissue dry weight−1 h−1 at 15, 20 and 25 °C, respectively; and for the smaller ones: 17.7, 20.8 and 29.5 ml mg−1 h−1. Differences between sizes and between temperatures (except 15 vs. 20 °C) were statistically significant. In absolute terms larger animals have higher clearance rates, but as a function of body mass smaller individuals feed more actively. Within the range of experimental values used, filtration rates were positively associated with water temperature. These clearance rates (125–350 ml individual−1 h−1) are among the highest reported for suspension feeding bivalves, including the invasive species Dreissena polymorpha, D. bugensis and Corbicula fluminea. High filtration rates, associated with the very high densities of this mollusc in the Paraná watershed (up to over 200,000 ind m−2) suggest that its environmental impact may be swiftly changing ecological conditions in the areas colonized.

Radiolarian vertical distribution patterns across the Southern California current

Abstract Polycystine radiolarians were identified in 36 plankton samples collected at depths ranging from 0 to 2000 m at four stations extending west from about the U.S.-Mexico border (approx. 32°N,117°W to 124°W), in November-December 1977. In total, 136 radiolarian taxa were recorded, but 90% of all individuals were accounted for by only 40 of these. Highest abundances were found either at the surface, or at 25–50 m. Based on maxima in the vertical profiles of the most abundant radiolarians, three major depth-intervals were defined in the upper 300 m: 0–50 m,100 m and 200–300 m. Between-station-similarities in the specific makeups of these layers, however, were low. Thirty-nine taxa had peak abundances below 300 m at one or more stations; 11 of these are probably deep-water forms. Although in terms of individuals per liter of water filtered, upper-layer taxa are noticeably more abundant than deep species, the latter have much more extended depth-ranges, which might significantly enhance their sedimentary output. The inshore and oceanic stations shared very similar, warmer-water radiolarian assemblages in the uppermost 25 m, whereas the intermediate station was dominated by colder-water forms at those depths. Below 50 m, however, the inshore station had enhanced proportions of deeper- and colder-water species, differing strongly from the oceanic site. We suggest that this pattern results from circulation of the Southern California Eddy, which transports Central Water from the oceanic station on the western edge of the California Current around the intermediate stations to the inshore stations. The coldwater signal at subsurface layers of the inshore station could be reinforced by coastal upwelling and southward transport by the California Current, thus further enhancing the abundances of deeperwater radiolarians at this site. Analyses of the effect of such vertical patterns on paleoceanographic interpretations stress the importance of the signal of “environmentally neutral” deep-living species, as well as that of shells produced in the near-surface layers of distant areas and transported at depth to the region of the study.

Population dynamics of Limnoperna fortunei, an invasive fouling mollusc, in the lower Paraná River (Argentina)

Settling and growth of the Asian freshwater mussel Limnoperna fortunei on experimental PVC frames in the Parana de las Palmas river, ca 130 km north of Buenos Aires was monitored at monthly intervals in 1998. Frames were deployed in January. In February and March colonization reached 3800044000 mussels m-*, with early juveniles ( 2 mm) mussels. In September through December densities grew steadily again, with early juveniles (< 2 mm) accounting for over 95% of the mussels recorded. During their first month, animals born in January grew to ca 34 mm in length; in March they reached 7-8 mm, and by mid April 11-12 mm. In late April through July the growth rate decreased to < 2 mm per month, and in August it stopped almost completely, resuming again in late September. During the first year animals born in January reached 20mm in length; by the end of the second year the estimated length was 30mm, with a maximum theoretical length of 35mm being reached after 3 years. The data agree with the reported population dynamics of L. fortunei in Hong Kong in that both populations are characterized by extended reproduction periods lasting ca 9 months, and that the spring onset of breeding is triggered by a rise in temperature above approximately 16-17°C. On the other hand, in the Parana river reproduction was found to be continuous between September and March, and the period of lowest yearly temperatures was characterized by a very strong breeding decline, whereas for the Chinese populations 2-3 yearly spatfalls and breeding pulses roughly coinciding with the lowest and highest water temperatures were described.

Feeding selectivity of Corbicula fluminea(Bivalvia) on natural phytoplankton

Phytoplankton in water samples from the lower delta of the Paraná river (Argentina) and in the gut contents of a local populaton of the Asiatic clam Corbicula fluminea was identified and counted monthly between April 1992 and March 1993. Relative abundances of algal species were generally similar in the medium and in the stomachs of clams, suggesting the absence of feeding selectivity on the basis of taxonomic group or size-class. Diatoms made up a slightly but consistently larger (yet not significantly different) proportion of the diet of C. fluminea than of the plankton; this pattern is attributed to enhanced preservation of algal siliceous frustules, rather than to feeding selectivity. It is suggested that non-selective feeding by the bivalve is a response to the overall scarcity of food and, probably, to food collection by a combination of deposit and filter feeding.

Population dynamics of Corbicula fluminea (Bivalvia) in the Paraná River Delta (Argentina)

Benthic individuals and drifting planktonic juveniles of Corbicula fluminea were sampled in the Lower Delta of the Paraná River (Argentina) at monthly intervals between October 1995 and October 1996. Densities of settled clams above 1 mm, around 300–1000 ind. m-2, varied little throughout the year. Below 1 mm benthic juveniles, on the other hand, showed a single conspicuous abundance peak in October-November (up to 1722 ind. m-2), and were practically absent during the rest of the year (overall annual mean: 1070 ± 797 ind. m-2). Drifting juveniles showed one major peak in December 1995 (160 ind. m-3), and a minor one at the end of March (24 ind. m-3). Length-frequency analyses of the monthly field data clearly indicate a highly structured population with a single well defined reproduction period centered on October–November. Population parameters derived from the seasonally oscillating version of von Bertalanffys growth formula were as follows: maximum shell length: 32 mm (maximum observed shell length: 33 mm); growth constant: 0.65; growth seasonality (i.e., span of summer-to-winter growth-rate difference): 0.7; winter point (i.e., time of the year when growth is minimum): 0.5 (June–July); estimated size range for one year-old individuals: 15.3–22.4 mm; for two years: 23.5–27 mm, and three years: 27.5–29.3 mm. Comparison with previous data confirm the influence of water temperature on the clams reproduction and growth and furnish additional evidence suggesting that food availability may be as important for recruitment as thermic regimes. Contrasts between traits of the population analyzed herein with those described previously from a nearby (ca. 10 km) site more influenced by industrial pollution point at the influence of water quality on Corbiculas recruitment and growth.

Planktic foraminifera from the southwestern Atlantic (30 °–60 °S): species-specific patterns in the upper 50 m

Abstract Planktic foraminifers were studied in 96 samples collected in the southwestern Atlantic (30 °–60 °S, along 53 °W) in November 1993, mainly from depths between 0 and 50 m. Very high proportions of juveniles (unidentified) were present throughout the area, especially north of 37 °S, where they accounted for up to 70–80% of all shells recorded. For most species no clear vertical specific stratification was detected in the 0–50 m layer. Zoogeographic grouping of the 18 species identified allowed the defining of 5 distinct zones along the transect: Subtropical (north of 31 °S, 80% warm water individuals); Warm-Transitional (34 °–37 °S, 35% warm water); Transitional (37 °–49 °S, 99% cold water); Subantarctic (49–55 °S, 100% cold water); and Antarctic (south of 56 °S, 100% cold water). Boundaries between foraminiferal assemblage zones are in good agreement with hydrological fronts described for the area. Comparison of the present data with planktic collections from the North Atlantic show large differences in the proportions of various taxa. In the 14–24 °C range, G. bulloides is much more abundant in the northern hemisphere than in the southern one, whereas G. quinqueloba G. inflata and G. rubescens show the opposite trend. On the other hand, temperature-related percentage contributions within the 14 °–24 °C range indicate that the preferred thermic regimes of the 9 species considered are remarkably similar in the North and South Atlantic collections compared. The southernmost planktic distributional ranges of selected warm water taxa are roughly coincident with those established previously on the basis of surface sediments, disagreements being chiefly attributable to selective dissolution on the bottom. In contrast, at the bottom percentages of cold water foraminifers ( G. bulloides G. pachyderma ) are significantly enhanced with respect to their planktic populations, and their sedimentary northward limits extend well beyond their maximum ranges in the upper-layer plankton. It is suggested that submergence of these cold water species and northward displacement at subsurface depths is chiefly responsible for the mismatching patterns observed. Dissimilar species proportions in both hemispheres and plankton-sediment uncoupling can conceivably engender erroneous conclusions when distributional data are used for paleoecologic reconstructions with the aid of numerical analyses such as the Imbrie-Kipp transfer-function technique.