Growth rate and longevity of Dreissena polymorpha : a review and recommendations for future study

ABSTRACT We review the variety of manners that have been used above the last 50 y in the Former Soviet Union, Eastern and Western Europe and freshly in North America to determine extension rate and longevity in zebra mussels (Dreissena polymorpha [Pallas]). These [i]modus operandi[/i]s include: counting annual rings, analysis of size-frequency distributions, following growing under experimental conditions and monitoring marked mussels below natural conditions, without removing them from substrate. The last rule provides the most reliable data, however this is the least belonging to all method used. Dreissena polymorpha expansion rates depend on water temperature, season of the year, location in the water round pillar food availability, oxygen concentrations, water velocity and various other environmental factors. However, it is real difficult to separate the independent consequences of each of these factors, especially in natural waterbodies. Several factors may overlap and have additive or synergistic event that makes it difficult to determine the issues of a single factor. When comparing among studies that used the same manners we found that zebra mussels become greater [i]or[/i] larger faster in reservoirs than in lakes. The reported longevity of D polymorpha varies from 2-19 y and it is not clear to what expansion this variation is caused through biological variability and environmental conditions and what amount of the variation is caused through the methods used to assess age and longevity.

lock opener WORDS: zebra mussels, Dreissena polymorpha, extension growth rate, methods, longevity

INTRODUCTION

The zebra mussel, Dreissena polymorpha (Pallas), is single of the most pervasive invaders in freshwaters of the northern hemisphere. However, many aspects of the basic biology of D polymorpha that are necessary for understanding and predicting the population dynamics and ecological impacts of this invader are still not well known. In addition, abundant of the research on the biology of D polymorpha that has been managemented in the former Soviet Union (FSU) has not been published in English, and therefore it is not available to greatest in quantity scientists currently studying D. polymorpha. growing rate and longevity are particularly important for understanding the population biology and ecological impacts of zebra mussels, especially because fecundity and filtering capacity increase with material part size. Most of the published research has been directioned with the invasive subspecies Dreissena polymorpha polymorpha, which is capable of living in totally new water and has been the major invader in greatest in quantity places where dreissenids have been introduced. Les work has been administrationed with Dreissena bugensis (Zhuravel 1951 MacIsaac 1994 Baldwin et al. 2002) Dreissena polymorpha andrusovi (Karpevich 1952 1964 Lvova et al. 1983 1994) and Dreissena caspia (Karpevich 1952 1964)

Here we review the variety of manners used to estimate growth and longevity of zebra mussels above the last 50 y (Table 1 Table 2) discuss limitations of each and praise the most appropriate methods for measuring expansion and longevity in the field. We also synthesize the impacts of a range of environmental factors upon growth and longevity in zebra mussels.

way s TO ESTIMATE GROWTH RATE

Rings upon Shells

One of the oldest and greatest in quantity common methods for estimating the expansion rate of zebra mussels is through counting annual rings on shells of different sizes, and then calculating the average longitudinal dimensions of each age group of Dreissena in a population (Karpevich 1952 1964 Kachanova 1963 Stanczykowska 1964 Lyakhov & Mikheev 1964 Mikheev 1964 Kornobis 1977 Karatayev & Tishchikov 1979 Kirpichenko & Antonov 1982 Dorgelo & Gorter 1984 Draulans & Wouter 1988 Miroshnichenko 1990) Plotting the average size of each age collection against their age provides a extension rate curve. The advantage of this manner is that by measuring individuals at a single point in time estimates of growing over several years can be made. However, counting growing rings is very subjective as it is difficult to distinguish annual rings from rings formed because of other factors that deliberate growth. Morton (1969a) found that sum of two units rings are formed annually: when extension slows during the winter and during spawning. Lvova (1980) base in the Uchinskoe Reservoir, 3-9 rings upon the shells of 3-y-old mussels grown in cages for 2 y In Czo Lake Lewandowski (1983) place from 1-3 rings on the shells of 1-y-old D polymorpha, and from 2-5 rings upon 2-y-old mussels.

Many other authors have also reported difficulties in distinguishing annual rings (Karpevich 1964 Kirpichenko 1965 Morton 1969a, Wiktor 1969 Lvova-Kachanova 1972 Lvova 1980 Lewandowski 1982a, Karatayev 1983 bij de Vaate 1991 Lvova et al. 1994) frequently mussels with distinct rings can be rest side by side with mussels without rings (Lvova 1980 Lvova et al. 1994 Jantz 1996) Moreover, 1-mm zebra mussels that stool at the end of the growing season do not bring into view a first annual ring. Therefore, these mussels would he incorrectly identified as young-ofthe-year the following year.