Estimating Productivity Of The Black Sea Mussels From Their Density And Biomass
ESTIMATING PRODUCTIVITY OF THE BLACK SEA MUSSELS FROM THEIR DENSITY AND BIOMASS
S.V. Stadnichenko, N.M. Shurova
Odessa Branch Institute of biology of Southern Seas, National
Academy of Sciences of Ukraine
Among many of population parameters which are especially important for evaluating the state of the species in given ecological conditions are characteristics of their productivity. Since productivity is an integral indicator of different life processes, it characterizes degree of reproductivity, growth and mortality of animals, and that is why the production characteristics of many species may be widely used in the systems of monitoring of the biological effects of water pollution.
The mussel Mytilus galloprovincialis is widespread in the coastal zones of the Mediterranean Sea, the Black Sea, and Sea of Azov. This commercial species is also an important subject of marine aquaculture, and characteristics of growth and production of mussels have been estimated for some Black Sea regions (Zaika, 1983; Vizhevsky, 1989; Zolotnitsky, 1990). However, the production characteristics of mussel settlements from the northwestern Black Sea are lacking. This area is characterized by heavy anthropogenic loads, and the shallow water shelf here is a place for the main settlements of mussels, therefore estimation of their production characteristics has actual purpose.
The methods for determining production of marine organisms have been developed in detail (Methods of determination…, 1968; Zaika, 1983; Crisp, 1984; Alimov, 1989). Most of them are based on determining the age structure and growth rate of organisms. In the Black Sea mussel, Mytilus galloprovincialis, the seasonal differently coloured increments are quite distinct in the nacre layer in the radial sections of the shells (Shurova, Zolotarev, 1988). That is why the determination of such population characteristics as age structure, growth rate, mortality and survival of mussels based on determination of the individual age of the mollusk is quite possible.
Samples of mussels were taken from stations in the northwestern Black Sea at depths of 5,5 – 35 m. The annual production of mussels was determined
by the method of single samples as the sum of the production of separate age groups of mollusks (Maksimovich, Pogrebov, 1986; Alimov, 1989):
P = 0,5(N1 + N2)(W2 – W1),
where N1 and N2 are retrospective and observed number of molluscs, W1 and W2 are retrospective and observed values of the mussel mass (total, mass of shells, wet tissue mass, dry tissue mass, ash free dry mass). The retrospective values of the mussel number one year before mussel sampling were determined according to the equation:
N1 = N2 · e-Z ,
where Z – is the mortality coefficient determined on the basis of the average age of molluscs (Ssentongo, Larkin, 1973).
The annual mussel production was calculated on the basis of four mass characteristics – total mass (P), shell mass (Ps), dry tissue mass (Pd) and ash free dry mass (PAFDM). It was found that there are significant spatial differences for the production characteristics received. The total production of mussels (P) at different northwestern Black Sea stations varies from 72,8 to 4873 g·m-2·year-1. Their highest values as a rule are characteristic for mussel stocks with a high fraction of juvenile mollusks (Odessa Bay, Danube estuary).
The production calculated for dry tissue mass of mussels (Pd) varies from 2,6 to 227 g·m-2·year-1, while for ash free dry mass (PAFDM) – from 2,26 to 197,8 g·m-2·year-1. The highest values also occur for the above mentioned mussel settlements.
Of special, interest is the annual production of calcium carbonate of the mussel shells (Ps). The quantative analysis of the process of biogenic carbonate formation is widely used in the evaluation of the balance of matter and energy (Bosence, 1989; Fabry, 1990). However, actually the carbonate production of the Black Sea mussels has been analyzed for the first time, although the fraction of shell mass in the total mussel biomass is quite large. In the autumn period in different benthic mussel populations the values of the shell mass production vary from 34,8 g·m-2·year-1 to 2250 g·m-2·year-1 and the fraction of shell biomass for this period makes up from 33 to 95% of the total mussel biomass. This confirms the rather high rate of the process of calcium carbonate production especially in the comparatively juvenile mussel populations.
The determination of annual production of mussels on the basis of the above-mentioned estimations of the individual age is quite precise, but quite labour consuming. For the system of ecological monitoring the most perspective evaluations of production are those according to empirical ratios between production parameters with such widespread population characteristics as biomass, density of population or average mass of one specimen.
For evaluating the possibility of determining the production of the Black Sea mussel according to mussel biomass and abundance, with revealing of the average mass of one specimen (W), the model of multiple regression was applied:
ln Pi = a + b ln B + c ln W ,
where Pi is one from the characteristics of annual mussel production (P,Pd,Ps,PAFDM), B means biomass, W is average mass of one specimen, a, b, and c are coefficients. This equation similar to that has been used for analysis of the productivity of marine macrobenthic invertebrates of the World Ocean (Brey, 1990).
It has turned out that empirical equations of multiple regression which determine the annual production (g·m-2·year-1), calculated according to total mussel mass (P), shell mass (Ps), dry (Pd) and ash free dry mass (PAFDM) of mussel tissue have quite a high determination coefficient R2:
ln P = 1,004 ln B – 0,484 ln W , R2 = 0,968 ;
ln Ps = 0,977 ln B – 0,660 ln W , R2 = 0,952 ;
ln Pd = 1,008 ln B – 0,688 ln W – 2 897 , R2 = 0,924 ;
ln PAFDM= 1,008 ln B – 0,688 ln W – 3,04 , R2 = 0,923 .
The production values established for the above equations are close to similar production characteristics revealed by direct methods on the basis of the individual age determination. Thus the above equations of multiple regression may be applied for calculations of values of Black Sea mussel production using standard hydrobiological data and may be widely used in the system of ecological monitoring.
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