Суточный рацион и пищевая конкуренция в планктонном сообществе лагуны р. Висла, Балтийское море

УДК 574.56 + 574.583

К. В. Опалинский*, К. Мациевская**

* Центр экологических исследований Польской академии наук, Дзиканов/Варшава, Польша
E-mail: krzysztof.opalinski@cbe.internetdsl.pl
**Институт морского рыболовства, Гдыня, Польша, E-mail: krystyna@mir.gdynia.pl

Ключевые слова: пищевой рацион, ювенильный, пищевая конкуренция, лагуна Вислы

DAILY FOOD RATION AND COMPETITION FOR FOOD
IN PLANKTON COMMUNITY
OF THE VISTULA LAGOON, BALTIC SEA

K. W. Opaliński*, K. Maciejewska**

*Center for Ecological Research, Pol. Acad. Scis, Dziekanów/Warsaw, Poland,
E-mail: krzysztof.opalinski@cbe.internetdsl.pl
**Sea Fisheries Institute, Gdynia, Poland, E-mail: krystyna@mir.gdynia.pl

Key words: food ration, juvenile fish species, food competition, Vistula Lagoon

Vistula Lagoon is brackish water body with mean water salinity of 2,5 PSU and mean depth of 2,4 m. It is 91 km long, it is supplied by freshwater by 18 small rivers and connected with Baltic Sea with PiławaPass which supply it with saline water. The damp and flood-gate on NogatRiver was build up at 1916 and it has closed the main fresh water inflow to the Vistula Lagoon. It was the reason of the rise of Vistula Lagoon water salinity up to 2–3 PSU and it start to be brackish water body. Its flora and fauna changed – typical freshwater species collapsed, marine (or rather – brackish) species penetrated it.

In late spring (May–June) the pelagic macroplankton community of the Vistula Lagoon is build up first of all by early developmental stages of several fish species, like Baltic Sea herring Clupea harengus membras Linnaeus, 1758, European smelt Osmerus eperlanus (Linnaeus 1758), perch Perca fluviatilis Linnaeus, 1758, stickleback Gasterosteus aculeatus Linnaeus, 1758, and only one crustacean – the mysid shrimp Neomysis integer (Leach, 1814).

Mysid shrimp, smelt, and herring are the most numerous elements of macroplankton community. The highest observed density of herring larvae in the Vistula Lagoon reached in May 4,95 ind./m³, in the same period the highest abundance of smelt larvae reached 11,74 ind./m³, the abundance of other fish species is much lower. But the food spectrum of early juvenile stages of fish species and mysid shrimp is practically the same, and those species must compete for food.

The aim of the present study was to measure daily food ration of main species forming the macroplankton community of the Vistula Lagoon. We hypothesized that the differences in daily food rations of early developmental stages of fish species do not play the main role in total food quantity utilized by each species.

The role of each species in total zooplankton utilization was determined on the basis of its abundance in the pelagic community in May–June period and on the individual daily food ration (C) measured as the sum of production (P), respiration (R), egestion (F – defecation), and excretion (U – urinary products), according to the equation of an energy budget C = P + R + F + U.

Production of the animals (P) was described as the average increase of animal body dry weight per unit of dry weight per day (mgDw/mgDw·d) over the 18-day period from May 30 to June 17, 2001 (mysid shrimp) and 21-day period from May 13 to June 3, 2004 for fish species.

The oxygen consumption (R) of individual animal was measured using closed vessel method with the WTW OXI 196 Oxygen Sensor and was expressed as mm³O₂/mgDw·d.

The quantity of feces produced by animals (F) was determined by weight. From five to ten animals were placed in glass aquarium and after 24 hours long exposure the water was passed through glass filters. The filters were dried, and than weighted. The amount of feces was expressed as mgDw/mgDw·d.

Ammonia production (U) were measured using indo-phenol method and expressed as mg ammonia–N/mgDw·d.

Elementary composition of animal body (P), feces (F) and feed (C) was measured using Carlo Erba CHN–S analyzer and than energetic value of P, F and C was calculated.

Data on production, respiration, egestion, excretion and calculated value of daily food ration of macrozooplanktoners from Vistula Lagoon are presented in the Table. The difference between the lowest (smelt) and highest (stickleback) food ration is 2,5 times, and between fishes and mysid – 5 to 10 times.

Table. Parameters of the energy budget (cal/mgDw·d) of macrozooplankton animals
from Vistula Lagoon

 

The biggest daily food ration was observed in the stickleback, but its abundance in the community is very low and consequently, its role in consumption of zooplankton by all community is very low. Also the daily food ration of the herring is rather high and its role in zooplankton utilization as food is rather low. The major part of zooplankton stock is eaten by smelt.

Smelt is one of the constant elements of the fish assemblages of the Vistula Lagoon. It spends its entire life in the brackish waters of the Vistula Lagoon, but ascends small rivers to spawn. After hatching in rivers, smelt larvae are transported down-stream to the Vistula Lagoon. For herring Vistula Lagoon is one of the main spawning grounds in the southern Baltic Sea. During early spring adults migrate from the southern Baltic Sea to the spawning area in the shallow, brackish waters of the Lagoon, characterized during this period by high temperatures and high zooplankton abundance. Herring larvae and juveniles spend up to three months in the Lagoon. Then, in June, they migrate to the open waters of the Baltic Sea.

The results of this study confirm our hypothesis – the differences in daily food rations of early developmental stages of fish species do not play the main role in total food quantity utilized by each species. The main role in quantity of zooplankton utilized by different zooplanktoner species is played by their abundance and body dimensions – bigger and more abundant species can eat more than small and rare one.

Begon (1984) suggested that size (here: growth rate) can be understood as fitness measure. This hypothesis translated into pelagic system of the Vistula Lagoon is as follows: who has higher growth rate (better ability to catch bigger prey and avoid predators (Hunter, 1972)) and lower cost of maintenance (cost of attack and suction the prey (Drost et al., 1988)), it wins the competition for food and it can utilize bigger part of food stock of the environment.

Our results demonstrate quite another picture – the smelt with the lowest growth rate (see the Table) and medium costs of maintenance wins in competition for food in Vistula Lagoon pelagic community. The place of herring (rather low production and the highest costs of maintenance) in this competition is comparable with the place occupied by mysid shrimp with the lowest production and the lowest cost of maintenance. It seems that Begons’s theory do not fit the system in which several species compete for the same food stock.

This work was granted in part by Center for Ecological Research PAS in Dziekanów and in part by Sea Fisheries Institute in Gdynia.

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Zoocenosis — 2005
 Біорізноманіття та роль зооценозу в природних і антропогенних екосистемах: Матеріали ІІІ Міжнародної наукової конференції. – Д.: Вид-во ДНУ, 2005. – С. 17-19.