A Model of Structural Interaction of Biophysical Factors during Invasive and Hydrological Changes in the Biosystem of the Caspian Sea

Abstract

Prediction of biophysical processes under the conditions of a rapid change in the composition of the interacting components of a biosystem requires flexible approaches and a logical analysis of the direction, time, and level of strength of systemic interactions. It is unrealistic to construct a predictive model based on the methods developed by the author for organizing hybrid computing structures for a key component of a biophysical system (such a link is usually considered the most valuable population for the economy) without a scheme for the mutual influence of factors acting on the biotic environment. Direct interaction of the “predator–prey,” “parasite–host,” or “resource–consumer” equations does not fully describe the dynamics of a real biosystem, especially after invasions of aggressive species. This article is devoted to the application of cognitive formalisms of model structuring of conceptual information about the interaction of natural and anthropogenic factors based on the development of graph theory methods. The purpose of the work is to mathematically formalize how a change in one factor will affect the state of other components of biosystems. The new model allowed us to explore mediated interactions that are not always immediately visible, but are critical. To understand the processes after invasions, we will develop a method for analyzing the distribution of indirect effects in biosystems on directly disconnected components. The results of computational studies are logically followed step by step by a theoretical interpretation of the observed changes in the behavior of the model trajectory. A formal analysis of impulses in a sign digraph in the context of the studied situation of bioresources degradation in the Caspian Sea after a large-scale intervention in the biosystem and due to the penetration of the harmful stenophora Mnemiopsis leidyi has been carried out. It is shown that the choice of a mathematical approach to the description of the situation is successfully based on the results of the analysis of cycles of influence of ecological interlinkages. Previously unaccounted-for links that led to the low efficiency of attempts to artificially reproduce bioresources were revealed. It was confirmed on the basis of the impulse process in the cognitive graph that the purposeful introduction of alien mollusks from the Black Sea into the Caspian Sea to increase the biomass of bottom fauna was one of the factors in the degradation of valuable biological resources with an increase in the level of the Caspian Sea. Alien mollusks (Abra ovata, Mytilaster lineatus) replaced the native benthic fauna. At the end of the 1980s, the salinity of the Northern Caspian decreased; then, the invaders adapted to more saline water drastically reduced the biomass. Competition in the trophic chains of unstable biosystems should not be aggravated in order to increase their productivity for valuable populations. The mass release of juveniles of valuable fish is not a panacea for the degradation of the entire Caspian biosystem. The results of the impact distribution analysis in the cognitive graph are applied to the original hybrid dynamic system for modeling the efficiency of artificial reproduction of the Caspian sturgeon. The model showed that degradation of the Caspian biosystem could have been avoided as early as 2005.