Potential Changes in Aquatic Biota in the Period of Global Climate Warming
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Water Resources, Vol. 31, No. 4, 2004, pp. 459464. Translated from Vodnye Resursy, Vol. 31, No. 4, 2004, pp. 498503.Original Russian Text Copyright 2004 by Beznosov, Suzdaleva.
Potential biotic consequences of changes in the tem-perature regime of water bodies due to climate warmingare mostly studied by analyzing long-term data on thestate of natural water bodies. When interpreting theresearch results, it is often difficult to elucidate thecauses of observed phenomena . The questionarises as to whether the observed changes are due to cli-mate warming proper or they result from various atten-dant processes (for example, alterations in the drainagebasin due to a prolonged drought or fires)? In mostcases, the above approach allows us only to recordchanges that have already occurred but not to predictthem based on the knowledge of principal tendencies inthe development of events.
When studying the biota of cooling ponds of ther-moelectric and atomic power stations (TEPS and APS),we obtain a unique opportunity of experimentallyinvestigating the changes that may occur in water bod-ies in the period of climate warming [2, 30]. The stan-dards accepted in the USSR for nature protection rec-ommend that when using natural waters at power plantsfor cooling, an increase in the water temperature incooling ponds should not exceed 5
C in winter and 3
Cin summer . This is approximately the rise in tem-perature that is expected in the middle latitudes in thefirst half of the 21st century. However, the effect ofoperating TEPS and APS on aquatic organisms is mul-tiform. It includes not only the alteration of temperatureregime [19, 27] but also the effects of other factorsassociated with the water used for cooling technicalaggregates (although these factors commonly do notreduce the diversity of flora and fauna in cooling ponds). Therefore, the approach based on observations incooling ponds is not quite adequate if applied to theproblem of climate warming.
EFFECT OF THE RISE IN TEMPERATURE OF THE MEDIUM ON THE COMPOSITION
OF AQUATIC BIOTAPreviously, it was repeatedly stated that the mean
temperature of the surface water in cooling ponds oftencorresponded to the mean temperature of water bodiesin another climatic zone [7, 12]. When planning firstcooling ponds, it was supposed that peculiar islets ofsubtropic and tropic biota would develop in them .Actually, this does not occur. Aquatic communities inheated up water bodies consist of the species character-istic of the given climatic zone . This cannot beexplained only by the short existence of cooling pondsand the difficulty of penetration of southern species intothem. For example, the cooling pond of the hydroelec-tric power station (HEPS) named after R.E. Klasson inthe Moscow Province has existed since 1914, and thecooling ponds of the Shatura and Gorky TEPSs havefunctioned since 1925. The probability of an accidentalentry of subtropic forms in these water bodies duringsuch long periods was sufficiently high.
The possibility of settling of organisms fromanother climatic zone into cooling ponds of the givenclimatic zone is demonstrated by the appearance ofindividual subtropic species [12, 13, 22]. For example,gastropod physella (Physella integra Haldeman) and anaquatic plant vallisneria spiral (Vallisneria spiralis L.)have inhabited many cooling ponds in Russia . How-ever, exotic species are not abundant in them. The exist-ing individual species are likely to be referred to synan-thropic forms [2, 13]. Their northward expansion isassociated not with the rise in temperature but with thedevelopment of a complex of conditions in coolingponds that are specifically favorable for the given spe-cies. Therefore, in common with other synanthropicorganisms, they cannot serve as an example of futurebiotic alterations.
Potential Changes in Aquatic Biotain the Period of Global Climate Warming
V. N. Beznosov* and A. L. Suzdaleva**
* Moscow State University, Leninskie gory, Moscow, 119992 Russia** Technological Branch of Rosenergoatom Concern, ul. Ferganskaya 25, Moscow, 109507 Russia
Received November 26, 2002
The results of investigations of water bodies subjected to constant many-year thermal pollution areproposed to use for the prediction of the consequences of climate warming. General tendencies in changes inthe aquatic biota and the distribution of aquatic organisms under the effect of thermal pollution are establishedby analyzing the materials collected at different cooling ponds of nuclear and thermal power stations.
WATER QUALITY AND PROTECTION:ENVIRONMENTAL ASPECTS
In sea areas subjected to thermal pollution, sub-tropic and tropic species are neither abundant, althoughthe transfer of pelagic larvae by sea currents provides abase for a fast colonization of these areas by the aboveforms. A relatively small number of exotic thermophilicspecies occur at the sites where warm water is dis-charged into sea, as it is observed in continental waterbodies . With this, a significant part of speciesdwells mainly on anthropogenic substrates (underwatersurfaces of hydraulic structures, vessels, and others).Thus, these species are also synanthropic to someextent.
The analysis of research results for cooling pondsshows that in most cases the general composition of thetotality of species inhabiting water bodies subjected tothermal pollution remains unchanged. However, thepopulation and spatial distribution of individual formsmay alter substantially [29, 30]. Dominating speciesbecome scanty, while the species of secondary impor-tance in ecosystems develop more intensely [2, 21];some of these latter become new dominants.
As a rule, psychrophilic organisms do not disappearcompletely . Some species classified as stenothermaldemonstrate the capability of adapting themselves tonew temperature conditions [21, 22]. Even in the tran-spolar cooling pond of the Kola Nuclear Power Station,a significant part of biota could adapt to an increasedtemperature in a shortest stretch of time . Anothercause of conservation of stenothermic forms is thestratification of water bodies in warm seasons, when theeffects of the human-induced rise in the temperature ofthe medium manifest themselves most strongly. As arule, heated up water discharged from power stationsaffects only the upper horizon of the water mass incooling ponds. In this case, psychrophilic stenothermalspecies disappear from the surface water layers but mayremain in the hypolimnion. For example, prior to thestart of operation of the Kalinin NPS, Cyclops strenuusFishcher and Daphnia cristata Sars dominated theplanktonic crustaceans in the epilimnion of LakeUdomlya (the cooling pond of the NPS) in summer.After the power station was put into operation, theabove species moved into the hypolimnion in summer[28, 29]. The dominant of the summer zooplankton inthe surface water layer is now a more eurythermicMesocyclops crassus (Fischer), which previously was asecondary species.
Analysis of the available data on flora and fauna incooling ponds shows that in different climatic zones,the same eurythermal species are getting more signifi-cant [2, 13, 16]. For example, the same species aredominants and subdominants in phytoplankton in thecooling ponds of the Ekibastuz HEPS-1 (NorthernKazakhstan, semiarid zone), the Kursk NPS (forest-steppe zone), the Smolensk and Kalinin NPSs (middlebelt of Russia), the Pechora HEPS (subpolar taigazone), and the Kola NPS (European polar regions).These species are blue-green (Microcystis aeruginosa
Kutz; Aphanizomenon flos-aquae (L.) Ralfs), diatomic(Melosira granulata (Ehr.) Ralfs., Fragillaria crotonen-sis Kitt., Synedra ulna (Nitzsch.) Ehr., S. acus Kutz.,Asterionella formosa Hass), and green algae from thegenera of Oocystis, Ankistrodesmus, and Scenedes-mus. Similar regularities are observed in other taxo-nomic groups of biota in cooling ponds. Consequently,we may suppose that the most likely change in theperiod of climate warming is not the expansion of ther-mophilic forms but an increase in the population ofeurybiontic species and the alteration of their roles inecosystems . The prevalence of the same forms willlevel the differences in flora and fauna in water bodiessituated in adjacent geographical zones. However, aconsiderable part of endemic fauna may survive adapt-ing to new temperature conditions or living in the sub-surface water layers through the warm period of theyear.
ALTERATION OF THE LIFE CYCLES AND SPATIAL DISTRIBUTION OF AQUATIC
ORGANISMS AT INCREASING TEMPERATURE OF THE MEDIUM
Climate warming that manifests itself in increasingmean annual temperature may essentially disturb theseasonal dynamics of weather conditions but would noteliminate it completely. A certain climate is associatedwith not only a definite degree of the biota thermophil-ity but also a certain character of the life cycles of theorganisms existing during the given period. These prop-erties (the response of the organism to the temperaturefactor and the organisms life cycle) cause an ambigu-ous response of the species to changes in climatic con-ditions. For example, an increase in the mean annualtemperature produces a negative effect on thermophilicforms, if this increase disturbs their life cycle .
Analysis of numerous data on the ecology of exist-ing artificially heated up water bodies testifies that theorganisms of different taxonomic groups response sim-ilarly to a temperature increase over a prolonged periodof time (table).
In the middle and high latitudes, most organismsgrow and develop only in summer. Artificial heating upextends the duration of the active life in water bodies.In some cases, the hydrobionts inhabiting the coolingponds of TEPSs and NPSs pass to the year-roundbreedingacyclicity. Presently, due to current climatechanges, similar phenomena are observed in naturalwater bodies .
The increased duration of the active phase may, inits turn, cause a complex of phenomena.
Alteration of the size distributions in populations.
The effect of the temperature rise on the dimensions ofaquatic organisms is quite ambiguous. The extension ofthe vegetation period entails an increase in the meanand maximal sizes of some species (for example, thesizes of amphipods , larvae of chironomids ,
POTENTIAL CHANGES IN AQUATIC BIOTA 461
and fish ). In this case, the increasing size and weightof species are due to both an increased period of theorganisms individual development and an increasedforage reserve due to a longer period of development oforganisms used as nourishment. However, other organ-isms, also inhabiting heated up water bodies, decreasein size. This is due to the fact that the temperature rise,while accelerating the development of the organism,provides the onset of its maturity at a smaller size. Forexample, in the cooling ponds of Ukrainian TEPSs, anincrease in the rate of growth of oligochaetas ,mysids , and cladocera  went together with adecrease in their size. In fish, the onset of sexual matu-rity is recorded at an earlier age and smaller size .
An increase in temperature leads not only tochanges in the size of organisms but, sometimes, to cer-tain morphological changes. For example, submergedwater plants are characterized by an increased size ofleaves . Various fish inhabiting artificially heatedup water bodies have alterations in the structure of fins,the number of vertebras, and the number of scales alongthe lateral line . Probably, some of these morpho-logical alterations are of adaptive nature. For example,there is an opinion that the decreased numbers of scalesalong the lateral line and of rays in the pelvic fin areadaptation to the movement in a warmer and, thus,more viscous water . Again, it is known that the tem-perature increase itself is only one of the factors caus-ing various anomalies in the organisms' development. This allows us to suppose that climate warmingwould lead to an increased percentage of species withvarious anomalies in their constitution.
Alteration of the age structure of populations.
Increased temperature of the medium entails an exten-sion of the period of breeding and the occurrence ofadditional generations in different groups of hydro-bionts (table). This leads to changes in the age structureof populations, in particular, to their rejuvenation,i.e., to increased shares of young species in populations.
Disturbance of the cycles of breeding and gameto-genesis.
Changes in the temperature of the medium areoften a signal for intensification of various physio-logical processes. Disturbances in the common courseof temperature conditions lead to disturbances in thenormal course of physiological processes, causing sim-ilar negative processes in taxonomically distant spe-cies. In different fish species, an increase in tempera-ture not only changes the time of development of sexualcells but also leads to sex reversion and hermaphrodit-ism; the rhythm of breeding is disturbed. This oftenleads even to the resorption of sexual cells, because ofwhich a considerable number of species do not partici-pate in reproduction [11, 15, 34]. For example, theincreased duration of the warm period in the coolingpond of the Moldavian HEPS has led to a disturbanceof hametogenesis even in such thermophilic species ascrucian carp; some specimens have no sexual products. Also, the earlier maturity of sexual cells may pro-duce a discrepancy between the fish readiness tospawning and the conditions in spawning biotopes.This leads to disorderly spawning with further destruc-tion of spawn .
Also, the extension of the vegetation period and thedisturbance in the life cycle entail a decrease in the pop-ulation of heterotopic insects. Intensification of thedevelopment of aquatic larvae of insects under the con-ditions of increased temperature results in the prema-ture escape of imago, when the conditions in the terres-trial biotopes are unfavorable. This was recorded, forexample, in the case of chironomid larvae, which arenot referred to psychrophilic species [1, 21]. Similarphenomena associated with the current climate warm-ing are recorded in water bodies with the natural tem-perature regime. For example, autumn increase in tem-perature entails the development of resting ova in somezooplankton species, but the hatched out fry fails tomature before the onset of winter and dies .
Changes in the life cycles of aquatic organisms under the effect of increased temperature of the medium
Group of organisms Response to the increase in the temperature of the medium Source
Phytoplankton Extension of vegetation periods and increase in biomass [21, 25]Microphytobentos Extension of vegetation periods and increase in biomass [9, 25]Macrophytes Extension of vegetation periods, earlier onset