Population Collapse of the Crayfish Orconectes virilis in Response to Experimental Whole-Lake Acidification

1989 ◽  
Vol 46 (6) ◽  
pp. 910-922 ◽  
Author(s):  
I. J. Davies
Keyword(s):  
Population Size ◽  
Population Decline ◽  
Fish Predation ◽  
Reference Population ◽  
Lake Acidification ◽  
Orconectes Virilis ◽  
Microsporidian Parasite ◽  
Experimental Lakes Area ◽  
Recruitment Failure ◽  
Northwestern Ontario

A population of Orconectes virilis in Lake 223 at the Experimental Lakes Area, northwestern Ontario, was monitored from 1976 to 1982 during an acidification experiment. O. virilis from nearby Lake 240 served as a reference population. Crayfish abundance remained stable as average epilimnion pH was gradually lowered from 6.49 (1976) to 5.93 (1978). In 1979 (pH 5.64) recruitment of young was poor and the overall population size [Formula: see text] fell from 105 800 to 60 300 animals. The decline continued in the complete absence of recruitment during 1980 (pH 5.59, [Formula: see text] and 1981 (pH 5.02, [Formula: see text]. Few crayfish survived until the spring of 1982. None were present from mid-summer 1982 to fall 1983 (average pH 5.09 to 5.13). Hatchling mortality and some egg loss appeared to have been the causes of recruitment failure. Acidification also produced a noticeable softening in the carapace of all intermoult crayfish. Growth, mortality, behaviour, and the basic reproductive functions of juvenile and adult crayfish did not change in response to acidification. Fish predation and the incidence of a microsporidian parasite apparently contributed little to the population decline.

Reproductive Impairment of the Crayfish Orconectes virilis in Response to Acidification of Lake 223

1987 ◽  
Vol 44 (S1) ◽  
pp. s97-s106 ◽  
Author(s):  
Robert L. France
Keyword(s):  
Egg Production ◽  
Lake Acidification ◽  
Orconectes Virilis ◽  
Experimental Lakes Area ◽  
Rate Of Development ◽  
Northwestern Ontario ◽  
Reproductive Impairment ◽  
Cement Compound ◽  
Acidification Of Lake ◽  
Egg Capsule

Reproductive characteristics of crayfish (Orconectes virilis) were examined during 1979–81 in four small Canadian Shield basins in the Experimental Lakes Area, northwestern Ontario. One of these lakes, Lake 223 (L223), has been experimentally acidified since 1976. Egg resorption, fertilization, and rate of development were not seriously affected by lake acidification to pH 5.1. Incomplete hardening of the glair–cement compound forming the egg capsule membrane and stalk resulted in a loss of eggs from the pleopods, causing the L223 population to suffer decreased reproduction. On an egg production basis, the reproductive impairment (defined as the % decrease in number of viable eggs prior to hatching) in reference populations averaged 3.2 ± 1.8 (95% C.I.) compared to levels of 18.7, 36.2, and 29.4% during 1979–81 in L223 at pH 5.2–5.6. Direct mortality of eggs accounted for little of the reduced natality in the L223 population and did not occur in reference lakes. Loss of crayfish populations exposed to lake acidification will probably result from reproductive failure before lake water becomes acid enough to be directly toxic to mature crayfish.

Measurements of Specific Rates of Net Methyl Mercury Production in the Water Column and Surface Sediments of Acidified and Circumneutral Lakes

1987 ◽  
Vol 44 (4) ◽  
pp. 750-757 ◽  
Author(s):  
Luying Xun ◽  
N. E. R. Campbell ◽  
John W. M. Rudd
Keyword(s):  
Water Column ◽  
Water Samples ◽  
Methyl Mercury ◽  
Lake Acidification ◽  
Sediment Surface ◽  
Mercury Methylation ◽  
Experimental Lakes Area ◽  
Northwestern Ontario ◽  
Decreasing Ph ◽  
Mercury Production

Specific rates of mercury methylation and demethylation were determined for water and surficial sediment samples taken from several lakes located in the Experimental Lakes Area, northwestern Ontario. Specific rates of mercury methylation were found to increase with decreasing pH in epilimnetic water samples in which pH was adjusted prior to incubation and in epilimnetic water samples taken from lakes of different pH. Reduction of pH also increased methyl mercury production at the sediment surface. Both increases and decreases in pH reduced specific rates of mercury demethylation. However, these changes were smaller than for methylation. Proportionally, specific rates of methylation increased faster than increasing concentrations of Hg2+, while specific rates of mercury demethylation increased linearly with increasing concentrations of methyl mercury. Overall, this study predicts that the net rate of methyl mercury production in the water column and at the sediment–water surface will increase as a result of lake acidification, and this may at least partially explain why the mercury concentration of fish appears to increase during lake acidification.

Decreased Survival and Calcium Uptake by the Crayfish Orconectes virilis in Low pH

1980 ◽  
Vol 37 (3) ◽  
pp. 364-372 ◽  
Author(s):  
D. F. Malley
Keyword(s):  
Acid Rain ◽  
Lake Water ◽  
Calcium Uptake ◽  
Physiological Responses ◽  
Low Ph ◽  
Lake Acidification ◽  
Orconectes Virilis ◽  
Molt Cycle ◽  
Experimental Lakes Area ◽  
Acidification Of Lake

As part of a study of the effects of the experimental whole-lake acidification of Lake 223 in the Experimental Lakes Area on the population of the crayfish Orconectes virilis physiological responses of adults from this population to low pH were examined in the laboratory. Crayfish survived pH 4.0 for 10 d when they were not moulting but suffered mortality when they were in postmolt stages. Postmolt crayfish held at pH 5.0 for 10 d survived but showed slower progression of molt cycle stages and of calcification of the exoskeleton than individuals held at pH 6.0 or in lake water at about pH 6.7. Uptake of Ca++ by postmolt crayfish measured by the use of 45Ca as a tracer was inhibited by pH below 5.75 and ceased altogether below pH 4.0 when these levels of acidity were applied acutely.Key words: Orconectes virilis, crayfish, molt cycle, mortality, pH, calcification, postmolt calcium uptake, acid rain, lake acidification

Survival and Development of Lake Trout (Salvelinus namaycush) embryos in an Acidified Lake in Northwestern Ontario

1990 ◽  
Vol 47 (2) ◽  
pp. 236-243 ◽  
Author(s):  
L. C. Mohr ◽  
K. H. Mills ◽  
J. F. Klaverkamp
Keyword(s):  
Lake Trout ◽  
Salvelinus Namaycush ◽  
Experimental Lakes Area ◽  
Embryo Survival ◽  
Embryo Mortality ◽  
Recruitment Failure ◽  
Northwestern Ontario ◽  
Survival And Development ◽  
Population Recruitment ◽  
Experimental Acidification

Survival and development of lake trout (Salvelinus namaycush) embryos from L223 in the Experimental Lakes Area, northwestern Ontario, were evaluated from 1979 (pH 5.6) to 1982 (pH 5.1). Survival of L223 embryos was not significantly correlated to lake pH during experimental acidification. Also, embryo mortality in L223 was not significantly different from that of lake trout embryos in two reference lakes, L224 and L468. Survival of L223 embryos was not improved when they were incubated in nonacidified lakes. Embryo mortality was highest in all lakes (33–81%) within 15 d of fertilization. Mortality was negligible from Day 15 until the termination of the seasonal observations (Day 120 or 150). High variability in embryo survival existed between individual females within a single lake. The mean size of eggs from L223 lake trout decreased significantly from 1979 to 1982. Recruitment failures occurred in L223 from 1980 to 1982. We hypothesize that lake trout recruitment failure in L223 occurred between the posthatching period (spring) and actual recruitment into the population as young-of-the-year (fall) and that embryo mortality in this lake was not critical to population recruitment.

Calcium and Trace Metal Composition of Crayfish (Orconectes virilis) in Relation to Experimental Lake Acidification

1987 ◽  
Vol 44 (S1) ◽  
pp. s107-s113 ◽  
Author(s):  
Robert L. France
Keyword(s):  
Trace Metal ◽  
Dry Weight ◽  
Lake Acidification ◽  
Orconectes Virilis ◽  
Tissue Concentrations ◽  
Experimental Lakes Area ◽  
Background Levels ◽  
Metal Composition ◽  
Mn Content ◽  
Subjective Estimates

Subjective estimates indicate that the carapaces of crayfish from experimentally acidified Lake 223 (pH 5.4–5.6) in the Experimental Lakes Area are becoming less rigid. Decreased carapace rigidity was inversely correlated with carapace dry weight and Ca++ content. Orconectes virilis from L223 have 25–35% less Ca++ in their exoskeletons (mean % dry wt ± SE = 13.90 ± 0.54) than do those from reference lakes (19.82 ± 0.33, 20.34 ± 0.63, and 22.18 ± 0.51). Lake 223 crayfish have accumulated higher tissue concentrations of both Mn (L223 value of 240 μg∙g−1 dry wt compared to a mean ± SE for reference populations of 48 ± 11 μg∙g−1 dry wt) and Hg(L223 value of 0.52 μg∙g−1 dry wt compared to reference mean of 0.26 ± 0.05 μg∙g−1 dry wt). Mn content of carapaces in crayfish from acidified L223 were also elevated threefold over background levels for the ELA region.

Relationship of Crayfish (Orconectes virilis) Growth to Population Abundance and System Productivity in Small Oligotrophic Lakes in the Experimental Lakes Area, Northwestern Ontario

1985 ◽  
Vol 42 (6) ◽  
pp. 1096-1102 ◽  
Author(s):  
R. L. France
Keyword(s):  
Sexual Maturity ◽  
Egg Production ◽  
Maximum Size ◽  
Reproductive Capacity ◽  
Phytoplankton Production ◽  
Orconectes Virilis ◽  
Experimental Lakes Area ◽  
System Productivity ◽  
Frequency Distributions ◽  
Northwestern Ontario

Crayfish growth in four lakes in the Experimental Lakes Area (ELA) was examined by analysis of size-frequency distributions, molt increment data, and calculation of instantaneous growth and mean size at onset of sexual maturity. Orconectes virilis growth rates at ELA are only 27–38% of those reported for other areas. Growth varied both among study lakes and between years. Higher temperatures and a longer growing season during 1980 increased growth an average of 12% over that of the preceding year. Crayfish growth and maximum size in four to six lakes were significantly correlated with phytoplankton production and chlorophyll a concentration. Growth regulated both the number of age 1 animals attaining sexual maturity and the per capita egg production, and was also directly related to the proportion of mature females that were fertilized. I believe population regulation is mediated through alterations in reproductive capacity that is correlated with system productivity.

Experimental reintroduction of the crayfish species Orconectes virilis into formerly acidified Lake 302S (Experimental Lakes Area, Canada)This paper is part of the series “Forty Years of Aquatic Research at the Experimental Lakes Area”.

2009 ◽  
Vol 66 (11) ◽  
pp. 1892-1902 ◽  
Author(s):  
Iain D. Phillips ◽  
Rolf D. Vinebrooke ◽  
Michael A. Turner
Keyword(s):  
Fish Predation ◽  
Boreal Lakes ◽  
Ecological Impacts ◽  
Total Biomass ◽  
Productive Capacity ◽  
Orconectes Virilis ◽  
Experimental Lakes Area ◽  
Important Species ◽  
Isotopic Analyses ◽  
Control Versus

Reintroduction of functionally important species is considered a key strategy for restoring damaged ecosystems. However, the sudden reappearance of an extirpated species may have adverse ecological impacts, degrading ecosystem services. Therefore, we experimentally reintroduced the crayfish Orconectes virilis into a biologically recovering, formerly acidified Boreal Shield lake (Lake 302S, Experimental Lakes Area, Canada) to determine its effect on the littoral food web following a 17-year absence. In June 2004, a single-factor experimental design consisting of two treatment levels (crayfish-less control versus 1.8 introduced crayfish·m–2) was replicated five times for a total of 10 littoral cages (4 m2). Orconectes virilis significantly (P < 0.05) suppressed the total biomass of other benthic invertebrates by 70% primarily because of declines in larval damselflies and midges. In addition, crayfish reduced periphytic biomass by 90% (P < 0.001). Stable isotopic analyses of the mesocosm food webs further indicated that O. virilis likely functioned as an omnivore, exerting direct and possibly indirect effects on other invertebrates and periphyton. Our findings highlight how the reintroduction of O. virilis must be balanced with adequate fish predation to prevent this species from becoming an invader and negatively affecting the productive capacity of boreal lakes.

scholarly journals Cost-efficient factors in local public spending: Detecting relationships between local environments, population size and urban area category

2021 ◽  
pp. 239980832110038
Author(s):  
Hiroki Baba ◽  
Yasushi Asami
Keyword(s):  
Population Size ◽  
Urban Area ◽  
Urban Areas ◽  
Local Governments ◽  
Statistical Significance ◽  
Population Decline ◽  
Public Spending ◽  
Local Environment ◽  
Environment Factors ◽  
Major Factors

This study examines regional differences in local environment factors to better understand the sustainability of local governments indexed by per capita public spending. Under the condition of heterogeneous population size, we examine how factor characteristics differ depending on the spatial context represented by the urban area category. By employing a Cobb–Douglas cost function with congestion effects on public service provision, the estimated factors enable us to articulate major factors and differences in cost-efficiency between urban area categories. We found that statistical significance and even the signatures of local environment factors differ depending on the urban employment area category. Regarding factors such as the ratios of employees in secondary and tertiary industries, these did not tend to be statistically significant in small-sized urban areas, while small-sized cities in large-sized urban areas were likely to gain confidence intervals. Moreover, we did not observe any statistical significance for the ratio of elderly people due to the balance of spending between national and local governments. These findings could contribute to sustainable management of cities in the advent of population decline.

scholarly journals Large numbers of vertebrates began rapid population decline in the late 19th century

2016 ◽  
Vol 113 (49) ◽  
pp. 14079-14084 ◽  
Author(s):  
Haipeng Li ◽  
Jinggong Xiang-Yu ◽  
Guangyi Dai ◽  
Zhili Gu ◽  
Chen Ming ◽  
...  
Keyword(s):  
Genetic Diversity ◽  
Population Size ◽  
Threatened Species ◽  
Driving Forces ◽  
Population Decline ◽  
Cumulative Effect ◽  
Extinction Time ◽  
Time Period ◽  
Large Numbers ◽  
The Difference

Accelerated losses of biodiversity are a hallmark of the current era. Large declines of population size have been widely observed and currently 22,176 species are threatened by extinction. The time at which a threatened species began rapid population decline (RPD) and the rate of RPD provide important clues about the driving forces of population decline and anticipated extinction time. However, these parameters remain unknown for the vast majority of threatened species. Here we analyzed the genetic diversity data of nuclear and mitochondrial loci of 2,764 vertebrate species and found that the mean genetic diversity is lower in threatened species than in related nonthreatened species. Our coalescence-based modeling suggests that in many threatened species the RPD began ∼123 y ago (a 95% confidence interval of 20–260 y). This estimated date coincides with widespread industrialization and a profound change in global living ecosystems over the past two centuries. On average the population size declined by ∼25% every 10 y in a threatened species, and the population size was reduced to ∼5% of its ancestral size. Moreover, the ancestral size of threatened species was, on average, ∼22% smaller than that of nonthreatened species. Because the time period of RPD is short, the cumulative effect of RPD on genetic diversity is still not strong, so that the smaller ancestral size of threatened species may be the major cause of their reduced genetic diversity; RPD explains 24.1–37.5% of the difference in genetic diversity between threatened and nonthreatened species.

Land water linkages: influences of riparian deforestation on lake thermocline depth and possible consequences for cold stenotherms

1997 ◽  
Vol 54 (6) ◽  
pp. 1299-1305 ◽  
Author(s):  
Robert France
Keyword(s):  
Thermal Stratification ◽  
Lake Trout ◽  
Salvelinus Namaycush ◽  
Thermocline Depth ◽  
Experimental Lakes Area ◽  
Northwestern Ontario ◽  
Riparian Trees ◽  
Tree Removal ◽  
Riparian Tree ◽  
Land Water

The purpose of the present study was to determine if riparian deforestation would expose lake surfaces to stronger winds and therefore bring about deepening of thermoclines and resulting habitat losses for cold stenotherms such as lake trout (Salvelinus namaycush). Removal of protective riparian trees through wind blowdown and two wildfires was found to triple the overwater windspeeds and produce thermocline deepening in two lakes at the Experimental Lakes Area. A survey of thermal stratification patterns in 63 northwestern Ontario lakes showed that lakes around which riparian trees had been removed a decade before through either clearcutting or by a wildfire were found to have thermocline depths over 2 m deeper per unit fetch length compared with lakes surrounded by mature forests. Riparian tree removal will therefore exacerbate hypolimnion habitat losses for cold stenotherms that have already been documented to be occurring as a result of lake acidification, eutrophication, and climate warming.

Sign in / Sign up

Export Citation Format

Share Document