Temporal settlement patterns of larvae of the broadcast spawning reef coral Favites chinensis and the broadcast spawning and brooding reef coral Goniastrea aspera from Okinawa, Japan

The faviid corals, Favites chinensis and Goniastrea aspera are widely distributed in the Indo-Pacific region. Both corals are hermaphroditic broadcast spawners, but G. aspera is also known to brood planula larvae in Okinawa. This study investigated the temporal settlement patterns of planula larvae of the scleractinian corals F. chinensis and G. aspera that developed from spawned gametes, and planula release and settlement of brooded larvae of G. aspera from Okinawa, Japan. Some of the broadcast-spawned larvae of F. chinensis and G. aspera had very short pre-competency periods of 1–2 and 2–3 days after spawning, and relatively long maximum settlement-competency periods of 56–63 and 63–70 days after spawning, respectively. These pre-competency periods are among the shortest reported for larvae of broadcast spawning coral species, and appear to be negatively correlated with seawater temperature. F. chinensis larvae tended to settle rapidly with 34–39% of larvae settling in the first week after spawning, while broadcast-spawned G. aspera larvae had a slower settlement pattern with 11–15% of larvae settling in the first week after spawning. Brooded larvae of G. aspera settled more rapidly, with settlement rates of 27–31% within the first 24 h and 45–65% within the first week after the start of the experiment. The production of planula larvae with rapid settlement capabilities may enable F. chinensis and G. aspera to establish and maintain populations in shallow reef sites at Okinawa. The release of the brooded planulae for up to 2 months may explain why G. aspera is locally more dominant on shallow reefs in Okinawa than F. chinensis. On a broader scale, the longer settlement competency periods of some of the broadcast-spawned larvae of these species increase their potential for longer-distance dispersal and may partly explain the wide biogeographic distribution of these species in the Indo-Pacific region.     

Fish assemblage structure in urban streams of Puerto Rico: the importance of reach- and catchment-scale abiotic factors

Cotylorhiza tuberculata is a common symbiotic scyphozoan in the Mediterranean Sea. The medusae occur in extremely high abundances in enclosed coastal areas in the Mediterranean Sea. Previous laboratory experiments identified thermal control on its early life stages as the driver of medusa blooms. In the present study, new ecological aspects were tested in laboratory experiments that support the pelagic population success of this zooxanthellate jellyfish. We hypothesized that planulae larvae would have no settlement preference among substrates and that temperature would affect ephyra development, ingestion rates and daily ration. The polyp budding rate and the onset of symbiosis with zooxanthellae also were investigated. Transmission electron microscopy revealed that zooxanthella infection occurred by the polyp stage. Our results showing no substrate selectivity by planulae and high polyp budding rates in high temperatures suggest increased benthic polyp populations, which would lead to higher medusa abundances. Rates of transition from ephyrae to medusae and the feeding of early medusa stages also increased with temperature. Continuing changes in coastal ecosystems such as future climate warming and marine construction may lead to increased populations of jellyfish to the detriment of fish globally.     

Effects of salinity and temperature on the recruitment of Aurelia coerulea planulae

The recruitment of scyphomedusae planulae to the benthic polyp stage is important for population size and may be affected under projected climate change scenarios. In a laboratory study, we determined the combined effects of elevated temperature and reduced salinity on the behaviour, survival and settlement of Aurelia coerulea planulae. Three temperature levels (21, 24 and 27°C) and two salinity levels (31 and 22) were used. Reduced salinity had a significant negative effect on the swimming behaviour and settlement of A. coerulea planulae. The planulae moved quickly and preferred to settle under ambient salinity conditions. The settlement rate of A. coerulea planulae was high during the current ambient summer temperature (24°C), and elevated temperature increased the mortality rate and reduced their settlement rate. A. coerulea planulae were significantly smaller under the combined conditions of elevated temperature and reduced salinity. Our study provides information on the response of A. coerulea planulae to temperature and salinity, which is helpful for understanding how environmental factors will influence the recruitment dynamics of A. coerulea.     

A low-molecular weight factor from colonial hydroids affects body proportioning and cell differentiation

Treatment of metamorphosing planulae of Hydractinia echinata with proportion altering factor (PAF) causes oversizing in the hypostome of developing primary polyps. With increasing concentrations more specimens fail to acquire the appearance of a primary polyp but remain as cones lacking tentacles. Yet, such specimens are true primary polyps as they contain neurons of RF-amide-like immunoreactivity that are typical of the polyp stage. Numbers of RF-amide-positive cells are increased up to 2.5 times compared with the normal value. In intact Hydra vulgaris, PAF increases the number of neurons that differentiate from cycling precursor cells, or even from stem cells. The effect is dose dependent.     

Density-dependent regulation of natural and laboratory rotifer populations

Density-dependent regulation of abundance is fundamentally important in the dynamics of most animal populations. Density effects, however, have rarely been quantified in natural populations, so population models typically have a large uncertainty in their predictions. We used models generated from time series analysis to explore the form and strength of density-dependence in several natural rotifer populations. Population growth rate (r) decreased linearly or non-linearly with increased population density, depending on the rotifer species. Density effects in natural populations reduced r to 0 at densities of 1–10 l^–1 for 8 of the 9 rotifer species investigated. The sensitivities of these species to density effects appeared normally distributed, with a mean r=0 density of 2.3 l^–1 and a standard deviation of 1.9. Brachionus rotundiformis was the outlier with 10–100× higher density tolerance. Density effects in laboratory rotifer populations reduced r to 0 at population densities of 10–100 ml^–1, which is 10⁴ higher than densities in natural populations. Density effects in laboratory populations are due to food limitation, autotoxicity or to their combined effects. Experiments with B. rotundiformis demonstrated the absence of autotoxicity at densities as high as 865 ml^–1, a much higher density than observed in natural populations. It is, therefore, likely that food limitation rather than autotoxicity plays a major role in regulating natural rotifer populations.     

Studying allozyme variation in sexual and apomictic <Emphasis Type="Italic">Taraxacum</Emphasis> and <Emphasis Type="Italic">Pilosella</Emphasis> (Asteraceae) populations

Allozyme spectra of peroxidase, esterase, superoxid dismutase, tyrosinase, alcohol dehydrogenase, lactate dehydrogenase, and acid phosphatase were examined in populations of sexual (Taraxacum serotinum and Pilosella echioides) and apomictic (T. officinale and P. officinarum) plant species. The heterozygosity in these populations (0.455–0.620) proved to be considerably higher than the average level characteristic of plant populations (0.058–0.185). The populations examined did not differ in the mean phenotype number , i.e., they exhibited the same diversity (3.188–3.380). The proportion of rare phenotypes h also did not differ between the sexual and apomictic species of the same genus, whereas this parameter in the Pilosella populations (0.150–0.174) was significantly higher than in the Taraxacum ones (0.093–0.114). The populations were characterized by numerous isozyme spectra (more than 11 per populations) and displayed multiple allelism (the mean allele frequency was 3.63–4.38 per locus). They exhibited a high percentage of rare (occurring at a frequency lower than 5%) spectra (35–80%). This indicates that agamic complexes, to which these populations belong, may have a more complicated genetic structure of both apomictic and sexual populations than the species that do not belong to agamic complexes.Translated from Genetika, Vol. 41, No. 2, 2005, pp. 203–215.Original Russian Text Copyright © 2005 by Kashin, Anfalov, Demochko.     

Metamorphosis and acquisition of symbiotic algae in planula larvae and primary polyps of Acropora spp.

Coral planulae settle, then metamorphose and form polyps. This study examined the morphological process of metamorphosis from planulae into primary polyps in the scleractinian corals Acropora nobilis and Acropora microphthalma, using the cnidarian neuropeptide Hym-248. These two species release eggs that do not contain Symbiodinium. The mode of acquisition of freshly isolated Symbiodinium (zooxanthellae) (FIZ) by the non-symbiotic polyp was also examined. Non-Hym-248 treated swimming Acropora planulae did not develop blastopore, mesenteries or coelenteron until the induction of metamorphosis 16 days after fertilization. The oral pore was formed by invagination of the epidermal layer after formation of the coelenteron in metamorphosing polyps. At 3 days after settlement and metamorphosis, primary polyps exposed to FIZ established symbioses with the Symbiodinium. Two–four days after exposure to FIZ, the distribution of Symbiodinium was limited to the gastrodermis of the pharynx and basal part of the polyps. Eight–ten days after exposure to FIZ, Symbiodinium were present in gastrodermal cells throughout the polyps.     

Substrate preferences of scyphozoan <Emphasis Type="Italic">Aurelia labiata</Emphasis> polyps among common dock-building materials

New habitat on proliferating marine construction may increase jellyfish polyp populations, and thereby increase jellyfish populations worldwide. In this investigation, we examined planula settlement and polyp immigration rates of the scyphozoan Aurelia labiata Chamisso & Eysenhardt, 1821 on six common dock-building materials. The planulae and polyps preferred plastics (expanded polystyrenes, low and high density polyethylene) to rubber and treated wood when choosing habitat on man-made surfaces. Substrate surface texture and the presence/absence of anti-fouling chemicals are discussed as possible causes for these substrate preferences. This study illustrates the potential effects of different man-made structures on jellyfish populations, and provides useful information to coastal managers and port authorities for reduction of biofouling and jellyfish bloom effects. Guest editors: K. A. Pitt & J. E. Purcell Jellyfish Blooms: Causes, Consequences, and Recent Advances     

Pattern of serotonin‐like immunoreactive cells in scyphozoan and hydrozoan planulae and their relation to settlement

The planulae of almost all investigated cnidarian species possess neuron‐like cells. The distribution of these cells is usually uneven throughout the long axis of the planula. The majority of these cells are located in the anterior half of the planula body. Scyphozoan planulae, as well as anthozoan planulae, have a sensory structure at the anterior pole called an apical organ, which is believed to take part in metamorphosis induction. Hydrozoan planulae also possess sensory cells. It has been previously shown in several cnidarian larvae that their neuronal cells contain the neurotransmitter, serotonin. The present study describes the peculiarities of serotonin‐like immunoreactive cells in Aurelia aurita (Scyphozoa) and Gonothyraea loveni (Hydrozoa) planulae. We show that several cells in the presumptive apical organ of A. aurita are immunoreactive to antibodies against serotonin, while G. loveni planulae have an accumulation of serotonin‐positive cells near the anterior pole. Additional serotonin‐like immunoreactive cells are found in the lateral ectoderm of both planulae. Treatment of A. aurita and G. loveni planulae with serotonin or its blockers show that serotonin is likely involved in the initiation of planula settlement.     

Neural system reorganization during metamorphosis in the planula larva of Clava multicornis (Hydrozoa, Cnidaria)

The planula larva of the hydroid Clava multicornis (Forskål, 1775) has a complex nervous system, characterized by the presence of distinct, anteriorly concentrated peptidergic populations of amidated neurons, presumably involved in the detection of environmental stimuli and metamorphic signals. Differently from other hydrozoan larvae in C. multicornis planulae GLW-positive cells with putative sensory role have a peculiar dome-shaped forefront organization, followed by a belt of RF-positive nerve cells. By immunohistochemistry, we investigated the transformation of the peptidergic (GLW-amide and RF-amide) larval neuroanatomy at different stages of metamorphosis and the subsequent development of the primary polyp nervous system. By terminal transferase-mediated dUTP nick end-labeling assay, apoptotic nuclei were first identified in the anterior pole of the settled larva, in the same region occupied by GLW-amide positive putative sensory cells. In primary polyps, GLW-amide positive signals first encircled the hypostome area, later extending downwards along the polyp column or upwards over the hypostome dome, whereas RF-amide positive sensory cells initially appeared at the tentacles base to later extend in the tentacles and the polyp column. In spite of the possession of distinct neuroanatomies, different cnidarian planulae may share common developmental mechanisms underlying metamorphosis, including apoptosis and de novo differentiation. Our data confirm the hypothesis that the developmental dynamics of tissue rearrangements may be not uniform across different taxa.     

Carbon dioxide exchange in Cladina lichens from subarctic and temperate habitats

Summary The survival potential of lichens in a given habitat is determined by the response of CO₂ exchange to photosynthetically active radiation (PhAR), thallus temperature, and thallus relative water content (RWC). Therefore morphologically similar lichens from contrasting climatic environments 1) should differ in their CO₂ exchange responses, and 2) these differences should reflect adaptations to their climatic regimes. The CO₂ exchange responses of a subarctic (55°N, 67°W) Cladina stellaris (Opiz) Brodo population and a temperate (29°N, 82°W) Cladina evansii (Abb.) Hale and W. Culb, population were used to test these two related hypotheses.Infrared gas analysis with lichens collected in September–October 1975 established that the two populations differed in their responses to incident PhAR, thallus temperature, and thallus RWC. Net photosynthesis in C. stellaris had an optimum at a lower temperature and a greater relative photosynthetic capacity at low temperatures than did C. evansii. Cladina evansii maintained net photosynthesis above 35°C thallus temperature; C. stellaris did not. In both species the optimum temperature for net photosynthesis increased with increasing irradiance. The C. stellaris light saturation point was consistently lower than that of C. evansii. Both species had maximal rates of net photosynthesis at 70–80% relative water content. In C. evansii the CO₂ exchange rates, expressed as percentages of the maximum rate, declined more rapidly under suboptimal conditions. The absolute CO₂ exchange rates of C. evansii were greater than those of C. stellaris. At 20°C and 90–95% RWC, resaturation respiration occurred in both species and continued until 6–7 h after wetting.Contrasts in the temporal patterns of thallus condition at each collection site suggest that not all differences in the two response surfaces reflect climatic adaptation. The two populations appear well adapted to incident PhAR and thallus temperature regimes but the 70–80% RWC optimum for net photosynthesis common to both species is puzzling since their water regimes differ markedly. The overall adaptedness of the CO₂ exchange responses in the two species cannot be judged without a comprehensive quantitative analysis of carbon balance under differing climatic regimes.     

Larval development of certain gamete-spawning scleractinian corals

Embryogenesis and larval development were documented in 19 species of hermatypic scleractinians which release gametes during the summer coral spawning season on the Great Barrier Reef. Cleavage of fertilized eggs began approximately 2 h after spawning in all species, and gave rise to blastulae after 7–10 h. Endoderm formation in Platygyra sinensis was by invagination, and this appeared to occur in all species studied. All species observed at 36 h after spawing were mobile and full mobility was reached by 48 h. Settlement of planulae placed in aquaria occurred between 4 and 7 days after fertilization. These results suggest that larval corals produced by most gamete-releasing coral species are likely to be dispersed away from the parent reef.     

Effect of mono- and divalent cations on polyp morphogenesis in isolated tentacles of Aurelia aurita(Scyphozoa)

Tentacles excised from syphistoma polyps of Aurelia aurita undergo rapid regeneration to form whole polyps following exposure to an excess or absence of specific ions. It has been shown that a 12–18 h exposure of isolated tentacles to 58 mM excess of Cs⁺ results in a rapid firing of nematocysts, followed by an accelerated, synchronous polyp morphogenesis. Absence of Mgt²⁺ from the culture solution for 4–24 h also led to an accelerated, synchronous polyp regeneration. In either experimental set-up, incubation in 5–10 mM hydroxyurea effectively halted regeneration. Exposure to an excess of Li⁺ (50–200 mm) or K⁺ (10–50 mM) caused no firing of nematocysts and a percentage of polyp regeneration only slightly higher than control tentacles. Use of the K⁺ channel blocker tetraethylammonium (TEA; 100–300 mM) lead to similar levels of regeneration. A Ca²⁺ or K⁺-reduced artificial culture solution did not enhance regeneration. Ouabain (1 mM) dampened the Cs⁺ induced acceleration of polyp morphogenesis, and when given without Cs⁺, elicited a control level response.     

A corrosive concoction: The combined effects of ocean warming and acidification on the early growth of a stony coral are multiplicative

Survival of coral planulae, and the successful settlement and healthy growth of primary polyps are critical for the dispersal of scleractinian corals and hence the recovery of degraded coral reefs. It is therefore important to explore how the warmer and more acidic oceanic conditions predicted for the future could affect these processes. This study used controlled culture to investigate the effects of a 1 °C increase in temperature and a 0.2-0.25 unit decrease in pH on the settlement and survival of planulae and the growth of primary polyps in the Tropical Eastern Pacific coral Porites panamensis. We found that primary polyp growth was reduced only marginally by more acidic seawater but the combined effect of high temperature and lowered pH caused a significant reduction in growth of primary polyps by almost a third. Elevated temperature was found to significantly reduce the amount of zooxanthellae in primary polyps, and when combined with lowered pH resulted in a significant reduction in biomass of primary polyps. However, survival and settlement of planula larvae were unaffected by increased temperature, lowered acidity or the combination of both. These results indicate that in future scenarios of increased temperature and oceanic acidity coral planulae will be able to disperse and settle successfully but primary polyp growth may be hampered. The recovery of reefs may therefore be impeded by global change even if local stressors are curbed and sufficient sources of planulae are available.     

Alteration of mitochondrial DNA sequence and copy number in nasal polyp tissue

This study was designed to investigate the possibility that mtDNA mutations might arise in inflammatory or chronically damaged nasal polyp tissue from 23 patients. Thirteen patients (57%) displayed nasal polyp tissue-specific mtDNA mutations in the hypervariable segment of the control region and cytochrome b gene, which were not found in the corresponding blood cells and/or adjacent normal tissue. Nasal polyp tissue-specific length heteroplasmic mutations were also detected in nucleotide position (np) 303–315 homopolymeric poly C track (39%), np 514–523 CA repeats (17%) and np 16184–16193 poly C track (30%). The average mtDNA copy number was about three times higher in nasal polyp tissue than in the corresponding peripheral blood cells and adjacent non-polyp tissues. The level of reactive oxygen species (ROS) was significantly higher in the nasal polyp tissues compared to those from the corresponding samples. High level of ROS in nasal polyp tissue may contribute to development of mtDNA mutations, which may play a crucial role in the vicious cycle of pathophysiology of nasal polyps.     

Effects of low salinity on settlement and strobilation of scyphozoa (Cnidaria): Is the lion’s mane <Emphasis Type="Italic">Cyanea capillata</Emphasis> (L.) able to reproduce in the brackish Baltic Sea?

Several species of scyphozoan medusae occur in river estuaries and other brackish waters but it is often unknown if the planulae settle and the scyphopolyps reproduce in those low-salinity waters. In the present study, scyphozoan species from the German Bight (North Sea) were tested in laboratory experiments to investigate their tolerance of low salinity. Planula larvae released from medusae in salinity 32 were still active after the salinity was reduced to 10 (Cyanea capillata, Cyanea lamarckii) and to 7 (Chrysaora hysoscella) in laboratory treatments. Planulae did not settle on the undersides of floating substrates when salinity was reduced to <20. By contrast, planulae released from C. capillata medusae in Kiel Bight (western Baltic Sea) in salinity 15 developed into polyps in laboratory cultures. Polyps reared from planulae in salinity 36 survived a reduction to 12 (C. capillata, C. lamarckii) and to 8 (Aurelia aurita). Polyps of all tested species strobilated and released young medusae (ephyrae) in salinity 12. These results show a high tolerance of planulae and polyps to low salinity, indicating their possible occurrence in estuaries and brackish waters. In addition to laboratory observations, young C. capillata ephyrae were collected in the western Baltic Sea (Kiel Bight) in salinity 15, which indicates that they were probably released by a local polyp population. We suggest that the polyps of the painfully stinging lion’s mane, C. capillata, may be more widespread in the Baltic Sea than previously assumed and that the occurrence of the medusae may not only depend on inflow of water masses from the North Sea.     

Application of ITS-2 sequences as markers for identification and phylogenetic inference within the genus <Emphasis Type="Italic">Geomylichus</Emphasis> (Acari: Listrophoridae)

Phylogenetic relationships among 18 samples from nine nominal species of Geomylichus (Acari: Listrophoridae), were analyzed based on internal transcribed spacer 2 (ITS 2) sequences, Prolistrophorus sp. was used as an outgroup. Maximum likelihood and neighbor-joining analyses indicated that Geomylichus is formed by at least three internal clades. Genetic distance among Prolistrophorus and Geomylichus was 27.8–35.5%, and among species, populations, and infrapopulations of Geomylichus it was 0.4–21.8%, 0.8–2.4%, and 0.8–1.2%, respectively. Differences between the results of this analysis with conventional taxonomy of the group, as well as the overlapping of genetic distances among species, populations, and infrapopulations, suggest that the definition of species within Geomylichus deserves reconsideration. For example, the recognition of inconsistencies among G. texanus populations associated to different host species, resulting from the molecular analysis, led us to collect new morphological evidence now suggesting that this taxon represents more than one species.This revised version was published online in May 2005 with a corrected cover date.     

Genetic structures of allopatric and sympatric populations in Pseudorasbora pumila pumila and Pseudorasbora parva

Pseudorasbora pumila pumila was collected to investigate its genetic relationships from 11 localities in Hokkaido and eastern Honshu of Japan with Pseudorasbora parva from 6 localities in Hokkaido, eastern Honshu, and Polovynka River (a tributary of the Amur River in eastern Russia) in 1996–1998. In Hokkaido and Akita prefectures (Honshu), three P. pumila pumila populations were distributed with P. parva sympatrically. Samples of P. pumila pumila and P. parva were analyzed based on 27 allozyme loci. Genetic differentiation between P. pumila pumila and P. parva (D = 0.522–0.622, average 0.601) was almost equal to or greater than that between other congeneric fish species previously reported. In the three sympatric populations of two species, which had arisen from artificial transplantation of the latter into localities of the former, the individual frequency composition of genetic types (P. pumila pumila, P. parva, F₁ hybrid, and later filial generation hybrid) were significantly different from each other. Differing from the previous studies, F₁ hybrids were fertile and coexisting populations of the two species included the F₁ hybrid and the later filial generation hybrid. These results suggest that genetic population dynamics of sympatric populations of the two species would be influenced not only by hybridization but also by ecological and environmental factors. Alternatively, the existence of populations that possessed both the alleles specific to P. pumila pumila and those specific to P. parva may indicate that introgressive hybridization, instead of species displacement, has occurred between the two species under a certain condition.     

In vitro culture of embryos of Cucumis spp.: heart-stage embryos have a higher ability of direct plant formation than advanced-stage embryos

Summary The ability of embryos at different developmental stages to form plants in vitro has been studied in cultivated Cucumis sativus L. and in the wild species C. zeyheri 2 x Sond. and C. metuliferus Naud. On MS medium containing 3.5% sucrose, 0.1 mg 1^–1 kinetin (Kn) and 0.01 mg 1^–1 indoleacetic acid (IAA), proembryos (0.03–0.05 mm) and early globular embryos (0.05–0.08 mm) from the wild species developed into plants in low frequencies of 8% and 21%, respectively. These embryos should be surrounded by the embryo sac tissue. On the same medium late globular (0.08–0.1 mm) and early heart-stage embryos (0.1–0.3 mm) developed into plants in moderately high and high frequencies of 48% and 83%, respectively. The presence of the embryo sac at these stages was still beneficial, but no longer a prerequisite. Late heart-stage embryos (0.3–0.8 mm) also showed high frequencies of plant formation, 63%, if Kn was applied at a concentration of 1 mg 1^–1. From the early cotyledon stage onwards, the frequency of plant formation gradually decreased, reaching a minimum at the late cotyledon stage. Subsequently it began to increase again up to the late maturation stage. The poor plant formation shown by the intermediate-aged embryos could be improved slightly by lowering the sucrose concentration to 0.5% and by increasing the Kn concentration to 10 mg 1^–1. Relative to the wild species, embryos of C. sativus showed lower percentages of plant formation. The optimum sucrose concentration was 2% for the heart-stage C. sativus embryos. In all three species the ability to form plants strongly decreased with increasing embryo age, from early to late cotyledon. This is thought to be caused by the increasing tendency of the embryos at these stages to continue in vitro the normal embryo development.     

Habitat Shift in Invading Species: Zebra and Quagga Mussel Population Characteristics on Shallow Soft Substrates

Unexpected habitat innovations among invading species are illustrated by the expansion of dreissenid mussels across sedimentary environments in shallow water unlike the hard substrates where they are conventionally known. In this note, records of population characteristics of invading zebra (Dreissena polymorpha) and quagga (Dreissena bugensis) mussels from 1994 through 1998 are reported from shallow (less than 20m) sedimentary habitats in western Lake Erie. Haphazard SCUBA collections of these invading species indicated that combined densities of zebra and quagga mussels ranged from 0 to 32,500 individuals per square meter between 1994 and 1998, with D. polymorpha comprising 75–100% of the assemblages. These mixed mussel populations, which were attached by byssal threads to each other and underlying sand-grain sediments, had size–frequency distributions that were typical of colonizing populations on hard substrates. Moreover, the presence of two mussel cohorts within the 1994 samples indicated that these species began expanding onto soft substrates not later than 1992, within 4 years of their initial invasion in western Lake Erie. Such historical data provide baselines for interpreting adaptive innovations, ecological interactions and habitat shifts among the two invading dreissenid mussel species in North America.