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Cyclopoid Predation on Lake Michigan Fish Larvae
Canadian Journal of Fisheries and Aquatic Sciences
Abstract
Cyclopoid predation on fish larvae, as evidenced by copepods attached to larvae in field collections, was quantitatively investigated during 1975–76 in southeastern Lake Michigan. Although six species of fish larvae were collected, predation occurred primarily (98%) on alewife (Alosa pseudoharengus); 2% of the predators were attached to spottail shiner (Notropis hudsonius) larvae. No cyclopoids were observed on rainbow smelt (Osmerus mordax), yellow perch (Perca flavescens), common carp (Cyprinus carpio), or sculpin (Cottus spp.) larvae. Most alewife larvae attacked were 3–8 mm long; older larvae and larvae of more robust species, such as yellow perch and spottail shiner, are apparently immune to such predation. Most predation (99%) occurred in July when alewife larvae were numerous and cyclopoids abundant. Fish larvae with attached copepods were found only in night collections. Most cyclopoid predators (99%) were adult female Diacyclops thomasi and Acanthocyclops vernalis. Other predaceous species of zooplankton, that occurred in close temporal and spatial proximity to fish larvae, apparently were not predaceous on these organisms.Key words: Alosa pseudoharengus larvae, Notropis hudsonius larvae, Diacyclops thomasi, Acanthocyclops vernalis, cyclopoid predation, Lake Michigan
... However, those organisms, even if they do not consume their prey instantaneously due to the differences in size of the Adapted from MILLS and FORNEY (1983) Studying the relationships of larvae and juveniles of gizzard shad (Dorossoma cepedianum) with the zooplankton and recruitment of sporting fish in four reservoirs, BREMIGAN and STEIN (1999) observed that the high abundance of young forms of this fish promotes reduction in the densities of total zooplankton in mesotrophic environments, and when latter, attach themselves to the larvae injuring their skin and fins and consequently causing their death (BEHR et al., 1997). Acanthocyclops vernalis copepods have been reported to prey on Alosa pseudoharengus larvae (Figure 8) by HARTIG et al. (1982) Figure 8. Three specimens of Acanthocyclops vernalis attacking a larva of Alosa pseudoharengus -Adapted from HARTIG et al. (1982) According to SUKHANOVA (1965), predation by Acanthocyclops vernalis significantly affects the survival rate of silver carp larvae (Hypophthalmichthys sp) reared in Asia, while DAVIS (1959) mentions the predation of rockbass (Ambloplites rupestris) larvae. NIKOLSKI (1963) reported that shad larvae (Alosa sp) were attacked by Mesocyclops sp and Acanthocyclops sp. ...
... However, those organisms, even if they do not consume their prey instantaneously due to the differences in size of the Adapted from MILLS and FORNEY (1983) Studying the relationships of larvae and juveniles of gizzard shad (Dorossoma cepedianum) with the zooplankton and recruitment of sporting fish in four reservoirs, BREMIGAN and STEIN (1999) observed that the high abundance of young forms of this fish promotes reduction in the densities of total zooplankton in mesotrophic environments, and when latter, attach themselves to the larvae injuring their skin and fins and consequently causing their death (BEHR et al., 1997). Acanthocyclops vernalis copepods have been reported to prey on Alosa pseudoharengus larvae (Figure 8) by HARTIG et al. (1982) Figure 8. Three specimens of Acanthocyclops vernalis attacking a larva of Alosa pseudoharengus -Adapted from HARTIG et al. (1982) According to SUKHANOVA (1965), predation by Acanthocyclops vernalis significantly affects the survival rate of silver carp larvae (Hypophthalmichthys sp) reared in Asia, while DAVIS (1959) mentions the predation of rockbass (Ambloplites rupestris) larvae. NIKOLSKI (1963) reported that shad larvae (Alosa sp) were attacked by Mesocyclops sp and Acanthocyclops sp. ...
... L -1 , respectively, and after 25 hours all treatments involving copepods presented lower survival rates compared to control. HARTIG et al. (1982) described the predation of alewife larvae (Alosa pseudoharengus) and spottail shiner (Notropis hudsonus) by cyclopoid copepods in Lake Michigan. The attack by the copepods Diacyclops thomasi and Acanthocyclops vernalis on larvae of six fish species in Lake Michigan and on larvae of five fish species in Lake Pigeon were studied by HARTIG et al. (1984). ...
This paper is a synthesis of the main aspects of the interactions between the young forms of fish (YFF) and the plankton community, describing biological factors and behaviors. The recruitment of fish populations depends on the success of YFF in the natural environment. Thus, the development of mechanisms that allow efficient food capture, as well as reduction of competition or also reduced predation by other organisms, are of fundamental importance for the maintenance of the populations of fish and their natural environments. YFF, which show ecological characteristics different from those of adults, depend on the availability of food organisms in terms of density, size, palatability, attractiveness, biological value and adequate swimming capacity for capture. Among the factors that determine the capture of food organisms by YFF are the fry length/prey length relationship, mobility and capacity of escape of the prey, body protection, palatability and prey abundance. The predation and feeding selectivity on the zooplankton by YFF can cause changes in the plankton community structure in natural environments. RESUMO Neste artigo apresenta-se uma síntese dos principais aspectos das interações entre as formas jovens de peixes (FJP) com a comunidade planctônica, evidenciando fatores biológicos e comportamentais. O recrutamento das populações de peixes depende do sucesso das FJP no ambiente natural. Desta forma, o desenvolvimento de mecanismos que possibilitem eficiência de captura do alimento, assim como redução da competição ou, ainda, menor predação por outros organismos são de fundamental importância para a manutenção das populações de peixes e seus ambientes. As FJP, as quais, em sua maioria, apresentam características ecológicas distintas daquelas de seus adultos, dependem da disponibilidade de organismos-alimento em densidade, tamanho, palatabilidade, atratividade, valor biológico e capacidade natatória adequados para serem capturados. Dentre os fatores que determinam a captura dos organismos-alimento pelas FJP estão a relação tamanho da larva/tamanho da presa, mobilidade e capacidade de escape da presa, proteção do corpo, palatabilidade e disponibilidade da presa. A predação e/ou a seletividade alimentar sobre o zooplâncton por FJP podem causar alterações na estrutura da comunidade planctônica dos ambientes naturais.
... While zooplankton consumption appears to play a large part in larval fish growth and survival, predation on larvae by adult female cyclopoid copepods also has been shown to occur in laboratory situations, and copepods have been found grasping fry in zooplankton tow catches (Davis 1959;Fabian 1960). Several studies have examined copepod predation in reservoirs and lakes, showing damage attributed to copepods that could have caused death of larvae (Smith and Kernehan 1981;Hartig et al. 1982;Hartig and Jude 1984). However, these studies were based on larvae collected in ichthyoplankton tows that would have artificially increased the densities of larvae and copepods, thereby raising the probability of encounter. ...
... While cyclopoid copepod predation was not a likely cause of mortality in my study, I was unable to quantify other types of predation in the culture ponds or whether damage caused by cyclopoid attacks could lead to mortality. Cyclopoid copepods that have been found attached to larvae from plankton tows are typically found grasping fins and yolk sacs, which if damaged could lead to larval mortality (Smith and Kernehan 1981;Hartig et al. 1982). Cyclopoids have been observed attacking the fins of larval fish, even removing large pieces during an attack (Davis 1959;Fregadolli 2003). ...
... Such potential predators, especially most of the invertebrates, are known to be non-visual predators and generally forage in low-illumination conditions. These predators are well known for threatening larval fish survival by attacking and injuring them (IHB 1976;Hartig et al. 1982;Jennings 1988;Bailey and Houde 1989). During our field sampling, we observed a high occurrence of such potential predators when we removed the collected materials from nets set in littoral and sublittoral zones at night. ...
Early life-history properties reveal a considerable variation among riverine fish species and may play a major role in the downstream drift of larval fish. This role, however, remains largely unexplored. Assemblages of drifting fish larvae and their condition during the peak seasons were analyzed along a cross-section from littoral to midstream zones in a free-flowing section in the middle Yangtze River. Assemblage structure and larval body injuries revealed pronounced transverse patterns. These patterns were mainly explained by hydraulic gradients. Highest species occurrence was recorded in the littoral zone. Larval abundance of most species and larval body injury rates were higher in littoral and sublittoral zones. Relative inshore and nearshore larval abundance revealed a significant negative relationship with species-specific initial body size, and varied among species. Larval abundance, body injury rate, and feeding intensity were all higher at night. Our findings revealed considerable habitat preferences of drifting larval fish and suggest important adaptations for reducing starvation- and predation risks. These factors should be considered in species conservation and river management.
... The inshore habitats of the middle reach of the Yangtze River are also inhabited by many small predators such as older larvae and juveniles of carnivorous fishes, shrimps and the larvae of aquatic insects, even large copepods and cladocerans. All have been recognized as predators of early stages of larval fish (Bailey & Houde, 1989;Chen, 1976;Hartig et al., 1982;IHB, 1976;Jennings, 1988). We believed that the shrimps and older larvae of aquatic insects could be the major predators causing the body injuries of larval fish, as we visually observed a high abundance of them in our nets along all types of shores. ...
Inshore habitats play a crucial role in the downstream drift of larval fish in large rivers. Natural inshore habitats of most of the world's large rivers have been heavily degraded by shoreline stabilization measures, but the knowledge about consequences for the condition and distribution of larval fishes is extremely limited. Investigations during the peak season of larval drift into species composition as well as into feeding intensity and body injuries of representative taxa were conducted at different inshore mesohabitats along semi‐natural and stabilized shores in a free‐flowing section in the middle Yangtze River. Species were unambiguously identified by a combination of DNA barcoding and morphological analyses. Overall, 37 taxa from seven families were detected from a total of 9,915 fish larvae caught. Earlier developmental stages greatly outnumbered the later stages in diversity and abundance in each investigated mesohabitat. Abundance and assemblage structure as well as the body injury rate differed significantly between mesohabitats. Generally, overall species richness and abundance tended to be lower, and divergence of the assemblage and body injury rates tended to be higher at heavily hardened shores, which could be contributed to the poor riparian vegetation and restricted suitable hydraulic conditions there. Our results may reflect the underestimated impact of inshore habitat degradation on larval fishes and highlight the demand for creating adequate areas of shallow and slow‐flow habitats with good riparian vegetation conditions along the shores. These measures will foster an appropriate connectivity between spawning areas and high‐quality nurseries for larval fishes.
... Copepods feed on a wide variety of foods including algae, pollen, detritus, bacteria, rotifers, crustaceans, dipteran larvae including mosquitoes, chironomids, and chaoborids, and even larval fish [24,121,130,131,175,256,300] . Therefore, they occupy three of the four major trophic positions in the food web: detritivore, herbivore, and carnivore. ...
Free-living freshwater copepods can be distinguished from other small aquatic invertebrates by a variety of morphological characteristics. They have a cylindrical, segmented body with numerous segmented appendages on the head and thorax, and two setose caudal rami on the posterior end of the abdomen. They possess an exoskeleton, conspicuous first antennae, and a single, simple, anterior eye. Copepods are common in a variety of aquatic and semi aquatic habitats ranging from moist soils, leaf packs groundwater, wetlands, and phytotelmata, to lakes, estuaries, and open oceans. Most species are omnivorous to some extent, with foods ranging from detritus and pollen, to phytoplankton, other invertebrates, and even larval fish. Copepods frequently comprise a major portion of the consumer biomass in these habitats. They play a pivotal role in aquatic food webs both as primary and secondary consumers, and as a major source of food for many larger invertebrates and vertebrates. This chapter focuses on the three orders that contain the widespread, abundant and primarily free-living copepods namely Calanoida, Cyclopoida, Harpacticoida, of which there are over 7750 species. The harpacticoids include approximately 3000 species, 10% of which inhabit freshwaters; calanoids include about 2300 species, 25% of which are freshwater, while there are about 2450 species of cyclopoids, 20% of which are freshwater. Many cyclopoids are parasitic. The remaining order, Gelyelloida, includes two recently discovered free-living species in the genus Gelyella from subterranean habitats in Europe. Another species are reported from a single location in North America.
... Both carp species tested in this study were stocked in ponds as small fry (Jinghran and Pullin, 1985;Reddy et al., 1996) and were assumed as highly susceptible to cyclopoid predation. However, the pond ecosystem remains a black box in which fish feed at several levels of the food web and are affected by the entire ecosystem (Hartig et al., 1982;Ludwig, 1993Ludwig, , 1999. For the pond aquaculture, we suggest that a preliminary experiment must be evaluated on the vulnerability of target fish larvae to the copepod predation. ...
Several marine and freshwater predatory copepods (Labidocera, Pontellopsis, Mesocycops and Acanthocyclops) exhibit a wide dietary niche, ranging from protists, rotifers, cladocerans, copepods, to insect and fish larvae. Predation-induced fish larval mortality in natural environments and hatcheries reduces larval abundance and may limit fish recruitment. However, few studies quantified the losses incurred by copepod predation. Therefore, this study quantified vulnerability, susceptibility, and loss of two crucial fish, Labeo rohita and Catla catla, to cyclopoid predation in relation to larval age and body length under laboratory conditions. In addition, we compared susceptibility of fish larvae to the copepod (Mesocyclops thermocyclopoides and Mesocyclops aspericornis) predation in the laboratory, based on probability of survival after attack in relation to age and size of the larvae. We also evaluated the modulatory role of alternate zooplankton species as common prey of fish larvae and copepods. Both cyclopoid species were able to subdue and kill both species of fish larvae. The two cyclopoid species did not differ considerably in their predation efficiency on larvae; the larvae of C. catla and L. rohita did not differ considerably in their respective vulnerability to cyclopoid predation. In both species of fish larvae, the copepod-imposed mortality was inversely related to larval age (R2 ≥ 0.97) and body length (R2 ≥ 0.93). The effect of alternate prey on copepod-imposed mortality was species-specific to prey. The presence of Paramecium caudatum, Brachionus calyciflorus and Ceriodaphnia cornuta resulted in decreased mortality of fish larvae by the copepod; however, the larvae were more susceptible to copepod predation in the presence of either Hexarthra mira or Daphnia similoides as alternate prey. The copepod-induced mortality of carp larvae was recorded, even in multispecies prey environment; however the mortality was considerably less than that in control. Overall, the maximal reduction (40–100%) in copepod-imposed larval mortality was achieved by the Rotifera B. calyciflorus, followed by the Cladocera C. cornuta and ciliate P. caudatum. The modulatory effects of the presence of alternate prey were more pronounced after fish larvae reached 4 days post hatch (dph). The susceptibility of carp larvae to copepod predation differed ontogenetically with maximal susceptibility between 0 and 4 dph. Threshold level for copepod-imposed mortality was estimated with bilinear model, which ranged from 5.2 to 8.4 dph and 6.8 to 7.8 mm body length. Our results provide insight and valuable inputs for enhancing the efficiency of nursery rearing.
Copepoda are one of the most significant animal groups present in aquatic ecosystems. Ecologists, evolutionary biologists, and biotechnologists continue to test new methods to study the application of Copepoda as model organisms in various fields of pure and applied science, from evolution and ecology to aquaculture as live feed, as biological control of mosquito larvae, as biological indicators of water and sediment quality, in environmental monitoring and as a source of protein in the food industry. This paper reviews the current progress and trends within copepod research from a number of different perspectives. We emphasize the importance of Copepoda and the necessity of strengthening research on various topics related to copepod biology, some of which are of great significance to local sustainable development.
Factors affecting abundance, growth, and survival of age-0 gizzard shad Dorosoma cepedianum were examined in Pomme de Terre and Stockton lakes, Missouri, during 1987–1991. Otolith ages were used to assign larvae (≤25 mm total length, TL) and juveniles (>25 mm TL) to weekly cohorts so that cohort-specific estimates of abundance, growth, and survival could be made. The distribution of initial abundances of larvae among weekly cohorts was influenced by water temperature and reservoir water level but not by characteristics of adult females (abundance, size, condition, fecundity). Intense periods of spawning activity during rising water levels resulted in high peaks in larval abundance and relatively few large weekly cohorts (e.g., 1990). In the absence of water level rises, peaks in larval abundance were much lower and abundances of larvae were more evenly distributed among several cohorts (e.g., 1988). Spring warming also affected spawning; early cohorts in warm springs (1987 and 1991) were relatively more abundant than those during cool springs (1989 and 1990). The initial distribution of larvae among weekly cohorts influenced subsequent interactions between the larvae and their environment. Growth of larvae was positively affected by water temperature and, to a lesser degree, food abundance. Early cohorts grew slower because of lower water temperatures, and they suffered higher mortality than did late cohorts. Survival was also density dependent; weekly cohorts with high initial densities experienced lower survival than cohorts with small initial densities. High survival of larvae occurred in 1988 when densities of larvae were low and evenly distributed among weekly cohorts and food abundance was high. Growth and instantaneous mortality of juveniles were not closely tied to any single variable. Growth was positively related to food abundance and negatively related to gizzard shad density. Mortality was not significantly related to any measured variable. Overall, findings indicate that cohort dynamics of age-0 gizzard shad are initially driven by climatic factors and later by a combination of climatic and biotic factors.
The amphipod Calliopius laeviusculus actively preys on the intertidal eggs of capelin (Mallotus villosus). From samples collected in 1988, we found that the patterns of changes in C. laeviusculus biomass closely matched changes in capelin egg biomass throughout the capelin egg development period. Calliopius laeviusculus and capelin egg biomass exhibited pronounced and overlapping peaks in mid June. Endogenous reproductive patterns influenced by exogenous seasonal stimuli in both C. laeviusculus and capelin could facilitate yearly biomass coupling between these two species. Calliopius laeviusculus exhibited a semiannual life cycle, overwintering adults releasing young in April, May and July. Cohorts released in April and May reached sexual maturity within the summer, reproduced and produced a second maximum in amphipod biomass at the beginning of August. This second abundance peak appeared to be a numerical response to predation on capelin eggs by the adult C. laeviusculus present in mid-summer. Given this response and the reported quiescence of C. laeviusculus during the winter, we speculate that amphipod biomass in spring may be strongly linked to feeding conditions in the previous year. The implications of this coupling for capelin egg survival are considered.
We evaluated the relative importance of starvation and predation as potential sources of mortality for larval bloater (Coregonus hoyi) in the laboratory. Fifty percent of starved bloater larvae survived 25 d after hatching; some individuals survived 35–40 d. Bloater larvae did not exhibit a point of no return, but length and weight after 30 d were inversely related to the delay in first feeding. Bloaters were swimming about half of the time within 1 h after hatching and almost continuously after 6 h. Twenty-one days after hatching, starved larvae were still swimming continuously at 0.9 cm∙s−1; fed larvae swam more than four times faster. Bloater larvae up to 30 d old were captured with about 80% success by 95- and 135-mm bloaters and 100-mm alewives (Alosa pseudoharengus). Susceptibility to predators generally decreased with increasing size, and starved larvae were more susceptible than similar sized fed larvae. Because of their swimming ability and resistance to starvation, it seems unlikely that bloater larvae starve to death in nature. However, starvation can contribute to mortality, as reduced growth and swimming capabilities may result in increased or prolonged susceptibility to predation.
Author Institution: Department of Biology, Geneva College, Beaver Falls, Pennsylvania
A variety of marine copepods have been shown to fatally injure or capture and ingest young anchovy larvae in the laboratory. Labidocera jollae, L. trkpinosa, and Poiztellopsis occidentcilis (family Pontel- lidae), species common to surface waters of the California Current, are effective predators of larval fish. The copepods can be attracted by the vibrations of the larval tail beat and react by biting or capturing the fish larvae. Cruising speeds for these copepods varies from 1.5 to 4 body lengths per second which, coupled with continuous swimming behavior, results in extensive searching by the copepod for prey. In laboratory experiments, when the ratio of larval fish prey to L. jollae female individuals was low (
1. Der Einfluß verschiedener Ernährungsarten auf Wachstum, Fruchtbarkeit und Lebenslänge von Acanthocyclops viridis (Jurine) wurde studiert, und zwar unter Laboratoriumsbedingungen bei Temperaturen zwischen 16° und 18° C. 2. Männchen wuchsen bei einer aus gemischten Algen bestehenden Diät ebenso schnell wie bei einer Diät aus mehreren tierischen Komponenten. Weibchen, die nur Algen erhielten, wuchsen ebenso gut wie solche, die tierische Nahrung vorgesetzt bekamen bis zum letzten Larvalstadium; aber dann häuteten sie sich entweder überhaupt nicht oder erreichten das adulte Stadium erst nach einer Verzögerung von mehreren Wochen. Von den tierischen Nahrungsquellen verursachten Stadium I-Nauplien des Salinenkrebses Artemia salina das schnellste Wachstum, des Wasserflohs Chydorus sphaericus das langsamste. Protozoennahrung gestattete schnelleres Wachstum als die getesteten Cladoceren. 3. Die Zeit bis zur ersten Brutablage war doppelt so lang bei Weibchen, die mit Algen gefüttert worden waren, als bei Weibchen, die tierische Nahrung erhielten. 4. Die wenigen Weibchen, welche das Adultus-Stadium mit einer gemischten Algendiät erreichten, wurden als letzte tragend. Die höchste Reproduktionsrate erreichten Weibchen, die mit Artemia salina-Nauplien gefüttert worden waren. Mit Protozoen gefütterte Weibchen hatten - unter den mit tierischer Nahrung versorgten Individuen - die geringsten Eizahlen. Das bedeutet: Obgleich A. viridis gut mit Protozoennahrung gedeiht, legen die Weibchen nur wenige Eier, es sei denn, sie fressen auch größere Nahrungsorganismen. 5. Die Lebensdauer schwankte zwischen 70 und 100 Tagen. Die Unterschiede in beiden Geschlechtern waren niemals groß. In drei Fällen lebten Männchen länger als Weibchen. Die kürzesten Lebensspannen wurden in beiden Geschlechtern bei Individuen registriert, welche Nauplien von Artemia salina gefressen hatten. 6. Adulte Weibchen von A. viridis fraßen während ihres ganzen Lebens als Adulti mehr kleine als große Simocephalus vetulus. Der wöchentliche Verbrauch an kleinen S. vetulus erreichte Maximalwerte während der zweiten Woche des Adult-Daseins und nahm danach ständig ab.
This paper describes the abundance, distribution, movements, and lengths of larval herring along the western coast of the Gulf of Maine. Larvae were most numerous in the catches throughout the coast in the autumn, reached a low in the winter, and increased in the spring. Growth in the autumn is estimated at 1 to 1.3 mm per 5-day intervals. Larval mortality was highest in th~ autumn, lower in the winter, and lowest in the spring. The mortality in the winter usually varied with their condition and determined the sub sequent level of spring abundance. We selected three different types of estimates as desirable for predicting the recruitment of immature herring to the sardine fishery of Maine: (1) winter mortality, (2) larval condition in the winter, and (3) spring abundance. The commercial catch of 2-year-old Atlantic herring, Clupea harengus harengus Linnaeus, fluctuates annually along the western coast of the Gulf of Maine. The Maine sardine industry processes these immature herring, but cannot anticipate the amount of fish available for can ning each year. One approach to this problem is to determine whether the abundance of her ring during their first year of life is related to the number of fish entering the fishery. To establish whether such a relationship exists, the desirable estimate of abundance or its correl ative must be determined first. We describe the distribution, abundance, movements, and lengths of larval herring along the western coast of the Gulf of Maine. We discuss the seasonal changes in larval abundance caused by their mortality and the relation of the sources of larvae to their distribution and movements. From these anal Yses we selected three types of estimates: (1) Winter mortality, (2) larval condition in the Winter, and (3) spring abundance. Larval herring occur throughout the Gulf of Maine-Georges Bank area. They concentrate in the offshore bank area (Tibbo et al., 1958); along the southeastern coast of Nova Scotia ----- : National Marine Fisheries Service Northeast Fish- ~~les Center, Boothbay Harbor Laboratory, W. Boothbay .uarbor, ME 04575.
The copepod Epischura nevadensis selectively preys on zooplankton communities in a way that reduces the abundance of the cladoceran Bosmina longirostris and favors larger‐bodied species. Bosmina responds to this predation by behavioral and morphological adjustments that frustrate the searching and handling strategies of the predatory copepods; this response implies considerable evolution between the two antagonists. Predation by copepods and other freshwater invertebrates seems an important factor in determining not only the size composition of lake communities, but the shape in some species.
Cores of bottom sediments and overlying waters were collected from depths of 6 and 9 m in southeastern Lake Michigan, Copepod, cladoceran, and ostracod abundances were assessed in terms of known plankton. Species could be roughly divided into euplanktonic species showing no affinity for the sediments, epibenthic species occurring in the plankton but concentrated near the sediments, and benthic species inhabiting the sediments and rarely encountered in the plankton. While several epibenthic species left the sediments at night to enter the plankton, only a small fraction of the benthic species showed this mi- gration. Epibenthic and benthic microcrustaceans in the lower 0.3 m of the water column accounted for 33-39s of the standing stock (by numbers) of the microcrustaceans within the 9-m depth contour. Preliminary information on the local food web indicates that the microcrustaceans have a significant role in the trophodynamics of the inshore area. Several of the species found in southeastern Lake Michigan are tolerant of eutrophic, mesotrophic, or moderately saline waters.
An account is given of the feeding mechanism of some freshwater cyclopoid copepods.
Chance encounter appears to play an important part in the finding of food in both carnivorous and herbivorous species, but the chemoreceptor organs apparently utilized by the herbivores to discriminate between edible and inedible particles may help to some extent in food seeking.
The structure, arrangement, and method of operation of the various mouthparts are described, and the raptatory method of feeding of the cyclopoids is demonstrated.
The route taken by the cyclopoids towards a parasitic mode of life is considered from a functional standpoint.
The phylogeny of the Cyclopoida and Calanoida is discussed. A carnivorous diet is considered to be the primitive diet of the Cyclopoida. A change from a carnivorous to an algal diet may have been of considerable importance in the adaptive radiation of the group.
An annotated checklist of the free-living copepods of the Laurentian Great Lakes is developed on the basis of published records. Synonymies are included for each species, relating, wherever possible, invalid names in the literature with currently recognized taxonomy. Twelve species of calanoids, six species of planktonic cyclopoids, nine species of benthic/ littoral cyclopoids, and fourteen species of harpacticoids have been reported from the Great Lakes. Ten of the calanoids and four of the cyclopoids are characteristic of limnetic waters. Three calanoids and two planktonic cyclopoids have been reported infrequently and are perhaps accidental occurrences. The composition of the planktonic copepod fauna in most subregions of the Great Lakes is well-known. In contrast, the sampling of benthic/littoral cyclopoids and harpacticoids has been so infrequent that their kinds, areas of occurrence, and relative abundances are still poorly understood.