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The humpbacked species richness-curve: A contingent rule for community ecology
Functional relationships involving species richness may be unimodal, monotonically increasing, monotonically decreasing, bimodal, multimodal, U-shaped, or with no discernable pattern. The unimodal relationships are the most interesting because they suggest dynamic, nonequilibrium community processes. For that reason, they are also contentious. In this paper, we provide a wide-ranging review of the literature on unimodal (humpbacked) species richness-relationships. Though not as widespread as previously thought, unimodal patterns of species richness are often associated with disturbance, predation and herbivory, productivity, spatial heterogeneity, environmental gradients, time, and latitude. These unimodal patterns are contingent on organism and environment; we examine unimodal species richness-curves involving plants, invertebrates, vertebrates, plankton, and microbes in marine, lacustrine, and terrestrial habitats. A goal of future research is to understand the contingent patterns and the complex, interacting processes that generate them.
Episodic nutrient addition affects water column nutrient processing rates in river-to-lake transitional zones
Storm-driven nutrient loading from tributaries can fuel eutrophication in nearshore and open water areas of lentic ecosystems. However, nutrient processing in river-to-lake transitional zones can substantially alter the amount and composition of nutrients transported to lakes from upstream surface waters. We measured the removal of nutrients and dissolved organic carbon (DOC) from the water column in the Fox rivermouth (Green Bay, Lake Michigan) to evaluate the response of rivermouth plankton to episodic nutrient enrichment. Light and dark water column incubations (8–12 hr) were conducted on four occasions from April through September to measure changes in dissolved nitrogen (N), phosphorus (P), and DOC concentrations in three locations along the Fox rivermouth. Two incubation experiments were conducted on consecutive days, (a) under ambient nutrient concentrations, and (b) under experimentally enriched N and P concentrations. Spatial and temporal variation was observed in nutrient uptake rates, but light incubations consistently had higher nutrient uptake rates than dark incubations. Nutrient enrichment increased total dissolved P and total dissolved N uptake and DOC release in light incubations, but only increased total dissolved P uptake in dark incubations. Moreover, nutrient uptake ratios (N:P) decreased from ambient to nutrient enriched conditions and indicated preferential P uptake by phytoplankton communities in light conditions. Our study substantiates that rivermouths can process nutrients bound for downstream ecosystems and demonstrates the potential of plankton communities to dynamically increase net uptake rates in response to episodic nutrient enrichment.
Shifting phenology in planktonic foraminifera in the Gulf of America (Mexico) with 21st century warming
We investigate trends in foraminiferal phenology using a 12-year (2008–2020), well-resolved (7 to 28-day resolution) time series of planktonic foraminiferal fluxes from a U.S. Geological Survey sediment trap in the northern Gulf of America (Gulf of Mexico; 27.5°N, 90.3°W). The total foraminiferal flux declined over this time. We used Horn-Morisita dissimilarity analysis, principal coordinate analysis, and correlation matrices to show that fall assemblages became more similar in composition to summer assemblages (July–September) over the 12 years. As a result, winter (January–March) and fall (October–December) assemblages, which dominate the total annual foraminiferal flux, became more dissimilar in composition. This pattern is consistent with multidecadal, non-uniform trends of increasing seasonal sea surface temperatures, affecting the seasonality and composition of foraminiferal communities through changing species phenology. We speculate that similar phenological changes across plankton communities might have led to trophic mismatch, causing the decline in total foraminiferal flux.
Food of young-of-the-year lake trout ( Salvelinus namaycush ) in Presque Isle Harbor, Lake Superior
The food habits of young lake trout ( Salvelinus namaycush ) were studied by examining the digestive tracts of 293 young-of-the-year collected in Presque Isle Harbor, Lake Superior. Lake trout in the 25 to 27-mm length range started to eat food organisms before all of their yolk material was absorbed. Organisms consumed by the 25 to 27-mm young-of-the-year included Chironomidae, Copepoda (Harpacticoida, Calanoida, Cyclopoida), and Cladocerea ( Daphnia spp., Bosmina sp., Chydorus sp.). Chironomid pupae and chironomid larvae accounted for 74% and 5%, respectively, of the total volume of food eaten by the young lake trout in Presque Isle Harbor. Although copepods, cladocerans, and mysids were present in many stomachs, their contribution to the total volume of food was only 15%. Some lake trout in the 32 to 54-mm length range had consumed fry of sculpin ( Cottus spp.) or rainbow smelt ( Osmerus mordax ), but the overall contribution of fish fry to the total volume of food was only 4% (frequency of occurrence, 10%). The lake trout in Presque Isle Harbor fed heavily on planktonic organisms, sparingly on benthic organisms, and were opportunistic feeders that appeared to prey on whatever forage organisms were available in the shallow nearshore waters.
Biostratigraphy and paleoenvironment of Miocene- Pliocene hemipelagic limestone: Kingshill Seaway, St. Croix, US Virgin Islands.
The Kingshill Limestone and younger carbonate rocks constitute the central portion of St. Croix, forming the remains of an ancient seaway that was flanked by emergent highlands. The seaway has been filled with thick epipelagic sediments alternating with carbonate turbidites and ash falls and capped with shallow-water reefal and terrigenous debris. Planktonic foraminifera indicate that ages of these rocks range sequentially in a SW direction from the middle Miocene to lower Pliocene. Scanning electron micrographs illustrate 42 species and subspecies of pelagic foraminifera and 13 selected paleoenvironmentally significant aberrant forms.-from Author
Hydroacoustic estimation of zooplankton biomass at two shoal complexes in the Apostle Islands Region of Lake Superior
Hydroacoustics can be used to assess zooplankton populations, however, backscatter must be scaled to be biologically meaningful. In this study, we used a general model to correlate site-specific hydroacoustic backscatter with zooplankton dry weight biomass estimated from net tows. The relationship between zooplankton dry weight and backscatter was significant (p < 0.001) and explained 76% of the variability in the dry weight data. We applied this regression to hydroacoustic data collected monthly in 2003 and 2004 at two shoals in the Apostle Island Region of Lake Superior. After applying the regression model to convert hydroacoustic backscatter to zooplankton dry weight biomass, we used geostatistics to analyze the mean and variance, and ordinary kriging to create spatial zooplankton distribution maps. The mean zooplankton dry weight biomass estimates from plankton net tows and hydroacoustics were not significantly different (p = 0.19) but the hydroacoustic data had a significantly lower coefficient of variation (p < 0.001). The maps of zooplankton distribution illustrated spatial trends in zooplankton dry weight biomass that were not discernable from the overall means.
A decade of predatory control of zooplankton species composition of Lake Michigan
From 1983 to 1992, 71 species representing 38 genera from the Calanoida, Cladocera, Cyclopoida, Mysidacea, Rotifera, Mollusca and Harpacticoida comprised the offshore zooplankton community of Lake Michigan. Our data demonstrate that the composition and abundance of the calanoid community after 1983 is not unlike that of 1960s and that species diversity of the calanoid community is more diverse than the cladoceran community in the 1990s as compared to the early 1980s. Even though the relative biomass of the cladocerans has remained similar over the 1983-1993 period, the species diversity and evenness of the Cladocera community in the early 1990s is unlike anything that has been previously reported for Lake Michigan. Cladocera dominance is centered in one species, Daphnia galeata mendotae, and only three species of Cladocera were observed in the pelagic region of the lake in 1991 and 1992. Nutrient levels, phytoplankton biomass, and the abundance of planktivorous alewife and bloater chub and Bythotrephes are examined as possible causes of these changes in zooplankton species composition. The increase in Rotifera biomass, but not Crustacea, was correlated with an increase in relative biomass of unicellular algae. Food web models suggest Bythotrephes will cause Lake Michigan's plankton to return to a community similar to that of the 1970s; that is Diaptomus dominated. Such a change has occurred. However, correlational analysis suggest that alewife and bloater chubs (especially juveniles) are affecting size and biomass of larger species of zooplankton as well as Bythotrephes .
Myxosoma cerebralis: A method for staining spores and other stages with silver nitrate
Eleven dye substances were tested for their ability to stain Myxosoma cerebralis and to be retained through either the pepsin-trypsin-dextrose or the plankton centrifuge method of releasing and concentrating spores. Silver nitrate proved to be the best; it produced a distinctive brown color that has been retained by spores through 2.5 yr of storage. The method has applications in histologic studies of whirling disease, in quantifying the efficiency of spore detection procedures, and in teaching.
Evaluation of methods for identifying spawning sites and habitat selection for alosines
Characterization of riverine spawning habitat is important for the management and restoration of anadromous alosines. We examined the relative effectiveness of oblique plankton tows and spawning pads for collecting the eggs of American shad Alosa sapidissima , hickory shad A. mediocris , and “river herring” (a collective term for alewife A. pseudoharengus and blueback herring A. aestivalis ) in the Roanoke River, North Carolina. Relatively nonadhesive American shad eggs were only collected by plankton tows, whereas semiadhesive hickory shad and river herring eggs were collected by both methods. Compared with spawning pads, oblique plankton tows had higher probabilities of collecting eggs and led to the identification of longer spawning periods. In assumed spawning areas, twice-weekly plankton sampling for 15 min throughout the spawning season had a 95% or greater probability of collecting at least one egg for all alosines; however, the probabilities were lower in areas with more limited spawning. Comparisons of plankton tows, spawning pads, and two other methods of identifying spawning habitat (direct observation of spawning and examination of female histology) suggested differences in effectiveness and efficiency. Riverwide information on spawning sites and timing for all alosines is most efficiently obtained by plankton sampling. Spawning pads and direct observations of spawning are the best ways to determine microhabitat selectivity for appropriate species, especially when spawning sites have previously been identified. Histological examination can help determine primary spawning sites but is most useful when information on reproductive biology and spawning periodicity is also desired. The target species, riverine habitat conditions, and research goals should be considered when selecting methods with which to evaluate alosine spawning habitat.
Pathways of food uptake in native (Unionidae) and introduced (Corbiculidae and Dreissenidae) freshwater bivalves
Nineteen species of adult freshwater bivalves were able to use water currents generated from within the mantle cavity to move non-suspended algae into the shell through non-siphon areas such as the anterior shell valve edge and the mid-ventral point of the shell. This was in addition to, and not in replacement of, uptake of planktonic algae through the inhalant siphon. Algae obtained from both the non-inhalant siphon areas and the inhalant siphon were equally captured and transferred to the stomach. Pseudofecal release was also more complex than typically stated. Pseudofeces were released from the inhalant siphon (as expected), plus from the anterior shell margin, and at the mid-point along the ventral shell edge (non-dreissenids). Pseudofeces that settled near the ventral shell margin was accessible for future uptake back into the mantle cavity. There were no species or body size differences in ability to capture food from non-planktonic sources. The extent to which natural populations utilize benthic food resources remains to be determined. However, our study demonstrates that bivalve communities are very adaptable in accessing a variety of food resources from both suspended material in the water column, as well as organic material from the sediments.
Apertural features and surface texture of upper Paleogene biserial planktonic foraminifers: links between Chiloguembelina and Streptochilus.
Several upper Paleogene species of Chiloguembelina have an internal apertural plate that is very similar to the internal plate typical of the Neogene genus Streptochilus. The type species of Chiloguembelina, C. midwayensis midwayensis (Cushman), however, lacks any internal apertural structure or modifications. Therefore, the following 'Chiloguembelina', which have an internal plate, are assigned to Streptochilus: S. cubensis (Palmer), S. martini (Pijpers) and S. sp.aff. S. martini. -Authors
Development of a real-time PCR assay for detection of planktonic red king crab ( Paralithodes camtschaticus (Tilesius 1815)) larvae
The Alaskan red king crab ( Paralithodes camtschaticus ) fishery was once one of the most economically important single-species fisheries in the world, but is currently depressed. This fishery would benefit from improved stock assessment capabilities. Larval crab distribution is patchy temporally and spatially, requiring extensive sampling efforts to locate and track larval dispersal. Large-scale plankton surveys are generally cost prohibitive because of the effort required for collection and the time and taxonomic expertise required to sort samples to identify plankton individually via light microscopy. Here, we report the development of primers and a dual-labeled probe for use in a DNA-based real-time polymerase chain reaction assay targeting the red king crab, mitochondrial gene cytochrome oxidase I for the detection of red king crab larvae DNA in plankton samples. The assay allows identification of plankton samples containing crab larvae DNA and provides an estimate of DNA copy number present in a sample without sorting the plankton sample visually. The assay was tested on DNA extracted from whole red king crab larvae and plankton samples seeded with whole larvae, and it detected DNA copies equivalent to 1/10,000th of a larva and 1 crab larva/5mL sieved plankton, respectively. The real-time polymerase chain reaction assay can be used to screen plankton samples for larvae in a fraction of the time required for traditional microscopial methods, which offers advantages for stock assessment methodologies for red king crab as well as a rapid and reliable method to assess abundance of red king crab larvae as needed to improve the understanding of life history and population processes, including larval population dynamics.
Prey selection for the exotic cladoceran Bythotrephes cederstroemi by selected Lake Erie fishes
The importance of zooplankton in the diet of yellow perch ( Perca flavescens ), white perch ( Morone americana ), walleyes ( Stizostedion vitreum vitreum ), and white bass ( M. chry-sops )was assessed in the central basin of Lake Erie in 1985–1988. Zooplankton were collected by vertical hauls in 1987–1988 and fish with a rock-hopper trawl. Although copepods (calanoid and cyciopoid) were the major zooplankton in the plankton samples, they were not well represented in the fish diet. From 1985 through 1988, Cladocera became an increasingly important food – particularly a recent invader from Europe, Bythotrephes cederstroemi . It was a major component in the diet of yellow perch from June to October in both 1987 and 1988. The zooplankton consumption by white perch was more diverse until September, when B. cederstroemi became the major food item.
Integrated foraminiferal biostratigraphy and chemostratigraphy of the querecual formation (Cretaceous), Eastern Venezuela
An integrated foraminiferal biostratigraphy and chemostratigraphy is presented for the Lower to Upper Cretaceous Querecual Formation exposed on Chimana Grande Island, Eastern Venezuela. The formation consists of >450 m alternating foraminiferal and organic-rich carbonates and laminated mudrocks, and is considered the main hydrocarbon source rock for the eastern Venezuela Basin. Biostratigraphic resolution within the Querecual Formation is poor, due to a paucity of keeled planktonic foraminifera and impoverished benthic faunas. Deposition occurred in a bathyal environment, with dysaerobic or anoxic bottom waters resulting from high rates of surface productivity associated with an upwelling environment. Biostratigraphic evidence indicates that the Querecual Formation ranges from the upper Albian Rotalipora ticinensis Zone to the Santonian Dicarinella asymetrica Zone. Iron and Al contents fall through the Albian-Cenomanian indicating a progressive decrease in the detrital supply, driven by rising eustatic sea level. A Ca profile demonstrates variations in carbonate production and dissolution. High total organic carbon (TOC) intervals occur in the upper Albian to mid-Cenomanian and Turonian, and high Ba/Al and Si/Al ratios characterize mid-Cenomanian and younger sediments. Variations in these elements primarily reflect changes in marine productivity, but are also affected by diagenetic processes. A stable carbon isotope curve established from analysis of organic matter (??13Corg) correlates well with published ??13C curves for carbonates from England and Italy. The Cenomanian/Turonian boundary cannot be identified using planktonic foraminifera, because key taxa are absent, but the base of the Turonian is clearly indicated by a sharp fall in ??13C immediately above a major positive excursion. The bottom of the Coniacian is placed below a ??13C minimum, towards the base of the Dicarinella concavata Zone. Combined with the foraminiferal data, the isotopic data enable much improved stratigraphic resolution compared to previous investigations of the formation.
Life histories and abundance of crustacean zooplankton in the outlet of Lake Superior, 1971-72
In sampling throughout a year, at about 3-wk intervals, of the crustacean zooplankton discharged from Lake Superior through the St. Marys River, 30 species were collected, including three not previously recorded for the lake: the copepod Cyclops strenuus , and the cladocerans Alona costata and Alonella acutirostris . Five copepods, Cyclops bicuspidatus thomasi , Diaptomus ashlandi , D . sicilis , Limnocalanus macrurus , and Senecella calanoides were present in the plankton throughout the year while three other copepods, Diaptomus minutus , Epischura lacustris , and Mesocyclops edax , along with all cladocerans, were present only during summer and fall. Five species of copepods, Diaptomus sicilis , D . minutus , Limnocalanus macrurus , Senecella calanoides , and Epischura lacustris produced a single generation annually; three other copepods and all cladocerans produced two or more generations. All species breed 1–3 mo later in Lake Superior than in lakes Michigan and Erie.
First record of Daphnia lumholtzi Sars in the Great Lakes
Adults of the cladoceran Daphnia lumholtzi , native to Australia, Africa, and parts of Asia, were first collected in August 1999 in Lake Erie. Individuals were collected near East Harbor State Park, Lakeside, Ohio from vertical plankton net tows. The average number of D. lumholtzi that were found (0.03/L) indicate that D. lumholtzi is beginning to establish itself in Lake Erie. The morphology of this Daphnia differs greatly from native species because of its elongated head and tail spine. This sighting is important because it acknowledges yet another exotic invader into the Great Lakes basin and it also shows that this, normally, warm water species continues to expand its range northward.
Reappearance of deepwater sculpin in Lake Ontario: Resurgence or last gasp of a doomed population?
Deepwater sculpin ( Myoxocephalus thompsonii ) were abundant in Lake Ontario in the 1920s and at least common into the 1940s. By the 1960s they were rare and, thereafter, some considered the population extirpated even though a synoptic survey of the lake in 1972 produced three, relatively large (148–165 mm total length, TL), and presumably old, specimens from the northern half of the lake. Deepwater sculpin were absent from annual survey catches in the 1980s and did not reappear until 1996, when three were caught in northern Lake Ontario. Isolated collections of deepwater sculpin continued during 1998–2004. Catches during 1996–2004 included five smaller individuals, 89–118 mm TL. In 2005, catches increased sharply, with 18 deepwater sculpin collected from southern waters and one from northern waters. Moreover, young, small sculpin were dominant in 2005—16 of the 19 sculpins averaged 68 ± 12 mm total length (± 1 s.d.). The young fish observed since 1996 could have originated from reproduction by the small in-lake population, from downstream drift of planktonic larvae from Lake Huron, or both. The presence of juveniles is a clear sign that conditions for survival of young deepwater sculpin are becoming more favorable, perhaps because of reduced abundance of alewife ( Alosa pseudoharengus ), a pelagic planktivore linked to depression of deepwater sculpin in Lake Michigan, and also low abundances of burbot ( Lota lota ) and lake trout ( Salvelinus namaycush ), benthic piscivores.