Frances P. Gelwick

Effects of an Algivorous Minnow on Temperate Stream Ecosystem Properties

We used a field experiment to test for effects of the algae-grazing minnow C ampostomna anomnalum on stream ecosystem dynamics. Eight whole pools in Brier Creek, in south-central Oklahoma (USA), served as replicates. Following a stream-resetting flood, four pools with natural densities of Campostotna and four pools with no Campostoma were maintained by fences across riffles for 61 d. Subsequently, a changeover was conducted. Fish were removed from two of the previously grazed pools and added to two of the previously nongrazed pools; the other four pools remained as grazed and nongrazed con- trols. The changeover was maintained for 33 d. A repeated-measures analysis of variance showed significant grazing or grazing x time effects for variables related to organic matter processing, algal primary productivity and community composition, and invertebrate density. Principal components analysis showed complete separation of grazing treatments on the combined first two axes (accounting for 34.6% of the variance). Correlations of variables with these axes corresponded to results of the univariate ANOVAs; pools with Campostoma had lower algal standing crops, higher biomass-specific net primary productivity, greater percent blue-green algae, lower areal coverage by filamentous green algae, lower bacterial density, smaller benthic particulate organic matter fractions, and higher invertebrate density than pools without Campostomna. The changeover indicated that effects of grazing by these fish can be rapid when they enter nongrazed pools, but that effects can linger in formerly grazed pools despite markedly reduced densities of these algivorous fish.

Stability and Persistence of Fish Faunas and Assemblages in Three Midwestern Streams

Long term stability of summer fish assemblages was examined in three distinct systems: Piney Creek, a medium-sized Ozark upland tributary of the White River, Arkansas; Brier Creek, a small prairie-margin stream, tributary to the Red River, Oklahoma; and the Kiamichi River, a medium-sized river in the Ouachita Uplands draining into the Red River, Oklahoma. Sampling periods and numbers of surveys of the three stream systems were 14 yr and six collections for Piney Creek, 17 yr and five surveys for Brier Creek, and 5 yr and three surveys for the Kiamichi River. The fish faunas of all three streams were persistent (regarding presence-absence of species). In all three streams overall faunal structure was stable, as indicated by similarity indices and by concordance of rank abundance of the common species in each stream across all collection years. The results corroborated a conclusion from earlier work that the total fish fauna is more stable in a more environmentally benign stream (Piney Creek) than in a stream subject to greater environmental extremes (Brier Creek). The fish fauna of the Kiamichi River was also stable across three survey periods with respect to rank order of species abundance. Stability of the fish assemblages at individual locations on all three streams was variable, but four of five locations on Brier Creek, and all five locations on Piney Creek exhibited significant concordance overall in ranks of species abundance. Of 59 possible cases, assemblages at 27 individual locations (=46%) on the three streams showed assemblage stability >0.60 between survey periods. We conclude that at the level of whole-stream faunas, all three of these midwestern streams were stable across the survey years, and that many, but not all, individual locations had relatively stable fish assemblages.

Seasonal and spatial variations in fish and macrocrustacean assemblage structure in Mad Island Marsh estuary, Texas

Fish and macrocrustacean assemblage structure was analyzed along an estuarine gradient at Mad Island Marsh (MIM), Matagorda Bay, TX, during March 1998–August 1999. Eight estuarine-dependent fish species accounted for 94% of the individual fishes collected, and three species accounted for 96% of macrocrustacean abundance. Consistent with evidence from other Gulf of Mexico estuarine studies, species richness and abundance were highest during late spring and summer, and lowest during winter and early spring. Sites near the bay supported the most individuals and species. Associations between fish abundance and environmental variables were examined with canonical correspondence analysis. The dominant gradient was associated with water depth and distance from the bay. The secondary gradient reflected seasonal variation and was associated with temperature, salinity, dissolved oxygen, and vegetation cover. At the scales examined, estuarine biota responded to seasonal variation more than spatial variation. Estuarine-dependent species dominated the fauna and were common throughout the open waters of the shallow lake during winter– early spring when water temperature and salinity were low and dissolved oxygen high. During summer–early fall, sub-optimal environmental conditions (high temperature, low DO) in upper reaches accounted for strong spatial variation in assemblage composition. Small estuarine-resident fishes and the blue crab (Callinectes sapidus) were common in warm, shallow, vegetated inland sites during summer–fall. Estuarine-dependent species were common at deeper, more saline locations near the bay during this period. During summer, freshwater species, such as gizzard shad (Dorosoma cepedianum) and gars (Lepisosteus spp.), were positively associated with water depth and proximity to the bay. The distribution and abundance of fishes in MIM appear to result from the combined effects of endogenous, seasonal patterns of reproduction and migration operating on large spatial scales, and speciesspecific response to local environmental variation. 2003 Elsevier Science B.V. All rights reserved.

Fish assemblage structure in relation to environmental variation in a Texas Gulf coastal wetland

We described seasonal fish-assemblages in an estuarine marsh fringing Matagorda Bay, Gulf of Mexico. Habitat zones were identified by patterns of fish species abundance and indicator species optima along gradients in salinity, dissolved oxygen (DO), and depth in our samples. Indicators of the lower brackish zone (lower lake and tidal bayou closest to the bay) were gulf menhaden (Brevoortia patronus), bay anchovy (Anchoa mitchilli), silver perch (Bairdiella chrysoura), and spotted seatrout (Cynoscion nebulosus) at salinity >15‰, DO 7–10 mg l−1, and depth <0.5 m. Indicators of the upper brackish zone (lake and fringing salt marsh) were pinfish (Lagodon rhomboides) and spot (Leiostomus xanthurus) at salinity 10–20‰, DO >10 mg l−1, and depth <0.5 m. In the freshwater wetland zone (diked wetland, ephemeral pool, and perennial scour pool), indicators were sheepshed minnow (Cyprinod on variegatus), rainwater killifish (Lucania parva), mosquitofish (Gambusia affinis), and sailfin molly (Poecilia latipinna) at salinity <5‰, DO <5 mg l−1, and depth ≥1 m. In the freshwater channelized zone (slough and irrigation canal), indicators were three sunfish species (Lepomis), white crappie (Pomoxis annularis), and gizzard shad (Dorosoma cepedianum) at salinity <5‰, DO <5 mg l−1, and depth >1.5 m. In brackish zones, seasonal variation in species diversity among sites was positively correlated with temperature, but assemblage structure also was influenced by depth and DO. In the freshwater zones, seasonal variation in species diversity among sites was positively correlated with depth, DO, and salinity, but assemblage structure was weakly associated with temperature. Species diversity and assemblage structure were strongly affected by the connectivity between freshwater wetland and brackish zones. Uncommon species in diked wetlands, such as tarpon (Megalops atlanticus) and fat sleeper (Dormitator maculatus), indicated movement of fishes from the brackish zone as the water level rose during natural flooding and scheduled (July) releases from the diked wetland. From September to July, diversity in the freshwater wetland zone decreased as receding waters left small isolated pools, and fish movement became blocked by a water-control structure. Subsequently, diversity was reduced to a few species with opportunistic life histories and tolerance to anoxic conditions that developed as flooded vegetation decayed.

Effects of fish, water depth, and predation risk on patch dynamics in a north-temperate river ecosystem

Spatial and temporal variation in water depth affected habitat use by prey fish and their predators, generating a dynamic mosaic of patches with different benthic ecosystem properties. Twelve 4,6-m 2 pens (5-mm mesh), closed or open to fish, were built in two pools of an upland river near Tahlequah, Oklahoma, USA. Fish effects were attributed primarily to the benthic algivores Campostoma anomalum, C. oligolepsis and Notrois nubilus, which comprised 60% of fish abundance in the reach and 83% of benthic fish. Furthermore, mean hourly removal of benthic organic matter (4.4 gm -2 h -1 ash-free dry mass) by these fish exceeded the mean daily accumulation (3.7 gm -2 ) in closed pens. Fish maintained a relatively silt-free grazed epilithon in open pens and unenclosed river, until large fish that predominated in one pool abandoned habitats where their predation risk became critical as water became shallow (<28 cm ). In closed pens and areas abandoned by fish, benthic algal biomass initially increased, but then visibly accumulated silt in an algal matrix that eventually sloughed and regrew in patches of substrata. Blue-green and green algae like that in areas with fish predominated in regrown patches. Closed pens with regrown algae had higher biomass-specific net primary productivity and higher percentage of organic matter than ones with an intact matrix. Invertebrate abundance was higher in closed pens with few sloughed patches than in open pens with fish, but similar in closed pens with regrown patches and open pens abandoned by fish, Invertebrate predators and collector-gatherers predominated in closed pens with an intact matrix and higher percentage of medium (157-507 μm) benthic particulate organic matter (BPOM); collector-filterers and scrapers predominated in open pens, which had higher percentage of ultrafine (0.44-40 μm) BPOM. Assemblages in closed pens with patches of regrown algae and open pens abandoned by fish were dominated by scrapers and collector-gatherers.

Effects of Algivorous Minnows on Production of Grazing Stream Invertebrates

The algivorous minnow, Campostoma anomalum, strongly influences the distribution and standing crop of periphyton in north temperate streams. We conducted a 5 wk experiment in large, recirculating artificial streams to examine the effects of Campostoma on secondary production of two invertebrate grazers, the crayfish Orconectes virilis and the pulmonate snail Physella virgata. Treatments included experimental streams with snails alone, crayfish alone, snails and fish together, crayfish and fish together, and a non-grazed control

Modular Experimental Riffle–Pool Stream System

Abstract We describe a modular method for building a large, outdoor experimental stream system that has great flexibility for research projects in fish ecology, behavior, conservation, or management. The system has been in use for more than a decade at the University of Oklahoma Biological Station (Kingston, Oklahoma) and has been used with modification at four other research facilities in the Midwest. Here, we document the system in detail, including specifications for construction of the original system and modifications or improvements at other sites. The system uses commercially available, customized fiberglass round tank and trough units that can be configured in many different ways to create flowing pool and riffle habitats. The system appears to be a good mimic of small natural streams based on system flow rates, establishment of natural substrates and cover, stream chemistry relative to that of a natural creek, and fish behaviors. At least 39 fish species have been used successfully in 1–14-month ...

Fish Assemblages of Reservoirs, Illustrated by Lake Texoma (Oklahoma-Texas, USA) as a Representative System

ABSTRACT We suggest six generalizations about the ecology of fishes of large, warm, reservoirs in the southern United States. We test these postulates with examples from more than 20 years of our studies in Lake Texoma (Oklahoma-Texas), and previous historic work in this impoundment. Such impoundments are dynamic systems in which precise predictions about fish faunas, local assemblages, or their potential effects in river-reservoir ecosystems are difficult. However, several generalizations can be supported: (1) fish faunas in reservoirs are a largely non-coevolved array of species, consisting of native and non-native species that may remain relatively unchanged for decades; (2) the fish fauna of a reservoir changes in response to introduction of some non-native species but not others; (3) The fish fauna of a reservoir can change in response to abiotic events that occur at a range of spatial and temporal scales, but effects may be inconsistent and transitory; (4) strong abiotic and biotic gradients in reservoirs influence fish distribution from uplake to downlake and from shallow to deep habitats; (5) Predictability of local fish assemblage structure in reservoirs is low and can vary between littoral and open-water zones; (6) Effects of fish on ecology of the reservoir relates to trophic groups represented, and to numbers of omnivorous fish.

5 – Gulf Coast rivers of the Southewestern United States

River catchments flowing into the Texas portion of the Gulf of Mexico encompass a broad geographic area, with latitude ranging from around 38°N in southern Colorado to 25°N in northern Mexico and longitude ranging from about 108°W in western New Mexico to 93°W in western Louisiana. Eleven major rivers discharge into the western Gulf of Mexico from the US, including the Rio Grande, which borders with Mexico. There are eight freshwater ecoregions within the western Gulf rivers. The climate of the region ranges markedly from humid continental in eastern Texas to humid subtropical in the south in Texas, to alpine in southern Colorado and northern New Mexico, to desert in southern New Mexico and western Texas. The rivers of the western Gulf of Mexico pass through 16 highly diverse terrestrial ecoregions, which include forests, grasslands, prairies, savannahs, shrublands, and deserts.

Relative nursery function of oyster, vegetated marsh edge, and nonvegetated bottom habitats for juvenile white shrimp Litopenaeus setiferus

Shallow estuarine habitats, including vegetated marsh edge (VME), oyster reefs (oyster), and nonvegetated soft bottom (NVB), provide important functions for estuarine resident and estuarine-dependent species. A paucity of information exists concerning relative nursery value of these habitats for juvenile fishes and invertebrates. In Grand Bay, MS and Weeks Bay, AL, National Estuarine Research Reserves (NERR), this study evaluated the potential of the three habitats to serve as nurseries by quantifying habitat-specific density, size, growth, and survival of juvenile white shrimp Litopenaeus setiferus. Drop sampling in Oct 2003 and Jul 2004 indicated that white shrimp density was significantly greater in oyster and VME when compared with adjacent NVB. No significant difference occurred in density between oyster and VME. Significantly larger shrimp were collected in NVB, intermediate-sized shrimp were collected in oyster, and smaller shrimp were collected in VME. Using field enclosures to study growth of juvenile white shrimp we found significantly higher growth in oyster when compared with NVB and VME. Predator mesocosm experiments indicated that when blue crabs were used as predators, white shrimp juveniles experienced significantly higher survival rates in VME and NVB when compared with oyster. Our study suggests that juvenile white shrimp may select for oyster over NVB because of higher food availability and not necessarily for refuge needs from predation by blue crabs. In addition, juvenile habitat needs may shift with individual growth, indicating that the relative nursery value of a habitat is not inclusive for all juvenile sizes. Similar to VME, oyster provides an important function in the juvenile stages of white shrimp and should be examined further as a potential nursery habitat.