摘要:

Prolonged extreme flooding during mid-summer 1993 provided an opportunity to investigate nektonic invertebrate dynamics in lower Illinois River floodplains and backwater lakes. We used plankton nets to sample flooded grass shorelines, flooded forests, and open water habitats during rising and falling stages of the flood. Transects oriented perpendicular to shore were sampled to investigate community composition along the floodplain gradient extending riverward. Invertebrate densities differed between samples collected on the rising stage of the flood (mean = 11,584 individuals m−3) and on the falling stage of the flood (mean = 78 individuals m−3). Density estimates from samples collected at the shoreline of the rising flood waters exceeded estimates from open water and the falling flood shoreline by two orders of magnitude. Corixids were the most abundant taxa found (78%) at flooded shorelines. Densities were highest in inundated grass habitats at the rising edge of the flood. Flooded trees had the next highest densities, followed by floating macrophytes and open water. Our findings exemplify the flood pulse hypothesis in that productivity, as measured by invertebrate density, increased dramatically on the rising flood but then fell just as dramatically on the falling flood.

ISSN:0270-5060    

DOI:10.1080/02705060.1999.9663708

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Zebra mussels (Dreissena polymorpha) were aerially exposed at temperatures of 5 C and 20 C for 12, 24, 36, and 60 h. Survivorship was nearly 100% in all control containers and for the 5 C replicates but declined substantially in the 20 C replicates after 36 and 60 h. Additional zebra mussels were aerially exposed at 5 C and 20 C on both wet and dry substrates for 60 h. Those aerially exposed on a wet substrate at 5 C had greater survivorship than did mussels on a dry substrate at 20 C. Larger zebra mussels (shell length > 16 mm) were significantly more likely to survive exposure for 36 or 60 h at 20 C than were smaller individuals. These results show that survivorship of freshly-collected zebra mussels under controlled, biologically-relevant conditions is strongly affected by length of aerial exposure, ambient temperature, substrate moisture, and mussel size. Our findings largely confirm results of companion field experiments, implying that temperature and moisture conditions caused the observed zebra mussel mortality in nature. Taken together, these studies suggest that aerial exposure at warm temperatures (≥ 20 C) may be an effective control for zebra mussels in regulated waters where water levels can be lowered for more than 24 h.

ISSN:0270-5060    

DOI:10.1080/02705060.1999.9663709

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

We investigated prevalence and intensity patterns of nine parasite taxa in 244 age-0 largemouth bass (Micropterus salmoides) collected from lake (high dissolved oxygen levels), riverine (high current velocities), and swamp (hypoxic canals and bayous) sites (N=6) in the Atchafalaya River Basin during the 1996 flood pulse. Ectoparasites were dominated by monogenetic trematodes (prevalence=100%; median intensities 27–91 per host) and glochidia (prevalence > 96% at all sites, median intensities 47–148 per host), whereasPosthodiplostomum minimum(Trematoda),Caecincolaspp. (Trematoda;C. parvulusand perhapsC. latostoma), Neoechinorhynchus cylindratus(Acanthocephala), andProteocephalus ambloplitis(Cestoda) accounted for 94.6% of bass endoparasites. Overall, lake sites supported the highest median parasite intensities in bass and most highly parasitized individuals.P. minimumwas prevalent in bass collected from all sites, but intensities were highest in bass from lake habitats. In contrast,P. ambloplitisexhibited lower than expected prevalence in bass from lake sites (P. < 0.05) and higher intensity (P < 0.02) in bass from riverine sites. Patterns of parasite abundance appeared to be related to habitat effects on intermediate host and parasite life-cycle dynamics rather than hypoxia-related suppression of bass immune responses.

ISSN:0270-5060    

DOI:10.1080/02705060.1999.9663710

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Limnological studies of Mountain Lake, Giles County, Virginia were conducted from June to October of 1997 and April to October of 1998 to evaluate the lake's trophic state, which was considered to be in an early stage of eutrophication from the late 1980s to early 1990s. Orthophosphate-P levels averaged 1.5μg/L in 1997 and 2.2μg/L in 1998, a return from 27.0μg/L in 1990 to early and mid 1980s levels. Ammonium-N also dropped, but nitrate-N increased in 1997–98 compared to 1990. The N:P ratio of 143:1 in 1997 and 244:1 in 1998 compared to 9.4:1 in 1990 clearly indicated P as the major limiting nutrient. Dissolved silica, hardness, alkalinity, and pH in the lake were similar to earlier studies. Phytoplankton taxa and cell densities were similar to those of the mid-1980s. Mountain Lake is thus oligotrophic and presently shows no signs of eutrophication. Input streams feeding the lake were also low in key nutrients, but precipitation constituted a major source of P, N, and acidity to the lake.

ISSN:0270-5060    

DOI:10.1080/02705060.1999.9663711

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The pirate perch (Aphredoderus sayanus) is common throughout its range; however, little is known about its reproductive ecology. Reports of spawning periods range from January to April, but it is unclear whether the pirate perch is a nest spawner or a branchial brooder. Results of this study indicated the major spawning period for pirate perch in the Atchafalaya River Basin, Louisiana, is February through March (12.6—22.8 °C). Larval pirate perch were collected in limnetic areas at 3.6-mm total length and were absent at 14-mm total length. It appears that adult pirate perch are not branchial brooders but release their adhesive eggs over leaf litter and woody debris.

ISSN:0270-5060    

DOI:10.1080/02705060.1999.9663712

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The invasive Asiatic clam,Corbicula fluminea(Müller, 1778), is reported from the Negro River, at Chimpay, in the Patagonian shrubland. The invasion seems to have occurred in 1997–1998, as revealed by its absence in the field assessments made up to January 1997 and the presence of a layer ofCorbiculaempty shells in the dry sand banks left by the flood of the river in winter 1998.

ISSN:0270-5060    

DOI:10.1080/02705060.1999.9663713

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

ISSN:0270-5060    

DOI:10.1080/02705060.1999.9663714

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

ISSN:0270-5060    

DOI:10.1080/02705060.1999.9663697

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor