Sue A. Perry

Effects of experimental flow regulation on invertebrate drift and stranding in the Flathead and Kootenai Rivers, Montana, USA

Studies were conducted to determine the effects of experimental manipulations of discharge on invertebrate drift in two regulated rivers in northwestern Montana, USA. During these studies the discharge regime in the Flathead River was characterized by frequent flow fluctuations, while in the Kootenai River high discharge was maintained for much longer periods before flow was reduced to minimum discharge. The magnitude of the response of invertebrates to disturbance was different in the two rivers, in part because of the different frequencies of flow changes. Midstream invertebrate drift increased an order of magnitude during increasing discharges in the Flathead River but was not substantially increased during decreasing discharges. When the prior discharge regime had been sustained at high levels in the Kootenai River, invertebrate drift densities as high as 300 000/100 m3 were measured along the shoreline following reductions in discharge, both immediately after flow began to decrease and after dark on the same day. There was also more recolonization of shoreline areas and more stranding of insects following dewatering of nearshore regions when there had been sustained high discharge levels prior to the flow reduction. More insect stranding occurred during a faster rate of decrease in discharge (50 000 to 100 000 organisms m−2).

Diapause in copepods (Crustacea) from ephemeral habitats with different hydroperiods in Everglades National Park (Florida, U.S.A.)

Water management practices in the Everglades have severely stressed the natural system, particularly by reducing the hydroperiods of much of the region. During the dry season of 1999, we investigated the influence of hydroperiod on the species composition and dormancy patterns of freshwater copepod communities in seasonal wetlands of Everglades National Park, Florida, U.S.A. The habitats were characterized by an annual dry season, from December through June. We sampled at two locations: the Long Pine Key area of the Rocky Glades region (short hydroperiod, ca. 4–5 months), and western Taylor Slough (intermediate hydroperiod, ca. 8–10 months). Both areas have experienced a reduction in natural hydroperiods and an increase in the frequency of dry-down. We collected weekly plankton samples from Rocky Glades solution holes to assess the potential species pool of copepods. To document the taxa capable of surviving dry-down by resting, we performed three immersion trials in which we rehydrated, in laboratory aquaria, sediment patches from solution holes and surface soils from all stations. Only a subset of the planktonic species collected emerged from the dried sediments. The cyclopoids Microcyclops rubellus and Paracyclops poppei were dominant. This is the first record of diapause for P. poppei. Species distributions from the different hydroperiod soil patches indicated that more diapausing species occurred at the sites that dried for shorter periods. Emerging individuals of M. rubellus and P. poppei were mainly ovigerous females, demonstrating a resting strategy seldom before recorded. The cyclopoid Diacyclops nearcticus had not been previously reported to diapause, but they emerged from the dried sediments in our trials. Our collections included six new records for Florida: Diacyclops nearcticus, Megacyclops latipes, Orthocyclops modestus, Elaphoidella marjoryae, Bryocamptus sp. and Bryocamptus cf. newyorkensis. Paracyclops poppei, Macrocyclops fuscus and Arctodiaptomus floridanus are new records for Everglades National Park. Clearly, diapause is an important strategy for the persistence of copepods in short-hydroperiod wetlands. The duration of the dry period appears to be inversely related to the number of species that emerge from diapause.

Effects of exported seston on aquatic insect faunal similarity and species richness in lake outlet streams in Montana, USA

The quantity of seston exported from a lake affected the qualitative composition and species richness of aquatic insects in 13 lake outlet streams in northwestern Montana. Mean values for chlorophyll and particulate organic carbon in lake effluent waters ranged from 0.5 to 2.7 and 80 to 601 mg m-3, respectively. Correlations between a detrended correspondence analysis of faunal similarities in outlet streams and measures of organic export from the lake indicated that distributional patterns were primarily dependent upon the general trophic status of the lakes. A comparison of faunal assemblages at stream stations located at the outlet and 100 m downstream demonstrated that species composition at the two stations was more similar in productive systems.

A List and Identification Key for the Freshwater, Free-Living Copepods of Florida (U.S.A.)

Abstract We present an inventory of the free-living freshwater copepod crustaceans recorded from the state of Florida, U.S.A. The list is based on previously published information and on new data collected during recent research on surface- and groundwater-dwelling copepods in Everglades National Park, and a few collections in temporary and permanent surface waterbodies elsewhere in the state. We provide information on the ecology and taxonomy of some of the species, and a key for the identification of all the taxa. A total of 65 taxa of free-living copepods: 9 calanoids, 41 cyclopoids, and 15 harpacticoids are now known from the peninsula. Forty-four of these are known from Everglades National Park and adjacent areas; we add four species to a previous checklist for this region. The historically more intensive sampling here has resulted in the discovery of five new named taxa and six that remain in open nomenclature, 10 of which have so far been found only in the Everglades. Of the species collected so far in central and northern Florida, two calanoids and one cyclopoid have been found only in the state so far, whereas all the others are widespread in North America and beyond. Among the predominant North American fauna is a small neotropical component consisting of one calanoid, six cyclopoids, and five harpacticoids. One cyclopoid species is considered to be introduced.

Exchanges of copepod fauna between surface- and ground-water in the Rocky Glades of Everglades National Park (Florida, U.S.A.)

We studied species composition and individual abundance of copepods in the surficial aquifer in short-hydroperiod habitats of Everglades National Park by collecting copepods from different depths at selected wells for two consecutive years. Subsurface copepod communities were dominated by surface copepods that colonized ground-water mainly at the beginning and at the end of the wet season, when ground-water levels dropped about 60 cm below ground level. Copepods entered ground-water, but decreases in community similarity with increasing distance between wells suggest that they did not disperse far from the input location. The five most abundant species were stygoxenes: Osphranticum labronectum, Arctodiaptomus floridanus, Orthocyclops modestus, Thermocyclops parvus, and Macrocyclops albidus. Two stygophiles were collected: Diacyclops nearcticus was abundant, whereas Elaphoidella marjoryae was rare. Elaphoidella fluviusherbae, and perhaps a Parastenocaris sp., were the only stygobites collected.

Spatially explicit population responses of crayfish Procambarus alleni to potential shifts in vegetation distribution in the marl marshes of Everglades National Park, USA

Hydropattern disturbance has had wide-ranging impacts on wetland communities of the Florida Everglades, especially on the habitats and the aquatic biota of the seasonally flooded marl marshes. We used the Everglades crayfish Procambarus alleni as a model to study the associations among hydrology, vegetation distribution, and population dynamics to assess the potential impacts of hydrological changes on the aquatic faunal community in Everglades National Park. To classify benthic habitats as sources or sinks for the crayfish population, we quantified vegetation community structure using GIS maps in which dominant vegetation types were weighted by local hydroperiod (length of inundation). Regression analysis showed that this habitat classification was associated with crayfish density distribution. We then used a spatially explicit, stage-structured population model to describe crayfish population fluctuations under current environmental conditions and to simulate the potential population-level responses to habitat changes that might occur following hydrological restoration. In habitat that was initially saturated with crayfish, the crayfish population size declined under current environmental conditions and then stabilized at about 13% of the initial density over a 50-year period. A 4-month increase in hydroperiod was then simulated by converting shorter-hydroperiod Muhlenbergia-dominated marsh habitat to longer-hydroperiod Cladium-dominated marshes. The model predicted a rapid 7-fold increase in crayfish density following the simulated habitat restoration. This indicated that several functional effects may result from the restoration of historical hydropatterns in marl marshes: (1) the areal extent of habitat sinks will be reduced to isolated patches, whereas the spatial distribution of aquatic source habitats will expand; (2) crayfish population size will increase and persist over time; (3) the minimum threshold needed to increase secondary aquatic productivity may be a 7-month hydroperiod over 90% of the marl marsh landscape. Restoration of historical hydropatterns could thus have cascading positive effects throughout the Everglades aquatic food web.

Temporal and Spatial Variations in Copepod (Crustacea) Communities in Groundwater in the Rocky Glades of Everglades National Park (Florida, USA)

ABSTRACT We studied species composition and individual abundance of copepods in the surficial aquifer in short-hydroperiod habitats of Everglades National Park by collecting copepods from different depths in wells for three consecutive years. The wells were cased and open at depths that corresponded to highly permeable layers. Groundwater communities were dominated by surface copepods which colonized groundwater mainly during the dry season. The total number of copepods collected decreased exponentially with depth; the decrease in copepod numbers and species richness below the 3 m depth was due to high permeability of the limestone above 3 m depth and to the presence of a semipermeable layer at lower depths. The calanoid Osphranticum labronectum and the cyclopoids Orthocyclops modestus and Thermocyclops parvus that were dominant in the collections can be considered stygophiles at least in Everglades National Park. Copepod groundwater communities were most similar on a local scale, indicating that when local surface water populations enter groundwater by following the receding water table, they do not disperse widely through the groundwater system. Densities of groundwater populations of stygophiles were low, which increases their risk of being impacted by changes in hydrology.