The seasonal community structure and drift of microcrustaceans in Valley Creek, Minnesota

Abstract

Microcrustaceans represent a poorly known component of stream systems. This study examined the seasonal abundance of copepods and cladocerans found in Valley Creek, Washington County, Minnesota. Both benthic densities as well as drift rates were quantified. A total of 16 species was collected in quantitative benthic samples and two additional species occurred in drift samples. The Valley Creek microcrustaceans could be classified into two general groups, those residing in depositional stream habitats similar to a lake or pond littoral and favoring an epibenthic lifestyle, and those found in more erosional habitats where a hyporheic lifestyle is more likely. The microcrustacean community also demonstrated a distinct seasonality with peak abundance in the spring and early summer. Sediment size compositon also demonstrated a seasonal change but detrital composition did not. Microcrustacean drift generally paralleled changes in benthic density but in several cases it tended to lag behind the changes in the benthos. This lag could be due to a seasonal siltation of the sediments, which would compress the habitat volume available to interstitial meiofaunal elements.

Meiofaunal communities associated with bryophytes and gravels in shaded and unshaded alpine streams in New Zealand

“…Thus, the cyclopoid copepods Bryocamptus vejdovskyi Mrazek and B. zschokkei Schmeil are found only in the hyporheos in fast-flowing waters of streams in Minnesota, United States (Shiozawa 1986). Consequently, the often abundant meiofaunal densities within bryophytes may reflect a use of these plants as a "biotic hyporheic zone", whereby instead of dwelling between interstices of inorganic substrata, animals dwell amongst bryophyte stems and the associated trapped detritus and periphyton where current velocities are low.…”

“…Although lotic meiofauna have been considered only occasionally, both their reported high densities (e.g., Williams & Hynes 1974;Zullini 1976;Shiozawa 1986) and high production values (O'Doherty 1985) imply that these animals contribute significantly to energy dynamics in streams. Unlike most insects which leave the stream upon emergence, meiofaunal taxa such as copepods and nematodes have no emergent stages and consequently most carbon assimilated and not respired by these animals will remain in the stream.…”

“…Although their importance to lentic ecosystems is well-known (e.g., Hutchinson 1967; Anderson & DeHenau 1980;Strayer & Likens 1986), their contribution to stream ecosystems is less understood. Most studies have concentrated on those animals in bare gravels (Rundle 1990;Rundle & Hildrew 1990), the hyporheic zone (e.g., Williams & Hynes 1974;Shiozawa 1986;Williams 1989), or leaf packs (O'Doherty 1985). Little work has been conducted on meiofauna in New Zealand where research has been restricted primarily to taxonomic and ecological investigations of lake faunas (e.g., Chapman & Lewis 1976;Forsyth & Lewis 1987).…”

“…Most lotic meiofauna cannot contend with high water velocities; this usually confines them to siltladen environments characterised by slow, laminarflowing water with thick boundary layers (Chapman & Lewis 1976;Shiozawa 1986). Such an environment is typical of that created around macrophyte beds (e.g., Gregg & Rose 1982), and indeed many members of the meiofauna are associated with aquatic macrophytes where they may obtain shelter and food (Chapman & Lewis 1976).…”

“…Although lotic meiofaunal communities have occasionally been examined (e.g., Williams & Hynes 1974;Jones 1986;Shiozawa 1986;Williams 1989;Rundle & Hildrew 1990), only Cox (1988) has investigated the occurrence of meiofauna within aquatic bryophytes.…”