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Macroinvertebrate diversity in streams

 

Macroinvertebrate diversity was investigated in biofilm samples collected during January, March, May, August and November, 2005.

For each sampling date, twenty similar sized sample rocks (mean surface area +/- SE, 550 +/- 34 cm2) were randomly selected at each site, and the organisms on each rock washed into a sample collection net before being transferred into individual sample containers. Identification of macroinvertebrate taxa was to tribe for Eriopterini and Tanytarsini; subfamily for Orthocladiinae, Tanypodinae and Acarina; family for Elmidae, Hydrophilidae, Chironomidae, Culcidae, Empidadae and Muscidae; subclass for Oligochaeta and phylum for Platyhelminthes.

  • Most notably, the highly impacted stream was dominated, almost exclusively, by members of the subfamily Orthocladiinae (non-biting midges, generally regarded as having high tolerance to various pollutants). This stream contained members of the proposed clean water taxa Ephemoptera (mayflies), Plecoptera (stoneflies) and Trichoptera (caddisflies) commonly referred to as ‘EPT taxa’. The highest proportion of these EPT taxa were detected within the very low impact stream, dominated by the mayfly Deleatidium.


Benthic invertebrates identified in Auckland streams
(click on picture to see the chart in full size)

  • The abundance of mayfly was far greater within the very low impact stream (more than 100 individuals per m2), compared to any other stream. Deleatidium was the most abundant taxon of mayfly within the very low impact site, but populations of Coloburiscus, Nesameletus and Zephlebia were detected on each sampling occasion.


Mayfly abundance in Auckland streams
(click on picture to see the chart in full size)

  • The abundance of stonefly was greatest in the medium impact site, which contained the greatest biofilm biomass (data not shown). The most abundant stonefly taxa within this site belonged to the genera Zelandobius and Acroperla. Despite being ‘EPT taxa’, these particular organisms are known to be relatively tolerant to various human impacts. In contrast, the very low impact stream was dominated by less pollution tolerant genera, including Austroperla, Zelandoperla and Stenoperla.


Stonefly abundance in Auckland streams
(click on picture to see the chart in full size)

  • The abundance of caddisfly was also greatest in the medium impact stream, although the community was again dominated by relatively pollution tolerant taxa (i.e., Oxyethera, Pycnocentriodes and Paraoxyethira). In contract, the low and very low impact streams were comprised of a larger number of caddisfly taxa, including highly pollution sensitive members (e.g. Olinga, Helicopsyche and Costachorema).


Caddisfly abundance in Auckland streams
(click on picture to see the chart in full size)

  • Fly and midge larvae were largely absent from the very low impact stream, and increased in accordance with the level of human impact. Within the most impacted stream, the community was comprised exclusively of members of the subfamily Orthocladiinae.


Fly and midge abundance in Auckland streams
(click on picture to see the chart in full size)

  • Summary. Different macroinvertebrate communities were detected within each stream site. As expected, the lesser impacted sites contained the highest abundance of clean water taxa, whilst the most important sites contained little diversity, being dominated by a single member of the Chironomidae. These findings support that the sites chosen for use in our study are subjected to a broad gradient of ecological impact, from relatively pristine, to highly impacted. These sites therefore provide an excellent opportunity to study the effects of human activity on the microbial community structure, composition and diversity within streams, in comparison with descriptions of macroinvertebrate community organization.

 

   

 

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© Stream Biofilm Project, The University of Auckland 2008-2010
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