Biological field and laboratory methods for measuring the quality of ...
Biological field and laboratory methods for measuring the quality of ...
Biological field and laboratory methods for measuring the quality of ...
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BIOLOGICAL METHODS<br />
technique, or combination <strong>of</strong> techniques, will<br />
completely sort out or make more readily<br />
discernible all types <strong>of</strong> organisms from all types<br />
<strong>of</strong> substrate material. In <strong>the</strong> end, <strong>the</strong> total<br />
sample must be examined. If technicians are<br />
routinely conducting <strong>the</strong> picking operation,<br />
<strong>the</strong>se techniques may lead to overconfidence<br />
<strong>and</strong> careless examination <strong>of</strong> <strong>the</strong> remainder <strong>of</strong> <strong>the</strong><br />
sample. If used with proper care, such aids are<br />
not objectionable; however, <strong>the</strong>y are not recommended<br />
as st<strong>and</strong>ard techniques.<br />
As organisms are picked from <strong>the</strong> de bris, <strong>the</strong>y<br />
should be sorted into major categories (i.e.,<br />
insect orders, molluscs, worms, etc.) <strong>and</strong> placed<br />
into vials containing 70 percent ethanol. All vials<br />
from a sample should be labeled internally with<br />
<strong>the</strong> picker's name <strong>and</strong> <strong>the</strong> lot number <strong>and</strong> kept<br />
as a unit in a suitable container until <strong>the</strong><br />
organisms are identified <strong>and</strong> enumerated, <strong>and</strong><br />
<strong>the</strong> data are recorded on <strong>the</strong> bench sheets. A<br />
typical <strong>laboratory</strong> bench sheet <strong>for</strong> fresh-water<br />
samples is shown in <strong>the</strong> Appendix.<br />
4.5 Identification<br />
The taxonomic level to which animals are<br />
identified depends on <strong>the</strong> needs, experience, <strong>and</strong><br />
available resources. However, <strong>the</strong> taxonomic<br />
level to which identifications are carried in each<br />
major group should be constant throughout a<br />
given study. The accuracy <strong>of</strong> identification will<br />
depend greatly on <strong>the</strong> availability <strong>of</strong> taxonomic<br />
literature. A <strong>laboratory</strong> library <strong>of</strong> basic<br />
taxonomic references is essential. Many <strong>of</strong> <strong>the</strong><br />
basic references that should be available in a<br />
tenthos <strong>laboratory</strong> are listed at <strong>the</strong> end <strong>of</strong> <strong>the</strong><br />
chapter.<br />
For comparative purposes <strong>and</strong> <strong>quality</strong> control<br />
checks, store identified specimens in a reference<br />
collection. Most identifications to order <strong>and</strong><br />
family can be made under a stereoscopic<br />
microscope (up to SOX magnification). Identification<br />
to genus <strong>and</strong> species <strong>of</strong>ten requires a compound<br />
microscope, preferably equipped with<br />
phase contrast (la, 45, <strong>and</strong> lOOX objectives) or<br />
Nomarski (interference phase) optics.<br />
To make species identifications, it is <strong>of</strong>ten<br />
necessary to mount <strong>the</strong> entire organism or parts<br />
14<br />
<strong>the</strong>re<strong>of</strong> on glass slides <strong>for</strong> examination at high<br />
magnification. Small whole insects or parts<br />
<strong>the</strong>re<strong>of</strong> may be slide-mounted directly from<br />
water or 70 percent ethanol preservative if CMC<br />
mounting media is used. Label <strong>the</strong> slides<br />
immediately with <strong>the</strong> sample log number <strong>and</strong><br />
<strong>the</strong> name <strong>of</strong> <strong>the</strong> structure mounted. Euparol<br />
mounting medium may be preferable to CMC<br />
<strong>for</strong> mounts to be kept in a reference collection.<br />
Place specimens to be mounted in Euparol in<br />
95 percent ethanol be<strong>for</strong>e mounting.<br />
To clear opaque tissue, heat (do not boil) in a<br />
small crucible (5-ml capacity) containing 5 to 10<br />
percent KOH solution (by weight) until it<br />
becomes transparent. The tissue can be checked<br />
periodically under a stereoscopic microscope to<br />
determine if it is sufficiently cleared. Then transfer<br />
<strong>the</strong> tissue stepwise to distilled water <strong>and</strong> 95<br />
percent ethanol <strong>for</strong> 1 minute each <strong>and</strong> mount<br />
with CMC or Euparol. Several different<br />
structures can be heated simultaneously, but do<br />
not reuse <strong>the</strong> KOH solution.<br />
The above <strong>methods</strong> work well <strong>for</strong> clearing <strong>and</strong><br />
mounting midges, parts <strong>of</strong> caddisflies, mayflies,<br />
stoneflies, o<strong>the</strong>r insects, crustaceans, <strong>and</strong><br />
molluscs; however, worms, leeches, <strong>and</strong> turbellarians<br />
require more specialized treatment be<strong>for</strong>e<br />
mounting (la, 47).<br />
Larval insects <strong>of</strong>ten comprise <strong>the</strong> majority <strong>of</strong><br />
macroinvertebrates collected in artificial<br />
substrate samplers <strong>and</strong> bottom samples. In<br />
certain cases, identifications are facilitated if<br />
exuviae, pupae, <strong>and</strong> adults are available. Collect<br />
exuviae <strong>of</strong> insects with drift nets or by skimming<br />
<strong>the</strong> water's surface with a small dip net near <strong>the</strong><br />
shore. Obtain adults with sweep nets <strong>and</strong> tent<br />
traps in <strong>the</strong> <strong>field</strong> or rear larvae t9 maturity in <strong>the</strong><br />
<strong>laboratory</strong>.<br />
The life history stages <strong>of</strong> an insect can be<br />
positively associated only if specimens are reared<br />
individually. Rear small larvae individually in 6to<br />
12-dram vials half filled with stream water<br />
<strong>and</strong> aerated with <strong>the</strong> use <strong>of</strong> a fine-drawn glass<br />
tubing. Mass rearing can be carried out by<br />
placing <strong>the</strong> larvae with sticks <strong>and</strong> rocks in an<br />
aerated aquarium. Use a magnetic stirrer inside<br />
<strong>of</strong> <strong>the</strong> aquarium (41) to provide a current.