Multiple Tube Sampler for Benthic and
Pelagic Invertebrates in Shallow Wetlands
Results
We estimated significantly different densities of aquatic invertebrates, except oligochaetes, using the 2 sampling methods (Table 1). The multiple tube sampler yielded lower density estimates for chironomids (F = 12.57; 1,10 df; P = 0.005), and higher density estimates for cladocera (F = 25.02; 1,10 df; P = 0.001) and cyclopoid copepods (F = 20.76; 1,10 df; P = 0.001) than the pooled sampling method. Both samplers yielded similar density estimates for oligochaetes (F = 0.58; 1,10 df; P = 0.465). Wetland did not affect either sampling method (P > 0.05), except for cyclopoid copepods (Table 1). For copepods, there was an interaction (F = 15.26; 1,10 df; P = 0.003) between wetland and sampler type. Both samplers yielded similar cyclopoid densities in the semipermanent wetland, but the multiple tube sampler yielded a higher density estimate (1.440 vs. 0.470) than the pooled sample (F = 15.26; 1,10 df; P = 0.003) in the seasonal wetland.
We examined the potential for over and undersampling by comparing the catches
of water column and benthic samplers with their pooled sample estimate. Each
sampler caught both pelagic and benthic invertebrates. Nearly 60% of the chironomids
in the pooled samples were obtained from the water column sampler, over 10%
of the cladocera were obtained from benthic samples, and roughly 25% of the
copepods were caught with the benthic sampler. Although both the multiple
tube sampler and the pooled sampling methods provided similar density estimates
of oligochaetes, over 60% of the pooled estimate was from the water column
sampler.
Our sampler was used for 4 years to collect wetland invertebrates in a variety
of sediment types. Water depths in our study area varied from 10-90 cm, but
longer tubes can be used to sample in deeper water. The device held up well
to the rigors of sampling and showed no signs of deterioration. The unit cost
approximately $300.00.
Table 1. Density of selected
macroinvertebrate taxa collected from 2 wetlands, Sacramento National
Wildlife Refuge, Willows, California, November 1986 - January 1987.
Taxa
Zone
Sampler typea
(individuals/m²)
Multiple tube
Combinedb
P valuec
SE
SE
Interactiond
Main effecte
Chironomidae
Benthic
2.45
0.12
2.93
0.12
0.492
0.005
Cladocera
Pelagic
3.01
0.12
1.99
0.17
0.416
0.001
Oligochaeta
Benthic
1.40
0.17
1.21
0.16
0.726
0.465
Cyclopoida
Interface
1.17
0.13
0.65
0.13
0.003
0.001
a Means
transformed to natural logs (n = 12).
b Sum of invertebrates in water column (Swanson 1978a)
and benthic samples (Swanson 1978c).
c Based on F-distribution from repeated measures ANOVA
with 1 and 10 df.
d Test for interaction between wetland and sampler type.
e Test for difference between sampler types.
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