Brief description
The impact of the introduced New Zealand screw shell, Maoricolpus roseus, were assessed using a cageing experiment in SE Tasmania (Bligh Point, D'Entrecasteaux Channel). Three treatments consisted of different substratum type (live, dead and empty shells, and dead shells with 50% occupancy by hermit crabs); which were crossed with 2 levels of screwshell density (high and low). Treatment groups were artificially maintained for 20 months before metabolic chambers were used to quantify the community metabolism of different treatment groups.Lineage
Maintenance and Update Frequency: notPlanned
Statement: Experimental design
Treatments included 3 levels of substratum type (live screwshells, dead and empty screwshells, and dead screwshells with 50% occupancy by hermit crabs) crossed with 2 levels of screwshell density (200m-2 and 500m-2). There were 4 replicates of each treatment group, and the experiment was maintained over 20 months. After this time, metabolic chambers (described below) were deployed over each experimental plot for 22 hours (encompassing both a day and night time period).
Treatment cages comprised 0.75m x 0.75m x 90mm PVC frames. Control groups included cages over unmanipulated areas without screwshells and unmanipulated areas without screwshells or cages.
After chamber incubations were complete, 3 x 80 mm sediment cores (30 mm diameter) were extracted from each plot. From these, the biomass of microphytobenthos (MPB) was calculated. Cores were stored at -80 C, MPB biomass was calculated using a 90% acetone extraction on the upper 5mm of each core. In plots containing screwshells, random sub-samples were collected and processed for epiphyte biomass using the acetone extraction method. Epifauna attached to screwshells were counted, removed and stored in 70% alcohol.
After cores and shells were removed from each plot, plots were suction-sampled to 100mm depth using a custom made air lift. Samples were fixed in 5% formaldehyde solution with Rose Bengal stain and stored for identification.
In the lab samples were sieved over 4mm, 2mm and 1mm mesh sizes. All infauna was removed from the 4mm portion, but the 2mm and 1mm samples were split using a Jones-style riffle splitter into quarters, and 2 of these were sampled. All infauna were removed and stored in 70% alcohol, counted and weighed (wet) using a balance accurate to 0.01g to quantify biomass. Epifaunal biomass were estimated.
Statement: Metabolism chambers - design
The chambers consisted of a transparent polyvinyl chloride (PVC) cylinder, 300 mm diameter x 200 mm high. One end was sealed (PVC), and the other open and chamfered. A magnetic stirrer attached to the chamber roof controlled circulation. The stirrer was driven by a 9V DC motor, rotated at ca. 8 rpm.
Gauges on the chamber sides allowed depth of insertion into the sediment and therefore volume of the chamber to be calculated.
An optic fibre dissolved oxygen (DO) probe (Aanderaa oxygen optode 4130) was inserted through the chamber roof and recorded DO concentration and water temperature (degrees) every 10 minutes onto a data logger which was mounted separate to the chamber in a translucent submersible housing (Icolite). The data logger was a Tattletale TFX 1-11.v2 and associated prototype board (Onset computer corp.). Separate data loggers enabled chambers to be controlled separately and data to be stored separately.
Photosynthetically Active Radiation (PAR) was measured and logged by 2 independent underwater sensors (Li-cor LI-192SA) mounted on the outer surface of the chamber. Activation of the PAR sensors was controlled by the data logger.
For the 10 minute interval between DO readings, the PAR sensor pulsed every 2 minutes and the averages of these 5x2 minute reading was stored on the logger.
Statement: Validation of chamber accuracy and use
When using a closed system chamber to quantify community metabolism, problems can arise if condition within the chamber change (e.g. if oxygen concentration becomes excessively low). To assess if communities responded to reductions in oxygen concentration, 2 paired chambers were deployed in the same randomly selected treatment plot - one with a 12 V DC bilge pump enabling the chamber to be flushed at selected intervals, and the second a standard set-up (no pump). Paired chambers were deployed in 10 randomly selected treatment plots and the flux estimates calculated from the flushed chambers were compared to those from the unflushed chambers. The absence of non-linear oxygen fluxes, coupled with the absence of differences between the oxygen flux obtained from both chambers on the same community, was a clear indication that the community within either chamber did not respond adversely to the changing oxygen concentration within the chambers.
Notes
CreditSchool of Zoology, University of Tasmania
Credit
Natural Heritage Trust (NHT) Grant from DEH
Natural Heritage Trust (NHT) Grant from DEH
Purpose
To assess community-level impacts of an introduced species on native soft-sediment assemblages in SE Tasmania.
To assess community-level impacts of an introduced species on native soft-sediment assemblages in SE Tasmania.
Created: 05 09 2008
Data time period: 01 12 2005 to 31 08 2007
text: westlimit=147.3; southlimit=-43.1; eastlimit=147.4; northlimit=-43.0
text: uplimit=12; downlimit=
Subjects
24 079001 |
AQUATIC ECOSYSTEMS |
Benthic Habitat |
Biological Sciences |
BIOSPHERE |
Biomass |
Biosphere | Ecological Dynamics | Competition |
COMMUNITY DYNAMICS |
Community Structure |
Community respiration |
EARTH SCIENCE |
Ecological Applications |
ECOLOGICAL DYNAMICS |
Ecology |
Environmental Sciences |
Epifauna density |
Invasive Species Ecology |
Maoricolpus roseus |
Marine and Estuarine Ecology (Incl. Marine Ichthyology) |
Net oxygen flux |
Oceans | Marine Biology | Marine Invertebrates |
Primary production |
biota |
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Other Information
Identifiers
- global : 302aaf80-7d37-11dd-a8f2-00188b4c0af8
