Poten)al effects of the varnish clam, Nu#allia obscurata, on biogeochemical cycling in the inter)dal Dept of Biological Sciences, Simon Fraser University Burnaby, BC V5A 1S6 Chan and Leah Bendell Kayi kca2@sfu.ca, bendell@sfu.ca Introduc)on Objec)ves Bri7sh Columbia (BC) in the early 1990’s. It is Results Tier 1: Field Survey Tier 3 To examine the rela7onship between the density of the benthic bivalve community believed to have been deposited into Vancouver and sediment parameters Harbour via ballast water from Asia. It has since Tier 2: Mesocosm Experiment rapidly spread at high densi7es (800 ind/m2). To determine if sediment parameters are affected by the varnish clam The effects of varnish clams on nitrogen cycling and sediment proper7es are currently unknown. Tier 3: Microcosm Experiment To determine the poten7al effects of varnish clams on ammonium flux Tier 1 Fillongley Provincial Park Depth Fillongley Provincial Park Parameter Surfical Intermediate Materials & Methods Tier 1: Field Survey Five transects were randomly selected perpendicular to sampled from each transect. Triplicate sediment cores were taken from each quadrat and spliced every 3 cm to create a sediment depth profile. Quadrats were sieved for the benthic bivalve community. Tier 2: Mesocosm Experiment Density exclusion cages were randomly seeded with varying densi7es of varnish clams. Sediment cores were taken from each cage and spliced every 3 cm to create a sediment depth profile. Ammonium flux was measured. S 0.0010 0.678 0.003 SV 0.0176 0.578 0.04
0.011 0.02
0.00
US 0.0003 0.336 0.061 5
10
15
20
USV 0.0000 0.0196 0.681 β1 r2 p-­‐value S 0.0001 0.349 0.055 SV 0.0006 0.927 <0.001 US 0.0000 0.401 0.036 USV 0.0000 0.321 0.069 25
p-­‐value S 0.1376 0.1734 S + FS S + FS + Ht 0.6864 0.7614 0.001 0.001 S + FS + CS + Ht 0.8481 0.0004 CS 0.3292 0.0253 CS + FS G + FS G + CS + FS 0.4979 0.5282 0.7018 0.0160 0.0110 0.0031 G + CS + FS + S 0.8042 0.0014 0.0020
0.0015
0.0010
0.0005
0.0000
0
5
10
15
20
25
Day
Note: upper panel shows ammonium concentra7on in the sediment for sterilized (S) , sterilized with varnish clams (SV), unsterilized (US) and unsterilized with varnish clams (USV) treatments. Lower panel shows ammonium concentra7on in the overlying waters for the four treatments. Corresponding tables show the slope (β1), r2 and p-­‐values of the linear regressions. Increases in ammonium concentra7ons in sediments and overlying waters were the result of the excretory processes of the varnish clam. Conclusions Nitrogen is a limi7ng nutrient in marine systems. Inorganic nitrogen in the form that abio7c factors best predicted bivalve densi7es. microphytobenthos, both which form the basis of all marine food webs. The Tier 2 increase in ammonium and poten7al accumula7on of organic maVer in the 8.0
7.5
Surficial (0-3 cm)
Intermediate (3-9 cm)
Bottom (9+ cm)
7.0
6.5
6.0
There appeared to be higher presence of high densi7es of varnish clams could result in changes to the concentra7ons of organic maVer in ecosystem func7oning of the inter7dal. the high density treatment at the Acknowledgements 5.5
intermediate (3-­‐9 cm) depth. 5.0
4.5
Control
Low
Medium
High
Ammonium concentra7ons were 0.035
Ammonium Concentration (mg/g)
added to sterilized and unsterilized treatments. p-­‐value of ammonium is preferen7ally used by phytoplankton as well as Tier 3: Microcosm Experiment sterilized by autoclaving. Varnish clams were r2 R2 max regressions for surficial (0-­‐3 cm) and intermediate (3-­‐9 cm) depths showed Sediments and seawater from Fillongley were r2 Max Value Note: parameters gravel (G), coarse sand (CS), fine sand (FS), 7dal height (Ht), organic maVer and ammonium concentra7ons were added to the regression. Organic Matter Concentration (mg/g)
the shore line. Three 7dal heights were randomly 0.06
0
Overlying Water Ammonium Concentration (M)
Results Studies were conducted at 0.08
S
S Regress
SV
SV Regress
US
US Regress
USV
USV Regress
0.0025
Study Area located on Denman Island, BC β1 0.10
Sediment Ammonium Concentration (mg/g)
Nu#allia obscurata, commonly known as the varnish clam, was first reported in 0.030
significantly higher in the high 0.025
density (800 ind/m2) treatments for 0.020
0.015
the intermediate (p < 0.001) and 0.010
0.005
Control
Low
Medium
Treatment
High
boVom depths (p < 0.001) I would like to thank Leah Bendell, Isabelle Côté and Mike Hart for all their support and insights. Thank you to the members of the Bendell lab and the mul7tude of volunteers and assistants that worked on this project. This project was funded by the following sponsors: