Healthy Estuary and Rivers of the City Water quality and ecosystem health monitoring programme of Ihutai
The sediments and biota of the Estuary of the Heathcote and Avon Rivers/Ihutai and tidal reaches of the Avon/Ōtākaro and Heathcote/Ōpawaho rivers Summary report on data collected in 2018
Report No. R19/131 ISBN 978-1-98-859383-8 (print) 978-1-98-859384-5 (web)
Report prepared by Lesley Bolton-Ritchie
June 2019
Data collected by EOS Ecology, for Christchurch City Council
Healthy Estuary and Rivers of the City Water quality and ecosystem health monitoring programme of Ihutai
The sediments and biota of the Estuary of the Heathcote and Avon Rivers/Ihutai and tidal reaches of the Avon/Ōtākaro and Heathcote/Ōpawaho rivers Summary report on data collected in 2018
Report No. R19/131 ISBN 978-1-98-859383-8 (print) 978-1-98-859384-5 (web)
Report prepared by Lesley Bolton-Ritchie
June 2019
Data collected by EOS Ecology, for Christchurch City Council
Name Date Prepared by : Lesley Bolton-Ritchie 30 May 2019 Senior Water Quality Scientist, Coastal Reviewed by : Helen Shaw October 2019 Surface Water Science Manager Approved by: Tim Davie November 2019 Chief Scientist
Report No. R19/131 ISBN 978-1-98-859383-8 (print) 978-1-98-859384-5 (web)
200 Tuam Street PO Box 345 Christchurch 8140 Phone (03) 365 3828 Fax (03) 365 3194
75 Church Street PO Box 550 Timaru 7940 Phone (03) 687 7800 Fax (03) 687 7808
Website: www.ecan.govt.nz Customer Services Phone 0800 324 636 Healthy Estuary and Rivers of the City Water quality and ecosystem health monitoring programme of Ihutai
Summary This report presents the results from the 2018 monitoring of the sediments and biota within the Estuary of the Heathcote and Avon Rivers/Ihutai and in the tidal reaches of the Avon River/Ōtākaro and the Heathcote River/Ōpāwaho. This monitoring programme is part of the four monitoring programmes described in The Healthy Estuary and Rivers of the City: Water quality and ecosystem health monitoring programme of Ihutai document (Batcheler, et al., 2009). This is the twelfth annual summary report on the sediment and biota. A report in which the data collected between 2007 and 2018 are analysed for trends and ecological state will be produced in the near future.
The sediments and biota at each of seven sites were sampled in March-April 2018. From each site: • three composite sediment samples were collected and analysed for grain size distribution. • twelve sediment core samples were collected and analysed for the presence and abundance of animal species larger than 0.5 mm. • twelve quadrat samples were viewed to assess the abundance or % cover of surface dwelling plants and animals. • the mudflat snails within the quadrats were measured and at two sites the cockles present within the quadrats were also measured. • the cockles present within the cores were measured.
The results are presented by site. The data are summarised in graphs and tables.
Environment Canterbury Technical Report i Healthy Estuary and Rivers of the City Water quality and ecosystem health monitoring programme of Ihutai
ii Environment Canterbury Technical Report Healthy Estuary and Rivers of the City Water quality and ecosystem health monitoring programme of Ihutai
Table of contents
Summary ...... i
1 Background ...... 1
2 Introduction ...... 1
3 Methods ...... 2 3.1 Sampling sites ...... 2 3.2 Collection of samples ...... 3 3.2.1 Sediments ...... 3 3.2.2 Biota ...... 3
4 Results ...... 4 4.1 Plover Street ...... 5 4.2 Pleasant Point jetty ...... 6 4.3 Avon River/Ōtākaro mouth ...... 7 4.4 Discharge point ...... 8 4.5 Humphreys Drive ...... 9 4.6 Heathcote River/Ōpāwaho mouth...... 10 4.7 Causeway ...... 11
5 References ...... 12
Environment Canterbury Technical Report iii Healthy Estuary and Rivers of the City Water quality and ecosystem health monitoring programme of Ihutai
iv Environment Canterbury Technical Report Healthy Estuary and Rivers of the City Water quality and ecosystem health monitoring programme of Ihutai
1 Background The monitoring of the sediments and biota within the Estuary of the Heathcote and Avon Rivers/Ihutai and tidal reaches of the Avon/Ōtākaro and Heathcote/Ōpawaho rivers is one of the monitoring programmes undertake as part of the Healthy Ecosystems component of The Healthy Estuary and Rivers of the City: Water quality and ecosystem health monitoring programme of Ihutai (Batcheler, et al., 2009). The Healthy Estuary and Rivers of the City monitoring programme, which is a collaborative programme between the Christchurch City Council, Environment Canterbury and the Avon Heathcote Estuary Ihutai Trust, assesses four environmental values of Ihutai. These values are: A. Safe for contact recreation B. Healthy ecosystems C. Food gathered is safe to eat D. Culturally acceptable mahinga kai values
The monitoring detailed in Batcheler, et al., (2009) has been underway since 2007.
2 Introduction Healthy intertidal estuarine sediment supports a diversity of animals, including anemones, snails, shellfish, worms, crabs and hoppers. The presence, survival and abundance of these animals (biota) depends on the quality and salinity of the water1 and the quality and grain size distribution of the sediment. The diversity and abundance of the animals provides food for fish and birds while shellfish, such as cockles, are a valued food item for many people. These sediment-living animals, by their normal actions of feeding and burrowing, keep the sediments well oxygenated and healthy.
The features of the sediment that influence the types and abundance of the animals that live on or in it are: • the size of the sediment grains that make up the sediment; • the amount of organic matter in the sediment; and • the concentrations of potentially toxic contaminants.
This 2018 annual summary report presents the sediment grain size distribution and summary data on the animals living in the sediment and the animals and obvious plant species on the surface of the sediment. It is the twelfth such annual summary report. The reader can refer to the previous annual summary reports (available at https://www.ecan.govt.nz/technical-reports/) to evaluate differences over time. There is also a report in which the data collected between 2007 and 2013 https://www.ecan.govt.nz/data/document- library/?ids=2270091,2485016,2238770,1589707,2026256,1142660,932291,691837,1274055,932286 are evaluated. A report in which the data collected between 2007 and 2018 are analysed for trends and ecological state will be produced in the near future.
1 The water within the estuary is primarily a mix of the freshwater flowing out of the Avon/ Ōtākaro and Heathcote/ Ōpāwaho rivers and the sea water from Pegasus Bay that flows into the estuary as the tide rises.
Environment Canterbury Technical Report 1 Healthy Estuary and Rivers of the City Water quality and ecosystem health monitoring programme of Ihutai
3 Methods
3.1 Sampling sites The seven sites sampled in 2018 are shown in Figure 3-1.
Figure 3-1: The sampling sites within the Estuary of the Heathcote and Avon Rivers/Ihutai in the tidal reaches of the Avon/Ōtākaro and Heathcote/Ōpāwaho rivers
2 Environment Canterbury Technical Report Healthy Estuary and Rivers of the City Water quality and ecosystem health monitoring programme of Ihutai
3.2 Collection of samples The methods used follow the national protocol for monitoring estuarine environments (Robertson et al., 2002). The GPS co-ordinates of each site were recorded. All sites were sampled in March and April 2018. The sites were sampled by EOS Ecology on contract to the Christchurch City Council.
3.2.1 Sediments The top 20 mm of sediment was collected. Three composite sediment samples from each site were analysed for sediment grain size distribution.
3.2.2 Biota Plants and animals on the surface of the sediment (epifauna) Twelve, 50 cm x 50 cm (0.25 m2) quadrats were sampled at each site. The number of each different type of animal on the surface of the sediment and the number of crab burrows in each quadrat was counted and recorded. The percentage of the surface covered by seaweeds and seagrass was determined using a grid overlying the quadrat.
Crab burrows Crab burrows are common in the estuary. Burrows are easily counted but whether a crab lives in the burrow is not known. The type of crab in the burrow is also not known. The two common crabs that burrow in the estuary are the stalk-eyed mud crab (Hemiplax hirtipes) and the mud crab (Austrohelice crassa).
Seaweed cover Green sea lettuce (Ulva sp.) and the red seaweed Gracilaria chilensis occur in the estuary. Where these seaweeds occur they cover the mudflat, so in a quadrat it is the percentage of the mudflat covered by seaweed that is used as a measure of seaweed abundance.
Animals living in the sediment (infauna) Twelve 130 mm diameter x 150 mm deep cores were sampled at each site. Each sample was sieved through a 0.5 mm screen and the material retained on the screen stored in alcohol for analysis. The number of each different type of animal in each core was counted and recorded.
Size distribution of some common animals The height of all mudflat snails present in the quadrats was measured. The length of all cockles in each core was measured. The length of cockles in the quadrats (dug to a depth of 120 mm) from the Plover Street and Causeway sites were also measured.
Environment Canterbury Technical Report 3 Healthy Estuary and Rivers of the City Water quality and ecosystem health monitoring programme of Ihutai
Mudflat snail (Amphibola crenata) Mudflat snails live on the sediment surface. They feed on the micro-organisms and organic matter in the sediment. As they feed they leave a string-like trail of waste. They lay their eggs into a tyre-like rim of mud. Mudflat snails can tolerate a wide range of salinity and temperature and exposure to air for considerable periods of time.
Tuaki/Cockles (Austrovenus stutchburyi) Cockles live just below the sediment surface. The size classes described in the results are: Recruits 0 – 5 mm Juveniles 5 – 20 mm Reproductive adults >20 mm Edible size >35 mm
4 Results The results are presented by site (Sections 4.1 - 4.7). The results for six sites Plover Street, Pleasant Point jetty, Avon River/Ōtākaro Discharge point, Humphreys Drive and Heathcote River/Ōpāwaho are each presented on one A3 page. The results for Causeway are presented on two A3 pages.
For each site • Sediment grain size data are presented as a table and a pie chart. • The invertebrate species present are listed. • The proportion of each invertebrate species in the cores samples is presented in a pie chart. • The number of taxa, abundance of individuals, species diversity and species evenness of the animals within the core samples are summarised in a table. • The total number of cockles present within the cores and quadrats is provided. • At sites where cockles were measured and there were a sufficient number of individuals to allow for graphing, the results are plotted in a histogram. • At sites where there were a sufficient number of mudflat snails to allow for graphing, the size distribution of individuals is plotted in a histogram. • A summary of the abundance of plants and animals living on the sediment surface is presented in a table.
4 Environment Canterbury Technical Report
4.1 Plover Street COCKLES Sediment grain size distribution (1442 individuals measured in quadrats)
% clay 0.3% recruits 31.3% juveniles % silt 68.4% reproductive adults % sand 0% edible size
Sample % clay % silt % sand Size distribution of cockles 1 8.9 26.3 64.8 600 2 8.8 26.7 64.5 500 3 11.3 29.0 59.7
400
300
200
Number of individuals 100 This graph shows the average percent of each grain size group. There is some variability in the 0 grain size composition between samples. The sediment at this site is muddy (mud=silt+clay) sand. 5 10 15 20 25 30 35 40 45
shell length (mm)
Proportion of each type of animal living in/on the sediment (core samples) blue colours are snails and shellfish red colours are worms grey colours are crustacea green are other Invertebrate animals present at this site tuaki/cockles Scientific name Common name Aonides sp. Amphibola crenata mudflat snail Arthritica sp. small bivalve topshell Austrovenus stutchburyi tuaki/cockle Capitella spp. Cantharidus tenebrosus topshell small limpet Cominella glandiformis mudflat whelk snails and shellfish Scoloplos cylindrifer Diloma subrostrata black topshell Macomona liliana wedge shell black topshell Mytilidae mussel Notoacmea elongata small limpet Prionospio sp. Perna canaliculus green-lipped mussel stalk-eyed mud crab Aonides sp. Heteromastus filiformis Armandia maculata Boccardia spp. pill-box crab Capitella spp. Scolecolepides benhami Glycera americana Heteromastus filiformis small bivalve worms Nicon aestuariensis wedge shell Pectinaria australis mudflat whelk Platynereis australis Prionospio sp. 2 other species Scolecolepides benhami hopper Scoloplos cylindrifer Oligochaetes Nicon aestuariensis Austrohelice crassa mud crab mud crab Halicarcinus sp. pill-box crab crustacea Glycera americana Hemiplax hirtipes stalk-eyed mud crab Paracalliope sp. hopper 3 snails and shellfish Anthopleura aureoradiata anemone other 5 worm species Nemertea ribbon worm
Summary of the presence and abundance of animals living in/on the sediment (core samples) TUAKI/COCKLES number of taxa per core number of individuals per square metre snails and snails and Species Species (171 individuals measured in the cores) worms crustacea other worms crustacea other shellfish shellfish evenness diversity 24% recruits Minimum 4 5 1 0 4135.5 1353.4 75.2 0 0.29 0.76 26.3% juveniles Average 6.3 6.6 2.3 0.7 12381.3 5595.4 457.4 68.9 0.56 1.54 49.7% reproductive adults Maximum 8 10 4 2 26241.3 15940.3 977.5 225.6 0.73 2.04 0% edible size
Size distribution of cockles Snails and shellfish are the most abundant taxa at this site. The species evenness is low as three 50 taxa (cockles, the worm Aonides sp. and the topshell) make up 81% of all individuals living in the sediment. The remaining 19% of individuals are distributed across 26 taxa. 40
30 Summary of the abundance of the plants and animals living on the sediment surface (quadrat samples) 20
crab burrows mudflat snail mudflat whelk black topshell topshell small limpet Number of individuals 10 number of individuals per square metre Minimum 0 0 0 0 0 0 0 Average 8 4 10 63 392 54 5 10 15 20 25 30 35 40 45 Maximum 16 28 20 144 2240 272 Shell length (mm)
Gracilaria Sea lettuce (red (Green Seagrass seaweed) seaweed)
% cover % cover % cover Minimum 0 0 0
Average 40.3 40 Maximum 4.1 100 89.8 No. quadrats in w hich present 2 11 10
4.2 Pleasant Point jetty
Sediment grain size distribution
% clay
% silt % sand
TUAKI/COCKLES Sample % Clay % silt % sand Individuals in the quadrats were not 1 5.5 16.7 77.9 measured. 2 6.2 19.7 74.1 There were 30 individuals in the cores
3 4.8 15.3 79.9
The graph shows the average percent of each grain size group. There is some variability in the grain size composition between samples. The sediment at this site is muddy (mud=silt+clay) sand.
Proportion of each type of animal living in the sediment (core samples) blue colours are snails and shellfish red colours are worms grey colours are crustacea green colour is an anemone
Invertebrate animals present at this site small bivalve Scientific name Common name
Amphibola crenata mudlfat snail Nicon aestuariensis Arthritica sp. small bivalve Scolecolepides benhami Austrovenus stutchburyi tuaki/cockle Cominella glandiformis mudflat whelk Capitella spp. snails and shellfish Diloma subrostrata black topshell tuaki/cockles Macomona liliana wedge shell Notoacmea elongata small limpet mudflat snails Potamopyrgus sp. small black snail stalk-eyed mud crab Aonides sp. Capitella spp. Oligochaeta
Manayunkia sp. small black snail Nicon aestuariensis worms Scolecolepides benhami Aonides sp. Scolelepis sp. Scolelepis sp. Scoloplos cylindrifer pill-box crab Oligochaetes Halicarcinus sp. pill-box crab hopper crustacea Hemiplax hirtipes stalk-eyed mud crab Paracalliope sp. hopper mudflat whelk
other Nemertea ribbon worm ribbon worm
3 snails and shellfish taxa 2 worm taxa
Summary of the presence and abundance of animals living in/on the sediment (core samples)
number of taxa per core number of individuals per square metre Worms are the most abundant animals but snails and snails and Species Species worms crustacea other worms crustacea other there is a high variability in the number of shellfish shellfish evenness diversity worm individuals between samples. Snails Minimum 2 2 0 0 602 827 0 0 0.56 1.09 and shellfish are the second most abundant Average 3.6 3.8 1.3 0.3 2362.2 2224.4 156.6 25.1 0.71 1.55 group of animals with the small bivalve the Maximum 6 5 2 1 4887 6090 376 75 0.91 2.18 most abundant animal at this site. The species evenness and diversity are moderate - high.
Summary of the abundance of the plants and animals living on the sediment surface (quadrat samples)
Size distribution of mudflat snails 80
Gracilaria Sea lettuce (red (Green 60 crab burrows mudflat snail black topshell small limpet seaweed) seaweed) number of individuals per square metre % cover % cover
Minimum 16 12 0 0 Minimum 0 0 40
Average 32 33 4 8 Average 0.9 2.2 Maximum 68 88 12 16 Maximum 4.1 10.2 20 No. quadrats in w hich present 4 4 Number of individuals
0 5 10 15 20 25 30 35 Shell height (mm)
4.3 Avon River/Ōtākaro mouth
Sediment grain size distribution
% clay % silt
TUAKI/COCKLES % sand There was one cockle in the cores
Sample % clay % silt % sand
1 18.0 59.4 22.6 2 17.4 57.9 24.7
3 20.3 54.1 25.6
This graph shows the average percent of each grain size group. There is some variability in grain size composition between samples. The sediment in all samples is sandy mud (mud = clay +silt).
Proportion of each type of animal living in the sediment (core samples) blue colours are snails and shellfish red colours are worms grey colours are crustacea
Invertebrate animals present at this site Scientific name Common name Amphibola crenata mudflat snail Arthritica sp. small bivalve small black snail snails and shellfish Austrovenus stutchburyi cockle/tuaki Cyclomactra ovata fragile-shell bivalve small bivalve Potamopyrgus sp. small black snail hopper Nicon aestuariensis worms Scolecolepides benhami Scolecolepides benhami Austrohelice crassa mud crab Nicon aestuariensis Hemiplax hirtipes stalk-eyed mud crab crustacea slater Paracorophium excavatum hoppers mudflat snail Isopod sp. slater Nemertea ribbon worm stalk-eyed mud crab Other Edwardsia leucomelos anemone fragile-shell bivalve ribbon worm
anemone
mud crab tuaki/cockle
Summary of the presence and abundance of animals living in/on the sediment (core samples) Snails and shellfish are the most abundant taxa with number of taxa per core number of individuals per square metre the small black snail dominating the biota at this site. snails and snails and Species Species worms crustacea other worms crustacea other The difference between the minimum and maximum shellfish shellfish evenness diversity number of snails and shellfish and crustacea Minimum 2 2 1 0 18046 1278 75 0 0.20 0.40 individuals indicates that the abundance of taxa Average 29436.9 2017.6 1372.2 25.1 2.7 2 1.7 0.3 0.35 0.66 (notably the small black snail, the small bivalve and Maximum 4 2 3 1 49851 3083 10451 75 0.53 1.05 hoppers) is patchy. The high number of these animals in some samples did result in a low species evenness and low species diversity in these samples.
Summary of the abundance of the animals living on the sediment surface (quadrats)
Crab burrows mudflat snail small black snail number of individuals per square metre Minimum 8 0 160 Average 18 3 288 Maximum 28 20 480
4.4 Discharge point
Sediment grain size distribution
% clay
% silt
% sand
Sample % Clay % Silt % Sand
1 1.9 13.0 85.2
2 1.1 11.3 87.6 TUAKI/COCKLES 3 3.8 21.0 75.3
Individuals in the quadrats were not
measured.
There were 15 individuals in the cores
This graph shows the average percent of each grain size group. There is considerable variability in the grain size composition between samples. The sediment at this site is muddy (mud=silt+clay) sand.
Proportion of each type of animal living in the sediment (core samples) blue colours are snails and shellfish red colours are worms grey colours are crustacea green colour is an anemone
Invertebrate animals present at this site Capitella spp. Scolecolepides benhami Group Scientific name Common name Scolelepis sp. Amphibola crenata mudflat snail Arthritica sp. small bivalve small bivalve Austrovenus stutchburyi tuaki/cockle Aonides sp. Cominella glandiformis mudflat whelk Snails and shellfish Oligochaeta Macomona liliana wedge shell Notoacmea elongata small limpet Nicon aestuariensis Paphies australis pipi mudflat whelk Potamopyrgus sp. small black snail worms Aonides sp. hopper Boccardia spp. tuaki/cockles Capitella spp. Glycera americana stalk-eyed mud crab Heteromastus filiformis mudflat snail Manayunkia sp. Scoloplos cylindrifer Nicon aestuariensis Orbinia papillosa ribbon worm Scolecolepides benhami Manayunkia sp. Scolelepis sp. Scoloplos cylindrifer pipi Oligochaetes 3 worm species Austrohelice crassa mud crab pill-box crab Halicarcinus sp. pill-box crab crustacea Hemiplax hirtipes stalk-eyed mud crab Heteromastus filiformis Paracalliope sp. hopper 3 snails and shellfish species other Nemertea ribbon worm mud crab
Summary of the presence and abundance of animals living in/on the sediment (core samples) Worms are the most abundant taxa with snails and shellfish the next most abundant taxa at number of taxa per core number of individuals per square metre snails and snails and Species Species this site. Six worm taxa and the small bivalve worms crustacea other worms crustacea other shellfish shellfish evenness diversity make up 85% of the individuals. The remaining
Minimum 1 5 0 0 301 1729 0 0 0.74 1.70 15% of individuals are distributed across 18
Average 3.3 6.8 1.4 0.7 902.3 3728.2 213.0 50.1 0.82 2.04 taxa. The species evenness and diversity are
Maximum 4 11 3 1 2556 8271 451 75 0.89 2.30 high at this site.
Summary of the abundance of the plants and animals living on the sediment surface (quadrat samples)
Size distribution of mudflat snails 100 Gracilaria crab burrows mudflat snail black topshell small limpet (red 80 number of individuals per square metre seaweed) % cover Minimum 0 48 0 0 60 Minimum 0 Average 20 86 4 13 Average 1.9 Maximum 56 116 12 28 Maximum 10.2 40
No. quadrats in w hich present 4 Number of individuals 20
0 5 10 15 20 25 30 35 Shell height (mm)
4.5 Humphreys Drive
Sediment grain size distribution
% clay
% silt
% sand
Sample % clay % silt % sand 1 1.5 13.2 85.3 TUAKI/COCKLES 2 1.5 12.6 85.9 Individuals in the quadrats were not 3 1.6 13.1 85.3 measured.
There were 16 individuals in the cores
This graph shows the average percent of each grain size group. There is low variability in the grain size composition between samples. The sediment at this site is muddy (mud=silt+clay) sand.
Proportion of each type of animal living in/on the sediment (core samples) blue colours are snails and shellfish red colours are worms grey colours are crustacea
Invertebrate animals present at this site
Scientific name Common name mudflat snail Amphibola crenata mudflat snail Arthritica sp. small bivalve Scolecolepides benhami Austrovenus stutchburyi tuaki/cockles small bivalve Cominella glandiformis mudflat whelk snails and shellfish Nicon aestuariensis Cyclomactra ovata fragile-shell bivalve Scolelepis sp. Macomona liliana wedge shell Manayunkia sp. Paphies australis pipi tuaki/cockles Potamopyrgus sp. small black snail Capitella spp. ribbon worm Manayunkia sp. Capitella spp. Nicon aestuariensis worms small black snail Scolecolepides benhami Scolelepis sp. stalk-eyed mud crab Oligochaetes mudflat whelk Hemiplax hirtipes stalk-eyed mud crab crustacea fragile-shell bivalve Paracalliope sp. hopper wedge shell other Nemertea ribbon worm Oligochaeta
hopper
pipi
Summary of the presence and abundance of animals living in the sediment (core samples) Snails and shellfish are the most abundant taxa number of taxa per core number of individuals per square metre snails and snails and Species Species at this site. The mudflat snail, the small bivalve worms crustacea other worms crustacea other shellfish shellfish evenness diversity and two worm taxa made up 75% of the
Minimum 2 2 0 0 376 827 0 0 0.64 1.33 individuals present, with the remaining 25% of
Average 1322.1 1134.1 37.6 56.4 individuals distributed across 13 taxa. The 3.8 4 0.4 0.6 0.82 1.76 Maximum 6 5 1 1 3308 1805 150 150 0.91 2.19 species evenness and diversity are moderate- high at the Humphreys Drive site.
Summary of the abundance of the animals living on the sediment surface (quadrat samples) Size distribution of mudflat snails 140
120 Gracilaria 100 (red crab burrows mudflat snail mudflat whelk seaweed) 80 number of individuals per square metre % cover Minimum 0 28 0 Minimum 0 60
Average 18 59 1 Average 0.7 40 Maximum 4.1 Number of individuals Maximum 24 80 8 3 20 No. quadrats in w hich present 0 5 10 15 20 25 30 35 Shell height (mm)
4.6 Heathcote River/Ōpāwaho mouth
Sediment grain size distribution
% clay
% silt % sand
TUAKI/COCKLES
Sample % clay % silt % sand Individuals in the quadrats were not
1 18.3 63.9 17.8 measured. 2 11.2 37.5 51.3 There were no cockles in the cores 3 8.2 29.5 62.3
This graph shows the average percent of each grain size group. There is considerable variability in grain size composition between samples. The sediment in one sample is sandy mud (mud = clay +silt). The sediment in two samples is muddy sand.
Proportion of each type of animal living in the sediment (core samples) blue colours are snails and shellfish red colours are worms grey colours are crustacean green colour is an anemone
Invertebrate animals present at this site
Group Scientific name Common name Amphibola crenata mudfalt snail snails and shellfish Arthritica sp. small bivalve Nicon aestuariensis Potamopyrgus sp. small black snail Capitella spp. small bivalve Manayunkia sp. worms Scolecolepides benhami Nicon aestuariensis anemone Scolecolepides benhami crustacea Austrohelice crassa mud crab mud crab Edwardsia leucomelos anemone other small black snail Hexatomini Insect larva Capitella spp. mudflat snail
insect larva Manayunkia sp.
Summary of the presence and abundance of animals living in/on the sediment (core samples)
number of taxa per core number of individuals per square metre In total ten taxa were present, with worms and snails and snails and Species Species snails are shellfish the most abundant animals, worms crustacea other worms crustacea other shellfish shellfish evenness diversity at this site. Two worm taxa and the small Minimum 0 0 0 0 0 0 0 0 0.71 0 bivalve made up 59% of the animal individuals. Average 1.7 1.8 0.8 1.1 463.7 789.5 150.4 269.4 0.84 1.32 There is high evenness and moderate Maximum 3 4 1 2 1579.0 2180.5 376.0 676.7 0.95 1.87 diversity.
Summary of the abundance of the animals living on the sediment surface (quadrat samples)
Size distribution of mudflat snails 120
Crab burrows mudflat snail 100 number of individuals per 80 square metre
Minimum 72 24 60 Average 176 47 Maximum 344 84 40
Number of individuals 20
0 5 10 15 20 25 30 35 Shell height (mm)
4.7 Causeway
Sediment grain size distribution TUAKI/COCKLES (978 individuals measured in quadrats) % clay 0% recruits % silt 9% juveniles
% sand 91% reproductive adults
3.5% edible size Size distribution of cockles 400 Sample % clay % silt % sand
1 2.2 8.1 89.7 350
2 2.6 9.8 87.6 300
3 2.6 9.3 88.1 250 200 150
100 Number of individuals The graph shows the average percent of each grain size group. There is some variability in the grain 50 size composition between samples. The sediment at this site is muddy (mud=silt+clay) sand. 0 5 10 15 20 25 30 35 40 45 Shell length (mm)
Proportion of each type of animal living in the sediment (core samples) blue colours are snails and shellfish red colours are worms grey colours are crustacea green colour is an anemone
Invertebrate animals present at this site tuaki/cockle Scientific name Common name Aonides sp. Arthritica sp. small bivalve wedge shell Austrovenus stutchburyi tuaki/cockle Nicon aestuariensis Cantharidus tenebrosus topshell small bivalve Cominella glandiformis mudflat whelk snails and shellfish Capitella spp. Cyclomactra ovata fragile-shell bivalve Diloma subrostrata black topshell Scolelepis sp. Macomona liliana wedge shell black topshell Notoacmea elongata small limpet topshell Aglaophamus macroura small limpet Aonides sp. ribbon worm Armandia maculata Prionospio sp. Capitella spp. Manayunkia sp. Glycera americana Scoloplos cylindrifer Heteromastus filiformis worms Manayunkia sp. hopper
Nicon aestuariensis stalk-eyed mud crab Orbinia papillosa mudflat whelk Prionospio sp. Heteromastus filiformis Scolecolepides benhami Scolecolepides benhami Scolelepis sp. Scoloplos cylindrifer Glycera americana Austrohelice crassa mud crab Orbinia papillosa Halicarcinus sp. pill-box crab fragile-shell bivalve crustacea Hemiplax hirtipes stalk-eyed mud crab 2 crustacea taxa Paracalliope spp. hopper 2 worm taxa Anthopleura aureoradiata anemone other anemone Nemertea ribbon worm
Summary of the presence and abundance of animals living in/on the sediment (core samples) number of taxa per core number of individuals per square metre COCKLES snails and snails and Species Species worms crustacea other worms crustacea other (106 individuals measured in the cores) shellfish shellfish evenness diversity 41.5% recruits Minimum 2 4 0 0 2932.4 451.1 0 0 0.27 0.63 8.5% juveniles Average 4.5 5.8 1.2 0.8 7462.6 3239.4 100.3 81.5 0.45 1.13 51% reproductive adults Maximum 7 9 2 1 12932.7 8195.7 225.6 225.6 0.68 1.62 4.7% edible size
Size distribution of cockles 50
40 Snails and shellfish are the most abundant animals at this site, however there are more worm
than snails and shellfish taxa. Cockles are the most abundant animal making up 63 % of the 30 individuals living in the sediment. The worm Aonides sp makes up 23 % of individuals, while the remaining 14% of individuals are distributed across 25 taxa. The number of individuals, of the 20 most abundant taxa in the cores, is patchy. In some cores the high number of individuals of
these animals did result in a low species evenness. Number of individuals 10
0 5 10 15 20 25 30 35 40 45 Shell length (mm)
Summary of the abundance of the plants and animals living on the sediment surface (quadrat samples)
Sea lettuce (Green crab burrows topshell black topshell small limpet seaweed) number of individuals per square metre % cover Minimum 4 0 48 0 Minimum 0 Average 12 28 107 27 Average 4.4 Maximum 24 176 156 76 Maximum 22.4 No. quadrats in w hich present 6
Healthy Estuary and Rivers of the City Water quality and ecosystem health monitoring programme of Ihutai
5 References
Batcheler, L., Bolton-Ritchie, L., Bond, J., Dagg, D., Dickson, P., Drysdale, A., Handforth, D and Hayward, S. 2009. Healthy Estuary and Rivers of the City: Water quality and ecosystem health monitoring programme of Ihutai. Environment Canterbury Report No RO9/8. 60pp.
Robertson, B., Gillespie, P., Asher, R., Frisk, S., Keeley, N., Hopkins, G., Thompson, S and Tuckey, B. 2002. Estuarine environmental assessment and monitoring: A national protocol. Part A. Development, Part B. Appendices, and Part C. Application. Prepared for supporting Councils and the Ministry for the Environment, Sustainable Management Fund Contract No 5096. Part A. 93p. Part B 159p. Part C. 40p plus field sheets.
Environment Canterbury Technical Report 12
Facilitating sustainable development in the Canterbury region ecan.govt.nz