Chairperson
Daly will welcome everyone in attendance. Member Cleave will lead a karakia.
2 Apologies
At the close of
the agenda no apologies had been received.
3 Declaration of Interest
Members are
reminded of the need to be vigilant to stand aside from decision making when a
conflict arises between their role as a member and any private or other
external interest they might have.
4 Confirmation of Minutes
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That the Great Barrier Environment Committee:
a)
confirm the ordinary minutes of its meeting, held on Thursday, 27
February 2014, as a true and correct record.
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5 Leave of Absence
At the close of
the agenda no requests for leave of absence had been received.
6 Acknowledgements
At the close of
the agenda no requests for acknowledgements had been received.
7 Petitions
At the close of
the agenda no requests to present petitions had been received.
8 Deputations
At the close of
the agenda no requests for deputations had been received.
9 Public Forum
A period of
time (approximately 30 minutes) is set aside for members of the public to
address the meeting on matters within its delegated authority. A maximum of 3
minutes per item is allowed, following which there may be questions from
members.
At the close of
the agenda no requests for public forum had been received.
10 Extraordinary Business
Section 46A(7)
of the Local Government Official Information and Meetings Act 1987 (as amended)
states:
“An item that is
not on the agenda for a meeting may be dealt with at that meeting if-
(a) The local authority by resolution so decides; and
(b) The presiding member explains at the meeting, at a time
when it is open to the public,-
(i) The reason
why the item is not on the agenda; and
(ii) The reason why the discussion of the item cannot be
delayed until a subsequent meeting.”
Section 46A(7A)
of the Local Government Official Information and Meetings Act 1987 (as amended)
states:
“Where an item
is not on the agenda for a meeting,-
(a) That item may be discussed at that meeting if-
(i) That item is a minor matter relating to the general
business of the local authority; and
(ii) the presiding member explains at the beginning of the meeting,
at a time when it is open to the public, that the item will be discussed at the
meeting; but
(b) no resolution, decision or recommendation may be made in
respect of that item except to refer that item to a subsequent meeting of the
local authority for further discussion.”
11 Notices of Motion
At the close of
the agenda no requests for notices of motion had been received.
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Great Barrier Environment Committee
26 March 2014
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Microdictyon and freshwater report
File No.:
CP2014/04893
Purpose
1. This report describes the
progress on the Microdictyon research program in Tryphena harbour and
outlines the findings and recommendations for consideration by the Great
Barrier Island Local Board and Environment Committee.
Executive Summary
2. Sarah Roth (University of
Auckland, Masters student) is nearing the end of her Masters program and is due
to complete her thesis in April 2014. Sarah has completed her sampling to
determine potential agents facilitating Microdictyon growth. These
findings represent her research efforts and considerable thanks is forwarded to
Sarah.
3. This research program was
designed to determine whether elevated nutrients were contributing to the
presence of a green algae (Microdictyon umbillicatum) washing up on the beaches of Tryphena Harbour. This
research program was equally funded by the Great Barrier Local Board and
Auckland Council's Research, Investigations and Monitoring Unit (RIMU).
Supervision of this research program was contributed to by the University of
Auckland (Dr Nick Shears) and RIMU (Dr Jarrod Walker).
4. In order to understand the relationship
between Microdictyon blooms and nutrient levels
at Tryphena Harbour, and in particular whether the blooms are associated with
nutrient enrichment in the harbour, a program of water and seaweed sampling was
carried out from October 2012 to February 2014. Measurements of seawater
nutrients (nitrogen and phosphorus) provided a direct measure of the nutrients
available for seaweed growth and an overall measure of nutrient enrichment.
Chemical analysis of seaweed tissue provides a measure of the overall nutrient
status of the plant (as indicated by the percentage nitrogen in the tissue) as
well as the main sources of Nitrogen (from stable isotope analysis). In
addition, growth experiments were carried out to compare growth rates between
Tryphena and adjacent Great Barrier Is sites.
5. Extensive video
tows in Tryphena Harbour and some surrounding bays revealed widespread beds of
the green alga Microdictyon umbillicatum within Tryphena and limited
amounts of Microdictyon in Okupu Bay on one occasion. The beds in
Tryphena were found drifting or loosely attached to the sandy bottom at depths
of 6 - 20 m. These drifts persisted year round over the course of this study
(October 2012 to Feb 2014). The amount of Microdictyon varied from one
season to the next and from year to year. The greatest quantities of Microdictyon
were observed between October 2012 and March 2013, but have been less
extensive over the past year.
6. Seawater nutrient monitoring did
not reveal elevated nutrients within Tryphena Harbour compared to offshore
waters and adjacent coastal sites. In general, total inorganic nitrogen and
phosphate levels were typical of open coast sites with limited terrestrial
inputs, and are comparable to seawater nutrient concentrations at Leigh on the
mainland. Nutrient levels in Tryphena harbor are considerable lower than
urbanised areas around Auckland (e.g. Waitemata Harbour).
7. Isotope analysis of Microdictyon
tissue from Tryphena Harbour revealed considerable variation over time.
Tissue-δ15N values were within the expected ‘natural’ range on most
sampling occasions, but elevated δ15N levels were recorded in spring 2012
and spring 2013. This provides some indication of periodic inputs of nitrogen
from an anthropogenic source within the harbour.
8. Growth experiments carried out
in summer and spring 2013, provided no evidence that the growth of Microdictyon
was higher in Tryphena compared to adjacent harbours, nor was there any
differences in nutrient concentrations or tissue-δ15N values between sites
in the Harbour and on the adjacent coast at that time. Sites to the south of
Tryphena tended to have the highest growth rates, seawater nitrogen
concentrations and percentage tissue nitrogen in Microdictyon than of
those found at Tryphena.
9. The unique
physical setting of Tryphena Harbour likely facilitates the presence of Microdictyon.
The harbour is protected from large ocean swells, is dominated by coarse
sand and shell hash, which provides substrate for Microdictyon attachment,
and the clear oceanic water provides optimal growing conditions. Nutrient
levels within the surrounding oceanic waters also appear to be sufficient to
allow macroalgal growth and these levels are comparable between Tryphena and
adjacent Great Barrier Island sites. The nitrogen isotope values of Microdictyon
do however suggest that anthropogenic sources periodically contribute to
nutrient loading within the harbour.
10. Overall, the
results do not provide strong evidence that the proliferation of Microdictyon
in Tryphena Harbour is due to elevated nutrient levels. However, the optimal
physical conditions for seaweed growth within Tryphena Harbour mean that even
relatively small amounts of anthropogenic-sourced nutrients will likely promote
the long-term persistence and proliferation of Microdictyon within the
harbour.
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Recommendation/s
That the Great
Barrier Environment Committee:
a) Receive the report
b) Explore the option of surveying
potential anthropogenic sources of nitrogen within the harbor.
c) Explore the option of including
Marine water quality monitoring on Great Barrier Island which can be included
in the regional Marine water quality monitoring program. This information
will be highly relevant to inform marine water quality concerns and provide
additional longer term data on nutrient status of harbour waters.
d) Explore the option of including
freshwater monitoring on Great Barrier Island which can be included in the
regional Freshwater quality monitoring program. This information will be
highly relevant to inform freshwater concerns and determine appropriate
management response.
e) Explore options to continue the
monitoring of Microdictyon within Tryphena Harbor. Continued and more
frequent collections of Microdictyon, and analysis of tissue %N and
δ15N, would provide further insights into the importance of
anthropogenic-derived nutrient sources in fuelling blooms within the harbor.
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Discussion
11. The Great
Barrier Island Local Board approached the Research, Investigations and
Monitoring Unit (RIMU) to investigate the potential nutrient sources
facilitating the growth of the green mossy alga Microdicyton umbilicatum.
In previous years this alga has washed up on beaches in Tryphena Harbour
following strong onshore (west to south-westerly) winds. Anecdotal evidence
suggests the presence of this alga is a new phenomena and information
describing the potential mechanisms underpinning the proliferation of this
green alga were warranted. This information can be used to facilitate the
identification of management options to best address this issue.
12. At the start of this program it
was assumed that the algal in question was Microdictyon muitable. After
visual and genetic identification we are certain this green algal is Microdictyon
umbilicatum. Microdictyon umbilicatum is non-toxic and not an
invasive species. It is also found at Leigh, other Great Barrier Island
locations, and in New South Wales, Australia.
13. Extent of Microdictyon
distribution
An underwater camera was employed
to assess the extent of Microdicyton in Tryphena Harbour and at a number
of additional Great Barrier Island sites. It was established that the majority
of Microdicyton was located in Tryphena Harbour with small patches in
Okupu Bay (only observed during 2012). Subsequent camera tows were conducted on
5 occasions (spring 2012, summer, winter and spring 2013, summer 2014) in
Tryphena Harbour and at times the camera was towed from one side of the harbour
to the other. Camera tows revealed Microdicyton to be widespread and in
drifts up to 40cm in thickness during spring 2012 and summer 2013 (see Figure
1C). Microdicyton was found to be less widespread and less abundant in
subsequent surveys. The highest quantities were generally observed in spring
and lowest during winter. In February 2014 Microdictyon was sparse and
mainly found in deeper water (>15m).
14. Water quality monitoring
(nutrients, sediments and turbidity)
To determine nutrient (nitrogen
and phosphorous) concentrations in seawater at Tryphena harbour, water samples
were taken at 4 sites during spring 2012, summer, winter and spring 2013 and
summer 2014. Water samples were also collected at Whangaparapara (N1), Blind
Bay (N3, N4), Schooner Bay (N5) and one location to the south (S2, see Figure 2).
The rationale here was to sample seawater close to beaches and streams which
would be more influenced by land based activates (and potentially contained
higher levels of nutrients) and then compare these samples to seawater
collected from the wider harbour, further offshore and at neighboring bays (see
Figure 2).
Phosphorus and total inorganic nitrogen concentrations were
similar across all sites monitored and there was no clear difference between
Tryphena and adjacent sites. Some seasonal variations were observed, with the
highest concentrations in winter and lowest in summer, which is typical for
coastal sites. When compared to the Marine water quality program carried out
throughout Auckland, these concentrations were similar to those observed at the
most pristine locations on the mainland (Leigh and Ti Point). There were very
small differences in nitrogen and phosphorous concentrations across all sites
(Tryphena to Whangaparapara) indicating that Tryphena is not subjected to
abnormally high concentrations of nutrients compared to other sites along the
southwestern coast of Great Barrier Island. Interestingly the highest nitrogen
concentrations were recorded at sites to the south of Tryphena, which are
situated on the northern side of the Colville Channel and exposed to higher
currents that likely drives localized upwelling.
Figure 1. Microdictyon umbillicatum at Great Barrier
Island. (A) Aerial imagery (2008) showing large subtidal drifts of Microdictyon.
(B) Drifts of Microdictyon on mega-ripple sand and (C) completely
covering the sandy substratum in Tryphena (Oct 2012). (D) Microdictyon
attached to subtidal rocky substrate at Katherine Bay (Oct 2012).
A B
C D
15. Growth rates
Growth of rates of Microdicyton was measured by placing ~5g
of Microdictyon in suspended mesh bags at depths of 7-9 m. This was
undertaken at the 12 coastal sites showing in Figure 2. The mesh bags (see Fig
3) were deployed at each site for 14 days and the experiment was repeated on
three separate occasions (summer 2013, and repeat trials in spring 2013).
Growth rates were highly variable among the three time periods. In the first
two experiments low rates of growth were observed, primarily due to the
occurrence of large southwesterly storms and the loss of tissue from mesh
bags. Weather conditions were calm during the third trial (spring 2013) and
there was consistent growth across all sites. During all three trials there was
no evidence that growth of Microdictyon was higher in Tryphena. Growth tended to
be higher at the southern-most sites, corresponding with higher concentrations
of nitrogen in the tissue and higher nitrogen in seawater samples. Overall, the
measured growth rates of Microdictyon were relatively slow compared to other nuisance algae such as Ulva in New Zealand and
overseas.
Figure. 2 Microdictyon umbillicatum study sites at
Great Barrier Island (see yellow, red and blue marks). Water quality was
monitored at sites located along an onshore to offshore gradient (see white
pins and white dashed box) Offshore, Harbour Mouth, Nearshore and Inshore (T2
and T3).
16. Analysis of Microdictyon tissue
Chemical analysis of seaweed tissue provides a measure of
the overall nutrient status of the plant (as indicated by the percentage
nitrogen in the tissue) as well as the main sources of nitrogen (from stable
isotope analysis). Stable isotope ratios such as δ15N (delta 15 N) are
useful in identifying the main sources of nitrogen. No previous information is
available on isotopic signatures of Microdictyon in New Zealand. In New
South Wales, Australia Microdictyon has been developed as a
bioindicator. This body of work indicates nitrogen from sewage inputs results
in high δ15N values (> 12 ‰) while agricultural runoff had low
δ15N (<6 ‰).
New Zealand's green seaweed Ulva from coastal sites
with low catchment modification has a narrow range of δ15N values from 6.6
to 8.8 ‰. This range reflects δ15N estimates of dissolved inorganic
nitrogen from oceanic seawater in the absence of terrestrial inputs of
nitrogen. Barr et al (2011) suggest that deviations in Ulva
tissue-δ15N values beyond the range’ of 6.6–8.8‰ is likely to
reflect an influence of either anthropogenic nitrogen (e.g.
wastewater or farming effluent) or other terrestrially derived nitrogen (e.g.
from freshwater runoff). In the context of the present study Microdictyon
tissue-δ15N allowed a broad assessment of the potential sources of
nutrients that may be facilitating the growth of Microdicyton.
Microdictyon at Tryphena exhibited considerable
variation in tissue-δ15N and %N over the sampling period. Autumn and
winter tissue-δ15N was similar and generally in the ‘natural’ range
expected (based on Barr et al 2013). However, tissue-δ15N was considerably
higher in spring 2012 (~9.5‰), and to a lesser extent in spring 2013 (~9‰).
These high δN15 values for Microdictyon at Tryphena may indicate a
potential anthropogenic nutrient source.
The %N values recorded in Tryphena reflect a typical
seasonal pattern with peaks in winter and minimum values in summer. The maximum
values of 2.5-3% in winter are typical for coastal seaweeds and do not indicate
nutrient enrichment. The %N values in summer (<1%) are also typical and
potentially indicate nutrient limitation. Therefore, while tissue-δN15 values
in spring 2012 are elevated and of potential concern, tissue-%N was relatively
low suggesting that plants were not particularly enriched in nitrogen.
Algal tissue from the growth rate experiments also allowed
for the comparison of δ15N between Tryphena and the surrounding
bays. Overall δ15N values were similar across all sites during
the growth experiments indicating that the source of nitrogen that Microdicyton
was ulitilzing at that time was similar. These values were all within the
‘natural’ range suggested by Barr et al 2013.
Figure. 2. In-situ growth measurements of Microdictyon using
suspended mesh bags.
17. Summary
The concentrations of seawater nutrients,
nitrogen and phosphorous, recorded in Tryphena Harbour are comparable to other
sites on the southwest coast of Great Barrier Island and are not indicative of
a nutrient enrichment problem. Growth rates of Microdictyon in Tryphena
were also comparable to other surrounding locations. Tryphena Harbour is
protected from large ocean swells and is typically bathed in clear oceanic
waters. This unique environmental setting appears to allow Microdictyon
to flourish in this relatively low nutrient system.
Isotope analysis allowed an assessment of
the potential sources of nutrients fuelling the growth of Microdictyon
at Tryphena and adjacent sites. Microdictyon tissue-δN15 from growth experiments at multiple sites in and around Tryphena
showed that the nutrient sources did not vary among sites. This provides some
evidence to suggest that the nutrients fuelling Microdictyon growth are
primarily oceanic in nature. However, seasonal variations in δ15N
signatures were recorded, with high δ15N values recorded in spring 2012.
Such high values of δ15N are indicative of anthropogenic sources of
nitrogen and suggest Microdictyon are periodically ulitising alternative sources of nitrogen within
Tryphena Harbour. The extent to which such anthropogenic inputs contribute to
the long-term persistence of Microdictyon requires further
investigation, but action should be taken to minimise any anthropogenic inputs
of nutrients that might facilitate Microdictyon blooms in this otherwise
pristine environment.
Consideration
Maori Impact Statement
18. The environmental information
obtained from the above programmes will be of interest and can empower Maori as
Kaitiaki and Tangata Whenua. This report will also be of value to inform the
Maori Plan and pertinent environmental indications that relate to water
quality.
Implementation Issues
19. NA
Signatories
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Authors
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Dr Jarrod Walker, Senior Marine
Scientist, Research, Investigations and Monitoring Unit
Dr Nick Shears, Lecturer, University
of Auckland
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Authorisers
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Greg Holland,
Manager, Research, Investigations and Monitoring Unit
John Nash - Senior Local Board
Advisor
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