The algal bloom and climate anomalies of 1992
Dr W J Ballantine
Leigh Laboratory Seminar, May 28th, 1993
[this paper has been reproduced here for those wishing to study
the plankton blooms of 1992 and their effects on the environment.
To our knowledge it is not available elsewhere. - Floor Anthoni.
Please note that this is not an official scientific publication!]
Use your BACK button to reverse out of this document.


A the end of August last year an intense microalgal bloom developed along the open coast at the Leigh Laboratory. This bloom was unusual in its intensity, seasonal timing, duration, geographic extent, composition and subsequent biological events. This seminar attempts to review the data about this bloom and discuss implications. It is unusual in several respects:

  1. It reports on the work of many people including:
  2. There was no formal project. No one had the task of investigating the bloom as such, or of assigning anyone to do so. Those who involved themselves all had different aims and interests, and none included a direct study of the bloom.
  3. It raises not only the standard scientific questions on the bloom itself - what was its nature, causes and consequences - but also wider questions such as:
  4. These questions are made more pointed because of:

1. The intensity, duration and extent of the bloom
Evidence at Leigh
  • Algal pigment, total seston and turbidity sampling by Alison Haywood.
  • Counts, cultures and identifications of algae by Leslie Rhodes, Cawthron.
  • Diver observations of underwater visibility
  • Routine observations of seawater colour from clifftop (during daily tea breaks!)

Evidence from further afield

Results and conclusions
2. The timing and species composition of the bloom


  • Whole water samples counted by Leslie Rhodes (Cawthron Inst):
    • In Leigh: 8th Oct, 19th Oct, 26th Oct, 11th Nov, 1st Dec, 16th Dec, 7th Jan, 9th Feb.
    • Ti Point to Browns Bay (5 sites) and Coromandel (3 sites) in November only.
  • Filter samples analysed by Allison Haywood: 2-3 times weekly from late May to October and daily during September.
  • Various published and thesis accounts of phytoplankton in the Hauraki Gulf in earlier years.
Results and conclusions:
  • The bloom commenced off the Leigh Laboratory at the end of August. It remained intense through November and declined to more normal levels and composition in December.
  • The bloom was dominated by three species:
  • A rhaphidophyte Fibrocapsa japonica (appr 30µm dia)
  • A silicoflagellate Dictyocha speculum (appr 40µm dia)
  • A prymnesiophyte Gephyrocapsa oceanica (appr 10µm dia)

  • N.B.
    By their usual size definitions, Fibrocapsa and Dictyocha are 'net' phytoplankton (20-200µm) but neither are likely to be recorded by net sampling and may not show in preserved samples. Gephyrocapsa is classed as 'nanoplankton' (2-20µm)
    There are problems with identification. First the species concept is of doubtful meaning at this level. There are few morphological characteristics, many of these are hard to detect in light microscopy, or are known to vary within the 'species'. Critical 'identification' involves culturing and comparing with known 'strains' and/or the use of electron microscopy (EM). Second, the original samples are very small compared to the sea and further sub-sampling is necessary for counts. Only a few specimens are selected for EM examination or culture. Third, very little work has been done on many of these 'species'.
  • Although diatoms and dinoflagellates were present throughout the bloom, and these were generally of the expected species, they formed a small to very small proportion of the total phytoplankton observed.
  • The contribution of picoplankton (0.2-2µm) to the biomass of the bloom is unknown (no checks or counts known for any site during the bloom), but may have been significant. Booth and Sonergaard (1989) sampling the Hauraki Gulf (mainly near Leigh) in 1986 found picoplankton proportionally more in winter (mean 33% of total chlorophyll-a) but absolutely more abundant in spring.

3. The physical background


  • Leigh Laboratory daily records 1967 to present, including sea surface temperature (SST), rainfall, solar radiation, wave surge, wind direction and run.
  • Satellite-derived sea surface temperature anomalies.
  • Southern Oscillation Index (SOI) calculations.
  • Sea surface temperatures (SST) were at their lowest when the bloom commenced but solar radiation had increased markedly some two weeks before.
  • During 1992 all climate factors (except SST) were not especially different from average or their variations were unrelated to the development of the algal bloom. Sea temperatures, however, were markedly colder than usual for six months prior to the bloom. The onset of the bloom immediately followed the coldest sea temperatures ever recorded at Leigh.

4. The triggering, limiting and forcing factors
  • While the precise triggers for the increase of particular species involved in the bloom and the limiting factors affecting their subsequent abundance are likely to vary both specifically and regionally, the widespread nature of the bloom and its duration suggest some general forcing factor.
  • The most obvious candidate is the extremely low, widespread and long-lasting sea surface temperature anomalies. These could have acted in several ways - e.g. to inhibit the normal phytoplankton community, to encourage cold-adapted species, to inhibit grazers or any combination of these.
  • The idea of a widespread climatic forcing factor is supported by the total set of biological patterns, especially those related to frequency of occurrence. The SST anomalies of 1992 were rare and extreme events, indeed unique in the 26 year record at Leigh. The algal blooms were also rare and extreme, both in themselves and in the subsequent biological disruptions.

5. Coincident and subsequent biological anomalies

Simon Hooker: (2 previous years observations)
(i) Mass mortality (100%) of a single isolated patch (20x1m) of pips Paphies (Amphidesma) australe, in Whangateau Harbour, Feb 1993.
(ii) Several occasions when all pipis observed were closed and non-feeding for several days at a time in the Whangateau Harbour entrance, Jan-Feb 1993.

Others: (1 previous years observation)
(i) mass mortality of juvenile scallops, Pecten novaezelandia, (appr 35-50mm) in east Great Omaha Bay, around Jan-Feb 1993
(ii) mass mortality of Dosinia ?subrosea in Omaha Bay (both sides), Jan-Feb 1993
(iii) Starfish disintegration: a low proportion of a scattered population of Ophidaster luidea? had multiple separated arms, Omaha Bay, Jan-Feb 1993.

W J Ballantine and various newspaper reports - local mass mortalities of 'shellfish'
(i) Dosinea subrosea - Te Muri, Jan 1992
(ii) grazing molluscs, kina and whelks - Waipu Cove, 5 Feb 1993

Chris Battershill: sponges (comparison with observations in 1980s)
(i) heavy mortality of sponges, especially Callyspongia (near 100%)
(ii) kelp mortality in 1983

Floor Anthoni (diving locally since 1970s), the earliest reports of:
(i) early kelp sickness and subsequent death, patterned by depth and geographic locality
(ii) sponge 'shut down' and later death and disappearance, and similar effects on other fauna.

Russ Babcock (new staff member) and Russell Cole (5+ previous years observations) (also compared to marine reserve survey 1977-78, see Ayling, 1978 and Ayling et all, 1981):
Analysis of video transects in the marine reserve  (in January 1993) showed earlier and continuing loss of kelp plants (Ecklonia radiata) from the deeper parts of the bed upwards (demonstrated by the sequential loss of canopy, stipe, holdfast and bare space). The deeper part of the kelp beds had 100% mortality and middle parts approximately 50%, throughout most of the marine reserve. Back calculation (estimating lag time) suggests a cause pre-December. Second survey in April 1993 showed continuing progressive mortality into shallower depths, although heavy recruitment has already occurred in the deeper 'vacant' spaces.
Patchy mortality recorded (in may) from Great Barrier's west coast, Little Barrier and Whangarei Heads. No sign of mortality on open coast further north to Cape Karikari, but unconfimred reports of patchy mortality at Spirits Bay. Similar events associated with cold water reported for a laminarian kelp in Japan.

P J Smith (MAF), F H Chang (NZOI) and L MacKenzie (Cawthron):
Have supplied a copy of their draft report for the Royal Society's Shellfish Toxin Workshop, entitled 'Toxic phytoplankton and algal blooms, Summer 1992-93'. This collates information for the whole country, mentioning the Hauraki Gulf events of 1992, but concentrating on events of 1993.

Department of Conservation: reports of high little blue penguin mortalities in Northland.

Maurice Miles, (North harbour Health): Orewa coughing outbreaks and sampling for Gymnodinium breve.

6. Probability, pattern and prediction
  • The question that unites all aspects of these events, in both theoretical and practical terms is: When are such events likely to occur? It is also the most important question from most viewpoints. Biologically we wish to know whether such events occur sufficiently often to form part of the 'normal' patterns, are a rarer but still significant disruption of the 'normal' or are very rare, and hence generally unimportant phenomena. Essentially the same distinctions are relevant to climatologists, resource managers and economists.
  • We do not have sufficient direct evidence to answer this question adequately for any aspect, even those concerning the physical climate anomalies. For most of the biological aspects there is little or no direct evidence on frequency distribution in time.
  • Consider as an example the SST anomalies, for which we have 26 years of comparable data, and using the term 'return period' borrowed from engineers concerned with flooding and similar phenomena. If the data are treated as single set normally distributed (i.e. the form a normal curve) then September 1992 sea temperatures (which had an anomaly of 3.2 standard deviations (SD) from the mean) would have a return period greater than 700 years. Even the 6 months April-September 1992 (SD 2.4) would, if treated as part of a unimodal non-skewed normal distribution, have a return period of 120 years.
  • There are, however, at least two reasons for not accepting this analysis. First, 'normal' distributions were originally derived to describe biological phenomena within populations and there is no good reason to presuppose that they apply to phenomena such as climate anomalies. Indeed, despite much use of statistics based on normal curves (whether transformed or otherwise) there is growing doubt that they are generally applicable. Professor G Austin, Geophysics, Auckland (personal communication) refers to 'chaotic' distributions, which have a spike in the centre and concave side slopes, giving proportionately more outlying values.

7. Conclusions
  • The magnitude of these events (geographically, temporally, ecologically and economically) requires, as a minimum, that we search for a reasonable level of knowledge on their frequency of occurrence.
  • The scarcity of data, especially long-term monitoring, will make this difficult. Even simple routine measurements (e.g. weekly chlorophyll concentrations) would have improved our understanding considerably.
  • There is no scientific agreement on how routine marine phytoplankton samples should be obtained and analysed for general comparability (i.e. for use as standards, signals and proxy data). Until this confusion is resolved, useful monitoring of phytoplankton is unlikely to be implemented. The primary problem is not suitable technology, economic cost or political will but a scientific consensus that such data is required.
  • The same points apply to other marine ecological or marine climate data.


Anthoni, J F, 1992: The disappearing fish act. Dive Log, Dec/Jan 1993:13 p31.
Anthoni, J F, 1993: Letter to Editor. Dive Log. Feb/March 1993:14 p7
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