Dolphin Lagoon water quality 16/10/08. A brief report.

Dolphin Lagoon is currently experiencing a monospecific bloom of the cyanobacterium genus Synechococcus sp. (~20×106 cells/ml) the same species that has been in bloom in the Gippsland Lakes since November, 2007. This species is tolerant of high salinity levels (marine = 35 practical salinity scale) and has been shown to bloom at temperatures above about 14°C (similar to tropical Synechococcus sp.) conditions now pertaining in the Lagoon (Table 1).

Dolphin Lagoon Algal Bloom Oct 2008

The ratio of major nutrients i.e. nitrogen to phosphorous is one critical factor which will either favour or disadvantage a particular algal species e.g. high nitrogen levels will favour Synechococcus sp. over some other cyanobacteria. A complex set of other physical/chemical factors including the availability of trace elements, micronutrients, temperature, salinity, light and competition from other species, may then coincide to favour one species over another.

Several factors now favour Synechococcus sp. in Dolphin Lagoon e.g. temperature, salinity, light level (ability to survive high light levels lethal to other species) and diminished competition. It is also probable that nitrogen levels are relatively high in the Lagoon (not currently monitored).

Why has the bloom occurred now, nearly twelve months after it began in the Lakes proper? One explanation may be that the species wasn’t previously present in the Lagoon, prior to the last high tide and storm surge several weeks ago, and that Lake water driven into the Lagoon carried with it a seeding population. This is only circumstantial evidence for the hypothesis that this Synechococcus sp. is of marine and possibly sub-tropical origin and has arrived here, as have other species, on the warming southward-flowing East Australia Current.

The bloom may have little long-term effect, as it should be eliminated by the wetland drying cycle. This species is not known to produce resting cysts or spores. However in the short term, it is unlikely that any other algal species will be able to compete with it, at least not until it has exhausted the nutrients to a level that affects cell growth and that may favour other species. It is generally considered a poor food species for zooplankton, although the evidence is conflicting. Therefore there exists the possibility that the bloom may be detrimental to zooplankton and in turn other animals that rely on small crustacea for food e.g. small native fish sometimes found in the Lagoon such as Tupong, Hardyhead and Blue-spot goby, and subsequently other larger predatory fish and bird species.

Persistent monospecific blooms are a feature of a degraded environment. Unfortunately this is a familiar scenario within the Gippsland Lakes which is likely to become worse with the pressures of development and changes to climate regimes.

Table 1.

 Water°C Sc ms/c DO mg/l  pH Sal pss DO % Biomm3/L
 15.58  58.6  8.81  8.2  38.48  111.8  60

Update 03-Nov-08

Synechococcus bloom has declined although still present. Hypersaline conditions (Table 1) have triggered a bloom of the phagotrophic (non-photosynthetic) dinoflagellate Oxhyrris marina. Dissolved oxygen level has declined and is unlikely to recover before evaporation effectively dries-out the lagoon for summer – failing flood. Water is becoming acidic (lower pH) with increased CO2  (carbonic acid) and lack of oxygenation (photosynthetic species in decline).

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