Myall Lakes Research Articles

Karyotypic description and comparison of Litoria (L.) paraewingi (Watson et al., 1971), L.ewingii (Duméril et Bibron, 1841) and L.jervisiensis (Duméril et Bibron, 1841) (Amphibia, Anura).

The karyotype of Litoria (L.) paraewingi (Watson et al., 1971) (Big River State Forest, Victoria) is described here for the first time. It is prepared following tissue culture of toe clipping macerates, cryopreservation, reculture and conventional 4',6-diamidino-2-phenylindole (DAPI) staining. The L.paraewingi karyotype is then compared to similarly processed IUCN (International Union for the Conservation of Nature) least concern members L.ewingii (Duméril et Bibron, 1841) (southern Victoria) and L.jervisiensis (Duméril et Bibron, 1841) (Myall Lakes National Park, New South Wales), all members of the same L.ewingii complex/group. The L.paraewingi diploid number is 2n = 26, the same as for the other two species. Litoriaparaewingi chromosomes 1, 2, 6 and 7 are submetacentric, chromosomes 3 and 5 are subtelocentric and the remainder are metacentric. No secondary constriction or putative nucleolus organiser region (NOR) was readily identifiable following conventional DAPI staining in any scored L.paraewingi metaphase spread. Conversely, a putative NOR was readily identifiable on the long arm of chromosome 1 in all examined metaphase spreads for the other two species. The karyotypes of L.ewingii and L.jervisiensis here further differ from L.paraewingi with chromosome 1 being metacentric and chromosomes 8 and 10 being submetacentric for both former species. The L.jervisiensis karyotype differs from those of L.ewingii and L.paraewingi by DAPI staining with: (i) apparent relative length inversion of subtelocentric chromosome 3 and metacentric chromosome 4 and (ii) chromosome 6 being metacentric rather than submetacentric. All three species have a highly conserved chromosome morphology with respect to chromosomes 2, 5, 7, 9, 11, 12 and 13. The greatest gross morphological difference karyotypically is observed between L.paraewingi and L.jervisiensis. These karyotype data support the previous phylogenetic separation of these three species based upon genetic compatibility and behavioural, biochemical and molecular genetic analyses.

Inferring interspecific killing of Red Fox by Dingo from wounds and inter-canine distance measures – and a call for more data

ABSTRACT The role of the Dingo (variously Canis familiaris, C. familiaris dingo or C. lupus dingo, and hereafter C. dingo) in suppressing Red Fox (Vulpes vulpes) populations in Australia has been investigated, with various data tending to show an inverse relationship between densities of the two species (e.g. Letnic et al. 2012; Johnson and VanDerWal 2009). There are very few examples in the literature where direct killing was either observed or inferred (but see Moseby et al. 2012), making each a valuable datapoint. Here, we present a short description of a young adult female Red Fox presumed to have been killed by Dingo in Myall Lakes National Park on the basis of: (1) the close proximity of a Dingo pack (within approximately 20m) to the carcass; (2) the overlap between recorded values of inter-canine distance in Dingo and the wounds on the Red Fox; and (3) the location of those wounds on the body.

Recruitment of Melaleuca quinquenervia (Myrtaceae) in the fringing forests of the Myall Lakes, NSW, Australia

Context Melaleuca quinquenervia is a widespread, keystone species of eastern Australian coastal forested wetlands. Populations of M. quinquenervia in the fringes of Myall Lakes, New South Wales, Australia exhibit low numbers of juveniles, infrequent recruitment and a dominance of mature individuals, raising concerns about stand replacement from conservation managers. In contrast, M. quinquenervia often recruits in large numbers and is highly invasive in wetlands around the world. Aims To explore factors that limit recruitment of M. quinquenervia within its native range. Methods Field deployed seed traps; soil-core sampling; a burial longevity trial and depth of emergence experiment; laboratory temperature, salinity and light germination experiments; a transplantation experiment; monitoring of field germination; and a litter/leachate experiment. Key results Low seed viability (5–26%) is offset by high canopy seed loads (250 000 to 120 million seeds per tree) released continuously throughout the year with a peak fall in summer (2000 to 5000 viable seeds per m2 per month), coinciding with optimal germination temperatures. Seedling emergence is reduced below 5 mm soil depth, there is a very low soil seedbank reserve, and germination is light-dependant. M. quinquenervia exhibited reduced germination percentage and rate as well as reduced survival of seedlings at salinities higher than 15 dS m−1 EC (electrical conductivity). The most favourable sites for seedling establishment are permanently moist with low salinity, protected from wave action via sedge vegetation, and sheltered from prevailing winds. There is an inhibitory effect of Casuarina leachate on germination. Conclusions Germination in the field is episodic, and tied to specific environmental conditions. Highest losses occur at the seedling establishment phase. Implications Future research avenues and management recommendations are provided.

New Carboniferous ophiuroid from central coastal New South Wales

The ophiuroid Bronthaster retus gen. et sp. nov. is described from a single specimen preserved as external dorsal and ventral moulds, and is assigned to the Protasteridae. It occurs in the Namurian (Levipustula levis Zone) Yagon Siltstone of the Myall Lakes district of central coastal New South Wales. This rock unit forms part of the structurally designated Myall Block at the southeastern coastal termination of the Tamworth Belt. This new genus is the first stelleroid to be described from the Carboniferous in Australia. Most distinctive of the new genus is the arrangement of many small, subrhomboidal to subpentagonal, overlapping ossicles on the dorsal surface of the arms. The clearly exhibited tight relationship between successive ambulacrals in one column in ventral view suggests that some revision of previously inferred relationships within ambulacral columns in protasterids is required. The position of prominent toehooks on each ambulacral ossicle shows that they functioned to prevent lateral movement of the ambulacral column, operating in conjunction with the strong longitudinal musculature to allow arm flexure in the horizontal plane. This feature could potentially identify, within the Protasteridae, an evolutionary lineage that proceeded through the middle Palaeozoic and maintained the linear arrangement of the ambulacral columns using the toehooks, rather than fusion of the ambulacral ossicles across the arm axis. Peter A. Jell [amjell@bigpond.com] and Alex G. Cook, School of Earth Sciences, The University of Queensland, St Lucia 4072, Australia.

Swimming in Sand: Long-term Changes in Frog Communities in Response to Sand Mining in the Myall Lakes National Park, New South Wales

ABSTRACT The long-term impacts of mining on frog communities have received scant attention in published literature. This study presents a 38-year survey of two sites bordering a sand mine at Bridge Hill in the Myall Lakes National Park, New South Wales (NSW). Mining occurred in the area close to the two survey sites between 1981 and 1983 and frog surveys were undertaken there between 1978 and 2016. One site was a dunal pond that supported up to 13 frog species, the other a wallum swamp that supported up to 12 frog species; however, frog community composition fluctuated dramatically during and immediately after mining at both sites. Some frog species became temporarily more abundant (e.g. Litora aurea, L. latopalmata, Crinia tinnula), some species became less abundant and eventually disappeared from the sites (e.g. Adelotus brevis, Limnodynastes tasmaniensis, Pseudophryne bibroni). Changes in species abundance were driven by changes in pH, salinity and emergent plant cover at both sites as a direct consequ...

Tracking the Response of Phytoplankton following Gyttja Disturbance: a Mesocosm Field Study in Myall Lakes, New South Wales, Australia

This study determined whether artificially mixing gyttja, an organic sediment that contains high levels of NH4, with its overlying waters, affected phytoplankton abundance and species composition in Myall Lake (NSW, Australia). A series of mesocosms was employed, with three mesocosms being designated as controls, i.e. no gyttja mixing, and three others termed impact mesocosms, i.e. in which gyttja was mixed with the overlying waters. Sampling was undertaken during a 5 day period in sediment disturbance, and phytoplankton community variables were recorded at seven intervals, i.e. just prior to disturbance and 30 minutes, 3 hours, 1, 2, 3, 4 and 5 days after gyttja disturbance. Comparisons of these community variables among treatments and over time convincingly demonstrated that overall phytoplankton abundance rose from 20,000 cells/mL just prior to disturbance to between 30,000 cells/mL and 55,000 cells/mL 2 to 4 days after gyttja mixing. This rise in abundance was attributable to a substantial increase in the cyanophycea over the same period. In contrast to the cyanophyceae, the abundance of bacillariophyceae increased sharply following disturbance from 150 to >1000 cell/mL and did not exceed 1000 cell/mL for the duration of the experiment. This supported the hypothesis that gyttja mixing does introduce benthic microalgae into the water column. Sediment disturbance caused differences in species composition in time, with cyanobacteria being mostly influenced taxa. Each period of disturbance between mesocosm have different assemblages of species. Keywords Phytoplankton; Sediment disturbance; Mesocosm; Community structure

Seasonal examination of phytoplankton abundance and assemblages in Myall Lake and Bombah Broadwater, New South Wales, Australia

The Myall Lakes are a series of interconnected, shallow and poorly flushed coastal lakes located within the Myall Lakes National Park in NSW, Australia. The following field study aims to uncover patterns in temporal variability in water quality and phytoplankton abundance, diversity and assemblage structure, in the upper and lower water bodies of the Myall Lakes system. The result showed that the two lakes differ greatly in their catchment to lake area ratios, freshwater inputs, degree of saline intrusion, light attenuation and submerged macrophyte biomass. The broadwater, which receives large inputs of freshwater from the catchment, and is influenced by saline inputs from the Port Stephen’s estuary, exhibited highly variable water quality and dissolved nutrient concentrations, and phytoplankton assemblages with much temporal variation in taxa present, biovolume, cell size and abundance, and taxonomic diversity. In contrast, the upper lake, Myall Lake, shows much greater stability in water chemistry and nutrient availability; the phytoplankton community is diverse, with relatively low and constant biovolume, and is dominated year-round by small-celled cyanobacteria. Differences in phytoplankton between the two lakes were greatest during the autumn and winter, and least during the summer, when the phytoplankton assemblages in both lakes were dominated by similar cyanophyte taxa.

Growth response of natural phytoplankton to enrichment of urea and other forms of dissolved nitrogen

The Broadwater of Myall Lakes, NWS Australia is brackish water which has a high variation in water quality in particular salinity and nutrient concentration. In these experiments, we determined the growth and species assemblages of natural phytoplankton community exposed to nutrient enrichment. Laboratory incubation condition was used to measure 10 days biomass and group-specific response of phytoplankton community. Four experimental occasions were conducted in autumn (April and May, 2005) and early summer (November and December, 2005) with two experiments each season. Biomass of phytoplankton was determined based on chlorophyll fluorescence, extracted chlorophyll a and cell abundance of phytoplankton, and community structure/species assemblages was based on manual identification until genus level using upright light microscope. During four experiment events, chlorophyll growth response was significantly higher in N+P treatment than control and N treatment only, with slow growth rate occurring 24 to 48 h following nutrient addition. There was an inconsistent trend of biomass in terms of cell abundance in respond to nutrient enrichment between experiment occasions, except for May experiment. Generally, our study found that the greatest difference of phytoplankton growth/biomass at the Broadwater of Myall Lakes was at site level instead of nutrient treatments. Our study also revealed that urea and other forms of dissolved N stimulated growth of group specific of phytoplankton, with P addition contributed considerably to changing in community structure of phytoplankton. The result of this study suggest that urea was not a factor for Cyanobacteria bloom as compared to the other dissolved N forms, consequently urea does not give a further enhance for Cyanobacteria bloom formation in The Broadwater of Myall Lakes system. This study revealed that enrichment of different forms of dissolved nitrogen stimulated the growth of phytoplankton taxa in ways that resulted in significant differences in species assemblages among treatments for most sites. Extra addition of P can initiate bloom conditions for cyanobacteria. In order to reduce this possibility, P flow from catchment areas has to be prevented. Key words: Phytoplankton, community structure, nutrient, urea

Unexpected post-settlement freshening and increase in charophytes in Bombah Broadwater (Myall Lakes, New South Wales, Australia)

Bombah Broadwater is a shallow coastal lake within the Ramsar-listed Myall Lakes system on the mid-north coast of New South Wales, Australia. Increased nutrient and sediment loads resulting from catchment modification are thought to have instigated the loss of aquatic plants in the lake, causing it to “switch” from a clear, macrophyte dominated system (similar to the conditions in present day Myall Lake) to a turbid, phytoplankton dominated system. To assess this hypothesis, charophytes, foraminifera and aquatic fauna remains from an 800 year sediment record were examined. The sediment chronology was established using 14C, 210Pb and 137Cs radiometric dating and sediment composition. Interestingly, a clear increase in charophytes since European arrival conflicted with the hypothesised aquatic plant loss. Hence, it appears Bombah Broadwater has not undergone a change in stable state since European arrival. An additional and unexpected finding in the patterns of the foraminifera and testate amoeba suggest that Bombah Broadwater has freshened substantially since European arrival. This freshening may have resulted from increased catchment run off as a result of the clearance of catchment vegetation. Since catchment vegetation clearance is widespread in Australia, this finding raises the possibility that post-settlement freshening of coastal lakes may be a common occurrence.

Zooplankton assemblages of the Myall Lakes; A unique coastal lake system of New South Wales, Australia

The Myall Lakes are a large coastal lake system located approximately 50km north of Newcastle, Australia. The three main lakes are generally fresh to brackish, with salinity often varying between the lakes at any one time, due to their unique hydrology and long water residence times. Sampling in November 2001 found the zooplankton assemblages to be comprised of crustaceans (copepods, prawn larvae, crab zoea, ostrocods and amphipods), insects, isopods, molluscs, rotifers, water mites and worms (polychaete and oligochaete). Zooplankton assemblages varied spatially as a reflection of salinity and habitat. At a coarse taxonomic level, the zooplankton of the Myall Lakes appear to be similar to those recorded in the 1970’s.

Vesicular-arbuscular mycorrhizal fungi in natural vegetation and sand-mined dunes at Bridge Hill, New South Wales.

Roots of 52 vascular plant species growing in mined and unmined sites at Bridge Hill, Myall Lakes National Park, were examined, vesicular-arbuscular mycorrhizal (VAM) were present in 47 of the species. Observations were made on replicate of unmined sites and mined sites of differing ages since mining. The percentage of root length infected by VAM fungi was estimated using the grid line intercept method, a standard procedure for which was developed based on tets of the effects of root thickness, length of root segment and grid size in influencing the score. VAM were not found in the members of Proteaceae and Epacridaceae examined. Many species of non-legume herbs and grasses. Wherever they were collected, had moderate to large percentages of root length infected by VAM fungi. However, percentages of root length infected in Fabaseae and Mimosaceae were small in the sites last mied two and four years before the survey. The mean percentage of root length infected by VAM fungi, the mycorrhizal organs observed, and the presence of root nodules and sand aggregations are listed for each species examined.

Effect of magnesium on charophytes calcification: implications for phosphorus speciation stored in biomass and sediment in Myall Lake (Australia)

We examined the effect of magnesium (Mg) on the charophytes calcite (CaCO3) encrustation and assessed whether charophytes, growing on non-calcareous sediments in the Myall Lake, a poorly flushed shallow coastal lake with salinity of 2–3 PSU, could function as an effective nutrient sink for phosphorus (P) in a similar manner to charophytes growing on calcareous sediments of the freshwater calcium (Ca)-rich hardwater, i.e., through the formation of Ca-bound P. Our results showed that high Mg in the Myall Lake water reduced the calcification in charophytes. Likewise, the addition of Mg into the tap water also produced the same effect. The inhibition of the calcite formation decreased significantly the percentage of Ca-bound P formation in the charophyte biomass as well as in the sediment. However, the inability of charophytes in Myall Lake to precipitate calcite does not reduce the plant beds' capability to act as a P nutrient sink. Instead of Ca-bound P, a large percentage of less bioavailable non-reactive organically bound P (NaOH–P: 40–65%) fraction in the biomass, together with the plant’s slow decomposition rate, will lead to burial of dead organic matter and an incomplete mineralization process. In particular, detritus of the charophyte plants’ thalli is relatively more resistant to mineralization. This mechanism was supported by the result of sedimentary P fractionation in which the refractory P and non-reactive organic P fractions accounted for at least 80% of the total P.

Myall Lakes, September 2008

Myall Lakes, September 2008

Biomass dynamics of charophyte-dominated submerged macrophyte communities in Myall Lake, NSW, Australia

The dynamics of submerged macrophytes were studied in a large and shallow near-pristine lake in New South Wales, Australia. The objectives were to investigate the seasonal dynamics in biomass of Chara fibrosa, Nitella hyalina and Najas marina both in time and space, and to characterise the underlying relationship between the plant biomass and both the gyttja and water depths. Charophytes were most densely grown in the north-east bays of the lake compared to the north-west bays. Average biomass of Chara fibrosa was highest at the north-east bays of this lake (e.g. 210 g d.w m−2) followed by north-west bays (e.g. 148 g d.w/m2), South-west bays (e.g. 60 g d.w/m2) and lastly central deep area of the lake (e.g. 31 g d./m2). A similar trend was displayed by Nitella hyalina biomass where at the north-east bays the biomass was the highest (e.g. 167 g d.w m−2) followed by north-west bays (e.g. 128 g d.w/m2), south-west bays (e.g. 38 g d.w/m2) and central deep area of the lake (e.g. 23 g d.w/m2). During the summer season the maximum total biomass of charophytes at Corrigans bay was recorded (e.g. 300 g d.w/m2), mostly being dominated by Nitella hyalina. Total biomass of charophyte was reduced during the winter season (e.g. 50 g d.w m−2). Najas marina biomass remained low both in time and space except in May at Bibby harbour and Shelly beach where its biomass peaked (e.g. 276 and 175 g d.w m−2 respectively). Gyttja depth showed a positive relationship with total charophyte biomass (r2 = 0.70; p<0.01) and it seemed to favour the growth of charophytes at the expense of other submerged macrophytes, e.g. Myriophyllum sp. and Vallisneria sp. Water depth displayed a negative relationship with total charophyte biomass (r2=−0.94; p<0.01). Both Chara fibrosa and Nitella hyalina correlated positively with gyttja depth (r, r; p<0.01) and negatively with water depth (r, r; p<0.01). Najas marina correlated positively only with water depth (r2=0.67, p<0.01).

Circulation and the nutrient budget in Myall Lakes

A two-dimensional model is used to study transport of material within Myall Lakes and is coupled to the ocean using a one-dimensional model of Lower Myall River. Runoff from the catchment is calculated from water levels and compares favourably with rainfall assuming an average runoff yield of 28% and a runoff coefficient of 47% for events above the 90th percentile. Most of the runoff enters Bombah Broadwater which is also the only basin connected to the ocean. Intermittent runoff events rapidly displace water from Bombah Broadwater into Boolambayte Lake and from Boolambayte Lake into Myall Lake. Displaced water is mixed within basins by wind-driven circulation within the time scale that levels fall as water drains from the lakes to the ocean. Only 7% of the nutrient load entering Bombah Broadwater becomes resident Myall Lake. About 40% of the nutrient load entering Boolambayte Lake becomes resident in Myall Lake. Median time scales for loss of conservative material entering each basin with the runoff are: 140 days for Bombah Broadwater, 118 days for Boolambayte Lake, and 535 days for Myall Lake. Salinity fluctuates greatly in Bombah Broadwater but is stable in Myall Lake. Material loss from Bombah Broadwater is characterized by many time scales associated with runoff from the catchment and low-frequency changes in ocean water level. Comparison of observed distributions of total nitrogen with simulations indicates that there are sources of total nitrogen in Boolambayte Lake and Myall Lake and sinks of total nitrogen in Bombah Broadwater. There appear to be sinks of total phosphorus throughout the Myall Lakes.

Nutrient and phytoplankton responses to a flood event in a series of interconnected coastal lakes: Myall Lakes Australia

Myall Lakes is a large brackish coastal lake on the east coast of Australia that was considered pristine until the occurrence of blue-green algal blooms in 1999. The temporal and spatial extent of chemical and biological changes to the water column of Myall Lakes was studied intensively after a rain event in 2002. Water quality profiles (T, EC, pH, DO), turbidity (secchi), nutrients (TN, NOx, NH4+, DON, TP, FRP, DOP, Si), and phytoplankton (chl a and cell counts) were measured at nine sites on eight occasions immediately after the rain event. Freshwater inflows affected a large area of the lake. Greatest changes were seen in areas close to the mouth of the upper Myall River which is the largest freshwater input to the lakes. Here, greatly elevated concentrations of NOx, TP, and FRP (up to two orders of magnitude higher than background) were recorded immediately after the rain event but persisted for only 2 to 8 days. Slightly elevated concentrations of TP and NOx were seen in inflows from the smaller Boolambayte Creek. Stratification was associated with bottom water anoxia and release of ammonia from the sediments. Identification of the sources of nutrient species delivered from different parts of the catchment, combined with studies of nutrient loads can assist managers to develop effective nutrient reduction strategies to reduce the incidence of blue-green algal blooms in Myall Lakes.

The trophic history of Myall Lakes, New South Wales, Australia: interpretations using δ13C and δ15N of the sedimentary record

In an attempt to determine the trophic history of the Myall Lakes complex (New South Wales, Australia) δ13Corg, δ15N and Corg:N profiles were determined for bulk organic matter of two short sediment cores from Bombah Broadwater and Myall Lake. 210Pb profiles and sediment types indicate significantly different trophic trajectories during the time periods examined. δ13Corg and Corg:N indicate Bombah Broadwater has been dominated by increasing inputs of terrestrial organic material over the last century, thought to be related to watershed disturbance including agricultural activity. Primary production appears to be dominated by phytoplankton. δ15N remained relatively stable at around 1‰ until the mid–1970s when there was a sharp increase to 4.7‰, interpreted as an influx of sewage-derived material. These observations offer an insight into the recent trophic changes at the site. Sedimentation rates are noticeably lower in Myall Lake and the most recent sediment is a flocculent organic rich deposit overlying mineral clay. δ13Corg and Corg:N values indicate a transition from plankton to macrophyte dominated primary production around 1800AD. δ15N values become increasingly negative from approximately 1900AD. This is interpreted as being due to increasing reliance by macrophytes on nitrogen recycled from decomposing sediments driven by natural infilling and eutrophication in this basin. The contrasting sedimentation rates, sediment types and geochemical profiles suggest the different basins of this water body are subject to substantially different internal and external influences which should be considered in management decisions.

Carbon and nitrogen stable isotope analysis indicates freshwater shrimp Paratya australiensis Kemp, 1917 (Atyidae) assimilate cyanobacterial accumulations

Large areas of uncompacted cyanobacterial accumulations (or “gyttja”) have been observed in Myall Lake, New South Wales, Australia. To determine whether the cyanobacterial accumulations were assimilated into the local food web, carbon and nitrogen stable isotopes were used to identify the primary food sources of a primary consumer in Myall Lake, the freshwater atyid shrimp Paratya australiensis. Suspended particulate organic matter (POM) and the macrophyte Myriophyllum salsugineum were identified as major dietary sources of P. australiensis. Enriched stable isotope signatures (δ13C and δ15N) of shrimp from gyttja-affected sites, relative to shrimp from unaffected locations, also indicated that P. australiensis were deriving a considerable portion of their dietary carbon and nitrogen requirements from gyttja. Stable isotope mixing models estimated that cyanobacterial accumulations might constitute up to 69% of P. australiensis biomass carbon and nitrogen requirements at gyttja-affected locations. To our knowledge, this is the first study to use stable isotope analysis to trace the assimilation of potentially toxic cyanobacterial accumulations into the trophic pathways of an affected system.

Mechanisms affecting biomass and distribution of charophytes and Najas marina in Myall Lake, New South Wales, Australia

Two years of measurements are explored with a view to formulating an ecosystem model for Myall Lake. Stable physical characteristics, low catchment loads, low light attenuation, flat-bottomed hypsometry, and soft gyttja substrate allow stable charophyte biomass throughout the year in Myall Lake. Chara fibrosa dominates the total biomass and is abundant over the depth range 0.5–4 m. Nitella hyalina is found over the same depth range but has diminished biomass at depths greater than 2 m due to increased incidence of zero-biomass samples at depths greater than 1.5 m. Upper bounds for biomass densities were estimated for charophytes. Najas marina has great seasonal variability and meadows can have very high biomass in waters 1.5–2.7 m deep. High biomass of Najas marina is associated with low biomass of Nitella hyalina and may be a factor determining how the biomass of Nitella hyalina is distributed with respect to depth. Patchiness of Najas marina is particularly high. Temperature and light can support two growing seasons for Najas marina but mechanical disturbance is often high in spring and high biomass was only observed in late autumn during the present study. Less than 5% of the present-day production of submerged macrophytes would have been required to produce organic material of the gyttja over a 1,000-year period. The spatial distributions of gyttja and the dominant macrophytes are consistent with wind patterns. Down-lake limits on the distributions of charophytes and Najas marina are related to a gradient in the coefficient of light attenuation that is, in turn, related to proximity to the bulk of the catchment load.

Temporal and spatial variability in the phytoplankton community of Myall Lakes, Australia, and influences of salinity

The variability in the phytoplankton communities of the Myall Lakes, a series of four interconnected coastal lakes on the lower north coast of New South Wales, was studied between 1999 and 2002. There was considerable spatial variability across the lake system. Bombah Broadwater experienced blooms of Anabaena in 1999 and early 2000, but these were replaced from late 2000 onwards by Chroococcus and a variety of eukaryotic taxa, particularly flagellates and diatoms. In comparison, the phytoplankton community of Myall Lake was dominated for much of the study period by Chroococcus, Merismopedia and chlorophyte taxa. The sites located midway between these two main lakes represent an ecotone, with elements of the phytoplanktonic flora of both main lakes being present. Changes in phytoplankton community composition in Bombah Broadwater occurred fairly frequently. In contrast, the phytoplankton community in Myall Lake changed little during the course of the study and can be considered as being at long-term equilibrium. The reasons for this lie in the morphology and hydrology of the lake system, which in turn create gradients in a number of physico-chemical water quality attributes. Bombah Broadwater is influenced by episodic and stochastic freshwater inflows from the upper Myall River catchment, and in times of drought by saline marine incursions via the lower Myall River. Myall Lake however represents a cul-de-sac, with only a small hydraulic connection to the remainder of the lake system. As it has little input from its small catchment, the limnological conditions within this lake remain relatively constant for long periods of time. Although no patterns of seasonal succession were discernable in any of the lakes, some longer-term (annual) changes did occur, and certain taxa displayed enhanced growth in summer. Salinity was found to be an important factor in determining phytoplankton community composition and abundance. Canonical Correspondence Analysis of phytoplankton and environmental data for all sites combined, showed ammonia, total nitrogen and salinity (measured as electrical conductivity) to have the most influence on the phytoplankton community composition and abundance. Anabaena growth was positively related to ammonia concentration and negatively related to conductivity.