Diet of Invertebrates and Fish in Tuggerah Lakes estuary

What are the fish eating in the Tuggerah Lakes estuary

Scientists at the Office of Environment and Heritage carried out a food web study in Tuggerah Lakes (and Lake Macquarie) to find out which plants the invertebrates and fish are obtaining most of their baseline nutrients from. The findings are presented as Conceptual Models showing the relative contributions of different plants to the diets of the invertebrates and fish.

concept image of diet of macroinvertebrates in Tuggerah Lakes

A conceptual model showing the relative contribution of different types of plants to the diets of the six macro-invertebrate groups included in the study. Large (or small) yellow arrows indicate that that plant type forms a relatively large (or small) proportion of the animal’s diet. 

concept image of diet of fish in Tuggerah Lakes

A conceptual model showing the relative contribution of different types of plants to the diets of the seven fish species included in the study. Fish in the first box are carnivores and fish in the second box are herbivores. Fish in the third box are detrivores/planktivores (feed primarily on detritus [decaying matter] and/or plankton) Large (or small) yellow arrows indicate that that plant type forms a relatively large (or small) proportion of the fishes diet.

These concept models do not necessarily mean that the fish are directly consuming the plant. In a nut shell both the invertebrates and fish get most nutrition from algal material more so than seagrass in Tuggerah (the table below shows this as a percentage). In earlier times the main source of nutrients for the lakes food web would of come from seagrasses but as the lake has become eutrophied and degraded there has been a shift to algal sources.

Table 1.

 

                          Tuggerah Lake

                   Lake Macquarie

Consumers

 

 Terrestrial

  Seagrass

  Macroalgae

  Microalgae

     Terrestrial

  Seagrass

  Macroalgae

  Microalgae

Whiting

 Median (%)

    12

     10

      38

      36

          4

      46

       32

      16

Tarwhine

 Median (%)

     8

     14

      40  

      32

          6

      40

       34

      18

Striped Trumpeter

 Median (%)  

    14

     10

      34

      38

          4

      44

       32

      16

 

 

 

 

 

 

 

 

 

 

 

Table 1. above shows the results of IsoSource modelling estimating median contributions (%) of terrestrial vegetation, seagrass, macroalage and microalgae to the diets of fish (whiting, tarwhine and striped trumpeter) in Tuggerah lakes and Lake Macquarie.

The Future

If the lake becomes degraded even more then the scientists expect, there will be a greater shift towards algal dependency and this may have subsequent further effects on types and abundances of invertebrates and fish in the lake.  

Want to know more about ‘Who eats whom in Tuggerah Lakes? read more.