GBR - Indicators of marine water quality - Benthic foraminifera (AIMS)

This research incorporated field and experimental work on benthic foraminifera as indicators for water quality in the Great Barrier Reef (GBR). Firstly, distribution of benthic foraminifera was examined on 20 reefs in four regions of the GBR (Princess Charlotte Bay, Wet Tropics, Whitsunday Area, and Mid/Outer-shelf reefs), and along a water quality (WQ) gradient in the Whitsunday region. Secondly, manipulative laboratory experiments were carried out to determine whether the distribution of symbiont-bearing foraminifera is controlled by light levels or other environmental factors.

To test if light is the main factor regulating communities of symbiont bearing benthic foraminifera, sediment samples from 3 different depths on 6 reefs (Reef 19-138 and Barb Reef; Edward, Lindeman and Repulse islands) along an environmental gradient in the Whitsunday Islands were investigated. In addition, an experiment was conducted quantifying growth and response to light levels using 3 abundant taxa with diatom symbionts.

Results

  • Twenty seven easily recognisable benthic foraminifera taxa (> 63 ┬Ám) were distinguished.
  • Several species were associated with either high nutrient/high turbidity or low nutrient/low turbidity conditions.
  • In general, large (algal symbiont bearing) foraminifera were more characteristic for clear water/low nutrient environments, while more turbid high-nutrient environments harbour heterotrophic taxa (free of algal symbionts).
  • Application of the Caribbean FORAM index showed significantly increasing values along the Whitsunday Islands WQ gradient (i.e. with increasing light and decreased nutrient availability).
  • Diversity of symbiotic taxa, and the abundances of most symbiont bearing species, increased along a WQ gradient away from the mainland in the Whitsundays region. Distance from the mainland alone explained nearly three times more of the variance than sampling depth and percent surface light in the distribution of species.
  • In the laboratory experiment manipulating light levels, two (Amphistegina spp. and Calcarina spp.) of the three symbiotic genera tested exhibited similar growth rates at 100%, 30% and 7% of sea surface light. This indicates a wide tolerance for light levels. In contrast, growth of Heterostegina depressa decreased significantly with increasing light intensity, suggesting that too much light inhibits growth in this species. All three taxa had the most efficient light use at the lowest light level tested. Reduced photosynthetic yield at high irradiance suggested that high light may exert stress on the photosystem of the symbionts.
  • Both field and laboratory studies suggest that light is unlikely to be the controlling factor for the distribution of foraminifera that were selected as potential bioindicators for water quality.
  • All four geographic regions differed significantly in their community composition, and analysis showed that sediment parameters only explained a small proportion of the variance in the community composition.
  • On 9 reefs along a previously studied water quality gradient, foraminifera showed a distinct shift in species dominance towards larger symbiont-bearing species from turbid inner shelf towards clearer outer shelf reefs. Analysis separated symbiotic and heterotrophic species.
  • Total suspended solid and water column chlorophyll concentrations were negatively, and optical depth and distance to the mainland were positively, correlated with the abundance of symbiont bearing taxa.
  • Heterotrophic rotaliids and a species retaining plastids (Elphidium sp.) were highly characteristic for low light, higher nutrient conditions.

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Further Reading

Foram atlas: Nobes K, Uthicke S (2008) Benthic Foraminifera of the Great Barrier Reef: A guide to species potentially useful as Water Quality Indicators. Report to the Marine and Tropical Sciences Research Facility. Reef and Rainforest Research Centre Limited, Cairns (44pp.).

MTSRF Project 3.7.1 webpage

Uthicke S, Thompson A, Schaffelke B (2010) Effectiveness of benthic foraminiferal and coral assemblages as water quality indicators on inshore reefs of the Great Barrier Reef, Australia. Coral Reefs 29: 209-225

Nobes KL, Uthicke S and Henderson R (2008) Is light the limiting factor for the distribution of benthic symbiont bearing foraminifera on the Great Barrier Reef? Journal of Experimental Marine Biology and Ecology 363: 48-57.

Uthicke S, Nobes K (2008) Benthic Foraminifera as ecological indicators for water quality of the Great Barrier Reef. Estuarine, Coastal and Shelf Science 78: 763-773

Uthicke S and Nobes KL (2007) A report on the use of benthic foraminifera as indicators for water quality on the Great Barrier Reef. Report to Marine and Tropical Sciences Research Facility (MTSRF), Cairns. Australian Institute of Marine Science. 48 p.