RC21. Ecological impacts of estuarine drift algae: a meta-analysis

30th November 2009, at Edith Cowan University, Perth, WA.

SPEAKERS INCLUDE Mads Thomsen (leader) - Edith Cowan U - coastal ecology, meta-analysis Thomas Wernberg - Edith Cowan U - algal ecology, meta-analysis Mat Vanderklift - CSIRO Marine and Atmospheric Research, Perth - estuarine ecology and seagrass biology Marianne Holmer - Syddansk U (Denmark) - biogeochemical impacts of estuarine drift algae Participating but not attending the meeting Brian Silliman - U Florida (USA)

On Monday 30th November there will be an intensive 1-day research course offered, open to interested researchers and ECR and HDR.

The purpose of the remainder of the week for working group participants will be to compile all estuarine manipulative drift algal ‘impact’ studies and extract and compare standardized effects sizes, i.e. mean and dispersal values for control plots (without drift algae) against treatment plots with experimentally added drift algae.

Program

9.30-.9.50: Mads Thomsen. Welcome; Introduction to algal effects in seagrass beds
10-10.20: Marianne Holmer: Effects of drift algae on seagrass performance due to biogeochemical alterations
10.30-10.50. Brian Silliman/Mads Thomsen (presented by Mads). Introduction to meta-analytical methods.
11-11.20: Thomas Wernberg. Synergistic effects of drift algae and invasive snails on seagrass performance – a case study from Swan River
11.30-11.50: Mat Vanderklift: Effects of epiphytes on seagrasses.
12-12.20: Mads Thomsen. Summary, additional questions to all speakers, open brain storm on objectives, methods and analysis.

Background
Drift algae are a natural and vital component of estuarine ecosystems in the same way as seagrass beds, oyster reefs and salt marshes. Drift algae can be important primary producers that filter out land-derived nutrients and provide structurally complex habitat and food for invertebrates and fishes. In addition, tumbling drift algae increase habitat-connectivity, by ‘transporting’ invertebrates and juvenile fishes between patches of suitable habitats (e.g. between seagrass patches).

However, drift algae can also be an unwanted nuisance if they accumulate in high densities; drift algae can smother seagrasses, compete for light and nutrients, filter out propagules before they reach a suitable substratum, and they can cause low oxygen levels in sediments and the water column due to respiratory processes and tissue decay. Such hypoxic or even anoxic conditions may lead to local extinctions of seagrasses, reef-formers (e.g. oysters, mussels), mobile invertebrates and fishes; indirectly cause sediment destabilization and ultimately large-scale regime shifts from clear water systems characterized by slow-growing habitat-formers to turbid systems composed of fast-growing ephemeral drift algae. Indeed, drift algal mass accumulations and associated anoxia and negative ecosystem effects are becoming increasingly common due to nutrient pollution (eutrophication). In addition, large masses often accumulate on popular beaches causing aesthetic problems that are expensive to mitigate.

Many experimental studies have documented negative ecosystem effects associated with drift algal accumulations. Specifically, it has been shown that the magnitude of effects typically depends on drift algal density and species identity, the affected habitat type, temperature, and nutrient levels. However, most studies have only focused on how a single environmental determinant impact a specific estuarine habitat and the literature of environmental drift algal drivers and impacts is highly scattered.

Last Updated July 2009