Beach-cast algae and seagrasses are essential for shorebirds

New research shows that the piles of seaweed that get washed up on our beaches are very important for our shorebirds – they provide both air-conditioning and heating, allowing birds to effectively regulate their body temperatures.

Most of us are familiar with the pieces of macroalgae and seagrasses that become washed up on our shores. While to us they may appear a nuisance to 4WD-driving or unsightly debris on our beautiful beaches, they are essential for shorebirds. We have known for a while that they provide a home for invertebrates, which in turn are important food sources for our shorebirds. My Masters student Tim Davis took a look at whether this beach-cast wrack also helps shorebirds to maintain their body temperatures.

Figure 1: Beach-cast algae at Point Danger, South Australia (Photo: Timothy J. Davis)

We found that beach-cast wrack functions like a reverse-cycle air-condition. Freshly washed up wrack can create cooler conditions when the weather is hot, as water evaporates. Early on cold mornings, it can also provide warmer conditions, as heat created by the warmer ocean waters dissipates. Older wrack is darker in colour and in the process of decomposition, absorbing and releasing heat on cooler days. The microclimatic conditions of these substrates are further moderated depending on how deep the wrack deposit is and whether it is sheltered from prevailing winds (by a sandbank or wrack deposits).

Figure 2: Temperature moderation by aged wrack, fresh wrack and wind shelter during a cool autumn day at Danger Point, South Australia (Graphics: Gunnar Keppel, Background Picture: Timothy J. Davis)

Therefore, a complex mosaic of different temperatures is created and can be exploited by shorebirds. We were able to show that shorebirds do indeed move between the different wrack types depending on the prevalent weather conditions. This way of conserving energy is likely to be particularly important for migratory shorebirds because these birds rely on accumulating sufficient energy stores in their Australian feeding grounds for successful migration to, and reproduction in, their breeding grounds.

Figure 3: Shorebirds roosting on fresh beach-cast wrack (Photo: TImothy J. Davis)

So why is this important? Beach-cast wrack is removed from many beaches worldwide, either for aesthetic reasons to increase tourism or to extract alginate. Alginates have important applications in the food and beverage industry, and the biomedical and bioengineering fields. As demand for alginates is predicted to increase, so will harvesting of wrack – particularly in Australia and New Zealand where beach-cast wrack is the main source of alginates. In Australia, there are also no guidelines for harvesting wrack and a code of practice is urgently needed.

Further Reading:

There is a more detailed summary of the publication by Graham Appleton on the Wadertales blog.

The publication is: Davis, TJ, Keppel, G. Fine‐scale environmental heterogeneity and conservation management: Beach‐cast wrack creates microhabitats for thermoregulation in shorebirds. J Appl Ecol. 2021; 00: 1– 11.‐2664.13865

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