Habitats are a work of art: habitat mosaics and fish production

Citation: Brenna, S.R., Schindler, D.E., Cline, T.J., Walsworth, T.E., Buck, G., and D.P. Fernandez. 2019. Shifting habitat mosaics and fish production across river basins. Science 364 (6442): 705-800.

Link: https://science.sciencemag.org/content/364/6442/783

Biodiversity is continually being threatened by human activities, and it is vital that we protect it. Conserving biodiversity means conserving species and the habitats they live in. We know that habitats vary through space and time, but does this variation impact fish production in the long term? Brennen et al. explores this question using Pacific salmon species in an Alaskan watershed.

A “mosaic” isn’t just a form of art!

When you hear the word “mosaic,” you might think of a beautiful piece of artwork (small pieces arranged together to make something different and new). Habitats, natural homes to organisms, can also be put together to create mosaics on a landscape (much like a piece of art): one minute you might be walking through a forest and the next minute a lake! Together, the mosaic breeds biodiversity (many different forms of life). However, unlike a mosaic hanging in a museum, habitat mosaics can shift over time.

Everything comes down to biodiversity!

Biodiversity comes from habitats that differ in terms of topography (shape of the land), and climate (temperature over the long term). This is why you find different plants and animals in the tropics versus the tundra; we all know there are many different organisms in both of these locations! A “shifting habitat mosaic” refers to a habitat’s ability to change through space and time. Why is this important? More biodiversity.

Can shifting habitat mosaics alter fish production?

Shifting habitat mosaics can refer to variations in habitats, populations, and how ecosystems are formed. Simply put, shifting habitat mosaics mean ecosystem change. It has been previously studied on a small scale, but there are not any studies done on a wider scale (over many years). The question is: can organisms use a shifting habitat mosaic to their advantage? Even further, can shifting habitat mosaics impact the services ecosystems provide, and thus, biodiversity?

Long-term study of habitat mosaics

Brennen et al. looked at Pacific salmon species in an Alaskan watershed; watersheds are excellent mosaics to study over the long-term. Why? They combine networks of rivers and streams – many “parts” coming together like a piece of art!  Nushagak River flows into the Bristol Basin in Alaska; it is remote, pristine, and has various landforms that contribute to the mosaic. The researchers wanted to see if this shifting habitat mosaic (which shift landscape patterns), impacted the chinook and sockeye salmon fisheries.

What did they do?

The researchers looked at the fishes’ otoliths, or ear stones, in order to track their migration patterns over three years: 2011, 2014, and 2015. Specifically, they measured strontium isotopes in the otoliths, which were tracked from their birth to their juvenile stages. Using this method, they were able to follow the fishes’ movements and calculate where the adults were returning. Why do they care about this? Shifting habitat mosaics can change landscape patterns, which could alter fish production. Looking at three different years provides enough of a landscape (mosaic) shift.

What did they find?

Over the three years of the study, the researchers found that salmon production varied quite a bit. Salmon from the Nushagak River continued to migrate and reproduce all three years. The habitat changes the salmon experienced were conducive to survival, though the two fish species charted different courses from birth to adulthood. The mosaic of this system allowed juvenile fish to find areas that were suitable for them to grow. Overall, the ever-changing habitat mosaic allowed for consistent salmon production in different locations in the watershed, in three different years.

The takeaway: habitat mosaics are great for biodiversity!

As industrial and urban growth continues, biodiversity is threatened. Overall, landscapes over large areas play a huge role in keeping environments stable. Humans rely on ecosystem services, which only remain in tact with high biodiversity.

Understanding how shifting habitat mosaics alter economically important populations could play a role in how we manage and conserve these species. When conserving areas of land, it is important to look at larger landscapes to keep our habitat mosaics in tact, especially in the face of global change. Shifting mosaic habitats keeps our ecosystems resilient.

Next time you look at a mosaic artwork, remember that habitat mosaics are key to maintaining biodiversity and the ecosystem services we rely on.