Photograph of algae presses
Sites and Critters

Red macroalgae artwork… and some science

Algae presses are a cool and creative way to document macroalgal specimens you encounter in the field (and they make great gifts too!). These specimens came from a dive site near Centennial Park in Elliott Bay, Seattle. They represent some of the more common and dominant species I see growing on riprap. I made the presses by placing them on thick paper between two pieces of plywood held together by bolts that I then tightened as the algae dried.

These are presses of red algae species I commonly find on riprap in Seattle.  Tiny pieces of these algae are mixed into adjacent sediments.

These are presses of red algae species I commonly find on riprap in Seattle. Tiny pieces of these algae are mixed into adjacent sediments.

Riprap, the rocky material that makes up jetties, breakwaters, and seawalls, supports an abundance and wide diversity of red macroalgae.  One of the questions I’ve been most interested in testing is whether the red macroalgae growing on riprap get incorporated into neighboring soft sediments.  I recently collected sediment samples along transects extending perpendicularly from riprap installations (see earlier post), and I’m happy to say that I have a finding to report!  After weeks of sorting through the sediment samples, I have found that the amount of red macroalgae that is mixed into soft sediment decreases as you move away from riprap.

The next step is to identify whether these differences in algal content might influence the community of organisms that live in soft sediment.  In ecology, food webs that are altered by the influx of resources from adjacent habitats are said to be “subsidized” or influenced by “spatial subsidies.”  (I’ll write a post soon to give more background on the spatial subsidies literature.)

To test for spatial subsidies, I’ll be conducting field experiments in which I enrich soft sediment plots with fixed volumes of shredded red macroalgae. At the end of 8 and 16 weeks, I’ll be collecting core samples from these enrichment plots and testing for differences in community structure. More to come on that.  In the meantime, I’m excited to say riprap-originating algae do in fact make it to neighboring soft sediments… what is their affect there?  The answer to that is coming soon!

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