USC Dornsife Scientific Diving: An Analysis of Sargassum horneri Ecosystem Impact

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The giant kelp forests of Catalina provide not only a subaquatic wonderland for divers, but also a habitat for countless marine organisms. However, their existence is jeopardized by a number of invasive species, namely Sargassum horneri (hereafter referred to as S. horneri). This species has no common name in English, but is referred to as akamoku in Asia, where it is native (Saccardi). S. horneri and S. filicinum, once thought to be two different strains but recently proven to be both classified as the horneri species by Uwai et al. in 2009, is an invasive seaweed found along the coasts of Southern California, the Channel Islands, and Baja Mexico. It behaves similarly to other invasives of S. CA such as S. muticum, Undari pinnatifida, and Caulerpa taxifolia. S. horneri is found in the intertidal zone and up to depths of 19 m, and exhibits a brown fern-like quality with many air bladders, often growing up to 20 feet (Smith). Its forests can grow to be very dense, blocking out sunlight and stealing nutrients and substrate from native species like the giant kelp. It is very apt at reproducing, as it is capable of self-fertilization (both the male and the female are in one plant) and matures early in its lifespan; this makes for rapid growth and out-competition of native species for resources. S. horneri is an annual species, completing its lifespan in less than a year – the dead individuals, often housing creatures like barnacles, diatoms, invertebrates, and even baby giant kelp plants, drift away carrying reproduction-capable structures of their own to colonize new areas. This colonizing mechanism makes the S. horneri difficult to contain; the amount of beached alga from this species is second only to the giant kelp (Miller). Removal of the S. horneri from S. CA and Baja Mexico is necessary to the livelihood of the natural ecosystem, and the current challenge is how we will accomplish this task.


This blog post was originally published in Scientific American in May 2013.


Scientific American