Giant kelp (Macrocystis pyrifera) absent around Isla Todos Santos

Observer: During the summer of 2015, Giant Kelp (Macrocystis pyrifera) was almost absent in the waters surrounding Isla Todos Santos, in contrast to the summers of 2014 and 2016, when large beds of this species were present.

Coastal ecology expert: The Giant Kelp (Macrocystis pyrifera, Figure 1) is an important ecosystem engineer, modulating ocean currents and available light while creating habitat for numerous invertebrate and vertebrate species. Urchins, fish, crabs, seals, sea otters and starfish utilize the resources within a kelp forest to create a rich and diverse community that depends on the presence, expanse and health of the kelp bed. In addition to providing habitat for a number of commercialized species, the kelp itself represents an important fishery, with kelp harvests dating back to 1956 along the Baja California peninsula¹.

M. pyrifera is most abundant in Bahía Todos Santos during spring and summer¹ due to spring upwelling which generally increases nutrient concentrations in the water column, particularly in the lower half. Increased nutrient concentrations in the water column, coupled with increased solar radiation result in increased algal growth. M. pyrifera captures nutrients from the lower portion of the water column and subsequently translocates them upwards to the canopy; however, if the lower portion of the water column is nutrient poor and the kelp is unable to absorb enough nutrients, the canopy will recede and the kelp may die off ².

Nitrate (an essential nutrient for kelp) concentrations and water temperatures in Southern California are known to have an inverse relationship, with water temperatures higher than 15.5°C generally containing less than 1 µM of nitrate³. El Niño events have been tied to massive kelp die offs, as a typical El Niño results in increased water temperatures coupled with decreased nutrient concentrations^{1, 4, 5}. The strong 2015-2016 El Niño most likely resulted in increased water temperatures around Isla Todos Santos and decreased nutrient concentrations that led to the massive kelp bed die-off.

Consultant:

Andrea Liévana MacTavish. Interdisciplinary Coastal Ecology. Biological Oceanography. CICESE.

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References:

1. Casas Valdez M, Serviere Zaragoza E, Belda DL, Marcos R, Aguila Ramírez, R. 2003. Effect of climatic change on the harvest of the kelp Macrocystis pyrifera on the Mexican Pacific Coast. Bull. Mar Sci. 73(3):545-556.
2. Jackson, GA. 1997. Nutrients and production of the giant kelp,(Macrocystis pyrifera, Phaeophyceae) recruitment near its southern limit in Baja California after mass disappearance during ENSO. J. Phycol. 35:1106-1112.
3. Zimmerman RC, Kremer, JN. 1984. Episodic nutrient supply to a kelp forest ecosystem in Southern California. J. Mar. Res. 42:591-604.
4. Tegner MJ, Dayton PK. 1991. Sea urchins, El Niños, and the long term stability of Southern California kelp forest communities. Mar. Ecol. Prog. Ser. 77:49-63.
5. Tegner MJ, Dayton PK, Edwards PB, Riser KL. 1996. Is there evidence for long-term climatic change in Southern California kelp forest? CalCOFI Rpt. 37:111-126.