Episodic nutrient supply to a kelp forest ecosystem in Southern California

Abstract

Temporal patterns of nutrient input into a Southern California kelp forest were measured using traditional hydrocast sampling coupled with high frequency temperature profiling. Patterns of nutrient input were related to growth rates of Macrocystis pyrifera located in an adjacent kelp forest. There were 2 distinct components to the pattern of nutrient availability. The long term, or seasonal, component was consistent with large-scale storm-induced mixing and horizontal advection during winter months. In addition, vertical motions of the thermocline, bringing nutrients into the kelp forest, occurred throughout the year with a frequency of about 2 per day and were strongest during the summer months. Weekly hydrocast sampling methods were inadequate for measuring these episodic events, and high frequency sampling was required to resolve the pattern of nutrient input accurately. Although measurable, nutrient input from vertical thermocline motion was inadequate to sustain maximum growth of Macrocystis pyrifera at 10m depth during the summer months. Thus, the major component of nutrient input came during the winter. These results indicate that nitrate limitation of M. pyrifera is a likely cause of reduced summer growth. Further, high frequency sampling is necessary to predict nutrient availability in nearshore ecosystems dominated by benthic macrophytes where the pattern of nutrient input is dominated by episodic events of short duration.

The response of giant kelp (Macrocystis pyrifera) in southern California to low‐frequency climate forcing

“…Gray line indicates GAM fit for separate regimes. Horizontal dashed line indicates NO 3 threshold for kelp growth (Zimmerman and Kremer 1984). Error bars indicate 95% confidence.…”

“…Their productivity and growth is limited by dissolved inorganic nitrogen (DIN; Wheeler and North 1980), mainly in the form of nitrate (Jackson 1977;Zimmerman and Kremer 1984, their fig. 9), which is the principal species of DIN that is delivered into the euphotic zone by physical processes, and has been shown to primarily limit kelp growth (Jackson 1977;Zimmerman and Kremer 1984). In the upper ocean (, 200 m), nitrate concentrations are strongly dependent on density and temperature (Kamykowski and Zentara 1986).…”

“…''resource'' or ''bottom-up''), cool high-nutrient periods such as La Niñ as are typically associated with increased levels of giant kelp productivity, growth, survival, and reproduction (Dayton et al 1999). Yet despite the well-established relationship between temperature and nitrate (Zimmerman and Kremer 1984), temperature accounts for less than half of the variability in proxies of giant kelp abundance such as canopy area, density, or harvest within the CCS (North et al 1993;Tegner et al 1996). Despite this, macroalgal stands at kelp-forest scales and greater are generally considered climate (cf.…”

Nutrient and growth dynamics of Halimeda tuna on Conch Reef, Florida Keys: Possible influence of internal tides on nutrient status and physiology

“…The effects of upwelling events on the productivity and physiology of marine macrophytes (Zimmerman and Kremer 1984;Fujita et al 1985Fujita et al , 1989Kiirikki and Blomster 1996) and phytoplankton (Maranon and Fernandez 1995;Kudela et al 1997) in temperate regions have been extensively studied. However, few researchers have documented community or species responses to these events on tropical reefs.…”

Population Dynamics of Edible Sea Urchins Associated with Variability of Seaweed Beds in Northern Japan

“…In the Sea of Japan in southwestern Hokkaido, the coastal water temperature has increased from 1980's for 104 years between 1897 and 2000 (Tanaka 2002). As nutrient concentration is inversely correlated with seawater temperature in this region (Nakata et al 2001) the same as the relation off southern California and Baja California (Jackson 1977;Zimmerman and Kremer 1984;Hernández-Carmona et al 2001), it is likely that nutrient concentrations have been decreased. Low nutrient concentrations have a negative impact on growth and maturation of sporophyte (Akaike et al 1998;Mizuta et al 1998Mizuta et al , 1999 and gametophyte (Mizuta et al 2001) of the laminarian kelps in northern Japan.…”