Nutrients and Productivity of the Giant Kelp, Macrocystis Pyrifera, in the Nearshore

Citation

Jackson, George Anthony (1976) Nutrients and Productivity of the Giant Kelp, Macrocystis Pyrifera, in the Nearshore. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/j42e-c605. https://resolver.caltech.edu/CaltechTHESIS:02172017-101827008

Abstract

The growth of giant kelp, Macrocystis pyrifera was studied by field measurements of nutrients and other water parameters. Gross primary production of the kelp bed at Point Loma, California was calculated at 1.5 moles-O₂/m²-day or 14.6 g-C/m²-day. This represents one of the highest measured values of gross primary production. A rate of production twice as high might be attained under optimal conditions.

The condition most limiting Macrocystis production was the low concentration of dissolved nutrients, especially nitrogenous substances, near the surface. Kelp compensated for this limitation by translocating nitrogenous compounds from depths where nutrient concentrations were higher. Summer dieoff of the surface canopy may be caused by inability of plants to translocate nutrients due to low availability of nutrients in deeper water.

Nutrient concentrations varied seasonally. Surface nitrate concentrations were low for most of the year (usually less than 1 μM), higher during the winter. Nitrate concentrations at 6 and 9 meters depth usually exceeded 1 μM. They were highest during spring upwelling months, lowest during summer months.

Nutrient concentrations in the kelp bed were not depleted by the kelp or enhanced by sediment nutrient regeneration, implying relatively fast exchange of water in the bed with outside waters.

Nutrient concentrations varied at different longshore locations. Surface nitrate concentrations were more likely to be higher near the tip of Point Loma than 5 kilometers farther north. Localized upwelling caused this.

In the shallow nearshore (depth<5 meters) the nutrient concentrations were higher than those in the kelp bed at comparable depths. The cause remains unknown.

Thesis Files