Kona-based Cyanotech Corp. said its earnings fell sharply in the final quarter of 2010 compared with the same period a year earlier as relatively strong sales of its nutritional microalgae products were largely offset by increases in the cost of materials and labor, as well as higher expenses for things like marketing and research.

Cyanotech earned $10,000 on sales of $3.92 million for the October-to-December period compared with earnings of $605,000 on sales of $3.98 million a year earlier, the company reported in a filing with the Securities and Exchange Commission.

Cyanotech’s main microalgae products are astaxanthin and spirulina, which accounted for 54 percent of sales and  46 percent of sales, respectively, in the third fiscal quarter.

Cyanotech also said it wrote of $360,000 in costs incurred during the quarter from spirulina pond contamination, heavy rains, cooler temperatures and a planned reduction in production of both spirulina and astaxanthin.

Cyanotech’s shares closed down 10 cents, or 3.5 percent, at $2.73 on the Nasdaq stock market.