Monday was relatively quiet on Wall Street, with major benchmarks' early losses largely fading away by the end of the trading session. Investors continued to wrestle with a variety of long-term issues, and in the absence of any resolution on key macroeconomic and geopolitical issues, many stocks continued to tread water. Yet a few companies had bad news that sent their share prices significantly lower. Aurora Cannabis (NYSE:ACB), Abiomed (NASDAQ:ABMD), and Gulfport Energy (NASDAQ:GPOR) were among the worst performers. Here's why they did so poorly.

Aurora keeps going lower

Shares of Aurora Cannabis dropped 17%, adding to its recent losses. The marijuana sector had a lot of trouble last week, as company after company had poor earnings results that cast doubt on the entire long-term investing thesis for the industry. For Aurora, news late last Thursday that it had decided to stop construction activity at two of its facilities, including the Nordic 2 project in Denmark and its Aurora Sun facility in Canada, pointed to the need to conserve capital. Investors might be slow to get back into shares of Aurora and its cannabis peers until the marijuana growers can demonstrate their next pathway to growth and consistent profitability.

Greenhouse lit with green light, with hundreds of cannabis plants in rows.

Image source: Aurora Cannabis.

Abiomed takes some heat

Abiomed saw its stock plunged 20% after the release of some clinical studies over the weekend called one of the medical device maker's products into question. Data at the American Heart Association annual meeting pointed to the idea that Abiomed's Impella heart pumps could produce increased risks of bleeding, stroke, or even death for angioplasty patients compared to older medical technology. The question at this point is how to reconcile this adverse study data with other studies that pointed to advantages for Impella heart pumps. Until that gets resolved, though, investors seem unwilling to assume that the news won't hurt Impella sales.

Gulfport hunkers down

Finally, shares of Gulfport Energy fell 8%. The oil and gas exploration and production specialist said that it will reduce its labor force by 13% in order to manage costs more effectively, and it will also stop using available cash to support stock buyback activity. Gulfport instead said it had focused its available capital on buying back debt at discounted prices as it seeks to cut its overall leverage. The energy company blamed low prices and unfavorable outlooks for natural gas in the near future for its decision to stop doing stock buybacks. Shareholders can only hope that a recovery in the energy markets comes quickly enough for Gulfport's efforts to make a difference.