After a yearlong recovery in the market, stocks have recently taken a turn for the worse. Despite strong corporate earnings in the first quarter and a rebound in consumer spending, investors are now bracing themselves for what could be a major correction or even a bear market.

So what happened?

The European debt crisis that began as a minor issue in Greece has spread like wildfire to the rest of the European Union. The energy sector has been pummeled as the BP oil spill continues to drag on, taking with it the share prices of almost every company involved with exploration, drilling, or services.

In times like this, it's not odd to see drastic movements in your portfolio, from stocks that move by 5% to 10% on barely any news at all. So let's see which stocks are the biggest market movers today and examine whether there was any logic to justify their shift.

Stock

Market Cap (Millions)

Change in Price (%)

Closing Price (Prior Day)

Patriot Coal (NYSE: PCX)

$1,300.00

(11.79%)

$16.20

Allied Irish Banks (NYSE: AIB)

$1,150.00

(5.84%)

$2.74

Bank of Ireland (NYSE: IRE)

$985.11

(5.26%)

$4.18

Source: The Wall Street Journal.

Sometimes, investors are caught off guard by what seems like irrational market movements, but not this morning. Patriot Coal got slaughtered in midday trading, as the company announced the closure of its valuable West Virginia mine because of a recent roof collapse. The mine was expected to produce 440,000 tons of metallurgical coal this year, and now profits are expected to be negatively affected into next year. To add insult to injury, Brean Murray Carret cut its price target from $30 to $26.

Both of the Irish financial institutions listed above have seen their shares hit today -- and possibly for good reason. According to Central Bank of Ireland Governor Patrick Honohan, the "net indebtedness of the banks to the rest of the world jumped from 10% of gross domestic product to over 60%." Even though many of Ireland's banks were stress-tested, they still remain vulnerable to property loans that will be difficult to fully recoup.

Other European banks are struggling today as well. Fitch recently cut the ratings of big-time French bank BNP Paribas, citing high exposure to investment banking and a decrease in asset quality. Barclays (NYSE: BCS) and Societe Generale also saw their shares drop yesterday amid similar concerns. However, there is a silver lining: Some early indicators point toward a healthy recovery for Spanish banks, as Banco Santander (NYSE: STD) could be one of the "healthiest banks in Europe," according to a recent Market Watch report.

The Foolish bottom line
In the choppy waters of today's market, you have to watch your portfolio carefully -- but be careful to distinguish between random volatility and a true change in fundamentals. If your stocks are jumping all over the radar screen but your investing thesis remains intact, then just sit back and hold on for the ride.

Jordan DiPietro owns no shares mentioned above. Try any of our Foolish newsletter services free for 30 days. The Motley Fool has a disclosure policy.