As of Friday, Puerto Rico’s bonds over all had already lost more than 10 percent of their value from the start of the year, closing at their lowest point since July 2009 as it became clear that the government was unlikely to make the $58 million payment.

J. R. Rieger, who tracks a broad sample of Puerto Rico’s bonds at S.&P. Dow Jones Indices, said that he was concerned not just about the portfolio losses but also that the market for Puerto Rico bonds might now dry up completely.

“Once a bond defaults, the number of buyers who are able to buy truly distressed debt is smaller,” he said, adding, “Will there be enough buyers to sustain an orderly market in Puerto Rico’s bonds?”

If demand for Puerto Rico’s debt dwindles, the financial institutions that now hold its bonds will be unable to unwind their positions without realizing losses. The scale of the losses could vary widely, though, because Puerto Rico’s total $72 billion of bonded debt has been issued by multiple entities, using a bewildering array of terms, repayment mechanisms, governmental guarantees and other features.

Confusing the situation further, the bonds that defaulted on Monday were sold with a guarantee, in the form of an irrevocable letter of credit issued by the Government Development Bank.

The letter of credit made the bonds look safer. It said that in the event the Public Finance Corporation failed to make a payment, a trustee for the bondholders would be able to draw the money owed them from the Government Development Bank.

But as investors have prepared for the default, they learned that the bonds’ prospectus does not describe this safety feature the same way the bonds’ indenture does, leaving confusion about what it takes to activate the letter of credit, or whether the guarantee is meaningful at all.