You rarely need to understand every single word in an academic passage to answer the questions correctly — passages are written for a general academic audience, and unfamiliar terms are usually either explained in context or not essential to the specific questions being asked.
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When you hit an unfamiliar word, keep reading rather than stopping to puzzle it out — the surrounding sentences often clarify enough of the meaning for your purposes, and stopping costs more time than it usually saves. Passages frequently define specialized terms directly ("coral bleaching, a stress response in which...") specifically so unfamiliar terminology doesn't become a barrier.
Before spending time decoding an unfamiliar word, check whether the current question even depends on it — many unfamiliar words are incidental detail rather than central to what's being asked. If a question doesn't reference that specific part of the passage, an unclear word there often doesn't matter for your task.
If an unfamiliar word appears in a sentence directly tied to your current question — especially for a detail or inference question referencing that specific part of the passage — it's worth a moment of careful re-reading, since accurately understanding that specific sentence matters more there than in incidental parts of the passage.
See the specific word list that shows up most often across TOEFL Reading.