15. What researchers such as Ransom Myers and Boris Worm have shown is just how fast things are changing.

【分析】复合句。本句中what引导主语从句，其中such as Ransom Myers and Boris Worm 表列举；is是系动词，how引辱的从句作表语。
【译文】兰森姆·迈尔斯和鲍里斯·沃尔姆等研究者给我们展示了事情正在迅速变化。

16. Their methods do not attempt to estimate the actual biomass (the amount of living biological matter) of fish species in particular parts of the ocean, but rather changes in that biomass over time.

【分析】简单句。本句主语是Their methods;谓语是do not attempt;宾语是不定式短语 to estimate the actual biomass…but rather changes。
【译文】他们的研究方法并非试图估计出某个特定海域中鱼类生物的实际单位面积数量（目前存活的生物数量），而是随着时间推移这些生物数量的变化。