Doldrums Heap

Though most sargassum heaps divide once they grow too large, occasionally a heap will continue to grow indefinitely. These "doldrum heaps" can tangle and immobilize ships, tearing them apart or feasting on the hapless passengers.

A sargassum heap is a mass of semi-intelligent seaweed that floats through the ocean, luring in its victims with hallucinogenic spores. Those affected by the spores are drawn towards the heap, envisioning their heart's desire. This might be a lost loved one, a child in need of help, an enchanting mermaid, the promise of dry land, and so on. Once their prey is close enough, the sargassum heap lashes out with its seaweed tendrils and crushes it to death.