Walking the High Tide Line and Asking, "Why?"

Jan 23, 2018

Seaweed laden wrack line.
Credit Steven Pinker bit.ly/2DyRpRK

Today I want to talk a bit about the “wrack line,” that more or less continuous line of debris left on the beach by the previous high tide. The content of the wrack line can be meager and ordinary – just a few bits of seaweed – or overwhelming and dramatic, like the 40-foot carcass of a dead humpback whale that washed up at Newcomb Hollow several years ago. But if we only investigate the content of the wrack line, big or small, I think we miss the bigger question. 

We tend to ask what is this, but not why this now?

For me the deepest and most persistent mystery of the wrack line is why the sea throws up certain items – kelp, sea clams, crabs - on one tide, and completely different one – seaweed, mussels, starfish - on the next?

For instance, one day in early January, after a hard one-night blow, I found in the wrack line a specimen of a ten-armed star fish. It was purplish on top, white on the bottom, with short, curled arms. My Peterson guide told me it was a Smooth Sun Star – Solaster endeca – a cold-water echinoderm living near the southern end of its range here, normally found at depths of 120 feet or more. That single sun start changed my idea of how deeply storms stir the ocean bottom.

During another blow one day in early March, the ocean threw up several large sections of old logs and trunks, some sixteen inches thick and twenty feet long. They were stranded high up on the beach. What, I wondered, caused such massive objects to come ashore now? Had they been ripped off the shores of Maine and Nova Scotia by storm waves and carried down here? Or is it possible, given the worn and rounded look of many of them, that these old waterlogged logs and trunks had lain buried for years under the offshore bars and had been dislodged and disinterred by the giant waves for one last wrecking?

The following week the logs had been removed or reburied, and instead the beach offered up blue mussels, clumps of them attached to lobster buoys. I took some home and cooked according to one of Provincetown chef Howard Mitchum’s recipes. They were large, tasty and juicy – as Mitchum says the ones growing in the deepest water are.

Over Memorial Day weekend the beach was blanketed with bright green flags of sea lettuce, whole green gardens of it – a sandy salad indeed! Never had I found such extensive rafts of sea lettuce on the beach. What caused it to be thrown up in such quantities on this weekend of the year and none other?

A few weeks later, in mid-June, there was an even odder phenomenon on the beach: the wrack line, for a distance of several hundred feet, consisted of a thin, nearly-continuous line of small desiccated fish about two inches long. There must have been at least three or four of these tiny fish in every foot of wrack line, thousands upon thousands of them. Moreover, their tails were all truncated, as if bitten off. The fins also seemed to be missing or flattened and pasted to the body. What caused such a beaching of these anonymous victims of the sea?

And finally, one day last July, I was walking the beach with my young neighbor Becky. The wrack line was studded with hundreds of tiny starfish of various colors.

“Why are there so many?” she asked. “Is it the time of year?  Where do they come from? Will they die?”

I could only answer her last question.            

This essay first aired in January 2015.