Blog Post
by David W. McGuire / Shark Stewards

Sharks and Seastars: Sometimes What You Don't See is Equally Important.

August 03, 2016

“It is a fabulous place: when the tide is in, a wave-churned basin, creamy with foam, whipped by the combers that roll in from the whistling buoy on the reef. But when the tide goes out, the little water world becomes quiet and lovely. The sea is very clear and the bottom becomes fantastic with hurrying, fighting, feeding, breeding animals.” — John Steinbeck

This summer as part of the MPA Collaborative Network I lead a Bio Blitz/Snapshot of the Coast for the California Academy of Sciences at Baker Beach at the western edge of the San Francisco Bay.  These "snapshots" also occurred in Marine Protected Areas along the California coastline to gather baseline observations with citizen scientists. A secluded beach with rocky outcrops, Baker beach is part of the Golden Gate National Recreation Area and has the dubious distinction of being the location of the only recorded fatality of a white shark attack on a human in the immediate Bay Area in 1959. But that is another story.

On a foggy Tuesday five volunteers from Cisco joined me for a coordinated Bioblitz along the California coast and a beach clean up. We didn't see any sharks but we did see a harbor seal (phoca vitulina) cavorting beyond the surf. We searched but did not see the humpback whales, bottle nosed dolphins and harbor porpoise I have been observing along this shoreline recently. Aside from a western gull (Larus occidentalis) the tell-tale Vs in the sand- seen yet unseen- at the margin of the receding waves indicated the presence of the burrowing mole carb (emerita analoga). 

One of the more familiar invertebrates along our coastline was conspicuously missing. Absent from the rocky intertidal is any sign of sea stars. Our population in and outside the San Francisco Bay has yet to recover from the epidemic sea star wasting disease caused by a densovirus that caused mass mortality among several species of sea stars along the west coast of North America.  Like the white sharks beyond the tideline, sea stars are a major predator and a keystone species that shape the structure of the communities they live in. In the absence of the ochre star (pisaster ochreaceous) the rocky outcrops exposed by the low tide are covered with the shotgun spray pattern of barnacles, mostly balunus glandula, and beds of blue mussel mytilus edulis and the stalked gooseneck barnacles, whose genus species-policipes polymerus - evokes the exploits of Odysseus. We also observed a brown kelp in the genus Laminaria covering the exposed outcrops and several species of limpets in the genus Lottia whose range is unrestricted by the absence of the predatory ochre star.  

One of my favorite intertidal organisms is the striped shore crab, pachygrapsus crassispes, a small but lovely shore crab that agilely patters along the rocks foraging on kelp and invertebrates and jams itself into rocks and interstices in the crashing surf. Their coloration is remarkably cryptic and when unmoving blend splendidly into the background. (Can you find the crab in the picture?)

These are close cousins to a southern species grapsus grapsus, whom Steinbeck termed the Sally Lightfoot.  He describes the crabs in a humorous anecdote in the novel Cannery Row, when one of the street characters Tiny is hired to assist Doc (the hero who is patterned after the real Cannery Row naturalist Ed Ricketts) collecting tidepool plants and animals to describe and for science.  

"Man reacts peculiarly but consistently in his relationship with Sally Lightfoot. His tendency eventually is to scream curses, to hurl himself at them, and to come up foaming with rage and bruised all over his chest. Thus, Tiny, leaping forward, slipped and fell and hurt his arm. He never forgot nor forgave his enemy. From then on he attacked Lightfoots by every foul means he could contrive and a training in Monterey street fighting has equipped him well for this kind of battle). He hurled rocks at them; he smashed at them with boards; and he even considered poisoning them. Eventually we did catch a few Sallys, but we think they were the halt and the blind, the simpletons of their species. With reasonably well-balanced and non-neurotic Lightfoots we stood no chance."

My attitude towards the shore crabs is much less sanguinary, and I always enjoy watching the lightening quick crabs dart among the rocks of the intertidal. Although originally described by the 18th century naturalist Linnaeus, the Grapsid crab's range and natural history were elucidated by Ricketts and Hedgepeth in the intertidal bible, Between Pacific Tides published two centuries later. 

During our field experience, we entered the striped shore crab and other species observed into a comprehensive citizen science online data base hosted by the California Academy of Sciences called iNaturalist.

Observations including images and geo-reference data can be added using the smartphone App in the field or by computer.  The species can be verified by research grade experts, and the observations can be used for comparison in the future. It is also a fun way to learn new plants and animals, while contributing to our knowledge of range and presence, or absence of species.

Although absent of other people we saw many signs of humans on the beach, including the ever ubiquitous cigarette butts. Over half the items we pick up in routine beach clean ups are cigarette butts, and we have quantified over 12,000 butts on the beach in our regular surveys at Aquatic Park. Few people are aware that filters are a non-biodegradable plastic and leach toxins into our waterways and Bay. At an estimated 3 billion butts hitting Bay Area streets each year, this little regarded marine debris is a serious problem poisoning marine wildlife and sea birds, and we are working with a Bay Area coalition to educate and mitigate this toxic trash.

Most of my attention in the past decades have been focused on sharks and their communities, and I have neglected the intertidal. Examining the diverse invertebrates of our coastal intertidal reminded me of exploring tide pools in my youth, and later learning from the esteemed ecologist Joseph H Connell at U.C. Santa Barbara who elegantly described competition and interaction between species in marine communities. I hope my Techie Cisco friends left as amazed as I at this panoply of strange and wonderful life forms living on the rocks at the tide’s edge, hiding in plain sight.

Join me and volunteers walking the beach and recording observations of wildlife, including sharks in the San Francisco Bay.  Learn more at Shark Stewards.

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