Red Rock Crabs (Grapsus grapsus): The Sally Lightfoots of Coastal America and the Galápagos Islands

Islands can be hotspots of biodiversity. Being smaller than continents and having watery borders gives them opportunities to encourage and protect fauna and flora that also exist -- precariously or not -- on mainlands and peninsulas or which express island-only biogeographies. Animals and plants sometimes have exclusively insular distributional ranges because of biological and geological events. For example, lemurs (Lemuroidea superfamily) hold endemic status because of rafting about 20,000,000 – 60,000,000 years ago, before the channel’s switched current flow from Mozambique-wards to Africa-wards. But that is not the case with red rock crabs. Wildlife-lovers link them most famously with the distant, unique Galápagos Islands. But red-colored, rock-dwelling Sally Lightfoot crabs in reality qualify also as coastal American wildlife.

Coastal configurations of food and shelter accommodate the Western Hemisphere lifestyles of red-colored, rock-loving Sally Lightfoot crabs along the Atlantic coasts of Brazil and Florida. They account for the day-active, non-territorial crustacean’s presence along the Pacific coasts of:

• Baja California and Mexico in North America;
• Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua, and Panama in Meso-America.
• Colombia, Ecuador, and Peru in South America.

They also attract the agile, crevice-resting rock-climbers to islands off the above-mentioned coasts. The most famous insular associations can be found along some of the 18 main Equator-straddling Islas Galápagos (“Galápagos Islands”), which Ecuadorians call Archipiélago de Colón (“Columbus’s Archipelago”), in honor of Genoa-born Italian explorer Cristoforo Colombo (August 26?, 1451 – May 20, 1506).

But historical records do not indicate Christopher Columbus’s arrival anywhere near the eastern Pacific Ocean islands. The earliest documented European presence goes back to March 10, 1535. It is preserved as the serendipitous drifting of the becalmed vessel of Soria-born Spanish Bishop Fray Tomás de Berlanga (1487 – August 8, 1551) en route from Panama to end the dispute between Peru-stationed lieutenants and Trujillo-born Spanish explorer Francisco Pizarro González (March 16, 1478 - June 26, 1541). It is succeeded centuries later by the equally impact-laden visits of:

• Shropshire-born English evolutionary theorist Charles Robert Darwin (February 12, 1809 – April 19, 1882) in September and October 1835;
• Larvik-born Norwegian ethnographer Thor Heyerdahl (October 6, 1914 – April 18, 2002) in 1955.

The Darwin and Heyerdahl expeditions are impressive in their environmental observations and scientific impacts. But they blaze no pathways uniquely elucidating Sally Lightfoot crabs. That honor goes to the earlier and later works of two gentlemen whose contributions arise from interactions with the nimble, striking crustacean outside the Galápagos. The previous insights link with the crab’s formal presentation in 1758 to wildlife-loving amateurs and professionals outside Latin America by Småland-born Swedish botanist, ecologist, physician, and zoologist Carl Linnaeus (May 23, 1707 – January 10, 1778). The subsequent insights proceed from the crab-inspired, whimsical descriptions by California-born American author John Ernst Steinbeck, Jr. (February 27, 1902 – December 20, 1968) in The Log from the Sea of Cortez of 1951.

Continental, insular, and peninsular America’s windy coasts -- with rocks above or at sea-spray levels -- uniformly attract beach-cleaning, internal body fluid-monitoring (osmo-regulating) Sally Lightfoots. Their low tides augur:

• Barnacles;
• Broken eggs;
• Carrion (bats, birds, fishes, seals);
• Corals, crabs;
• Green and red algae;
• Green turtle (Chelonia mydas) and masked booby (Sula dactylatra) hatchlings;
• Mollusks, mussels;
• Sponges.

They also host:

• Crashing waves;
• Predatory brown boobies (Sula leucogaster), chain (Echidna catenata) and peppered (Gymnothorax pictus) moray eels, Galápagos lava herons (Butorides sundevalli), Kemp’s ridley sea turtles (Lepidochelys kempii), isopods (Bopyridae family), octopuses (Octopoda), wahoos (Acanthocybium solandri), and yellowfin tuna (Thunnus albacares).

But they likewise inspire predator-busting symbioses when sharp-clawed Sally Lightfoots remove ticks (Amblyomma darwini) from marine iguanas (Amblyrhynchus cristatus).

Precarious lifestyles do not impede year-round breeding south of the Tropic of Cancer’s 23°North latitude. Matings follow:

• Egg-laying every 24 days;
• Sperm-regenerating every 10 – 20 days.

Clutches of 20 – 100 eggs hatch from maternal underbodies into calm shallows. Larvae 0.2 inches (0.5 millimeters) long hike to shore after:

• Consuming phytoplankton;
• Molting into black-/green-bodied, red-limbed juveniles.

Growth is lifelong, with carapaces signaling:

• Female and male sexual maturities respectively at 1.33 (33.8) and 2.02 inches (51.4 millimeters);
• Physical maturity at 1.97+ – 4.96+ inches (50+ – 80+ millimeters).

Adults juxtapose:

• 8 black-/green-jointed, orange-/yellow-tipped, spine-covered, tiptoe-friendly legs;
• 4 antennae;
• 2 red-clawed, segmented frontals.

Pale-underbellied carapaces mix:

• Black and green dots near 2 compound eyes;
• Black edges;
• Brown, orange, pink, red, yellow spots.  

Conservationists do not worry about red-pincered, rock-scrambling Sally Lightfoots outside the ecologically fragile Galápagos Islands. They find pro-sustainability action plans in such hallmark behaviors as:

• Escape-routing through rocky crevices;
• Information-gathering through auditory (vibration-sensing), chemical (pheromones), tactile (antennae, spines), and visual means;
• Self-defending through claw-snapping, limb-throwing, and water-spitting volleys.

The bad-tasting, domestication-amenable scavenger’s savvy survivalism ultimately inheres in 3 feats recorded by Chicago-born American marine biologist Edward Flanders Robb Ricketts (May 14, 1897 – May 11, 1948) and his (subsequent) Nobel and Pulitzer Prize-winning friend, John Steinbeck, alongside the Gulf of California (Sea of Cortez), March 11, 1940 – April 20, 1940:

• Mind-reading antagonists;
• Outrunning adversaries;
• Regenerating limbs.

But environmental education, scientific research, and wildlife-loving support always will be welcome.

NASA satellite photo Image:Galapagos-satellite-2002.jpg + labeling by Storpilot: U.S. National Oceanic and Atmospheric Administration (NOAA), Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Galapagos-satellite-esislandnames.jpg; Public Domain, via NASA Visible Earth @ https://visibleearth.nasa.gov/images/57939/galapagos-islands

Española Island, also known as Hood Island: Galápagos Islands, Ecuador: David Berkowitz, CC BY 2.0, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Grapsus_grapsus-Galapagos-2.jpg

Reales Alcázares de Sevilla, Sevilla, España: Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Fernandez-Virgin_of_the_Navigators_(proper_inversion).jpg

Palacio de los Duques de Frías, Berlanga de Duero, Soria Province, Castile and León, northwestern Spain: Amio Cajander, CC BY 2.0, via Flickr @ https://www.flickr.com/photos/10209472@N03/1334748781/

Safari Voyager in the Sea of Cortés: Un-Cruise Adventures, CC BY SA 3.0, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Safari_Voyager_in_the_Sea_of_Cortés.jpg

Española Island (also known as Hood Island), southeastern Galápagos Archipelago: D. Gordon E. Robertson (Dger), CC BY SA 3.0, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Marine_Iguana_(A._c._venustissimus),_male,_Espanola_Island,.jpg

Santa Cruz Island (Isla Santa Cruz), Galápagos: Joseph C Boone, CC BY SA 3.0, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Sally_Lightfoot_Crab.jpg

Galápagos Islands, eastern Pacific Ocean: blinking idiot (blinkingidiot), CC BY-ND 2.0, via Flickr @ https://www.flickr.com/photos/45325473@N04/4572460606/

Galápagos Islands, eastern Pacific Ocean: Dan Lundberg, CC BY SA 2.0, via Flickr @ https://www.flickr.com/photos/9508280@N07/5735181020/

photo by Lieutenant Elizabeth Crapo, NOAA Corps: National Oceanic and Atmospheric Administration (NOAA), Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/w/index.php?title=File:Grapsus_grapsus_Galapagos_Islands.jpg

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