Pachygrapsus transversus

Mottled Shore Crab

A persistent mottled intertidal shore crab in the Marine Shore and Seagrass Meadow, strongly associated with algae, cyanobacteria-like surface growth, and hard-surface grazing.

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Identity & Origin +

Common Name: Mottled Shore Crab
Scientific Name: Pachygrapsus transversus
Realm: Saltwater
Biome: Marine Shore, Seagrass Meadow
Date First Introduced: July 14, 2024

Population Dynamics +

Current Estimated Population: 2
Population Status: Vulnerable
Date Last Observed: June 10, 2026

Section Notes

Two individuals introduced on July 14, 2024 remain documented in the Seagrass Meadow as of April 21, 2026. Their nearly two-year persistence is a strong survival signal for this system, but the population should still be treated as vulnerable because only two individuals are present and self-sustaining recruitment has not been confirmed.

Trophic Ecology +

Trophic Level: Primary Consumer
Feeding Niche / Method: Grazer / opportunistic omnivore
Dietary Inputs: Algae, cyanobacteria-associated mats, plant/algal material, detritus, and opportunistic animal material.
Known Predators: None documented in miniBIOTA.

Section Notes

In miniBIOTA, the Mottled Shore Crab is functioning primarily as a surface grazer in the Seagrass Meadow. It has been observed grazing algae from shoal grass, hard surfaces, tank walls, and the macroalgae/cyanobacteria clump at the far end of the biome. Published literature describes Pachygrapsus transversus as omnivorous, with algae as an important food source and animal material taken opportunistically.

Environmental Tolerances +

Section Notes

Marine intertidal species associated with hard-bottom habitats such as rock, rubble, pilings, seawalls, mangroves, and sheltered marine shorelines. Exact miniBIOTA tolerance ranges for temperature, pH, salinity drift, and dissolved oxygen have not been measured.

Life Cycle & Reproduction +

Reproductive Strategy: Females brood eggs under the abdomen; larvae are released into the water column after hatching.
System Reproduction Status: Egg carrying observed; viable reproduction not confirmed
Growth Rate: Slow

Section Notes

Egg carrying has been observed in miniBIOTA, but viable reproduction is not confirmed. The current recorded population is two females, so eggs are treated as infertile unless a male is introduced and later evidence confirms successful fertilization, larval survival, and juvenile settlement. Published literature describes brooded eggs and planktonic larval release in this species, with reproductive timing varying by region.

Ecological Role & Symbiosis +

Ecological Role: Long-term surface grazer and algae-pressure modifier in the Seagrass Meadow.
Microhabitat Preference: Rockwork, hard surfaces, upper water-column structures, tank walls, and algal or macroalgal growth surfaces.

Section Notes

The strongest miniBIOTA evidence shows the Mottled Shore Crab grazing through the macroalgae/cyanobacteria clump before sea urchins were added. Cyanobacteria later appeared reduced or checked, making the crab a likely contributor to that self-correction beat. This should not be treated as proof that the crab can resolve the full macroalgae problem; Graceful redweed remains a separate light-layer pressure.

Marine/Saltwater

A marine meadow where seagrasses, macroalgae, grazers, filter feeders, worms, crabs, and small invertebrates compete over light, nutrients, and detritus.

Marine/Saltwater

A sandy, limestone shoreline where beach grasses, crabs, snails, and detritivores move nutrients across the waterline.

Mottled Shore Crab

Section Notes

Section Notes

Section Notes

Section Notes

Section Notes

Biomes This Species Lives In

Seagrass Meadow

Marine Shore

Mottled Shore Crab checks cyanobacteria growth in the Seagrass Meadow

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Mottled Shore Crab Cleans the Seagrass Meadow

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Female Shore Crab Carries Eggs

Best algae eating crab I've seen #saltwateraquarium #aquarium #crabs #ecosystem #ecology

Related Subjects

Mottled Shore Crab

Biomes This Species Lives In

Mottled Shore Crab checks cyanobacteria growth in the Seagrass Meadow

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