Abstract—Crabminer is a city builder played on the sea floor. The player runs a crew of robot crabs that turns buried metal into money. Scouts flag deposits, drills dig them up (and sometimes come up dry), and haulers, crushers, and smelters carry the ore through a pile, a press, and a lava cave until it is refined metal on a stockpile. A riser sells that metal at the surface. Things break. Drill bits snap, energy bots wear out, and any crab can lose a leg. Repair bots and maintenance bots forge replacement parts in the lava from the line's own ingots and bars. Crabs that work without rest tire and break down more, so the player chooses between all hands, A and B shifts, and three-shift relief, and must keep every job covered in every part of the day. Steady deliveries earn a flow bonus and bank overclock, a burst of speed the player can spend. Research unlocks sixteen worker upgrades. The line's buildings stand on movable plots, and energy bots refuel at a post on an extension cord that they drag to where the work is. A thermal vent lifts crabs up the lava column, and they swim down and sideways to their work. The sea joins in: tides wash nodules up and bury flags, storms stir the dunes, the lava surges, an octopus raids the ore pile, a moray eel makes haulers drop their load, rich deposits hide pearls, cargo ships post orders, and whales pass overhead. The crabs talk in emoji sentences, pull more than a hundred animations, walk claw in claw to help one another, and dance with idle neighbours, which recharges them, lifts the crabs around them, and earns a fresh start the next morning. Around the line a closed food web of small fry, hunters, sharks, gulls and a fisherman replenishes itself, and the page keeps a lab report of it. This paper sets out the rules and reviews the economy using the deterministic simulation the page itself runs.

Index Terms—Bottleneck, city builder, game economy, maintenance, serious games, shift work, stigmergy, swarm robotics.

I. The Game

The game opens on three layers of dunes, cut from paper and stacked one behind another. The front dune holds the processing line: an ore pile, a crushing yard, a bar stack, a stockpile of refined metal, and the collector at the foot of the riser. A basalt outcrop on the right holds a pool of lava. Beside it stand a Stirling engine and the energy bots' base station, and above it a thermal vent sends warm water and bubbles up to near the surface. The middle and back dunes start out roped off. They hold richer deposits, and the player can buy the claims to them.

The player starts with nine crabs, room in the den for ten, and 120 credits. The aim is to earn money by selling metal upward. Lifetime earnings set the player's rank, and each new rank pays a bonus of a tenth of its threshold. The ranks are Pebble Boss at 150 credits, Nodule Baron at 400, Ingot Magnate at 1,000, Lava Lord at 2,500, and Crab Tycoon at 6,000. Reaching Crab Tycoon wins the game, and the time taken is the player's score. Play can continue afterwards. The game saves itself in the browser every ten seconds and whenever the page is hidden or closed, so a reload carries on where it stopped; New game in the introduction starts over.

The Crew tab hires and retires crabs and sets the shift pattern. Each further crab of a role costs 15% of the base price more than the one before, and a retired crab refunds half of what it cost. Any kind can also be hired as an apprentice for half that price: it works and walks at half pace, wears a paper cap, and graduates into a full crab after a day on the job, keeping its name, its record and any stars it earned meanwhile. The Ledger's capacity estimate counts an apprentice as half a crab. It is the early game's cheap hire, and the five-graduation achievement is called Teacher. The Build tab buys upgrades. The top bar shows the day and shift, the flow bonus, and the overclock button, and it sets how many ingots to hold back from sale. The Ledger tab holds the analysis, and its crew table draws a little portrait of each crab, wearing the mood of the moment. An advisor names the slowest stage, or the job nobody covers on some shift, in plain words.

The tutorial and the sound. Every new game opens a six-step tutorial in a card over the field: hire a second smelter, follow the advisor, overclock when the bank fills, try A and B shifts, claim the middle dune, and a closing note. Each step moves on by itself when it is done, Skip closes it, and a saved game that never finished it picks it up again. The sound is off by default behind a button in the top bar (N) and is synthesised on the spot: clicks on the buttons, a coin for every sale, a chime for pearls, chests and achievements, a crack for a snapped bit or a lost leg, a fanfare and a bouncy riff for rank-ups, festivals and filled contracts, bubbles and a splash for a vent ride, a rumble for an earthquake, wind for a storm, and a long sliding note for the whale.

Named crabs and veterans. Every crab has a name and a record of its jobs, backup trips, pearls, sunken chests, vent rides, dances, and lost legs, shown when it is clicked and in a crew table in the Ledger. A crab that does enough of its own job earns a star, up to three, at roughly 6, 18, and 36 minutes of steady work. Each star makes it 5% faster at its own job, working and walking, but not at the backup job. Retiring always takes the newest crab of a kind, so a stable crew keeps its veterans.

Big field. The game opens straight into play, on the big field. The front dune fills the lower half of the screen, and the world is wider than the window, so it scrolls sideways. The panel floats on the field as a sheet of paper with five tabs: Crew, Build, Tech, Ledger, and View. View tucks the rest away and leaves a slider for scrolling the field. The Big field button (or the B key) switches to a side panel instead, and the ? button brings up the introduction.

Drill bits. Every hole carries a 4.5% chance of breaking the bit. A drill with a broken bit keeps working, badly. Its holes take 60% longer, it strikes 40% less often, and while it drills it draws three times its usual power. Hardened bits cut the chance to 2.5%, then 1.2%.

Energy bots. Every charge an energy bot hands over carries a 3% chance of wearing it out. A worn bot moves at under half speed and takes twice as long over each charge.

Legs. Any crab can lose a leg while it works, energy bots and the repair crews included. The base rate is about one leg per crab per hour of work, and wear raises it (Section IV). A crab with a leg missing limps at 55% of its walking speed, and the leg lies on the sand where it fell until a maintenance bot fits a new one.

The forge. Every part is made in the lava. A repair bot takes an ingot off the stockpile, and a maintenance bot takes a bar off the bar stack. Each carries its metal to the lava's edge and holds it in the heat for 1.4 seconds until it becomes a bit or a leg, then takes the part to the crab. Repairs therefore cost product twice over: the ingot is never sold, and the bar is never smelted. A stockpile reserve keeps ingots back for repairs. Bars have no reserve, so maintenance competes with the smelters for them.

Wear. Each crab counts the seconds it has worked without a break. The first four minutes cost nothing. After that, every five more minutes add up to double the breakdown chances (bits, cells, and legs) and slow the crab by up to a fifth. Standing idle wears off a second each second. Sleeping wears off four, and it recharges the battery for free at about 3% a second.

The clock. A day lasts three simulated minutes, and it is 24 hours of crab time, so an hour passes every 7.5 seconds. The game starts at dawn, 06:00. Night runs from 20:00 to 06:00. A crab can work at night, but at half speed unless it slept or danced within the last four hours, or stands in a patch of glowing plankton (see Plankton light). Scouts are the exception: they like the dark and work nights at full speed.

The workday. The player picks a pattern in the Crew tab, and a 24-hour timeline shows who is on duty when. All hands: everyone works around the clock. 8-hour day: everyone works 08:00 to 16:00 and rests the rest. Two 8-hour shifts: 05:00 to 13:00, a 3-hour rest, then 16:00 to 24:00. A and B shifts: everyone works 06:00 to 18:00. At night half of each role sleeps, a different half each night, while repair and maintenance bots work on 30% faster, untroubled by the dark. That is the night repair crew, and sleeping crabs make easy patients because they hold still. Three-shift relief: 06:00 to 14:00, 14:00 to 22:00 and 22:00 to 06:00, and each crab sleeps through one of the three. Custom: the player sets the start hour, the shift length (2 to 12 hours), one or two shifts a day, the rest between them, and one to three groups whose shifts start in turn, evenly spread through the day. Under the 8-hour, two-8s and custom patterns, scouts take the night by default. Crabs finish the task in hand before they go to sleep.

Friends. Two crabs standing idle side by side, a crusher waiting for ore beside a smelter waiting for bars, for example, pair up and dance. Dancing recharges them a little (1.2% a second) and clears their wear at two seconds a second. These are the clean thoughts. At dawn, every crab that slept or danced for at least 20 seconds the day before starts fresh, 25% faster for the first 90 seconds of the new day.

Moods. Every crab carries a mood from 0 to 1 that drifts back toward the middle on its own. Dancing, rest, a dance nearby, a fresh morning, a decorated den and a festival lift it a little each second; wear past four minutes, tired work in the dark, a flat battery and a missing leg drag it; and moments move it at once, a pearl or a star up, a snapped bit or a lost leg down. A happy crab, at three quarters or more, hums and sways when idle and pairs up to dance from half again as far. A grumpy one, at a quarter or less, sulks and grumbles and works and walks 5% slower. Its card and the crew list say which. Over half an hour the starting crew on all hands spends about a third of its time happy and a fifth grumpy, a crew on A and B shifts is happy more than half the time and almost never grumpy, and a crew of thirty on all hands is grumpy two thirds of the time: the moods say in faces what the wear figures say in numbers, and the 5% is small enough that the player feels it as a mood rather than a penalty.

The den. The crabs' den is a round house on the first plot. Idle time is not wasted. Every five crab-minutes of standing about, counted across the crew, turns into a decoration for the den, made by the idle crab nearest to it. Most are everyday crafts: a shell garland, a sea-glass mosaic, a pebble cairn, a kelp wreath, a coral sculpture, a sand castle, a nodule totem. A big moment inspires something special: a trophy after a rank-up, a pearl lamp after a pearl, an octopus-ink painting after a shoo, a driftwood sculpture after a storm, a ship in a bottle after a filled order, and a lava lamp after a surge, and a filled contract hangs a brass bell, a golden anchor, a plaque or a ship's wheel. Each decoration adds a point to the morning bonus and three seconds to it, and makes dancing recharge 5% faster. The den holds four, and each den upgrade makes room for two more.

Festival day. Every tenth day is a crab festival. At its dawn every crab starts fresh whether it rested or not, the crew raves for twenty seconds, bunting goes up from the den's flagpole for the day, and the den gets a string of festival lanterns that glow at night, a decoration given outright even to a full den. All day the flow bonus is doubled: each delivery in a row adds 4% to the price instead of 2%, up to 80%. A festival falls at 27 minutes and every 30 after, so it reaches runs that go the distance: over 40 minutes the automatic player on all hands earned about a sixth more with the festivals than without, most of it from the fresh starts on a crew that never rests.

Pets. A sea slug moves in by the den at Nodule Baron and a baby octopus at Lava Lord, and the trader sells a starfish and then a sea snail for two ingots. They are pure charm. They wander by the den, the baby octopus jets along after crabs passing the door, they sleep by the porch at night, and an idle crab beside one stops to pet it and says so. A tide pool lies in a hollow on the front dune just seaward of the trader's pitch: dry sand with shells and an anemone at low water, it fills as the tide comes in, and near high water the pets wander over for a paddle while crabs wading through it splash and stop for a wallow. Nothing in the economy changes, which is the point: a den with pets is a den worth coming home to.

Lending a claw. When its own job is stuck, a crab first looks for someone to help, takes their claw, and goes where they go. Holding a drill steady makes it drill 30% faster, and handling for a crusher makes it press 30% faster. A hauler's helper takes another nodule each time the hauler bends for one. Two energy bots run hand in hand, 25% faster, and repair and maintenance bots walk together, claw in claw, and fix 25% faster. Fast crabs like to help haulers and slow crabs like to help drills, and each kind has its own order of preference. A helper goes back to its own work the moment there is some. Now and then a stuck crab just waits about instead, and that is when neighbours dance.

The backup job. No crab stands idle while there is work on the sand. When nobody needs a claw, a crab carries nodules to the ore pile instead, at its own walking pace. That means a drill crab whose bit is broken (it keeps working while it waits for the repair bot), a drill when the sand is littered, a scout when its flags are all standing, a crusher with no ore, a smelter with no bars, and an energy, repair, or maintenance bot with nothing to do. It goes back to its own job as soon as there is one, after delivering whatever it is carrying. So hauling is everyone's second trade, and a slow crusher on the backup job is a slow hauler.

Coverage. A role with one crab disappears whenever that crab sleeps, and the line stops at that stage. The ledger lays out how many crabs of each role are on duty in each part of the day. The advisor names the first gap it finds, for example "nobody covers smelter crab work in shift 3". This enforces the rule of thumb any round-the-clock plant uses: at least one worker able to do every job on every shift.

Income. The riser sends one ingot to the surface every 3 seconds while the stockpile holds more than the reserve. Riser pump upgrades shorten that to 1.8 and then 1.0 seconds. Each ingot fetches the current metal price. The price centres on 12 credits. A slow swell, a faster ripple, and a seeded random walk move it between 6.6 and 18.

Flow. A delivery that follows the last one within 6 seconds keeps the flow going, and each one in a row adds 2% to the price, up to 40% for 20 in a row. A gap resets the flow. Steady production pays more than the same metal in bursts, which rewards a balanced line over a lopsided one.

Overclock. Every delivery banks 0.6 seconds of overclock, more while the flow runs, up to 30 seconds. The player spends it with the ⚡ button (or the O key). While it runs, the whole crew moves and works 50% faster, but uses 60% more power and wears twice as fast. It is best spent while the crew is fresh and the engine has charge to spare.

Spending. Credits buy crabs and upgrades (Table II). Repairs are paid in metal. There is no upkeep, unless the player takes out insurance.

Insurance. The Build tab's Insure button takes a policy out: thirty credits at once and thirty at every dawn after, for as long as there are thirty in the bank at dawn. While it stands the insurer pays six credits for every nodule the octopus gets away with or an earthquake buries and eight for every flag the tide, a storm or a quake buries, straight into the bank and toward rank. Over twenty minutes of the starting crew on all hands, premiums and payouts came out within a few tens of credits of each other, which is the intent: the policy smooths a run rather than feeding it, and the choice is whether a bad night of octopus raids matters more than thirty credits a day. The Ledger keeps premiums against payouts.

Surface news. Seven minutes in, and every five to nine minutes after a headline passes, news reaches the sea floor from the surface and holds for a minute. A copper boom lifts the metal price by 40%, a glut cuts it by 35%, and a rumour, as often as either, moves nothing at all. The top bar shows the boom or the glut with the time left, and the advisor says the obvious: drop the reserve and overclock in a boom, raise it and wait out a glut unless a ship order matters more. The Ledger keeps the count of headlines and the credits the booms and gluts were worth, which over an hour tend to cancel out: the news is a reason to watch the price, not a source of income.

Contracts. Eight minutes in, and every nine to fourteen minutes after one ends, the surface offers a contract: so many ingots within three days, the number set at 80% of what the last five minutes' pace would send in that time, between 25 and 999. The offer stands for ninety seconds on a button over the field and a card in the Build tab, where it can be accepted or let lapse. Accepted, every ingot up the riser counts, ship orders or not, and the top bar keeps the tally. Filled, it pays five credits an ingot, raised by a tenth for each reputation star, and the crabs hang a unique decoration by the den: a brass ship's bell, then a golden anchor, a contract plaque and a ship's wheel. Run out, it costs a reputation star, like a missed order. Left to lapse, nothing happens. The sizing makes a contract a stretch for a line that stands still and an easy win for one that grows, and the advisor says which it looks like at the offer and, a minute in, whether the line is behind the rate it needs. In a forty-minute run with a growing crew, two contracts are offered, and a crew that keeps growing fills them more often than not, for a few hundred credits each.

A new dig site. Once Crab Tycoon is reached, the win card, and after it a button in the Ledger's career note, offers a new dig site: fresh dunes on a new random stream, the starting crew, the same workday, and one perk carried over. The perk is a technology already researched, chosen from a list; the den's decorations, all of them, however many; or the best crab, by stars and then by jobs, with its name, record, stars and mood, as an extra member of the starting crew. Everything else starts over, achievements included, and the earlier sites' credits, ingots and crab time go on a career record in the Ledger with the list of what came along. The site number shows in the top bar and the run summary. A new game under the ? button starts site 1 again.

Achievements. Thirty-four marks along the way, each won once and listed in the Ledger with the time it was won: the first pearl, a sunken chest, a hundred and then a thousand ingots, ten turtle rides, five crabs swept along by the manta, a full den, five stars with the ships, a night's work with no breakdown, a three-star crab, a crew of twenty, every technology, a festival, ten shoos, five orders filled, three races won against the lobsters, all four pets, a happy crew, an earthquake lived through, five apprentices graduated, a contract filled, ten rides up a hydrothermal chimney, ten minutes of night work under the lighthouse lamp, twenty deposits flagged in the kelp forest, two hundred nodules ridden on the conveyor, ten batteries' worth from the charging pad, a second dig site, a hundred credits from the insurer, three rescues by the shark, fifty fine ingots delivered, two hundred nodules on the annex pile, a swap at the night market, a wreck stripped bare, and Crab Tycoon. They pay nothing but a toast, a little confetti and a line in the run summary.

Plots and the post. Seven buildings stand on seven plots along the front dune, from 560 to 818: the crabs' den, the workshop, ore pile, crushing yard, bar stack, stockpile, and the riser's collector. By default they run right to left from the lava in the order the metal flows, with the den at the field's edge. In the Build tab's arrange mode the plots show as paper tiles, and any building can be picked up and set on another plot, swapping with whatever is there. Moving the stockpile nearer the lava, for example, shortens every smelter's walk. The tiles are hidden the rest of the time, so the sand stays sand. The refuel post stands at the end of a 520-unit extension cord from the Stirling engine's outlet. The player can put it anywhere along the front dune. Otherwise the energy bots drag it, every 25 seconds or so, toward the middle of the crew. The post also has a home, which is wherever it was last set down. The tide's current pushes it along the sand, one way on the rising tide and the other on the falling one, at up to 3 units a second near high and low water and three times that in a storm. Once it has slipped 40 units from home, an energy bot goes to drag it back: an idle bot, a bot that has just refuelled at it, or, if it has drifted three times that far, the next bot free from charging. A pinned post goes back to its home, and a free one to the middle of the crew. Bots plugged in or parked at the post follow it as it slides. In tests, a pinned post never strayed more than about 80 units and was out of place for under a seventh of the time.

The conveyor and the pad. Two more buildings stand off the plots. The ore conveyor, for 300 credits, is a belt from the field's edge at 546 to ten units short of the ore pile, wherever that stands, running behind whatever is in between. Haulers and crabs on the backup job queue at its head instead of walking to the pile, drop each nodule on it and turn straight back; the belt carries them at 60 units a second, seven apart, onto the pile, and when the pile is full they queue on the belt, up to fourteen, before the haulers have to wait. With the pile on its default plot that saves a hauler a hundred units each way, and the capacity estimate counts haulers 30% stronger. The charging pad, for 180 credits and 420 for its second level, is a disc halfway between the ore pile and the crushing yard. Every crab but an energy bot within 40 units of it charges 0.8% of its battery a second, 1.6% at the second level, whether it is working, waiting or idle, so the crushers at their presses and the haulers at the belt's head top up as they stand, and the energy bots have fewer trips to make. The second smelting rim, for 280 credits, is a pocket of lava that opens in the cavern side between the last plot and the Stirling engine, at 846. A smelter leaving the bar stack goes to whichever rim has fewer smelters at it or on the way (a tie sends it to the one it did not use last), and the repair crews forge at the pocket, which is the nearer. From the default bar stack the pocket is 34 units nearer than the rim, and the stockpile is 34 nearer again on the way back, so each smelting round trip is about 1.3 seconds shorter and no three smelters share one spot. In twenty-minute runs with three smelters and smelting the slowest stage, output rose from 13.4 to 15.0 ingots a minute; with a maxed crew of thirty, whose pace the riser sets, it changed nothing, as expected. The capacity estimate counts smelters 10% stronger with it.

The annex. Once the middle dune is claimed, 500 credits lay three plots in the middle of it, at 300, 343 and 386, among the deep deposits, with a second ore pile and a second crushing yard (the third plot is spare, and the two can be moved along the three). Scouts leave the annex's ground alone. A hauler with a full load heads for whichever pile is nearer, counting a climb over a dune's lip as 24 units of walking, so middle- and back-dune nodules go up to the annex and front-dune nodules from the right of the field go down to the line. When the annex opens, every other crusher walks up to its yard; after that crushers follow the ore: one left waiting four seconds at a pile with fewer than two nodules while the other holds six or more walks to the other yard and takes a press there, so the yards staff themselves to the flow. Bars pressed at the annex ride a cableway of buckets down to the bar stack. The gain is in hauling and only in hauling: in forty-minute runs with two haulers and six drills on two dunes, where hauling set the pace, output rose from 10.8 to 14.1 ingots a minute, and with a balanced crew it did not move. The capacity estimate counts haulers 15% stronger with it. An earlier placing at the field's edge, beside the plots, saved too little walking to measure, which is why the annex stands in the field.

Metal grades. A deposit of richness 0.85 or more yields fine nodules, marked by a gold glint and a gold star on the flag, and the grade travels with the metal. Haulers count the fine nodules in their loads and set them down first, the pile keeps them on top, and the conveyor carries the grade along. A crusher that finds two fine nodules presses a fine bar; a mixed pressing comes out plain. Smelters take fine bars first and stack fine ingots on a shelf of their own beside the stockpile, with their own reserve in the top bar, and the riser sends a fine ingot up ahead of a plain one whenever the shelf holds more than that reserve. A fine ingot fetches half as much again. The forge, the trader and the octopus all take plain metal first. On the front dune, where richness runs from 0.45 to 0.85, almost nothing is fine; the sharper scanner, the middle and back dunes, the kelp forest and the treasure map each push more deposits over the line, and a maxed crew on all three dunes sells three ingots in four as fine. The grade therefore pays for depth rather than for speed: in the balance runs the fixed crews' ingots a minute did not move, while the automatic player's earnings by minute 40 rose by a tenth to a quarter and its time to Crab Tycoon fell by one to two and a half minutes, most with research, which buys the scanner and the deep sonar early.

Getting about. The track is 1,000 units long. The field runs from 20 to 540, its first 110 units the kelp forest that scouts keep out of until it is claimed (Section VI), and the plots fill the stretch from 560 to the Stirling engine at 852, beside the lava at 888. A crab climbing over the lip from one dune to the next goes at half speed. Crossing from the back crest to the front of the dunes costs as much as 300 units of track. Each kind walks at its own pace. Slowest to fastest: crushers 45 units a second, smelters 52, drills 56, repair bots 60, maintenance bots 64, haulers 68 (88 with spring legs), scouts 78, and energy bots 95. A crab on the lava side of the line with a long trip to the left can instead step into the thermal vent. It floats up with the bubbles into the top tenth of the sea, which takes about 1.8 seconds, and then swims down and sideways at 200 units a second, landing on its target. Each crab checks the time both ways and only rides when riding is at least 10% quicker. Short trips are always walked. While a hydrothermal chimney is open behind the plots (Section VI), any crab with at least 120 units to go may ride that instead, up in 1.2 seconds and down either way, on the same 10% rule.

Tides. The sea rises and falls on a four-minute cycle, and the surface moves with it. Through the highest quarter of the cycle, every 12 seconds the current washes one or two nodules up somewhere on the claimed dunes, free for the haulers. Through the lowest quarter, every 20 seconds there is an even chance that the shifting sand buries one flag nobody is working. A tide marker in the top bar says which way it is running.

Storms. Five minutes in, and every six to nine minutes after each one ends, a storm blows through for 40 seconds, with a warning 20 seconds ahead. The water darkens, the surface heaves, rain streaks the top of the sea, lightning flashes, and the ship at the top of the riser rocks. Crabs walk at 85% speed against the current, and the riser sends ingots at half speed. Every 8 seconds the storm has a 60% chance to bury a flag nobody is working. But every 4 seconds the waves stir two or three nodules up out of the sand, so a storm is a windfall for a crew with haulers to spare.

Lava surges. Just over three minutes in, and every five to eight minutes after each one ends, the lava swells for 30 seconds and throws out burning blobs. Smelting and forging take half the time, the Stirling engine makes double charge, and the vent lifts crabs faster. The advisor suggests spending banked overclock then, because the slowest stage of many lines, the lava, is briefly twice as fast.

Ship orders. Two and a half minutes in, and every three to five minutes after each order closes, a cargo ship sails in over the riser and posts an order. It asks for a little more than the line has been making, 15% over the last minute's rate across a 100-second deadline, between 5 and 40 ingots. Each ingot sent up while the order is open pays a 30% premium. Filling the order pays a bonus of 6 credits an ingot and adds a star of reputation, up to five. Each star adds 5 points to later premiums and 10% to later bonuses. Missing the deadline costs a star. In tests over half an hour, a line left alone filled about 40% of its orders. Dropping the stockpile reserve and spending overclock while an order was open filled nearly half and earned more. Orders added about a sixth to revenue.

The rival crew. From Ingot Magnate on, a crew of lobsters behind the basalt ridge races the player for every order. For each order it sets a pace that would fill the order in 75% to 120% of the deadline, divided by its drive. Its count shows beside the player's, and its ingots rise up a red line from behind the ridge to the ship's stern. If it fills the order first, the ship sails with its metal, and the player loses a star of reputation as for a missed order. Each order the player wins raises the rival's drive by 8%, and each it wins lowers it by 6%, so a strong line meets a hungrier rival and a struggling one gets some room. Over eight seeds the automatic player lost 18 of 58 orders to the rival on all hands, 10 of 60 with A and B shifts and overclock, and 5 of 64 with research. Most of what it took were orders a slow line would have missed anyway, so time to Crab Tycoon and earnings by minute 40 moved by less than 2%. The rival adds a race to the late game rather than a tax on it.

The hermit-crab trader. Four minutes in, and every four to six minutes after each visit, a hermit crab walks in from the left with a striped market stall on its shell. It keeps shop beside the den for a minute and offers three goods out of six, paid in bars or ingots taken straight off the piles. Spare drill bits or spare legs (two for a bar) let the repair crews skip the walk to the stockpile and the forge. A treasure map (two ingots) plants three rich flags on the claimed dunes. A crate of cells (one ingot) fills the engine and every energy bot. A gold gear (three bars) gives the whole crew the morning bonus at once. A lucky shell (four bars) guarantees a pearl on the next rich strike. The trade is metal for time, and it pays best when a pile is full and the line is waiting on something else. On the eve of every festival the trader holds a night market instead: as night falls it sets out at once (or stays on, or turns back if it was leaving), strings lanterns along the stall, and keeps shop until dawn with four goods, among them one sold nowhere else, a festival cake for an ingot. The cake is a slice for every crab, lifting each mood by a fifth, and its stand goes on the den's porch for good. The market is a mood piece, not an economy: ten hours of shop instead of one, on the night the crew is waiting for the party anyway.

The sea turtle. Three minutes in, and every two and a half to four and a half minutes after that, a sea turtle swims across the dunes at 85 units a second. It comes in from the side the travelling crabs are heading away from, dips to pick up one crab with at least 160 units to go its way (a flat or limping crab first), and can turn back once for a passenger it has just passed. It sets the crab down where it was going. In half-hour tests it gave four to eight lifts.

The manta ray. Six and a half minutes in, and every four to seven minutes after it leaves, a manta ray glides straight along the deepest claimed dune at 70 units a second. It does not steer or turn. Every walking crab it passes over that is heading its way with at least 40 units to go is swept up onto its back, several at once, carried up to 140 units or to where it was going if that is nearer, and set down there. In half-hour tests with a crew of thirty it carried about three crabs a sweep, and with the starting crew about one. Like the turtle it costs nothing and moves the figures in Tables I to III within seed noise.

Earthquakes. Nine minutes in, and every ten to fifteen minutes after, one claimed dune shakes for six seconds. The whole sea judders, walking drops to 60% speed, the crabs reel, and sand flies up along the band that is about to go. Then a 120-unit stretch of that dune slides: every free nodule and every flag nobody is working in it is buried, and the slide bares three flags of richness 0.8 to 0.95 somewhere else on the claim. Flags being drilled and nodules already in a hauler's claws are safe. In half-hour runs a quake buries half a dozen nodules and a flag or two, and the fresh patch is worth more than what was lost, so a quake is a nudge to send the scouts and drills somewhere new.

The kelp forest. The field's left end, 20 to 130 along the track on every dune, is a stand of tall kelp, roped off until claimed for 350 credits, so the open field is 400 units wide until then. Claimed, it is the richest ground on each dune: a deposit flagged in it is richer by a tenth and a nodule bigger, which on the back dune puts most flags into pearl territory. The price is the walk: every step through the fronds is at 70% speed, and the fronds part and sway round each crab that pushes through. Idle crabs weave kelp into new pieces for the den: a kelp-rope garland, a hammock, a lantern. Twenty deposits flagged there is the Forester achievement.

The hydrothermal chimney. Five minutes in, and every six to ten minutes after the last one goes cold, a chimney opens on one of three spots behind the plots and stands for two days, growing over its first seconds and fading over its last twenty. It is a second, smaller vent: a crab near it with a long way to go rides its column up and swims down to its target, to the left or the right, and in a forty-minute run the chimneys together give as many rides as the main vent, or more. The Stirling engine draws half again as much charge a minute while one is open. The achievement for ten rides is called Hot shortcut.

Whales. Every two to four minutes a whale glides through the open water, singing. Its shadow sweeps across the dunes, and the crabs beneath it look up and wave. The whale has no effect on the economy.

The food web. The open water and the seabed hold a closed ecosystem, decoration like the whale but alive: a bottom-heavy pyramid of species that hunt one another and are replaced as they are eaten. At the bottom are shoals of minnows, shrimp that keep to the rocks, drifting jellyfish, and tiny crawlers on the sand a tenth the size of a crab. Above them hunt seahorses, a school of piranha, squid, eels, sea snakes that surface to breathe, frogs kicking under the surface, small turtles that eat the jellyfish, and lobsters on the seabed. At the top cruise one or two sharks. Every predator picks the nearest prey it eats within sight and turns toward it slowly, prey flee when one comes close, and a meal leaves the hunter full for a while. Every species has a target count. Whatever is eaten is born again a few seconds later at that species' nursery, minnows among the weeds, shrimp under the rocks, jellies near the surface, so the pyramid keeps its shape. Gulls fly above the water, dive at minnows near the surface, and land on the ships to rest. Nothing in the web chases a crab.

The web's bites. The web runs on its own random numbers in the view and never reads the game, but it bites it in exactly two places, each through the game's own levers as a click would be, so the headless simulation never sees them and stays reproducible. When the shark passes close to the octopus swimming in, the octopus flees as if shooed and drops what it took, at most once every ninety seconds a shark; three such rescues are the Nature's way achievement. And a crab carrying nodules along the top of the back dune, where the sky is close, is within a gull's reach: every so often a gull dives through the water to it, follows it for a few seconds, and flies off with one nodule in its beak. The loss is one nodule, the lab report logs it, and the Ledger counts both bites.

The fisherman. A rowboat sits on the surface. Its fisherman nets a drifting jellyfish for bait, casts, and waits. Fish that eat jellyfish, and the curious kinds, come for the bait, and whichever reaches it eats it: the bait feeds the web, and the fish swims off full. Only some bites end on the hook. Minnows never do; a piranha is landed one time in two, a turtle or a squid about one time in three, a shark one time in seven. A landed fish is reeled up into the boat and, like any animal eaten, is replaced by a birth. The Ledger's lab report keeps the count of each species, who ate whom, the fisherman's casts, bites, catches and escapes, and the latest observations in plain sentences.

Plankton light, and the lamp. The lighthouse lamp, an upgrade in the Build tab, is a striped tower at the field's edge that lights the sand within 120 units at night, 220 at its second level: a tired crab in its light keeps full speed, as it does in the plankton light below, and its glow shows warm rather than blue-green. It covers the den, the near field and the first plots, where haulers, crushers and the repair crew spend the night. Three patches of glowing plankton lie on the sand, one on each dune. They creep to the right and the tide sweeps them to and fro, so over a few days each one passes the field, the plots and the lava cave. At night a tired crab inside a patch sees its way and works at full speed, and its lamp turns blue-green. A patch is 30 units across when the sea is quiet. Storms, and every ship that comes or goes, feed a bloom that doubles that, and it ebbs back over a few minutes. Over ten seeds the patches move the figures in Tables I to III by a few percent either way, about as much as changing the seed. They are a nudge toward working nights, not a reason to.

The octopus. About a minute and a half in, and every two to three minutes after that, an octopus creeps in from the left. It makes for the ore pile, or, if the pile is empty, for the nodule on the sand nearest the line. It says 🐙🪨❓ as it comes. If a crab is standing within 28 units of its target when it gets there, it flees in a cloud of ink. Otherwise it spends a second and a half grabbing up to two nodules and escapes the way it came. The player can click it, or press Shoo the octopus, at any time to shoo it off. If it is already carrying loot, it drops the loot on the sand. Unguarded, it takes about 15 nodules in half an hour, roughly seven ingots. That is less a drain than a reason to watch the field.

The moray eel. A moray eel lives in a crack between two stones on the front dune, right in the haulers' way from the field to the ore pile. Five and a half minutes in, and every three to five minutes after it goes back in, it comes out for a minute. It snaps at any crab that carries nodules within 34 units of the crack, at most once every four seconds, and the crab drops its whole load on the sand. While the eel is out the haulers leave the nodules within its reach alone, and they fetch them once it has gone. Nothing is lost but time: in twenty minutes the starting crew drops 13 to 33 nodules this way, out of about 175 stacked. Clicking it, or pressing Shoo the eel, sends it back into its crack early.

Pearls. A strike on a flag of richness 0.75 or more turns up a pearl one time in 25. A pearl is a jackpot paid in credits straight away: 60 on the front dune, 90 on the middle, and 130 on the back. It counts toward rank, and the pearl floats up the riser to fanfare. Over half an hour with all three dunes claimed, a mid-sized crew found four or five pearls worth 390 to 540 credits. That is a fair reward for scouting deep and drilling rich.

Sunken chests. One deposit in about seventeen flagged on the back dune turns out to be a sunken chest. It sits half buried with a glint under its lid, and drill crabs go for it before any flag. The first hole into it breaks it open, whatever the state of the bit: 150 to 250 credits straight away, which count toward rank, and one of the trader's goods at random, free. Over half an hour with all three dunes claimed, a crew with two scouts and two extra drills opened between none and four, about two on average. Like pearls, chests reward claiming the back dune.

The wreck. Once the back dune is claimed, a sunken boat settles on it seven minutes in and every nine to fourteen minutes after the last one sinks away, with six to ten metal plates riveted along its hull. Salvage is the scouts' job and comes before scouting: up to two at a time walk to it, prise a plate off in five seconds of work, and carry it to the bar stack, where it counts as a plain bar, then go back for more. Each plate is a job on the scout's record. Stripped bare, the hull sinks into the sand over a minute. A wreck is worth eight bars or so, two or three minutes of a crusher's work, delivered by the kind of crab that is most often resting; it is a small, occasional gift rather than a stage of the line, and the automatic player's output moves by less than the noise between seeds.

The Tech tab holds five technologies. Each one unlocks the worker upgrades for one or two roles (Table IV). A worker upgrade is bought once and fits every crab of its kind, present and future. The cheapest path is the Sonar lab at 150 credits, and four of its six scout upgrades are about the night and cost 80 to 120. The full set of five technologies and twenty upgrades costs 4,450.

A night of scouting. With the night upgrades, a single scout working nights leaves the drills a field of flags each morning. With an 18-crab crew on two 8-hour shifts, the flags standing at dawn rose from about 7 to about 14, and output rose from 6.2 to 9.0 ingots a minute. Without the flag bundle, night scouts stop at eight flags and the drills run dry by midday. On an 8-hour day, putting the scouts on the day shift then does better (6.6 against 4.4). The advisor says so when it happens.

Crab talk. Crabs speak in short emoji sentences with a fixed grammar: a thing, then a verb, then sometimes who or a feeling. The things are 🔋 charge, 🦵 leg, ⛏️ drill bit, 🪨 nodule, 🧱 bar, 🪙 ingot, 🚩 flag, 🔥 forge, 🌋 vent, 🌊 tide, 🐙 octopus, 🦪 pearl, and 🦀 for you or me. The verbs are ❓ I need, 👍 on my way, ➡️ bringing it, ✅ got it or done, 💔 broke, ⛔ full, ❗ found one, and ❤️ thanks. A crab with a flat battery says 🔋❓. The energy bot that picks it answers 🔋➡️🦀, and the crab says 🔋✅❤️ when it is charged. A crab that loses a leg says 🦵💔😭. The maintenance bot answers 🦵👍, says 🧱➡️🔥 on its way to the forge, and arrives with 🦵➡️🦀. Crabs that are stuck say why: 🪨⛔ at a full ore pile, 🧱❓ at an empty bar stack, 🔥❓ at a post the engine cannot feed. On a device without colour emoji the crabs spell the words instead.

Telling the kinds apart. Each kind has its colour and its gear: the scout's dish, the drill's bit, the hauler's hopper, the crusher's press plates, the smelter's hood, the energy bot's cell rack, the repair bot's hard hat and wrench, the maintenance bot's welder's cap. Each also wears a mark on its shell, in its own dark tone, so no two kinds are told apart by colour alone: scout ▲, drill ◆, hauler two bars, crusher ■, smelter ● with a hot centre, energy bot a bolt, repair bot +, maintenance bot ○. The same mark sits in the coloured dot beside each kind in the Crew tab, the crew list and the Tech tab, and the View tab can swap the shapes for letters or turn them off. A check of the eight colours through simulated protanopia, deuteranopia and tritanopia (kept with the tests) found the hauler's orange-red and the maintenance bot's brown almost the same under the first two, a colour difference of about 6 in CIELAB where 20 is the least that reads at a glance at crab size, and the crusher's blue-grey and the repair bot's grey close under all three; the marks are the answer to that.

The repertoire. Crabs have 119 animations, each a pose of eyes, mouth, claws, legs, a tilt of the whole body, and sometimes a prop. There are 14 celebrations (fist pump, clap, spin, jazz hands, cheer, shimmy, moonwalk, head-bang, the robot, floss, disco, eye twirl, happy hop, and the crab rave) and 7 acrobatics (twirl, backflip, front flip, cartwheel, hop and twirl, breakdance). There are 11 side-steps and shuffles (side-step, grapevine, cha-cha, slide, bounce, twist, Charleston, running man, shuffle kick, can-can) and 16 dances on the spot (wiggle, body roll, limbo, hula, boogie, dab, sprinkler, arm wave, big wave, double wave, pointing up, air guitar, claw clicks, arm circles, windmill, swim arms). There are 21 moves for two crabs (wave, high-five, sway, hug, salsa, do-si-do, cheek to cheek, conga, bow, swing, mirror, seesaw, patty-cake, tango, bump, two-step, line dance, a paired spin, waltz, high ten, and one crab twirling while the other claps), 5 for lending a claw (walking claw in claw, cheering a friend on, the helped crab's dance and walk, and thanks), and 6 for being caught up in a dance nearby (bop, nodding along, tapping along, snapping, claw clicks, wiggle). There are 21 idle routines (foot tap, looking around, yawn and stretch, eye-roll, folded arms, sigh, whistling, juggling a pebble, side stretch, sitting down, peekaboo, blowing bubbles, a sneeze, scratching the head, stretching up, shaking off, daydreaming, push-ups, balancing, drumming, looking up). And there are 22 moods (determined, struggling, flexing, thinking, stomping, slumping, shivering, dizzy, relief, ouch, shock, shrug, salute, a sleepy nod, sparkle eyes, grumbling, nervous, smug, curious, sulking, facepalm, cheering up). About 70 triggers choose among them. These include every event in the economy, from a strike or a dry hole to a fix, a charge, a sale, a flow streak, a rise in price, research, a new hire, a crab leaving, and a building moved. They also include states such as a flat battery, a heavy load, a limp, overclock, and wear, and the length of a wait: the longer a crab waits, the sillier it gets. On a rank-up the whole crew does the crab rave for five seconds under confetti. Everyone waves their claws one way while side-stepping the other, back and forth. A crab lending a claw walks claw in claw with the friend it helps, the two high-five when they meet, the helped crab does a little dance, and they part with a patty-cake, a high ten or a bow. Two idle neighbours dance one of the 21 moves for two, and everyone within 60 units of them bops, nods or snaps along, at work or not, and sheds a little wear as they do.

The review was run in Node.js on the same simulation script the page runs. It steps in fixed sixtieths of a second with its own seeded random numbers, so a given crew, shift pattern, and seed always give the same result. Figures are ingots sold per minute, averaged over two to four seeds. The balance runs are kept with the game's source, beside a fuzzer and browser checks.

Workday patterns compared. Table III compares the patterns over twenty minutes, averaged over three seeds. A and B shifts lead at every crew size. They work the whole day but rest everyone through part of every night, so few crabs work the dark tired. All hands comes second or third. Its crabs never sleep, so through the ten night hours most of them work at half speed, and wear piles up. The 8-hour day and two 8-hour shifts trade output for rest: they are gentle patterns, best with night scouts and, for two 8s, a crew big enough to cover both shifts. Over a short session all hands still leads. The starting crew sells 3.8 ingots a minute on all hands over five minutes against 3.5 on A and B. By ten minutes A and B is ahead, 3.7 to 3.1, and by twenty, 3.6 to 2.5.

Rest pays. Dancing and the morning bonus were measured by switching them off for an 18-crab crew over twenty minutes. They add 12% on all hands (7.5 against 6.7 ingots a minute), 24% on A and B shifts (10.4 against 8.4), and little on three-shift relief (8.2 against 8.0), whose crabs are rested anyway. A first version with a smaller morning bonus (15% for one minute) made no measurable difference, so it was raised to 25% for 90 seconds.

Working configurations. Hill-climbing, moving one crab between roles at a time and averaging two seeds, found these crews. With ten crabs on all hands over eight minutes, the best was one scout, one drill, one hauler, one crusher, three smelters, one energy bot, and two repair bots, at 6.2 ingots a minute. That is only a little ahead of the starting crew plus a smelter. Over twenty minutes, the best ten-crab crew had no haulers at all: 2 scouts, 2 drills, 1 crusher, 2 smelters, 1 energy bot, 1 repair bot, and 1 maintenance bot, at 4.9. The backup job does the hauling, because every crab carries nodules whenever its own work is stuck. Dedicated haulers come back into their own as the line grows. With 18 crabs on A and B shifts the best was 3 scouts, 3 drills, 3 haulers, 2 crushers, 3 smelters, 2 energy bots, 1 repair bot, and 1 maintenance bot, at 12.7. With 30 crabs and every upgrade it was 3, 7, 5, 3, 6, 3, 2, and 1, at 28.1.

Pace. These runs were made before crabs earned veteran stars; the next paragraph measures what veterans change. An automatic player that fixes the advisor's bottleneck, fills shift gaps, and spends spare money on upgrades was run three times for each strategy. Staying on all hands without overclock, it reached Pebble Boss at 1.8 minutes, Nodule Baron at 4.0, Ingot Magnate at 8.1, Lava Lord at 17.2, and Crab Tycoon at 34.7, and earned 7,700 credits in 40 minutes. Switching to A and B shifts at 14 crabs, with overclock, reached Lava Lord at 14.4 and Crab Tycoon at 24.4, and earned 17,500. That is about six minutes of real time at 4× speed. Three-shift relief from 18 crabs reached Crab Tycoon at 26.8. Adding research to the A and B strategy delays Crab Tycoon to 28.1 minutes, because the money goes into labs first. It pays back by the end: 53 ingots a minute and 20,400 credits by minute 40, against 42 and 17,500 without it.

Veterans. A rebuilt automatic player of the same kind was run over six seeds with veteran stars on and off. Stars come early: by minute 40 almost every crab has at least one. They change little in the first ranks and help most later. With A and B shifts and overclock, Crab Tycoon came at 28.1 minutes instead of 30.9, and earnings by minute 40 rose by a quarter. With research it came at 24.3 instead of 26.0. Under three-shift relief Tycoon came about a minute later, at 31.2, but output at minute 40 was 56 ingots a minute against 44. On all hands, earnings by minute 40 rose by 6%. With fixed crews, output over 40 minutes rose by 13%.

The vent. For an 18-crab crew the vent carries a few rides a minute, mostly energy bots and repair crews heading back to the field, and raises output by about 4%. It earns its place more as spectacle than as economics, and the crabs only take it when it saves time.

Changes made in review. The first version of wear grew without limit, and a crew on all hands spiralled into breakdowns. Wear now does nothing for four minutes and at most doubles breakdowns and slows a crab by a fifth. A and B shifts at first left half of each crew working day and night, so the resting half now alternates night by night. All hands also showed night shading and sleepy faces, though nobody sleeps in that mode. The shading now only falls when there are shifts, and a crab with a flat battery looks exhausted and asks for charge rather than dozing.

Second review. After the rounds that added metal grades, the second rim, the annex and the wreck, the same harness was run again over three seeds, with an automatic player that now also spends spare money on the cheapest upgrade still to buy, keeping a hundred credits in hand. The fixed crews of Table III come out close to the figures above: the starting crew makes 3.6 ingots a minute over five minutes on all hands (3.8 in the first review), the best eighteen 11.8 (12.7), and the best thirty with every upgrade 28.6 (28.1). The one clear change is the starting crew left for twenty minutes, up by a third to 3.3 on all hands and 4.5 with A and B shifts, which has gained from the systems added since. Table V gives the automatic player's times. Without upgrades they match the earlier runs to within a minute, which is the noise between seeds. Upgrades tell late: with A and B shifts, overclock and research, buying them too brings Crab Tycoon from 21.3 minutes to 19.7 and raises the forty-minute earnings by 30%, and on all hands it brings Tycoon from 31.9 to 28.9 minutes with earnings up by two thirds. The early ranks do not move, because there is no spare money before Ingot Magnate. tests/balance.js prints these figures beside its own, so the next review can start from them.

No crab knows the plan. Each one runs the rule in Table I, and each rule reads only local facts: the nearest nodule, the best flag, the height of a pile, the level of a battery, whether the vent is quicker. The piles and the flags do the coordinating. This is stigmergy, the name Grassé gave to coordination through traces left in a shared workplace [1], and it is a founding idea of swarm intelligence [2]. Insect colonies divide work by giving each worker a threshold for each task [3], and robots have been built to share foraging in the same way [4]. Here the player acts as the threshold, moving crabs to whichever stage is short and choosing who rests when. The line can deliver no faster than its slowest stage [5], and the Ledger tab exists to show which stage that is.

The nodules are real. Polymetallic nodules lie on abyssal plains and consist mainly of manganese and iron oxides, with nickel, copper, and cobalt in smaller amounts [6]. Lava erupts on the sea floor too, and basaltic lava is roughly 1,100 to 1,200 °C. Octopuses are real, clever, and known to raid traps and tanks for food, though not, so far, for manganese. Pearls grow in molluscs, not in nodule fields. Tides reach the deep floor only as slow currents, and storms do not reach it at all, though deep currents can be strong. Submarine eruptions do pulse. Hot water rising from the sea floor is real as well: hydrothermal vents send up plumes of warm, buoyant water. A Stirling engine runs on a temperature difference rather than on fuel, so one placed between lava and cold seawater is at least sound in principle.

The smelting and the forging are game rules. Copper melts at 1,085 °C, which basaltic lava can reach. Manganese melts at 1,246 °C and nickel at 1,455 °C, which it cannot, and turning an oxide ore into metal needs a reducing agent as well as heat. Vent plumes rise slowly, so a crab could not ride one to near the surface in two seconds. Sunlight does not reach a floor this deep, and the night shift is lit only by the crabs' lamps. The model is faithful about the economics: breakdowns tax output, repairs consume product, tired workers break more, and the slowest stage sets the pace.

Eight local rules, three piles, a stockpile, and a refuel post make a production line that looks managed and is not. Uncertain mining, breakdowns paid for in the line's own metal, wear that only rest removes, and a price that rewards steady flow turn it into a game with real decisions. The review finds that the economy works: every role pays for itself, every upgrade raises output, shifts beat working flat out over any real length of game, and a sensible player reaches Crab Tycoon in under half an hour of simulated time. The lesson is the old one with a night shift added: find the stage that sets the pace and feed it, keep every job covered around the clock, and let the crew sleep and dance.