Crabby’s Reef

FOR MOBILE: This game is now playable on mobile devices but we cannot guarantee it will be compatible with all devices. You need to orientate you device to landscape. Move Crabby by swiping in the direction you want them to move.

FOR DESKTOP: You may need to click your mouse on the game window to enable keyboard controls. As well as WASD, you can move using arrow keys. The game works best in the Chrome browser. Press the full screen icon on the bottom-right for the best experience.

The game has a familiar classic arcade style, however, with each new level you are transported further into a potential future with an increasingly acidic ocean. How does this effect your ability to play the game?

We have launched Crabby’s Reef for World Oceans Day and to help our friend’s, The Deep. The Deep is an international player in marine conservation, working on pioneering research schemes to protect the future of our oceans. Conservation is at the heart of everything they do. Without visitors during the Covid-19 lockdown, The Deep have lost valuable income required to continue this work. We urge you to please support them in any way you feel appropriate – visit their sitebuy from their gift shopdonate directly.

Welcome to Crabby’s Reef where food is plenty for a hungry crab but so are the predators, the equally hungry octupuses looking for a tasty crabby snack.

Navigate the maze to collect food whilst avoiding becoming food yourself. But life is going to get harder as the ocean becomes more acidic, dampening your senses and your ability to sniff out food and predators.

You can check your position on the Leader Board at the bottom of this page.


Our resources are still being prepared and will appear here when ready – keep an eye on Twitter for updates.


The idea for Crabby’s Reef fledged over a coffee break and soon went from a short chat to becoming a full-grown outreach project. It is based on research of Dr. Christina Roggatz and the desire to communicate the abstract process of ocean acidification in a more tangible way.

Ocean acidification happens beneath the waves, hidden out of sight for most people. But this process, described as the evil twin of climate change, is directly linked to the increasing carbon dioxide concentrations we emit into the atmosphere. The oceans take up a large part of this carbon dioxide (CO2). Once absorbed, the CO2 reacts with the water to form carbonic acid, which dissociates and releases protons that lower the pH. This makes the oceans more acidic. At the current rate of increasing CO2 emission, ocean pH is predicted to drop from today’s average of pH 8.1 to a pH below 7.8 by the year 2100 [RCP8.5 scenario, IPCC synthesis report 2014].

FINAL_ocean_acid_infographicInfographic by The Deep used here with permission.

Impacts of this invisible process on marine life include issues in calcification, reduced fitness, and changes to the organisms’ metabolism [Kroeker et al. 2013]. Over the past decade, it also emerged that enhanced CO2 concentrations and reduced pH alter the behaviour of marine animals [Clements & Hunt 2015]. Fish were observed to become unable to identify their home corals or avoid predators [Munday et al. 2009] and hermit crabs couldn’t find their food as well anymore [de la Haye et al. 2012, Roggatz et al. 2020].

A female shore crab with eggs (left) and a hermit crab (right) [Photos by Mike Park, University of Hull]

Many of these behaviours are mediated by chemicals, for example the smell molecules of a specific food item or a predator, which signal the animals to respond accordingly. Christina found during her PhD, that ocean acidification changes the peptide molecules used by shore crabs and other invertebrates during brood-care and larval settlement [Roggatz et al. 2016]. In experiments, she observed that a pH reduction of as little as 0.4 units causes the crabs to lose their ability to detect the smell molecule at the same concentration. Chemical investigations revealed that the reduced pH changed the charge and 3D-structure of the peptide molecules, so they likely can no longer be recognised by the crabs. That means the animals become more and more ‘nose-blind’ with ongoing acidification.


The increasing difficulty and blurry screen in Crabby’s Reef reflect how ocean acidification would progressively impair the crab’s sense of smell and thereby reduce its ability to find food or detect predators. Starting in Level 1 with the current pH of 8.1, the pH drops 0.05 with every additional level and the shimmering and shadows on screen intensify to make it more difficult to spot the octopuses and food items and play the game. This serves as a fairly good representation of how a crab might feel like in future ocean conditions and helps to illustrate this otherwise invisible effect.


This project was inspired by an initial conception by Flo Halstead, designed by Chris Skinner and Christina Roggatz, and developed by BetaJester Ltd. The initial development was funded directly by the Energy and Environment Institute, with free development support by BetaJester Ltd to develop the online version in aid of The Deep. A Public Engagement grant from the European Geoscience Union (EGU) will support the construction of an arcade booth to house the game at events.

Leader Board