{"id":4486,"date":"2022-07-18T22:00:00","date_gmt":"2022-07-18T22:00:00","guid":{"rendered":"https:\/\/modernsciences.org\/staging\/4414\/?p=4486"},"modified":"2022-07-06T06:27:18","modified_gmt":"2022-07-06T06:27:18","slug":"thousands-of-giant-crabs-amass-off-australias-coast-scientists-need-your-help-to-understand-it","status":"publish","type":"post","link":"https:\/\/modernsciences.org\/staging\/4414\/thousands-of-giant-crabs-amass-off-australias-coast-scientists-need-your-help-to-understand-it\/","title":{"rendered":"Thousands of giant crabs amass off Australia\u2019s coast. Scientists need your help to understand it"},"content":{"rendered":"\n
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\n \n Julian Finn\/Museums Victoria<\/span><\/span>\n <\/figcaption>\n <\/figure>\n\nElodie Camprasse<\/a>, Deakin University<\/a><\/em><\/span>\n\n

Am I not pretty enough?<\/a><\/strong> This article is part of The Conversation\u2019s series introducing you to little-known Australian animals that need our help.<\/em><\/p>\n\n

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Every winter in shallow waters off Australia\u2019s southern coast, armies of native spider crabs appear in their thousands. They form huge underwater piles, some as tall as a person. These fascinating crustaceans are on a risky mission \u2013 to get bigger.<\/p>\n\n

Crabs cannot simply grow like humans and other soft-bodied creatures. They must break free from their shells, expand their soft flesh and harden a new shell \u2013 all while dodging hungry predators on the hunt for a soft, easy meal.<\/p>\n\n

This moulting process leaves crabs clumsy and uncoordinated, making any escape tricky. That\u2019s thought to be one reason they clump together in such big numbers \u2013 to keep each other safe.<\/p>\n\n

The spectacular gatherings attract tourists from interstate and overseas and have even been featured in a BBC documentary<\/a>. But despite all this attention, scientists know very little about these quirky creatures. We need your help to investigate.<\/p>\n\n

\n \"A\n
\n There\u2019s still much to learn about spider crabs.<\/span>\n Julian Finn\/Museums Victoria<\/span><\/span>\n <\/figcaption>\n <\/figure>\n\n

Safety in numbers<\/h2>\n\n

Southern Australia\u2019s spider crabs (Leptomithrax gaimardii<\/em>) are usually orange to red-brown. They can reach 16cm across their shell and 40cm across their legs, and are commonly known as great spider crabs.<\/p>\n\n

Spider crabs are believed to be widely dispersed in deeper waters. But they\u2019re most visible to humans when they congregate near shore in winter<\/a>, and occasionally at other times of year.<\/p>\n\n

Once together, spider crabs shed their old shells in a synchronised act thought to take about an hour<\/a>. The crabs stay together until their new hard shells form, which probably takes a few days. <\/p>\n\n

The aggregation can last a few weeks. Soft crabs are thought to take refuge in the middle of the piles, protected by crabs yet to moult.<\/p>\n\n

Afterwards, spider crabs return to deeper waters and their solitary lives, leaving the seafloor littered with discarded shells. <\/p>\n\n\n\n

\n \"Freshly\n
\n A freshly moulted spider crab, left, next to its old shell.<\/span>\n Elodie Camprasse<\/span><\/span>\n <\/figcaption>\n <\/figure>\n\n

Plenty of mysteries to solve<\/h2>\n\n

Spider crab aggregations have been officially reported along the Victorian and Tasmanian coasts. Historically, most winter sightings have been reported on the Mornington Peninsula \u2013 particularly near the Rye and Blairgowrie piers. <\/p>\n\n

Anecdotal evidence suggests the gatherings can also happen elsewhere. For instance, an aggregation was reported this year on the western side of Port Phillip Bay.<\/p>\n\n

But there\u2019s still so much we don\u2019t know about spider crabs, such as:<\/p>\n\n

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  • how many spider crabs are out there?<\/li>\n
  • how many gather en masse? <\/li>\n
  • how long do the crabs stay?<\/li>\n
  • what signals do crabs use to know it\u2019s time to come together? <\/li>\n
  • why do the crabs aggregate at one location in several consecutive years then not return? <\/li>\n<\/ul>\n\n

    Most spider crab gatherings seem to occur in winter, but they\u2019re known to come together at other times. For example, aggregations in late spring, midsummer and early autumn have been reported in parts of Port Phillip Bay and elsewhere Victoria and Tasmania.<\/p>\n\n

    Those aggregations don\u2019t seem related to moulting \u2013 in fact, we have no idea why they occur! <\/p>\n\n

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