Unidentified

This is not Paragrapsus laevis it is Guinusia chabrus the taxon on this site needs updating as the genus is wrong outdated for this species

@BushRenegade thanks so much for your IDs today. You seem to have a good knowledge of Marine Seaweeds and Marine invertebrates.
Could I interest you in becoming a moderator for these categories? It would be greatly appreciated as we seem to be short of someone who can identify sightings in these categories in this and other areas.
Cheers,

@trevorpreston Firstly thanks for the comments I had only just sent an application through for this a short Time ago to the NatureMapr team with some more info about myself and the areas I have most of my knowledge in to see if I could be of some help

I do not agree that the crab is Ginusia chabrus (previously Plagusia chabrus or Red bait crab/ red rock crab). That species has definite ridges along its legs, is reddish and is not estuarine.

@Jennyncmg at first look without going deeper it looked more like Plagusia glabra

how ever i talked myself out of it based on the actual features, if you look at the above note the chelae and the strong longitudinal rows of tubercles or granules evident on the carpus and the propodus that is the first key feature, P. glabra has sparse small granules that are not as strong and not easy to see this also excludes many other species.

Next look at the carapace and the shape of the frontal region note the deep antennular notches this is another key feature that excludes other species especially Paragrapsus laevis that has no notches along the frontal region and is slightly rounded downwards with a central groove but no notches in the frontal edge.

Then still on the carapace note the three spines posteriorly on the anterolateral margin another key feature that excludes a lot of species including P. laevis that has two notches or (three teeth one being at the orbital edge with two set behind that)

Next The walking legs and you can easily see a large spine on the distal end of the merus on all pics then looking at the third pic as it gives the clearest view walking legs 2 and 3 have numerous other spines on the upper margin of the merus (it is common for these spines to be worn off or not evident in some specimens) Again this feature rules out other species.

Next the walking legs again and you can see distally along the frontal edge of the propodi a row of fine hairs another feature of this species

The colouration as you pointed out is not red but this crabs colouration can be much darker and nearer to black in some specimens hence you need to be cautious when using colour to ID a crab as there are some that have many variations but the key features are what should be the focus as they define the crab and how to truly identify them.

Just to note colour variations in pictures is common too as cameras depending on how that image is taken i.e. focal length, aperture etc. along with post editing can all make colours look very different than they do in real life.

I cannot comment as to the location as I cannot see that, keep in mind this family is called rafting crabs for a reason and can often travel outside of normal ranges attached to anything floating then drop off where ever also human intervention can be cause of species not being where they should be.

Based on the above characteristics there is no doubt at all that this is Guinusia chabrus

As a note my main expertise is in southern Australian crabs, I am personally asked to ID this crab species and family from South Africa to New Zealand and am very familiar with it and state with certainty this is Guinusia chabrus

As a point of reference here is a pic from crab database as a type sample from New Zealand

https://www.crabdatabase.info/data/original/brachyura/eubrachyura/thoracotremata/grapsoidea/plagusiidae/guinusia/guinusia-chabrus/live/dsc_0119.jpg

and to support the colouration and features again here from iNats

https://inaturalist.ala.org.au/photos/63779714
https://inaturalist.ala.org.au/photos/91932110
https://inaturalist.ala.org.au/photos/323263052
https://inaturalist.ala.org.au/photos/221285104
https://inaturalist.ala.org.au/photos/171276070

Thanks Bush renegade
It is great to have an expert helping. I look forward to learning more