White-handed Fiddler Crab, Uca albimana (Fiddler Crab of the Week)

The White-handed Fiddler Crab, Uca albimana, is found throughout the Red Sea, the southeastern Arabian peninsula, and along the entrance of the Persian Gulf in the United Arab Emirates. Although originally described in 1877, it was largely considered a form of another similar species, Uca annulipes, until 2010 (in fact, Uca annulipes has been split into at least four different species in the last decade).

Not a lot is known about the behavior of this species; most historical work would have been performed on one of the closely related species rather than this one (when they were all lumped together) and it is not entirely clear how much of that work can carry over to this species.

Perplexing Fiddler Crab, Uca perplexa (Fiddler Crab of the Week)

The Perplexing Fiddler Crab, Uca perplexa, is found throughout most of the islands of the western Pacific, from Japan down to Malaysia across Indonesia, the Philippines and Papua New Guinea, the eastern coast of Australia and out toward remote islands such as Fiji, Samoa, and French Polynesia. It’s name comes from the confusion that arose in trying to separate this species from closely related forms, particularly Uca annulipes and Uca lactea with which its range overlaps in many areas. In the field these species can be told apart somewhat by color: the major claw in Uca perplexa tends to be more yellow while that of Uca annulipes is more red, although there are other similar species which may also have red and/or yellow claws so its not an absolute indicator.

Because of its spread over so many remote Pacific Islands, in terms of raw area (as well as longitudinal range), it is one of the most widespread fiddler crab species, likely second only to Uca tetragonon (which resides in much of the same area, but is also common throughout the Indian Ocean as well). Given that most of its range area is open ocean, it’s an open question as to whether it actually occupies more shoreline than a widespread continental species such as Uca tangeri.

New Features on the Site

This month’s site update contains a number of new features beyond the standard citation and reference updates. In particular, three new elements are now on the site. Two of these were discussed as upcoming in previous posts, but are now live. The third has its own description posted earlier today:

  1. Charts showing the chronology of name usages
  2. Word clouds of name usages
  3. Point location pages

Hopefully these all add a little more information that may prove useful.

Point Location Data

My previous discussions of range maps (see part 1 here) focused on areal (or linear) representations of where different species might be found. Another type of location data has been part of the site for awhile but was never explicitly compiled into a useful form…until now.

Individual records of species usages (such as those found on the citation pages) often list the particular location to which the name applies. This location can be fairly specific (e.g., a particular river mouth) or extremely broad (e.g., a country or ocean basin). These location names are stored as part of the database; a number of years ago I decided to standardize the names to allow for better analysis and consistency. As much as possible, the names found on the website reflect the current name of the location, rather than the historical name that might have appeared in the original publication, although the historical names are kept as synonyms (invisible until now).

Beyond just standardizing the names, every location was given a latitudinal and longitudinal representation. These coordinates lack precision, but represent a quick-and-dirty estimate of what the location name might represent. For a broad area, the coordinates usually match a major coastal city or the rough center of the coastal area; for smaller islands, the center of the island might have been used.

I’ve been using the coordinates for a few years to help identify misidentified records and/or errors in the database. By plotting the locations associated with different names, it is fairly easy to find major outliers; these can then be examined to determine if the error was a recording error on my part or a (potential) error made by the original authors.

In this new release, the point location data is now public and is used in a variety of different ways and places on the site.

Species Pages

The species pages (as well as the general geography page) now show a point location map in addition to the traditional range map. These point location maps represent all of the places where the database believes a particular species is actually found (as opposed to where an author said it was found). These should generally match the range maps, although there are certainly cases where they diverge; at some point these differences will be used to update/fix the range maps and/or the underlying point-species references. Additionally, the point maps are only up-to-date based on citation records added to the database. Aberrant locations where no fiddler crabs are found are indicated by a different color symbol.

Every recorded point location of a fiddler crab in the database. Blue points represent clearly erroneous entries where no fiddler crabs are actually found. The point in central northern Africa (border of Libya and Niger) was a lat/lon error in the database which has already been corrected.

Name Pages

The name pages (both compound and specific name) now show a point map indicating all of the places where a particular name was used, if any (some names are not associated with any specific location so maps are left off of those pages). This is different than the species pages, because this indicates author usage rather than the algorithmicaly and/or expertly adjusted species meanings found on the species pages.

Location Pages

Every location has its own page as well. Each location page includes the latitude and longitude used to indicate its position (as well as a map of the point), cross-references to locations that contain or are contained within the location based on the hierarchy mentioned below, lists of currently recognized species found within the location, and lists of names (both compound and specific) which have been used for species at the location.

The species and name lists automatically fill in missing names by including all names found at any sublocation of the hierarchy (names inferred as such are indicated by a symbol). This should allow one to more readily access complete lists of names or species for an area without having to worry about the vagaries of historical records.

Location pages can be accessed in two ways. First, from the general geography page, there are now a pair of indices of all locations. The first index represents a rough hierarchical sorting of locations, lumping sub-locations into larger locations (e.g., a city within a state within a country). The second index is a pure alphabetical listing of all locations, including the historical names, not just the modern names. Second, all location pages can also be accessed from any page/record which mentions that location; the locations in the tabular records automatically link to the associated location page.

Problems and Limitations

These location data are not perfect. Some known problems include:

  • Species may be missing from locations just due to holes in observations. For example, Uca pugilator is not recorded for Deleware, even though it falls right in the middle of the known range of the species and is found in neighboring states.
  • Less precise records may have a point location which seems to indicate the presence of a species well outside its actual range. Thus a species recorded from “Central America” might use a point location to indicate this area well outside the actual range of the species in question if it is limited to only one end of the region.
  • The hierarchy is imperfect in a number of ways. This limits how readily it can combine and infer records from subregions into large regions. Some of this can be fixed and updated over time, but other parts may be very difficult to fix, or impossible to put into a strict hierarchy. For example, take the country of Panama. We can combine all of the subrecords of Panama under the country entry to indicate all of the species found in Panama. However, once we do that, we cannot readily also combine the coasts of Panama into the individual Atlantic or Pacific regions which have separate species assemblages. Under the hierarchical structure, we either have to keep the two coasts of Panama separate or we have to abandon the Atlantic and Pacific basins as part of the natural hierarchy (for now I’ve done the latter).
  • Most of the Google maps of individual point locations default to a higher zoom than one would prefer (essentially, the begin maximally zoomed). There’s an easier, imperfect solution to this and a tedious, better solution. I’m working on the latter, but it’ll be awhile before the default zoom will be fixed for all locations.

All of the point location data in the database are directly based on what has been reported in publications. There are other potential sources of location records that might be integrated at some point, including more formal museum specimen records such as those found in GBIF or more informal, citizen-science records such as those from iNaturalist (although I note that at least some of the latter records are included in the former). For now I’d prefer not to mix and match these with the data on this site, but in the long run it will be worthwhile to explore how to combine them.

I’ve been playing with these location data for a few years and the new pages offline for a few months. It seems time to make them generally available; if you find obvious problems or flaws, please let me know so we can endeavor to make them better.

Gulf Marsh Fiddler Crab, Uca longisignalis (Fiddler Crab of the Week)

The Gulf Marsh Fiddler Crab, Uca longisignalis, is found along the Gulf of Mexico coast of the United States, from northwestern Florida through Texas. It’s a medium-sized species, sometimes mixed up with close relatives such as Uca minax or Uca rapax. It has a medium to pale turquoise/blue carapace, brown legs, and a white/yellow major claw.

The name of this species (essentially “long signalling”) comes from its extended waving and acoustic display relative to similar species from which it was originally distinguished.

The Gulf Marsh Fiddler has not been the primary focus of many studies, although it has often been examined in comparative cross-species studies, particularly by Carl Thurman and his students and collaborators.


Bonin Islands Fiddler Crab, Uca boninensis (Fiddler Crab of the Week)

The Bonin Islands Fiddler Crab, Uca boninensis is fairly unique in that it is both endemic to the Ogasawara Islands of Japan (“Bonin Islands” is a historical name) and is not sympatric with any other species, being the only fiddler crab found on these islands. The only other fiddler crab with no sympatric fiddler associates is Uca tangeri, which has an immense range across most of the west coat of Africa and even the southern edge of Europe. There are a few other species endemic to small islands, but each of these overlaps with one or more other fiddler crabs.

Figure from Shih et. al (2013)

Until its recent description, this species was thought to be Uca crassipes. Shih et al. (2013) identified the new species through clear genetic differentiation between it and other populations of U. crassipes; they also found some minor morphological differences between these two very similar species, although nothing so striking as to allow easy identification. Little is known about the ecology of Uca boninensis since almost all previous work simply noted its presence on these islands. It is a medium sized fiddler crab, found in the upper intertidal zone of the estuaries of small rivers, in fragmented rock and muddy-sand substrates.

Because this species is known from only a few remote islands in the Pacific Ocean, its existence is likely threatened by climate change and is a candidate for conservation evaluation and protection. The Ogasawara Islands contain many endemic, unique, and endangered species across all forms of life and were added to the UNESCO World Heritage List in 2011.

Bowed Fiddler Crab, Uca arcuata (Fiddler Crab of the Week)

The Bowed Fiddler Crab, Uca arcuata, is one of the more widespread and better known species from eastern Asia, found along the coasts of China, South Korea, Taiwan, and Japan.  It is a large species, with a dark brown or maroon carapace (often with cream edges and highlights), cream eyestalks, black-to-red legs, and a robust major claw with a red hand and cream fingers.

In parts of its range, both males and females of this species build chimneys around the mouths of their burrows, extending the entrance upward from the muddy surface. They are often found on open mud flats and banks near the mouths of rivers. This species has been the focus of many studies by marine ecologists in both China and Japan.

Jocelyn Crane reported that this species could sometimes be found canned in local seafood markets in Japan, making it one of only two species eaten by humans.

Word Cloud of Names

I recently happened to stumble across the lab page of a faculty member who used a word cloud based on his research papers to display the key words that come up most often in his own research. I thought this was a rather interesting way to get an objective view of ones research so started playing with the idea for my own work. Unfortunately, this turned out to be more difficult than I expected, not because building a word cloud was hard (there are plenty of available tools for that), but because extracting the text from the PDFs of all of my publications led to a lot of weird biases and errors (this is a PDF issue) and it’ll take a lot more effort to dig up the original raw text documents than I’m willing to go through right now.

It occurred to me secondarily, however, that we could use the same approach on the fiddler name data to get a visualization of how often each name appears in the literature.

First we have the occurrences of binomial/compound names in the literature. The frequencies are based on the number of publications each name appears in if used as a valid name (thus, a paper which states that name A is a junior synonym of name B would only count the senior synonym B and not the junior synonym A). No matter how many times the name is used within the paper, it counts as only one occurrence with respect to this exercise.

The results are pretty much what one would expect, but it does provide a somewhat interesting (if not particularly statistical) rendering of the relative name uses.

As with other parts of the site, we can do the same thing with the specific names only (ignoring both genera and lumping alternate/misspellings). Again, the major names are what one would expect.

I may need to play with the visualization a bit (color schemes, shape, etc.), but these images will be added to the name summary part of the website on the next monthly release.


Beebe’s Fiddler Crab, Uca beebei (Fiddler Crab of the Week)

Note: the fiddler crab of the week series was temporarily derailed due to some unexpected health issues, but will hopefully be back on track going forward.

This week we find another species from the Pacific coast of the Americas, Uca beebei, named after the famous naturalist, explorer and author William Beebe. This small species is found from El Salvador through Peru on open mudflats. In the Pacific entrance of the Panama canal it tends to be one of the more numerous species, often found mixed with larger species such as Uca stylifera or Uca heteropleura or more similarly sized species such as Uca deichmanni. Relative to many other species, it is also more of a generalist when it comes to substrate preference, ranging across both sandier and muddier mudflats. Not the most colorful species, it tends to be a grayish-brown with some teal on the back of the carapace; the long, slender fingers of the large claw are white, while the rest of the major limb often has dark purple highlights. The eyestalks are thick and yellow.

Photo provided by Pat Backwell.

Unlike many of the other species in the series so far, Uca beebei is actually fairly well studied. John Christy and colleagues spent many years studying the behavior of this species in Panama. It has a fairly classic, basic wave, quickly moving laterally its claw to the side, then forward in an overhead circle back to the rest position. The small claw often goes up and down as well. The waving can be done either standing in place or sometimes shuffling toward or away from another crab.

Beebe’s Fiddler Crab is one of a number of species which build structures around the mouth of their burrow. As seen in the photo below, the males build a sort of wall or pillar or partial hood on one side of the burrow opening. The exact purpose of these structures is unknown, but in part it seems to be used as a beacon to allow themselves to find their burrow more quickly if they’ve wandered away from it.

Photo provided by Pat Backwell.


The Slender-legged Fiddler Crab, Uca tenuipedis (Fiddler Crab of the Week)

The Slender-legged Fiddler Crab (Uca tenuipedis), is a very small species from the eastern Pacific Ocean, ranging from about El Salvador to northern Peru. It is similar in size to some of its sympatric associates, such as Uca batuenta, Uca intermedia, and Uca saltitanta, but is readily distinguishable from the first of these by the somewhat triangular shape of the pollex and manus, and the latter two by its color: a fairly cryptic-colored brown and gray body, with a white pollex and pinkish-salmon dactyl and top part of the major claw.

Photos by M. Rosenberg, Panama, 1997.

The waving display of this species involves bringing both the large and small claws straight out to the side, pausing for a moment, then bringing them up and forward in a circle back to the starting open-wide position. The whole body rocks backwards slightly with this motion and sometimes the first few legs may come off the ground as well.

Unlike some of the other local species, this one seems to stay closer to the shoreline, found among the muddy stream banks or the fringes of mangroves rather than out on the open mudflat.