Sentinel Crab Research Articles

Sediment temperature characteristics and their relation to distribution patterns of two sentinel crab species in intertidal flats in western Japan

In the context of global climate change, monitoring focused on temperature and benthic animals in intertidal flats and the development of metrics to assess climate change and ecosystem responses are essential for a sustainable society. However, few studies have assessed the relationship between intertidal sediment temperature and the distribution of benthic animals. To address this gap, in the present study, intertidal sediment temperatures were observed in 12 intertidal flats in 11 survey areas over 335 days, from October 2, 2019, to August 31, 2020, using water temperature data loggers. The characteristics of intertidal sediment temperatures were variable among the survey areas, and a correlation analysis suggested that such characteristics are possibly influenced by various spatial-scale factors, such as geographical, basin, and habitat scales. Furthermore, two sentinel crab species, Macrophthalmus japonicus and Macrophthalmus banzai were collected, and the number of wintering individuals of each species was estimated based on their carapace width to analyze the changes in abundances of the two species in each survey area. The results show that the number of days with daily minimum temperature ≥ 19 °C was the factor that influenced the abundance rate, suggesting that M. japonicus and M. banzai populations may decrease and increase, respectively, according to future climate change in Japan. Our findings emphasize the importance of long-term monitoring of sediment temperatures and benthic animals in intertidal flats to evaluate the influence of future climate change.

First record of <i>Macrophthalmus japonicus</i> (De Haan, 1835) (Brachyura: Macrophthalmidae) population from the Pacific coast of Iwate Prefecture, northern Japan

The tidal flats at Otomo-ura (Iwate Prefecture), which had been converted to farmland through a reclamation project from 1959 to 1969, have been partially restored after the tsunami caused by the Great East Japan Earthquake in 2011. In the course of monitoring the benthic fauna of the tidal flats for 11 years after the tsunami, we found some adult sentinel crabs of the genus Macrophthalmus at a muddy area for the first time on July 28, 2022. During subsequent observations of the mud flat, we noted that the adult male crabs exhibited waving display of vertical non-forward-pointing type. Allocleaning, performed by both sexes, was also observed. Morphological characters include: the carpus and propodus of the ambulatory leg 3 of the adult male are not associated with tuft of setae on their ventral surfaces, and the subdistal tooth of leg 3 is not distinct. Based on these behavioral and morphological characteristics, the macrophthalmid crab was identified as Macrophthalmus japonicus. This is the first record of this species along the coast of Iwate Prefecture. In addition, five of six females captured on July 28 and August 14, 2022, were ovigerous (range in carapace width: 19.1–25.0 mm), which indicates that the crabs are reproducing on the tidal flat.

Pemanfaatan dan pusim penangkapan kepiting jangkang (Macrophthalmus japonicus de Haan 1835) di perairan pesisir timur Kota Surabaya

Aktivitas perikanan tangkap di pesisir timur Kota Surabaya menggunakan beragam alat tangkap yang sederhana. Salah satu diantaranya adalah perikanan tangkap dengan cara memungut kepiting jangkang sebagai target tangkapan. Nelayan menggunakan papan untuk meluncur di atas hamparan lumpur guna menangkap target tangkapan berupa kepiting jangkang (Macrophthalmus japonicus) yang kondisi karapasnya masih lunak. Nelayan tidak menangkap kepiting yang kondisi karapasnya keras. Penelitian bertujuan menentukan jenis spesies sumber daya kepiting jangkang target tangkapan, lokasi penangkapan kepiting jangkang serta pola musim penangkapannya. Penelitian menggunakan metode deskriptif yang bersifat survei. Penelitian dilaksanakan pada bulan Februari sampai dengan Juli 2018. Lokasi penelitian di perairan pesisir Kota Surabaya. Responden adalah nelayan penangkap kepiting jangkang dengan lokasi tangkapan di pantai timur Kota Surabaya. Untuk penentuan jenis spesies, dilakukan sepuluh kali sampling terhadap hasil tangkapan, masing-masing sebanyak 25 ekor kepiting dalam kondisi karapas lunak. Lokasi penangkapan ditentukan oleh nelayan, pembuatan peta lokasi dengan menggunakan program Arcview 3.3. Pola musim penangkapan dilakukan dengan penentuan nilai Indeks Musim Penangkapan (IMP). Hasil penelitian sebagai berikut: 1). Jenis kepiting yang menjadi target tangkapan nelayan adalah jenis Macrophthalmus japonicus; 2). Daerah penangkapan kepiting adalah pada hamparan pasut dengan dasar berlumpur di wilayah pesisir timur Kota Surabaya pada koordinat 7014’24”–7015’05” LS dan 112048’09”–112049’04” BT; 3). Pola musim penangkapan kepiting berdasarkan IMP adalah, musim puncak secara berturut berlangsung pada bulan: April (612,96%), dan Mei (164,68%). Musim sedang pada bulan: Juli (77,76%), Maret (68,61%), Februari (64,04%), dan Januari (59,47%). Musim paceklik pada bulan: Juni (42,69%), November (36,59%), Agustus (32,02%), Oktober (18,30%), Desember (18,30%), dan September (4,57%).

Bioaccumulation of heavy metals (Hg, Cd and Ni) by sentinel crab (Macrophthalmus depressus) from sediments of Mousa Bay, Persian Gulf.

The presence of heavy metals (HMs) in the environment can increase their risk of transfer to the food chain. The present study was conducted to investigate the bioaccumulation of HMs including Hg, Cd and Ni in soft and hard tissues of sentinel crab (Macrophthalmus depressus Rüppell, 1830) in sediments of Mousa Bay in northwest of the Persian Gulf. The average (mean±SD) amounts of Hg, Cd and Ni in the sediments were 6.27±3.66, 3.8±1.48 and 71.6±5.09μg/g, whereas the relevant amounts for soft tissues were 6.16±4.64, 3.3±1.7 and 19.7±3.96μg/g, and for hard tissues were, 2.9±1.67, 3.5±1.35 and 10.44±3.1μg/g, respectively. Accordingly, soft tissues of the crab could be suitable bioindicators of Hg and Cd, whereas the hard tissues could be used as Cd bioindicator. Since the bioaccumulation of Ni was the most, it might have a higher risk among the metals to enter the food chain in the region.

Mangrove metal pollution induces biological tolerance to Cd on a crab sentinel species subpopulation

Metals are persistent pollutants, able to accumulate in the biota and magnify in trophic web. In the specific case of cadmium contamination, it has been the subject of considerable interest in recent years because of its biological effects and it is one of major pollutant in estuarine areas. Ucides cordatus is considered a mangrove local sentinel crab species in Brazil and there are previous studies reporting crab subpopulations living from pristine to heavily metal impacted areas in São Paulo coast (Southeastern Brazil). Taking into account the background knowledge about these subpopulations, we proposed the hypothesis that crabs from a highly polluted mangrove (Cubatão - CUB) have developed biological tolerance to cadmium compared to animals from an Environmental Protected Area (Jureia - JUR). Aiming to verify this hypothesis, we have investigated total bioaccumulation and subcellular partition of Cd, besides biomarkers' responses during a long-term exposure bioassay (28 days, with weekly sampling) using a supposedly safe Cd concentration (0.0022 mg L−1). Specimens from the pristine area (JUR) accumulated higher total Cd, as such as in its biologically active form in gills. Animals living in the polluted site (CUB) presented higher amounts of Cd in the mainly detoxifying tissue (hepatopancreas), which could be considered a pathway leading to tolerance for this metal. Multivariate analysis indicated that bioaccumulation (active, detoxified and total Cd) is linked to geno-cytotoxic damages. CUB subpopulation was considered more tolerant since it presented proportionally less damage and more capacity to allocate Cd in the main detoxifying forms and tissues.

Occurrence of heavy metals in sediment and their bioaccumulation in sentinel crab (Macrophthalmus depressus) from highly impacted coastal zone

The current study aimed to investigate the eight heavy metals (Fe, Cu, Zn, Cr, Ni, Co, Pb, and Cd) occurrence and risk assessment in the sediment and sentinel crab (Macrophthalmus depressus) from the mangrove and coastal environment of industrialized and mega city Karachi, Pakistan. The sediment analyzed for physiochemical properties (grain size composition, organic matter, and heavy metals), that presented significant variability (p < 0.05) among the selected sites. The environmental health and eco-toxicological profile of the habitat determined through the enrichment factor (EF), adverse effect index (AEI) and potential ecological risk index (RI) that revealed high anthropogenic influences along the Karachi coast. All heavy metals in crab showed significant spatial differences (p < 0.001) and the strong correlation between the essential and non-essential metals. Sediment-biota accumulation factor (SBAF) suggested active bio-accumulation (>1.0) in crabs for all metals, except Cr. Pb accumulation in crabs showed a significant increase (p < 0.05) with the exposure Pb levels in sediment, which indicated the potential of crab as a bioindicator of Pb contamination. Principal component analysis (PCA) concluded that environmental factors like seawater temperature, salinity, sediment grain size and organic matter had a significant association with different metal accumulation in crabs. The current study revealed the ecological significance of sentinel crab, M. depressus, as they endure with wide range (low to serious RI) of metal contaminated environment.

Effect of Mudflat Trampling on Activity of Intertidal Crabs

Many people visit intertidal mudflats to collect bait and seafood, or for eco-tourism and recreation, and as a consequence trample on the mudflats frequently. Trampling would not be life threatening to most animals in the intertidal flats as they have evolved hiding behavior to escape predation. However, what is the effect of trampling on the behavior of intertidal animals? In this study, the effect of mudflat trampling on the activity of crabs (e.g. fiddler crabs, sentinel crabs) living on the mudflat was explored. The number of crabs active on the mudflat surface in experimental plots (1.5 × 1.5 m2) before and after (10 min. and 30 min.) trampling of three different intensities (Heavy trampling = 60 steps; Moderate trampling = 20 steps; and No trampling) was compared in two different mudflat systems. After trampling, the number of crabs active on the surface decreased and was significantly lower than that of control plots. The more intensively trampled the mudflat was, the fewer crabs were active on the mudflat surface. Surprisingly, the number of active crabs did not recover even 30 min. after trampling. The results clearly support the hypothesis that trampling can severely interfere with the behavior of crabs living on intertidal mudflats.

Microhabitat differences in crab assemblage structures in a subtropical mangrove estuary on Iriomote Island, southern Japan

Crab assemblage structures in sandy flat, muddy flat and mangrove forest microhabitats in a mangrove estuary of the Urauchi River, Iriomote Island, southern Japan, differed clearly among the three microhabitats, species and individual numbers being greater inside the mangrove forest than on the flats. A similarity index showed distinct differences in species composition among the microhabitat assemblages, primarily due to the differential distributions of dominant species, such as the soldier crab Mictyris guinotae, sentinel crab Macrophthalmus convexus and sesarmid crab Perisesarma bidens. A canonical correspondence analysis indicated that the differences likely arose from among-microhabitat differences in the physical environment, the mangrove forest being characterized mainly by structurally complex mangrove roots, lower soil porewater temperatures and higher relative substrate elevation, the sandy flat by lower organic content of the sediment and higher porewater oxygen amount, and the muddy flat by higher levels of sediment water and organic material. The findings suggested that microhabitat-related physical differences are important factors determining crab distribution patterns in mangrove estuaries.

Patterns in the natural transmission of the parasitic dinoflagellate Hematodinium perezi in American blue crabs, Callinectes sapidus from a highly endemic area

The dinoflagellate Hematodinium perezi is a highly pathogenic endoparasite that infects blue crabs Callinectes sapidus and other decapods. Annual outbreaks of the parasite along the eastern seaboard of the USA indicate that transmission occurs at high rates; however, the timing and incidence of new infections are unknown. The aim of this study was to investigate the patterns and factors associated with the natural transmission of Hematodinium in juvenile crabs from a highly endemic site. A novel field experiment, using naive crabs as sentinels, was implemented to measure transmission. Over 965 juvenile crabs (instars C3–C10) collected from a non-endemic site were deployed for set periods of 3, 7, 10, and 14 days at a highly endemic site. Prevalence was 5.1% after a 3-day deployment and 88% after a 10-day deployment. This corresponded to a daily incidence of new infections of 1.7 and 8.8%, in the population, respectively. New infections progressed very quickly; 50% of infected crabs developed heavy infections after only 14 days. The influence of host molting on the transmission of the parasite was investigated by tagging 467 crabs using cyanoacrylate glue and small plastic tags. After 7-, 10-, and 14-day deployments, sentinel crabs were assessed and infections were found not to be associated with host molting. Lastly, two storm events, with high rainfall, strong winds, and lower temperatures, disrupted the natural transmission of H. perezi to sentinel crabs, essentially halting transmission in the coastal system. These sentinel studies indicate that transmission can occur rapidly and at very high levels in endemic sites and that it can be quickly modulated by changes in environmental conditions following storm events. Infections by Hematodinium may increase host mortality and thus may be a threat to blue crab populations in endemic areas.

A new species of Macrophthalmus Desmarest, 1823 (Crustacea: Decapoda: Brachyura: Macrophthalmidae) from Taiwan, with notes on four new records.

A new species of sentinel crab (family Macrophthalmidae), Macrophthalmus (Mareotis) purpureocheir sp. nov., from coral reefs is herein described from southern and eastern Taiwan. The new species can be distinguished from other species by a suite of characters, including the narrower and more convex carapace, the first anterolateral tooth protruding forward, the short and stout chelipeds, and the male first gonopod with short apical process, as well as the distinctive reddish purple chelae of the male. The identity of this new species is also supported by molecular evidence using the mitochondrial 16S rDNA and cytochrome oxidase subunit I (COI). Three additional species of Macrophthalmus, viz. M. crinitus Rathbun, 1913, M. definitus Adams & White, 1849, and M. milloti Crosnier, 1965, as well as Ilyograpsus paludicola (Rathbun, 1909) of the subfamily Ilyograpsinae Števčić, 2005, are also confirmed from Taiwan.

Allocleaning behavior by the sentinel crab Macrophthalmus banzai: a case of mutual cooperation

Abstract The macrophthalmid crab Macrophthalmus banzai performs allocleaning behavior, in which an individual feeds off the carapace or walking legs of a conspecific male or female. Cleaning continues until the recipient (‘cleanee’) rejects the cleaning or the cleaner ceases cleaning. In cases where the recipient did not reject the cleaning, the cleanee often retreated to its own burrow site after the cleaner ceased cleaning, allowing the cleaner to feed on its territory. We suggest that this is mutual cooperation, in which the cleaner assists the recipient to clean the body surface, and the recipient in return provides a feeding ground for the cleaner. Using field observation, we explored the factors responsible for the retreat of the cleanee in response to the cleaning behavior. Factors influencing the retreat of the cleanee were the time of the cleaning incident relative to low tide, the cleanee’s position relative to its own burrow, and the duration of the cleaning bout. The third factor showed that retreat was more common when the cleaning was thorough, which suggests that allocleaning is a form of mutual cooperation in M. banzai.

Population Divergence of the Sentinel Crab Macrophthalmus banzai is Consistent with Regional Breeding Season Differences

We compared the breeding season and genetic population structure of six sentinel crab (Macrophthalmus banzai) populations in southwestern Japan. Ovigerous females from Northern group populations (Wakayama, Kochi, and Tanega-shima) were observed from March to September, whereas ovigerous females from Southern group populations (Amami-oshima, Okinawa-jima, and Iriomote-jima) were observed from October to May. Genetic analysis using two markers corresponding to mitochondrial DNA encoding cytochrome oxidase subunit I (COI) and the large subunit of ribosomal RNA (16Sr-RNA) revealed a marked genetic difference between the Northern and Southern groups. A genetic boundary exists between the Tanega-shima and Amami-oshima populations, which is consistent with the interpopulation difference in the breeding season.

Setae for Gill-Cleaning of Six Species of Japanese Sentinel Crabs (Macrophthalmus)

Abstract The setae involved in the gill-cleaning mechanism of six species of Japanese sentinel crabs are described. The setae are classified as belonging to five types: anchor, serrate, simple, digitate-scale-setule, and normal setule setae. The anchor setae are further divided into ten sub types based on the combinations of digitate-scale setule, normal setule, anchor type, and the shape of their tip. Setae on out-growths and tips were compared with those identified in previous studies. As a result, the single row half anchor setae were found only in the subgenus Macrophthalmus and might be used as a special characteristic in the subgenus.

A new dwarf sentinel crab from Mayotte Island, western Indian Ocean (Decapoda: Brachyura: Macrophthalmidae)

A new sentinel crab of the genus Macrophthalmus is described from Mayotte Island, western Indian Ocean. The new species is remarkable by its very small size, with a carapace width not longer than 5.5 mm for the largest ovigerous females. It is closely related to Macrophthalmus (Chaenostoma) boscii Audouin, 1826.Affinities of these two species are discussed.

A remarkable case of fiddler crab, Uca spp., alpha diversity in Wallacea

A preliminary attempt was made to quantify the alpha diversity of fiddler crabs (Uca spp.) along a short transect across the interface between an intertidal mudflat and a largely Avicennia mangrove at Ambeua on the Indonesian island of Kaledupa in Sulawesi Tenggara, by means of visual counts within 2 m2 quadrats. An astounding diversity of up to six seemingly coexisting species per quadrat—and a total of seven such species within an area of 4 m2—was revealed. Four species of the ecologically equivalent sentinel crabs (Macrophthalmus) were also present in the quadrats. Seven fiddler crab species equates to more than half those known from Wallacea, more than one-third of all those known from Indonesia, and almost one-fifth of the entire Uca fauna of the Indo-West-Pacific.

Gender and Species Differences in Sentinel Crabs (Macrophthalmus) Feeding on an Indonesian Mudflat

Abstract This study investigates the influence of gender on feeding and habitat niches in the ocypodid sentinel crabs Macrophthalmus convexus and M. definitus feeding on a mudflat in the Wakatobi Marine National Park, Indonesia. Male M. convexus possess sub-equal chelae that are considerably larger than those of females and of those of both genders of M. definitus. Habitat location, food (Chl a) biomass index in microalgae and seagrass mats on muddy sediments, faecal material, and feeding rates were analysed in females and males of both species throughout the lunar cycle in July and August 2002. Food biomass content was significantly higher in the upper than in the lower mudflat (P = 0.008). The particle size of faecal material did not vary between species or between genders of M. definitus, but the faeces contained larger particles in males of M. convexus compared with females and both gender of M. definitus. Macrophthalmus convexus predominantly inhabited pools on the upper and mid mudflats, whereas M. ...

Why do eastern curlews Numenius madagascariensis feed on prey that lowers intake rate before migration?

Eastern curlews Numenius madagascariensis spending the nonbreeding season in eastern Australia foraged on three intertidal decapods: soldier crab Mictyris longicarpus, sentinel crab Macrophthalmus crassipes and ghost‐shrimp Trypaea australiensis. Due to their ecology, these crustaceans were spatially segregated (=distributed in ‘patches’) and the curlews intermittently consumed more than one prey type. It was predicted that if the curlews behaved as intake rate maximizers, the time spent foraging on a particular prey (patch) would reflect relative availabilities of the prey types and thus prey‐specific intake rates would be equal. During the mid‐nonbreeding period (November–December), Mictyris and Macrophthalmus were primarily consumed and prey‐specific intake rates were statistically indistinguishable (8.8 versus 10.1 kJ×min−1). Prior to migration (February), Mictyris and Trypaea were hunted and the respective intake rates were significantly different (8.9 versus 2.3 kJ×min−1). Time allocation to Trypaea‐hunting was independent of the availability of Mictyris. Thus, consumption of Trypaea depressed the overall intake rate. Six hypotheses for consuming Trypaea before migration were examined. Five hypotheses: the possible error by the predator, prey specialization, observer overestimation of time spent hunting Trypaea, supplementary prey and the choice of higher quality prey due to a digestive bottleneck, were deemed unsatisfactory. The explanation for consumption of a low intake‐rate but high quality prey (Trypaea) deemed plausible was diet optimisation by the curlews in response to the pre‐migratory modulation (decrease in size/processing capacity) of their digestive system. With a seasonal decrease in the average intake rate, the estimated intake per low tide increased from 1233 to 1508 kJ between the mid‐nonbreeding and pre‐migratory periods by increasing the overall time spent on the sandflats and the proportion of time spent foraging.

Allocleaning, fighting, waving and mating behavior in sentinel crabs (Brachyura: Ocypodoidea: Macrophthalmus)

Allocleaning, fighting, waving and mating behavior in sentinel crabs (Brachyura: Ocypodoidea: Macrophthalmus)

Sex-specific intertidal habitat use in subtropically wintering Bar-tailed Godwits

Habitat use by sexually dimorphic Bar-tailed Godwits (Limosa lapponica) was examined in an Australian estuary during the midwintering (November–December) and premigratory (March) periods of a nonbreeding season. In an area with two available habitats, Zostera seagrass beds and unvegetated sand flats, males occurred almost exclusively in seagrass, whereas the females occurred at equal densities in both habitats. Estimates of intake rates seemed greater for individuals foraging in seagrass (0.114–0.128 g dry mass (DM)·min–1) than on sand (0.064–0.087 g DM·min–1). Males appeared less well adapted for foraging on sand than in seagrass, and the presence of females could interfere with males' foraging on sand. The reason for the equal distribution of the females between the habitats probably lies in the inability of one particular habitat to support the entire population of females. Little interhabitat movement by individuals was detected. Within a habitat, sexes moved synchronously at the 1-ha scale but showed a degree of segregation at the individual scale, suggesting that some avoidance existed. Three diet types were observed in the godwits in the area: (1) dominated by soldier crabs (Mictyris longicarpus) on sand, (2) dominated by sentinel crabs (Macrophthalmus spp.) in seagrass, and (3) dominated by soft-bodied prey in seagrass.

Genetic relationship among Japanese sentinel crabs (Decapoda: Ocypodidae: genus Macrophthalmus)

Seven species (eight populations) of sentinel crabs (genus Macrophthalmus) from the Japan coast and Uca vocans and Ocypode ceratophthalma, were examined electrophoretically for genetic variations in 13 enzymatic and one non-enzymatic protein comprising 17 loci. Most species were highly differentiated from each other (Nei's genetic distance, 0.29–1.63). The least genetic distance was found between M. japonicus and M. banzai, the genetic distinctiveness of the two taxa being supported by three divergent loci with no common allele. The genetic relationships among Macrophthalmus species differed greatly from those inferred from morphological features, with a UPGMA tree suggesting that the sub-genus Macrophthalmus is polyphyletic.