Crab Species Research Articles

The spatiotemporal changes of crab community in the Yangtze River Estuary after the fishing ban

The Yangtze River Estuary is the traditional habitat of fishery resources in China and also one of the crab fishing sites, but nowadays the crab resources have been seriously affected by high-intensity anthropogenic disturbance. To understand the composition and diversity of crab community following the fishing ban, six surveys were conducted from August 2022 to November 2023 using the single-bag trawl method. This study examined the crab community composition, biodiversity, resource density, spatiotemporal distribution patterns, and main influencing factors. Results indicated that a total of 14 crab species lived in the Yangtze River Estuary. Matuta planipes and Portunus trituberculatus were dominant crabs in summer 2022. P. trituberculatus, Eriochier leptognathus, and Charybdis japonica were dominant crabs in autumn 2022. Then, E. leptognathus and Eriocheir sinensis were dominant crabs in winter 2023. Notably, the largest numbers of dominant crabs appeared in spring 2023, including M. planipes, P. trituberculatus, E. leptognathus, C. japonica, and E. sinensis. Three same dominant crabs (M. planipes, P. trituberculatus, C. japonica) were identified in the summer and autumn of 2023. Thereinto, P. trituberculatus was the most dominant crab. The abundance and biomass trends of estuary crabs were winter< spring< autumn< summer. The community diversity index, evenness index, and richness index were winter< summer< autumn< spring, indicating the seasonal changes in abundance, biomass, and biodiversity. Correlation and redundancy analysis revealed that dissolved oxygen and salinity were the most critical environmental factors, which affect the changes in crab community in the estuary. This study revealed the changing characteristics of crab resources in the Yangtze River Estuary after the fishing ban, and provided the essential data and scientific basis for resource conservation and management decisions.

A new species of freshwater crab from the East Usambara Mountains of Tanzania, East Africa, with a redescription of Telphusa infravallata Hilgendorf, 1898 (Brachyura: Potamoidea: Potamonautidae)

This work describes a new species of freshwater crab from the East Usambara Mountains of Tanzania from previously unidentified museum material. A second species from these mountains, T. infravallata Hilgendorf, 1898, is redescribed based on reexamination of the type material, and its gonopods and mandible are illustrated for the first time. Diagnoses, illustrations, and a distribution map are provided for these species.

Regional range extension of two xanthid crab species (Decapoda, Brachyura) to the mid-Sanriku Coast, the coldest waters off Honshu, Japan

Abstract This paper reports the first occurrences of two brachyuran crab species of the family Xanthidae MacLeay, 1838, viz., Actaea semblatae Guinot, 1976 and Gaillardiellus orientalis (Odhner, 1925), from the mid-Sanriku Coast, along the Pacific coast of northeastern Japan. While these records do not represent the northern limit of distribution of these species, they do show a range extension into the coldest waters of Honshu, the main island of Japan, probably due to global warming and changes in flow patterns of the local sea currents.

Unveiling the population structure and breeding patterns of Petrolisthes boscii (Audouin, 1826) a common intertidal inhabitant of Shivrajpur, Saurashtra Coast, Gujarat

The present study focused on investigating the population structure and breeding biology of a species of Porcellanid crab, Petrolisthes boscii (Audouin, 1826). Evaluating the population ecology of the species is essential considering its crucial role in ecological functions including the nutrition cycle and its potential vulnerability to environmental stressors. The samples were collected over a period of 12 consecutive months (from March 2019 to February 2020) in an area of 500 m2 during low tide, utilizing the catch-per-unit-effort (CPUE) method when the water receded. The collected specimens (859 individuals) were categorized into males (407 individuals), non-ovigerous females (452 individuals), and ovigerous females (303 individuals). The assessment of fecundity was conducted by measuring the egg characteristics, including the total number, size, and weight of the eggs, as well as the carapace width of the ovigerous females. There was an evident difference in size, with males (8.60 ± 2.76) being significantly larger compared to females (8.39 ± 2.46) (p < 0.001). The overall and monthly sex ratios were female-biased (1:1.17). Moreover, the size frequency distribution revealed a bimodal distribution in male as well as female individuals. Ovigerous females occurred in all the months, which shows that the species breeds continuously throughout the year, with peaks in the months of March to May and August to October. There was a significant positive relationship observed among the size of ovigerous females and their total number of eggs (130.39 ± 83.31), egg mass weight (150 ± 110 mg). The study may provide baseline information for future studies on the impacts of a continuously altering environment and the consequences of increasing anthropogenic pressure on coastal areas.

Food Habits of Eriphia Verrucosa (Eriphiidae) and Pachygrapsus marmoratus (Grapsidae) in the Mediterranean Coast of Eastern Libya in Sosa

The current study aims to determine the type and abundance of food for two species of crabs, Pachygrapsus marmoratus and Eriphia verrucosa, that inhabit the rocky beaches in the south. Mediterranean coast. A total of 40 crabs of each species collected during 2022 were used. We found that P. marmoratus and Eriphia verrucosa are carnivores, meaning they feed on what is available in their environment. Gastric fullness was determined. Food availability in habitats. The abundance of food in the stomach varies according to varieties, but the general trend was molluscas and crustaceans > Cnidarians > Algae > Seaweed > Fish; this is for the Pachygrapsus crab. Marmoratus, but the general trend was molluscas and cnidarians > And fish > Seaweed > And crustaceans > And algae. This is for the crab Eriphia verrucosa. This study provides information on the abundance and type of food by examining the stomach and knowing the percentage of its fullness and the type and abundance of food in the stomach.

Population structure and feeding habits of Carcinoscorpius rotundicauda in the bay environment, Southern Gulf of Thailand

This study presents the first comprehensive assessment of the population structure and feeding habits of Carcinoscorpius rotundicauda in Thailand. Sample collection was conducted using crab gill nets at seven sampling sites characterized by distinct ecosystem attributes in Pattani Bay between February 2019 and March 2020. Our findings indicate the presence of a single Asian horseshoe crab (HSC) species within the bay, with a sex ratio of approximately 1:1 (48.1 % males, 51.9 % females) that did not deviate significantly from parity. Habitat variation within the bay did not influence HSC abundance (P > 0.05) whereas monthly abundance fluctuations were highly significant (P < 0.001), peaking in March and reaching the lowest in September. Positive correlations were observed between HSC abundance and environmental factors including dissolved oxygen, temperature, water pH, water depth, and chlorophyll c concentrations. Linear regression analysis revealed a positive correlation between morphometric characteristics and body weight. However, multiple linear regression analysis indicated a negative relationship between body weight and telson length (TEL) and opisthosoma width (OW) of males, as well as TEL of females. The size at which 50 % of the HSC population reached maturity (L50) was estimated to be 12.2 cm for males and 13.5 cm for females based on prosomal width (PW). The average PW measurements of HSC at different egg stages (1–4) from developing to mature females was 14.4 cm, with corresponding body weights ranging from 224 to 243 g. Females at egg of stages 3 and 4 were found throughout the year, indicating multiple spawning events, particularly prevalent in January-April, and predominantly abundant at stations 1, 2, 5 and 6. HSC primarily consumed bivalves (22.1±21.2 %), followed by fishes (5.9±13.0 %) and crustaceans (2.9±9.0 %) by volumetric contribution (%V). This comprehensive study provides novel insights into the population dynamics and feeding ecology of HSC within Thailand. The findings establish a foundational framework for future research endeavors and offer critical data to inform the management and conservation of their habitats.

Comparative analysis of embryonic development and growth performance among two mud crab species and their hybrids

In modern aquaculture, inter-specific hybridization enhances traits, but its effects on embryonic development and growth in mud crabs (genus Scylla) remain underexplored. This study investigated the embryonic development and growth performance of Scylla paramamosain, Scylla serrata, and their hybrid offsprings from reciprocal crosses. We found that S. paramamosain and the hybrid (S. paramamosain ♀ × S. serrata ♂) produced smaller eggs with shorter development periods than S. serrata and the hybrid (S. serrata ♀ × S. paramamosain ♂). Both hybrids exhibited higher growth rates in the crablet stage than their purebred parents. Notably, the hybrid (S. serrata ♀ × S. paramamosain ♂) demonstrated significant heterosis in body weight and height, while the hybrid (S. paramamosain ♀ × S. serrata ♂) showed single-parent heterosis. While the shape of the frontal lobe spines in hybrids depended on the male parent. Development durations varied, with the longest observed in the hybrid (S. paramamosain ♂ × S. serrata ♀). Discriminant analysis of growth traits showed high accuracy across developmental stages, supporting the potential of inter-specific hybridization for enhancing mud crab aquaculture. This research provides valuable insights and germplasm resources for the aquaculture industry.

Feeding Behavior and Bait Selection Characteristics for the Portunidae Crabs Portunus sanguinolentus and Charybdis natator

Understanding the feeding behavior of Portunidae crabs with different baits can improve bait selection and is crucial for improving the effectiveness of crab fishing gear. This study, conducted in indoor experimental tanks, used trajectory tracking software and two types of natural baits (mackerel (Scomber australasicus) and squid (Uroteuthis chinensis)) to understand the behavior of Portunus sanguinolentus and Charybdis natator. Spatial distribution results showed that P. sanguinolentus was frequently present in the starting area (S1) and bait area (S3) in the control and treatment groups. However, C. natator was frequently present and concentrated in the S1 area compared to the middle areas S2 and S3, and only in the mackerel treatments were they observed to move to the S3 areas. The spatial distribution results indicate that P. sanguinolentus shows a stronger willingness to explore its surroundings, while C. natator is generally in a stationary, wait-and-see state. The swimming speeds of P. sanguinolentus and C. natator showed different trends. P. sanguinolentus showed continuous movement with no fixed speed when no bait was present in the control groups. However, when treated with mackerel and squid, the average swimming speed of P. sanguinolentus was faster (&gt;5 cm/s) in the first 10 min and showed a more stable movement speed when searching for the baits. C. natator showed a stationary or low movement speed when no bait was present in the control groups. However, when C. natator perceived the presence of the baits in the treatment groups, their movement speed increased in the first 10 min. In addition, there was no significant difference between male and female crabs of P. sanguinolentus and C. natator in movement speed in the control and treatment groups. Compared to C. natator, P. sanguinolentus might be more sensitive to natural baits, as shown by its movement from S1 to S3. The results indicate that the species of Portunidae crabs show different bait selections. Natural baits (mackerel and squid) are recommended for catching P. sanguinolentus in crab fisheries.

Panel data analysis to forecast the nutritional values of crab species caught in the United States between 1950 and 2021

Data from twelve distinct crab species collected in the USA between 1953 and 2021 were used in this investigation. By using the panel data analysis approach, estimates were generated on the data between 2007 and 2021 in light of the information gathered after gathering the nutritional values of the linked species. Based on the species of crabs that are cultivated or harvested, the purpose of these calculations is to ascertain the nutritional values of the crabs that will be available in the upcoming years. Knowing this is crucial because of the growing population and depletion of food supplies. The study's findings were compared with the actual values, and it was highlighted that it would be appropriate to estimate values that are closest to the actual values and investigate whether these estimates will be sufficient to fulfill the world's growing food supply.

Long-term PS micro/nano-plastic exposure: Particle size effects on hepatopancreas injury in Parasesarma pictum

With the widespread use of plastic products, microplastics and nanoplastics have emerged as prevalent pollutants in coastal aquatic ecosystems. Parasesarma pictum, a common estuarine crab species, was selected as a model organism. P. pictum was exposed to polystyrene (PS) particles of sizes 80 nm (80PS), 500 nm (500PS), and 1000 nm (1000PS), as well as to clean seawater (CK) for 21 days. Histological and fluorescent staining results showed that PS particles of all three sizes induced hepatopancreatic nuclear pyknosis, cell junction damage, and necrosis. The degree of damage was observed as 1000PS > 80PS > 500PS. Transcriptomic analysis revealed that major differentially expressed genes (DEGs) were associated with cellular processes, membrane components, and catalytic activity. The respiratory chain disruptions and immune exhaustion induced by 1000PS were notably stronger than those by 80PS and 500PS. Additionally, necrosis caused hepatopancreas injury in P. pictum rather than apoptosis or autophagy after long-term PS particle exposure. Furthermore, PS particles of all three sizes inhibited innate immunity, while the complement pathway was not significantly affected in the 80PS group. This study elucidated potential distinctions in how plastic particles of varying sizes (nanoplastics, microplastics, and micro/nanoplastics) impact P. pictum, providing a reference for toxicological mechanism research on microplastics and nanoplastics in aquatic organisms. Future research should focus on exploring long-term effects and potential mitigation strategies for microplastics and nanoplastics of more types and a wider range of particle size pollution in aquatic environments.

First report on the occurrence of &lt;i&gt;Microphallus indicus&lt;/i&gt; in the &lt;i&gt;Sartoriana spinigera&lt;/i&gt; freshwater crab in Bangladesh

Sartoriana spinigera is an edible freshwater crab species that plays an important role as an intermediate host of Microphallus indicus and Paragonimus westermani. P. westermani, the lung fluke, has been reported from northeastern India bordering Bangladesh and other parts of India. Nonetheless the existence of P. westermani in Bangladesh is yet to investigate. Therefore, the objective of the study was to estimate the prevalence of lung flukes in Bangladesh. During the survey, the metacercariae of food-borne trematodes were investigated from a total of 261 fresh-water crabs collected from different locations in Bangladesh. Only the metacercariae of M. indicus were recovered. The overall prevalence of M. indicus metacercariae was 26% with intensity of 1–63 per crab. The highest prevalence was recorded from Naogaon district (83.33%), followed by Sirajgonj (57.5%), Rajshahi (40%), Brahmanbaria (16%), Narsingdi (15%), Faridpur (10%), and Sunamgonj (7%). None of the crabs from Rangpur, Thakurgoan, Jashore, Meherpur, Magura, Barguna, Sylhet, Kishorgonj, Cox’sBazar, and Bandarban were infected. Among the water bodies, the highest number of infected crabs was found in the rivers (56%) followed by haor, canal, and ditches (5%). To the best of our knowledge, this study reports M. indicus for the first time from Bangladesh.

Spatio-temporal variation in mangrove crab diversity in five estuaries of Kerala, India

The present study investigated the community structure and faunal composition of mangrove crab assemblage of five estuaries in Kerala. Mangrove crabs were collected from different estuaries namely Puthuvype, Ayiramthengu, Dhalavapuram, Pullichira and Kottaramthuruth from January 2015 to December 2015. The numerical abundance was directly enumerated by handpicking crabs from the estuarial mangrove region from 100×100 cm quadrats from the estuarine mangrove regions. Thirteen brachyuran crab species were identified across the five estuaries, along with environmental and sedimentological parameters. Various diversity indices were calculated for spatial temporal comparisons. The study revealed that four of the estuaries exhibited similar crab species diversity, while Pullichira differed, displaying the lowest diversity due to habitat characteristics such as small islands or sand dunes and shallow depth. The calculated indices for species diversity, richness, dominance, evenness, taxonomic and phylogenetic relationships provide insights into the spatio-temporal variations of mangrove crab diversity. This study serves as a benchmark reference for future studies in these estuaries, and further monitoring and assessment of mangrove ecosystem health could support the development of ecosystem-based management strategies for deteriorating mangrove ecosystems.

Pseudolitochira spinosa, a new species of pilumnid crab from Panglao, Philippines, with a note on P. setosa (A. Milne-Edwards, 1873) (Crustacea, Brachyura, Pilumnoidea)

A new species of pilumnid crab, Pseudolitochira spinosa sp. nov., is described from a seagrass bed in Panglao, Bohol, central Philippines. The new species is morphologically most similar to P. maenosonoi Ng &amp; Clark, 2022, from Okinawa, Japan, in its proportionately wide carapace, but can be distinguished by the possession of prominent anterolateral spines, distinct spines on the merus of the cheliped and the presence of a well-developed sharp tooth on the inner angle of the cheliped carpus. The taxonomy of the poorly known P. setosa (A. Milne-Edwards, 1873) from New Caledonia is also discussed and a lectotype selected.

A documented checklist of the Crustacea (Stomatopoda, Decapoda) of the southern Guianas (Guyana, Suriname, French Guiana, Brazil Amapá)

A documented checklist of the Crustacea (Stomatopoda, Decapoda) is provided for the southern Guianas region (sGuianas), a homogeneous ecoregion including Guyana, Suriname, French Guiana and the Brazilian State of Amapá. The history of crustacean collections undertaken there between 1759 and 2022 is summarized. In total, 529 species are listed. Biodiversity varies between countries: 165 species in Guyana; 317 in Suriname, 343 in French Guiana, and 315 in Brazil Amapá, as a direct result of different sampling efforts. There are 22 Stomatopoda and 507 Decapoda, ranked by numerical diversity as Brachyura (206), Caridea (113), Anomura (85), Dendrobranchiata (67) and others (36). The list is analyzed with the species classified by major biotopes, distinguishing those from freshwater, mangroves and estuaries, and frankly marine environments. Regional comparisons are made in the Western Atlantic showing that the sGuianas marine fauna is depauperate compared to that of other regions. This is explained by the influence of the Amazon River plume, carrying desalinated water and fine sediments, which leads to the reduction of coral reef formations in sGuianas. Only a few species of freshwater crabs (genera Kunziana and Microthelphusa) are endemic to the region. The pace of species discovery over the years indicates that the sGuianas fauna remains still imperfectly known and that probably more than 600 species are present in the region.

Predation scars provide a new method to distinguish native and invasive crab predation on mollusc prey.

Crab species are increasingly important socioeconomic resources that are threatened by human exploitation, climate change, and invasive species, such as European green crabs (Carcinus maenas). However, the continued health of their populations is often uncertain given the limited long-term population data, necessitating alternate approaches to ensure their continued viability. Furthermore, C. maenas are one of the most highly invasive and destructive marine species globally, posing a threat to local ecosystems and species, including socioeconomically important crabs and their mollusc prey. Improved understanding of C. maenas invasions and their impacts on local crab and mollusc resources is therefore vitally important. Here, we present a new method for identifying species-level presence and relative abundances of important crab species, including invasive C. maenas, from the scars they leave on their prey. We conducted controlled manipulative feeding experiments in which individuals of Dungeness crabs (Metacarcinus magister), red rock crabs (Cancer productus), and C. maenas, were allowed to attack snails (Tegula funebralis) and produce sublethal shell damage. Resulting shell damage was photographed and landmarked for geometric morphometric analyses to determine any differences in the shape of shell damage between crab species. There were statistically significant differences between the shape of shell damage created by all three crab species (p < .0001). Shell damage formed a gradient from narrow/deep (C. productus) to shallow/wide (C. maenas) with M. magister as an intermediate form. Our method provides a novel, cost-effective tool for long-term species-specific reconstructions of crab populations and assessing the broader ecological impacts of C. maenas invasions that can inform management and mitigation for these three important crab species.

Species diversity and catch per unit effort (CPUE) of Portunidae in Batubara, North Sumatera, Indonesia

Abstract Crabs from the family of Portunidae are distributed widely in Indonesian waters, including the blue swimming crabs which has been exploited as a target species to meet the export demand and economic needs 3 of the capture fisheries sector. Crab catches from Portunidae family makes a major contribution to marine fisheries production in Batubara Regency, North Sumatra, Indonesia. The purpose of this study was to analyze the species diversity and catch per unit effort (CPUE) of crabs of Portunidae family in January–March 2023 in Tanjung Tiram Waters, Batu Bara Regency, North Sumatra, Indonesia. The fishing area was located right across the Malacca Strait, which is congested with international shipping traffic. Data were obtained through observations and community interview. Catch per unit effort (CPUE) of crabs was analyzed. The results showed about five species of crab from the Portunidae family were caught, including Portunus pelagicus, Scylla serrata, Charybdis feriata, Charybdis affinis, and Charybdis natator. The avearga CPUE value of target species Portunus pelagicus was 8,8 kg/trip.

Mapping the habitat distribution of horseshoe crabs (Tachypleus gigas) in Pamekasan, Madura Island, Indonesia

Abstract Horseshoe crabs, often known as Belangkas or Mimi, is one of the ancient marine faunas with protected conservation status. Horseshoe crabs are distributed in coastal waters of Indonesia of the islands of Sumatra, Java, Kalimantan, and Sulawesi, which are often caught as bycatch. Horseshoe crabs’s bloods were uniquewhich contain amebocytes as a test material for the presence of endotoxin bacteria. The purpose of this study was to identify the species of horseshoe crabs and to analyze environmental conditions, as well as the distribution of horseshoe crabs in the coastal waters of Pamekasan, Madura Island. This study was conducted in June 2023 by collecting data from crab fishers. ArcGIS was applied to delineate the distribution of horseshoe crab. The identification results showed that there was one species horseshoe crab of the Tachypleus gigas in the waters of Polagan Village, Galis District, Pamekasan Regency. The environmental condition of the waters in Polagan Village, Galis District, and Pamekasan Regency was relatively good. Habitat mapping is one way to protect these animals from the threat of extinction and support conservation efforts.

Generalist species exhibit more genetic structure in comparison to a habitat specialist: Evidence from a phylogeographic study of two freshwater crabs (Decapoda: Potamonautidae: Potamonautes), implications for habitat conservation.

During the present study, the phylogeography of the wetland specialist, freshwater crab, Potamonautes flavusjo, was investigated and compared to that of the ubiquitous, generalist, P. sidneyi, using DNA sequence data from the mitochondrial cytochrome oxidase subunit one (COI). We inferred the evolutionary history of each species and compared their population-level genetic structure by constructing haplotype networks and using an analysis of molecular variation. Additionally, we explored the evolutionary relationship between southern African lentic and lotic freshwater crab species by examining the usefulness of carapace attributes in relation to genetic indices and a species' assumed dispersal capacity. In the lentic species, P. flavusjo, a single interconnected haplocluster characterized by shared haplotypes was observed, suggesting marked maternal dispersal, a result corroborated by the low F ST values. In contrast, for the lotic species, P. sidneyi two distinct haploclusters and marked genetic differentiation was observed indicating the absence of maternal dispersal, a result corroborated by the high F ST values. The phylogenetic relationship in P. sidneyi was further investigated using a maximum likelihood and Bayesian inference analyses with the addition of sequence data from the mitochondrial 16S rRNA locus to estimate divergence times. Three species delimitation methods (ASAP, PTP, and bGMYC) were used to explore the presence of distinct lineages in P. sidneyi. The phylogenetic results indicated that within P. sidneyi two clades were present, while divergence time estimates suggest cladogenesis during the middle to late Pleistocene. The species delimitation methods used showed moderate congruence, however all oversplit the number of putative lineages. Our results indicated that P. sidneyi is a species complex comprised of two cryptic lineages, occurring in sympatry contemporarily possibly alluding to secondary contact. Carapace height was found to have no discernible influence on the genetic indices and presumed dispersal capabilities of mainland southern African freshwater crab species. The importance of our results are discussed in terms of conservation of freshwater habitats.

Haplotype diversity of coastal horseshoe crab (Tachypleus gigas, Muller 1785) based on 16S rRNA gene markers as a basis for conservation

Abstract Tachypleus gigas is one of horseshoe crab species found in Indonesia, but does not have sufficient molecular biology information available. This study aims to predict the populations health of T. gigas from the waters of Langkat, Semarang, and Bintan; through analysis of haplotype diversity based on 16S rRNA gene markers. The observation was conducted from November 2022 until April 2023. Sample’s total DNA was isolated, extracted, amplified and then sequenced to obtain the nucleotide base sequence. The BLASTn results showed that the samples were validated as Tachypleus gigas and the genetic distance between locations showed a close kinship relationship between the three. The population health of the horseshoe crabs from Langkat and Semarang were indicated good with high haplotype diversity values, meanwhile the Bintan indicated poor health with low haplotype diversity values. This study of haplotype diversity provided the starting point to the conservation of horseshoe crab T. gigas

Competition is stronger between than within species in two coexisting hermit crab species

Both intra- and interspecific competition influence the partitioning of limited resources; the relative importance of each type of competition in resource distribution is influenced by several factors, including resource availability and population abundance. Several hermit crab species of the genera Calcinus and Clibanarius coexist, competing for the shells of the same gastropod species. The relative abundance of these species varies along the intertidal gradient, from a bias toward Clibanarius in the upper intertidal to a tendency toward Calcinus in the lower intertidal. We assessed the strength of intra- versus interspecific competition in Cli. albidigitus and Cal. californiensis by comparing the number of successful usurpations of preferred shells in single-species versus mixed-species trials. We performed these comparisons under four scenarios, varying the total individuals and their relative abundance (1.7:1, 1:1, or 1:1.7 ratio) to simulate demographic conditions along the intertidal gradient. There were more shell usurpations in mixed-species trials under all scenarios except for the 1:1 ratio at high total abundance. Calcinus californiensis usurped more shells than Cli. albidigitus in all mixed-species treatments, even in cases where Cli. albidigitus was more abundant. Our results show that interspecific competition is stronger than intraspecific competition, which could drive the competitive exclusion of Cli. albidigitus, the comparatively weaker species.