Ecophysiological Studies of Cambarellus montezumae Crayfish from Xochimilco, Mexico: Population Phenology and Water Quality Habitat

Due to the antropogenic impact in Xochimilco channels area, the objective of this research focused on updating the status of the population of Cambarellus montezumae crayfish, in relation to the spatial-temporal variation of the physical-chemical dynamics of its habitat. Five samplings were carried out covering the warm and cold seasons of the annual cycle of the species. Thirteen surface and bottom water quality variables from six sampling stations were evaluated using multivariate analysis. Population phenology was analyzed using meristic indicators (wet weight WW, total length TL, and cephalothorax length CLT), abundance (catch per unit effort: CPUE), growth pattern, sex ratio, and sexually active forms. The habitat of the species showed great environmental heterogeneity by month and season. The dynamics of the population indicated that the period of greatest abundance, reproduction and active growth occurs predominantly in the warm season when temperatures are above 20°C. The results point out a high impact and disturbance on the population and habitat due to multiple stressors of human activity. Immediate measures are suggested that take into account adjustments to the Management Plan of the protected natural area, permanent monitoring programs and sustainable projects for the mitigation, rescue and productive management of the species.

Introduction

The Mexican crayfish fauna comprises around 10% of the total species worldwide (Crandall & De Grave, 2017). However, little is known about the status of native species, which are subject to severe environmental pressures due to fragmentation and disappearance of their habitat, introduction of exotic species, overexploitation of natural populations and various aspects of pollution, which affect their biodiversity (Vörösmartyet al., 2010, Latournerié-Cerveraet al., 2021, 2023). This unique heritage of Mexico, is threatened and at risk of disappearing. An example of this is the species Cambarellus montezumae, which has been recorded since the first indigenous settlements in the great lake of the Valley of Mexico, a site that has experienced enormous environmental impact, and which still persists in the remnants of the Xochimilco lake system, with the status of RAMSAR site, (FICHA RAMSAR, 2004), and natural protected area (ANP) (Paot, 2006). Previous studies of this species in the area, have phocused on the analysis of the C. montezumae population at the Cuemanco canoeing trail in Xochimilco, (Álvarez & Rangel, 2007), the dynamics of the population in relation to environmental parameters in the channels area, (Villa Narciso, 2010), as well as the estimation of the energy balance in natural conditions, and reproductive aspects carried out by García-Padilla (2010, 2014), which have guided our line of research on the rescue of native species and sustainable productive activities in Xochimilco. At this time, the purpose of this research was centered on correlating the environmental dynamics with the abundance of the natural population of C. montezumae to define its most recent status and delimit possible recovery and productive management strategies.

Materials and Methods

Study Area

Ejidos de Xochimilco y San Gregorio Atlapulco, Mexico City. Sampling stations: C–Cuemanco, B–Bordo, Tl–Tlilac, Am–Ampampilco, Vm–Valle Muñecas, J–Japon. SGA–W, San Gregorio Atlapulco wetland lagoons. Modified from Google Earth, 2024 (Fig. 1).

Fig. 1. Study area.

Habitat Characterization

Bi-monthly samplings were conducted at six locations in the Xochimilco channels area between the months of March and November during an annual cycle. The canals studied were: El Bordo, Japón, Tlilac and Cuemanco (external locations) and Ampampilco and Valle de las Muñecas (internal locations, see map). Water samples were taken from the surface and bottom strata with a 2.5 L van Dorn bottle. Thirteen physicochemical factors were measured (temperature, pH and conductivity) with a HANNA multianalyzer, redox potential, O₂ with a YSI 51B oximeter, NH₄, NO₂, NO₃ and P- ortho-PO₄ with a HACH DR870 equipment and alkalinity, total Ca and Mg hardness according to APHA methods (Bairdet al., 2017).

Analysis of Crayfish Population

Collections of C. montezumae were carried out in the same locations. We estimated the capture effort: catch per unit of effort (CPUE) which was standardized to 30 hauls per location, the organisms were captured in the first meter of the water column, adjacent to the riparian vegetation. A meristic analysis of all collected organisms was carried out measuring: wet weight (WW), Total Length (TL) and Cephalothorax Length (CTL), separation by sex was carried out, and males were also separated by morphs (MF-I: sexually active form) and MF-II, male inactive form. The abundance was recorded by sampling, sex and type of morph, calculating the proportion of sexes and the CPUE of each collection. To define the growth pattern of the organisms, the WW – TL relationship (W = K × TL^α) was calculated by sex and in all individuals of the sampled population.

Statistical Analysis

The dynamics of the habitat was analyzed using a fixed-effects factorial design, taking into account the factors: months, locations, strata and months grouped by seasons (warm and cold) and locations by position (external and internal). Tukey post hoc tests (p < 0.05) were performed to detect subsets. Multivariate analysis in principal components mode and discriminant type, was also used. The abundance of the crayfish population was determined by ANOVA contrasting the months of collection, with Tukey’s post hoc test (p < 0.05). The equality in the sex ratio (H₀:1:1) was analyzed by X² (p < 0.05). Linear regression was used to correlate the CPUE with the temperature of the sampling month and the growth pattern of the crayfish was adjusted by means of power regression. The analyses were performed using SPSS ver. 20 and JMP v. 10 (IBM SPSS Statistics. 20, 2011; SAS Institute Inc. JMP 10, 2012).

Results

Water Quality Indicators

Table I summarizes the thirteen water quality variables measured, contrasting the warm rainy season (May to September) with the cold season (November to March). It also indicates whether the contrast by season shows significant differences. The results pointed out significant differences by month, strata, spatial location and various interactions. To visualize these interactions, Fig. 2 is presented as a canonical graph of the discriminant analysis by months and seasons, where the variables that interacted significantly are shown as vectors. In the case of months, the discriminant variables were nine: conductivity, alkalinity, temperature (p < 0.000), phosphates, ammonium, redox potential, nitrites, oxygen and nitrates (p < 0.001). For the seasons, the discriminant variables were seven: temperature, phosphates, conductivity (p < 0.000), oxygen, nitrites, alkalinity and nitrates (p < 0.00), all of them show a very complex space-time variation in the water quality of the C. montezumae population in the study area.

Table I. Habitat Characterization

WQV	Season	Mean ± SE	CI 95%
T.°C	W	21.5A ± 0.27	20.9 – 22.1
	C	18.6B ± 0.27	18.0 – 19.1
O2	W	4.9 ± 0.25	4.4 – 5.5
	C	5.2 ± 0.37	4.5 – 6.0
Conductivity (mS)	W	764.6A ± 14.0	736.1 – 793.1
	C	442.7B ± 59.0	319.9 – 565.5
Redox potential (mv)	W	620.2A ± 77.2	463.5 – 776.9
	C	162.2B ± 34.9	89.4 – 234.9
pH	W	9.06A ± 0.11	8.82 – 9.29
	C	8.46B ± 0.16	8.11 – 8.81
Alkalinity	W	517.2 ± 60.9	393.6 – 640.8
	C	487.3 ± 82.8	314.9 – 659.6
NH4	W	0.31B ± 0.02	0.27 – 0.34
	C	0.61A ± 0.08	0.45 – 0.77
NO2	W	0.45B ± 0.06	0.32 – 0.58
	C	0.73A ± 0.13	0.44 – 1.01
NO3	W	63.8B ± 6.2	51.2 – 76.4
	C	85.2A ± 7.4	69.7 – 100.7
P-ortoPO4	W	15.7A ± 1.4	12.9 – 18.5
	C	12.7B ± 1.3	9.9 – 15.5
Total hardness	W	773.9B ± 27.2	718.7 – 829.0
	C	849.4A ± 36.2	774.1 – 924.7
Ca hardness	W	240.5 ± 10.6	219.1 – 261.9
	C	241.4 ± 15.9	208.3 – 274.5
Mg hardness	W	184.4B ± 6.5	171.2 – 197.6
	C	202.7A ± 8.8	184.4 – 221.1

Fig. 2. Multivariate means of the discriminate analysis of water quality in the Xochimlco canals, comparison by months (A) and seasons of the year (B).

Population Dynamics

From 996 crayfishes collected (we recorded 664 females and 305 males), a sex ratio to 2.1:1 female/male which was significantly different from the sex ratio (H₀ = 1:1), X² = 13.62 (p < 0.001). TL distribution with a clear right-tail asymmetry is showed in Fig. 3, (Mean ± SD = 1.87 cm ± 0.69 cm), goodness of normal fit was rejected, Shapiro-Wilk = 0.972, p < 0.001, specimens ranged from 0.51 cm TL to 4.96 cm TL.

Fig. 3. Abundance of the size class distribution (TL) of C. montezumae.

Fig. 3 includes a Quantile box plot and outliers (five females including the largest crayfish collected: WW. 2.68 g, TL 4.96 cm, and one male, MF-I), all corresponding to cold season. The comparison of TL distributions by seasons also showed asymmetry, but with a higher range in cold season.

The growth pattern, WW – TL equation of C. montezumae crayfish population is presented in Fig. 4.

Fig. 4. Relationship WW = β₀ TL^β for C. montezumae crayfish. (β₀ = 0.022, β = 3.022 ± 0.03, r² = 0.928, n = 957). Bivariate normal ellipse (P = 0.99).

Exponent β of the global WW – TL relationship was not significant different of 3, (isometric growth pattern), similar to female relationship exponent, β = 3.0, n = 664, r² = 0.91. Nevertheless, Morph I males had a 2.3 times higher WW average, than the females that could be their partners and β = 3.32, n = 76, r² = 0.92 (positive allometry growth), also they reached 3.5 times higher body weight than the sexually inactive form II, β exponent 2.89, n = 229, r² 0.86.

The abundance records and meristic characteristics of the crayfish in relation to the sampling months and by season are presented in Table II. These comparisons are shown with superscript notation, where averages with different letters indicate statistically significant differences (p < 0.05, Tukey post hoc test).

Table II. Abundance and Meristic Indexes of C. montezumae by Month and Season. Data are Mean ± SD

Month/Season	N	WW (g)	TL (cm)	CTL (cm)
March	106	0.49A ± 0.49	2.45A ± 0.86	1.18A ± 0.40
		.01 – 2.68	0.091 – 4.96	0.41 – 2.20
May	155	0.25B ± 0.19	2.09B ± 0.52	1.03B ±0.23
		0.01 – 1.31	0.83 – 3.61	0.41 – 1.66
July	360	0.17B ± 0.21	1.71C ± 0.59	0.84C ±0.27
		0.01 – 1.22	0.67 – 3.63	0.34 – 1.83
September	259	0.13B ± 0.16	1.60C ± 0.59	0.81C ±0.27
		0.01 – 1.20	0.51 – 3.72	0.26 – 1.67
November	89	0.27A ± 0.31	2.25A,B ± 0.75	1.07A ± 0.34
		0.01 – 1.30	0.51 – 3.72	0.40- 1.92
Warm season	774	0.17B ± 0.19	1.75B ± 0.60	0.87 ± 0.28
Cold season	195	0.39A ± 0.44	2.36A ± 0.81	1.13 ± 0.38

The lowest sizes and weights were recorded in the months of May to September, in contrast to March and November; similar trends were recorded in the comparison by season (warm – cold). The abundance values were highly significant for months, (X² = 268.7) and also for seasons X² = 345.9, p << 0.000, pointing out that the abundance of the crayfishes from May to September (warm season), corresponds to 80% of the total organisms collected in the annual cycle.

Fig. 5 shows the box plot and size distributions for both periods, the smallest sizes (5 mm TL to 7 mm TL) were recorded in the warm season, in the months of July and September, see Table III.

Fig. 5. Box plot and total length distributions of C. montezumae by seasons.

Table III. Total Length (TL) of C. montezumae Population from Xochimilco Mexico, in Relation to Months Samplings, Seasons and Sex Composition

Month	Sex	N	Mean	SD	Min	Max
Mars	Female	75	2.49	0.89	0.91	4.96
	MF-I	16	2.68	0.9	1.03	4.08
	MF-II	15	2	0.46	1.11	2.86
May	Female	118	2.09	0.53	0.92	3.61
	MF-I	11	2.53	0.36	1.81	2.98
	MF-II	26	1.91	0.43	0.83	2.76
Jul	Female	241	1.67	0.62	0.67	3.63
	MF-I	25	2.52	0.44	1.49	3.18
	MF-II	94	1.6	0.31	0.95	2.42
Sep	Female	168	1.52	0.54	0.51	3.09
	MF-I	15	2.39	0.53	1.33	3.72
	MF-II	76	1.64	0.6	0.64	3.33
Nov	Female	62	2.26	0.83	0.87	3.62
	MF-I	9	2.65	0.35	2.14	3.22
	MF-II	18	2.04	0.48	1.32	2.83
Warm	Female	527	1.72	0.61	0.51	3.63
	MF-I	51	2.48	0.45	1.33	3.72
	MF-II	196	1.66	0.47	0.64	3.33
Cold	Female	137	2.38	0.87	0.87	4.96
	MF-I	25	2.67	0.74	1.03	4.08
	MF-II	33	2.02	0.46	1.11	2.86

When we compare TL distributions by sex, Fig. 6, only MF-I distribution was normal, (Mean ± SD = 2.54 ± 0.57 cm. N = 76, Shapiro-Wilk, W Test = 0.972, p < 0.09), and minimum and maximum TL size of MF-I were recorded in Mars and November collections respectively. According to the data, the fraction of crayfishes with reproductive potential (sizes greater than 2 cm TL, see Fig. 6) would be equivalent to (37.6%) of the females in the population sample (n = 250), which could mate with (n = 76) of the MF-I males, Table III.

Fig. 6. Total length distributions of C. montezumae by sex.

This would involve a probability of successful encounters between sexes of 30.4% and taking into account that the proportion of MF-I males recorded between seasons was: n = 25 (cold) n = 51, (warm), the probability of mating would be double during the warm-rainy season of the year.

In Fig. 7 we correlate total abundance by month and sex, and CPUE which was standardized to 30 hauls at each sampling station, with the temperature data measured by month. From this data, a close correlation r² = 0.81 was obtained among these variables.

Fig. 7. Abundance, sex composition and CPUE – temperature - months of C. montezumae at Xochimilco channels.

Discussion

In recent decades, the human impact on aquatic habitats associated with industrial development, agricultural activities, excessive urban growth and multiple discharge of pollutants with limited or no regulation in environmental guidelines, has significantly influenced the deterioration of biodiversity in natural ecosystems located in the transverse volcanic belt of Mexico, sites where most species of the genus Cambarellus live (Vörösmartyet al., 2010, Nagendra & Ostrom, 2014, Pedraza-Laraet al., 2023).

On the other hand, as far as we have evidence, the design of this research condenses the most detailed study that has been carried out on the physical-chemical factors of water quality, as well as the spatial-temporal components of the population of the crayfish C. montezumae in the Xochimilco canals, covering the most contrasting periods of climatic variation, as well as the diverse human activities and their impacts that take place on the site. Thus, the prevailing water quality conditions in Xochimilco indicate that this habitat is an extremely heterogeneous area in its spatial component (canals in the inner area of the chinampas in contrast to those in the outer zone of the ANP, as well as in the strata of the water column). Also, highly significant variations are recorded in the levels of the physical-chemical parameters measured throughout the warm and cold months of the annual cycle. This environmental mosaic has become more complex and stressful in recent decades for the flora and fauna that still persists in the canal area.

According to the results of this study, the greatest abundance of the crayfish population is concentrated during the warm season (temperatures above 20°C), spanning the months of April to September. During this period, the factors that significantly intervene in the regulation of the physical-chemical dynamics of the species habitat were eight: temperature, conductivity, (ammonium + ammonia), redox potential, pH, phosphates, nitrates and nitrites. This period is characterized by a complex range of interactions that are combined with the rainy season and high levels of nutrients in the study area, which cause an increase in the aquatic productivity of the ecosystem, which is reflected in a greater abundance and diversity of phytoplankton species (Latournerié-Cerveraet al., 2021), which act as cascading triggers of various trophic levels, for example, they affect the modulation of the “charal”, (Chirostoma jordani) population in the channel area (Latournerié-Cerveraet al., 2023) and, which in turn are synchronized with the phenology of the crayfish population, triggering the reproduction and higher growth rates of the organisms.

Phenology is the study of the chronology of recurring seasonal biological events in the life cycle of a species. This capacity is critical, since it determines the state of development reached by an organism or population, while combining with particular components of its environment. At the same time, it is a key process that can link climate change to population persistence and possibly to community composition. Likewise, it has been reported that in the temperate zone, variation in phenology is often correlated with environmental variables, especially temperature (Forrest & Miller-Rushing, 2010).

In previous studies, focused on evaluating the growth of the crayfish in natural conditions, carried out in months of the warm season, we have reported for C. montezumae growth values of 0.1 mm/day (Latournerié-Cerveraet al., 2016c), as well as a greater intake of animal items, which increases the protein value of the ingested food (Latournerié-Cerveraet al., 2016b), such conditions define that the warm season at the study site, is the time of greatest reproductive activity, the data collected indicate that the proportion of male crayfish MF-I increases significantly in relation to the cold season (X² = 8.9, p < 0.005), which as a result, increases the probability of successful encounters between couples, an event that affects the active recruitment of offspring to the population, these data are confirmed by the record of very small sizes during the collections made during this period (5 mm TL to 7 mm of TL), in this way the abundance of the organisms during the warm season corresponds to the 80% of the total abundance of the measured cycle. It is thought that breeding at the right time confers fitness benefits both in terms of increased survival of offspring, and possibly improved parental fitness to survive until the next breeding season (Forrest & Miller-Rushing, 2010).

In the case of iteroparous species such as C. montezumae, the breeding season in the study area occurs predominantly during the warm months of the year, where various factors that act as drivers combine: temperatures above 20°C, overlap with the rainy season and high levels of nutrients from wastewater discharges, and runoff from the chinampa area coming from crops, which together trigger greater productivity in the channels area. This process that increases the resources for the growth of the crayfish, is not exempt from stressful levels in the concentrations of nitrites and toxic fraction of ammonia, since they can occur under particular conditions of high temperature and alkaline pH, and these conditions can produce: oxidative stress, reduced growth, susceptibility to pathogens, immune suppression and even mortality in the crayfish, Linget al., 2023. However, there is a positive “tradeoff” effect between the environmental mosaic and the controlling factor temperature, (Fry, 1971) that in conjunction with the greater availability of resources, trigger the reproduction and growth of the population.

On the other hand, although we have found females with eggs during the cold season, the interaction of the physical-chemical variables in the habitat of the species, turn out to be limiting for the reproductive event, survival and growth, given that the decrease in temperature, high concentrations of ammonium and nitrites, as well as low concentrations of dissolved oxygen and low levels of redox potential at the bottom of the channels, have an impact on a significant decrease in the recruitment and abundance of the crayfish population as we have referred to in Fig. 6 of this study.

Now, if we consider the current status of the C. montezumae population, in relation to the perception that fishermen in this locality have, on how the diversity and abundance of species in the Xochimilco channels has evolved from forty years ago until today, they report that the populations of frogs, “juiles”, white fish, “charales”, axolotls and crayfish, among other species, have been decreasing due to contributions of treated water, dredging of canals, installation of clandestine drains, contribution of agrochemicals, and the introduction of exotic species (carps and tilapias), (Von Bertrab Tamm, 2013, p. 156.). This information, coming from the actors directly involved in the exploitation of aquatic resources that form part of their family income, as well as a nutritional supplement in their diet, reflects the environmental problems that occur in the channels area, and indicates an extremely uncertain and conflictive future for this aquatic habitat and its native species such as C. montezumae. For this reason, it is relevant to point out that the information collected in this research is closely linked to previous studies on the status of the “charal” population in Xochimilco (Latournerié-Cerveraet al., 2021, 2023), as well as to the variability of water quality in this site and San Gregorio Atlapulco wetland (SGA) lagoons, (Latournerié-Cerveraet al., 2021, see map), where it is mentioned that this last locality presents greater homogeneity in its physical-chemical dynamics with respect to the channels area that defines this location as a site of lower impact, so it could be used to preserve and give continuity to the native species that still persist in the remnants of the lake system of the Valley of Mexico. Additionally, with the information collected in the present study, and previous research carried out in our laboratory on C. montezumae related to: growth of offspring with plant detritus, (Latournerié-Cerveraet al., 2006), bioenergetics of growth in field and laboratory conditions, (García-Padilla, 2010; 2014), effect of density and cover on survival and growth, (Latournerié-Cerveraet al., 2016a), it would be feasible to implement sustainable productive projects on native species in the chinampa area, using treated water from an artificial wetland, as has been demonstrated by Ramírez-Carrilloet al. (2009).

Concluding Remarks

The residual population of C. montezumae in the Xochimilco channels is subject to chronic environmental stress due to anthropogenic stressors of pollution and disturbance that vary spatially and temporally, degrading the ecological and environmental integrity of its habitat, and seriously threatening it with disappearance. These threats require immediate attention from all actors involved in the management and conservation of the ANP Ejidos de Xochimilco and San Gregorio Atlapulco, as well as adjustments to the management plan for this area. Taking into account the results of this study, it is evident that mitigation measures are required for these stressors, through continuous monitoring of the habitat, as well as research programs that impact the productive rescue of the species, and that contribute to avoiding and repairing these effects to improve the sustainability of the economy of the human groups settled in the area, and provide continuity to the habitat and preserve biodiversity in this site that is a unique heritage of Mexico.