Non-lethal sampling for stable isotope analysis of pike Esox lucius: how mucus,scale and fin tissue compare to muscle

Stable isotope analysis (SIA) was used to examine the isotopic relationships between dorsal muscle and fin, scale and epidermal mucus in pike Esox lucius. δ¹³C and δ¹⁵N varied predictably within each tissue pairing, with conversion factors calculated for the surrogate tissues, enabling their application to the non-lethal sampling of E. lucius for SIA.     

Fin tissues as surrogates of white muscle when assessing carbon and nitrogen stable isotope levels for Arctic and brook char

Arctic char (Salvelinus alpinus) are a fish species ubiquitous to the fresh waters of Arctic region and brook char (Salvelinus fontinalis) are similarly common across the sub-Arctic region of eastern Canada. Populations can be small in numbers, especially farther north thus it is important to develop non-lethal methods of sampling these fish to minimize the invasiveness and impact of scientific research. We examined the stable isotopes of nitrogen and carbon in white muscle, caudal fin, and adipose fin tissues of Arctic char and brook char (S. fontinalis) from northern Quebec and Labrador, Canada. Our results revealed several broad conclusions. First, differences among muscle, caudal fin, and adipose fin tissues were ~1?‰ for freshwater Arctic and brook char. Second, the two species within the same drainage had similar stable isotope levels and tissue differences. Third, anadromous Arctic char show similar, non-significant differences among these tissues for δ¹⁵N, but muscle δ¹³C was highly enriched. Fourth, the stable isotope levels and tissue differences were the same for anadromous Arctic char from two watersheds where char use distinctly different ocean environments. Overall, it appears that caudal fin tissue in particular is a useful surrogate for white muscle δ¹³C and δ¹⁵N levels for Arctic and brook char in this region and thus, a non-lethal collection of a small sample of caudal fin tissue will provide an accurate measure of white muscle isotope levels.     

Is filament clipping an effective tool for tissue sampling in <Emphasis Type="Italic">Hippocampus guttulatus</Emphasis>?

Examining genetic diversity, population structure, and geographic distribution has become an important part in the conservation strategies of endangered populations. However, these studies rely on tissue samples collection for DNA analysis which may be problematic for species with a sensitive conservation status. Partial fin-clipping has been employed for tissue collection, due to the increased popularity of DNA-based analysis for ecological and fisheries studies, however, fin clipping can potentially affect behavior, swimming performance, predator avoidance and the ability to find and capture prey. This study aimed to test the effects of filament clipping using captive breed seahorses (Hippocampus guttulatus) as an alternative tool for tissue sample. Clipped filaments regrew on average 0.05?±?0.02 mm/day for 3 months and no mortality or disease was observed during the experiment. Filaments provided enough tissue for DNA analysis. This study provided valuable information regarding a new sampling technique that does not impair the seahorse locomotion. This methodology may be used in population’s genetic studies of other species that have skin filaments as a morphological trait.     

Application of non‐lethal stable isotope analysis to assess feeding patterns of juvenile pallid sturgeon Scaphirhynchus albus: a comparison of tissue types and sample preservation methods

Traditional techniques for stable isotope analysis (SIA) generally require sacrificing animals to collect tissue samples; this can be problematic when studying diets of endangered species such as the pallid sturgeon Scaphirhynchus albus. Our objectives were to (i) determine if pectoral fin tissue (non‐lethal) could be a substitute for muscle tissue (lethal) in SIA of juvenile pallid sturgeon, and (ii) evaluate the influence of preservation techniques on stable isotope values. In the laboratory, individual juvenile pallid sturgeon were held for up to 186 day and fed chironomids, fish, or a commercially available pellet diet. Significant, positive relationships (r² ≥ 0.8) were observed between fin and muscle tissues for both δ¹⁵N and δ¹³C; in all samples isotopes were enriched in fins compared to muscle tissue. Chironomid and fish based diets of juvenile pallid sturgeon were distinguishable for fast growing fish (0.3 mm day^?1) using stable δ¹⁵N and δ¹³C isotopes. Frozen and preserved fin tissue δ¹⁵N isotopes were strongly related (r² = 0.89) but δ¹³C isotopes were weakly related (r² = 0.16). Therefore, freezing is recommended for preservation of fin clips to avoid the confounding effect of enrichment by ethanol. This study demonstrates the utility of a non‐lethal technique to assess time integrated food habits of juvenile pallid sturgeon and should be applicable to other threatened or endangered species.     

Variation in stable‐isotope ratios between fin and muscle tissues can alter assessment of resource use in tropical river fishes

Carbon and nitrogen stable‐isotope ratios were compared of fin and muscle tissue from 15 fish species collected from seven headwater rivers in eastern and western Thailand. In addition, two‐source stable‐isotope mixing models were used to derive estimates of each fish's reliance on allochthonous and autochthonous energy based on fin and muscle tissues. Across the dataset, fish fin was enriched in ¹³C relative to muscle by c. 1·5‰. Variation in δ¹⁵N between tissues was below statistically significant levels. Estimates of autochthonous resource use calculated from fin tissue were on average 15% greater than those calculated from muscle. Linear mixed‐effects models indicated that inter‐tissue variation in estimates of resource use was predominantly related to inter‐tissue variation in δ¹³C. Fish fin is a credible and desirable alternative to tissues such as muscle or liver which require destructive sampling of fishes. Care must be taken, however, when estimating resource use or interpreting previous estimates of resource use derived from different tissues.     

Variation in carbon and nitrogen isotopic ratios of fin and muscle tissues of Longnose Gar (Lepisosteus osseus) and Smallmouth Buffalo (Ictiobus bubalus)

Fin clips have been proposed as a non-lethal and non-invasive alternative to dorsal muscle samples in stable isotope analysis. However, potential differences in elemental composition and turnover rates can bias inferences when different tissues are combined. Here, we tested the average difference and correlation of the isotopic signature of δ¹³C and δ¹⁵N between muscle and fin samples in two arge-bodied fishes: Longnose Gar (Lepisosteus osseus) and Smallmouth Buffalo (Ictiobus bubalus). We found that δ¹⁵N signatures of muscle and fin tissues were strongly and positively correlated for both species, although the muscle tissue for Smallmouth Buffalo was slightly more enriched in δ15N. δ¹³C signatures of both tissues were significatively different and not strongly correlated for Longnose Gar, but similar and strongly correlated for Smallmouth Buffalo. Our results suggest that fin and muscle tissue can be combined for analyses of δ¹⁵N, but correction for higher enrichment of muscle tissue may be necessary for Smallmouth Buffalo. Conversely, combining fin and muscle tissue for analysis of δ¹³C requires more caution due to their weaker correlation and dependence of species identity.     

Using Bayesian stable isotope mixing models to estimate wolf diet in a multi-prey ecosystem

Stable isotope analysis (SIA) of wolf (Canis lupus) tissues can be used to estimate diet and intra-population diet variability when potential prey have distinct δ¹³C and δ¹⁵N values. We tested this technique using guard hairs collected from 44 wolves in 12 northwestern Montana packs, summer 2009. We used hierarchical Bayesian stable isotope mixing models to determine diet and scales of diet variation from δ¹³C and δ¹⁵N of wolves and potential prey, white-tailed deer (Odocoileus virginianus), mule deer (Odocoileus hemionus), elk (Cervus canadensis), moose (Alces alces), snowshoe hare (Lepus americanus), and other prey. As a check on SIA results, we conducted a separate diet analysis with temporally matched scats (i.e., collected in summer 2008) from 4 of the same packs. Wolves were centered on the ungulate prey in the isotope mixing space. Both methods revealed differences among pack diets and that wolves may consume moose in greater proportions than predicted by available biomass. Stable isotope analysis, and scat results were not entirely concordant; assumptions related to tissues of use in SIA, hair growth period in wolves, and scat sampling may have contributed to a mismatch between methods. Incorrect fractionation values, insufficient separation of prey in the isotope mixing space, choice of prior information in the Bayesian mixing models, and unexplained factors may have distorted diet estimates. However, the consistently high proportion of moose in pack diets suggests that increased population monitoring would benefit management of moose and wolves. Our results also support suggestions of other researchers that species-specific fractionation values should be used whenever possible, and that SIA may sometimes only provide indices of use for general groups of prey (e.g., large ungulates). © 2012 The Wildlife Society.     

Effect of nutritional condition on variation in δ13C and δ15N stable isotope values in Pumpkinseed sunfish (Lepomis gibbosus) fed different diets

Stable isotope analysis is frequently used to infer resource use in natural populations of fishes. Studies have examined factors, other than diet, that influence δ¹⁵N and δ¹³C including tissue-specific rates of equilibration and starvation. Most such studies completed under laboratory conditions tightly control food quantity and its isotopic composition, but it is also necessary to evaluate the influence of these factors under more natural conditions. Using pumpkinseed sunfish (Lepomis gibbosus) we evaluated whether restricted rations below minimum daily requirements affects tissue equilibration to a change in diet by holding fish on two treatments that often reflect divergent resource use in natural populations (pelagic zooplankton or littoral macroinvertebrates). Over 42 days, δ¹⁵N values increased while δ¹³C values did not change, additionally neither were related to diet treatment. Increased δ¹⁵N values were negatively related to body condition while δ¹³C values were not, indicating that stable isotope values were more affected by decreasing body condition than by diet. Additionally, δ¹⁵N values changed more in the blood and liver tissues than in white muscle tissue, indicating that restricting food availability had greater effects on tissues with greater metabolic activity. We hypothesize that stable isotope values of consumers are subject to a tissue-specific trade-off between sensitivity to changes in resource use and resistance to the effects of low resource availability. This trade-off may require consideration in stable isotope studies of wild populations facing periodic limitations of food availability.     

Seahorse (Hippocampinae) population fluctuations in the Ria Formosa Lagoon,south Portugal

Comparisons of three sets of surveys in the Ria Formosa Lagoon, Portugal, over a 13 year period (2001–2002, 2008–2009 and 2010–2013) revealed significant population fluctuations in at least one of the two seahorse (Hippocampinae) species living there, and that those fluctuations were potentially associated with habitat changes in the lagoon. After a significant decline between the first two survey periods (2001–2002 v. 2008–2009), long‐snouted seahorse Hippocampus guttulatus populations increased significantly between 2008–2009 surveys and new 2010–2013 surveys. There were no significant differences in H. guttulatus populations between the 2001–2002 and 2010–2013 surveys. In contrast, there were no significant differences in short‐snouted seahorse Hippocampus hippocampus densities among the 16 sites surveyed throughout the three sampling periods, although the ability to detect any change was hampered by the low densities of this species in all time periods. Fluctuations in H. guttulatus densities were positively correlated with the percentage of holdfast coverage, but with none of the other environmental variables tested. These results highlight the importance of holdfast availability in maintaining stable seahorse populations. While population fluctuations are certainly more promising than a consistent downward decline, such extreme fluctuations observed for seahorses in the Ria Formosa Lagoon could still leave these two species vulnerable to any additional stressors, particularly during low density periods.     

Estimation of growth and food consumption in juvenile Japanese flounder Paralichthys olivaceus using carbon stable isotope ratio δC under laboratory conditions

To estimate the accumulated food consumption and growth of juvenile Japanese flounder Paralichthys olivaceus, we investigated the relationships between individual food consumption and growth, and the change in the stable carbon isotope ratio (δ¹³C). Japanese flounder juveniles were individually reared and their diet was switched from one formulated feed EP1 (δ¹³C = − 19.47‰) to another EP3 (δ¹³C = − 17.21‰) and fed at different feeding regimes. After the switch, the δ¹³C content of the dorsal muscle was exponentially shifted to a different level in proportion to the feeding and growth rates. Therefore, measuring the carbon stable isotope ratio is a useful tool for estimating the food consumption and growth rate of juveniles. In addition, since the velocity of change and the asymptotic value of the carbon stable isotope ratio varied in muscle, caudal fin and liver tissue, different tissues can be used for different time scale estimations.     

Nonlethal sampling for stable isotope analysis of juvenile Chinese sturgeon (Acipenser sinensis): Comparing δ13C and δ15N signatures in muscle and fin tissues

We compared δ¹³C and δ¹⁵N values of muscle with fin from juvenile Chinese sturgeon (Acipenser sinensis), to evaluate the feasibility of using nonlethal (fin) as an alternative to lethal (muscle) sampling. Size and lipid effect on the relationship between fin and muscle were also investigated. Dorsal muscle (DM) and fin clip (FC) were collected from A. sinensis with different body length (120–373 mm) in the Yangtze Estuary for isotope analysis. The result showed that (1) muscle isotope values could estimated by the values of fin, from either use the regression model (δ¹³C_DM = 0.939 × FC ? 2.577; δ¹⁵N_DM = 0.737 × FC + 4.638) or constants factors (δ¹³C_DM = δ¹³C_FC ? 1.27; δ¹⁵N_DM = δ¹⁵N_FC + 0.59); (2) no size‐based relationships with δ¹³C and δ¹⁵N from either fin or muscle; (3) lipid extraction significantly improving the fin and muscle regression model fit for both δ¹³C and δ¹⁵N values. Therefore, this study support the use of nonlethal fin tissues for isotope analysis of juvenile A. sinensis, and will allow trophic studies to avoid the effect of lipid accumulation from muscle.     

Tissue turnover and stable isotope clocks to quantify resource shifts in anadromous rainbow trout

Stable isotopes can illuminate resource usage by organisms, but effective interpretation is predicated on laboratory validation. Here we develop stable isotope clocks to track resource shifts in anadromous rainbow trout (Oncorhynchus mykiss). We used a diet-switch experiment and model fitting to quantify N stable isotope (δ¹⁵N) turnover rates and discrimination factors for seven tissues: plasma, liver, fin, mucus, red blood cells, muscle, and scales. Among tissues, diet-tissue δ¹⁵N discrimination factors ranged from 1.3 to 3.4 ‰. Model-supported tissue turnover half-lives ranged from 9.0 (fin) to 27.7 (scale) days. We evaluated six tissue turnover models using Akaike’s information criterion corrected for small sample sizes. The use of equilibrium tissue values was supported in all tissues and two-compartment models were supported in plasma, liver, and mucus. Using parameter estimates and their uncertainty we developed stable isotope clocks to estimate the time since resource shifts. Longer turnover tissues provided accurate estimates of time since resource switch for durations approximately twice their half-life. Faster turnover tissues provided even higher precision estimates, but only within their half-life post-switch. Averaging estimates of time since resource shift from multiple tissues provided the highest precision estimates of time since resource shift for the longest duration (up to 64 days). This study therefore provides insight into physiological processes that underpin stable isotope patterns, explicitly tests alternative models, and quantifies key parameters that are the foundation of field-based stable isotope analysis.     

Small Tails Tell Tall Tales – Intra-Individual Variation in the Stable Isotope Values of Fish Fin

Background

Fish fin is a widely used, non-lethal sample material in studies using stable isotopes to assess the ecology of fishes. However, fish fin is composed of two distinct tissues (ray and membrane) which may have different stable isotope values and are not homogeneously distributed within a fin. As such, estimates of the stable isotope values of a fish may vary according to the section of fin sampled.

Methods

To assess the magnitude of this variation, we analysed carbon (δ ¹³C), nitrogen (δ ¹⁵N), hydrogen (δ ²H) and oxygen (δ ¹⁸O) stable isotopes of caudal fin from juvenile, riverine stages of Atlantic salmon (Salmo salar) and brown trout (Salmo trutta). Individual fins were sub-sectioned into tip, mid and base, of which a further subset were divided into ray and membrane.

Findings

Isotope variation between fin sections, evident in all four elements, was primarily related to differences between ray and membrane. Base sections were¹³C depleted relative to tip (~ 1 ‰) with equivalent variation evident between ray and membrane. A similar trend was evident in δ ²H, though the degree of variation was far greater (~ 10 ‰). Base and ray sections were ¹⁸O enriched (~ 2 ‰) relative to tip and membrane, respectively. Ray and membrane sections displayed longitudinal variation in ¹⁵N mirroring that of composite fin (~ 1 ‰), indicating that variation in¹⁵N values was likely related to ontogenetic variation.

Conclusions

To account for the effects of intra-fin variability in stable isotope analyses we suggest that researchers sampling fish fin, in increasing priority, 1) also analyse muscle (or liver) tissue from a subsample of fish to calibrate their data, or 2) standardize sampling by selecting tissue only from the extreme tip of a fin, or 3) homogenize fins prior to analysis.     

Stable isotope fractionation between maternal and embryo tissues in the Bonnethead shark (<Emphasis Type="Italic">Sphyrna tiburo</Emphasis>)

Evaluating tissue fractionation between mothers and their offspring is fundamental for informing our interpretation of stable isotope values in young individuals and can provide insight into the dynamics of maternal provisioning. The objectives of this study were to investigate the isotopic relationships between maternal reproductive (i.e., yolk, yolk-sac placenta) and somatic tissues (i.e., muscle and liver) relative to embryos in the Bonnethead Shark Sphyrna tiburo, to evaluate the fractionation of stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopes between these tissues. Additionally, we examined intra-uterine variability in the isotopic relationships to ascertain whether this species may exhibit variable nutrient allocation. Embryos showed similar magnitudes of enrichment in ¹³C (i.e., Δδ¹³C, difference between adult and embryo) relative to adult tissues (Δδ¹³C?=?~1.0‰). However, embryos were depleted in ¹⁵N relative to adult muscle tissues (Δδ¹⁵N?=??1.0‰), a finding that contrasts Δδ¹⁵N values reported for other placentotrophic sharks. Embryo-muscle Δδ¹⁵N was correlated with length, supporting the contention that the magnitude of enrichment between embryonic and maternal tissues results from the shift from yolk to placental feeding. Embryo δ¹⁵N and Δδ¹⁵N values showed significant intra-uterine variability; a result not observed for δ¹³C and Δδ¹³C values. The contrasting patterns in fractionation among placentotrophic sharks highlight the importance of evaluating these relationships across elasmobranch taxa with consideration for different tissues, reproductive strategies and stages of gestation. The divergent findings support future evaluation of stable isotope relationships between mothers and offspring for purposes of estimating inherent isotopic variability and how this variability may inform physiological and dietary mechanisms.     

Tracing prey origins,proportions and feeding periods for predatory beetles from agricultural systems using carbon and nitrogen stable isotope analyses

Predatory beetles are an important component of the natural enemy complex that preys on insect pests such as aphids within agroecosystems. Tracing diet origins and movement of natural enemies aids understanding their role in the food web and informs strategies for their effective conservation. Field sampling and laboratory experiments were carried out to examine the changes of carbon and nitrogen stable isotope ratios (δ¹³C and δ¹⁵N) among crops (cotton and maize), pests (cotton and maize aphids), and between wing and abdomen of predatory beetles, Propylea japonica, and to test the hypothesis that prey origins, proportions and feeding periods of the predatory beetles can be deduced by this stable isotope analysis. Results showed that the δ¹³C values both in wing and abdomen of adult P. japonica were changing from a C₃- to a C₄-based diet of aphids reared on maize or cotton, respectively; the isotope ratio of their new C₄ substrates were detectable within 7 days and the δ¹⁵N values began to reflect their new C₄ substrates within 3 days. The relationship between δ¹³C and δ¹⁵N values of P. japonica adults in wing or abdomen and diets of aphids from a C₃-based resource transitioning to a C₄-based resource were described best in linear or quadratic equations. Results suggest that integrative analysis of δ¹³C and δ¹⁵N values can be regarded as a useful method for quantifying to trace prey origins, proportions of diets and feeding periods of natural enemies. The results can provide quantifying techniques for habitat management of natural enemies.     

Stable isotope analysis and fin whale subpopulation structure in the eastern North Atlantic

The North Atlantic fin whale was subject to heavy exploitation in the past and, despite partial recovery, it is still considered endangered. Recent research has questioned its currently accepted subpopulation structure and migratory movements, challenging management and conservation efforts. Here we contribute to this discussion by presenting results of stable isotope analysis of fin whale bones and krill samples collected from fin whale stomachs from two exploited areas, west Iceland and northwest Spain, and comparing these results with North Atlantic isoscapes. In krill, δ¹⁵N values were highly variable and no significant differences in δ¹⁵N and δ¹³C between areas emerged. δ¹⁵N and δ¹³C values in bone were higher than in krill, due to trophic enrichment, and were not significantly different between areas. Both krill and bone results were slightly inconsistent with the local isoscapes, maybe due to seasonal variations in local productivity and in krill diet and, in the case of bone, to its capability to integrate long‐term isotopic values, derived from food consumed in distant areas. Conversely, δ¹⁸O values, which reflect the basal signal of sea water, were consistent with isoscapes and significantly higher in whales from northwestern Spain, possibly indicating migration to breeding grounds located at lower latitudes.     

Species identification and genetic structure of threatened seahorses in Gran Canaria Island (Spain) using mitochondrial and microsatellite markers

A non-invasive DNA analysis of seahorse populations was carried out after extensive underwater surveys in Gran Canaria Island (Spain). In this geographical area, the presence of two species, Hippocampus hippocampus and H. guttulatus, has been previously reported. Sequencing of 16S ribosomal DNA (16S rDNA) was used for specific identification of live seahorses sampled in situ, as a previous step to evaluate genetic structure based on ten microsatellite markers. Phylogenetic analyses revealed the presence of a single species, H. hippocampus, in the seahorse communities found at Gran Canaria. No evidences of H. guttulatus or interspecific hybrids were found based on 16S rDNA and microsatellite data. The nuclear markers revealed low genetic diversity and lack of population structure across populations of Gran Canaria Island, with evidence of small population sizes. This study provides critical information to support conservation strategies of Gran Canaria seahorses.     

Fractionation and turnover of stable carbon isotopes in animal tissues: Implications for δ13C analysis of diet

The use of stable carbon isotopes as a means of studying energy flow is increasing in ecology and paleoecology. However, secondary fractionation and turnover of stable isotopes in animals are poorly understood processes. This study shows that tissues of the gerbil (Meriones unguienlatus) have different δ¹³C values when equilibrated on corn (C₄) or wheat (C₃) diets with constant ¹³C/¹²C contents. Lipids were depleted 3.0‰ and hair was enriched 1.0‰ relative to the C₄ diet. Tissue δ¹³C values were ranked hair>brain>muscle>liver>fat. After changing the gerbils to a wheat (C₃) diet, isotope ratios of the tissues shifted in the direction of the δ¹³C value of the new diet. The rate at which carbon derived from the corn diet was replaced by carbon derived from the wheat diet was adequately described by a negative exponential decay model for all tissues examined. More metabolically active tissues such as liver and fat had more rapid turnover rates than less metabolically active tissues such as hair. The half-life for carbon ranged from 6.4 days in liver to 47.5 days in hair. The results of this study have important implications for the use of δ¹³C values as indicators of animal diet. Both fractionation and turnover of stable carbon isotopes in animal tissues may obscure the relative contributions of isotopically distinct dietary components (such as C₃ vs. C₄, or marine vs. terrestrial) if an animal's diet varies through time. These complications deserve attention in any study using stable isotope ratios of animal tissue as dietary indicators and might be minimized by analysis of several tissues or products covering a range of turnover times.     

Relationships between growth traits and scale stable isotopes (δ13C, δ15N) of adult chum salmon Oncorhynchus keta in Hokkaido,Japan

Stable isotope analysis (SIA) in combination with growth analysis using scales collected from adult chum salmon Oncorhynchus keta migrating back to Hokkaido, Japan, was performed to describe the variation of isotopic composition of carbon (δ¹³C) and nitrogen (δ¹⁵N) in scales and to examine relationships with growth traits [age, fork length (FL), and relative growth ratio in the last growth period [(RGR^last)]. Scale stable isotope (SI) values in 3‐ to 6‐year‐old fish were highly variable, ranging from ?17.6‰ to ?14.3‰ for δ¹³C and 9.5‰ to 13.4‰ for δ¹⁵N. The δ¹⁵N was positively correlated with FL, and this tendency may indicate changes in trophic level with growth. Significant effect was not detected between δ¹⁵N and RGR^last, it can be inferred that factors potentially yielding high δ¹⁵N may not necessarily result in higher growth rates. No trend found between FL and δ¹³C may imply that there is no clear segregation in feeding locations between the 3‐ to 6‐year groups. This study provided basic information for scale SI values of chum salmon adults and indicated that SIA using scales could be a new approach to elucidating the trophic ecology of chum salmon.     

Population dynamics of the long-snouted seahorse (Hippocampus guttulatus Cuvier, 1829) in the Mar Menor coastal lagoon

A 10-year monitoring program was developed to quantify the population dynamics of the long-snouted seahorse population in the Mar Menor coastal lagoon. Based on 985 underwater visual censuses, we estimated the long-snouted seahorse (Hippocampus guttulatus Cuvier, 1829) population size in the Mar Menor lagoon and its reduction in size in the last decades, as well as the effect of eutrophication crises in 2016 and 2019 on the species. The annual recruitment for the 2013–2020 period was estimated by comparing the relative abundance of early seahorse life stages in the ichthyoplankton. The density ranged from 0.0458 specimens/m³ at the beginning of the sampling period to 0.0004 at the end, showing a statistically significant difference between the three analyzed periods (H_gl=2 = 14.0, p = 0.001). The long-snouted seahorse population from the Mar Menor lagoon exemplifies the impact of fishing activities and human pressure, especially euxinic episodes and habitat destruction. As a result of this, the Mar Menor population has decreased from several million specimens to a few thousand, in only three decades. This species showed considerable resilience, the seahorse population began to recover once fishing activity stopped. In contrast, the long-snouted seahorse showed high vulnerability to habitat loss and an episodic flooding event. Adult seahorses showed preferences for highly complex habitats, especially Caulerpa prolifera–Cymodocea nodosa mixed meadows and habitats of high complexity and anthropogenic origin, such as harbors, jetties, or breakwaters. In contrast, juvenile seahorses preferred monotonous seabeds with low complexity, such as the sandy beds that are characteristic of the Mar Menor lagoon littoral.