Reproductive Effort Research Articles

Modelling differences in reproductive effort between iteroparous and semelparous reproductive strategies in Bromeliaceae

Abstract Quantifying reproductive effort (RE), the trade-off between devoting resources to reproduction versus individual growth, in plants presents a number of challenges. Of particular interest is comparing RE between reproductive strategies, such as those in Bromeliaceae: semelparous, where individuals undergo a one-time and subsequently lethal sexual reproductive event, versus iteroparous, where individuals reproduce sexually multiple times by producing clonal offshoots called pups. We introduce a dynamic model of vegetative and reproductive growth in long-lived Bromeliaceae rosettes accounting for the allocation of resources over developmental time. We compare multiple definitions of RE in semelparous and iteroparous Bromeliaceae at critical times during development and over the entire reproductive life of the individual. While others have posited that semelparous taxa exhibit higher RE than comparable iteroparous taxa, our results indicate that this will only occur in limited circumstances: when RE is calculated over the lifespan of a rosette started from seed, semelparous RE is greater when pup mass is accounted for as if it were purely vegetative; or when RE is calculated over the lifespan of the genetic individual, semelparous RE is greater when the ratio of vegetative to inflorescence mass in each pup is greater than that of the originating rosette started from seed.

Widespread Hybridization between Invasive Bleak (Alburnus alburnus) and Iberian Chub (Squalius spp.): A Neglected Conservation Threat

Hybridization between native and nonnative fish species is a major conservation issue, especially in ecosystems with high levels of endemism, such as Iberian streams. To date, hybridization with the invasive bleak Alburnus alburnus has been reported for the Iberian chub Squalius alburnoides and S. pyrenaicus and in scattered locations only. However, the bleak is spreading in the region, potentially increasing the risks of hybridization with other Squalius species. To gather a more comprehensive picture on the current geography of hybridization, we compiled records on hybrids between bleak and chub in Portugal and conducted genetical assessments of hybrids between bleak and S. carolitertii. We found that hybridization with bleak is widespread throughout Portuguese river basins and involves at least S. alburnoides, S. pyrenaicus and S. carolitertii. Hybridization with bleak may not only cause waste of reproductive effort and damage the genetic integrity of these endemic species but also promote shifts in the reproductive dynamics of the S. alburnoides hybrid complex, which includes individuals with various ploidy levels and combinations of parental genomes, reproducing sexually and asexually. We recommend that future studies characterize the fitness of bleak hybrids and their ecological and genetic interactions with native fish, in order to design effective conservation measures.

Growth and reproductive traits of deep-sea pen Anthoptilum murrayi Kölliker, 1880, from Iceland (North Atlantic)

ABSTRACT Sea pens (Octocorallia: Pennatulacea) constitute one of the most important structural species in soft bottom benthic communities. Most pennatulacean species are deep-water organisms inhabiting depths from 200–6000 m. Among these deep-sea pens, a representative set of colonies from the northeastern Atlantic Anthoptilum murrayi Kölliker, 1880 was collected thanks to the BIOICE research surveys. In this study, 18 colonies of A. murrayi were used to acquire information on essential biological traits such as age and growth rates. Our results showed that the colonies collected ranged between 6–17 years, with a diametric growth rate between 0.10–0.17 mm year−1 and a linear growth rate between 14.97–15.75 mm year−1. Moreover, the number and diameter of oocytes per polyp (PRF, ERF), and the reproductive effort at the colony level (PRE, ERE) were determined. These values were compared between colonies of different sizes and within each colony. The largest observed diameter was 1179 μm for oocytes and 711.3 μm for spermatocysts. Both approaches (growth and reproduction) were correlated, indicating that a given large A. murrayi colony (∼300 mm) might be ∼17 years old and contain >7000 oocytes, from which possibly about 2000 oocytes (∼27%) would be spawned per year.

Disentangling the effects of jasmonate and tissue loss on the sex allocation of an annual plant.

Selection through pollinators plays a major role in the evolution of reproductive traits. However, herbivory can also induce changes in plant sexual expression and sexual systems, potentially influencing conditions governing transitions between sexual systems. Previous work has shown that herbivory has a strong effect on sex allocation in the wind-pollinated annual plant Mercurialis annua, likely via responses to resource loss. It is also known that many plants respond to herbivory by inducing signaling, and endogenous responses to it, via the plant hormone jasmonate. Here, we attempt to uncouple the effects of herbivory on sex allocation in M. annua through resource limitation (tissue loss) versus plant responses to jasmonate hormone signaling. We used a two-factorial experiment with four treatment combinations: control, herbivory (25% chronic tissue loss), jasmonate, and combined herbivory and jasmonate. We estimated the effects of tissue loss and defense-inducing hormones on reproductive allocation, male reproductive effort, and sex allocation. Tissue loss caused plants to reduce their male reproductive effort, resulting in changes in total sex allocation. However, application of jasmonate after herbivory reversed its effect on male investment. Our results show that herbivory has consequences on plant sex expression and sex allocation, and that defense-related hormones such as jasmonate can buffer the impacts. We discuss the physiological mechanisms that might underpin the effects of herbivory on sex allocation, and their potential implications for the evolution of plant sexual systems.

Tumors alter life history traits in the freshwater cnidarian, Hydra oligactis

SummaryAlthough tumors can occur during the lifetime of most multicellular organisms and have the potential to influence health, how they alter life-history traits in tumor-bearing individuals remains poorly documented. This question was explored using the freshwater cnidarian Hydra oligactis, a species sometimes affected by vertically transmitted tumors. We found that tumorous polyps have a reduced survival compared to healthy ones. However, they also displayed higher asexual reproductive effort, by producing more often multiple buds than healthy ones. A similar acceleration is observed for the sexual reproduction (estimated through gamete production). Because tumoral cells are not transmitted through this reproductive mode, this finding suggests that hosts may adaptively respond to tumors, compensating the expected fitness losses by increasing their immediate reproductive effort. This study supports the hypothesis that tumorigenesis has the potential to influence the biology, ecology, and evolution of multicellular species, and thus should be considered more by evolutionary ecologists.

Effects of maternal age and offspring sex on milk yield, composition and calf growth of red deer (Cervus elaphus)

Differential maternal allocation theory states that mothers will invest more heavily in the offspring sex that will secure higher reproductive output. Senescence theory is concerned with the gradual deterioration of physiological function with age. We analysed the offspring sex-dependent response of calf growth and milk traits to mother age in an Iberian population of captive red deer (Cervus elaphus) using a 22 year time series longitudinal data set. Previous studies revealed that there was little evidence for the differential allocation theory on milk traits and that most studies lacked proper control for confounding factors. Our results indicated that (i) calf growth was offspring male-biased, negatively affected by mother age and positively influenced by mother weight and parity, and (ii) there was no support for differential allocation offspring sex-dependence in milk traits (yield, energy density, fat, protein and lactose content). Our findings suggest that maternal allocation responds to offspring energy requirements, which are mainly driven by offspring body weight, and contingent on mother age and weight and previous maternal reproductive effort.

White plumage color as an honest indicator: feather macrostructure links reflectance with reproductive effort and success

The structural condition of feathers may generally have a decisive role in shaping the color properties of the plumage. However, the information content of structurally mediated color differences is poorly known. This makes it particularly hard to determine the meaning of color variation in pigment-free white plumage patches. The white wing patch of the collared flycatcher (Ficedula albicollis) is an important sexual trait, and changes in its reflectance are partly due to macrostructural condition. We used 2 years of macrostructural, reflectance, and breeding data from both sexes to examine whether wing patch macrostructure lends information content to actual reflectance in terms of reproductive effort and success. Macrostructure strongly predicted actual reflectance in males but only weakly in females. Furthermore, in males, feather vane width was related positively to current year reproductive effort, and negatively to previous year reproductive effort. This indicates that macrostructurally mediated reflectance attributes may inform the receiver not only of actual reproductive capacity but also of individual quality via reproductive costs.Significance statementColoration of animals takes a central place in their communication and in advertising reproductive abilities. Although white plumage is widespread among animals, usually we have little knowledge on how its structure is linked to reproduction. We investigated this link in a wild population of collared flycatchers. We demonstrated that white feather structure was related to coloration and with current year and previous year reproductive capabilities in males. Our results suggest that white feather structure has the potential to connect reproductive costs with coloration.

Female reproduction and viral infection in a long-lived mammal.

For energetically limited organisms, life-history theory predicts trade-offs between reproductive effort and somatic maintenance. This is especially true of female mammals, for whom reproduction presents multifarious energetic and physiological demands. Here, we examine longitudinal changes in the gut virome (viral community) with respect to reproductive status in wild mature female chimpanzees Pan troglodytes schweinfurthii from two communities, Kanyawara and Ngogo, in Kibale National Park, Uganda. We used metagenomic methods to characterize viromes of individual chimpanzees while they were cycling, pregnant and lactating. Females from Kanyawara, whose territory abuts the park's boundary, had higher viral richness and loads (relative quantity of viral sequences) than females from Ngogo, whose territory is more energetically rich and located farther from large human settlements. Viral richness (total number of distinct viruses per sample) was higher when females were lactating than when cycling or pregnant. In pregnant females, viral richness increased with estimated day of gestation. Richness did not vary with age, in contrast to prior research showing increased viral abundance in older males from these same communities. Our results provide evidence of short-term physiological trade-offs between reproduction and infection, which are often hypothesized to constrain health in long-lived species.

Combined effect of salinity and temperature on copepod reproduction and oxidative stress in brackish-water environment

Climate-induced warming and increased river inflows are forcing the Baltic Sea to radical changes in the near future; organisms living in this brackish-water ecosystem are already experiencing osmotic stress, which, together with thermal stress, may have severe consequences on the ecosystem. The aim of this work was to study the combined effect of decreasing salinity and increasing temperature on reproductive success and oxidative stress in zooplankton by using a calanoid copepod Acartia sp. as a model organism. The field study was conducted during summer 2020 in the western Gulf of Finland, using three sampling sites with naturally differing salinity levels. Additionally, the copepods from these sites were experimentally exposed to ambient or 3°C elevated temperature for 72 h. The copepods derived from the deepest and the most saline sampling site suffered less oxidative damage and exhibited relatively high reproduction, while the temperature treatment itself had little effect. On the other hand, the field-based monitoring data showed otherwise; temperature increased lipid peroxidation, glutathione-s-transferase activity, or both in all three sampling sites. Meanwhile, egg production rate was negatively associated with temperature in the area with the lowest salinity. Moreover, egg production rate decreased from June to September along with increasing temperatures in the mid-salinity sampling site, while similar change occurred also in the highest-salinity site between August and September. The combined effect of salinity and sampling date on reproduction indicates the importance of even subtle salinity changes on copepods. Moreover, the data suggest that the unusually strong heatwave was responsible for increased oxidative stress during the sampling season and possibly forced a trade-off between antioxidant activity and reproductive effort.

Age Effects on Women’s and Men’s Dyadic and Solitary Sexual Desire

While most studies on sexuality in later life report that sexual desire declines with age, little is known about the exact nature of age effects on sexual desire. Using self-reported dyadic sexual desire relating to a partner, dyadic sexual desire relating to an attractive person, and solitary sexual desire from a large (N > 8000) and age diverse (14.6–80.2 years) online sample, the current study had three goals: First, we investigated relationships between men and women’s sexual desire and age. Second, we examined whether individual differences such as gender/sex, sexual orientation, self-rated masculinity, relationship status, self-rated attractiveness, and self-rated health predict sexual desire. Third, we examined how these associations differed across sexual desire facets. On average, the associations between age and both men and women’s sexual desire followed nonlinear trends and differed between genders/sexes and types of sexual desire. Average levels of all types of sexual desire were generally higher in men. Dyadic sexual desire related positively to self-rated masculinity and having a romantic partner and solitary desire was higher in people with same-sex attraction. We discuss the results in the context of the evolutionary hypothesis that predict an increase of sexual desire and female reproductive effort prior to declining fertility. Our findings both support and challenge beliefs about gender/sex specificity of age effects on sexual desire and highlight the importance of differentiating between desire types.

Are the Temporal Changes Observed in the Reproductive Biology of the Estuarine Conguito Sea Catfish Related to Increased Small‐Scale Fishing Effort on the Northwestern Pacific Coast of Mexico?

AbstractBiological parameters relating to the reproductive biology of Conguito Sea Catfish Cathorops liropus were investigated in 1979–1984 and 2015–2018 from an estuarine system on the northwestern Pacific coast of Mexico. In the first period, the spawning season occurred during the dry–warm season (April–June), according with the percentage of mature females and the highest gonadosomatic index (GSI) values. Mean TL was 12.3 cm, two cohorts were found, length at maturity was 18.6 cm, and fecundity was 24.47 oocytes/organism. In the second period, the spawning season extended to the rainy–warm season (July–November), as reflected by the percentage of mature females and the GSI values. Mean TL was 11.6 cm, length at maturity decreased to 17.1 cm, and fecundity decreased to 20.67 oocytes/organism, indicating a reduction in the size‐based indicators and a change in the spawning period and reproductive effort as time passed. The number of fishing skiffs increased from 1,103 in 1980 to 2,434 in 2019, representing a 220% increase, and the landings increased from 400 to 3,432 metric tons in the same period. Temporal trends in surface water temperature, salinity, and the Oceanic Niño Index did not explain the observed changes between the study periods. These results suggest that the observed changes in the reproductive potential of Conguito Sea Catfish have been at least partially due to fishing.

The effects of experimental temperature increase on gametogenesis and heat stress parameters in oysters: Comparison of a temperate-introduced species (Crassostrea gigas) and a native tropical species (Crassostrea corteziensis)

The effect of thermal stress during reproduction was experimentally evaluated in the oyster Crassostrea gigas, a temperate species, and in the tropical oyster Crassostrea corteziensis. The temperature was gradually increased (1 °C day−1) from 20 °C to 34 °C for two weeks. As expected, C. gigas was the species most affected by heat stress, with the highest mortality rate (P < 0.05) starting at 28 °C, while mortality in C. corteziensis was significant only at 34 °C. The reproductive effort at higher temperatures was reflected in C. gigas as the highest index of mature oocytes and the largest rate of atresic and degenerated oocytes. C. corteziensis showed significant increases in the proliferation of early-developing oocytes at maximum temperatures. Lipid peroxidation and lipofuscin accumulation significantly increased in both species at maximum temperatures, with levels in C. gigas being 8-fold higher than in C. corteziensis. A significant loss of biomass and glycogen reserves stored in gonads was found in C. gigas at 34 °C. The mRNA signal of Hsp70 was detected in gonadic tissues from both oysters after thermal stress for in situ hybridization (ISH), with a temperature increase in both species; the cover area of Hsp70 was significantly higher in C. gigas during the experiment. Hemocyte infiltration significantly increased with increasing temperature in both oyster species, and apoptosis was strongly correlated with Hsp70 in both species (r = 0.93; P < 0.05). These results could explain the high tolerance that C. corteziensis has to thermal stress compared to C. gigas and could be used to adapt aquaculture strategies to the use of native species in subtropical climates to reduce summer mortality events.

Life-history constraints, short adult life span and reproductive strategies in coral reef gobies of the genus Trimma.

Body size influences many life-history traits, with small-bodied animals tending to have short life spans, high mortality and greater reproductive effort early in life. In this study, the authors investigated the life-history traits and reproductive strategies of three small-bodied coral reef gobies of the genus Trimma: Trimma benjamini, Trimma capostriatum and Trimma yanoi. The authors found all Trimma species studied attained a small body size of <25 mm, had a short life span of <140 days and experienced high estimated daily mortality of 3.0%-6.7%. Furthermore, the pelagic larval phase accounted for 25.3%-28.5% of the maximum life span, and maturation occurred between 74.1 and 82.1 days at 15.2-15.8 mm, leaving only 35%-43% of the total life span as a reproductively viable adult. All mature individuals had gonad structures consistent with bidirectional sex change, with bisexual gonads including both ovarian and testicular portions separated by a thin wall of connective tissue. In the female and male phases, only ovaries or testes were mature, whereas gonadal tissue of the non-active sex remained. One T. benjamini individual and one T. yanoi individual had ovarian and testicular tissue active simultaneously. The results of this study highlight the life-history challenges small CRFs face on their path to reproduction and reproductive strategies that could be beneficial in fishes with high and unpredictable mortality and short reproductive life spans.

The relative influence of environmental cues on reproductive allocation of a highly iteroparous coral reef fish

Pelagic eggs and larvae of many coral reef fishes will encounter a dynamic and risky environment as they disperse between the reef and offshore habitats. Life-history theory predicts that spawning adults should synchronize their reproductive effort with specific environmental conditions that facilitate offspring survival. Favourable conditions for reproduction may be determined by local environmental conditions at the spawning site, or signalled by larger-scale environmental cues, such as the lunar cycle. Multiple cues may interact in complex ways to cause additional variation in spawning intensity. We evaluated a set of environmental variables that potentially determine temporal and spatial variation in spawning patterns of a highly iteroparous fish, the sixbar wrasse (Thalassoma hardwicke). Specifically, we monitored focal territories of terminal-phase males over a 5-month period, quantified spawning activities, and evaluated a hierarchical set of predictive models using a model selection approach (AICc). Temporal variation in spawning (and population densities at the spawning site) was most strongly associated with the lunar cycle and maximal around the new moon. Local hydrodynamic conditions and other environmental variables observable at the spawning site were less strongly correlated with temporal variation in spawning. Territory proximity to the reef edge was a strong predictor of spatial variation in spawning intensity; territories closest to the reef edge experienced more spawning. These observations suggest that females make predictable decisions about where and when they spawn. Females appear to recognize strong, persistent spatial gradients in spawning habitat quality, and primarily vary their spawning effort in accordance with a large-scale environmental cue (the lunar cycle).

Sexual and asexual reproduction in a Mediterranean Tethya (Porifera, Demospongiae) species

BackgroundThe reproductive cycle of the recently described sponge Tethya meloni was investigated for a period of 15 months (September 2018 – November 2019) in the Mar Piccolo of Taranto (Southern Italy) and was compared with data previously collected for the other two sympatric species of the same genus known for Mediterranean Sea, T. citrina and T. aurantium.ResultsT. meloni is a gonochoric species with a sex ratio strongly shifted towards females. Asexual budding was a seasonal process, limited to few specimens. In a specimen collected in September 2018 both oocytes and buds occurred, suggesting that in T. meloni the sexual and asexual phases may coexist both at the population and individual levels.ConclusionsThe data obtained from this research compared with the available literature confirm the high temporal variability of the reproductive cycles in the Mediterranean species of Tethya, but with common general characteristics. In sexual reproduction, the oocyte production period lasts several months, with a peak between summer and autumn while spermatogenesis, shorter but with greater reproductive effort, follows the onset of oogenesis. The asexual reproduction phase of T. meloni, on the other hand, occurs in a short period and seems to have less importance in the overall reproductive process.

Bystander fallow deer engage in third-party behaviour based on similarities in contestant resource-holding potential

Competitive dyadic interactions frequently attract the attention of bystanders that follow and disrupt the ongoing contest. The motivation for bystanders to engage in such third-party behaviour is considered by several different theoretical approaches; one such model argues that bystanders intervene to prevent subordinates from gaining a winner effect, thereby becoming a threat to the individual's dominant status within the group. This study investigates the role of contestant morphology as a motivating factor in initiating third-party behaviour. We investigated whether two correlates of resource-holding potential, prerut body weight and antler weight, were associated with third-party behaviour in rutting male fallow deer, Dama dama . In addition, we examined whether a third factor, reproductive effort (weight loss during the rut) was associated with third-party behaviour. There was a positive relationship between antler weight and the number of times individual males experienced third-party behaviour during contests. This relationship was not evident for either prerut weight or weight loss. An analysis of third-party behaviour showed that as the difference in both prerut and antler weight between the competing males declined, there was an increase in the probability that the dyad would experience third-party behaviour. However, there was no such association between the difference in weight loss between contestants and third-party behaviour. Thus, dyads of males closely matched in terms of individual quality were likely to experience third-party behaviour. We show for the first time that morphological traits associated with resource-holding potential are important cues used by rivals as a basis for engaging in third-party behaviour. • Dyadic fights are often disrupted by third-party group members. • Larger weapons were associated with experiencing more third-party behaviour. • Dyads similar in body and antler weight experienced more third-party behaviour. • Bystander males gather information about fighting rivals' size and quality. • This information is used to inform decisions to engage in third-party behaviour.

¿Cómo afecta el ganado doméstico a la biomasa y la fecundidad de distintos tipos sucesionales de especies en el Monte Patagónico?

Plants respond to disturbances according to their physiological characteristics, their lifeform, and their ecological role or function within the community. We assessed the response, in terms of biomass and fitness, to a gradient of stocking density (measured as livestock units.year.ha-1) considering different successional types of species (early, intermediate and late species) from Patagonian Monte Desert. We estimated plant biomass and fitness through different variables such as plant size (diameter x height of the plant), reproductive effort (% flowering or fruiting branches) and percentage of viable seeds (seed set). We observed that browsing decreased plant biomass and fitness, both through reproductive effort and seed set. However, the successional types of species showed different seed set in response to grazing intensity. With increased stocking density, the size of early species decreased, the size of intermediate species increased and the size of late species did not show significant changes. In general, browsing negatively affected the reproductive effort of all species, and the seed set only in late specie, while early and intermediate species showed an increase in seed set. These results suggest that late species are the most affected by livestock in terms of fecundity, which might reduce their recruitment. The increase in their biomass with stocking density in intermediate species suggests a compensatory response, which could give them a short-term advantage. Tissue loss suffered by plants due to livestock consumption impacts the seed set, with possible consequences on the rate and time of seedling emergence. These results aid to understand plant population dynamics under disturbances, providing useful information to elaborate adequate conservation, sustainable management and restoration strategies for arid ecosystems.

The expression of demographic costs of reproduction varies among coexisting plants with different life history traits

Abstract Demographic costs of reproduction in flowering plants should depend on life history and reproductive efforts, but how the expression of costs varies with life‐history traits is poorly understood. We experimentally increased and reduced reproductive effort (fruit production) to quantify demographic costs of reproduction in four coexisting species with contrasting growth forms (clonal vs. non‐clonal) and flower production (single‐ vs. multi‐flowered). We repeated the experiment for 3 years and measured the demographic rates the year after the treatment. In 2 years, we also quantified the costs of flower maintenance by contrasting the performance of non‐fruiting plants with intact flowers and plants with their flowers removed. Costs varied among species, in both magnitude and demographic rate affected. Costs of natural reproduction were expressed as reductions in size and fecundity next year, whereas increased reproduction additionally reduced sprouting probability. The magnitude of demographic costs of both reproduction and flower maintenance was highest in the non‐clonal, multi‐flowered species, and costs were more frequently detected in the two multi‐flowered species than in the single‐flowered ones. This may be explained by higher biomass allocation to reproductive parts and a longer flowering period in the former. Demographic costs of reproduction did not depend on clone size. Synthesis. These results document that demographic costs vary among coexisting species sharing similar niches and are associated with divergence in life‐history traits. Such trait‐dependent variation in costs may reduce competition among coexisting species and facilitate diversity.

Prolactin promotes parental responses and alters reproductive axis gene expression, but not courtship behaviors, in both sexes of a biparental bird

Prolactin, a hormone involved in vertebrate parental care, is hypothesized to inhibit reproductive hypothalamic-pituitary-gonadal (HPG) axis activity during parenting, thus maintaining investment in the current brood as opposed to new reproductive efforts. While prolactin underlies many parental behaviors in birds, its effects on other reproductive behaviors, such as courtship, remain unstudied. How prolactin affects neuropeptide and hormone receptor expression across the avian HPG axis also remains unknown. To address these questions, we administered ovine prolactin (oPRL) or a vehicle control to both sexes in experienced pairs of the biparental rock dove (Columba livia), after nest removal at the end of incubation. We found that oPRL promoted parental responses to novel chicks and stimulated crop growth compared to controls, consistent with other studies. However, we found that neither courtship behaviors, copulation rates nor pair maintenance differed with oPRL treatment. Across the HPG, we found oPRL had little effect on gene expression in hypothalamic nuclei, but increased expression of FSHB and hypothalamic hormone receptor genes in the pituitary. In the gonads, oPRL increased testes size and gonadotropin receptor expression, but did not affect ovarian state or small white follicle gene expression. However, the oviducts of oPRL-treated females were smaller and had lower estrogen receptor expression compared with controls. Our results highlight that some species, especially those that show multiple brooding, may continue to express mating behavior despite elevated prolactin. Thus, mechanisms may exist for prolactin to promote investment in parental care without concurrent inhibition of reproductive function or HPG axis activity.

Increased Coastal Nutrient Loading Enhances Reproductive Intensity of Zostera marina: Implications for Seagrass Meadow Resilience

Because sexual reproduction is essential for the establishment and persistence of seagrass meadows, flowering intensity is an important trait that influences the resilience and stability of seagrass populations. Although the effects of excessive coastal nutrient loading on seagrass vegetative growth have been extensively documented, the effects on seagrass reproductive phenology and intensity remain unclear. To examine the reproductive responses of seagrass populations to increased coastal nutrient loading, the flowering phenology and intensity of Zostera marina were compared between sites with high-nutrient, low-light conditions (Deukryang Bay and Dongdae Bay) and low-nutrient, high-light conditions (Koje Bay) on the southern coast of Korea. Nutrient contents of the above- and below-ground tissues of Z. marina reflected in situ nutrient and light availability at the study sites. Reproductive shoot density and biomass, as well as flowering frequency and reproductive effort, were much higher (1.5–4.6-fold) at the high-nutrient, low-light study sites of Deukryang Bay and Dongdae Bay than at the low-nutrient, high-light site of Koje Bay. Consequently, potential seed production was higher in Deukryang Bay and Dongdae Bay than in Koje Bay. Chronic high-nutrient and low-light conditions significantly increased the reproductive intensity of Z. marina, supporting the persistence and resilience of Z. marina populations. The results of this study could provide insights into the conservation and management of seagrass meadows under increased coastal nutrient loading.