Planktonic Larvae Research Articles

Ecological speciation by sympatric host shifts in a clade of herbivorous sea slugs, with introgression and localized mitochondrial capture between species

Host shifting in insect-plant systems was historically important to the development of ecological speciation theory, yet surprisingly few studies have examined whether host shifting drives diversification of marine herbivores. When small-bodied consumers feed and also mate on a preferred host, disruptive selection can split a population into host races despite gene flow. Support for host shifts is notably lacking for invertebrates associated with macroalgae, where the scale of dispersal by planktonic larvae often far exceeds the grain of host patchiness, and adults are typically less specialized than terrestrial herbivores. Here, we present a candidate example of ecological speciation in a clade of sea slugs that primarily consume green algae in the genus Caulerpa, including highly invasive species. Ancestral character state reconstructions supported ‘sea grapes’ (C. racemosa, C. lentillifera) as the ancestral host for a tropical radiation of 12 Elysia spp., with one shift onto alternative Caulerpa spp. in the Indo-Pacific. A Caribbean radiation of three species included symaptric host shifts to Rhipocephalus brevicaulis in the ancestor of E. pratensis Ortea & Espinosa, 1996, and to C. prolifera in E. hamanni Krug, Vendetti & Valdes 2016, plus a niche expansion to a range of Caulerpa spp. in E. subornata Verrill, 1901. All three species are broadly sympatric across the Caribbean but are host-partitioned at a fine grain, and distinct by morphology and at nuclear loci. However, non-recombining mtDNA revealed a history of gene flow between E. pratensis and E. subornata: COI haplotypes from E. subornata were 10.4% divergent from E. pratensis haplotypes from four sites, but closely related to all E. pratensis haplotypes sampled from six Bahamian islands, indicating historical introgression and localized “mitochondrial capture.” Disruptive selective likely fueled divergence and adaptation to distinct host environments, indicating ecological speciation may be an under-appreciated driver of diversification for marine herbivores as well as epibionts and other resource specialists.

Spatio-temporal occurrence of different early life stages of Periophthalmus modestus in a tropical estuary

Abstract To elucidate the distribution pattern of Periophthalmus modestus, an amphibious fish, at its southernmost habitat, an investigation was conducted monthly at different locations along the Red River Delta area over two years. Spatially, planktonic larvae were caught abundantly at sampling sites along the Ba Lat Estuary and at a single site in the nearby mangroves close to the river’s main tributary. The benthic and amphibious juveniles were caught mainly in the mangroves. This finding suggests that P. modestus larvae may be transported up the river from the spawning ground by the tidal current and may use the main tributary of Ba Lat Estuary as a nursery habitat for the planktonic larval stage and expand their habitat to the mangrove along the estuary during the settling stages. Temporally, planktonic larvae occurred from February to July and peaked in May, suggesting that the main reproductive season of this fish in Vietnam is from February to July, which is earlier than in temperate areas. The abundance of larvae and juveniles of this species over time was positively correlated with water temperature. Nonmetric multidimensional scaling (NMDS) models based on size-class assemblages, months of sampling and samplings sites, together with an overlay of environmental vectors, revealed that water temperature was significantly correlated with fish size. Fish in the smaller size class tended to occur at lower temperatures, and fish in the larger size class tended to occur at higher temperatures. The distribution pattern of this species revealed in this study may partly contribute to its successful adaptation to circumstances in this tropical area.

Broodstock development, final oocyte maturation and breeding of the newly described sparid fish, Fanged seabream, Sparidentex jamalensis Amir, Siddiqui & Masroor, 2014

Broodstock development, induced maturation and breeding of the newly described seabream, Sparidentex jamalensis collected from Kali estuary, Karnataka, India were achieved successfully for the first time. Taxonomy of the fish was confirmed employing morphological and molecular tools. Majority of the brooders collected were in the 20–30 cm length class (140–510 g) and were ideal for developing matured broodstock. Periodic microscopic observation of ovarian biopsy indicated progressive gonadal development in the broodstock. The broodstock developed for this protandrous hermaphrodite consisted of females having maturing oocytes and males with oozing milt during the breeding season. Final maturation and spawning of the females (520 ± 8 g; ova diameter above 400 µm) was achieved using cholesterol-based LHRH analogue pellets (50 µg/kg fish) and the males (450 ± 54 g) were not treated with hormones. Pelagic fertilized eggs (720 ± 8 µm) with a single oil globule were obtained with an absolute fecundity of 0.42 ± 0.06 million/kg fish and a fertilization rate of 82 ± 2.4%. Major embryological stages were recorded and the fertilized eggs hatched after 18–20 hours with 80 ± 4.6% hatching rate at 28°C. The newly hatched planktonic larvae measured 1.8 ± 0.12 mm in total length. Mouth opening of the larvae was observed on second day post hatch (dph). Resorption of the yolk sac was observed on third dph. These results will act as a baseline for developing a breeding programme for this species.

The first evidence for genetic differentiation of a non-native false mussel Mytilopsis sallei (Récluz, 1849) in southern Thailand.

ABSTRACT The false mussel Mytilopsis sallei (Récluz, 1849) is a bivalve indigenous to the tropical western Atlantic that has become invasive in Southeast-Asia. Establishment of M. sallei populations in Thailand was reported in 2008 and it has spread to several locations along both the Gulf of Thailand and Andaman Sea coasts. The survival of planktonic larvae of M. sallei in oceanic salinity is known to be poor so these populations may be a result of multiple introductions, and propagule exchanges between populations may be limited. To test this, we investigated the variability of cytochrome oxidase subunit I in M. sallei within and between spatially isolated locations, as well as between the Gulf of Thailand and Andaman Sea coasts. In total, 407 base pairs from 60 individuals across five locations were analysed. Differences in the genetic structure of M. sallei among the five populations from southern Thailand suggest that there is no connectivity between the Gulf of Thailand and Andaman Sea populations. The results revealed the presence of six of the 15 haplotypes known among Southeast-Asian populations of M. sallei. This study contributes to the understanding of population genetic structure of the non-native false mussel, M. sallei, in Southeast-Asia.

Sampling multiple life stages significantly increases estimates of marine biodiversity.

Biodiversity assessments are critical for setting conservation priorities, understanding ecosystem function and establishing a baseline to monitor change. Surveys of marine biodiversity that rely almost entirely on sampling adult organisms underestimate diversity because they tend to be limited to habitat types and individuals that can be easily surveyed. Many marine animals have planktonic larvae that can be sampled from the water column at shallow depths. This life stage often is overlooked in surveys but can be used to relatively rapidly document diversity, especially for the many species that are rare or live cryptically as adults. Using DNA barcode data from samples of nemertean worms collected in three biogeographical regions—Northeastern Pacific, the Caribbean Sea and Eastern Tropical Pacific—we found that most species were collected as either benthic adults or planktonic larvae but seldom in both stages. Randomization tests show that this deficit of operational taxonomic units collected as both adults and larvae is extremely unlikely if larvae and adults were drawn from the same pool of species. This effect persists even in well-studied faunas. These results suggest that sampling planktonic larvae offers access to a different subset of species and thus significantly increases estimates of biodiversity compared to sampling adults alone. Spanish abstract is available in the electronic supplementary material.

Direct and latent effects of ocean acidification on the transition of a sea urchin from planktonic larva to benthic juvenile

Ongoing ocean acidification is expected to affect marine organisms and ecosystems. While sea urchins can tolerate a wide range of pH, this comes at a high energetic cost, and early life stages are particularly vulnerable. Information on how ocean acidification affects transitions between life-history stages is scarce. We evaluated the direct and indirect effects of pH (pHT 8.0, 7.6 and 7.2) on the development and transition between life-history stages of the sea urchin Strongylocentrotusdroebachiensis, from fertilization to early juvenile. Continuous exposure to low pH negatively affected larval mortality and growth. At pH 7.2, formation of the rudiment (the primordial juvenile) was delayed by two days. Larvae raised at pH 8.0 and transferred to 7.2 after competency had mortality rates five to six times lower than those kept at 8.0, indicating that pH also has a direct effect on older, competent larvae. Latent effects were visible on the larvae raised at pH 7.6: they were more successful in settling (45% at day 40 post-fertilization) and metamorphosing (30%) than larvae raised at 8.0 (17 and 1% respectively). These direct and indirect effects of ocean acidification on settlement and metamorphosis have important implications for population survival.

Internal ultrastructure of the planktonic larva of the coral Porites panamensis (Anthozoa: Scleractinia)

Introduction: The scleractinian coral life cycle includes planktonic larvae that settle on the benthos, allowing the primary polyp to clone and build a sexually reproducing adult colony. The larval physiology and ecology of Eastern Tropical Pacific scleractinians needs the exploration of basic aspects such as the internal morphology of planulae. Objective: To describe histological and cytological characteristics of Porites panamensis larvae. Methods: During August-July 2019, at Islas Marias Biosphere Reserve, Central Mexican Pacific, we made 14 collections of coral larvae and identified the species with C cytochrome oxidase subunit 1 gene. We used a scanning electron microscope and other techniques. Results: The ectoderm was composed by heterogeneous, mono-ciliated, columnar epithelial cells. Nematocysts were clustered at the oral pole of the ectoderm, and cells were evident in the aboral pole of the ectoderm gland. The endoderm had secretory cells, lipids and symbionts. Conclusions: The abundance of secretory cells and nematocysts in the aboral pole suggests their importance in substrate exploration and larval settlement. Our results support previous descriptions of larval ultrastructure in other coral species.

Estuarine retention of larvae: Contrasting effects of behavioral responses to turbulence and waves

AbstractThe intensity of small‐scale fluid motions varies among coastal seascapes, which could drive species‐specific behavioral adaptations in planktonic larvae. For example, inlets and estuaries typically have stronger turbulence and weaker surface gravity waves than the continental shelf. In the Mid‐Atlantic Bight, eastern mudsnails (Ilyanassa obsoleta) inhabit inlets and estuaries, whereas threeline mudsnails (Ilyanassa trivittata) inhabit the continental shelf. The two species' larvae respond differently to hydrodynamic signals: both hover in calm conditions and sink in response to vorticity, a signal of turbulence, while only shelf snail larvae also sink and swim up in response to accelerations, which can be large under waves. We investigated how these observed larval behaviors and more idealized ones affect retention and settlement in estuaries using numerical experiments. Virtual larvae were released and tracked in a regional model of Delaware Bay and the adjacent shelf. Behaviors that involved downward motions, including vorticity‐induced behaviors, helped concentrate larvae near the bottom and enhanced retention in the bay. In contrast, behaviors that involved upward motions, including acceleration‐induced behaviors, promoted export onto the shelf. Compared to neutral buoyancy, the vorticity‐induced behaviors also conferred longer residence times in the bay, higher settlement probabilities, and shorter pelagic larval durations, all of which would be advantageous to estuarine species. This integration of larval observations with simulations provides evidence that behavioral responses to coastal physics can reduce larval mortality by enhancing retention and settlement in native seascapes.

Does the Kuroshio Current transport planktonic larvae of the hydrothermal-vent crabXenograpsusTakeda & Kurata, 1977 (Decapoda: Brachyura: Grapsoidea)?

AbstractThe grapsoid crab XenograpsusTakeda & Kurata, 1977 inhabiting shallow-water hydrothermal vents shows a limited distribution in the western Pacific, thus providing a good opportunity to observe how a species expands its distribution and establishes and maintains a metapopulation. We analyzed four Japanese populations of Xenograpsus (Kueishan-dao, Showa Iwo-jima, Shikine-jima, and Omuro-dashi) distributed along the Kuroshio Current to assess whether population connectivity is affected by the current. The reconstructed phylogenetic tree indicated that the specimens analyzed belong to a single clade, including X. testudinatusNg, Huang & Ho, 2000 in Kueishan-dao. We could not include genetic data of X. novaeinsularisTakeda & Kurata, 1977 and tentatively refer to the specimens analyzed as X. testudinatus. All four populations shared the two major haplotypes. Statistically significant population differentiation was nevertheless recognized between Showa Iwo-jima and Omuro-dashi, about 1,000 km apart. The number of individuals analyzed in Shikine-jima (N = 11) and Kueishan-dao (N = 5) might not be enough to detect differences. The relative age of population expansion seemed to correlate with the direction of the Kuroshio Countercurrent. Together with knowledge on the distribution of the planktonic larvae, larvae of X. testudinatus stay and mostly contribute to its source population. The Kuroshio Current system occasionally transports the larvae and juveniles, or even adult individuals on floating pumice and other materials, to eventually settle into newly formed habitats after volcanic eruptions, thus expanding the distributional range of the species.

Large-scale connectivity of the sandy beach clam Mesodesma mactroides along the Atlantic coast of South America, and climate change implications

The yellow clam Mesodesma mactroides is a cool-water species that typifies sandy beaches of the Southwestern Atlantic Ocean (SAO), which embraces one of the strongest ocean warming hotspots. The region is influenced by the Rio de la Plata (RdlP), which represents a zoogeographic barrier that restricts its larval exchange. We investigated yellow clam larval connectivity patterns using an individual based model (IBM). The IBM combined outputs from a 3D hydrodynamic model with a clam submodel that considered salinity- and temperature-dependent mortality for the planktonic larvae. Connectivity across the RdlP estuary occurred only for larvae released in spring during a strong La Niña event. Mortality due to freshwater precluded larval transport across the RdlP, whereas larval mortality induced by warmer waters reduced connectivity, leading to self-recruitment in most areas. Warming acceleration in this hotspot could further restrict larval connectivity between populations in the SAO, with conservation implications for this threatened species.

Hoplonemertean larvae are planktonic predators that capture and devour active animal prey

AbstractThe superficially simple ciliated planktonic larvae of hoplonemerteans have been assumed to be lecithotrophic direct developers, even though many develop from such small eggs that it is hard to imagine how they could give rise to a viable juvenile without some phase of larval feeding. Indeed, attempts to raise such larvae to settlement without food invariably fail. Observations that some hoplonemertean larvae are found in plankton samples at a range of sizes, and much larger than hatchlings, suggest that they must indeed feed somehow. Because these so‐called planuliform larvae lack apparent means to concentrate suspended algae or other unicellular food, one alternative hypothesis is that they are planktonic predators that hunt large prey. Here we provide direct evidence that this is indeed the case for six distinct species of hoplonemerteans. We recorded wild‐caught larvae of Paranemertes californica, Paranemertes sp., Gurjanovella littoralis, Emplectonema viride, Carcinonemertes epialti, and Ototyphlonemertes sp. attacking, subduing, and devouring pelagic crustaceans, including barnacle nauplii, cyprids, copepods and their nauplii, and others. Although there is no doubt that some hoplonemerteans are genuine lecithotrophs, our evidence suggests that many species in this group both feed and grow during an extended planktonic larval period. This conclusion has important consequences for biogeographic and life history studies in this group, because it implies enhanced potential for long‐distance dispersal. More broadly, the possibility that many animal larvae are actually carnivores invites reconsideration of prevailing stereotypes about metazoan developmental modes and the trade‐offs between them.

Planktonic sea urchin larvae change their swimming direction in response to strong photoirradiation.

To survive, organisms need to precisely respond to various environmental factors, such as light and gravity. Among these, light is so important for most life on Earth that light-response systems have become extraordinarily developed during evolution, especially in multicellular animals. A combination of photoreceptors, nervous system components, and effectors allows these animals to respond to light stimuli. In most macroscopic animals, muscles function as effectors responding to light, and in some microscopic aquatic animals, cilia play a role. It is likely that the cilia-based response was the first to develop and that it has been substituted by the muscle-based response along with increases in body size. However, although the function of muscle appears prominent, it is poorly understood whether ciliary responses to light are present and/or functional, especially in deuterostomes, because it is possible that these responses are too subtle to be observed, unlike muscle responses. Here, we show that planktonic sea urchin larvae reverse their swimming direction due to the inhibitory effect of light on the cholinergic neuron signaling>forward swimming pathway. We found that strong photoirradiation of larvae that stay on the surface of seawater immediately drives the larvae away from the surface due to backward swimming. When Opsin2, which is expressed in mesenchymal cells in larval arms, is knocked down, the larvae do not show backward swimming under photoirradiation. Although Opsin2-expressing cells are not neuronal cells, immunohistochemical analysis revealed that they directly attach to cholinergic neurons, which are thought to regulate forward swimming. These data indicate that light, through Opsin2, inhibits the activity of cholinergic signaling, which normally promotes larval forward swimming, and that the light-dependent ciliary response is present in deuterostomes. These findings shed light on how light-responsive tissues/organelles have been conserved and diversified during evolution.

Responding to the signal and the noise: behavior of planktonic gastropod larvae in turbulence.

Swimming organisms may actively adjust their behavior in response to the flow around them. Ocean flows are typically turbulent and are therefore characterized by chaotic velocity fluctuations. While some studies have observed planktonic larvae altering their behavior in response to turbulence, it is not always clear whether a plankter is responding to an individual turbulence fluctuation or to the time-averaged flow. To distinguish between these two paradigms, we conducted laboratory experiments with larvae in turbulence. We observed veliger larvae of the gastropod Crepidula fornicata in a jet-stirred turbulence tank while simultaneously measuring two components of the fluid and larval velocity. Larvae were studied at two different stages of development, early and late, and their behavior was analyzed in response to different characteristics of turbulence: acceleration, dissipation and vorticity. Our analysis considered the effects of both the time-averaged flow and the instantaneous flow, around the larvae. Overall, we found that both stages of larvae increased their upward swimming speeds in response to increasing turbulence. However, we found that the early-stage larvae tended to respond to the time-averaged flow, whereas the late-stage larvae tended to respond to the instantaneous flow around them. These observations indicate that larvae can integrate flow information over time and that their behavioral responses to turbulence can depend on both their present and past flow environments.

Composition and distribution of zooplankton species in the subtropical areas of the Northwestern Pacific Ocean

Based on the investigation data of 44 stations in the area 28°－35° N, 147°－154° E of the Northwestern Pacific Ocean by the research ship 'Songhang' in March 2019, we analyzed species composition and distribution of zooplankton to understand zooplankton community structure in the subtropical areas of the Northwestern Pacific Ocean. The results showed that a total of 456 zooplankton species (including planktonic larvae and unidentified species) were recorded in the surveyed area, which were belonged to 8 categories and 14 groups. There were 163 species of copepods, as the dominant group. The dominant species included 9 warm-water species, Eudoxoides spiralis, Neocalanus gracilis, Pleuromamma gracilis, Sagitta enflata, Doliolum nationalis, S. hexaptera, Euchirella rostrata, Nannocalanus minor and Mesocalanus tenuicornis, and one temperate species, Calanus jashnovi. Both the warm current indicator species S. hexaptera and the cold current indicator species C. jashnovi occurred simultaneously in the subtropical area, indicating that the Kuroshio Current and the Oyashio Current had an important impact on the diversity and temporal-spatial distribution of marine zooplankton. The average biomass was (31.64±23.81) mg·m-3, and the average abundance was (22.2±17.6) ind·m-3. The average values of purity index (C), eveness index (J), Shannon diversity index (H) and richness index (D) were 0.09±0.10, 0.76±0.10, 4.88±0.71, and 23.53±8.08, respectively. The spatial distribution of the four indices were uneven and irregular. During the study period, species composition of zooplankton in the Northwest Pacific was rich, species distribution was uneven, and community structure was stable.

A novel method for the rapid enumeration of planktonic salmon lice in a mixed zooplankton assemblage using fluorescence

The relative rarity of the planktonic larval stages of salmon lice in comparison to other animals captured in a zooplankton assemblage is an obstacle to estimating their abundance and distribution. Due to the labour intensiveness of standard plankton sorting approaches, the planktonic stages of salmon lice remain understudied and unmonitored despite their importance to the spread of the parasite between salmon farms and to wild salmonids. Alternative methods of identification have been investigated and in a previous study a fluorescence signal was identified. Using filters to target that signal with fluorescence microscopy (excitation/emission wavelengths of 470/525 nm), the salmon louse has a fluorescence intensity 2.4 times greater than non-target animals, which distinguishes it from the zooplankton assemblage and enables rapid enumeration. Here, we present a novel method for the enumeration of planktonic salmon lice larvae, nauplius and copepodid stages, in a mixed zooplankton sample using fluorescence-aided microscopy. Performance of the method was evaluated with a blind trial which found a median accuracy of 81.8% and a mean sample processing time of 31 min. Compared with previously published findings, the novel method provides satisfactory accuracy and enumeration that is more than 20 times faster than traditional light microscopy approaches. Factors influencing the performance of the method are identified and recommendations are made for targeted sampling and automated enumeration.

Gene expression alterations from reversible to irreversible stages during coral metamorphosis

For corals, metamorphosis from planktonic larvae to sedentary polyps is an important life event, as it determines the environment in which they live for a lifetime. Although previous studies on the reef-building coral Acropora have clarified a critical time point during metamorphosis when cells are committed to their fates, as defined by an inability to revert back to their previous states as swimming larvae (here referred to as the “point of no return”), the molecular mechanisms of this commitment to a fate remain unclear. To address this issue, we analyzed the transcriptomic changes before and after the point of no return by inducing metamorphosis of Acropora tenuis with Hym-248, a metamorphosis-inducing neuropeptide. Gene Ontology and pathway enrichment analysis of the 5893 differentially expressed genes revealed that G protein-coupled receptors (GPCRs) were enriched, including GABA receptor and Frizzled gene subfamilies, which showed characteristic temporal expression patterns. The GPCRs were then classified by comparison with those of Homo sapiens, Nematostella vectensis and Platynereis dumerilii. Classification of the differentially expressed genes into modules based on expression patterns showed that some modules with large fluctuations after the point of no return were biased toward functions such as protein metabolism and transport. This result suggests that in precommitted larvae, different types of GPCR genes function to ensure a proper environment, whereas in committed larvae, intracellular protein transport and proteolysis may cause a loss of the reversibility of metamorphosis as a result of cell differentiation.

Evolutionary game of life-cycle types in marine benthic invertebrates: Feeding larvae versus nonfeeding larvae versus direct development

Many marine invertebrates have a benthic adult life with planktonic long feeding larval stages (planktotrophy). In other species, planktonic larvae do not eat, and after a rather short period, they settle and initiate their benthic stages (lecithotrophy). Still other species skip planktonic larval stages altogether, and adults produce benthic offspring (direct development). In this paper, we develop an evolutionary game among different life-cycle types and examine the conditions for each life-cycle type to win in a seasonal environment. The growth rate and mortality of benthic individuals are the same among all three life-cycle types, the local habitat (patches) for benthic individuals have a finite longevity, and adults may engage in a limited dispersal just before breeding. Planktotrophy evolves if the planktonic stages are more efficient in terms of biomass gain than benthic life. Otherwise, lecithotrophy or direct development should evolve. Among them, direct development is more advantageous than lecithotrophy if the cost of having planktonic larvae is large, the habitat for benthic individuals is stable, and adults engage in some dispersal.

Internal controls for quantitative RT-PCR analysis of gene expression in response to ocean acidification in edible oysters

The increase of CO2 by anthropogenic activities leads to a decrease of pH in the ocean surface due to ocean acidification (OA) process. Generally, OA not only reduces the rate of calcification in marine environments but also affects various physiological activities, especially in calcifiers, including edible oysters. Quantitative real-time PCR (qRT-PCR) is often used to detect gene expression in response to OA, which relies on the stability of internal control. However, the appropriate internal controls for OA experiments remain scarce especially in the marine calcifiers. Hence, this study developed internal controls for qRT-PCR assays using the Hong Kong oyster (Crassostrea hongkongensis) as a model to reveal gene expression profile during development under OA. In this study, 17 housekeeping genes were selected as the possible candidate of the internal controls. After a comprehensive interpretation from the multiple algorithms and software, GAPDH paired with RL23 is recommended for the normalization for planktonic larvae and benthic juveniles, but beyond that, TUBB and EF2 are recommended for post-metamorphic stage. Moreover, GAPDH and EF2 were suitable for various pH treatments, and TUBB, RL35 and RL23 could be the alternatives for OA experiments. These results are instrumental for the selection of internal control in Crassostrea hongkongensis during the development, and shed light on other molecular OA experiments in marine invertebrates for reference.

Dorsal-ventral axis formation in sea urchin embryos.

Most sea urchin species produce planktonic feeding larvae with distinct dorsal-ventral polarity. Such morphological indicators of polarity arise after gastrulation, when several morphogenesis and cell differentiation events occur differentially along the dorsal-ventral axis. For instance, the gut bends toward the ventral side where the mouth will form, skeletogenesis occurs initially near the ventral side with the forming skeleton extending dorsally, and pigment cells differentiate and embed in the dorsal ectoderm. The patterning mechanisms and gene regulatory networks underlying these events have been extensively studied. Two opposing TGF-β signaling pathways, Nodal and BMP, play key roles in all three germ layers to respectively pattern the sea urchin ventral and dorsal sides. In this chapter, I describe our current understanding of sea urchin dorsal-ventral patterning mechanisms. Additionally, differences in the patterning mechanisms observed in lecithotrophic sea urchins (nonfeeding larvae) and in cidaroid sea urchins are also discussed, along with evolutionary insights gained from comparative analyses.

鸭绿江口近岸海域水质环境对冬季浮游动物群落结构的影响

定量分析滨海湿地近岸海域水质环境与浮游动物群落结构之间的关系对揭示海水水质环境健康状态具有重要意义。2019年12月在鸭绿江口湿地国家级自然保护区近岸海域开展了浮游动物和水环境因子调查，运用冗余分析和结构方程模型等方法探讨了水质环境对冬季浮游动物群落结构的影响。研究区共鉴定出浮游动物14种以及浮游幼虫5大类，桡足类最多占比52.63%；保护区不同功能分区间浮游动物群落结构总体差异不大，多样性指数、均匀度指数和丰富度指数平均值分别为1.34、0.51和0.59；浮游动物的种群分布与海水化学需氧量、溶解性无机氮、浮游植物群落多样性指数和铜元素含量关系显著；结构方程模型模拟结果表明，海水富营养化水平对浮游动物丰富度的效应系数为-0.26，具有显著的直接影响（P=0.01），重金属污染水平通过影响浮游植物丰富度（效应系数为-0.41，P<0.001）间接对浮游动物丰富度产生作用（间接效应系数为-0.2）。研究结果将有助于深化对海水环境和浮游动物群落结构协同演变过程的认识，为滨海湿地近岸海洋生态系统科学管理提供理论支撑。;Quantitative analysis of the relationship between the water environmental factors and zooplankton community nearshore of the coastal wetland is of great significance for assessing the sea water quality. Based on the investigation and sampling of the seawater and zooplankton nearshore of Yalu River Wetland National Nature Reserve in December 2019, the influence of environmental factors on zooplankton community structure was analyzed using Redundancy Analysis (RDA) and the Structural Equation Modeling (SEM). A total of 14 species of zooplankton and 5 groups of planktonic larvae were identified, of which the number of copepods was the highest with proportion of 52.63%. None significant difference of zooplankton community was detected among different subareas of the nature reserve. The diversity index, evenness index and richness index of zooplankton community in the study area were 1.34, 0.51, 0.59, respectively. Simulation result of the SEM showed that richness index of the zooplankton community was directly affected by the eutrophication status of the sea water with a coefficient of -0.26 (P=0.01), and was indirectly affected by the heavy metal pollution status with a coefficient of -0.2. This study provides useful insight for the relationship between sea water environmental factors and the zooplankton community, and provides basis for the scientific management of the offshore marine ecosystem of coastal wetland.