Advances in marine biology最新文献

The Cells of Ecosystem Functioning are natural units of management and conservation, allowing for an ecosystem-based maritime spatial planning based on an accurate knowledge of marine biodiversity and ecosystem functioning which, however, is presently insufficient and fragmentary. A five-step roadmap to fill current knowledge gaps and make ecosystem-based marine sustainability possible is proposed: Step 1: make the inventory of biodiversity. Step 2: unveil the roles of species. Step 3: understand the ecological relationships that link species with each other and with the physical environment. Step 4: frame marine biodiversity and ecosystem functioning in a five dimensional spatial and temporal context (the Cells of Ecosystem Functioning). Step 5: plan our activities so as to preserve a healthy state of ecosystems. EU legislation has drawn a careful map to guide us along this road, with a series of directives that, if successfully enforced, will be conducive to knowledge-based marine sustainability.

The morphology of members of the order Rhizostomeae is revisited considering all life cycle stages, but with emphasis on the medusa. The current classification of the group is presented, and some aspects of species diversity are discussed. The main issues investigated since the 1970s are briefly presented by decade.

In the present study we reviewed the life cycles and reproduction strategies of the order Rhizostomeae. We found 28 species with described life cycles representing ∼30% of the valid species. The metagenetic life cycle of most scyphozoans, which includes the benthic asexually-reproducing polyp and the pelagic sexually-reproducing medusa, is exhibited by all rhizostome species. Rhizostomeae are dioecious with only two exceptions described as hermaphroditic. Sexual dimorphism can be found in species with special external structures utilised for brooding but others show no sexual dimorphism despite the colour of mature gonads. Six asexual reproduction modes have been described for the production of new polyps but rhizostome polyps propagate through a main mode that differs among taxa. Species belonging to Dactyliophorae produce new polyps by podocysts whereas the Kolpophorae new polyps develop from free-swimming buds. The number of ephyrae formed per strobila differs between taxa with monodisc and polydisc strobilation in the Kolpophorae and Dactyliophorae, respectively. Given the low number of studied species it is expectable that new reproductive strategies will be discovered when additional species are investigated. We recommend increasing (1) descriptions on life cycles and reproductive strategies for a greater number of species, (2) attempts to locate the polyps in the field, (3) the study of species in their natural environment, to understand the population dynamics of Rhizostomeae and to clarify the potential of artificial structures to increase medusa populations. In addition, experimental studies are needed to improve our understanding of the factors affecting transitions between life cycle stages and medusa production rates.

Max Egon Thiel's chapter on the ecology of rhizostomes in his review up to 1970 covered a bewildering variety of topics, many of which are the focus of other chapters in this volume: their interactions with humans; their associations with other organisms; their venoms. Although he also discussed their habitats and habits, the effects of environmental conditions on distribution, and patterns in seasonality, he paid scant attention to blooms, he did not write about their role in the wider ecosystem, and he ignored alien introductions. It is clearly impossible to comprehensively update Thiel's review in a similar vein - we don't have the space - and so we have decided to focus our efforts here on either those topics that particularly fascinated him (seasonality), or those that he did not write about (alien introductions, their role in the ecosystem). Our narrative is based on case studies of well known taxa, from which we attempt to draw patterns of commonality, where appropriate. We conclude our account with a discussion of rhizostomes as Discomedusae, and whether we should be considering them separately from semaeostomes in terms of ecology.

Rhizostomeae species attract our attention because of their distinctive body shape, their large size and because of blooms of some species in coastal areas around the world. The impacts of these blooms on human activities, and the interest in consumable species and those of biotechnological value have led to a significant expansion of research into the physiology and functional biology of Rhizostomeae jellyfish over the last years. This review brings together information generated over these last decades on rhizostome body composition, locomotion, toxins, nutrition, respiration, growth, among other functional parameters. Rhizostomes have more than double the carbon content per unit of biomass than jellyfish of Semaeostomeae. They swim about twice as fast, and consume more oxygen than other scyphozoans of the same size. Rhizostomes also have faster initial growth in laboratory and the highest body growth rates measured in nature, when compared to other medusae groups. Parameters such as body composition, nutrition and excretion are highly influenced by the presence of symbiotic zooxanthellae in species of the Kolpophorae suborder. These physiological and functional characteristics may reveal a wide range of adaptive responses, but our conclusions are still based on studies of a limited number of species. Available data indicates that Rhizosotomeae jellyfish have a higher energy demand and higher body productivity when compared to other jellyfish groups. The information gathered here can help ecologists better understand and make more assertive predictions on the role of these jellyfish in their ecosystems.

Written to serve as a guideline for future research in this field, this roadmap provides some perspectives on the main developments and remaining challenges in the field of marine animal acclimatisation, adaptive potential and resilience to climate change. There has been extensive research conducted on the impact of climate change stress on marine animals, with studies recognising the potential for cross- and multi- generational impacts. Parents can potentially pass on resilience to offspring. The response of marine animals to climate change stressors is complex where utilising marginal and extreme systems as natural laboratories can help to address key research gaps and provide an understanding of the plastic and adaptive changes necessary for survival under stress.

Why females would mate with multiple partners and have multiple fathers for clutches or litters is a long-standing enigma. There is a broad dichotomy in hypotheses ranging from polyandry having benefits to simply being an unavoidable consequence of a high incidence of male-female encounters. If females simply give in to mating when it is too costly to avoid being harassed by males (convenience polyandry), then there should be a higher rate of mating as density increases. However, if females actively seek males because they benefit from multiple mating, then mating frequency, and consequently the incidence of multiple paternity of clutches, should be high throughout. To explore these competing explanations, here we review the incidence of multiple paternity for sea turtles nesting around the World. Across 30 rookeries, including all 7 species of sea turtle, the incidence of multiple paternity was only weakly linked to rookery size (r²=0.14). However, using high resolution at-sea GPS tracking we show that the specifics of movement patterns play a key role in driving packing density and hence the likely rate of male-female encounters. When individuals use the same focal areas, packing density could be 100× greater than when assuming individuals move independently. Once the extent of adult movements in the breeding season was considered so that movements and abundance could be combined to produce a measure of density, then across rookeries we found a very tight relationship (r²=0.96) between packing density and the incidence of multiple paternity. These findings suggest that multiple paternity in sea turtles may have no benefit, but is simply a consequence of the incidence of male-female encounters.

Max Egon Thiel worked as curator of the aquatic invertebrates collection at the Zoological Museum in Hamburg until 1963. Specialising in marine planktonic megafauna, he compiled a broad review of the research history on the Scyphozoa (Coronatae, Cubomedusae, Semaeostomeae) including the Staurozoa (as Stauromedusae), written in German. After publishing major parts in 1936 and 1938, World War II delayed further chapters until 1959 and 1962. A complete bibliography covering references up to 1970 was not printed until 1977. The final section on the taxon Rhizostomeae was completed as a typescript before his death, but was never published. In the present paper, the authors provide a synopsis of the published volumes in English. Following Thiel's original outline, the research history, as well as reviews of the current knowledge at the time about morphology, histology, ontogeny (life cycle), physiology, ecology, and phylogeny of the taxa are presented. The paper is complemented by two electronic supplements: A translated and revised version of the left-behind typescript of Max Egon Thiel about the taxon Rhizostomeae, and the revised digital list of references published in Thiel (1977).

Rhizostomeae research based on morphological approaches was reinforced and diversified by new techniques after the 1970s, including developing methodologies for phylogenetic analysis, the rise of the polymerase chain reaction, and the emergence of different sequencing technologies. Here, we summarize the contribution of morphological and molecular data to the study of the classification and phylogenetic relationships of Rhizostomeae in addition to the use of molecular data in studies at the population, species, and supraspecific levels. Throughout the history of the study of the Rhizostomeae systematics, morphological data have been neglected when it comes to phylogenetic inferences, which is reflected in the lack of a phylogenetic analysis of the taxa within Rhizostomeae based on phenotypic characters of the adult medusa. Concerning molecular data, ca. 3,200 nucleotide sequences are available in GenBank and are mainly used for discovering, delimiting, describing, and identifying species. Molecular approaches have also allowed species monitoring by qPCR and metabarcoding of environmental DNA, as well as unveiling the distribution and genetic diversity of jellyfish populations, shedding light on introduction events, conservation, and health of edible jellyfish stocks. Nucleotide sequences have also been key for the development of phylogenetic hypotheses that serve as basis for investigations on the origin and diversification of morphological, ecological, and behavioral traits within Cnidaria; however, despite the progress achieved, phylogenetic uncertainty still exists, especially within the formerly known superfamily Inscapulatae. Future directions in Rhizostomeae research involve generating molecular and morphological data of neglected taxa, which represents a golden opportunity to understand the evolution of Rhizostomeae.

Two species of digenean trematodes of the family Brachycladiidae were obtained from two male dwarf sperm whales Kogia sima that stranded along the island of Kyushu, southern Japan in 2017. From the liver of the first animal, a single, large gravid specimen of a digenean species was collected. The morphological features were consistent with those of the genus Brachycladium. The worm had a large body and was characterized by anterior caeca without lateral diverticula, the shape of testes, ovary, and eggs. Molecular analyses using gene sequences of the 28S rRNA and the mitochondrial NADH dehydrogenase subunit 3 also supported the inclusion of this specimen into the genus Brachycladium. The identity of this worm is undetermined due to the lack of information on the genus and is reported as Brachycladium sp. From the cranial sinuses of the second animal, 33 specimens of digeneans were collected that were morphologically identified as Nasitrema gondo. This report documents a new host record for N. gondo, and the sequence information is provided for this digenean for the first time. This is the second record of digenean parasites for the family Kogiidae, and the first record with morphological and molecular information. The possibility of digenean infection in the liver and cranial sinus should be kept in mind during the necropsy of stranded kogiids.