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Helgoland Marine Research
Journal Prestige (SJR): 0.599

Citation Impact (citeScore): 1
Number of Followers: 2

This is an Open Access Journal

Open Access journal
ISSN (Print) 1438-3888 - ISSN (Online) 1438-387X
Published by Springer-Verlag

[2469 journals]

Variation characteristics of ocean sediment Fe levels and their
relationship with grain sizes in culture areas over a long period
- Abstract: Abstract Iron (Fe) is an essential component for marine ecosystems, and it is related to the growth of phytoplankton communities and environmental evolution in coastal area. However, the effect of aquaculture activities on sediment Fe levels is not well studied. Fe levels and grain sizes are determined in two cores (respectively Core C in the culture area and Core A in the control area) in Sishili Bay to reveal the influence of cultivation on sediment Fe levels over an extended period. The sediment Fe levels are distinguished in the upper sections (culture period) but equal in the lower sections (non-culture period) of the two cores. The core C has the same Fe levels as Core A before 1950s (non-culture period). However, the sediment Fe levels of Core C increased during 1950s–1970s (the algae culture period) and decreased after the 1970s (shellfish culture period) compared with Core A, indicating the algae and shellfish culture impose opposite effects on sediment Fe levels. Similarly, sediment grain sizes are observed to be finer during the algae culture period but coarser during the shellfish culture period, and the variation of sediment grain sizes because of culture activities is the important factor affecting sediment Fe levels. The slowing down of ocean current due to algae culture causes finer particles and higher Fe levels in sediment. However, during the shellfish culture period, bio-deposition and re-suspension play major roles in coarsening sediment particles and decreasing sediment Fe levels.
  PubDate: 2021-12-02
  DOI: 10.1186/s10152-021-00554-z
Who lives where' Macrobenthic species distribution over sediment types
and depth classes in the eastern North Sea
- Abstract: Abstract An extensive data set of macrozoobenthos from the eastern North Sea was evaluated in order to describe the distribution of infaunal species with respect to water depth and median grain size of the sediment. The resulting data are presented for 134 species, in 104 species abundance correlated significantly with water depth, with most species decreasing in abundance towards the hydrographically turbulent shallow areas. This suggests hydrography is a limiting factor for most of the species in this area while very few species only seem to favour the turbulent side of the gradient. With respect to median grain size, two thirds of the species showed significant abundance variations and one third did not. Most of the latter species were either represented by rather poor data or are known to be highly motile. Thus, true sediment generalists seem to be few. Conversely, no species was exclusively restricted to a single sediment type. Significant depth × sediment type interaction terms in a regression model indicate that abundance distribution over sediment types varied with depth level in 60% of the species, indicating that these populations were restricted to a part of their species-specific tolerated ranges in the study area. Hence, the distributional patterns over water depth and sediment types shown here represent realised niches. These data may help to locate populations and, in the light of global change, may serve as a baseline for future comparisons.
  PubDate: 2021-11-04
  DOI: 10.1186/s10152-021-00552-1
In the Asia-Pacific region, the COI DNA test revealed the divergence of
the bivalve mollusc Mactra chinensis into three species; can these species
be distinguished using shell coloration and sperm structure'
- Abstract: Abstract According to COI DNA barcoding testing, the marine bivalve mollusc Mactra chinensis, which is native to the Asia-Pacific region, diverged into three species. These species were preliminary characterized as M. chinensis COI clade I, M. chinensis COI clade II and M. chinensis COI clade III. To find out whether it is possible to morphologically distinguish samples representing genetic clades, we examined the color of the shells and the structure of the spermatozoa. It was found that the number of detected coloration types exceeds the number of detected species. In addition, it was shown that individuals belonging to the same genetic clade can have shells of different colors. Consequently, it is impossible to choose one type of shell coloration as a species-specific trait. For sperm, the sperm morphological patterns found in each of the three species are consistent with the M. chinensis sperm model described in previous reports. However, the single sperm variant is also not applicable to discriminate between species derived from M. chinensis, since heterogeneous variants of spermatozoa differing in the length of the acrosomal rod were found. We hypothesized that genetic divergence of species could cause a shift towards predominance of one of the sperm variants, and that species-specific sperm morphs could be quantitatively dominant in molluscs belonging to different clades. However, the dominant sperm morphs were the same in COI clade I and COI clade III. Thus, dominant sperm morphs are useless as species-specific traits. However, shell color and sperm parameters are specific to different geographic regions, and it seems that unique environmental factors can determine shell color and sperm morphology. As a result, both shells and spermatozoa can be used to distinguish the geographical forms of M. chinensis, regardless of the belonging of the forms to a particular genetic clade. Here we propose the introduction of geographic identifiers, in which the shell color and parameters of sperm sets are used as morphological criteria to determine the geographical origin of mollusc specimens belonging to the M. chinensis species complex.
  PubDate: 2021-10-30
  DOI: 10.1186/s10152-021-00553-0
Living and dead foraminiferal assemblage from the supratidal sand Japsand,
- Abstract: Abstract Supratidal sands are vitally important for coastal defence in the German Wadden Sea. They are less affected by human activities than other areas as they are located far off the mainland shore, touristical and commercial activities are generally prohibited. Therefore, supratidal sands are of high ecological interest. Nevertheless, the faunal inventory and distribution pattern of microorganisms on these sands were studied very little. The composition of living and dead foraminiferal assemblages was therefore investigated along a transect from the supratidal sand Japsand up to Hallig Hooge. Both assemblages were dominated by calcareous foraminifera of which Ammonia batava was the most abundant species. Elphidium selseyense and Elphidium williamsoni were also common in the living assemblage, but Elphidium williamsoni was comparably rare in the dead assemblage. The high proportions of Ammonia batava and Elphidium selseyense in the living assemblage arose from the reproduction season that differed between species. While Ammonia batava and Elphidium selseyense just finished their reproductive cycles, Elphidium williamsoni was just about to start. This was also confirmed by the size distribution patterns of the different species. The dead assemblage revealed 20 species that were not found in the living assemblage of which some were reworked from older sediments (e.g., Bucella frigida) and some were transported via tidal currents from other areas in the North Sea (e.g., Jadammina macrescens). The living foraminiferal faunas depicted close linkages between the open North Sea and the mainland. Key species revealing exchange between distant populations were Haynesina germanica, Ammonia batava and different Elphidium species. All these species share an opportunistic behaviour and are able to inhabit a variety of different environments; hence, they well may cope with changing environmental conditions. The benthic foraminiferal association from Japsand revealed that transport mechanisms via tides and currents play a major ecological role and strongly influence the faunal composition at this site.
  PubDate: 2021-09-28
  DOI: 10.1186/s10152-021-00551-2
Benthic community establishment on different concrete mixtures introduced
to a German deep-water port
- Abstract: Abstract Concrete is a widely used building material in coastal constructions worldwide. However, limited natural resources used in the production process, as well as high CO2-emission due to the calcination process of limestone and the thermal energy demand for Portland cement clinker production, raise the demand for alternative constituents. Alternative mixture types should be environmentally friendly and, at best, mimic natural hard substrates. Here five different concrete mixtures, containing different cements (Portland cement and blast furnace cements) and aggregates (sand, gravel, iron ore and metallurgical slags) were made. Three replicate cubes (15 × 15 × 15 cm) of each type were then deployed in a German deep-water Port, the JadeWeserPort, to study benthic community establishment after one year. Results are compared to a similar experiment conducted in a natural hard ground environment (Helgoland Island, Germany). Results indicate marked differences in settled communities in the Port site compared to natural environments. At the Port site community composition did not differ with the concrete mixtures. Surface orientation of the cubes (front/top/back) revealed significant differences in species abundances and compositions. Cubes hold more neobiota in the Port site than in natural hard ground environments. Implications for the usage of new concrete mixtures are discussed.
  PubDate: 2021-06-19
  DOI: 10.1186/s10152-021-00550-3
An example for transatlantic hitchhiking by macrozoobenthic organisms with
a research vessel
- Abstract: Abstract In 2019 the RV Meteor cruised from Guadalupe in April/May to Cape Verde in June/July and to Namibia in August/September. The distance is about 10,000 km. The ship has a moon pool for installation of instruments. In Cape Verde we had a first glimpse of the already sparsely populated moon pool. We reached Namibian waters in mid-August. In mid-September, 47 days later and 6000 km south, the ship's moon pool was sampled in the port of Walvis Bay. 13 different taxa could be identified belonging to two phyla, four classes, six orders and 10 families. Most of these species have not yet been observed in the port or in the adjacent areas and are new records for the entire Namibian coast. The goose barnacles Conchoderma auritum (Linnaeus, 1767), Conchoderma virgatum Spengler, 1789 and Lepas anatifera Linnaeus, 1758 were particularly noticeable. They were only surpassed by the large number of amphipods. The species Ericthonius brasiliensis (Dana, 1853), Jassa marmorata Holmes, 1905, Stenothoe senegalensis Krapp-Schickel, 2015 and Paracaprella pusilla Mayer, 1890 are particularly noteworthy here. In addition, the pycnogonid species Endeis straughani Clark, 1970 and the titan acorn barnacle Megabalanus coccopoma (Darwin, 1854) should be mentioned, which occurred very frequently as well. The present study shows, on the one hand, an example of the transatlantic spread of bioinvasive species by ships as vectors and, on the other hand, a convenient method for sampling ship hulls.
  PubDate: 2021-06-03
  DOI: 10.1186/s10152-021-00549-w
Methods to study organogenesis in decapod crustacean larvae II: analysing
cells and tissues
- Abstract: Abstract Cells and tissues form the bewildering diversity of crustacean larval organ systems which are necessary for these organisms to autonomously survive in the plankton. For the developmental biologist, decapod crustaceans provide the fascinating opportunity to analyse how the adult organism unfolds from organ Anlagen compressed into a miniature larva in the sub-millimetre range. This publication is the second part of our survey of methods to study organogenesis in decapod crustacean larvae. In a companion paper, we have already described the techniques for culturing larvae in the laboratory and dissecting and chemically fixing their tissues for histological analyses. Here, we review various classical and more modern imaging techniques suitable for analyses of eidonomy, anatomy, and morphogenetic changes within decapod larval development, and protocols including many tips and tricks for successful research are provided. The methods cover reflected-light-based methods, autofluorescence-based imaging, scanning electron microscopy, usage of specific fluorescence markers, classical histology (paraffin, semithin and ultrathin sectioning combined with light and electron microscopy), X-ray microscopy (µCT), immunohistochemistry and usage of in vivo markers. For each method, we report our personal experience and give estimations of the method’s research possibilities, the effort needed, costs and provide an outlook for future directions of research.
  PubDate: 2021-06-02
  DOI: 10.1186/s10152-021-00547-y
Methods to study organogenesis in decapod crustacean larvae. I. larval
rearing, preparation, and fixation
- Abstract: Abstract Crustacean larvae have served as distinguished models in the field of Ecological Developmental Biology (“EcoDevo”) for many decades, a discipline that examines how developmental mechanisms and their resulting phenotype depend on the environmental context. A contemporary line of research in EcoDevo aims at gaining insights into the immediate tolerance of organisms and their evolutionary potential to adapt to the changing abiotic and biotic environmental conditions created by anthropogenic climate change. Thus, an EcoDevo perspective may be critical to understand and predict the future of organisms in a changing world. Many decapod crustaceans display a complex life cycle that includes pelagic larvae and, in many subgroups, benthic juvenile–adult stages so that a niche shift occurs during the transition from the larval to the juvenile phase. Already at hatching, the larvae possess a wealth of organ systems, many of which also characterise the adult animals, necessary for autonomously surviving and developing in the plankton and suited to respond adaptively to fluctuations of environmental drivers. They also display a rich behavioural repertoire that allows for responses to environmental key factors such as light, hydrostatic pressure, tidal currents, and temperature. Cells, tissues, and organs are at the basis of larval survival, and as the larvae develop, their organs continue to grow in size and complexity. To study organ development, researchers need a suite of state-of-the-art methods adapted to the usually very small size of the larvae. This review and the companion paper set out to provide an overview of methods to study organogenesis in decapod larvae. This first section focuses on larval rearing, preparation, and fixation, whereas the second describes methods to study cells, tissues, and organs.
  PubDate: 2021-06-02
  DOI: 10.1186/s10152-021-00548-x
Macrofaunal assemblages associated with two common seagrass‐dwelling
demosponges (Amorphinopsis atlantica and Haliclona implexiformis) in a
tropical estuarine system of the southern Gulf of Mexico
- Abstract: Abstract Among the ecological roles that sponges play in marine ecosystems, one of the highlights is their ability to host a wide diversity and abundance of epibenthic organisms. However, of the different marine environments, this role has been less investigated in seagrass-dwelling sponges. In this study, the main objective was to determine whether the structure of the associated faunal assemblages in two common sympatric species of seagrass-dwelling sponges (Amorphinopsis atlantica and Haliclona implexiformis) vary depending on the volume and morphology of the host sponge as well as the environment to which both sponges are exposed. Even though the collection sites had the same habitat type (seagrass meadows composed by Thalassia testudinum and Halodule wrightii) and depth, there were substantial differences in faunal composition (ANOSIM test, R = 0.86) between both sponge species. The value of the data on species richness, diversity, and abundance of associated organisms was significantly higher in the individuals of A. atlantica than in those of H. implexiformis. These differences in the community structure of associated fauna could be influenced by the differential growth form of the hosts (e.g. growth form and oscula diameter) as well as their distinct environmental preferences (sites with different degrees of exposure to wind-generated waves and levels of human disturbance). This study contributes to the knowledge on the functional role that sponges play in seagrass meadows, one of the world’s most endangered ecosystems. Furthermore, it underlines the importance of examining both, the sponge morphology and the local environmental conditions, to explain spatial variations in the macrofaunal assemblages associated with sponges.
  PubDate: 2021-02-16
  DOI: 10.1186/s10152-021-00546-z
Diversity of mangrove root-dwelling sponges in a tropical coastal
ecosystem in the southern Gulf of Mexico region
- Abstract: Abstract Sponges are one of the most conspicuous groups of epibionts in mangrove prop root habitats. However, with the exception of the Caribbean and the Indo-Pacific regions, studies focused on species diversity are lacking in other locations that have high mangrove coverage and are relatively distant from coral reef environments. Because mangrove-root epibiont communities, in general, have been understudied worldwide, this research contributes to filling this knowledge gap. In this study, a total of 30 sponge species (belonging to three subclasses, 14 families and 19 genera) were recorded as epibionts on prop roots of the red mangrove Rhizophora mangle in a tropical coastal ecosystem of the Southern Gulf of Mexico. Of these, five were new records for the Gulf of Mexico, 14 were new for the Mexican coasts of the gulf and 25 were new for the study area. Moreover, a similarity analysis based on presence/absence data of mangrove-associated sponges reported throughout the Western Central Atlantic region revealed that the sponge assemblage from the study area was more similar to those documented in most of the Caribbean locations (Jamaica, Cuba, Martinique, Panama, Venezuela, Belize and Colombia) rather than with those of the Northeast of the Gulf of Mexico, Guadeloupe and Trinidad. This relative intra-regional dissimilarity in the structure of mangrove-associated sponge assemblages may be related to differences in environmental conditions as well as taxonomic effort. The study area, unlike most of the Caribbean locations, is characterized by estuarine conditions and high productivity throughout the year. The inter-site variability recorded in the composition of mangrove-associated sponges was influenced by a set of factors such as salinity, dissolved oxygen and hydrodynamism. This study shows the importance of exploring the mangrove-associated sponge assemblages from different regions of the world as it furthers knowledge of the biodiversity and global distribution of this group.
  PubDate: 2020-12-02
  DOI: 10.1186/s10152-020-00545-6
Ovary resorption in the Norway lobster (Nephrops norvegicus) and its
possible causes with special reference to sperm storage
- Abstract: Abstract The Norway lobster, Nephrops norvegicus, is an important fisheries species in the North-East Atlantic area. In some circumstances, mature females of Nephrops norvegicus can resorb their ovary rather than completing spawning, but the implications of this phenomenon to reproductive biology and fisheries sustainability are not known. To understand after effects of ovary resorption, we studied long-term demographic data sets (1994–2017) collected from the western Irish Sea and the North Sea. Our considerations focused on potential correlations among the frequency of resorption, female insemination, and body size of resorbing females. Resorption was continuously rare in the western Irish Sea (less than 1%); whereas much higher rates with considerable year-to-year variation were observed in the North Sea (mean 9%). Resorption started in autumn after the spawning season (summer) had passed. The frequency stayed high throughout winter and declined again in spring. As sperm limitation can occur in male-biased fisheries, we expected a lack of insemination could be responsible for resorption, but affected females were indeed inseminated. Resorbing females were significantly larger than other sexually mature females in the North Sea, but the opposite trend was observed in the western Irish Sea. It is therefore possible that other, environmental factors or seasonal shifts, may trigger females to resorb their ovaries instead of spawning. Resorption may as well represent a natural phenomenon allowing flexibility in the periodicity of growth and reproduction. In this sense, observations of annual versus biennial reproductive cycles in different regions may be closely linked to the phenomenon of ovary resorption.
  PubDate: 2020-10-27
  DOI: 10.1186/s10152-020-00543-8
Culture of benthic diatom Nitzschia sp. with macroalgae carriers and its
application as feed of juveniles Stichopus japonicus
- Abstract: Abstract Carrier culture is the combination of suspension culture and adherent culture. Carriers could be used to improve the culture efficiency of large-scale culture of adherent benthic diatom. In order to identify a suitable carrier for mass suspension culture of the benthic diatoms Nitzschia sp. powders of seven macroalgae were used as carriers for diatom attachment including Ulva pertusa, degummed Laminaria japonica, Sargassum muticum, Chaetomorpha valida, Zostera marina, Sargassum fusiforme and Sargassum thunbergii. Diatoms could grow on the surface of the suspended carriers and could effectively utilize the nutrients released by the decomposition of these carriers. Among the seven carriers, Ulva pertusa powder was the most effective for Nitzschia culture when comprehensively considering the nutrition of the harvested diatoms and nutrient utilization of the algae carrier by diatoms. The seaweed powder was dried at 80 °C before used as carrier, this process should meet the sterilization requirements for microalgal culture and is easy to implement in the large-scale cultivation of diatoms. Diatoms cultured with carriers were used to feed juveniles Stichopus japonicus with a wet weight of 5.0 ± 2.0 g, as well as diatoms cultured using conventional methods without carriers, and no significant differences were observed between the two kinds of feed. Compared to sea cucumbers fed with commercial feed, the growth rate of S. japonicus fed with carrier-cultured diatoms was approximately 1.5 times greater, and the activities of non-specific immune enzymes were improved in the coelomic fluid including acidic phosphatase, alkaline phosphatase and superoxide dismutase. Feeding sea cucumber with fresh diatoms could effectively reduce the total nitrogen and total phosphorus in the culture water, improve the water quality, and promote the breeding of sea cucumbers, regardless of whether the carrier culture was adopted.
  PubDate: 2020-10-16
  DOI: 10.1186/s10152-020-00544-7
Changes in thiamine concentrations, fatty acid composition, and some other
lipid-related biochemical indices in Baltic Sea Atlantic salmon (Salmo
salar) during the spawning run and pre-spawning fasting
- Abstract: Abstract Salmonines in the Baltic Sea and North American lakes suffer from thiamine (vitamin B1) deficiency, which is connected to an abundant lipid-rich diet containing substantial amounts of polyunsaturated fatty acids (PUFAs). In the Baltic region, this is known as the M74 syndrome. It affects both adult salmon (Salmo salar) and especially their offspring, impairing recruitment. However, very little is known about the thiamine and lipid metabolism of salmon during feeding and spawning migrations in the Baltic Sea. In this study, salmon females were sampled along the spawning run from the southern Baltic Proper in four locations at sea and finally at spawning in a river at the Bothnian Bay in a year with insignificant M74 mortality. Changes in concentrations of thiamine and its components in muscle, ovaries, and the liver and other biochemical indices potentially relating to lipid and fatty acid metabolism were investigated. The results provide further evidence of the role of peroxidation of PUFAs in eliciting thiamine deficiency in salmon: During the entire spawning run, the muscle total lipid content decreased by 50%, palmitic acid (16:0) by 62%, and docosahexaenoic acid (DHA, 22:6n-3) by 45%. The concentration of total thiamine decreased significantly until the spawning in the liver and ovaries, 66 and 70% respectively. In the muscle, the proportion of thiamine pyrophosphate of total thiamine increased with the use of muscular lipid stores. There was no trend in the concentration of total carotenoids during the spawning run. The doubling of the concentration of hepatic malondialdehyde indicated peroxidation of PUFAs, and the mobilisation of body lipids suppressed the activity of glucose-6-phosphate dehydrogenase, as consumed dietary lipids would also have done.
  PubDate: 2020-08-28
  DOI: 10.1186/s10152-020-00542-9
A cross-genus comparison of grazing pressure by two native marine
herbivores on native, non-native naturalized, and non-native invasive
Sargassum macroalgae
- Abstract: Abstract In marine systems, algal abundance and community composition is often heavily influenced by top-down control by herbivores. As a result, examining the extent to which native herbivores exert grazing pressure on non-native marine algae can provide valuable insight into mechanisms controlling invasion success. The purpose of this study was to examine the grazing preferences of two common intertidal and subtidal herbivores on three congeneric species of marine algae with unique colonization histories in San Diego, California, USA, to determine if grazing pressure, or lack thereof, may help explain invasion success. We provide evidence that neither native Sargassum agardhianum, nor non-native Sargassum horneri, are particularly palatable to purple urchins or black turban snails, but that non-native Sargassum muticum is consumed by both native herbivores. We also provide evidence that when given a choice of all three species neither herbivore exhibits a significant grazing preference for any algal species. We suggest that other mechanisms may determine the invasion success of the two non-native algal species and the overall distribution and abundance patterns of these species, and we discuss potential directions for future work.
  PubDate: 2020-08-12
  DOI: 10.1186/s10152-020-00541-w
Giant planktic larvae of anomalan crustaceans and their unusual compound
eyes
- Abstract: Abstract Crustacean larvae are usually recognised as small organisms, below one millimeter body size. However, in different crustacean groups such as Stomatopoda, Polychelida, or Achelata, also very large larvae occur with sizes of 20 mm and beyond. Also from few meiuran species (“short-tailed” crustaceans, including crabs, hermit crabs, or squat lobsters), rather large larvae are known, though still considerably smaller than 20 mm. We present here two specimens of anomalan meiuran larvae, each with a total length of 24 mm, which by far exceed the previously known/reported maximum sizes of meiuran larvae. Yet, both specimens exhibit characters that indicate their identity as zoea larvae (first larval phase with several stages), most likely shortly before the metamorphosis to the megalopa (second larval phase with one stage). Due to this early developmental state, it is difficult to provide a narrower systematic identification of the larvae. In addition to the description of the developmental status of all appendages, we also investigated the gizzard and especially the compound eyes. The latter possess a mixture of hexagonal, intermediate, and square-shaped facets in an unusual arrangement. We documented the exact arrangement of the facets in both specimens and discuss the possible re-structuring during metamorphosis. The arrangement of the different types of facets indicates that transformation to an adult eye structure takes place over several moults and that the facets are being rearranged in this process. The findings demonstrate that also meiuran larvae contribute to the fraction of the macro-plankton.
  PubDate: 2020-08-06
  DOI: 10.1186/s10152-020-00540-x
Micro- and mesozooplankton at the edges of coastal tropical reefs
(Tamandaré, Brazil)
- Abstract: Abstract Tropical reef ecosystems are generally considered to be sinks of marine zooplankton, mainly due to the predation by scleractinian corals and other planktivores. The present study aims to evaluate the zooplankton community of a coastal reef in two specific environments: the reef edge and open-water channels between patch reefs. Sampling was carried out at two patch reefs that border the Tamandaré coastal lagoon system (Pernambuco State, Brazil). Two passive stationary nets (64 μm mesh size) were used: the Reef Edge Net (REN) and the Channel Midwater Neuston Net (CMNN). Sampling was performed simultaneously at both reefs during eight nocturnal sampling campaigns, always at new moon ebb tides. Zooplankton was classified by “origin” (estuarine, reef, neritic and neritic/estuarine). During all campaigns and at both sites, a significant buildup of zooplankton at the reefs was observed. Reef edges showed significantly higher abundance (77,579 ± 73,985 ind. m−3) and biomass (48.9 ± 45.5 mg C m−3) of zooplankton compared to open-water channels (9982 ± 11,427 ind. m−3 and 11.4 ± 21.9 mg C m−3, respectively). A total of 65 taxonomic groups were identified. Copepods were the most abundant group with a contribution of 69% for total zooplankton abundance, followed by foraminiferans, gastropod veligers, appendicularians, cirripedians nauplii, and polychaete larvae. Copepods from neritic/estuarine environments dominated the reef edges in both relative abundance and relative biomass (91% and 88%, respectively). The unexpectedly high abundance of copepods and other holoplankton at the reef edges, when compared to Indo-Pacific and Caribbean reefs, is probably due to very low cover of corals and other zooplanktivorous sessile animals (< 0.2%) on these coastal reefs, which leads to a very low predation mortality for zooplankters. Also, we propose that the reduced water column above the reef top leads to a buildup of very high densities in these environments.
  PubDate: 2020-05-22
  DOI: 10.1186/s10152-020-00539-4
Reproduction of the endangered endemic saffron coral to the Gulf of
California Porites sverdrupi (Anthozoa: Scleractinia): implications for
its long-term maintenance
- Abstract: Abstract The biology of the scleractinian Porites sverdrupi, endemic to the Gulf of California, is poorly studied. In order to fill that gap, the present study documents the reproductive biology of this coral which is to date protected by the IUCN’s as “vulnerable” and listed as “in risk of extinction” in the Mexican Federal Law for species protection. Also, potential distribution models were constructed to evaluate the status of the remaining species’ populations, and the role that reproduction has in their permanence. Porites sverdrupi show a gonochoric brooding reproductive pattern, with asynchronous gamete development regulated by sea surface temperature and light. The potential distribution models suggest that this coral currently covers less than 6% of its original range of distribution. Furthermore, the results suggest that, despite the drastic decline of the species, the remaining populations have the ability to persist even under current changing ocean conditions as successful sexual reproduction was documented even during the strong 2014–2015 ENSO event producing sexual recruits to maintain themselves.
  PubDate: 2020-05-12
  DOI: 10.1186/s10152-020-00538-5
Timing of the reproductive cycle of waved whelk, Buccinum undatum, on the
U.S. Mid-Atlantic Bight
- Abstract: Abstract Development of the unmanaged waved whelk (Buccinum undatum) fishery on the Mid-Atlantic continental shelf of the United States has initiated investigation into fisheries-related biological and population attributes of the species in this region. Maturation and reproduction timing vary by location for this species and are likely linked to bottom water temperature. This study examined the seasonal fluctuations in relevant body metrics and gonadosomatic index in relation to bottom temperature to assess the timing of the reproductive cycle of the B. undatum population in the southern-most extent of this species’ range in the Atlantic. To characterize variation over the maturation schedule, nine locations in the Mid-Atlantic Bight (MAB) were sampled five times between January 2017 and September 2017. Maturity was assessed macroscopically, with morphological methods, and via gonadosomatic indices. Male behavioral maturity estimates, based on a penis length to shell length index (PL50), were compared to estimates made using other methods for assessing maturity to test the efficacy of this commonly used ratio. Mature whelk were found in all months and peak reproductive activity was observed in spring and early summer. This timing suggests that ideal sampling to visually identify maturity to estimate size of maturity would be late winter or early spring. Unique oceanographic dynamics in the MAB, such as strong seasonal stratification results in large changes in annual bottom temperature which appears to be closely linked to the reproductive cycle in this region. Our data suggest that B. undatum in the MAB experience spawning and development at ~ 7–8 °C; temperatures warmer than Canadian populations and cooler than some UK conspecifics. To our knowledge, this is the first study to document the annual reproductive cycle of waved whelk in the United States.
  PubDate: 2020-03-02
  DOI: 10.1186/s10152-020-00537-6
Antifouling and antibacterial activities of bioactive extracts from
different organs of the sea cucumber Holothuria leucospilota
- Abstract: Abstract In this study, antifouling and antibacterial properties of polar, semi polar and non-polar bioactive compounds derived from the sea cucumber Holothuria leucospilota were investigated. A series comprising n-hexane, ethyl acetate and methanol extracts from four different organs of sea cucumber (body wall, gonad, digestive tract and respiratory tree) were investigated for their antibacterial and antifouling activity against two species of microalgae, larvae of barnacle Amphibalanus amphitrite and a non-target organism: larvae of Artemia salina. Results showed that the highest antibacterial activity was found in the ethyl acetate extract of body wall against Staphylococcus aureus with minimum inhibitory concentration (MIC) of 0.250 mg/mL. The MIC of ethyl acetate extract of body wall ranged between 0.062 and 0.250 mg/mL against two microalgal strains. All extracts showed moderate to low toxicity against larvae of barnacles. The most pronounced anti-barnacle activity was found in the ethyl acetate extract of body wall with median lethal concentration (LC50) value of 0.049 mg/mL. Among the twelve extracts, the ethyl acetate extracts of body wall showed the maximum antibacterial and antifouling activities. The bioactive compounds of the ethyl acetate extract of the sea cucumber body wall were determined using gas chromatography coupled with mass spectrometry. Fatty acids and terpenes were the major compounds, which may be responsible for antibacterial and antifouling activity of the ethyl acetate extract of body wall of the sea cucumber H. leucospilota.
  PubDate: 2020-02-06
  DOI: 10.1186/s10152-020-0536-8
Combined effects of ocean acidification and hypoxia on the early
development of the thick shell mussel Mytilus coruscus
- Abstract: Abstract Ocean acidification has become serious, and seawater hypoxia has become evident in acidified waters. The combination of such stressors may have interactive effects on the fitness of marine organisms. In order to investigate the interactive effects of seawater acidification and hypoxia on the early development of marine bivalves, the eggs and sperm of the thick shell mussel Mytilus coruscus were exposed to combined treatments of pH (8.1, 7.7, 7.3) and dissolved oxygen (2, 6 mg/L) for 96 h culture observation to investigate the interactive effects of seawater acidification and hypoxia on the early development of marine bivalves. Results showed that acidification and hypoxia had significant negative effects on various parameters of the early development of the thick shell mussel. However, hypoxia had no effect on fertilization rate. Significant interactions between acidification and hypoxia were observed during the experiment. Short-term exposure negatively influenced the early development of the thick shell mussel but did not affect its survival. The effects of long-term exposure to these two environmental stresses need further study.
  PubDate: 2020-01-24
  DOI: 10.1186/s10152-020-0535-9