Changes in the population structure of Calanus sinicus during summer–autumn in the southern Yellow Sea

Calanus sinicus is a calanoid copepod widely distributed in coastal waters of China and Japan, and oversummering strategies may have major impacts on their population dynamics which in turn affect local marine food web structure. The abundance, stage composition, and sex composition of the planktonic copepod C. sinicus were studied from August to October 2002 in the southern Yellow Sea to understand how its population recovers from the over-summering state. Results showed that C. sinicus had low reproduction in August due to high temperature, except in waters near the Cheju Island with rich food and moderate bottom temperature, but the reproduction rates here decreased in September–October as food availability declined. When temperature dropped in September–October, C. sinicus actively propagated in coastal shallow waters. However, reproduction rates of C. sinicus individuals inhabiting the Yellow Sea Cold Water Mass(YSCWM) remained low during the three months of the study. The percentage of C. sinicus females was high during the reproductive period, which suggests that the sex composition of adult C. sinicus may reflect whether or not the population is in the reproductive mode.Numerous fifth copepodite stage(CV) C. sinicus aggregated in the YSCWM in a suspended developmental stage during the three months of this study, and they potentially served as the parental individuals for population development when conditions became optimal for reproduction later in the year.     

Growth and population dynamics of the non‐indigenous species Branchiomma luctuosum Grube (Annelida,Sabellidae) in the Ionian Sea (Mediterranean Sea)

The population dynamics and gametogenesis of the non‐indigenous polychaete species Branchiomma luctuosum Grube, 1869 (Annelida, Sabellidae) has been investigated at three sites in the Taranto Seas (Ionian Sea, Mediterranean Sea). The species, probably introduced from the Red Sea, has been reported in the Mediterranean Sea since 1983. The species is hermaphrodite, and the reproductive season is between June and October when the largest mean size of oocytes was recorded together with the presence of mature spermatozoa. Small oocytes are present in specimens reaching about 20–25 mm in length. Therefore oogenesis seems to begin early during the first year of life, but the first reproduction can occur when the worms attain a larger size and are at least 6 months of age. Although most of the individuals reproduce seasonally within a discrete period, some individuals can reproduce in different periods during the year, the oogenesis of individuals not being synchronous. A life span of at least 2 years is highlighted, with a faster growth rate during the first months (about 20 mm per month) decreasing to about 10 mm from the 3rd to the 8th months and slowing down again after the worm reaches 100 mm in size. Some differences in growth performance are discussed, enhanced by comparing the sites located at greater depth (5–7 m) and those located at 0.5 m depth, together with the possible interactions of this alien species with the autochthonous sabellid Sabella spallanzanii.     

Population size structure, spatial distribution, and life cycle of the hydromedusa Aglantha digitale (O.F. Müller, 1766) in the White Sea

Seasonal variations of the abundance, size structure, and vertical distribution of the population of the hydromedusa Aglantha digitale are studied using the materials collected during multiyear observations in the White Sea from 1961 to 2003. The wide distribution of the species in the Basin of the White Sea and in Kandalaksha, Dvina, and Onega bays is shown. Usually, the maximum bell height of the specimens did not exceed 12 mm, although a few individuals up to 22 mm high were found. The maximum abundance of A. digitale is observed during the reproductive period, which lasts from the second half of June to August. The reproduction starts when the water temperature near the surface reaches 9–11°C. By the onset of winter, specimens with a height of 4–5 mm representing a new generation dominate. By the beginning of the subsequent spring, their average size reaches 5–6 mm, and, by the end of June, specimens with bell heights of 8 mm become mature. During the spring and the summer, the A. digitale population concentrates in the upper 0-to 25-m water layer; during the autumn and winter, it concentrates below the 50-m depth. At the end of the autumn and in the winter, the population is spread over the water column and inhabits all the water layers. At the end of the winter, in April, the ascent of the population starts. An analysis of the seasonal dynamics of the population abundance and size structure indicates that A. digitale in the White Sea has a one-year life cycle.     

Sexual reproduction of Hippospongia communis (Lamarck, 1814) (Dictyoceratida,Demospongiae): comparison of two populations living under contrasting environmental conditions

The study of the reproductive processes of benthic invertebrates is essential to the understanding of their population dynamics and is also important in formulating conservation plans, especially for exploited species. The sexual reproduction of Hippospongia communis, the ‘honeycomb’ bath sponge, was studied at two locations in the Mediterranean Sea: the Kerkennah Islands (Tunisia, South Mediterranean), where the mean annual seawater temperature is 19 °C, and Marseille (France, Northwestern Mediterranean Sea), where the mean annual water temperature is 16 °C. The aim of this comparative study was to determine whether different environmental conditions could affect reproduction patterns. At both locations, H. communis was found to contain sexual reproductive elements year‐round. Oogenesis and embryogenesis occurred throughout the year, whereas spermatogenesis occurred during shorter periods between October and November, in both populations. While gametogenesis seemed to be synchronized, indicating that fertilization could occur at the same time at both locations, spawning was observed in late summer in Marseille, whereas it started in late spring for the Kerkennah population. Larval development of H. communis seems to take longer for sponges living at cooler locations such as Marseille. Reproductive effort calculated for both sexes showed significantly higher values for specimens from Kerkennah Islands. By comparing sexual reproductive patterns of populations living in two contrasted environments, we suggest that a change of thermal regime can affect H. communis phenology.     

Transplantation of Spongia officinalis L. (Porifera,Demospongiae): a technical approach for restocking this endangered species

The present study focuses on the reproductive success of transplants of the bath sponge Spongia officinalis Linnaeus, 1759, with the aim of investigating the possibility of restocking this species, one of the most endangered organisms of the Mediterranean sessile zoobenthos. Transplants of S. officinalis, collected from a wild population along the Apulian coasts (Ionian Sea, Italy), have been moved into an area where the species was present in the past. The transplants consisted both of specimens in toto and of fragments of different sizes, obtained after having cut the mother sponge into pieces. All transplanted sponges showed complete cicatrisation of the cut surfaces within a month of the initial manipulation and had a survival rate of 100% throughout the 12 months of the study. From the present investigation, it has emerged that the reproductive effort and the larval release by the transplants do not differ significantly from those shown by the source population. This successful technical approach supports its application as a strategy for restocking the population of this endangered species.     

Reproductive synchrony in a diverse Acropora assemblage,Vamizi Island,Mozambique

Multi‐specific synchronous spawning has never been documented for East Africa, but coral spawn‐slicks are observed annually around Vamizi Island, Northern Mozambique. We monitored gamete development in Acropora species from July 2012 to October 2013 and from August to September 2014 to describe patterns of reproductive seasonality and synchrony within and amongst species of Acropora. Gamete maturation was highly synchronized within and amongst Acropora species and culminated in multi‐specific spawning events lasting 1–3 nights in each year of the study, in late August or September. In 2013 and 2014, 50% or more of the colonies of over 50% of the species sampled prior to the spawning events had mature gametes. In all years, 91–99% colonies sampled after the spawning events had no visible gametes. The percentage of colonies with mature gametes was up to 100% for some species. In other species, the absence of mature gametes throughout the study period indicates that they might not spawn in certain years. The analysis of a 8‐year record of observations of spawn‐slicks showed that spawning generally occurred once a year for a few consecutive days between September and December, during periods of rising sea surface temperature and low wind speed and rainfall. This study is the first to quantitatively document coral reproduction in Mozambique and multi‐specific synchronous spawning off the coast of Africa. These findings contrast with the asynchronous breeding reported for Kenyan reefs and support the absence of breakdown in coral reproductive synchrony towards low latitudes.     

Population dynamics of Callichirus major (Say, 1818) (Crustacea, Thalassinidea) on a beach in northeastern Brazil

We describe the structure, reproductive cycle, fecundity, growth, and mortality of a harvested population of the ghost shrimp Callichirus major. Samples were collected at monthly intervals from September 1999 to October 2000 on an urban sandy beach (08°11′S 34°55′W) in northeastern Brazil. During this period the sex ratio did not differ significantly from 1:1 (0.98 M: 1 F). Minimum and maximum sizes of the Dorsal Oval were 2.59 and 12.19 mm for males and 4.46 and 12.62 mm for females, respectively. Ovigerous females were found throughout the period, except between August and September 2000. Maximum lifespan was estimated as 3.3 and 3.4 years for females and males, respectively. This northeastern population differed from others previously studied in southern and southeastern Brazil, in regard to sex ratio, maximum attained size, maturation size, period and duration of the reproductive cycle, and fecundity. We interpret these regional differences as evidence for over-fishing at the study site, and suggest that large-scale management plans for callianassid populations should use regional population parameters.     

Comparative reproductive biology of two southwestern Atlantic populations of the hermit crab Pagurus exilis (Crustacea: Anomura: Paguridae)

Pagurus exilis (Benedict, 1892) is an endemic South Atlantic hermit crab with a distribution ranging from Rio de Janeiro State, Brazil, to Buenos Aires Province, Argentina. The present study analyzed the reproduction of two populations at the extremes of this geographical distribution, and compared their reproductive period, fecundity, and changes in egg size and egg volume during the incubation period in order to assess the variability over this latitudinal range. Hermit crabs were collected monthly over a 2‐year period. In total, 108 females were analyzed for Brazil (44 non‐ovigerous and 64 ovigerous), and 141 for Argentina (87 non‐ovigerous and 54 ovigerous). Reproduction in Brazil occurs year‐round, with peaks in the fall and winter seasons; in Argentina reproduction occurs only in spring and summer. The Brazilian ovigerous females were significantly larger than the Argentina ones (Brazil: SL = 5.33 ± 1.45 mm; Argentina: SL = 4.15 ± 0.52 mm; P < 0.001). The fecundity was 1447 ± 831 eggs (317 to 2885) in Brazil and 987 ± 711 eggs (114 to 2665) in Argentina, with a trend towards higher fecundity in Brazil. Eggs in the Argentina population were larger than those in Brazil for all the three stages investigated, and no changes in egg volume were found during egg development for both populations. The reproductive traits of the two populations showed some important differences, which may reflect adaptations to local environmental conditions, demonstrating a high plasticity of reproductive features of the species in Brazilian and Argentine waters. The strategy adopted by the Argentina population involves a lower production of larger eggs compared to the population in Brazil; this lower production is associated with reproduction in cold‐water regions.     

Analyses of the Relationship Between Mucous Aggregates and Phytoplankton Communities in the Gulf of Trieste (Northern Adriatic Sea) by Multivariate Techniques

Abstract. Multivariate techniques (cluster analysis and Principal Component Analysis) applied on phytoplankton data collected in June, July, August, and September 1990, 1991, 1992, and 1993 in the Gulf of Trieste (Northern Adriatic Sea) highlighted a clear temporal pattern from 1990 to 1993. In the summer of 1991, phytoplankton communities showed a dramatic increase in the dinoflagellatddiatom ratio. In particular, during June and July 1991 only few specimens of diatoms ( Cylindrorhecu closreriurn. Probosciu alata, Nirzschio longissimu , and Nitzschiu spp.) were collected; this confirmed the diatom scarcity in the phytoplankton communities before and during the appearance of large mucous aggregates (mucilage) in July 1991 in the Gulf of Trieste. The differences observed between the structure of the phytoplankton communities inside the aggregates and in the ambient waters suggested two hypotheses: 1) the aggregates were not produced in the gulf, but were carried ints the gulf by the eastern bordering current; 2) the aggregates were produced by a few, scarce species with a high exudate production that are capable of quickly reaching a high reproductive rate within the aggregates.     

Sexual reproduction in Sarcotragus spinosulus from two different shallow environments

The reproductive cycle of the demosponge Sarcotragus spinosulus from two different shallow environments (La Pierta and La Strea) of the Ionian coasts of Apulia (SE Italy) was studied from February 2006 to February 2007 in 20 tagged specimens. The sponge is viviparous. All the monitored specimens showed sexual reproduction, even if the process usually involved small portions of the sponge tissue. Most of the specimens showed hermaphroditism, with contemporaneous production of oocytes and spermatic cysts in the same reproductive season. Young oocytes occurred from June to September in specimens from La Pierta and from June to October in those from La Strea. Large mature eggs, measuring up to 200 μm, showed a peak in August to September, concomitant with the appearance of spermatic cysts, whose density values were about 100 times higher than those estimated for female elements. At La Pierta, embryos were present for 11 months, whereas at La Strea they were very scarce during the first 4 months of observation, with the results that there was a significant difference in the production of embryos between the two groups of sponges. Embryo development occurred in patches inside the choanosomal region. Cleavage started in September and led in June to a solid stereoblastula, which, only at La Pierta, produced parenchymella larva (371.3 + 31.3 μm on average) from June to July. In the specimens from La Strea, larvae were never observed. The slight differences in the reproductive cycle between the two groups of sponges may be explained in the light of the major variability of the environmental parameters which could have affected the specimens from La Strea negatively.     

Annual Variation of the Reproductive Activity of Three Exogoninae Species (Polychaeta: Syllidae) from the Western Mediterranean

Abstract.  During a 12-month period (from May 2000 to the end of April 2001), the reproductive activity of three Exogoninae species was studied: Grubeosyllis clavata (Claparède, 1868), G. vieitezi (San Martín, 1984) and Sphaerosyllis (Sphaerosyllis) hystrix Claparède, 1863. A sample consisting of two replicates was collected every second month, and the individuals of each species were counted and assigned to different reproductive categories (immature, mature, and bearing eggs or embryos). The populations of the three species showed a dramatic decline in numbers during summer 2000. In regard to the reproductive activity, the two species of Grubeosyllis showed a continuous activity during the whole year, with a peak in July for G. vieitezi and in September and November for G. clavata . In contrast, S. (S.) hystrix had a pause in its reproductive activity in late summer when no mature or offspring-carrying specimens were found. A relationship between the reproductive cycle and the brooding type (dorsal eggs versus ventral embryos) is likely, although further studies on other exogonin species are necessary to confirm the hypothesis suggested by the present results.     

Size distribution of individuals in the population of Asterias amurensis(Echinodermata: Asteroidea) and its reproductive cycle in China

To obtain baseline information on the size distribution of individuals in the population and reproductive features of sea star Asterias amurensis, monthly surveys of the population were carried out from May to December 2010 and March to May 2015 in coastal waters off Yantai, China. Spawning period was predicted by gonad and pyloric caeca indices as well as anatomical and histological methods. In the A. amurensis population, both large individuals(143 mm) and small ones(42 mm) were present in all sampling months. The population size structure was driven by the appearance of big cohorts of individuals less than 55 mm from May to August. The appearance of small individuals in all months suggested a prolonged spawning period at other sites in this bay or sea stars growing slowly because of food shortage. An arm length is a good predictor to wet body weight for A.amurensis. The development of gonad was relative slow from May to September but rapidly reached a peak of20.95 in October 2010, and then dropped remarkably, indicating its spawning lasted from October to November.The same phenomenon was found from March to May 2015, suggesting another spawning during March to May,which was also verified by the results of histologic analysis on ovary. The gonad index(GI) and pyloric caeca index(PCI) tended to show a negative relationship. Due to the poor food availability, the reproductive characteristics of sea star were most likely affected by the shellfish mariculturein Yantai coastal waters.     

Growth and reproduction of the bivalve Spisula subtruncata (da Costa) in Dutch coastal waters

The bivalve Spisula subtruncata is usually abundant in shallow coastal waters along the Dutch coast. However, its biomass has been decreasing since 1995. In order to assess whether reproductive failure may be the cause of the observed decline over the last decades, the energy investment in reproduction of a population of S. subtruncata from central Dutch coastal waters was studied. The population studied consisted of individuals of up to four years old. Shell length reached maximum values of around 32 mm and individual total body, somatic and gonadal ash-free dry mass reached maximum values of about 278 mg AFDM, 252 mg AFDM and 76 mg AFDM, respectively. A clear seasonal cycle in somatic and gonadal mass was observed. Somatic and gonadal mass indices increased in early spring and reached maximum values during summer, followed by a decrease to minimum values at the beginning of the following year. Spawning was in June–July and settlement of spat seems to have occurred in July–August. Mean oocyte diameter was 57.43 ± 0.03 μm, corresponding to a volume of 98972 μm³. These results suggested that reproductive failure was not the cause of the current population decline. Most likely, unsuccessful settlement of spat and/or severe predation during the first months of life were responsible for the observed patterns.     

Reproductive biology of Diopatra neapolitana (Annelida,Onuphidae), an exploited natural resource in Ria de Aveiro (Northwestern Portugal)

Diopatra neapolitana Delle Chiaje, 1841 (Annelida, Onuphidae) is an important economic natural resource in Ria de Aveiro (northwestern coast of Portugal) and throughout Europe. The species is intensively harvested for use as fresh bait. However, there is only limited knowledge about its life cycle derived from a previous study in Mediterranean Sea. Reproduction and development patterns are known to vary biogeographically, making it important to base management decisions on locally appropriate information. This work examines reproduction patterns for populations from the Eastern Atlantic, which have not previously been assessed, with an eye towards drawing Atlantic–Mediterranean comparisons and informing local management strategies. The study was conducted from May 2007 to April 2009 in Ria de Aveiro. The reproductive biology of D. neapolitana was described from the proportional variation of worms with gametes in the coelom and from the progression of the oocyte diameter. Individuals with gametes inside the coelom were found all year round, but the peak reproductive period occurred between May and August, when almost all individuals had gametes in the coelom and females contained more oocytes than at any other time of the year. The overall male:female ratio was close to 1:1 and the oocyte diameter ranged from 40 to 240 μm. In vitro fertilization was performed and the results compared to other studies. Based on the present results, some protection measures are suggested to implement a sustainable exploitation of the species.     

First distribution record of the invasive copepod Oithona davisae Ferrari and Orsi, 1984, in the coastal waters of the Aegean Sea

The occurrence of the invasive nonindigenous copepod Oithona davisae Ferrari and Orsi, 1984, is reported for the first time in the Aegean Sea. The data we collected in August 2017 from 14 stations along the Turkish coast of the Aegean Sea reveal the spatial distribution of O. davisae between the openning of the Dardanelles Strait in the north and the Izmir Bay in the south. The O. davisae individuals, in seven mesozooplankton samples collected from a single station, were consistently found in the inner part of the Izmir Bay from April 2015‐October 2016. The abundance of female O. davisae ranged from 4 ind./m³ in April 2015 to 31,524 ind./m³ in July 2016 and contributed to the total oithonid female population by 10.8% in April 2015 and 92.8% in September 2016. Our results show that this species is well established in the inner part of Izmir Bay and that it has become a permanent component of the copepod community in the area.     

The Air-Sea Exchange of CO2 in the East Sea (Japan Sea)

During CREAMS expeditions, fCO₂ for surface waters was measured continuously along the cruise tracks. The fCO₂ in surface waters in summer varied in the range 320–440 μatm, showing moderate supersaturation with respect to atmospheric CO₂. In winter, however, fCO₂ showed under-saturation of CO₂ in most of the area, while varying in a much wider range from 180 to 520 μatm. Some very high fCO₂ values observed in the northern East Sea (Japan Sea) appeared to be associated with the intensive convection system developed in the area. A gas-exchange model was developed for describing the annual variation of fCO₂ and for estimating the annual flux of CO₂ at the air-sea interface. The model incorporated annual variations in SST, the thickness of the mixed layer, gas exchange associated with wind velocity, biological activity and atmospheric concentration of CO₂. The model shows that the East Sea releases CO₂ into the atmosphere from June to September, and absorbs CO₂ during the rest of the year, from October through May. The net annual CO₂ flux at the air-sea interface was estimated to be 0.032 (±0.012) Gt-C per year from the atmosphere into the East Sea. Water column chemistry shows penetration of CO₂ into the whole water column, supporting a short turnover time for deep waters in the East Sea. This revised version was published online in August 2006 with corrections to the Cover Date.     

Determining the correct identity of South African Marthasterias (Echinodermata: Asteroidea)

Marthasterias glacialis are found in the cool-temperate waters of the north-eastern Atlantic Ocean, in the subtropical waters of the Mediterranean Sea and along the south-western tip of Africa. The South African Marthasterias population includes two morphotypes, a smooth, spineless rarispina form and a spiny africana form, that have been described as separate species, subspecies, or forma by various authors over the past century. To test whether these two morphotypes represent separate species, and whether either, or both, are conspecific with the North-East Atlantic species, 78 Marthasterias were collected from the Cape Peninsula of South Africa. Morphological comparisons between individuals of the two forms showed no significant clustering of samples, indicating that there is no morphological separation of the two South African forms into distinct groupings. The africana and rarispina forms were also shown to be genetically indistinguishable, using a fragment of the mitochondrial cytochrome c oxidase subunit I (COI) gene and the nuclear internal transcribed spacer 1 (ITS1). In addition, the COI sequences were also compared to those from European specimens, and phylogenetic reconstruction and intra- and interspecific levels of divergence suggested that the South African specimens form a single group that is genetically distinct from the European M. glacialis. Although the allopatric distribution, high genetic divergence (more than 3% for the COI fragment) and morphological differences suggest that the South African form should be raised to species status under the name Marthasterias africana, further work must assess an independent genetic marker (nuclear) to support raising the COI clade to species level. True M. glacialis have a spine-armament pattern of a series of three or more regular spine rows down the length of each arm, whereas M. africana are either covered in many irregularly spaced spines, or have an extraordinarily bare surface with only two spine rows per arm. Marthasterias africana may also have an actinal spine simulating the presence of a third inferomarginal spine. This work tentatively resolves the taxonomic dispute, elucidates the separation and amalgamation of the two African forms and suggests a single, uniquely South African Marthasterias species that might be distinct from the north Atlantic M. glacialis, although further analyses to test reproductive isolation between the North-East Atlantic and South African forms are required.     

Reproduction of Donax venustus Poli 1795, Donax semistriatus Poli 1795 and Intermediate Morphotypes (Bivalvia: Donacidae) in the Littoral of Málaga (Southern Spain)

The reproduction and sexual cycles of Donax venustus Poli 1795, Donax semistriatus Poli 1795, and individuals with intermediate shell morphotypes were studied in the littoral of Málaga (Southern Spain) from February 1990 to January 1991, using histology and analysing the changes in flesh dry weight. The littoral of Málaga has mild seawater temperatures and several upwellings with high levels of chlorophyll a. Due to these environmental conditions, the reproductive periods of these bivalve species are very extensive, from February to November. The histological study shows asynchronous sexual cycles, with continuous but partial individual spawnings from April to November in about 50% of the D. semistriatus population, and percentages higher than 40% of the sample in most months for D. venustus. An important decrease in the ratio flesh dry weight/length³ was noted from June to August in the three populations; this is apparently related with peaks of spawning. Based on the macroscopic observation of the gonads, on the flesh dry weight study and on histological data, the sexual cycle of the intermediate morphotypes is simultaneous and similar throughout the year with those of D. venustus and D. semistriatus .     

Lack of mitochondrial genetic structure in the endangered giant clam populations of Tridacna maxima (Bivalvia: Cardiidae: Tridacninae) across the Saudi Arabian coast

The present investigation focuses on population genetic structure analysis of the endangered giant clam species Tridacna maxima across part of the Red Sea,with the main aim of assessing the influence of postulated potential barriers to gene flow(i.e.,particular oceanographic features and marked environmental heterogeneity)on genetic connectivity among populations of this poorly dispersive bivalve species.For this purpose,a total of 44 specimens of T.maxima were collected from five sampling locations along the Saudi Arabian coast and examined for genetic variability at the considerably variable mitochondrial gene cytochrome c oxidase I(COI).Our results revealed lack of population subdivision and phylogeographic structure across the surveyed geographic spectrum,suggesting that neither the short pelagic larval dispersal nor the various postulated barriers to gene flow in the Red Sea can trigger the onset of marked genetic differentiation in T.maxima.Furthermore,the discerned shallow COI haplotype genealogy(exhibiting high haplotype diversity and low nucleotide diversity),associated with recent demographic and spatial expansion events,can be considered as residual effect of a recent evolutionary history of the species in the Red Sea.     

Seasonal abundance and reproductive strategy of Tetrastemma fozensis (Hoplonemertea, Nemertea) in the Villaviciosa estuary (Asturias, Northern Spain)

The seasonal occurrence and reproductive strategy of the nemertean Tetrastemma fozensis, which inhabits the mantle cavity of the bivalve Scrobicularia plana, was studied through the analysis of the temporal diversity of a T. fozensis population. Bimonthly sampling was carried out from February 2001 to January 2002 at mudflats of Villaviciosa estuary (Asturias, Northern Spain). Nemerteans were found throughout the study period, but variations in their abundance were detected, with a maximum during winter months and a minimum during summer months. Moreover, variations in mean size of nemerteans were found, with maximal sizes at the end of the spring and the beginning of the summer and minimum size at early autumn. The annual variations in population parameters (decrease in abundance and complete disappearance of large individuals in summer) suggest that T. fozensis has a distinct reproductive season and a semelparous reproductive strategy.