Population dynamics and chemical ecology of New Zealand Demospongiae Latrunculia sp. nov. and Polymastia croceus (Poecilosclerida: Latrunculiidae: Polymastiidae)

For 3 years aspects of the population dynamics, growth, and bioactivity (measure of biologically active metabolite biosynthesis) of the Demospongiae Latrunculia sp. nov. and Polymastia croceus (Kelly‐Borges & Bergquist) were examined on a subtidal reef on the Wellington south coast, New Zealand. For both species, survival of adult sponges was high in all seasons, whereas juvenile sponges had poor survival. Recruitment of Latrunculia sp. nov. occurred in all seasons indicating that this species is reproductively active throughout the year. P. croceus recruited mostly in autumn, supporting previous work that found the sponge to be reproductively active in summer and early autumn only. For both sponge species, growth rates varied greatly between individuals and were unaffected by initial sponge size within the range examined. Sponges generally grew during winter and spring as the water temperature rose, and shrank during summer and autumn as the water temperature fell. This growth pattern may relate to seasonal variation in food abundance, and for P. croceus it may result also from seasonal differences in reproductive investment. After 2 years, Latrunculia sp. nov. and P. croceus had on average, halved and doubled in size, respectively. Latrunculia sp. nov. showed a seasonal pattern of bioactivity, being most active in spring possibly to prevent the surface overgrowth of fouling organisms. P. croceus had no seasonal pattern of bioactivity, but individuals were either very active or inactive. The bioactive metabolites in both species possibly aid in competitive interactions and prevent predation and biofouling.     

Variability in the structure of epiphytic assemblages of the Mediterranean seagrass Posidonia oceanica in relation to depth

The aim of the present study was to evaluate whether the variability in the structure of the epiphytic assemblages of leaves and rhizomes of the Mediterranean seagrass Posidonia oceanica differed between depths at a large spatial scale. A hierarchical sampling design was used to compare epiphytic assemblages at two different depths (10 and 20 m) in terms of both species composition and abundance and patterns of spatial variability in the Tuscan Archipelago (North Western Mediterranean Sea, Italy). Results showed significant differences in the structure of assemblages on rhizomes and leaves at different depths. These differences were related to species composition and abundance; differences were not significant for total biomass, total percentage cover and percentage cover of animals and algae. Whereas the higher variability was observed among shoots in all the studied systems, patterns of spatial variability at the other spatial scales investigated differed between the two studied depths. Moreover, in the present study, analogous patterns between depths resulted for both the assemblages of leaves and rhizomes, suggesting that factors that change with depth can be responsible for the spatial variability of both the assemblages (leaves and rhizomes), and operate regardless of the microclimatic conditions and the structure of assemblages.     

Organic matter in sediments of canyons and open slopes of the Portuguese,Catalan, Southern Adriatic and Cretan Sea margins

We describe the quantitative and compositional (phytopigment, protein, carbohydrate and lipid) patterns of sedimentary organic matter along bathymetric gradients in seven submarine canyons and adjacent open slopes located at four European regions: one along the NE Atlantic and three along the Mediterranean continental margins. The investigated areas are distributed along a putative longitudinal gradient of decreasing primary production from the Portuguese (northeastern Atlantic Ocean), to the Catalan (western Mediterranean Sea), Southern Adriatic (central Mediterranean Sea) and Southern Cretan (eastern Mediterranean Sea) margins. Sediment concentrations of organic matter differed significantly between the Portuguese margin and the Mediterranean regions and also from one study area to the other within the Mediterranean Sea. Differences in quantity and composition of sediment organic matter between canyons and open slopes were limited and significant only in the eutrophic Portuguese margin, where the differences were as large as those observed between regions (i.e. at the mesoscale). These results suggest that the overall trophic status of deep margin sediments is controlled mostly by the primary productivity of the overlying waters rather than by the local topography. Moreover, we also report that the quantity and nutritional quality of sediment organic matter in canyons and adjacent open slopes do not show any consistent depth-related pattern. Only the Nazaré and Cascais canyons in the Portuguese margin, at depths deeper than 500 m, displayed a significant accumulation of labile organic matter. The results of our study underline the need of further investigations of deep margins through sampling strategies accounting for adequate temporal and spatial scales of variability.     

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.     

Seasonal dynamics, environmental preferences and habitat selection of John Dory (Zeus faber)

Spatial distribution patterns of John Dory (Zeus faber, L.) were examined in relation to sea bottom temperature, bathymetry, locational covariates and season. Data were collected during a 2-year period (1996–1997) of seasonal sampling using demersal trawl surveys in the Aegean Sea (eastern Mediterranean). The ecological preferences of the species throughout four seasons were elucidated and the degree in which these environmental relationships might be modulated by the different hydrographic and topographic regime was also considered. Key determinants of the species' spatial aggregation in all four seasons were the water depth, the sea bottom temperature and the latitude. The sea bottom temperature had a significant effect on seasonal John Dory abundance both directly, as a main effect, and indirectly, through its interactive effect with the water depth. John Dory seasonal abundance was consistently greater in the shallower regions of the area having warmer bottom waters. Results indicated a distinct southward shift as progressing through the year, with peak abundances being observed in gradually lower latitudes of shallow areas as seasons evolved. John Dory appeared to avoid the deeper waters regardless of their bottom temperature and geographic position. The present results also suggested a seasonal pattern of habitat associations for specific locations characterised by weak hydrographic activity. John Dory preferences for certain water depth zones, sea bottom temperatures and substrate types are hypothesized to modulate the seasonal spatial aggregation of the species to preferred grounds.     

Macrofauna Associated With Sponge Species of Different Morphology

Abstract. The macrofaunas associated with the three morphologically different North Aegean Sea sponge species Agelas oroides, Aplysina aerophoba , and Axinella cannabina were compared. The faunal abundance was not related to sponge surface area for any of the three species. Each sponge species supported a significantly different number of individuals per unit canal volume; A. aerophoba supported the most, A. oroides the least. A. aerophoba supported the highest species richness, A. cannabina the lowest. Canal volume was a good predictor of associated faunal abundance and species richness for two of the three sponge species. Faunal abundance was also directly related to sponge mean canal diameter. The species composition of associated fauna was similar on A. aerophoba and A. oroides and significantly different on A. cannabina .     

Habitat Selection and Ecology of Two Speleophilic Gobiid Fishes(Pisces: Gobiidae) from the Western Mediterranean Sea

The life habits and microhabitat selection of speleophilic gobiid fishes were investigated on the Balearic Island of Ibiza (western Mediterranean Sea). Corcyrogobius liechtensteini (Kolombatović, 1891) was the most frequent species within submarine crevices, cavities and caves. Didogobius splechtnai Ahnelt & Patzner, 1995 co-occurred with C. liechtensteini in several cases but showed a clear spatial separation based on a different microhabitat preference. The microhabitat selection of both species was confirmed by habitat-choice experiments in anaquarium. Corcyrogobius liechtensteini was frequent in depths between 5 m and 25 m and attained abundances of 14.2 individuals · m⁻². This species inhabited the ceilings and upper parts of the walls within the caves. D. splechtnai was mainly found between 7 m and 11 m and showed abundances of approximately 2 indivi-duals · m⁻². This species occupied the fine sediment bottoms in the innermost parts of crevices and caves. The growth and the maximum age of both species were determined by length-frequency distributions. The overall sex ratio from catches of three different years are given for C. liechtensteini .     

A facies of Kophobelemnon (Cnidaria,Octocorallia) from Santa Maria di Leuca coral province (Mediterranean Sea)

During a research cruise carried out in April 2010, aimed at updating the knowledge on the biodiversity of the Santa Maria di Leuca (SML) cold‐water coral province (Mediterranean Sea), a facies of the sea pen Kophobelemnon stelliferum (Muller, 1776) was found on mud‐dominated bottoms. This finding represents a new species and a new habitat record from the SML coral province as well as a new bathyal facies in the whole Central Mediterranean Sea. The colonies were collected using an epi‐benthic sledge, at depths between 400 and 470 m. A significant positive relationship between polyp number and colony length was detected. Density of the colonies ranged from 0.003 to 0.038 N·m^?2. Differences and affinities between Mediterranean and Atlantic occurrences of K. stelliferum are discussed.     

Species composition and spatial distribution of euphausiids of the yellow sea and relationships with environmental factors

We investigated species composition and spatial distribution of the euphausiid community in the Yellow Sea and identified the relationship with environmental factors (temperature, salinity, chlorophyll a, nitrate, phosphate, and silicate) using bimonthly data from June, 1997 to April, 1998. The environment varied during the sampling period. In warm seasons, thermocline was well developed rendering lower temperature and higher salinity and nutrient concentrations in the bottom layer. During cold seasons the water column was well mixed and no such vertical stratification was noted. Horizontal distribution of temperature, however, differed slightly between near-coast and offshore areas because of the shallow depth of the Yellow Sea, and between southern and northern areas because of the intrusion of water masses such as Yellow Sea Warm Current and Changjiang River Diluted Water. Four euphausiid species were identified:Euphausia pacifica, E. sanzoi, Pseudeuphausia sp. andStylocheron affine. E. sanzoi andS. affine were collected, just one juvenile each, from the southern area in June and December, respectively.Pseudeuphausia sp. were collected in the eastern area all the year round except June.E. pacifica occurred at the whole study area and were the predominant species, representing at least 97.6% of the euphausiid abundance. Further, the distribution pattern of the species was varied in regards to developmental stages (adult, furcilia, calyptopis, egg). From spring to fall,E. pacifica adults were abundant in the central area where the Yellow Sea Bottom Cold Water prevailed. Furcilia and calyptopis extended their distribution into nearly all the study area during the same period. From late fall to winter, adults were found at the near-coastal area with similar pattern for furcilia and calyptopis. The distribution pattern ofE. pacifica was consistent regarding temperature, salinity, and three nutrients during the sampling period, whereas chlorophyll a showed a different pattern according to the developmental stages. The nutrients should indirectly affect via chlorophyll a and phytoplankton concentration. With respect to these results, we presented a scenario about how the environmental factors along with the water current affect the distribution ofE. pacifica in the Yellow Sea.     

中国北部黄海近岸水体周丛硅藻的群落群集动态特征的研究

The colonization features of periphytic diatoms were studied in coastal waters of the Yellow Sea, northern China from May to June 2010, using glass slides as an artificial substratum. Samples were collected at a time interval of 1, 3, 7, 10, 14, 21 and 28 d from two depths of 1 and 3 m. The dynamics of diatom colonization process had a similar pattern in community structure and fitted the logistic model in growth curve at both depths. The maximum abundance and the time for reaching 50% maximum abundance （10 d） showed no significant differences （P〉0.05） between two depths 1 and 3 m. Although the diatom communities repre- sented similar taxonomic composition, they differed in the temporal pattern of structural parameters and in succession dynamics of dominant species between the two layers. The species richness showed significantly higher values during the colonization period more than 14 d, while the species diversity and evenness rep- resented a higher variability with significantly different values （P〈0.05） at a depth of 1 m than at a deeper layer. The results suggest that the diatom colonization follows the logistic model growth curve and differs in colonization features between different depths in the coastal waters, and that the sampling strategy at i m is more effective to detect the ecological features for bioassessment in marine ecosystems.     

Spatial and temporal variation of Palaemon adspersus, Palaemon elegans, and Crangon crangon (Decapoda: Caridea) in the southern Black Sea

In order to characterize the seasonal, bathymetric, and spatial distribution of the species, Palaemon adspersus, Palaemon elegans, and Crangon crangon, shrimps were sampled with a beam trawl in four stations at depths between 1 and 30 m from February 2002 to January 2004 on the Sinop Peninsula coasts of the southern Black Sea. One-way analysis of similarity (ANOSIM) results demonstrated that the caridean composition was significantly different (p < 0.001) between seasons and between sampling areas. No significant relationship of the caridean composition was evident between depth zones ranging from 1 to 30 m. These three carideans occurred together in 28.5% of the sampling occasions. Different seasonal migration pattern was evident for all the three species. Palaemon adspersus migrated inshore during relatively higher water temperatures, whereas C. crangon density decreased in the shallow waters during the same period, and P. elegans population was mostly observed at depth zones of 5–10 m and was only observed in the 30 m depth zone in winter. The abiotic factors that characterize the coexistence of these three carideans were primarily determined by the habitat types and bottom structures.     

Spatio-temporal patterns of abundance,size structure and body condition of Atherina boyeri (Pisces: Atherinidae) in a small non-tidal Mediterranean lagoon

Sand smelt, Atherina boyeri, is a very abundant, widespread, locally harvested species, able to successfully survive and reproduce over a wide range of abiotic conditions and aquatic ecosystem types. In the North Sea and in the Mediterranean Sea transitional ecosystems its life history is well known, but very little information is available about the influence of intra-ecosystemic abiotic gradients on micro-scale patterns of distribution, body size and condition of individuals. In a small non-tidal Mediterranean lagoon, the cohorts' structure and evolution of sand smelt was described and the temporal and spatial variability of abundance, size structure and body condition was addressed. The study was carried out at the Acquatina lagoon (Lecce, Italy) where four stations, situated in two habitat types along a confinement gradient, were sampled twice per month for one year with fyke nets. The abundance of collected individuals was very high throughout the sampling period, with a peak in Summer and a constant decrease afterwards. Measured Standard Length ranged from 20 to 90 mm and the majority of individuals were estimated to be within 2 years old. The confined station resulted more abundantly colonized, especially by smaller size classes, and characterized by a narrower size frequency distribution. Also relative body condition showed significant spatial variations, with larger individuals having a better condition than smaller ones where optimal temperature and dissolved oxygen levels were available. Size-specific temporal patterns of body condition followed the seasonal climatic oscillations and the species' cycle of growth and reproduction, with larger individuals reaching higher fatness than smaller ones during Autumn and Winter, thus having more chances to survive and contribute to the reproductive effort. The results of the present study emphasised that, even at a very small scale, the presence of strong environmental gradients can drive movements, habitat preference and condition of individuals and thus promote an intra-ecosystemic spatial heterogeneity comparable to that observed between ecosystems at the land–ocean or geographical scale.     

Temporal and bathymetric variation of epiphyte cover and leaf biomass in a southern Posidonia oceanica (L.) meadow: the case of Mahdia coast,Tunisia

The aim of this research was to study spatial and temporal variation in epiphyte cover and leaf biomass of Posidonia oceanica in Eastern Tunisia. Sampling was conducted at four stations on the Mahdia coast during October and December 2010, and April and August 2011, which correspond respectively to autumn, winter, spring and summer in this area. Posidonia oceanica shoots were collected at two depths (5 and 10 m). Cover of macroinvertebrates and macroalgae was estimated on adult leaves. The results showed that leaf and epiphyte biomasses vary significantly according to sampling date, with the highest values recorded in August. We found a high diversity of epiphytic assemblages on the leaves of P. oceanica with clear qualitative and quantitative dominance of Rhodophyceae compared to other groups, followed by Phaeophyceae. Most epiphyte species on the leaves of P. oceanica in Eastern Tunisia are the same as those in other parts of the Mediterranean Sea. No bathymetrical variation in the epiphytic community was found in our study area, which can be explained by the high levels of water clarity in Mahdia.     

Reproductive biology of Parazoanthus axinellae (Schmidt, 1862) and Savalia savaglia (Bertoloni, 1819) (Cnidaria,Zoantharia) from the NW Mediterranean coast

Despite the wide distribution of zoanthids, little is known about their pattern of reproduction. Here we investigate the reproductive biology of two Mediterranean species, the common Parazoanthus axinellae (Schmidt) and the rare Savalia savaglia (Bertoloni). For both species, samples were collected during an annual cycle, from January to December 2005, in the Western Mediterranean (Ligurian Sea, Italy). Both species are gonochoric. In P. axinellae the sex‐ratio (n colonies = 30) showed a slight predominance of male colonies (M/F = 1.35), whereas in the population of S. savaglia (n colonies = 15) a predominance of females was found (M/F = 0.3). In P. axinellae the first gametocytes were visible in March, whereas in S. savaglia they became visible in May. Both species reproduce at the end of autumn when seawater temperature begins to decrease. Parazoanthus axinellae (10 m depth) spawns eggs and sperms in November, whereas S. savaglia (67 m depth) spawns in December. In P. axinellae sexes were segregated on a rocky wall, with males occurring deeper, whereas male and female colonies of S. savaglia were irregularly dispersed in the population. The maximum number of oocytes differed between the species, being higher in P. axinellae than in S. savaglia.     

Biogeography, Taxonomical Status and Ecology of Alcyonium (Parerythropodium) coralloides (PALLAS, 1766)

Abstract. Ecology and morphology of Alcyonium (Parerythropodium) coralloides were studied in different sites of the Eastern Atlantic and the Mediterranean. The species is extremely variable in size, colony shape and colour. In the Mediterranean population, encrusting red colonies are mostly encountered, although lobate colonies also exist. White and pink colonies are considered mutants, which tolerate the stable environment of deeper habitats better than the conditions encountered in shallow biotopes. Mediterranean colonies are dioecious and reproduce sexually. In the Eastern Atlantic, lobate pink colonies are the most common form, and show little variability. These (at least partly) parthenogenic populations are considered offspring from stray larvae from more southern regions. This explains the rather patchy distribution of the Atlantic populations, as compared to the widespread distribution throughout the entire Western Basin of the Mediterranean and the Adriatic Sea. A study of the most important systematic characters of the species (growth form, sclerites and solenial network) leads to the conclusion that coralloides belongs to the genus Alcyonium. As a result, coralloides being its type-species, the genus Parerythropodium will have to be suppressed.     

First in situ observations of the deep-sea carnivorous ascidian Dicopia antirrhinum Monniot C., 1972 in the Western Mediterranean Sea

Dicopia antirrhinum C. Monniot, 1972 is a rare species of deep-sea ascidian belonging to the Family Octacnemidae, reported at depths of 1000–2500 m in European Atlantic waters. Adult individuals have never been reported before in the Mediterranean Sea, where only seven juvenile specimens were found in 1975 at 500 m water depth in the Central basin (Malta). The affinities of these specimens with D. antirrhinum were noted, but lack of some typical characters of the species in juveniles prevented a definite taxonomical identification. No other member of the Octacnemidae has ever been found in the Mediterranean. In this study we describe the sampling of an adult specimen of D. antirrhinum at around 1100 m water depth on the flank of the La Fonera (Palamós) canyon, Northwestern Mediterranean, confirming their presence in the Mediterranean Sea. We also observed 5 individuals of this species on their natural habitat with a Remotely Operated Vehicle (ROV). Our results highlight the potential occurrence of Octacnemidae, the presence of which has been largely overlooked, in several deep-sea canyon areas within the Western Mediterranean basin. These observations are important because they indicate the need for increased sampling effort with new technologies, such as ROVs, in ecologically relevant habitats such as canyons, in order to obtain a more accurate picture of deep-sea biodiversity in the Mediterranean Sea.     

Distribution patterns of the invasive herbivore Siganus luridus (Rüppell, 1829) and its relation to native benthic communities in the central Aegean Sea,Northeastern Mediterranean

The present study explores the distribution of the invasive herbivore fish Siganus luridus (Rüppell 1829) and its relationship to native herbivores and macroalgal assemblages in the shallow sublittoral of the Cyclades Archipelago, Aegean Sea, Greece. In situ underwater surveys of herbivore abundance (fishes and sea urchins) and algal coverage were carried out at 180 sampling sites in 18 islands. Siganus luridus accounted for 17% of the total herbivore abundance, with a decrease in relative abundance from the southeastern to the northwestern islands. In Santorini Island (in the southeast of the study area) S. luridus abundance accounted for 90% of the total herbivore fish abundance, while in Kea Island (at the northwestern limit of the study area), S. luridus was absent. The spatial variation of minimum sea surface temperature is possibly the reason for its distributional pattern. Siganus luridus abundance was found to be positively correlated to the native herbivore Sparisoma cretense (Linnaeus 1758). A significant negative relationship was found between the abundance of the invasive species and the sum of erect and canopy algae cover (Dictyotales and Cystoseira spp.), which are the main components of its diet in the region. On the other hand, its occurrence was particularly high in barren sites. The results arising from this study reinforce evidence from studies in the Eastern Mediterranean Basin that the expansion of the invasive species S. luridus may have profound impacts on native communities in the Mediterranean infralittoral zone.     

Genetic heterogeneity in populations of the Mediterranean shore crab, Carcinus aestuarii (Decapoda,Portunidae), from the Venice Lagoon

Heterogeneity in genetic composition among recruits, mostly due to a large variance in reproductive success mediated by oceanographic processes, has been reported for marine species but is less understood in coastal lagoons' organisms. Temporal genetic variation in natural populations of the Mediterranean shore crab Carcinus aestuarii was quantified over a multi-year sample. A total of 486 adult crabs were collected at eight different sites of the Venice Lagoon during the period 2005–2007 and screened for genetic variation using 11 microsatellite loci. Two additional samples (N = 115) from neighbouring sites, located approximately 100 km North and South to the Venice Lagoon, were included for the sake of comparison. Our results show significant differences in allelic frequencies at the micro-geographic scale of the Venice Lagoon, observed between sites of collection, typologies of habitat, and areas with different class of ecological risk or pattern of hemocyanin expression. However, this pattern was not constant between years, with significant differences observed mainly in 2005 and 2006, but not in 2007. Our results indicate significant temporal differences suggesting the existence of dynamic processes that act on the genetic pool of this species. Although natural selection and gene flow might play a role, we suggest that genetic drift linked to large variation in the reproductive success of individuals is the most probable scenario to explain the local genetic patterns of differentiation in the Mediterranean shore crab. Our study, by providing the first evidence for the existence of genetic differences in this species at the micro-geographic scale, suggests that a better comprehension of the link between reproduction, recruitment and oceanography is critical to understand how colonization and maintenance of genetic variation is achieved in ephemeral and vulnerable environments such as coastal lagoons.     

Isolation By Distance (IBD) signals in the deep-water rose shrimp Parapenaeus longirostris (Lucas, 1846) (Decapoda,Panaeidae) in the Mediterranean Sea

The identification of boundaries of genetic demes is one of the major goals for fishery management, and few Mediterranean commercial species have not been studied from a genetic point of view yet. The deep-water rose shrimp Parapenaeus longirostris (Lucas, 1846) is one of the most important components of commercial landings in Mediterranean, its fishery aspects have received much attention, regrettably without any concern for the genetic architecture of its populations. The population structure in the central and eastern Mediterranean Sea (captures from six Italian and two Greek landings) has been analysed on the basis of surveys carried out with mitochondrial and AFLP markers. Data revealed the presence of a gradual discrepancy along a west–east axis. This species, occurring mainly at a depth of between 100 and 400 m, is not strongly confined in isolated demes, but it demonstrates an ‘Isolation By Distance’ model, within the Mediterranean Sea, which includes geographical areas with a some degree of isolation. The role of hydrodynamic forces, such as currents, water fronts, is discussed; and a further evidence of the ‘Levantine isolation’ within Mediterranean basin is shown.     

Submarine ridges do not prevent large-scale dispersal of abyssal fauna: A case study of Mesocletodes (Crustacea, Copepoda, Harpacticoida)

We examined the large-scale distribution of deep-sea harpacticoid copepods at the species level, in order to clarify the underlying processes of copepod dispersal. The study was based on samples collected from 12 regions and a total of 113 stations: 57 stations at depths between 1107 and 5655 m on abyssal plains in the South and North Atlantic, Southern Ocean, southern Indian Ocean, and the Pacific Ocean, and 56 stations above 900 m in the North Atlantic and eastern Mediterranean Sea.We chose the genus Mesocletodes Sars, 1909 as an ideal group to study the large-scale distribution of harpacticoid copepods in the deep oceans. Clear apomorphies and a comparatively large body size of about 1 mm allow rapid recognition of allied species in meiofauna samples. In addition, Mesocletodes represents more than 50% of the family Argestidae Por, 1986, one of the most abundant harpacticoid families in the deep sea.The geographical distributions of 793 adult females of Mesocletodes belonging to 61 species throughout the South and North Atlantic, Southern Ocean, southern Indian Ocean, Pacific Ocean, and eastern Mediterranean Sea indicated that most species are cosmopolitan. Neither the topography of the sea bottom nor long distances seem to prevent species from dispersing. Passive transport by bottom currents after resuspension is likely the propulsive factor for the dispersal of Harpacticoida, while plate tectonics and movement of individuals in the sediment may play relatively minor roles.