Marine Biodiversity

Species of the nudibranch Pseudovermidae Thiele, 1931 are rare but conspicuous inhabitants of the marine mesopsammon. Their characteristic vermiform body with reduced cerata and acorn-shaped head lacking appendages is well adapted to life in the interstices of sand grains. Traditionally, species descriptions are based mainly on external morphology and radula characteristics; knowledge on their anatomy is scarce. Here we provide the first microanatomical redescription of a member of Pseudovermidae based on 3D-reconstruction from histological semi-thin section series. The present study on Pseudovermis salamandrops Marcus, 1953 reveals several discrepancies to the original description especially within the complex triaulic genital system (i.e., absence of a connection between vas deferens and kidney, presence of a receptaculum seminis and a large muscular penial sheath gland). We also add microanatomical details such as the presence of gastroesophageal ganglia in the central nervous system, described for the first time in Pseudovermidae. Concluding from the nematocysts found in the cnidosacs of P. salamandrops, this species is a cnidarivore which likely preys on various meiofaunal cnidarians. We show that microanatomical redescriptions of poorly known Pseudovermidae are needed to gather comparative data as a backbone to place these neglected meiofaunal slugs in a phylogeny and trace their evolutionary pathway into the mesopsammon. Traditional characters used for species delineation are insufficient to diagnose Pseudovermis and an integrative approach is needed to reliably address pseudovermid diversity in the future.

The copepod Eurytemora herdmani, native to coastal waters of the north-west Atlantic and north Pacific Oceans, was discovered at a marine sampling station in the Firth of Forth, Scotland, UK. The species was present in the summer zooplankton assemblage over three successive years. Peak abundance followed peak chlorophyll a concentration in surface waters. Given that previous studies on the Firth of Forth had only found species native to Europe, a survey of the Forth estuary was undertaken in summer 2014. Eurytemora herdmani was found at sampling stations where the salinity was greater than 20, while Eurytemora affinis was found at sampling stations with lower salinity further upstream. The impact of this introduction on the native zooplankton community is not known, and will require further study. The Firth of Forth has a high level of shipping traffic, and this species may have been introduced by ships’ ballast water.

A variety of analytical techniques were used to quantify and describe small-scale (centimetre to decimetre) spatial patterns of meiofauna taxa, with emphasis on nematode species, at a bathyal site in the Arctic deep sea. Three cores (10-cm diameter) taken from the same multicorer were each subsampled as 12 contiguous subcores (1.2-cm diameter) for meiofauna and 16 contiguous subcores (0.9-cm diameter) for bacteria (eight subcores) and phytodetritus (chl a and phaeopigment concentration) (eight subcores). Coefficients of variation and the variance component from PERMANOVA were estimated to compare variability between cores (20–50 cm) versus within cores (≤10 cm). Both methods showed that spatial variation within cores contributed the main part of total heterogeneity for all parameters, while differences between cores were less important. To further investigate distribution patterns at this small scale (≤10 cm), indices of dispersion were calculated and autocorrelation analyses were performed on the complete data set. Abundances of nematodes, nauplii and 65.5% of the nematode species were significantly aggregated at the scale of subcores (2 cm). Nematode species aggregations were discordant on the small scale, suggesting that processes maintaining diversity in the deep sea can be expected to operate at scales smaller than 10 cm. Autocorrelograms suggested that nematode patch sizes were smaller than 4 cm2, while adult harpacticoid copepods and nauplii showed aggregations of ca. 9–25 cm2 and 64 cm2, respectively. Significant spatial autocorrelation at the core scale was also observed for 24 nematode species. These species were grouped in ten different spatial patterns according to their scale of heterogeneity. The spatial patterns observed for the meiobenthos were neither explained by the concentration of chloroplastic pigments nor by bacterial densities. Nevertheless, observations on nematode morphology suggest that morphological characters linked to their locomotion and feeding behaviour may be involved in pattern formation. Finally, our data provide evidence that studies based on few replicates to characterise large-scale or long-term patterns of deep-sea benthic communities may be confounded by inadequate assessment of small-scale variability.

An examination of a syntype of Cuspidaria cochinensis Preston, 1916, focusing on the characters of the hinge, supports the transfer of this species to the family Corbulidae. Recently collected material from the Cochin Backwater is used to describe the shell and anatomy of the adult form. The ctenidia are composed of two demibranchs, both flat and homorhabdic, this further confirming that this species is eulamellibranch and not septibranch. The most appropriate generic placing of this species is in Cuneocorbula; thus, it is the first recorded extant species of the genus.

We describe three new and one poorly-known species of psamminid xenophyophores (giant foraminifera), all of which were found attached to polymetallic nodules in the Russian claim area of the Clarion-Clipperton Fracture Zone (CCFZ; abyssal eastern equatorial Pacific, 4,716–4,936 m water depth). Semipsammina licheniformis sp. nov. is the second species of the genus to be formally described. The test encrusts the surface of the host nodule forming a flat structure with a rounded outline and rather irregular concentric zonation. The wall comprises a single layer, composed mainly of radiolarian skeletons, covering granellare branches and stercomata strings that lie directly adjacent to the nodule surface. Psammina multiloculata sp. nov. has an approximately semi-circular, upright test with a weak concentric zonation that is attached to the nodule by a short stalk. The outer test layer comprises radiolarian fragments, sponge spicules, and mineral grains; the interior is divided into small compartments containing the stercomare and granellare. Psammina limbata sp. nov. has a plate-like, sometimes curved, semi-circular test attached to the nodule surface by basal root-like structures. The composition of the test is similar to that of P. multiloculata, but the interior is not compartmentalised. The most distinctive feature is the lighter colour of the curved outer margin compared to other parts of test. With the addition of these and other species described during recent decades, Psammina has become a rather unwieldy taxon that requires revision. Spiculammina delicata Kamenskaya 2005, previously known from a single specimen, is the most abundant species in our collection. The test exhibits considerable morphological variation, particularly in terms of the degree of branching. The new specimens confirm the placement of this species in the family Psamminidae rather than the Syringamminidae, which it superficially resembles, as well as its sessile mode of life. Two additional species in our material, Stannophyllum radiolarium Haeckel, 1889 and Stannophyllum sp., belong to the order Stannomida. Like the psamminid species, both were found attached to nodules. Xenophyophores are a dominant megafaunal taxon within the CCFZ. Although limited, our new material suggests that this region hosts many novel taxa.

Terpios hoshinota is a threat to coral reefs. It is an encrusting sponge that kills scleractinian corals by overgrowing them. Predominantly reported from the Indo-Pacific region, the sponge seems to be progressively expanding its range by moving towards the western Indian Ocean. It is still unclear what causes its outbreaks. We report for the first time its presence at our study site at the southwestern Indian Ocean island of Mauritius (20°10′S, 57°31′E). Our surveys showed that T. hoshinota could grow linearly by 11.5 ± 3.60 mm month−1. In 2014, T. hoshinota had covered 11 % out of 500 m2 of available hard substrate. We also report a rare encounter with Montipora aequituberculata, a scleractinian coral species that was able successfully to overgrow established sponge colonies. The sponge colonies did not react to the overgrowth by putting out tendrils and made no attempt to cover the Montipora aequituberculata. The coral was able to overgrow T. hoshinota because it did not directly attack the growing front of the sponge. The high growth rate and high plasticity of M. aequituberculata helped the coral to overgrow and take the space of the sponge.

In the South Eastern Black Sea, anchovy (Engraulis encrasicolus), sprat (Sprattus sprattus), and horse mackerel (Trachurus mediterraneus) are the most important small pelagic fish both ecologically and economically. The stomach contents of 1485 fish, including anchovy, sprat, and horse mackerel, were examined. Fish fed on 35 prey taxa, and there were dietary differences among predators. Anchovies predominantly consumed calanoid copepods and bivalves; sprats had a diet dominated by calanoid copepods and Chaetognatha (Parasagitta setosa); horse mackerel consumed mainly decapods and calanoid copepods. Copepods in the stomachs of sprat were more abundant and more frequent than in the stomachs of anchovy or horse mackerel during all year. As the anchovies and horse mackerel grew, their copepod consumption increased, but despite their size, sprats consumed a similar amount of copepods. Seasonal shifts in diet were observed in all three species. In winter and autumn months, all small pelagic fish consumed copepod species. The bivalve larvae were mostly consumed in summer by anchovies (N%: 72.98) and in spring by sprats and horse mackerel (N%: 88.59 and 81.08, respectively). Decapod species were preferred in spring months by horse mackerel. P. setosa was mostly consumed in autumn and winter by sprat. Anchovy showed a low dietary overlap with sprat but had a high dietary overlap with horse mackerel. The feeding strategy of anchovy seems to be mixed, while horse mackerel is a generalist at the individual level, and sprat is a specialist at the population level.