Ruth Böttger-Schnack

The microcopepod fauna in the eastern Mediterranean and Arabian Seas : a comparison with the Red Sea fauna.

Multiple opening-closing nets of 0.05 mm mesh size were employed to study the community structure and vertical distribution of microcopepods at selected stations in the Red Sea, Arabian Sea and Eastern Mediterranean Sea down to a maximum depth of 1850 m. Calanoids, cyclopoids (Oithona and Paroithona) and poecilostomatoids (mainly Oncaea) were the 3 most abundant orders. In the epipelagic zone (0–100 m), these orders occurred at similar abundance levels, whereas in the meso- and bathypelagic zones the poecilostomatoid genus Oncaea dominated numerically by about 60–80% of all copepodids.The species diversity of Oncaea in the Red Sea is compared with preliminary results from the two adjacent regions. In the deep Eastern Mediterranean Sea, the number of species appears to be similar to that in the deep Red Sea and low as compared to the deep Arabian Sea. In this latter area an extremely speciose Oncaea fauna was found at depth below the oxygen-minimum-zone (900–1850 m). The results are related to the differences in the hydrographic conditions of these 3 areas.

Community structure and vertical distribution of cyclopoid copepods in the Red Sea

The species abundance, vertical distribution and diurnal vertical migration of cyclopoid copepods was analyzed in the central Red Sea in October–November 1980. Samples were taken to a depth of 450 m with a multiple opening — closing plankton net with 0.1-mm mesh-size. Selected important species were allocated to five different groups according to their depth distributions during daytime. The greatest number of species (9) was found in the lower epipelagic zone (40 to 100 m), below the strong seasonal thermocline. The lowest number of species (1) occurred in the upper part of the upper mesopelagic zone (100 to 250 m), which is characterized by a strong dissolved oxygen gradient. Five species had a bimodal vertical distribution, with dual peak abundances in the epipelagic and upper mesopelagic zones. Distinct differences in distribution patterns were noted between sexes and/or developmental stages. The vertical range of diurnally migrating species was small, usually less than 50 to 100 m. Characteristic diurnal changes in the vertical succession of dominant species occur within the epipelagic zone (0 to 100 m). Species-specific vertical distribution patterns are compared with published data from other areas. A conspicuous difference in the proportion of carcasses was noted between species: small species (<0.5 mm in length) had a much higher proportion of carcasses, usually between 20 and 40% of the total standing stock, than larger ones (<5%). The potential causes of this phenomenon, which may be due to (1) methodological bias, (2) a lower sinking velocity of small carcasses, or (3) a higher mortality rate of small species, are discussed.

Observations on the taxonomic composition and vertical distribution of cyclopoid copepods in the central Red Sea

The taxonomic composition and vertical distribution of cyclopoid copepods, including very small species, in the central Red Sea were analyzed. Samples were taken in a multiple opening and closing net with 0.1 mm mesh size to a depth of 450 m. Most species belong to the genus Oncaea (13 identified and 6 unidentified forms). Nearly one half of these are smaller than 0.4 mm in length. Nine cyclopoid species and three groups of very similar species and forms of Oncaea predominate. In the upper 450 m of the water column, each of these species or groups account for more than 1 % of all cyclopoid specimens. In the epipelagic zone (0–100 m) Oithona simplex predominates, accounting for 20 % of the total. In the upper mesopelagic zone Paroithona sp. and one of the unidentified Oncaea forms are most numerous from 100 to 250 m, and two groups of Oncaea are most abundant from 250 to 450 m. The dominance of single species among cyclopoids is less pronounced than that reported for calanoids in the mesopelagic zone of the central Red Sea.

Taxonomy of Oncaeidae (Copepoda, Poecilostomatoida) from the Red Sea. III. Morphology and phylogenetic position of Oncaea subtilis Giesbrecht, 1892

Both sexes of Oncaea subtilis Giesbrecht, 1892, a small oncaeid species commonly occurring in temperate and tropical regions, are redescribed on the basis of material from the Red Sea. It is placed in a new monotypic genus, Monothula, on the basis of the loss of the outer spine on the third segment of the endopod of legs 2–4, and the presence of a single dorsal egg-sac, which is attached medially to the genital double-somite. The latter character is unique among oncaeids. The geographical distribution of M. subtilis comb. nov. is reviewed, and additional taxonomic data based on material from the eastern Mediterranean, the Arabian Sea and the eastern Indian Ocean are presented. The phylogenetic relationships of M. subtilis within the Oncaeidae are discussed.

Size polymorphism in Oncaea venusta Philippi, 1843 and the validity of O. frosti Heron, 2002: a commentary

The morphological characters used to describe Oncaea frosti Heron, 2002 (Copepoda, Poecilostomatoida), an Atlantic medium-sized form variant of O. venusta Philippi, 1843, appear to be inadequate in view of the great polymorphism known for this ubiquitous species. Comparative analysis of published and newly collected length data of O. venusta variants worldwide demonstrates that O. frosti cannot be unequivocally delineated in the Indo-West Pacific. The validity of O. venella Farran sensu Heron (2002) is questioned and comments are given on Herons synonymization of O. venusta f.venella sensu Ferrari (1975) and sensu Böttger-Schnack (2001) with O. frosti. As long as the significance of the morphological characters used to separate O. venusta form variants is not substantiated by data emerging from alternative taxonomic methods, such as the analysis of gene sequences, the species names O. frosti and O. venella Farran sensu Heron (2002) are regarded as species inquirendae in the genus Oncaea.

Depth structuring of pelagic copepod biodiversity in waters adjacent to an Eastern Indian Ocean coral reef

We compared pelagic copepod communities at three (400+ m) stations adjacent to Scott Reef (14°S), a shelf-break reef in Australias Indian Ocean territory, with those within the shallow (c.50 m) atoll lagoon. The metazooplankton assemblage sampled by our 100-μm multinet system was dominated by small (< 1.0 mm) copepods. We identified over 220 copepod species, belonging to five of the nine orders. Of these, 68 (31%) are new records for Australian waters and at least 14 are likely to be undescribed. Redundancy analysis indicated that depth stratum was the most important determinant of community structure: distinct communities were associated with the epipelagic (within which the atoll lagoon community was further distinguished by reef-associated copepods), the chlorophyll maximum/thermocline, the upper mesopelagic and the hyper-benthos. The family Oncaeidae was highly speciose (> 52 taxa) and progressively more important with increasing depth.

Definition of species groups of Oncaeidae (Copepoda: Cyclopoida) as basis for a worldwide identification key

The copepod family Oncaeidae is widely distributed in the worlds oceans and includes many small and abundant species. Due to their small size and the existence of sister and sibling species in different parts of the ocean, species identification is very difficult. Quantitative studies on copepod communities usually consider oncaeids at the family level only, or present uncertain species names, when based on regional identification keys not established for the study area. This paper aims to develop the basis for an improved taxonomic resolution of oncaeids in ecological studies. It summarizes the most relevant morphological elements to characterize the seven presently known genera and to define in addition 16 species groups within the paraphyletic taxon Oncaea s.l. On this basis, a worldwide identification key for oncaeids is presently being developed, restricted to genera and species groups, with species included as far as the state of knowledge allows.

A new species of the dentipes-subgroup of Triconia and a redescription of T. giesbrechti and T. elongata (Copepoda: Cyclopoida: Oncaeidae) from the tropical Pacific and the Korea Strait

A new species of Triconia in the family Oncaeidae, Triconia pacifica sp. nov., and a new form variant each of Triconia giesbrechti Böttger-Schnack and Triconia elongata Böttger-Schnack are described from two sites in the Pacific. Triconia pacifica can be distinguished from its sibling Triconia dentipes (Giesbrecht) by (1) morphometric characters, including the proportional lengths of distal endopod spines of swimming leg 4, and the relative length of the outer basal seta on P5, and by (2) a number of micro-structures on the appendages. The Pacific specimens of T. elongata and T. giesbrechti resemble the typical forms in morphometric characters, with some minor differences in proportional spine lengths on the swimming legs, and differ in a few micro-structures. The hitherto unknown male of T. giesbrechti is newly described. For all species/forms described, the intraspecific variability of proportional spine lengths on the endopods of P2–P4 is examined and discussed. http://www.zoobank.org/urn:lsid:zoobank.org:pub:6B41B0E2-0A5C-458B-8F9C-25000F208E24

Development of an interactive identification key for Oncaeidae (Copepoda: Cyclopoida)

The current state of development of an interactive electronic identification key for females of the marine pelagic microcopepod family Oncaeidae is presented. To date, 112 species have been described, allocated to seven genera (Archioncaea, Conaea, Epicalymma, Monothula, Oncaea s.str., Spinoncaea, and Triconia) and 16 species groups within the speciose paraphyletic taxon Oncaea s.l. Only two species of Oncaea s.l. show an uncertain group status. Of all described oncaeids, seven species are not yet included in the key due to inadequacies in morphological description and/or lack of type material for re-examination. In addition, seven morphologically distinct species and two new species groups are considered that have not yet been formally described. The key uses easily distinguishable morphological characters as far as possible (e.g. body size, proportional lengths of urosomites, length of P5 exopod) and includes more difficult characters (e.g. spine counts on swimming legs, proportional spine lengths) where required for unequivocal identification. The characters used in the key allow the identification of genera and species groups by investigators with limited taxonomic experience; species separation in most cases requires some advanced dissection skills. Potential identification problems caused by difficulties discerning minute morphological features or intraspecific morphometric variability are discussed. The present version of the identification key still requires complementary illustrations of character states and inclusion of fact sheets summarizing the characteristics of each species with notes on taxonomic uncertainties and links to databases providing zoogeographical and genetic information.