Heterochrony and heterotopy in the phylogeny of sea urchins

The role of heterochrony is evident in ontogeny and phylogeny of irregular (exocyclic) sea urchins. After metamorphosis, a juvenile passes the stage of regular (endocyclic) sea urchin, in which the periproct is surrounded by plates of the apical system. A shift of the periproct in the area of the fifth interambulacrum occurs in extant taxa at early stages of postlarval development and is accompanied by the reduction of genital plate 5. In some ancient (Jurassic) adult irregular sea urchins, the endocyclic state of the apical system is retained for a long time and the derivative of the fifth genital plate is sometimes observed even in Early Cretaceous species. Considerable transformations in the structure of the lower test surface in members of the order Spatangoida are manifested in changes in the relative positions of plastron plates and ambulacral areas I and V, separation of sternal plates from the labrum, etc. The mechanism of these changes is connected with translocation or “sliding” of sutures of particular plates as a result of nonuniform growth and partial resorption. The study of evolutionary lineages of Cretaceous and Cenozoic sea urchins has shown that the evolution was connected with the directional changes in some morphological characters at late ontogenetic stages. The process was accompanied by either extension, peramorphosis (lineages of the genera Micraster, Infulaster–Hagenowia in the European Province), or the loss of these stages, paedomorphosis (Hemiaster (Bolbaster) lineage, Late Eocene–Middle Miocene of Australia). The phenomena of heterochrony and heterotopy in the development of peripetal, marginal, and lateroanal fascioles in the Late Cretaceous and Paleocene families Hemiasteridae, Schizasteridae, and Paleopneustidae are described. The heterotopy is also illustrated by the example of the development of additional genital pores on ocular plates II and IV of the Middle Jurassic species Pygomalus analis (Disasteroida); its apical system has five pores instead of four. In the Late Cretaceous species Guettaria roccardi (Holasteroida), ocular plates II and IV have two pores each; in the apical system, there are eight genital pores instead of four. In some members of the order Holectypoida, the place of lost genital plate 5 is occupied by a new plate sometimes pierced by a pore, but judging from crystallographic data, it is not homologous to other genital plates. The order Clypeasteroida is characterized by the development of very small pores in both ambulacral and interambulacral fields; they provide passage for numerous accessory tube feet.     

Experimental morphology of coronar growth in regular echinoids

Summary The coronar growth of a cidaroid and an aulodont echinoid are investigated by means of tetracycline labelling. The results are compared with earlier investigations on a stirodont and on a camarodont echinoid in order to evaluate the general features of coronar growth. In all echinoids new coronar plates are added at the apical end of the corona throughout the life cycle. The plates are shifted towards the peristome and they grow peripherically.In cidaroids ambulacral (A-) plates are detached from the firm corona. They are transformed into scales covering the peristomial field. The interambulacral (IA-) plates, however, are partially reabsorbed at the peristomial margin. In this manner the oldest solitary interambulacral plates are lost. The subsequent plates are arranged in pairs. The cidaroids thus show interradial growth even at their peristomial margin. This is unique to echinoids.In non-cidaroids there is a perignathic girdle made up of paired ambulacral auricles with interambulacral ridges in between. In some species the ridge is a solitary element. Therefore interradial growth cannot occur in the peristomial margin. In other species the ridge consists of several elements, but it also grows as a whole. Slight resorption of calcite occurs in places at the peristomial margin. In other places, however, calcite is added onto the peristomial edge. In non-cidaroids, therefore, the widening of the peristome is achieved solely by means of lateral growth in the plates bordering the peristome. The shift of the coronar plates from apicad to orad in noncidaroids is a relative shift only.In all echinoids the coronar plates are arranged in meridional columns. All plates grow up to the peristome. Their growth rates are relatively uniform towards the adambulacral sutures (which run between A- and IA-columns). Their growth rates towards the perradius and the interradius respectively are high in younger plates which are positioned above the ambitus, and decrease rapidly in plates located below the ambitus. Near the peristome the interradiad and perradiad growth rates are always considerably lower than adradiad growth rates. Perradial and interradial growth serve to adjust the plates in size and shape to their respective position in the corona.     

Effects of salinity on competitive interactions between two Juncus species

A glasshouse study investigated the effect of salinity on growth and competitive interactions between two closely related rush species, an Australian native (Juncus kraussii) and an exotic (J. acutus) species. Overall, both species exhibited decreases in height and total biomass with increasing salinity, although tolerance of J. acutus was marginally lower. We observed asymmetric responses at each salinity, due to the presence of the other species. In fresh-water, co-presence of J. kraussii facilitated the growth (increases in height and total biomass) of J. acutus. However, at 10 ppt salinity direct interspecific competition with J. kraussii adversely affected total biomass of J. acutus. When grown with J. acutus, at 5 ppt but not at 10 ppt, salinity reduced total biomass of J. kraussii. We suggest that interspecific interactions vary with salinity, dependant on relative salinity tolerance of each species. It would appear that in areas receiving regular fresh-water inputs, which reduce salinity stress, J. acutus has the potential to displace J. kraussii.     

Morphology and biomechanical implications of isolated discocystinid plates (Edrioasteroidea, Echinodermata) from the Carboniferous of North America

Detailed examination of isolated thecal plates belonging to three discocystinid edrioasteroids, Spiraclavus nacoensis Sumrall, Hypsiclavus kinsleyi Sumrall, and Giganticlavus bennisoni Sumrall and Bowsher, reveals striking similarity in morphology among these species. Stereom observed in the ambulacral floor plates indicates that ligamentous connective tissue opened the ambulacral cover plates and muscle tissue closed them. The ambulacral floor plates are interpreted as rigid supports for the oral surface with the interambulacral areas acting as flexible integuments of plates. The aboral surface is interpreted as flexible and highly contractile. All discocystinid thecal openings are consistent in morphology with adaptations for thecal pressurization. Extension and contraction of the theca was accomplished by pumping water in and out of an inflatable sac associated with the periproctial opening. The pedunculate zone is interpreted as passively expanding and contracting by relaxing of mutable collagenous tissue and stiffening when the theca was in the desired position. All of these features illustrate that discocystinid edrioasteroids have highly–evolved morphology and function.     

Plattenanomalien beiEchinocorys sulcata (Goldfuss 1826) aus dem Dan (Alttertiär) von Dalbyover,Dänemark

In a collection of 2000 specimens of the echinoidEchinocorys sulcata from the Danian of Dalbyover, northern Jutland, Denmark, two percent of the coronae investigated show characteristic coronal plate anomalies which are largely missing in other echinoid species. These anomalies are formed by split coronal plates or mosaic-like plate arrangements instead of regularly grown plates. Plate anomalies occurring in ambulacral and interambulacral zones, classified into 14 different types, have been used for a statistical analysis. Data on the relative age of the echinoid animals with anormal coronal plates, and on the most abundant types of plate anomalies are given. Two specimens ofEchinocorys sulcata from the same locality show deviations from the regular pentameric pattern and comparable finds from other localities and of otherEchinocorys species were incorporated in the analysis. The anomalies described here are named forma aegrainconstans n.f. Literature data on echinoid coronal plate anomalies, which have been related to coronal deformations caused by evironmental parameters, are discussed.     

Effects of Pratylenchus zeae and Quinisulcius acutus Alone and in Combination on Sorghum

Host-parasite relationships of Pratylenchus zeae and Quinisulcius acutus, alone or in combination, were studied on sorghum in the greenhouse and laboratory. Q. acutus at 1,000 or 5,000 nematodes per 15-cm-d pot and P. zeae at 500 nematodes per pot significantly suppressed plant height and fresh and oven dry shoot and root weights. A mixture of 1,000 Q. acutus and 500 P. zeae per pot resulted in greatest suppression of growth. Roots of plants inoculated with Q. acutus alone were reduced in number and size and showed lesions and discoloration. Reproduction of this nematode 42 days after inoculation was much greater in treatments of 100 or 1,000 than 5,000 nematodes. The population density of the two species at 6 weeks after inoculation was significantly less when combined than for each species alone. When the two species were combined, reproduction of P. zeae was greater than that of Q. acutus, but the final populations per gram of root weight were the same. Q. acutus fed ectoparasitically on epidermal cells of sorghum roots in the zone of elongation and differentiation when observed under in vitro conditions.     

Taxonomic significance of spine morphology in the echinoid genera Diadema and Echinothrix

Abstract. The spine morphology of all established species of Diadema and Echinothrix, including 2 color morphs of E. calamaris, were examined externally and internally via transverse sectioning to identify diagnostic species features and to assess the morphological relationship between species. Forty‐nine different morphological characters were measured and analysed using ordination by multi‐dimensional scaling (MDS) and cluster analysis. Specimens of Diadema paucispinum and D. setosum had very distinct spine structures. In D. paucispinum, the spines were more robust than those of other species of Diadema. This was evident in the spine's internal structure, with large, closely packed solid wedges, a small axial cavity, and rings of trabeculae throughout the spine's length. The spines in D. setosum were distinctive because of their length in relation to test size and the reduced flaring of their verticillations. The spines of other members of this genus were very similar to each other. Without careful sectioning, the spines from specimens of D. antillarum, D. ascensionis, D. mexicanum and D. savignyi were difficult to differentiate. The internal structures of spines for each species did, however, possess a combination of features that differentiated the species. Such features included the shape, orientation, and number of solid wedges, the presence or absence of spokes and rings of trabeculae between the solid wedges, and the presence or absence of tissue within the axial cavity. Individuals of Diadema palmeri also had spines morphologically similar to other species, however, the red pigmentation of these spines (in life and when preserved) made them easily distinguishable. The spine structures of the 2 species of Echinothrix were starkly different, while the white and brown color morphs of E. calamaris had morphologically distinctive ambulacral and interambulacral spines. The blunt, open‐tipped interambulacral spines, with reticular tissue present in the axial cavity of the white color morph, were easily distinguished from the pointed, closed‐tipped spines, with a hollow axial cavity found in the brown color morph. Such differences indicate that the brown color morph is either a subspecies or a separate species. Taken together the data show that each species has significant morphological differences in the structure of the spines. It is evident from our data that spine morphology is a useful tool to differentiate these commonly confused species.     

Holotestoid: a computational model for testing hypotheses about echinoid skeleton form and growth

Regular echinoid skeletons, or tests, comprise plate patterns and overall shapes that have proven challenging to analyse solely on the basis of any one approach or process. Herein, we present a computational model, Holotestoid, that emulates four macrostructural ontogenic processes involved in test growth (plate growth, plate addition, plate interaction, and plate gapping). We devise a geometric representation for analysing tests and describe how we use analogies (bubble interactions and close-packing) to emulate the processes. In the computational model, the emulated processes are used to determine the plate size and plate shape and combined to simulate a growth zone. We simulated growth zones for Arbacia punctulata and for Strongylocentrotus franciscanus by changing the value for one parameter, the ambulacral column angle. We quantitatively compared morphological features for simulated forms to those for real specimens to test the computational model. Additionally, we simulated growth zones for A. punctulata, S. franciscanus, Eucidaris thouarsii, and Mellita quinquiesperforata by changing three parameters, ambulacral column angle, peristome radius to apical system radius ratio, and apical system radius to column length ratio. Holotestoid can be used to explain morphological disparity among echinoid tests.     

Description of two new species of Hisonotus Eigenmann & Eigenmann, 1889 (Ostariophysi,Loricariidae) from the rio Paraná-Paraguay basin,Brazil

Two new species of Hisonotus are described from the rio Paraná-Paraguay basin in Brazil. The most remarkable features of the new species are the odontodes forming longitudinally aligned rows (one odontode after the other, but not necessarily forming parallel series) on the head and trunk (vs. odontodes not forming longitudinally aligned rows), a pair of rostral plates at the tip of the snout (vs. a single rostral plate), the functional v-shaped spinelet (vs. spinelet non-functional, square-shaped, or absent). These features suggest close phylogenetic relationships with Hisonotus bockmanni, H. insperatus, H. luteofrenatus and H. piracanjuba. Additionally, both new species are distinguished from their congeners by characters related to head length and depth, orbital diameter, suborbital depth, caudal peduncle depth, pectoral-fin spine length, snout length and counts of teeth. Hisonotus paresi sp. n. further differs from its congeners by having contrasting dark geometric spots on the anterodorsal region of the body, a character lacking in H. oliveirai sp. n. The variation in number and shape of the rostral plate, posterior rostrum plates, infraorbitals and the preopercle in both new species and in H. insperatus are discussed.     

Description of Quinisulcius solani n.sp. (Nematoda: Tylenchorhynchidae) with a Key to the Species and Data on Scutylenchus koreanus from Pakistan

A new species. Quinisulcius solani, is described and illustrated from specimens on Solanum tuberosum from Murree Hills, Pakistan. Q. solani n.sp. differs from its closest relative, Q. acutus (Allen, 1955) Siddiqi, 1971, by its spiral to open ''C'' shaped body and stylet length of 19 μn, vs. 17 μm in Q. acutus. In Q. acutus the stylet knobs project anteriorly but slope posteriorly in Q. solani n.sp. Tail annules number 17 in Q. acutus but 38 in Q. solani n.sp.; also the phasmids in the former species are at mid-tail and in the latter are in anterior half of tail, at about 34%. Q. solani n.sp. is also closely related to Q. capitatus (Allen, 1955) Siddiqi, 1971 but differs in some characters. Head annules number eight and stylet length is 17 μm in Q. capitatus, but head annules are six and stylet length is 19 μm in Q. solani n.sp. In Q. capitatus T/ABW is 3 vs. 2.2 in Q. solani n.sp. Also, phasmids are located at mid-tail on Q. capitatus but at ahout one-third of the tail on Q. solani n.sp. A key to the 10 species of Quinisulcius is also presented. Scutylenchus koreanus (Choi &Geraert, 1971) Siddiqi, 1979 is recorded for the first time in Pakistan and morphometric data and illustrations given.     

The efficacy of Scenedesmus morphology as a defense mechanism against grazing by selected species of rotifers and cladocerans

Phytoplankton often develop various defense mechanisms in response to zooplankton grazing, such as spines and colonies. While it is now known that increased spine length and cells in a colony of members of the genus Scenedesmus, when zooplankton grazing is intense, helps in reducing zooplankton filtering rates, the effect of these defense mechanisms at the population level has been observed in few studies. Here we present data on the growth rates of four zooplankton species, Brachionus calyciflorus, B. patulus, Ceriodaphnia dubia and Daphnia pulex at two food levels using two species of colony-forming Scenedesmus spp.: S. acutus (cell length = 18.2 ± 0.4 µm; width = 4.2 ± 0.1 µm; average colony length = 90 µm; width: 21 µm) and S. quadricauda (cell length: 21 ± 0.5 width 7.5 ± 0.3 µm; average colony length: 84 µm; width: 30 µm). Whereas S. acutus had no spines, S. quadricauda had spines of 6–10 µm. Population growth experiments of the test rotifers and cladocerans were conducted in 100 ml containers with 50 ml of the medium with test algae. Algae concentrations used were: 13 and 52 mg dw l^–1 of each of the two algal species offered in colonial forms. We used an initial inoculation zooplankter density of 1 ind. ml^–1 for either of the rotifer species and 0.2 ind. ml^–1 for either of the cladoceran species. In all, we had 64 test containers (4 test species of zooplankton × 2 test species of algae × 2 algal densities × 4 replicates). We found a significant effect of algal size on the growth rates of all the four tested species of zooplankton. The population growth rates of zooplankton ranged from ?0.58 to 0.66 and were significantly higher on diet of S. acutus than of S. quadricauda. Thus, our study confirms that the larger colony size and the formation of spines in S. quadricauda were effective defenses against grazing by both rotifers and smaller sized cladoceran Ceriodaphnia dubia but that larger-bodied Daphnia pulex could exploit both the algal populations equally.     

Tintinnophagus acutus n. g., n. sp. (Phylum Dinoflagellata), an Ectoparasite of the Ciliate Tintinnopsis cylindrica Daday 1887, and Its Relationship to Duboscquodinium collini Grassé 1952

ABSTRACT. The dinoflagellate Tintinnophagus acutus n. g., n. sp., an ectoparasite of the ciliate Tintinnopsis cylindrica Daday, superficially resembles Duboscquodinium collini Grassé, a parasite of Eutintinnus fraknoii Daday. Dinospores of T. acutus are small transparent cells having a sharply pointed episome, conspicuous eyespot, posteriorly positioned nucleus with condensed chromosomes, and rigid form that may be supported by delicate thecal plates. Dinospores attach to the host via a feeding tube, losing their flagella, sulcus, and girdle to become spherical or ovoid cells. The trophont of T. acutus feeds on the host for several days, increasing dramatically in size before undergoing sporogenesis. Successive generations of daughter sporocytes are encompassed in an outer membrane or cyst wall, a feature not evident in trophonts. Tintinnophagus acutus differs from D. collini in host species, absence of a second membrane surrounding pre‐sporogenic stages, and failure to differentiate into a gonocyte and a trophocyte at the first sporogenic division. Phylogenetic analyses based on small subunit (SSU) ribosomal DNA (rDNA) sequences placed T. acutus and D. collini in the class Dinophyceae, with T. acutus aligned loosely with Pfiesteria piscicida and related species, including Amyloodinium ocellatum, a parasite of fish, and Paulsenella vonstoschii, a parasite of diatoms. Dubosquodinium collini nested in a clade composed of several Scrippsiella species and Peridinium polonicum. Tree construction using longer rDNA sequences (i.e. SSU through partial large subunit) strengthened the placement of T. acutus and D. collini within the Dinophyceae.     

Análisis morfométrico de las especies de Echinocereus sección Triglochidiati (Cactaceae) en México

Echinocereus section Triglochidiati has been accepted in the most recent taxonomic treatments of the genus. However, the number of included species has varied from one to 14. This study aims to define the species number of section Triglochidiati in Mexico through multivariate analysis, and to identify quantitative characters that can be used to recognize them. We used canonical discriminant analysis and classification discriminant analysis for 11 putative taxa native to Mexico and 20 morphometric characters. The number of stem ribs, number of central spines, stem diameter, length of radial spines (position 09), length of flower, receptacular tube length / perianth length ratio, and the receptacular tube trichome length permitted the differentiation of six taxa: E. acifer, E. arizonicus, E. coccineus, E. koehresianus, E. polyacanthus and E. scheeri. A key to the species is included.     

Systematic consideration of petiole anatomy of species of Echinodorus Richard (Alismataceae) from north-eastern Brazil

Petiole anatomy of the north-eastern Brazilian species Echinodorus glandulosus, E. palaefolius, E. pubescens, E. subalatus, E. lanceolatus and E. paniculatus were examined. All species had petioles with an epidermis composed of tabular cells with thin walls. The chlorenchyma just below the epidermis alternates with collateral vascular bundles. The interior of the petiole is filled by aerenchyma with ample open spaces or lacunas. The lacunas are bridged at intervals by plates, or by diaphragm-like linkages. There are lactiferous ducts and groups of fibres throughout the entire length of the petiole, but more frequently in the chlorenchyma. Important taxonomic characteristics for the genus Echinodorus include the shape and outline of the petiole in transversal section, the presence of winged extensions, and the number of vascular bundle arcs. Exceptions occur in E. lanceolatus and E. paniculatus, whose petioles have similar anatomic patterns. A comparative chart of the petiole anatomic characteristics analyzed is presented.     

Amphidoma parvula (Amphidomataceae), a new planktonic dinophyte from the Argentine Sea

Amphidoma is an old though poorly studied thecate dinophyte that has attracted attention recently as a potential producer of azaspiracids (AZA), a group of lipophilic phycotoxins. A new species, Amphidoma parvula, sp. nov. is described from the South Atlantic shelf of Argentina. With a Kofoidean thecal plate pattern Po, cp, X, 6′, 6′′, 6C, 5S, 6′′′, 2′′′′, the cultivated strain H-1E9 (from which the type material of Am. parvula, sp. nov. was prepared) shared the characteristic plate arrangement of Amphidoma each with six apical, precingular and postcingular plates. Amphidoma parvula, sp. nov. differs from other species of Amphidoma by a characteristic combination of small size (10.7–13.6 µm in length), ovoid shape, high length ratio between epitheca and hypotheca, and small length ratio between apical and precingular plates. Other morphological details, such as the number and arrangement of sulcal plates and the fine structure of the apical pore complex support the close relationship between Amphidoma and the other known genus of Amphidomataceae, Azadinium. However, Am. parvula, sp. nov. lacks a ventral pore, a characteristically structured pore found in all contemporary electron microscopy studies of Amphidoma and Azadinium. As inferred from liquid chromatography coupled with tandem mass spectrometry, Am. parvula, sp. nov. did not produce AZA in measurable amounts. Molecular phylogenetics confirmed the systematic placement of Am. parvula, sp. nov. in Amphidoma (as sister species of Amphidoma languida) and the Amphidomataceae. The results of this study have improved the knowledge of Amphidomataceae biodiversity.     

Initial predation and parasitism by muricid whelks demonstrated by the correspondence between drilled holes and their apparent enveloper

The morphologies of drilled holes enveloped by three coexisting muricid whelks, Morula musiva, Cronia margariticola and Ergalatax contractus, were compared. The results were used to demonstrate the replacement of feeders using drilled holes, and to estimate the frequency of this occurrence in the field. In the laboratory, M. musiva made circular internal holes, whereas C. margariticola and E. contractus made oval holes, when they preyed upon the mussel Hormomya mutabilis. The maximum inner diameter of the hole correlated with the driller's shell height in all three muricid species. In the field, mussels enveloped by M. musiva had circular drilled holes, as was found in the laboratory, and the correlation between maximum diameter and enveloper's shell height was not significantly different from that found in the laboratory. In contrast, holes enveloped by C. margariticola in the field were more circular than those observed in the laboratory, and there was no correlation between maximum diameter and enveloper's shell height. Statistical analyses of these results indicated that more than half of the mussels being ingested by C. margariticola had been drilled by M. musiva, i.e. C. margariticola would often kleptoparasitize or scavenge M. musiva's prey by taking over the drilled hole. Few M. musiva would take over the holes drilled by C. margariticola or E. contractus. Furthermore, probably few M. musiva would take over the hole made by a conspecific initial drilling predator. It appears that E. contractus rarely initiates predation by drilling.     

Effects of various salts on the germination of three perennial salt marsh species

We studied the germination responses of Arthrocnemum macrostachyum, Juncus acutus and Schoenus nigricans to saline stress caused by different salt types. The germination percentage and mean time to germination data were obtained by incubating seeds for 30 d in 1, 2, 3, 4 or 5% saline solutions of NaCl, MgCl₂, MgSO₄ and Na₂SO₄ at 30/20 °C and with a 12 h photoperiod. A. macrostachyum was the most tolerant species to salinity during the germination (65% in 2% NaCl). S. nigricans showed the lowest germination (none germinated in salt and only 26% in distilled water). J. acutus showed intermediate behaviour between the two above species, its germination being inhibited by high salt concentrations. The sulphates had less inhibitory effect than the equivalent chloride concentrations.     

Roost characteristics as indicators for heterothermic behavior of forest-dwelling bats

Many forest-dwelling bats spend their diurnal inactivity period in tree cavities. During this time bats can save energy through heterothermy. A heterothermic response (torpor) is characterized by a lowered body temperature, reduced metabolic rate, and reduction of other physiological processes, and can be influenced by the microclimatic conditions of roost cavities. The thermal and physical characteristics of roosts used by the sympatric, ecologically, and morphologically similar bat species Myotis bechsteinii, M. nattereri, and Plecotus auritus were compared. These three species differ in their heterothermic behavior, with the lowest skin temperatures observed for P. auritus. Therefore, we hypothesized that roosts occupied by the three species should differ in roost characteristics and microclimatic conditions, whereby P. auritus should select colder and thermally less stable roosts. The results showed that horizontal depth of the cavity, diameter of the roost tree, and microclimatic conditions within roosts differed among species. Roosts of P. auritus had the lowest horizontal depth, lowest thermal stability, and lowest mean minimum roost temperatures. Height of the roost, diameter of the roost tree, and vertical depth were also shown to influence microclimatic conditions. With increasing diameter of the tree and increasing horizontal depth, mean minimum roost temperature increased and thermal stability improved. Furthermore, with ascending height above ground insulation and mean roost temperatures increased. Our results imply that species such as P. auritus, which use pronounced torpor as a primary energy saving strategy, prefer colder cavities that support their heterothermic strategy.     

Effects of a rapidly receding ice edge on the abundance,age structure and feeding of three dominant calanoid copepods in the Weddell Sea,Antarctica

Open-water, marginal-ice and in-ice zones were sampled in the Weddell Sea during November and December, 1993 in an effort to examine the influence of the early spring bloom on the diet and population structure of the three biomass dominant copepods: Metridia gerlachei, Calanus propinquus, and Calanoides acutus. The abundance of all three species in the upper 200 m was highest at stations in the open water, but individually, each species displayed a unique trend. M. gerlachei, which showed the least variability, was significantly more abundant in open water than in the marginal-ice zone. The abundance of Calanus propinquus was higher in open water than in the marginal-ice zone or in the ice. Calanoides acutus displayed the highest variability, with significant differences between all three ice-cover zones. Diet analysis revealed no significant differences in the number of food items within each ice-cover zone and diatoms were the most numerous item identified in the guts of all three species. However, M. gerlachei and Calanus propinquus also contained metazoan material, while Calanoides acutus did not. There were dramatic differences in the age composition of the species between the zones. Early copepodite stages of all three species predominated at the ice edge and in open water. Numbers of M. gerlachei adult females were roughly equivalent in all three zones while Calanoides acutus and Calanus propinquus adult females composed a higher fraction of the total population within the ice. These results compare well with life-history data compiled by other authors and reinforce the importance of the ice edge to bloom-dependent Antarctic zooplankton. Accepted: 5 April 1999     

Competition as a determinant of the upper limit of subtidal kelp Ecklonia stolonifera Okamura in the southern coast of Korea

Experiments in the subtidal zone of the southeastern coast of Korea examined the role of competition in determining the upper limit of perennial kelp, Ecklonia stolonifera, which is a dominant species in the subtidal community, but rarely found shallower than 5 m depth. Replicate clearings of dense algal turfs simulating natural disturbance at 1 and 3 m depth zones showed that E. stolonifera is able to settle and develop adult sporophytes in the upper zone. However, these adult sporophytes were eventually excluded from the clearings within one year after clearing. Two-year succession patterns at the clearings fell into three sequential categories: E. stolonifera and polychaete worms (Serpula vermicularis Linnaeus), mussels (Mytilus edulis Linnaeus), and turf-forming algae. A competitor removal treatment revealed that competition with M. edulis for primary space is the direct cause resulting in exclusion of E. stolonifera from the clearings. Recolonization of E. stolonifera after exclusion did not occur at clearings due to preemptive competition with other sessile organisms, which occupied 75-99% of bottom cover during the reproduction period of E. stolonifera (Autumn). Algal turfs, the final colonizer of the clearings, recovered more than 80% of bottom cover within 10 months after exclusion of M. edulis, and their species composition and abundance were not significantly different to those of adjacent controls. Experiments using artificial substrata showed that recruitment of E. stolonifera from spores is essentially impossible on the plates occupied by other sessile organisms (>86% cover). These results indicate that preemptive competition with dense algal turfs for the settlement and competition with M. edulis for survival in the course of succession are two most important factors determining the vertical distribution limits of E. stolonifera.