Induction of Settlement and Metamorphosis of the Veliger Larvae of the Nudibranch,Onchidoris bilamellata

Summary

Onchidoris bilamellata veligers were reared in the laboratory on a combination of phytoñagellates and diatoms. They attained metamorphic competence after a period of 28 to 32 days at 11°C, or 60 to 80 days at a temperature averaging 7.5° C.

Experimental evidence suggests that settlement is stimulated by a diffusible chemical emanating from living barnacles, whereas metamorphosis is induced by a chemical or mechanochemical cue, which is also associated with barnacles. Settlement and metamorphosis are considered to be separable events in O. bilamellata. The settlement response is reversible and can be repeated; it involves a characteristic behavioral repertoire including descent to the bottom, foot contortions and crawling on the pedal sole. Settlement occurs only in seawater that contains, or had previously contained, living barnacles. Metamorphosis is irreversible and involves the resorption of the velum, loss of the larval shell, and incorporation of the visceral mass into the cephalopedal mass. Metamorphosis is triggered only when physical contact with living or dead barnacles is made (dead barnacles refers to shell and tissue fragments which are only effective in inducing metamorphosis when they are used in combination with seawater that had previously contained living barnacles).

Settlement and metamorphosis in O. bilamellata is compared with that of other nudibranch species, and its unique settlement response is discussed.     

Effects of temperature and salinity on the larvae of two species of rhizocephalan (Crustacea: Cirripedia)

Summary

Responses of larvae of two rhizocephalan species to changes in seawater temperature and salinity were studied under laboratory conditions. Peltogasterella gracilis parasitizes the hermit crab Pagurus pectinatus, which occurs at stable salinity and gradually changing temperature in summer. Sacculina polygenea is a parasite of the crab Hemigrapsus sanguineus, which lives in the intertidal zone in summer where salinity and temperature can fluctuate during the day. The development of both species is comprised of five naupliar stages and the cyprid stage, and it was considered successful if more than 50% of the nauplii attained the cyprid stage. P. gracilis nauplii successfully developed at 12–20°C and 30–34‰, but at 22°C successful development occurred in a narrower salinity range (32–34‰). All nauplii died both at 25°C and in 26‰. S. polygenea nauplii successfully reached the cyprid stage at higher temperatures (18–25°C) and a wider salinity range (18–34‰) than P. gracilis nauplii, but at 12°C and 16‰ larval development of S. polygenea was suppressed. Under favorable conditions, naupliar development lasted 3.5 days in P. gracilis and 2–3 days in S. polygenea. The cyprids of both rhizocephalan species demonstrated a greater resistance to temperature and salinity changes than nauplii. However, P. gracilis cyprids were active in a narrower salinity range (16–34‰), as compared to S. polygenea cyprids (8–34‰). Under favorable conditions the cyprids of both species survived for 6 to 10 days.     

Cirripedia of Madeira

We give a list of Cirripedia from Madeira Island and nearby deep water, based on specimens in the collection of the Museu Municipal do Funchal (História Natural) (MMF), records mentioned in the literature, and recent collections. Tesseropora atlantica Newman and Ross, 1976 is recorded from Madeira for the first time. The Megabalanus of Madeira is M. azoricus. There are 20 genera containing 27 species, of which 22 occur in depths less than 200 m. Of these shallow water species, eight are wide-ranging oceanic forms that attach to other organisms or to floating objects, leaving just 13 truly benthic shallow water barnacles. This low diversity is probably a consequence of the distance from the continental coasts and the small area of the available habitat. No endemic species have been found.     

The comparative photobehavior of laboratory-hatched and plankton-caught Balanus improvisus (Darwin) nauplii and the effects of 24-hour starvation

Stage II nauplii of Balanus improvisus (Darwin) were obtained from laboratory-maintained adult barnacles. The immediate phototactic and photokinetic response of laboratory nauplii to light stimuli of known wavelength (460–540 nm) and quantal intensity was determined through use of closed-circuit videotape recordings quantified for computer analysis. Spectral and light intensity responses were compared with previous results using nauplii collected from the plankton. In both cases, nauplii exhibit a primary peak response to light near 480 nm and a secondary peak near 520 nm. Although the spectral response and basic patterns of photobehavior remain similar in field and laboratory nauplii, sensitivity to light intensity is significantly reduced in laboratory nauplii. Responses of fed and 24-h starved laboratory nauplii were also compared at three salinities (15, 20, 30‰). Starvation for 24 h, although inducing no major change in photopositive and photokinetic response of nauplii, can slightly depress spontaneous swimming speed and raise the threshold of intensity response for phototaxis.     

The distribution of cirripede larvae (Cirripedia: Thoracica) in the Amursky and Ussuriisky bays of the Sea of Japan

Based on data from plankton surveys that were carried out in the waters of the Amursky and Ussuriisky bays of the Sea of Japan from May to October 2007 and 2008, the species composition, time of occurrence, density, and distribution of cirripede larvae (Cirripedia: Thoracica) were studied. The larvae of five species of this group were revealed. Their average density does not exceed 400 ind./m3 and their proportion in the total meroplankton does not exceed 22%. In the summer season, the larvae of Amphibalanus improvisus prevailed and in the autumn season the nauplii of Balanus rostratus prevailed. The number of larvae of barnacles was higher in Amursky Bay, with deep-sea species nauplii being concentrated in its central part and shallow water ones in the northern and central parts, in the zones of costal gyres. In Ussuriisky Bay, the density of larvae of most species decreased seaward from the coast. The abundance of larvae of invasive species A. improvisus show that it has successfully become naturalized in Amursky Bay and is gradually replacing the native species Chthamalus dalli and Balanus crenatus in the lower littoral and upper sublittoral zones.     

Possible noncalcareous algae in the upper part of the bell canyon formation (Permian), New Mexico

A new genus and species of alga called Sinoglypha nassichuki is identified and described from Guadalupian rocks of the Delaware Basin, New Mexico. It occurs in tilted to almost upright position in laminites generally accepted as being deposited in deep, anoxic water. The fossils are noncalcareous, having a wavy nature. They are not classed as trace fossils of animals. They are leafy, 2–5 cm long and may be preserved in original position.

If Sinoglypha is an alga it leads to the tentative, but not new, conclusion that perhaps the water was not deep but shallow enough for light penetration—30 meters for the upper part of the Bell Canyon Formation.     

Mechanisms of propagule release in the carnivorous sponge Asbestopluma occidentalis

Carnivorous sponges characteristically inhabit the deep sea, so extensive observations of the biology of living specimens are rare. We report on newly discovered shallow‐water (<30 m depth) populations of the carnivorous sponge Asbestopluma occidentalis and on observations of living adults and larvae from this unique group of sponges. In the Salish Sea, British Columbia, Canada, populations of A. occidentalis exist at depths as shallow as 18 m, where they co‐occur with hexactinellid sponges. Adults with and without embryos (n =127) were collected and easily maintained in the laboratory for several months, allowing continuous examination of live specimens. Parent sponges naturally disassociated their tissue, facilitating larval release and dispersal. Dispersed larvae had actively beating cilia, but no swimming was observed. Larvae settled and attached from several hours to several days post‐release. After larval release, parent sponges reaggregated their disassociated bodies into spherical balls of apparently undifferentiated tissue, which could also disperse and settle. Sexually mature adults were sampled in the field from August to November, with a high proportion of adults containing mature embryos in late November. High‐resolution photography and electron microscopy verified that adults were covered with anisochelae spicules, and used these to capture nauplii of Artemia sp. under experimental conditions; however, time‐lapse photography showed that some captured prey could free themselves with vigorous swimming. The occurrence of abundant shallow‐water populations of A. occidentalis in the Salish Sea provides a rare opportunity to study the evolution and ecology of carnivory in the Porifera.     

Food and feeding habits of Mesocyclops leuckarti (Claus) in Lake Kinneret (Israel)*

SUMMARY. The diet and feeding habits of natural and cultured populations of Mesocyclops leuckarti were studied. Nauplii and copepodid stages I–III are herbivorous. Copepodid stages IV–V and adults preferentially preyed upon Ceriodaphnia and Diaphanosoma whereas Bosmina was not preyed upon. Rate of predation on Ceriodaphnia and newborn Artemia nauplii was higher between 15–22°C than between 22–27°C. Under starvation conditions, the survival time for males was shorter than for females.     

Differences in investment and functioning of cluster roots account for different distributions of Banksia attenuata and B. sessilis,with contrasting life history

Aims

Banksia attenuata is a resprouting species growing in deep sand, while B. sessilis is a fire-killed species occurring in shallow sand over laterite or limestone. We aimed to discover the ecophysiological basis for their different distributions by exploring their investment in deep non-cluster roots and shallow cluster roots, and their cluster-root functioning.

Methods

Deep-pot (1 m), shallow-pot (400 mm), hydroponic experiments and phosphorus (P)-extraction experiment were carried out. Biomass allocation, cluster-root exudation, plant P and leaf manganese (Mn) concentrations were measured.

Results

Banksia attenuata allocated more biomass to deep roots and less biomass to cluster roots than B. sessilis did in deep pots. The two Banksias released similar carboxylates in all experiments, with similar carboxylate-exudation rates in hydroponics. The carboxylate amount per unit cluster root of B. sessilis grown in shallow pots was greater than that of B. attenuata, and B, sessilis acquired more P than B. attenuata did in limestone substrate.

Conclusions

Greater investment in deep roots for water uptake accounts for the presence of B. attenuata in deep sand, and vice versa for the absence of B. sessilis. A larger investment in cluster roots, which released greater amounts of carboxylates, likely accounts for B. sessilis occurring over limestone. Trade-offs in investment and cluster-root functioning support the species’ distribution patterns and life histories. Leaf Mn concentration was a good proxy for the plant capacity to acquire P.

     

The Halomonhystera disjuncta population is homogeneous across the Håkon Mosby mud volcano (Barents Sea) but is genetically differentiated from its shallow‐water relatives

The deep sea has a high biodiversity and a characteristic bathyal fauna. Earlier evidence suggested that at least some shallow‐water species invaded the ecosystem followed by radiation leading to endemic deep‐sea lineages with a genetic and/or morphological similarity to their shallow‐water counterparts. The nematode Halomonhystera disjuncta has been reported from shallow‐water habitats and the deep sea [Håkon Mosby mud volcano (HMMV)], but the morphological features and the phylogenetic relationships between deep‐sea and shallow‐water representatives remain largely unknown. Furthermore, nothing is known about the genetic structure of the H. disjuncta population within the HMMV. This study is the first integrative approach in which the morphological and phylogenetic relationships between a deep‐sea and shallow‐water free‐living nematode species are investigated. To elucidate the phylogenetic relationships, we analysed the mitochondrial gene Cytochrome oxidase c subunit I (COI) and three nuclear ribosomal genes (Internal Transcribed Spacer region, 18S and the D2D3 region of 28S). Our results show that deep‐sea nematodes comprise an endemic lineage compared to the shallow‐water representatives with different morphometric features. COI genetic divergence between the deep‐sea and shallow‐water specimens ranges between 19.1% and 25.2%. Taking these findings into account, we conclude that the deep‐sea form is a new species. amova revealed no genetic structure across the HMMV, suggesting that nematodes are able to disperse efficiently in the mud volcano.     

Lepadiform and scalpelliform barnacles from the Oligocene and Miocene of the Paratethys sea

Abstract: A review on the Oligocene and Miocene stalked barnacles of the Paratethys Sea is presented. The fauna comprises two lepadiform and eight scalpelliform species. Only two species are known from Oligocene deposits, four are documented from Lower Miocene formations, and another four species occur in the Middle Miocene. Only one Oligocene and one Miocene species occur in two different Paratethyan basins in roughly coeval environments, and only a single Middle Miocene species is also known from the adjacent Mediterranean Sea. This low degree of biogeographical similarity is probably a result from the still low number of publications dealing with this group. Stalked barnacles are often indicating bathyal or at least deep sublittoral environments. Especially, the abundance of the benthic deep‐water lepadiform Poecilasma in evaporitic deposits of the Middle Miocene Badenian Salinity Crisis may serve as new evidence for a deeper marine depositional environment. Scalpellum paratethyianum sp. nov. and Lepas sattmanni sp. nov. are described as new species; Arcoscalpellum renevieri (Mayer and Gümbel in Gümbel, 1861) is introduced as new combination.     

The distribution of Oligochaeta on an exposed rocky shore in southeast Ireland

The distribution of oligochaetes was studied on a wave-exposed, granite shore at Carnsore Point, County Wexford. Habitats sampled were crevices and shallow surface cracks in rock, Lichina pygmaea turf, a Mytilus edulis bed, barnacles, Laurencia pennatifida turf, Corallina officinalis turf and pools. Lichina, mussels, barnacles greater than 8 mm in height, Laurencia and Corallina were sampled quantitatively.Three species of Tubificidae and nine species of Enchytraeidae were recorded including two new species described from this locality and five which are undescribed. Oligochaetes were present in all the habitats sampled but were rare in pools and numbers were low on barnacle-covered rock except where barnacles were more than 8 mm in height. The number of species increased with decreasing tide level and was highest in lower shore crevices. Highest densities were recorded from Corallina turf and in barnacles > 8 mm. Lumbricillus semifuscus was the most widespread species, occurring in crevices and mats at all tide levels; other species had more restricted distributions. Grania species were confined to Corallina turf. Only three species of oligochaete were recorded from cracks where they were almost the only fauna present. Species diversity and density were influenced by physical structure of the habitat, particularly the amount of retained sediment.The oligochaetes are members of a rich cryptofauna in habitats which provide them with organic matter and moisture and protect them from environmental extremes and wave damage and from predators during immersion. Reasons for the scarcity of oligochaete records from exposed rocky shores and the high proportion of new species in this study are discussed.     

Intraspecific variability in the life histories of endemic coral-reef fishes between photic and mesophotic depths across the Central Pacific Ocean

Mesophotic coral ecosystems (MCEs) represent the lowest depth distribution inhabited by many coral reef-associated organisms. Research on fishes associated with MCEs is sparse, leading to a critical lack of knowledge of how reef fish found at mesophotic depths may vary from their shallow reef conspecifics. We investigated intraspecific variability in body condition and growth of three Hawaiian endemics collected from shallow, photic reefs (5–33 m deep) and MCEs (40–75 m) throughout the Hawaiian Archipelago and Johnston Atoll: the detritivorous goldring surgeonfish, Ctenochaetus strigosus, and the planktivorous threespot chromis, Chromis verater, and Hawaiian dascyllus, Dascyllus albisella. Estimates of body condition and size-at-age varied between shallow and mesophotic depths; however, these demographic differences were outweighed by the magnitude of variability found across the latitudinal gradient of locations sampled within the Central Pacific. Body condition and maximum body size were lowest in samples collected from shallow and mesophotic Johnston Atoll sites, with no difference occurring between depths. Samples from the Northwestern Hawaiian Islands tended to have the highest body condition and reached the largest body sizes, with differences between shallow and mesophotic sites highly variable among species. The findings of this study support newly emerging research demonstrating intraspecific variability in the life history of coral-reef fish species whose distributions span shallow and mesophotic reefs. This suggests not only that the conservation and fisheries management should take into consideration differences in the life histories of reef-fish populations across spatial scales, but also that information derived from studies of shallow fishes be applied with caution to conspecific populations in mesophotic coral environments.

     

The effect of temperature on phototaxis and geotaxis by larvae of the crab Rhithropanopeus harrisi (Gould)

Investigations of the effect of sudden temperature change on the phototaxis of Stage I and IV zoeae upon stimulation from horizontal and vertical directions with 500-nm light indicate a temperature-induced geotactic response in larvae of the crab Rhithropanopeus harrisi (Gould). For the horizontal tests both zoea stages were reared at 20 °C. Stage I showed positive phototaxis at temperatures between 15 ° and 35 °C, while Stage IV responded over the range of 10–30 °C. For the vertical tests, larvae, reared at 25 °C, were stimulated with overhead lights. Stage I zoeae ascended at 15 °, 20 ° and 25 °C and descended at 5 °, 10 °, 30 ° and 35 °C. Stage IV zoeae ascended at 20 ° and 25 °C and descended at 5 °, 10 °, 15 °, 30 ° and 35 °C. Although the descent at high temperatures could result from a negative phototaxis, a reversal in phototactic sign at high temperatures was not found in the horizontal experiments and the same vertical movement pattern is observed in total darkness. Upon exposure to high temperatures near the water surface, larvae would descend by means of a positive geotaxis rather than a negative phototaxis. This response involves active swimming by Stage IV larvae and passive sinking by Stage I.     

Reproductive strategy of two deep-sea scalpellid barnacles (Crustacea: Cirripedia: Thoracica) associated with decapods and pycnogonids and the first description of a penis in scalpellid dwarf males

We investigated the sexual system in two pedunculate barnacles of the family Scalpellidae. Both inhabit deep water and are attached to mobile arthropod hosts. Verum brachiumcancri was attached to the majid crab Rochinia hertwigi, and Weltnerium nymphocola to the pycnogonidan sea spider Boreonymphon rubrum. Both barnacles have separate sexes and females almost always carry two dwarf males that are almost fully embedded in a pair of symmetrically situated receptacles inside the rim of the mantle cavity. The dwarf males of V. brachiumcancri have a complex penile structure extending into the female mantle cavity. This is the first time a copulatory structure has been described in detail for a dwarf male of a scalpellid barnacle. Both species lack free nauplii and their larvae are released as cyprids; the brood size is small. This is probably an adaptation for settling close to the parent population. We compare reproductive strategies among scalpellids and suggest that the present males are highly specialized and that the females are allocating resources to few offspring.     

Habitat Characteristics of Eurytemora lacustris (Poppe, 1887) (Copepoda,Calanoida): The Role of Lake Depth,Temperature,Oxygen Concentration and Light Intensity

Field observations, laboratory experiments and a literature survey were conducted to evaluate the habitat characteristics of Eurytemora lacustris (Poppe 1887), a freshwater calanoid copepod species. Combined effects of temperature and oxygen concentration in the deep water of thermally stratifying lakes seem to be the ultimate factors governing the occurrence of the species throughout its home‐territory. E. lacustris is largely restricted to relatively deep lakes (>30 m) providing a hypolimnetic refuge characterised by low temperatures (<∼10 °C) and oxygenated water during summer. Therefore, although the species is spread over much of Europe it was only found in a small number of lakes. Long‐term records in different lakes revealed E. lacustris to be perennial with relatively high biomasses occurring from May to September. During thermal stratification on average 87% of the nauplii and 72% of the copepodite biomass was found in hypolimnetic waters colder than 10 °C. Diurnal vertical migration was observed for the copepodid stages, but the migration amplitude clearly decreased from May to September. The migration amplitude was significantly related to light intensity. According to its special habitat requirements, E. lacustris might be considered a glacial relict sensitive to temperature increase and oxygen depletion. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Trace fossils from arenig flysch sediments of eire and their bearing on the early colonisation of the deep seas

A sequence of Lower Ordovician (Arenig) turbidites in Co. Wexford, Eire, has yielded one of the earliest diverse ichnofaunas yet recorded from deep water sediments comprising: Chondrites, Glockerichnus, Gordia, Helminthopsis, Lorenzinia, Neonereites, Palaeophycus, Paleodictyon, Planolites, Sublorenzinia, Taenidium, Taphrhelminthopsis, Teichichnus and Tomaculum. This ichnofauna is critical in any analysis of the colonisation of the deep seas by trace fossil‐producing animals.

A world‐wide review shows that the earliest trace fossils are mainly from Late Precambrian shelf sea environments, but many more evolved during very rapid diversification in the pre‐trilobite Lower Cambrian.

There was little increase in diversity in shallow water after the Lower Cambrian but a progressive colonisation of the deep ocean took place and this accelerated during the Ordovician, when the main lineages of deep sea trace fossils were established there. Rosetted, patterned, meandering and simple spiral forms evolved in shallow water in the Upper Precambrian and pre‐trilobite Lower Cambrian and only later migrated into the deep sea, whereas complex, closely programmed, spiral traces may have evolved there.     

THE IMPORTANCE OF SHALLOW SEDIMENTS IN THE RECRUITMENT OF ANABAENA AND APHANIZOMENON (CYANOPHYCEAE)1

Recruitment of Anabaena and Aphanizomenon from the sediments to the water column was investigated in shallow (1–2 m) and deep (6–7 m) areas of Lake Limmaren, central Sweden. Recruitment traps attached to the bottom were sampled weekly throughout the summer season (June through September). A comparison between the two sites shows that the largest part of the recruited cells originated from the shallow site, although recruitment occurred at all depths in the lake. There were also differences between the species, regarding the site as well as the timing of the recruitment. The contribution of the inoculum to the pelagic population was calculated to vary between 0.003% and 0.05% for the different species. From these results we conclude that shallow sediments are more important than deep ones for the recruitment and that the inoculum in Lake Limmaren is small but may still be an important factor in the population dynamics.     

In situ ATR–FTIR characterization of primary cement interfaces of the barnacle Balanus amphitrite

A method is presented for characterizing primary cement interfaces of barnacles using in situ attenuated total reflection–Fourier transform infrared spectroscopy. Primary cement of the barnacle, Balanus amphitrite (Amphibalanus amphitrite), was characterized without any disruption to the original cement interface, after settling and growing barnacles directly on double sided polished germanium wafers. High-quality IR spectra were acquired of live barnacle cement interfaces, providing a spectroscopic fingerprint of cured primary cement in vivo with the barnacle adhered to the substratum. Additional spectra were also acquired of intact cement interfaces for which the upper portion of the barnacle had been removed leaving only the base plate and cement layer attached to the substratum. This allowed further characterization of primary cement interfaces that were dried or placed in D₂O. The resulting spectra were consistent with the cement being proteinaceous, and allowed analysis of the protein secondary structure and water content in the cement layer. The estimated secondary structure composition was primarily β-sheet, with additional α-helix, turn and unordered components. The cement of live barnacles, freshly removed from seawater, was estimated to have a water content of 20–50% by weight. These results provide new insights into the chemical properties of the undisturbed barnacle adhesive interface.