Comparison of herbivory in the closely-related marine fish genera Girella and Kyphosus

  Specimens of the nominally herbivorous, closely-related, fish genera Girella and Kyphosus were collected from Australian waters in 1994 and 1995. The diet of three Girella species (G. cyanea, G. elevata, and G. tricuspidata) consisted mainly of chlorophytes and rhodophytes, with an animal component of␣15.9 ± 4.2% in G. tricuspidata. The diet of four species of Kyphosus (K. bigibbus, K. cinerascens, K. sydneyanus, and K. vaigiensis) included phaeophytes, chlorophytes and rhodophytes, and almost no animal material. Concentration of total short-chain fatty acids in the posterior intestine was <11.4 mM in the Girella spp. and >39.2 mM in the Kyphosus spp. These results suggest that microbial fermentation plays a role in algal digestion in Kyphosus spp., but not in Girella spp. Girellids and kyphosids appear to function quite differently as herbivores. Girellids should be considered as omnivores that complement readily-available energy from algae with protein from invertebrates. Kyphosids appear to be strict herbivores that can derive adequate nutrition from algae poor in easily assimilable energy, through microbial fermentation in the hindgut. Received: 8 July 1996 / Accepted: 2 August 1996     

Population genetic structure in brooding sea anemones (Epiactis spp.) with contrasting reproductive modes

Effects of dispersal and mating systems on the genetic structure of populations were evaluated by comparing five sea anemones: four Epiactis species that brood their offspring to the juvenile stage and one Anthopleura species that broadcasts gametes and has pelagic, planktotrophic larvae. The anemones were sampled at sites ranging from British Columbia to southern California between 1988 and 1992 and were analyzed by enzyme electrophoresis and by multilocus DNA-fingerprinting. Results were only partially consistent with expectations. While all four brooding species had lower observed heterozygosities than the broadcasting species, not all brooding species had greater population subdivision than the broadcasting species. The self-fertile E. prolifera had the expected evidence of intense local inbreeding ( f = 0.955); unexpectedly, the cross-fertile E. lisbethae and E. ritteri also had similar departures from random mating ( f = 0.957 and 0.831, respectively) probably due to biparental inbreeding among near neighbors in small, highly subdivided populations. Received: 24 May 1996 / Accepted: 12 July 1996     

Grazing of phytoplankton by copepods in eastern Antarctic coastal waters

Chlorophyll a, primary productivity and grazing by copepods on phytoplankton were measured in the upper water column during the summer of 1994/1995 at a coastal site near Davis Station, East Antarctica. Chlorophyll a was at a maximum in mid-December, then dropped markedly as the coastal fast ice melted and broke‐out. Phytoplankton biomass increased again from mid‐ to late‐February. Copepods accounted for at least 65% of zooplankton biomass in the water column before sea ice break‐out, whereas larval polychaetes and ctenophores dominated after ice break‐out. Oncaeacurvata was the numerically dominant species throughout the study. The highest grazing rate (8.7 mg C␣m⁻³␣d⁻¹) was recorded on 21 December when O.␣curvata accounted for 64% of the total. Grazing had decreased markedly by 28 December (0.9 mg C m⁻³ d⁻¹); again O. curvata accounted for over 50% of the total ingested. Copepod grazing increased after ice break-out until the last experiment on 20 February (⋍5 mg C␣m⁻³␣d⁻¹). The main species responsible for grazing during this period were O. curvata, Oithonasimilis, Calanoidesacutus and unidentified copepod nauplii. It was estimated that copepods removed between 1 and 5% of primary productivity. Received: 11 October 1996 / Accepted: 22 October 1996     

Tolerance to low oxygen and sulfide in Amphiura filiformis and Ophiura albida (Echinodermata: Ophiuroidea)

The brittle stars Amphiura filiformis (Müller) and Ophiura albida (Forbes) were exposed to different oxygen saturations (100, 10, 5, 3, and <1% oxygen saturation) and to physiological anoxia (<1% oxygen saturation) at different total sulfide concentrations (0, 2, 20, 200 μM). The mortality was followed during experiments and the median survival time (LT₅₀) was determined. The infaunal A. filiformis had a significantly higher tolerance to both hypoxia and sulfide than did the epibenthic O. albida. After exposure to 10% oxygen saturation for a month, only 2.0% A. filiformis and 0% O. albida were dead. In oxygen saturations <1% A. filiformis and O. albida had a LT₅₀ of 7.5 and 2.5 d, respectively. The presence of even very small concentrations of sulfide decreased the survival significantly. Sulfide is shown to be the key factor for the survival of the two species. Received: 11 October 1996 / Accepted: 12 November 1996     

Population dynamics and production of the planktonic copepods in a eutrophic inlet of the Inland Sea of Japan. IV. Pseudodiaptomus marinus, the egg-carrying calanoid

Population dynamics and production of the egg-carrying calanoid copepod Pseudodiaptomus marinus were studied for a year in Fukuyama Harbor, a eutrophic inlet of the Inland Sea of Japan. This species was perennial, with a large numerical peak in June and small peaks in September/October and November/December. During the study period, at least 11 generations could be detected. For each generation, the stage-specific survival from egg to Copepodite Stage (C) V was determined; it was very high during early life stages (egg to NIII), and gradually decreased beyond. On average, 94% of eggs recruited into NIII, which is strongly contrasted with very high (>ca. 90%) mortality during the corresponding stages for free-spawning copepods, i.e. Acartia omorii, Centropages abdominalis and Paracalans sp. This demonstrates that the egg-carrying strategy has a great advantage to reduce mortality in egg stage. The biomass of this species showed marked seasonal variations largely in parallel with numerical abundance. The instantaneous somatic growth rate increased linearly with temperature. The population production rate was estimated as the sum of somatic growth of larval stages and egg production of adult females; the annual integration was 51.0 mg C m⁻³ yr⁻¹ or 0.38 g C m⁻² yr⁻¹. Received: 11 November 1996 / Accepted: 7 December 1996     

Seasonal reproductive biology of the egg-carrying calanoid copepod Pseudodiaptomus marinus in a eutrophic inlet of the Inland Sea of Japan

In situ egg production of the egg-carrying calanoid copepod Pseudodiaptomus marinus was investigated in Fukuyama Harbor, a eutrophic inlet of the Inland Sea of Japan, at 3- to 5-d intervals for a year. This species reproduced throughout the year, and the adults showed a large abundance peak in June/July and a small peak in September/October. Females usually outnumbered males, comprising 61.4% of the annual mean. The composition of ovigerous females varied from 7.9 to 100%, with an annual mean of 55.7%. Adult prosome length was consistently large throughout winter and spring, and decreased with increasing temperature in summer and fall. Egg diameter varied from 98 to 121 μm, and was negatively correlated to temperature. The seasonal variation in clutch size (range: 15.1 to 38.2 eggs) was bicyclical, with peaks in May and December. The egg production rate of breeding females was low in January to March (mean: 2.3 eggs female⁻¹ d⁻¹), while it was constantly high from mid-May to early October (mean: 12.1 eggs female⁻¹ d⁻¹). The specific egg production rate for the breeding females was highly correlated to temperature; it increased linearly from 0.03 d⁻¹ at 9 °C to 0.27 d⁻¹ at 26 °C. Compared to other co-occurring copepods, the reproductive rate of P. marinus was lowest, which is one of the reasons why this species never dominates in this inlet. Received: 11 November 1996 / Accepted: 7 December 1996     

Population structure, growth and recruitment of the euryalinid brittle-star Astrobrachion constrictum (Echinodermata: Ophiuroidea) in Doubtful Sound, Fiordland, New Zealand

The euryalinid brittle-star (snake star) Astrobrachion constrictum (Farquhar) lives coiled around the branches of black coral (Antipathes fiordensis) colonies. Twenty-two vertical transects, 10 m wide by 30 m deep, were swum in Doubtful Sound over a 2.5 yr period from 1993 to 1995. Numbers, disc diameters and colour morphotypes of brittle-stars inhabiting coral colonies were recorded. 36.3% of the coral colonies >200 mm tall (n = 292) hosted ≥1 Astrobrachion constrictum (range 0 to 12). Overall, the population was patchily distributed on the available coral habitat. The dark red colour morphotype of A. constrictum was most common (87%, n = 279) followed by the yellow, striped, and then spotted varieties. The population was comprised mainly of large (≥10 mm disc diam) individuals, and juveniles were rarely encountered, indicating low rates of recruitment or a high mortality of recruits. Disc-diameter data gathered from this and previous studies indicated that growth in A. constrictum is initially rapid, with individuals reaching a disc diameter of 15 mm in ≃2.5 yr; growth decreases with age, as in other deep-sea ophiuroids. Growth rate within years, however, was not constant, with faster growth in the spring/summer. Maximum size for A. constrictum is reached in ≃8 yr at ˜23 mm disc diam. Anecdotal evidence indicates that A. constrictum may not be confined solely to black coral colonies. Received: 25 September 1996 / Accepted: 16 October 1996     

A possible hybrid zone in the Mytilus edulis complex in Japan revealed by PCR markers

The adhesive protein allele of mussels collected at 13 points in Japan from Hokkaido to Kyushu was analyzed by the polymerase chain reaction using a set of primers which amplifies a part of the nonrepetitive region of the adhesive protein gene. While most mussels exhibited a 126 bp fragment, characteristic of the pure Mytilus galloprovincialis, 55 of 64 mussels sampled at Hiura and 1 of 14 mussels at Hakodate Port exhibited 168 and 126 bp fragments. Sequence analysis of the two fragments indicated that the 168 and 126 bp fragments are almost identical to previously reported sequences in M. trossulus and M. galloprovincialis, respectively. Since the frequency of heterozygous individuals in Hiura is very high, it is unlikely that they are simple hybrids. However, it is evident that mixing of genes occurred between the two species off Hokkaido. Received: 6 September 1996 / Accepted: 9 October 1996     

Characterization of barnacle (Balanus eburneus and B. cenatus ) adhesive proteins

Cements from two species of barnacles, Balanuseburneus Gould and Balanus crenatus Bruguiére, were analyzed to identify the number and nature of proteins present. B. crenatus cement was composed mainly of a small peptide cross-linked into aggregates ranging in size from ˜ 3 kD to 40–50 kD. These aggregates could be reduced with 2-mercaptoethanol (2-ME) in the presence of sodium dodecyl sulfate (SDS) but only after incubation at 40 °C for 12 to 24 h and only when the cement was recently formed. Reductive alkylation of cysteine residues with 4-vinylpyridine produced a water-soluble peptide of less than 5 kD. By comparison, the cement of B. eburneus could be dissolved only partially in SDS and 2-ME when heated at 100 °C for 10 min. Five major proteins were identified by SDS-PAGE: 7, 22, 36 and 58 kD bands for which N-terminal sequence and amino acid compositions are presented; and a 52 kD band for which sequence data are given. A minor protein band of ˜ 80 kD has the same N-terminus as the 36 kD band. CNBr digests of individual proteins produced peptides for which sequence and composition data are also presented. The study was conducted during 1993 to 1995. In general, the proteins identified from B. crenatus cement are similar to those characterized from B. eburneus, and they are different in composition and sequence than those previously reported from Mytilus edulis. Received: 7 August 1996 / Accepted: 8 October 1996     

Resting spore formation of the marine planktonic diatom Chaetoceros anastomosans induced by high salinity and nitrogen depletion

The marine planktonic diatom Chaetoceros anastomosans, which was isolated from Sagami Bay, was used for a study of resting spore formation mechanisms in batch culture experiments. Vegetative cells could grow at salinities ranging from 20.7 to 45.5‰, and resting spore formation was enhanced significantly in nitrate-depleted, high salinity media (40.0 to 45.5‰). The rate of resting spore formation (1.9 d⁻¹) was comparable to the specific growth rate (1.8 d⁻¹) of vegetative cells in the exponential growth phase in normal salinity medium. The size of resting spores formed under high salinity conditions was smaller than that of spores formed in normal salinity media. Unlike vegetative cells, resting spores seemed to possess some mechanisms to survive over a wider range of salinities by resisting bacterial attacks on their cell walls. Received: 4 August 1996 / Accepted: 27 August 1996     

Haemolymph constituent levels and ammonia efflux rates of Nephrops norvegicus during emersion

Nephropsnorvegicus (L.) were subjected to 8 h of emersion, either between layers of seawater-soaked hessian with periodical (20 min) flushes of seawater (high humidity, HH) or to unprotected emersion (low humidity, LH). Blood ammonia levels rose during emersion in both groups but reached higher levels under LH conditions. Ammonia efflux rates after re-immersion were higher than those of control prawns, and amounts of ammonia excreted at such times were considerably higher than those calculated to have accumulated in the blood during emersion. Possible explanations for such differences are discussed. C _aO2 and C _vO2 decreased rapidly to ca. 10% normoxia values within 2 h of HH and LH emersion and remained low throughout the remaining emersion time. Emersion-induced tissue hypoxia increased blood concentrations of glucose and lactate. Lactate accumulation was higher during LH emersion, compared with HH emersion. Blood pH dropped ca. 0.40 units but increased again after 2 h of re-immersion. Acidosis was probably related more to respiratory difficulties (CO₂ accumulation) than to lactate accumulation, as blood lactate values remained high after 2 h of re-immersion. The ability of N. norvegicus to cope with emersion appears to be little influenced by high humidity conditions. Received: 26 June 1996 / Accepted: 5 August 1996     

Interception and dispersal of artificial food falls by scavenging fishes in the abyssal Northeast Atlantic: early-season observations prior to annual deposition of phytodetritus

The hypothesis that the behaviour of deep-sea scavenging fishes is influenced by seasonal input of organic matter from the ocean surface was investigated by observing responses to baits placed on the sea floor at 4800 m depth in the NE Atlantic (48°50′N; 16°30′W) during spring (April 1994). Data from the present study are compared with those from previous studies of the same location made in summer 1989. The first fishes to arrive at baits were the grenadier Coryphaenoides (Nematonurus) armatus and the eel Histiobranchus bathybius, after delays of 28 and 29 min, respectively; these results are not significantly different from those of summer 1989. Similarly, other indices of activity (staying time and swimming speed) showed no evidence of differences between years/seasons. However, the rate of radial dispersal of bait (0.009 m s⁻¹) by C. (N.) armatus was much slower than in all previous studies. A change in the size distribution of C. (N.) armatus to smaller individuals in spring 1994 was also evident. It is suggested that the fish on the abyssal plain may not comprise a steady-state population and that major episodic or seasonal migrations may occur. Received: 18 October 1996 / Accepted: 20 December 1996     

Ant gardens: interspecific recognition in parabiotic ant species

 In French Guiana, parabiotic societies (natural mixed colonies) are frequently found in ant gardens. Crematogaster limata parabiotica (Myrmicinae), often associated with Camponotus femoratus (Formicinae), was found for the first time in parabiosis with ponerine ants: Pachycondyla goeldii and Odontomachus mayi. A detailed study of the relationships between Cr. l. parabiotica and O. mayi showed that each species is aggressive towards allospecific or conspecific individuals belonging to another colony, but tolerates allospecific individuals from the multi-species society. Studies of cuticular substances of the four ant species were made using gas chromatography. The results showed that each species, living alone or in parabiosis, possesses a specific chemical profile. Thus, the ants are able to recognise nestmate and non-nestmate individuals of the associated species, even though their cuticular profiles are different. The hypothesis that the nestmate allospecific profile is learned is suggested to explain this pattern of recognition. Received: 5 June 1996 / Accepted after revision: 17 October 1996     

Polyandry in the genus Apis, particularly Apis andreniformis

Using four polymorphic microsatellite loci, we found that four Apis andreniformis queens collected in Thailand each mated at least 10–20 times, producing an average relatedness, g _ww, of workers of 0.30 ± 0.007, and an average effective number of matings of 9.1 ± 2.2. The degrees of polyandry and intra-colonial genetic relatedness in A. andreniformis are similar to those in A. mellifera, slightly more than in A. florea, and up to 6 times less than in A. dorsata. We argue that while presently favoured hypotheses for the evolution of polyandry in monogynous social insects may adequately explain the evolution of up to five or six matings, they are inadequate to explain the extreme polyandry (10–60 matings) observed in Apis. One alternative possibility is that colony fitness is a non-additive function of the fitness of individual subfamilies. Such behavioral over-dominance may mean that queen fitness is increased by high levels of polyandry, which increase the probability of desirable combinations of worker genotypes occurring in one colony. The special attributes of honey bees which may lead to behavioral over-dominance include colony aggregation (which may increase the incidence of disease), and frequent long-distance migration. Received: 8 May 1996/Accepted after revision: 9 August 1996     

Feeding association of the copepod Rhincalanus gigas with the tunicate salp Salpa thompsoni in the southern ocean

During a repeat grid survey and drogue study carried out in the Lazarev Sea in the austral summer of 1994 to 1995, a sudden collapse of a rich population of the tunicate Salpa thompsoni was observed at the onset of a phytoplankton bloom. This may have been related to the inability of salps to regulate their filtration rate and avoid clogging of their filtering apparatus at particle concentrations ≥1 mg (chlorophyll a) m⁻³. It was at this stage that large numbers of salp individuals had their branchial cavities invaded by the copepod Rhincalanus gigas. Incubations, to compare the feeding rates of R.␣gigas in the presence and absence of salps, showed that copepods are able to utilize the high concentrations of microplankton accumulated in the food strand of the salp, thus enhancing their grazing efficiency. This is likely to represent a typical form of opportunistic parasitism. However, the timing of the invasion, and the observation that most salps could survive prolonged exposure to R. gigas invasion, suggest that the association may also constitute a novel type of symbiosis. S.␣thompsoni could potentially benefit from R. gigas cleaning its filtering apparatus when clogging due to high particle concentrations occurs. Received: 15 July 1996 / Accepted: 20 July 1996     

Genetic structure of populations of two species of Chthamalus (Crustacea: Cirripedia) in the north-east Atlantic and Mediterranean

Protein electrophoresis on starch gels was used to investigate population genetic structure of the barnacles Chthamalus montagui Southward and C. stellatus (Poli) over their north-east Atlantic and Mediterranean ranges. In each species, a single locus exhibited marked differentiation of allele frequencies between Atlantic and Mediterranean localities; in C. stellatus, genetic differentiation between the two basins had not previously been noted. In both species, mean heterozygosity per locus appeared higher in the Mediterranean samples than in the Atlantic, and Mediterranean populations had more alleles at the loci studied. Possible explanations for the differentiation between the Atlantic and the Mediterranean populations are discussed. Received: 30 May 1996 / Accepted: 17 September 1996     

Molecular phylogeny of vestimentiferans collected around Japan, revealed by the nucleotide sequences of mitochondrial DNA

The phylogenetic relationships among local populations of undescribed vestimentiferan species that belong to the genera Lamellibrachia and Escarpia and had been collected at six sites around Japan were analyzed on the basis of the partial (1023 bp) nucleotide sequences of the mitochondrial gene for cytochrome oxidase I (COI), using a pogonophoran and a polychaete as outgroups. The identical amino acid sequence was deduced from the nucleotide sequence obtained from each of the vestimentiferans analyzed. The strong similarity among deduced amino acid sequences of COI suggested a close relationship between vestimentiferans and pogonophorans. On the basis of the phylogenetic relationships, the analyzed vestimentiferan populations were classified tentatively as five species. The genetic differentiation of vestimentiferans was suggested to occur bathymetrically as well as being a consequence of horizontal segregation. Two of these tentatively identified species inhabit both a hydrothermal area and a cold seep area, as is the case for some species of bivalves that belong to the genera Bathymodiolus and Calyptogena. Received: 28 August 1996 / Accepted: 2 October 1996     

Genetic structure and allozyme variation of sea bass (Dicentrarchus labrax and D. punctatus) in the Mediterranean Sea

This paper reports data on 28 allozyme loci in wild and artificially reared sea bass (Dicentrarchus labrax) samples, originating from either coastal lagoon or marine sites in the Mediterranean Sea. F _ST analysis (θ estimator) indicated strong genetic structuring among populations; around 34% of the overall genetic variation is due to interpopulation variation. Pairwise θ estimates showed that, on average, the degree of genetic structuring was much higher between marine populations than between samples from lagoons. Six polymorphic loci showed differences in allele frequencies between marine and lagoon samples. Multivariate analyses of individual allozymic profiles and of allele frequencies suggested that different arrays of genotypes prevail in lagoons compared to marine samples, particularly at those loci that, on the basis of previous acclimation experiments, had been implicated in adaptation to freshwater. On the other hand, variation at “neutral” allozyme loci reflects to a greater extent the geographic location of populations. Allozyme differentiation was also studied in a D. labrax population from the Portuguese coast. Average genetic distance between this population and the Mediterranean populations was quite high (Nei's D = 0.236) and calls into question the taxonomic status of the Portuguese population. Finally, genetic relationships between D. labrax and D. punctatus were evaluated. Average Nei's D was 0.648, revealing high genetic differentiation between the two species, even for two sympatric populations of these species in Egypt; thus gene flow was not indicated between species. Received: 24 October 1996 / Accepted: 27 November 1996     

Attachment of mature oysters (Saccostrea cucullata ) to natural substrata

It has been suggested that mature oysters attach to their natural substrata by means of a combination of a modification of the prismatic outer-shell layer formed within the periostracum and a “pressing” action of the mantle (Yamaguchi 1994). However, marine surfaces are seldom smooth enough to allow adhesion without the addition of a fluid adhesive to allow electromagnetic interactions to hold the two bodies together. An electron microscope study of the attachment of the oyster Saccostrea cucullata to its natural substrata has confirmed the presence of a crystalline calcareous cement. The cement shows a range of spherulitic and irregular blocky textures that are reminiscent of diagenetic cement fabrics. Their form suggests that the cement crystallises from a calcium-carbonate-saturated liquor trapped between the underside of the shell and the substratum, with crystallites nucleating on all bounding surfaces of the void. Received: 30 May 1996 / Accepted: 9 August 1996     

“Seed bank” of coastal planktonic diatoms in bottom sediments of Hiroshima Bay, Seto Inland Sea, Japan

Abundance and temporal distribution of viable (able to germinate) resting stage cells of planktonic diatoms in bottom sediments have been investigated almost monthly during 1989 to 1992 in Hiroshima Bay, western part of Seto Inland Sea, Japan. The abundance of viable resting stages in bottom sediments was enumerated with the extinction dilution method (most probable number method, MPN). In bottom sediments of Hiroshima Bay, dominantly distributed species and/ or genera of the diatom resting stages were Skeletonema costatum, Chaetoceros spp. and Thalassiosira spp. Viable resting stages of these diatoms were densely distributed on the orders of 10³ to 10⁶ (MPN g⁻¹ wet sediments), and persisted in bottom sediments throughout the investigation period. Conversely, vegetative cells of these diatoms fluctuated remarkably in the water column and disappeared sporadically. Survival of the resting stages in a collected sediment sample was also determined with the MPN method, at different storage temperatures (5, 10, 15, 20, 25 °C). The survival test demonstrated that the diatom resting stages could survive in the dark for several months or years in sediments. Resting stages survived longer at the lower storage temperature, and the order of longevity was consistent within three diatoms (Chaetoceros spp. > Thalassiosira spp. > S. costatum) at each storage temperature. The present study suggests that these diatom resting stages in the coastal bottom sediments could serve as a “seed bank”, analogous to those of terrestrial plants. The seed bank would ensure the survival of diatoms within highly fluctuating coastal environments, while it would also be the source of sporadic and autochthonous diatom blooms in coastal waters. Received: 29 November 1996 / Accepted: 16 December 1996