13C/12C ratios and the trophic importance of algae in Florida Syringodium filiforme seagrass meadows

Over 380 stable carbon isotope (¹³C) analyses made during 1981–82 showed that Syringodium filiforme Kutz seagrass meadows in the Indian River lagoon of eastern Florida have food webs based on algal rather than seagrass carbon. Seagrasses averaging approximately-8 were isotopically distinct from algae epiphytic on seagrass blades (X=-19.3) and particulate organic matter in the water column X=-21.6. ¹³C values of most fauna ranged between-16 and-22, as would be expected if food web carbon were derived solely from algal sources. These results counter the idea that seagrass detritus is the dominant carbon source in seagrass ecosystems. Two factors that may contribute to the low apparent importance of seagrass in the study area are high algal productivities that equal or exceed S. filiforme productivity and the high rates of seagrass leaf export from meadows.     

Temporal patterns of shell-gape in Mytilus edulis

Hitherto published evidence of the presence or absence of endogenous activity rhythms in bivalve molluscs is equivocal. Mytilus edulis L. were collected from a North Wales (UK) estuary in 1985, and shell-gaping was investigated in individual mussels under constant conditions in the laboratory. Results suggest that there is no endogenous circatidal rhythm of shell-gaping in this species, This is consistent with the view that, unlike mobile species, sessile intertidal species are much more likely to exhibit exogenous rather than endogenous responses to tidal fluctuations. There is some evidence of weak circadian rhythmicity of shell-gaping in M. edulis, with greater duration of shell-closure during hours of expected daylight. Such behaviour could represent an adaptational defence against visually-feeding predators.     

Temporal variation and distribution of trace metals in freshwater and fish from Calabar River, S.E. Nigeria

An investigation on the abundance and distribution of trace metals (Fe, Cu, Zn, Mn, Cr, Cd and Pb) in water, and nine species of fish samples from Calabar river was carried out in 1992. The concentrations of iron (6000–7240gl^–1), zinc (4910–7230gl^–1), and cadmium (3–7gl^–1) showed moderate pollution while those of copper (420–630gl^–1), manganese (23–48gl^–1), chromium (<10–20gl^–1) and lead (<1–10gl^–1) in water were well below WHO permissible levels. Significant seasonal changes (0.001p0.25) were obtained for iron, copper, zinc, manganese and cadmium in water. Furthermore, iron, zinc and cadmium showed statistically significant spatial changes (0.005p0.10). Of the nine fish species studied, no statistically significant relationship between body weight and the concentrations of the metals was observed. The concentrations of the metals per mean total body weight apparently decreases in the order Fe>Zn>Cu>Mn>Pb>Cd=Cr and were within the limits that were safe for consumption.     

Chitinolytic enzymes in the integument and midgut-gland of the shrimpPalaemon serratus during the moulting cycle

Chitinase andN-acetyl--D-glucosaminidase activity were quantified inPalaemon serratus (Pennant) integument and midgut gland during the moulting cycle. Studies were performed on specimens collected near Concarneau, France, in July 1989. The changes in specific activity are different in the two organs: in the midgut gland enzymatic activity is high throughout the whole moulting cycle with a weak peak at the early premoult Stage D1, whereas in the integument the activity of both enzymes is very low throughout post- and intermoult stages and rises only after premoult Stage D1. The highest specific activity is reached in D1 for chitinase and somewhat earlier (D1) forN-acetyl--D-glucosaminidase. The increase in specific chitinolytic activity coincides with an increase in ecdysteroids.     

Salinity tolerance of benthic estuarine diatoms as tested with a rapid polarographic measurement of photosynthesis

Measurements of net photosynthesis of benthic estuarine diatoms were made by polarographic registration of oxygen saturation. A measuring cell was constructed in which media with salinities of 2.0 to 100.7 were pumped over the algae between measurements. Diatoms from unialgal cultures and mixed populations from intertidal flats appeared to be highly tolerant of extreme salinities. During short-term exposures (20 min) the net photosynthesis of the algae did not drop below 70% of the initial values, within the salinity range 4.0 to 60.0. Prolonged exposure (up to 6 h) gave essentially the same results. Populations of benthic diatoms, sampled from field stations with mean salinities of about 30, 12, and below 5, showed only gradual differences in their tolerance of salinities between 2.0 and 33.7. Two species, Navicula arenaria and Nitzschia sigma, were cultured in media ranging in salinity from 8.0 to 45.0 and from 2.0 to 45, respectively. The tolerance to changing salinity was only slightly affected by the salinity of the medium in the preculture. The role of salinity in the production and distribution of intertidal diatoms is discussed.     

The enantiomeric composition of monoterpene hydrocarbons in the defensive secretions ofNasutitermes termites (Isoptera): Inter- and intraspecific variations

Summary Frontal gland secretions of termite soldiers of the speciesNasutitermes costalis, N. ephratae, N. nigriceps, N. rippertii, andN. hubbardii were analyzed. The chiral compositions of the monoterpene hydrocarbons were investigated by means of two-dimensional gas chromatography. Two of them, 3-carene and-pinene were present in the form of (–)-enantiomers of high purity in the majority of the samples. The other monoterpenes,-pinene, camphene, sabinene, limonene, and-phellandrene, exhibited a great variation in the enantiopurity between different species.-Pinene and limonene varied significantly even between different colonies within the species.N. costalis was the only species with an invariable composition of the secretion, independent of the locality or origin.     

Populational distribution I: The digital simulation

This paper presents a method of investigating the distributional pattern of a biological population, using a technique of simulation. The method consists of the comparison of the empirical frequency curve of a population, obtained using the Method of Quadrats, with a simulated one, since the pattern of the simulated curve depends on the simulated distribution. An example is given.     

Space partitioning and interactions in an intertidal sand-burrowing amphipod guild

A nine-year study at a moderately exposed, fine sand intertidal beach at Long Sands, Maine, USA identified marked seasonal changes in the foci of sand-burrowing amphipod activities. These included seasonal population movements, degree of interspecific horizontal overlap, life stage segregation within and between species, and sand depth stratification. Behavioral interactions related to competition for available space are considered important in affecting the distribution and abundance of amphipod species, and community structure. Significant negative correlations were shown between the abundance and upper distributional limits of the smaller, lower shore Acanthohaustorius millsi and the abundance of the larger, higher shore species Haustorius canadensis. Tolerance limits to a variety of prevailing physical factors alone, were not considered a serious obstacle to occupation of higher intertidal level sands by A. millsi. Summer brooding females of both species occupied similar 5 to 10 cm sand depths, but were strongly segregated horizontally. Laboratory coexistence experiments during the reproductive period showed increased mortality of adults and negligible reproductive output of A. millsi when in combination with H. canadensis compared to controls where the former species was alone. A third species, Amphiporeia virginiana, occupied primarily very shallow sand (0 to 2.5 cm), and performed seasonal movements opposite in direction to A. millsi and H. canadensis. The presence, amount, and refinement of biological interactions across the wave exposure gradient requires further study. Until then, we consider as inappropriate the blanket designation of all types of intertidal sand communities as physically controlled.     

Seasonal photosynthetic characteristics of Ascoseira mirabilis (Ascoseirales,Phaeophyceae) from King George Island,Antarctica

Monthly variation in photosynthesis, dark respiration, chlorophyll a content and carbon: nitrogen (C:N) ratios in different lamina sections of adult plants of Ascoseira mirabilis Skottsberg from King George Island, Antarctica, was investigated between September 1993 and February 1994. Light saturated net photosynthesis (P _max) showed maximum values in September (12 to 25 mol O₂ g^-1 fr wt h^-1), and decreased towards the summer to values ranging between 2.0 and 5.0 mol O₂ g^-1. In the distal section, however, a second optimum occurred in December (25 mol O₂ g^-1 fr wt h^-1). Dark respiration rates were also highest in October and November and decreased strongly in December to February (6.0 and 1.0 mol O₂ g^-1 fr wt h^-1, respectively). Gross photosynthesis exhibited high values between September and December. Concomitant with the seasonal decrease of photosynthetic efficiency () from mean values of 1.2 mol O₂ g^-1 fr wt h^-1 (mol photons cm^-2 s^-1)^-1 in September to 0.3 mol O₂ g^-1 fr wt h^-1 (mol photons cm^-2 s^-1)^-1 in January, the initial light saturating point (I _k) gradually increased from 19 to 60 mol photons m^-2 s^-1. Likewise C:N ratios were low in spring (12 to 13) and increased in summer (20). In general, the photosynthetic parameters P _max, gross photosynthesis, and Chl a concentrations were significantly higher in the distal section of the thallus. In contrast, C:N ratios were lower in the distal section of the lamina. The results show that photosynthesis obviously strongly supports growth of the alga in late winter to spring, as it does in some morphologically related brown algae from temperate and polar regions. The question whether growth is additionally powered     

Exudation of biologically-active metabolites in the sponge Aplysina fistularis

Specimens of the demosponge Aplysina fistularis forma fulva (Pallas) from the intertidal zone at La Jolla, California, USA, contain two antimicrobial metabolites, aerothionin (1) and homoaerothionin (2). Both metabolites are exuded into seawater. The rates of exudation into artificial seawater were measured under near in situ conditions (7.7x10^-4 g aerothionin min^-1 g^-1 dry weight of sponge) and in an aquarium (8.9x10^-3 g min^-1 g^-1) for undamaged sponges. Sponges responded to a simulated injury by exuding 10 to 100 times as much of these metabolites. The exudation of aerothionin and homoaerothionin may inhibit surface overgrowth by fouling organisms and tissue damage by mobile animals.Please address requests for reprints to Dr. J. E. Thompson     

Population and species diversity fluctuations in a rocky intertidal community relative to severe aerial exposure and sediment burial

From a series of 10 quarterly assessment between October 1975 and May 1978 (inclusive), fluctuations in abundance were determined for macroinvertebrates and macrophytes of a rocky intertidal community on Santa Cruz Island, California, USA. During afternoon low tides in late fall and winter of the first 2 yr of study, organisms of the upper and middle intertidal zones were subjected to prolonged aerial exposure. Many species there tolerated this exposure, but die-backs occurred for a barnacle (Chthamalus fissus/C. dalli) and several algae (Endocladia muricata, Pelvetia fastigiata f. gracilis, Corallina officinalis var. chilensis, Corallina vancouveriensis, Cylindrocarpus rugosus and Codium fragile). These die-backs were succeeded by blooms of Ulva californica and Porphyra perforata. In the upper and middle intertidal zones, the major cover organisms that could tolerate prolonged aerial exposure were disproportionately prevalent and appeared to be maintained by the periodic repression of species intolerant to such exposure. In February 1978, heavy rainfall caused sediment inundation of the middle and lower intertidal zones. This event was followed by declines in abundance of a barnacle (Tetraclita rubescens) and several algae (Pelvetia fastigiata f. gracilis and corallina spp.). Shannon-Wiener H species diversity fluctuated from a high in October to a low the following May during both 1975–1976 and 1976–1977 in conjunction with the period of increased daytime aerial exposure in late fall and winter. A further decline in diversity following sediment inundation in February 1978 contributed to a long-term trend of declining H species diversity (3.06 in October 1975 to 1.87 in May 1978). We hypothesize that predictable late fall to winter aerial exposure stresses, in combination with a random physical disturbance (sediment burial), exceeded an optimal intermediate level of disturbance predicted for maximal species diversity.     

Effect of daylight variations on the energy budgets of shallow-water corals

Energy budgets were determined for small pieces (nubbins) of the coralsPocillopora damicornis, Montipora verrucosa andPorites lobata living at a water depth of 3 m on the fringing reef of Coconut Island, Kaneohe, Hawaii. The budgets were determined for three different types of day: an ideal day with no cloud and an in situ daily integrated irradiance at 3 m of 14.385 E m^–2 d^–1; a normal day with sporadic cloud cover and daily irradiance of 11.915 E m^–2 d^–1; and an overcast day with daily irradiance of 6.128 E m^–2 d^–1. On the ideal day, the energy fixed in photosynthesis was more than that required for respiration and growth of both zooxanthellae and animal components of the association, and there was a predicted loss of between 19.3 and 32.4% of the energy fixed. On a normal day, the total photosynthetic energy fixation was lower and the excess was between 12.1 and 27.9% of the energy fixed. On the overcast day, however, in bothPocillopora damicornis andPorites lobata energy expenditure exceeded photosynthetic energy fixation and the budget was in deficit. Estimates of rate of mucus secretion on an overcast day were derived and, when incorporated into the energy budget, it was predicted that all three species would have a deficit budget, necessitating the catabolism of lipid reserves. From published values for lipid storage in these species it was calculated that the reserves would last from 28 d inPocillopora damicornis to 114 d inM. verrucosa. A model is suggested in which corals draw upon their extensive lipid stores on days of sub-optimal light, replenishing the reserves again when daily light levels are high, and finally excreting the excess energy fixed, as mucus-lipid when the lipid stores are replete.     

Exosmosis and “free space” in marine benthic algae

In distilled water, marine benthic algae immediately lose ions. This can be demonstrated by means of chloride titration or conductivity measurements. The rapidity and the complete reversibility of this process show that ion movements out of and into the free space are involved. When Laminaria saccharina thalli, exposed to a series of increasing NaCl-concentrations, are subsequently transferred into distilled water, the external concentration increases proportionally to rate of ion loss. Through its free space, the alga establishes an ionic equilibrium with its external medium. If the alga thallus is killed (20 sec boiling in isosmotic sea water), the extent of chloride loss is much higher. Because of thermal destruction of the osmotic space, the chloride can then escape from the entirc thallus. Since sublittoral algae die upon drying, chloride loss from dry thalli is much higher than that from wet thalli: this difference is small in littoral algae, which tolerate short periods of dryness. A close relationship exists between extent of chloride loss and degree of resistance to drying.     

Spermatozoon structure of some North American prosobranchs from the families Lottiidae (Patellogastropoda) and Fissurellidae (Archaeogastropoda)

The spermatozoa of four species of the patellogastropod family Lottiidae (Lottia pelta, L. digitalis, L. strigatella, Tectura scutum) and one species of the archaeogastropod family Fissurellidae (Diodora aspera) were examined in 1990 using transmission electron microscopy. All have primitive or ect-aquasperm, typical of invertebrates using external fertilization. Sperm of the lottiid limpets are characterized by a 5 to 9 m-long head composed of a conical acrosome which constitutes >50% of the head length, and a cylindrical nucleus. The acrosome of all species of lottiids is differentiated internally, and has a posterior invagination 0.9 to 1 m in depth, into which an elongate acrosomal lobe protrudes. Between the posterior acrosomal lobe and the nucleus, the subacrosomal material is aggregated as a fibrous column. The midpiece of the sperm has a ring of 4 to 5 spherical mitochondria of 0.6 m diam, posterior to which is a collar of cytoplasm 1 m long, which sheaths the anterior portion of the axoneme. The size and morphology of the acrosome and large cytoplasmic collar clearly distinguish the spermatozoa of the Lottiidae from other families of Patellogastropoda. The sperm of D. aspera (Fissurellidae) is typical of the family of archaeogastropod; the head has a length to breadth ratio of 4:1, and the cylindrical nucleus is capped by a small acrosome, <25% of the total head length, which is deeply invaginated.     

Dominance of larval forms in euphausiid (Crustacea:Eucarida) ontogenesis

Variability and dominance of Euphausia superba Dana larval forms (Furcilia-I and Furcilia-II stages) in the plankton of the Scotia and Weddell Seas have been investigated. New forms (1, 2, 3 and 14) have been recorded. The dominant forms of Furcilia-I stage are proposed to represent the initial dominants. In accordance with the initial dominance, five types of larval form combinations have been established. During the initial dominance change — from 5 to 2, the larval form number increases. This phenomenon is due to parallel development of euphauiid larvae; it results from a developmental pathway change in the main larval mass. Such deviations are reflected in an initial dominance change. In each pathway, the larvae pass through an unequal number of moults before reaching Form 5 (in accordance with the proposed moult scheme of Furcilia-I stage larvae). In the case of initial dominance of less-developed forms, the presence of different parallel pathways increases. As a result, the total number of larval forms present in the plankton changes, causing increased variability of the total number of larval forms. Each type of larval form combination is the result of summation of all larval forms, which derive from different developmental pathways of the larvae in different localities. The most usual developmental pathway for Euphausia superba is through Form 5, which may, thus, be regarded as the main developmental pathway for this species. This pathway probably corresponds to optimal environment conditions for larval growth and morphogenesis with maximal synchronisation of both processes. Consequently, it may be suggested that changes in developmental pathways of larvae are connected with suboptimal environmental conditions.     

Etude des eaux rouges dues à la prolifération des bactéries photosynthétiques sulfo-oxydantes dans l'étang du Prévost,lagune saumâtre méditerranéenne

Dystrophic crises or malaígues with red water, were observed in summer, in Mediterranean brackish lagoons near Montpellier, France. During July 1976, the photosynthetic sulfide-oxidizing bacteria causing this phenomenon were isolated from the Prévost lagoon. The most important genera isolated from this red water wereChromatium, Thiocystis andThiocapsa (Chromatiaceae): the predominant species wasThiocapsa roseopersicina. Water and sediment samples from the same lagoon were collected during the winter season (October 1976 and January 1977) and were enriched with organic matter. The samples were incubated in aquaria under artificial light (800 to 1000 lux) at room temperature (ca. 22°C). Eight to 10 days later, red water developed which was similar to that observedin situ in summer. These red waters develop under conditions of anaerobiosis and H₂S production. Such conditions are necessary for the growth of Chromatiaceae. Excessive deposists of organic matter in the lagoon water lead to increased oxygen consumption and overproduction of hydrogen sulfide, which can be oxidized by photosynthetic sulfideoxidizing bacteria. This bacteria bloom (causing the red water) removes the hydrogen sulfide, thus re-establishing aerobiotic conditions in the water of the Prévost lagoon.     

“Free space-photosynthesis” in the algae Fucus virsoides and Laminaria saccharina

This paper deals with the role of bicarbonates in the apparent free space (AFS) and their importance for the photosynthetic process. Both the littoral alga Fucus virsoides (Mediterranean Sea) and the sublittoral alga Laminaria saccharina (Baltic Sea) show the same response. Unloading of Clions and subsequent reloading of HCO₃-ions result in a positive photosynthetic rate in distilled water (free of CO₂). Time of exposure of an algal thallus to bicarbonate solutions, as well as the concentration of these solutions, influences AFS-assimilation of the ions.     

Transmission of symbiotic dinoflagellates through the sexual cycle of the host scyphozoan Linuche unguiculata

Intracellular symbiotic dinoflagellates are associated with the tropical scyphozoan Linuche unguiculata (Swartz, 1788) throughout all stages of the host's life cycle. During sexual reproduction, eggs are released in mucus strands that contain symbiotic dinoflagellates. Fertilization and development take place externally in the water column. Epifluorescence and transmission electron microscopy showed that unfertilized eggs did not contain intracellular algae, but that infection of the developing embryo was generally successful by the 128-cell stage (10 h after fertilization at 23° C). However, experiments with artificially provided Cellufluor-labeled algae demonstrated that older embryos and planulae could be infected by algae through at least 24 h post-fertilization, indicating that the L. unguiculata symbiosis represents a semi-closed system. This novel mode of symbiont acquisition results in most sexually-produced offspring becoming infected with maternally-transmitted algae during early development, but allows for acquisition of non-maternally-provided algae later in development. Most of the algal symbionts during the early stages of embryonic and larval development are located within ectodermal cells. This is in contrast to the other life-cycle stages of L. unguiculata (i.e., scyphistoma, medusa, ephyra), where symbionts are found within the gastrodermis of the host.     

Development of the pericalymma larva of Solemya reidi (Bivalvia: Cryptodonta: Solemyidae) as revealed by light and electron microscopy

Solemya reidi Bernard 1980 is a gutless protobranch bivalve known to possess intracellular chemoautotrophic bacterial symbionts in its gill. A light and electron microscope study on the embryology and larval development of S. reidi provides data for the bivalve Subclass Cryptodonta. S. reidi spontaneously spawned large eggs (271 m in diameter), which developed within individual gelatious egg capsules. The first several cleavages were equal and a distinct molluscan cross was formed at the animal pole of the embryo, features previously unreported in bivalve development. Lecithotrophic pericalymma larvae (similar to the larvae of paleotaxodont protobranch bivalves and aplacophoran molluscs) hatched at 18 to 24 h and remained in the water column for a further 5 d at 10°C. At hatching, larvae measured from 360 to 440 m in length and from 225 to 265 m in cross-sectional diameter. Definitive adult structures developed within an epithelial locomotory test entirely covered with compound cilia. The test histolysed at metamorphosis and was ingested throught the mouth into the perivisceral cavity. Length and height of the shell following metamorphosis was 433 m (±42 m, n=16) and 282 m (± 29 m, n=13), respectively. Primary data and data from the literature show that the type of larval development in both paleotaxodont and cryptodont bivalves cannot be reliably estimated from egg or prodissoconch sizes.     

Macrozoobenthic community structure in the Ría de Foz,an intertidal estuary (Galicia,Northwest Spain)

The community structure of the macrobenthic (>1 mm) fauna of an intertidal soft-bottom estuary, the Ría de Foz (Galicia, Northwest Spain) was investigated on 99 occasions during June, September and December 1984 and March 1985. The infaunal data were subjected to classification and ordination techniques. The analyses indicated that sediment characteristics (grain size, percentage silt-clay and organic-matter content) and tidal height are the most important factors governing the distribution and abundance of the intertidal communities. Three faunal assemblages were identified and examined in terms of species dominance, constancy and fidelity. In the clean sands of the outer estuary two main assemblages were distinguished; one, corresponding to the boreal LusitanianTellina community, inhabited the middle and lower tidal levels; the other, typical of a biocoenosis of sands and slightly muddy mediolittoral sands, inhabited the upper tidal level. The third benthic assemblage occupied the muddy sands and mud of the inner estuary and displayed some features in common with theCardium edule-Scrobicularia community described by Thorson.