Characterization of disjunct populations of Zostera marina (eelgrass) from California: genetic differences resolved by restriction-fragment length polymorphisms

Comparative restriction-fragment analysis was used to analyze the nuclear ribosomal DNA, and alcohol dehydrogenase-1 loci of Zostera marina L., for variation within and among populations. Eelgrass is a perennial marine flowering plant that is widespread and ecologically significant throughout the temperate northern hemisphere. A chemical method was developed to obtain restriction-quality DNA without CsCl fractionation from experimentally relevant quantities of seagrass tissues (0.5 to 1.0 g). The yield was 25 g g^-1 fresh weight. The three morphologically distinct forms of Z. marina from disjunct populations examined in this study were found to be genetically distinct; morphologically similar populations were indistinguishable genetically. Genetic distinction also correlated with habitat depth, as subtidal and intertidal populations were clearly divergent. Homologous probes for the 17S and 28S ribosomal DNA genes were used to map 24 restriction sites on the rDNA repeat of Z. marina, which was determined to be about 14 kb in length. At least 1 length mutation and 5 restriction-site changes were identified that distinguished Z. marina populations from San Diego and Monterey Bay (Del Monte Beach) from Z. marina populations from Elkhorn Slough and Tomales Bay. Estimated sequence variation (100×p) between eelgrass populations ranged from 0.00 to 0.69. Individual plants were observed to contain as many as four different rDNA-repeat length variants. The mean number of rDNA-repeat length variants per individual in Z. marina was about two. Intrapopulation variation in rDNA-repeat type was observed in only one individual from the Tomales Bay population.     

Feeding rates and diel vertical migration of copepods near South Georgia: comparison of shelf and oceanic sites

Seventeen Longhurst Hardy Plankton Recorder profiles were taken over a diel cycle in January 1990 to study the feeding of four major copepods over the South Georgia shelf. Ontogenetic changes in vertical migration were followed and feeding cycles determined by gut fluorometry for Calanoides acutus Stage CV, Calanus sinillimus CV and CVI, C. propinquus CV and Rhincalanus gigas CV and CVI. In common with a neighbouring oceanic site visited two weeks later and reported elsewhere, all four species had a diel cycle of feeding and migration. The vertical distributions of C. simillimus (all stages), R. gigas (nauplii) and Euphausia frigida (postlarvae) were similar at both sites, the night being spent within the chlorophyll maximum at 15 to 30 m. However, the biomass dominants, C. acutus and R. gigas, dwelt below the chlorophyll maximum, about 30 m deeper than their oceanic counterparts. Unlike the oceanic site, feeding at the shelf site was not restricted to darkness, but increased 6 to 10 h before nightfall and finished at dawn; the intervening period coincided with sinking and digestion. Daylight feeding may have been induced by the shorter night, lower light levels or greater food requirements at the shelf site, despite planktonic predators being over three times more abundant. Daily ration estimates for R. gigas at both sites were only 2% body carbon per day. These low values contrast with its smaller competirors, whose rations were in the range 5.6 to 27%.     

The surface attachment structure: a unique type of integumental formation in neustonic copepods

A unique type of integumental formation is described for several members of the copepod family Pontellidae. This surface attachment structure (SAS) consists of a mass of fine setules arranged in two semicircles on a flattened area of the anterodorsal surface of the cephalosome. Using transmission electron microscopy, the SAS was shown to be continous with the cuticle and not linked to chemo- or mechanosensory cells; its function is purely mechanical. This structure is probably an energy-saving means for these large and heavy neustonts to stay attached to the surface film. The SAS is species-specific and may thus be of potential importance to the systematics and phylogeny of the Pontellidae, in the same manner as integumental pores and sensilla, which form patterns characteristic of several copepod families and genera.     

Comparative feeding preference of Strongylocentrotus droebachiensis (Echinoidea) for the invasive seaweed Codium fragile ssp. tomentosoides (Chlorophyceae) and four other seaweeds

Laboratory experiments conducted during 1987 on Appledore Island, Maine, USA, tested whether feeding preference or the absence of an attractant was the cause for the occurrence of beds of Codium fragile ssp. tomentosoides (herein referred to as Codium fragile) within rocky barrens grazed clear of kelp by the sea urchin Strongylocentrotus droebachiensis. Consumption of C. fragile in single-diet experiments (1 seaweed/sea urchin) was highly variable and was not significantly different from that for several other seaweeds (Agarum cribrosum, Ascophyllum nodosum, Chondrus crispus, and Laminana saccharina) important in the field diet of the green sea urchin. In multiple-diet experiments (5 seaweeds/sea urchin) significantly less Codium fragile was eaten than Chondrus crispus, but significantly more Codium fragile was eaten than A. cribrosum. Chemosensory experiments suggest that C. fragile does not attract the sea urchin. Sea urchins are unable to detect C. fragile but will eat it when they come in contact with it.     

Ultrastructure of sperm and spermathecae in Micromaldane spp. (Polychaeta: Capitellida: Maldanidae)

Assessing the possibility that external fertilization has re-evolved requires the study of monophyletic groups that exhibit various reproductive methods. Maldanid polychaetes show a range of reproductive mechanisms, though previous studies of reproduction have hitherto been restricted to larger species with external fertilization. Micromaldane pamelae Rouse and M. nutricula Rouse are small, gonochoristic maldanids that brood directly developing larvae. Both species have sperm with elongate nuclei and an acrosome extending down each side of the anterior end of the nucleus. A true midpiece is absent; two mitochondria extend along the posterior region of the nucleus. Spermatids develop synchronously in large clusters connected by a cytophore. In M. pamelae sperm are released into the water as spermatozeugmata. These are comprised of clusters of sperm with their tails oriented to the centre and the sperm heads facing outwards. Females of M. pamelae and M. nutricula bear pairs of spermathecae ventrally (M. pamelae three pairs, between setigers 10 and 11, 11 and 12 and 12 and 13 and M. nutricula two pairs, between setigers 10 and 11 and setigers 11 and 12). The blind sacs are epidermal invaginations bound closely together. The entrance to each spermatheca may only be 1 to 2 m across with each spermatheca holding several hundred sperm. This represents the first detailed study of spermathecae in the Capitellida. The occurrence and structure of spermathecae and spermatozeugmata in other groups are discussed and compared with Micromaldane spp. Comparisons are made with non-polychaetes with the purpose of discussing functional aspects of reproductive mechanisms in marine metazoans in general. Elongate sperm nuclei are associated with sperm storage and/or large egg size. The lack of an elongate sperm midpiece may be an indicator of having to swim in water but does not contraindicate sperm storage. Spermatozeugmata may serve as an indication of sperm storage and brooding of larvae. Speculations on the phylogenetic significance of these reproductive features are limited by the fact that supposedly modified (i.e., derived) states may reflect functional/structura, constraints of small body size.     

Loch fleet: liming to restore a brown trout fishery

This project has been successful in meeting its objectives in terms of demonstrating that catchment liming techniques can restore acidified waters to conditions suitable for fish populations for relatively long periods. This improvement in conditions has extended to the inlet stream, which provides vital fish spawning and nursery areas, which are difficult to treat effectively be other means in remote locations. The project has also provided an assessment of the effectiveness of differing rates and modes of lime application, which suggest that only quite restricted parts of a catchment require treatment. This not only maximizes the cost-effectiveness of the treatments, but also helps to minimize any side-effects on, for example, moorland vegetation. The biological monitoring programme at Loch Fleet has also provided an assessment of the overall ecological consequences of adding limestone to naturally acidic and calcium-deficient ecosystems.     

Stabilimenta characteristics of the spider Argiope argentata on small islands: support of the predator-defense hypothesis

Summary A variety of orb-weaving spider species construct stabilimenta, patterned areas of dense silk, typically near the hub of the orb. The adaptive significance of this construction, along with associated behaviors such as shuttling and vibrating, is much debated. Arigiope argentata on small islands of the Bahamas frequently possess stabilimenta; we studied 397 individuals of this species to investigate possible functions of their stabilimenta, paying particular attention to predator-defense hypotheses. Cruciform stabilimenta were commoner in all size classes of spiders than discoid stabilimenta or no stabilimentum at all; discoid stabilimenta occurred mostly among intermediate size classes. Within the cruciform type, two-segmented stabilimenta were especially common among the very smallest spiders. Size of cruciform stabilimenta showed a curvilinear relation to spider body length; the fitted curve for total segment length had a maximum at an intermediate spider length. We argue that this relationship (among other phenomena) supports an apparently-larger-size hypothesis, whereby intermediate-sized spiders in particular appear much larger than they actually are. This could discourage predators, including those that are gape-limited such as lizards. We argue that stabilimenta in the smallest spiders, in which typically two segments are opposed, so that they more or less line up, serve as camouflage. When disturbed experimentally, spiders with discoid stabilimenta shuttle to the opposite side of the centrally located stabilimentum. This seems an obvious defensive behavior and occurs less frequently among spiders with cruciform stabilimenta. Large spiders vibrate more frequently than small ones, but no relation exists between vibration frequency and stabilimentum type. We argue (see also Tolbert 1975) that vibrating behavior, in which the spider can become a blur, renders its location more difficult to discern and the spider more difficult to grasp, rather than increasing apparent size. Correspondence to: T.W. Schoener     

Ozone in the urban southeastern United States

Ozone measurements (daily maximum values) from the Aerometric Information Retrieval System database are analyzed for selected sites, during 1980 to 1988, in southeastern USA. Frequency distributions, for most sites during most years, show a typical bell-shaped curve with the higher frequency around the yearly daily maximum ozone mean of about 100 to about 110 microg m(-3) (50-55 ppbv). Abnormal years in ozone concentration may skew the distribution as the mean shifts. A correlation of daily maximum ozone concentrations above 140 microg m(-3) (70 ppbv) between sites shows a division between the sites in the northern protion of the region and those in the southern portion of the region. Variations in ozone levels are well correlated over distances of several hundred kilometers, suggesting that high values are associated with synoptic scale episodes. An ozone exposure analysis also shows higher ozone exposures (250-300 ppm days) in the northerly sites as compared to the southerly sites (150-170 ppm days).     

Contribution of canopy leaching to sulphate deposition in a Scots pine forest

Radioactive sulphate (35SO4) was applied to the soil below a Scots pine forest on 23 June 1989, and its movement into the canopy and into throughfall and stemflow was measured over 4 months. The specific activity, Bq (mg S)(-1), of the canopy increased monotonically; uptake by current-year (1989) expanding needles was initially twice as fast as by older needles or live twigs. By 10 October the canopy average specific activity was 62 Bq (mg S)(-1). The specific activity of net throughfall (throughfall + stemflow - rain), deduced from measurements from six throughfall collectors, six stemflow collectors and two rain collectors, fell rapidly from 12.6 Bq (mg S)(-1) in late July to <1 Bq (mg S)(-1) in mid-August. The results suggest (assuming rapid equilibration of 35S with sulphate in soil) that root-derived sulphate contributed c. 3% of sulphate in net throughfall and that dry deposition of SO2 and sulphate particles contributed c. 97% of the 0.56 g S m(-2) measured in net throughfall over the period. Simultaneous measurements of SO2 at canopy height and of NH3 above and within the canopy gave mean concentrations of 5.9 and 0.86 microg m(-3), respectively, sufficient to account for the sulphate measured in net throughfall only if codeposition of NH3 and SO2 occurred to canopy surfaces. The large values of specific activity observed in July, however, indicate that throughfall composition may be closely related to recent soil input of sulphate, and that equilibrium cannot be safely assumed. The possibility of a significant contribution of soil-derived sulphate to sulphate deposition in net throughfall cannot be ruled out on the basis of this experiment.     

Impact of atrazine-bearing agricultural tile drainage discharge on planktonic drift of a natural stream

Preliminary results are reported from a co-operative study between Agriculture Canada and Environment Canada on environmental impacts of atrazine measured in a field stream receiving agricultural drainage. Systematically, tile drained plots of known crop rotation, area, flow and pesticides use were used in the study. A maximum tile drainage concentration of 13.9 microg liter(-1) atrazine was measured while the maximum measured stream concentration was 1.89 microg liter(-1). Phytoplankton and zooplankton samples were collected on a bi-monthly basis during the growing season. The study indicated possible negative impacts of low concentrations of atrazine on planktonic drift populations, when natural stream flow was reduced, resulting in a lower dilution capacity. A 20 m section of the stream was affected by the tile drainage waters as measured by the resident biological community. Both atrazine and ambient environmental conditions were felt to be contributing to the measured results. No negative impacts on planktonic drift populations were evident beyond 50 m downstream of the tile drainage and stream confluence.