Differential meiospore size and tolerance of ultraviolet light stress within and among kelp species along a depth gradient

 Kelp are differentially stratified along a gradient of UV exposure (as a function of water depth). The role of ultraviolet light in seaweed zonation has not been fully explored. This study found a significant meiospore size difference within and among the kelp species examined: Pterygophora californica Ruprecht (high to mid-subtidal), Macrocystis integrifolia Bory (high to mid-subtidal), Laminaria groenlandica Rosenvinge (high-subtidal), Alaria marginata Postels and Ruprecht (low-intertidal) and Hedophyllum sessile Setchell (mid-intertidal). This size difference was correlated with the depth distribution of adult plants, with the largest meiospores originating from shallow-dwelling adult kelp exposed to high UV light. Under UV stress in the laboratory, meiospores from adults growing in high-UV environments displayed greater germination and survival rates than the progeny of adult kelp occupying lower-UV environments. This suggested that in Barkley Sound, British Columbia, Canada, differential tolerance to UV (possibly determined by meiospore size) may limit the upper settlement position of kelp species and individuals. Tolerance to UV may be an important determinant of kelp zonation on rocky shores. Received: 16 June 1998 / Accepted: 6 January 2000     

Red algae as hosts for endophytic kelp gametophytes

We observed kelp gametophytes endophytic in the cell walls of 17 species of red algae from the San Juan Islands, Washington, USA. Host algae were collected primarily from three sites dominated by different kelp assemblages, including (1) a subtidal site dominated by Agarum fimbriatum Harvey, (2) a second subtidal site dominated by Nereocystis luetkeana (Mertens) Postels et Ruprecht, and (3) a floating dock on which the dominant kelp species were Alaria marginata Postels et Ruprecht, Laminaria groenlandica Rosenvinge, and Costaria costata (C. Agardh) Saunders. Most hosts were filamentous [e.g. Pleonosporium vancouverianum (J. Agardh) J. Agardh, Callithamnion acutum Kylin], or polysiphonous [e.g. Polysiphonia paniculata Montagne, Pterosiphonia dendroidea (Montagne) Falkenberg]; however, similar endophytes were also observed in membranous or bladed red algae [e.g. Membranoptera platyphylla (Setchell et Gardner) Kylin, Polyneura latissima (Harvey) Kylin]. Dozens to hundreds of separate kelp gametophytes were associated with single host thalli. In many cases, the gametophytes developed conspicuous oogonia raised above the thallus surface on characteristic stalks. Presumed zygotes developed through typical embryonic stages into juvenile sporophytes. We argue that the endophytic habit plays an important role in the biology of kelp gametophytes. Received: 5 May 1998 / Accepted: 6 May 1999     

Calcification in the articulated coralline alga Corallina pilulifera,with special reference to the effect of elevated CO2 concentration

Calcification in Corallina pilulifera Postels et Ruprecht displayed diurnal variations in aerated (350 ppm CO₂) culture media, with faster rates during the light than during the dark period. Addition of CO₂ (air+1250 ppm) inhibited calcification. This was attributable to the decreased pH resulting from CO₂ addition. Both photosynthesis and calcification were enhanced in seawater, with elevated dissolved inorganic carbon concentrations at a constant pH of 8.2.     

Green and blue fluorescing dinoflagellates in Bahamian waters

At three stations in Bahamas waters, in 1989, 15 to 30% of all the dinoflagellates >20µm diameter observed in near-surface waters fluoresced green under blue excitation light, 55 to 66% fluoresced red, and the remainder did not fluoresce at all. The abundance of these green-fluorescing dinoflagellates ranged from ca 5 to 10 cells l^–1 at the study sites. Under UV excitation, however, the dinoflagellates had a blue to blue-green appearance. Almost all the blue-green fluorescing dinoflagellates appeared to be heterotrophic, except for one species,Phalacroma rapa Stein, which also contained red-fluorescing (under blue light) chlorophylla. The emission spectra from all species examined were of three basic types. Type 1 typically had two fluorescence emission peaks (ca 440 and ca 510 nm). Type 2 spectra possessed one sharp peak at 495 nm. Spectra belonging to Type 3 had a broad peak around 470 to 480 nm. The green fluorescence thus is likely caused by different substances in individual species. The attempt to reconstitute observed spectra with nicotinamide adenine dinucleotide (NADH) and riboflavin 5-phosphate (FMN) solutions was unsuccessful.     

DNA synthesis and the cell cycle in the noxious red-tide dinoflagellateGymnodinium nagasakiense

Gymnodinium nagasakiense is a noxious red tide dinoflagellate often associated with damage to fisheries in Japan. DNA synthesis and the cell cycle in this organism were investigated from 1989 to 1990 by determining relative DNA contents of individual cells using an epifluorescence microscopy-based microfluorometry system. The nuclei were stained with the DNA-specific fluorochrome 4-6-diamidino-2-phenylindole (DAPI). Because photosynthetic pigment interferes with the fluorescence from the DAPI-DNA complex, the pigment was eliminated by methanol treatment as a first step in quantitative microfluorometry. Nuclear DNA contents, cell size distribution, cell density, and frequency of paired cells were determined every 2h for 24h using cells grown on a 12h light:dark cycle. DNA synthesis and cell division were tightly phased to a particular period of the light:dark cycle. DNA synthesis (S phase) occurred from 10:00 to 22:00 hrs and was followed by cytokinesis. The presence of such a distinct S phase strongly suggests thatG. nagasakiense has a typical eukaryotic cell cycle. This type of cell cycle makes it possible to estimate speciesspecific in situ growth rate based on the diel pattern of DNA synthesis.     

Variability over space and time in the genetic structure of the winged kelp Alaria marginata

The genetic structure of Alaria marginata Postels & Ruprecht was investigated spatially and seasonally using amplified-fragment length polymorphisms (AFLP). Using one primer, 206 scoreable bands were produced. Individual plants that were separated by as little as a few decimeters to >100 km could be distinguished, and followed an isolation-by-distance model. Genetic similarity (average April data) ranged from 76% for patches (a few decimeters in diameter), to 71% for individual kelp stands (15 m across) and 67% for a group of stands separated by 185 km. Greater genetic similarity of patches occurred at a wave-sheltered site than at a wave-exposed site. The lower wave action may limit meiospore dispersal, resulting in patches of related sporophytes. Genetic similarities between A. marginata stands indicated a pattern of gene flow that is consistent with local currents. In one stand, genetic similarities were markedly different between seasons. This seasonal pattern may be the result of different age groups dominating the sampled stands over time. The genetic structure of A. marginata comprises local scale (patch and within-stand) heterogeneity and larger scale (between-stands) homogeneity. Received: 30 September 1998 / Accepted: 26 October 1999     

Endogenous swimming rhythms in estuarine crab megalopae: implications for flood-tide transport

Up-estuary migration of crab larvae to adult habitats is thought to be accomplished by selective tidal transport in which late-stage larvae enter the water column on flood tides and remain on or near the bottom on ebb tides. This study measured endogenous rhythms in swimming by the last larval stage (megalopa) of blue crabs Callinectes sapidus and fiddler crabs Uca spp. Previous field studies found that megalopae of both species were only abundant in the estuarine water column on nocturnal rising tides. Megalopae were collected from the Newport River Estuary, North Carolina (34°41N; 76°40W) during August–September 1992 and swimming activity was recorded for 4.5 to 7 d under constant conditions with a video system. Rhythms exhibited by both genera in the laboratory were not identical to those recorded in the field. Uca spp. displayed a circatidal rhythm, with maximum swimming occurring near the time of high tide in the field. Rhythm amplitude increased when crushed oyster shells were present, which suggested that megalopae bury or cling to the substrate during quiescent periods. In contrast, C. sapidus had a circadian rhythm in which maximum swimming coincided with the day phase in the field. In most trials, the activity of blue crab megalopae was unrelated to the expected tidal cycle. It was concluded that a tidal rhythm in swimming was the behavioral basis of flood-tide transport for fiddler crab larvae. The endogenous rhythm in blue crabs does not participate in transport, which probably results from behavioral responses to environmental cues associated with flood tide.     

Studies of the pigments in the shrimp Crangon crangon (Crustacea: Malacostraca)

The material examined consisted of adult specimens (male and female) of the shrimp Crangon crangon (L.) collected during the summer of 1967 from the Gdask Bay of the Baltic Sea. Column and thin-layer chromatography was used for the separation of the carotenoids. The ester compounds and protein complexes of carotenoids were hydrolized with 15% KOH in methanol at room temperature in a nitrogen atmosphere for 48 h. The absorption maxima of the various fractions and spots were determined on the spectrophotometer Specol after eluation. The identification of the carotenoids was based mainly on the absorption maxima in appropriate organic solvents and on the R_t values. The acetone extract from the Crangon crangon specimens gave a light blue fluorescence and absorption maxima at wavelengths of 447, 463, 595 to 596 and 667 m. The following carotenoids were found to be present in the adult specimens of Crangon crangon: -carotene, cantaxanthin, astaxanthin, free and esterified lutein, zeaxanthin, and a form of xanthophyll which was not precisely identified. In addition to the above, biliary dyes were also found, probably of the mesobiliviolin and mesobilirhodin type.     

Background levels of soil beryllium in several countries

Beryllium and aluminium contents in uncontaminated soils from six countries are reported. The means and ranges of beryllium in the surface soils were as follows: 1.43(0.20–5.50)g g^–1 in Thailand (n=28), 0.7 (0.31–1.03) g g^–1 in Indonesia (n=12), 0.99(0.82–1.32) g g^–1 in New Zealand (n=3), 0.58(0.08-1.68)g g^–1 in Brazil (n=16), 3.52(2.49–4.97)g g^–1 in the former Yugoslavia (n=10), and 1.56(1.01–2.73) g g^–1 in the former USSR (n=8). The mean and range of beryllium contents of the surface soils in Japan (1.17(0.27–1.95)g g^–1 n=27) are situated within the values of the soils from these countries except for the Yugoslav soils derived from limestones. The mean of the mean beryllium contents of the surface soils in all these countries is 1.42 g g^–1 which will be used as a tentative average content of beryllium in uncontaminated surface soils, except for the soils derived from parent materials high in beryllium content. The beryllium contents of the subsoils were higher than those of the surface soils in New Zealand and Yugoslavia as is the case with Japan. The correlation coefficient between the contents of beryllium and aluminium in all the soil samples (n=113) including surface soils and subsoils was 0.505 (p < 0.001).     

Characteristic features of body composition and metabolism in some interzonal copepods

Protein, lipid, phosphorus, and organic carbon contents, as well as electron transport system (ETS) activity, lactatedehydrogenase activity, and gut evacuation rate, were measured in four interzonal species of Pacific copepods:Calanus australis, C. pacificus, Eucalanus inermis, andE. elongatus f.hyalinus, collected at the upwelling areas off Peru (8°S) and California (27°N), and in the middle of the North Pacific (30°N), from February to April 1987. The two Eucalanidae species —E. inermis andE. elongatus — have distinctive biochemical and elemental body composition and rates of main physiological processes. Relative protein, lipid, phosphorus, and organic carbon contents (µg mg^–1 wet weight) in these species were, respectively, ca. 1/7 to 1/10, 1/5 to 1/20, 1/5 to 1/10, and 1/5 those inCalanus spp. Likewise, oxygen uptake rate per unit of wet weight (based on ETS activity) inE. inermis andE. elongatus was 5 to 10% of that in calanids; a similar difference was found in phosphorus excretion rate. In addition, gut evacuation rates inE. inermis andE. elongatus were ca. one-fifth of those inCalanus spp. Based on these data, we considered the eucalanids as belonging to a distinctive physiological group, figuratively named jelly-body copepods. In contrast with calanids, active lactatedehydrogenase has been found in the bodies ofE. inermis andE. elongatus, apparently allowing them to survive for a long time in layers of extremely low oxygen content (<0.2 ml l^–1). The adaptive value of physiological features in these eucalanids and typical calanids is compared.     

Inorganic nitrogen metabolism inUlva rigida illuminated with blue light

Inorganic nitrogen metabolism in blue light was studied for the green algaUlva rigida C. Agardh collected in the south of Spain (Punta Carnero, Algeciras) in the winter of 1987. NH₄ ⁺ has been reported to inhibit NO₃ ^- uptake; however,U. rigida showed a net NO₃ ^- uptake even when the NH₄ ⁺ concentration of the external medium was three or four times greater than the concentration of NO₃ ^-. NO₃ ^- uptake rates were similar in both darkness and in blue light of various photon fluence rates (PFR) ranging from 17 to 160 mol m^-2 s^-1. Since NO₃ ^- uptake is an active mechanism involving the consumption of ATP, respiratory metabolism can provide enough ATP to maintain the energetic requirement of NO₃ ^- transport even in darkness. In contrast, NO₃ ^- reduction inU. rigida was highly dependent on the net photosynthetic rate. After 7 h in blue light, intracellular NO₃ ^- concentrations ([NO₃ ^-] _i ) were higher in specimens exposed to intensities below the light compensation point (LCP) than in those incubated at a PFR above the LCP. When PFR is below the light compensation point, NO₃ ^- reduction is low, probably because all the NADH produced by the cells is oxidized in the respiratory chain in order to produce ATP to maintain a steady NO₃ ^- transport rate. The total nitrogen (TN) and carbon (TC) contents decreased from darkness to 33 mol m^-2 s^-1 in blue light. In this range, catabolic processes prevailed over anabolic ones. In contrast, increases in TN and TC contents were observed above the light compensation point. The C : N ratio increased with light intensity, reaching a stable value of 17 at 78 mol m^-2 s^-1 in blue light. Intracellular NO₃ ^- concentration and NO₃ ^- reduction appear to be directly controlled by light intensity. This external control of [NO₃ ^-]_i and the small capacity ofU. rigida to retain incorporated NO₃ ^-, NO₂ ^- and NH₄ ⁺ ions may explain its nitrophilic character.     

Photosynthetic characteristics of phycoerythrin-containing marine Synechococcus spp.

Marine Synechococcus spp. are sufficiently abundant to make a significant contribution to primary productivity in the ocean. They are characterized by containing high cellular levels of phycoerythrin which is highly fluorescent in vivo. We sought (Jan.–Apr., 1984) to determine the adaptive photosynthetic features of two clonal types of Synechococcus spp., and to provide a reliable physiological basis for interpreting remote sensing data in terms of the biomass and productivity of this group in natural assemblages. It was found that the two major clonal types optimize growth and photosynthesis at low photon flux densities by increasing the numbers of photosynthetic units per cell and by decreasing photosynthetic unit size. The cells of clone WH 7803 exhibited dramatic photoinhibition of photosynthesis and reduction in growth rate at high photon flux densities, accompanied by a large and significant increase in phycoerythrin fluorescence. Maximal photosynthesis of cells grown under 10–50 E m^-2 s^-1 was reduced by 20 to 30% when the cells were exposed to photon flux densities greater than 150 E m^-2 s^-1. However, steady-state levels of photosynthesis maintained for brief periods under these conditions were higher than those of cells grown continuously at high photon flux densities. No photoinhibition occurred in clone WH 8018 and rates of photosynthesis were greater than in WH 7803. Yields of in-vivo phycoerythrin fluorescence under all growth photon flux densities were lower in clone WH 8018 compared to clone WH 7803. Since significant inverse correlations were obtained between phycoerythrin fluorescence and P_max and for both clones grown in laboratory culture, it may be possible to provide a reliable means of assessing the physiological state, photosynthetic capacity and growth rate of Synechococcus spp. in natural assemblages by remote sensing of phycoerythrin fluorescence. Poor correlations between phycoerythrin fluorescene and pigment content indicate that phycoerythrin fluorescence may not accurately estimate Synechococcus spp. biomass based on pigment content alone.     

Genetic parentage in the indigo bunting: a study using DNA fingerprinting

Summary Parentage of nestlings in a North Carolina population of indigo buntings (Passerina cyanea) was analyzed using DNA fingerprinting. Three minisatellite DNA probes (wild type M13, Jeffreys' 33.15 and 33.6) were used to analyze nuclear DNA isolated from muscle biopsies of 63 nestlings, their parents, and other local adults. Each probe detected approximately 15 scorable fragments per individual, with 18%–39% overlap between probes. The proportion of bands shared (using all fragments over all three probes) between presumably unrelated adults averaged 0.23. Of the 63 offspring analyzed, 35 had at least one fragment not present in either putative parent. The distribution of offspring with novel fragments was distinctly bimodal. The lower mode (offspring with 0, 1, or 2 novel fragments, N=41) fit a Poisson distribution, a pattern expected if mutation (estimated rate per fragment= 0.01) were the source of the novel fragments. The remaining 22 offspring had more novel fragments than could be explained by mutation alone (minimum of four independent fragments across all three probes, =8.2). A low band-sharing proportion with the resident male ( =0.24) and high band-sharing with the resident female ( =0.60) implicated extra-pair fertilizations as the source of all 22. Thus in this sample, 35% of all nestlings came from extra-pair fertilizations and none from intra-specific brood parasitism. Of 25 broods sampled, 12 (48%) had at least one excluded offspring. In 3 broods all of the offspring excluded the resident male. Band-sharing proportions between excluded nestlings within a brood could not distinguish between single and multiple extra-pair paternity. Although young males tended to be excluded less often than older males, wing length and weight were not associated with the frequency of exclusion. Weight and wing length of females also were not associated with involvement in EPCs. Six of the 22 excluded offspring (in 3 broods) shared a large proportion of bands and had fewer than four novel fragments when compared to the fingerprints of a neighboring territorial male, implicating those males as actual fathers. The parentage of the remaining 16 offspring (in 9 broods) could not be clearly assigned because (1) one or more neighbors were not sampled or (2) difficulties in scoring across gels prevented confident alignment of fingerprint bands, and insufficient DNA was obtained from muscle samples to allow reanalysis of potential actual fathers on the same gel as excluded nestlings.     

Copulation behavior and paternity in the chaffinch

Summary We investigated two aspects of sperm competition in a wild population of chaffinches Fringilla coelebs: copulation behavior and genetic parentage determined by DNA fingerprinting. Pairs copulated at a high rate before laying, peaking at 4.4 copulation attempts per hour on day –3 relative to laying, with an average of 207 copulation attempts (83 behaviorally successful) per clutch. Extra-pair copulation attempts (n = 20) made up 7.8% of all copulation attempts that females were involved in. The rate at which pairs copulated was lower during egg-laying, but there was no evidence that this was due to the male of the pair timing copulations to coincide with an insemination window; it was more likely due to the fact that females solicited copulations at a lower rate. Both sexes solicited copulations but males solicited mainly extra-pair copulations. DNA fingerprinting showed that 17.0% of chicks (n = 47) in 23% of broods (n = 13) were fathered by a male other than the one paired to their mother. There was no evidence of intraspecific brood parasitism. In three cases where we were able to identify the father of extra-pair offspring it proved to be a neighboring male.Correspondence to: B.C. Sheldon     

Alkaline phosphatase activity in marine macrophytes: histochemical localization in some widespread species in southern Spain

Alkaline phosphatase activity (APA) was determined in 44 species of marine macrophytes collected throughout 1991 and 1992 along the southern coast of Spain. Activity varied between 0.83 mol paranitrophenol (pNP) released g^-1 dry wt h^-1 in Ulva rigida var. gigantea and 238.8 mol pNP g^-1 dry wt h^-1 in Bangia fuscopurpurea. Using a histochemical method, APA sites were located in five of these species: Corallina elongata Ellis et Soland, Gelidium latifolium (Grev.) Thur. et Born., G. sesquipedale (Clem.) Born. et Thur., Porphyra umbilicalis (L.) Kützing and Zostera noltii Hornem. Enzymatic activity was found in the outer part of the thallus, either on the cell wall or in the cortical cells. In the marine phanerogam Z. noltii activity was also located in the vascular bundle. The results suggest that APA is present in many, if not all, marine macrophytes from southern Spain, and plays a relevant role in the utilization of dissolved organic phosphorus compounds.     

Grazing rates of the copepods Calanus glacialis and C. finmarchicus in arctic waters of the Barents Sea

Natural feeding rates of Copepodite Stages IV and V, and adult female Calanus glacialis (Jaschnov) and Copepodite Stage V and adult female C. finmarchicus (Gunnerus) were estimated using fluorescence analysis of gut contents. Measurements were made on copepods sampled from arctic waters east of Svalbard (Barents Sea) during the spring phytoplankton increase, in the period from 27 May to 13 June, 1983. Observations on Copepodite Stages IV and V and adult female C. glacialis suggest that the gastric evacuation rate is independent of developmental stage, whereas C. finmarchicus Copepodite Stage V showed a lower gastric evacuation rate than adult females. Gut fullness displayed a low correlation with the ambient chlorophyll concentrations. Ingestion rates calculated for C. glacialis were 0.3, 2.3, and 11.0 g C h^-1 for Copepodite Stages IV and V and adult females, respectively. Copepodite Stage V and adult female C. finmarchicus ingested 0.9 and 1.1 g C h^-1 at a temperature of ca.-1.0°C. The maximum ingestion rate in terms of percent body carbon d^-1 was higher for adult female C. glacialis and C. finmarchicus than for the respective Copepodite Stage V's. The results are discussed both in relation to the physiological state of the species and to the environmental conditions.     

Particulate DNA in subtropical oceanic and estuarine planktonic environments

Particulate DNA was measured in estuarine, coastal, and oligotrophic oceanic environments near the southwest coast of Florida and in the Gulf of Mexico. Particulate organic carbon and nitrogen (POC and PON), chlorophyll a, bacterial direct counts, DNA, and bacterial activity as determined by thymidine incorporation all showed a high degree of intercorrelation. Normalization of the data for offshore/onshore similarities by dividing by POC yielded significant correlations only for DNA, direct counts, and bacterial activity. Most (70–99%) of the particulate DNA in offshore samples was in the 0.2- to 1-m fraction, while DNA in nearshore and estuarine samples was associated with larger particles. Cellular DNA contents obtained by dividing DNA by direct counts in the 0.2- to 1-m fraction were in the range of reported bacterial genome weights. However, DNA nitrogen comprised a greater proportion of the PON than reported for microorganisms in culture. Collectively, these results suggest that (1) most of the particulate DNA in oceanic environments is contained in bacterioplankton; (2) DNA is a significant proportion of the cell biomass, possibly due to growth under nutrientlimiting conditions.     

Ultrastructure of tetrasporogenesis in the red alga Osmundea spectabilis var. spectabilis (Rhodomelaceae: Ceramiales: Rhodophyta)

Tetrasporogenesis in Osmundea spectabilis (Postels and Ruprecht) K.W. Nam var. spectabilis proceeds through three developmental stages. A uninucleate tetraspore mother cell with synaptonemal complexes depicted during early prophase of meiosis I comprises the youngest stage. Subsequently, the nuclear envelope obtains a highly irregular profile and is surrounded by perinuclear endoplasmic reticulum (ER) and numerous mitochondria. Proplastids with peripheral thylakoid and numerous straight-profiled dictyosomes are present. Dictyosome vesicles discharge their contents, initiating tetraspore wall formation. A four-nucleate tetraspore mother cell is formed prior to tetrahedral cleavage. During the second stage of tetraspore formation the nuclei are very irregular in outline and move toward the central region where they fuse. The formation of fibrous vacuoles originates from the fibrous vacuole associated organelles (FVAOs). Thylakoid formation from concentric lamellar bodies (CLBs) seems to occur in plastids. Extremely hypertrophied dictyosomes with two tightly compressed and densely laminated mid-regions produce vesicles which contribute to enlargement of the fibrous vacuoles. During the second stage of tetraspore development striated vesicles are formed and starch granule formation increases. Mature tetraspores are characterized by numerous cored vesicles and abundant starch granules. Plastids have a fully developed system of internal thylakoids, and cleavage is usually complete at this stage. Mature tetraspores are surrounded by a bi-layered wall and the tetrasporangial wall. Unbranched, tubular structures connecting the plasmalemma with the peripheral sheets of ER are possibly involved in wall deformation. A distinct blebbing nuclear envelope appears to sequester vesicles into the cytoplasm.     

Sorted samples and quantitative counts in appendicularian catches

Sorting centers are important for processing material collected during extensive oceanic expeditions. Based on information obtained from samples of appendicularians, this paper demonstrates that usual procedures adopted in sorting centers produce samples which contain only a fraction of the organisms present in the original catch (or subsample). In addition, the proportion of individuals sorted varies considerably. In four Indian Ocean Standard Net catches collected in the Arabian Sea, subsamples (called sorted samples in this paper) are compared with careful microscopical counts (quantitative counts) performed by the author. The numbers of appendicularians found in quantitative counts were 2.4 to 19.2 times higher than those in the sorted samples. Sorting efficiency varies in different forms of appendicularians; it is particularly low in Fritillaria sp. Bad preservation and small body size further reduce the portion sorted out. Under certain conditions (e.g. net clogging), numerous small appendicularians are retained which normally would pass easily through the meshes of the plankton net.