Subsurface chlorophyll maxima and vertical distribution of zooplankton in the Gulf of Maine

The vertical disthbution of chlorophyll, zooplankton and physicalstructure were measured using a pumping system and CTD on twocruises in the Gulf of Maine during June and September 1982.The vertical distribution of chlorophyll was closely relatedto the density structure of the water column. In waters witha pronounced pycnocline subsurface chiorphyll maxima (SCM) werelocated at or just above the pycnocline. Chlorophyll concentrationswere maximal in the surface waters at those stations sampledin June where the pycnocline was not well defined. The relationshipbetween the zooplankton and chlorophyll distribution differedbetween cruises. In June, the zooplankton, particularly post-naupliarcopepods, were associated with the depth of the chlorophyllmaxirnum, while in September the post-naupliar copepods weremost abundant in the surface waters above the SCM at the stratifiedstations. During the September cruise we observed that the copepodnauplii were most abundant at the depth of the SCM, and thatthe larger protozoans (>35 µm) were most abundant atdepths of 55–85 m, which were well below the SCM and pycnocline. ^*Bigelow Laboratory for Ocean Sciences Contribution No. 83025     

Relationships between zooplankton community structure and phytoplankton in two lime-treated eutrophic hardwater lakes

1. North Halfmoon Lake and Lofty Lake (Alberta, Canada) were chosen for whole-lake liming experiments as a new restoration technology to enhance calcite precipitation and reduce eutrophication. During a 3-year study (1991–93) the relationships between zooplankton and phytoplankton were assessed, together with the effects of lime additions. 2. Zooplankton communities were numerically dominated by rotifers, while the major contribution to biomass was due to large filter-feeding Daphnia during the first half of the summer season. In Lofty Lake, cladocerans made up to 93% of biomass, whereas in North Halfmoon Lake both cladocerans and calanoids were strongly represented. 3. Total zooplankton and cladoceran biomasses were inversely correlated with chlorophyll a (chl a). The same relationship was found between large Daphnia (≥ 1 mm) and chl a. These relationships suggest that the decline in Daphnia may have been caused by an increase in cyanobacteria biomass during bloom events. 4. There were minor changes in rotifer populations after liming; however, these changes have been caused by natural year-to-year variation rather than liming. In general, cladocerans showed an increase in body size and population biomass when pre and post-treatment data were compared by means of ANCOVA. Statistical analysis showed that there were more cladocerans per unit of chl a after liming; however, further research is needed to relate these patterns unambiguously to the application of lime as a restoration technology.     

Relationships between benthic biota and hydrological indices in New Zealand streams

1. The objective of this study was to identify the most ecologically relevant hydrological indices for characterizing hydrological regimes in New Zealand streams. To do this we related measures of periphyton chlorophyll a, ash-free dry mass (AFDM), species richness, and diversity and invertebrate density, species richness and diversity, to thirty-four hydrological variables derived from daily flow records at eighty-three sites. The hydrological variables included some describing average flow conditions, flow variability, floods, and low-flow characteristics. 2. A principal components analysis showed that the interrelationship between many of the hydrological variables was high, and most variables correlated significantly with Principal Component 1 (PC1). The flood frequency variables formed a distinct component of the flow regime and were the main contributor to PC2. 3. We found that both the average flow conditions and some measure of variability were significantly related to most of the biological variables, and these individual hydrological variables were more strongly correlated to the biological measures than the composite principal components. Only four of the thirty-four flow variables were significantly correlated (P < 0.05) with measures of periphyton biomass (chlorophyll a and AFDM), whereas twenty-four variables were correlated with periphyton diversity. Conversely, thirty-one of the thirty-four flow variables were correlated with total invertebrate density, whereas only four variables correlated with diversity. 4. We selected the flood frequency (FRE₃), where a flood is defined as flows higher than three times the median flow, as the most ecological useful overall flow variable in New Zealand streams because it explained a significant amount of the variance in four out of the six main benthic community measures, and it had a clear mechanism of control of the biota which was commensurate with current stream ecosystem theory. Periphyton biomass decreased with increasing FRE₃, whereas invertebrate density had an increasing/curvilinear relationship with FRE₃. Periphyton species richness and diversity decreased with increasing FRE₃.     

Relationships between zooplankton abundance and trophic state in seven New Zealand lakes

The zooplankton communities of seven Rotorua, New Zealand, lakes of different trophic status were studied in 1977–78. They were generally dominated by the calanoid copepod, Calamoecia lucasi. Bosmina meridionalis occurred in all the lakes and Ceriodaphnia dubia in most. Only small numbers of Macrocyclops albidus ever occurred. Rotifers were not studied in detail. Community composition was similar to that in other northern New Zealand lakes. No well defined patterns of seasonal change in abundance were found and the timing of changes, which were of low magnitude, was different in each lake. Clutch sizes in all species were small. Calamoecia population parameters were analysed using multivariate methods and shown to be related to lake trophic level. Population densities were higher in more productive lakes whereas breeding levels were inversely related to indices of trophic status and population abundance. It is suggested that the populations, as in other northern New Zealand lakes, are food-limited, probably as a consequence of a lack of marked climatic seasonality and the absence of major predation pressures. Groupings of the lakes based on the Calamoecia data are in general agreement with those derived from parallel studies of water chemistry, phytoplankton and macrobenthos.     

The relations between larval fishes and zooplankton in two inshore areas of the Gulf of Maine

Larval fishes and zooplankton were sampled in two hydrographicallydifferent areas on the coast of the Gulf of Maine: SullivanHarbor, an embayment in eastern Maine, and the DamariscottaRiver estuary in western Maine. Sampling was conducted at weeklyintervals from late winter to early summer in each area in 1979and 1980. Phytoplankton chlorophyll concentrations were determinedin each area in 1979. The time of peak catch rates of the dominantlarval fish species occurred one to three weeks earlier in thewestern sample area, the Damariscotta estuary, than in SullivanHarbor in the east. The phytoplankton and zooplankton bloomsalso occurred one to three weeks earlier in the Damariscottaestuary than in Sullivan Harbor. These timing trends are believedto result from the differences in the seasonal hydrographicchanges of the inshore and coastal source waters. Analyses ofthe feeding, length-frequencies, and condition factors of thedominant larval fish species, Pholis gunnellus, are used torelate the apparent survival of the larvae to the timing ofappearance of their forage organisms, the dynamics of whichare determined by the local hydrography and resultant phytoplanktondynamics.     

Abundance and diversity of surface zooplankton in the Gulf of Aqaba, Red Sea, Egypt

Surface zooplankton were studied in Egyptian coastal watersof the Gulf of Aqaba, from bimonthly samples from July 1994to May 1995. Species diversity, numerical abundance and dynamicswere analysed for each taxon, at six sites, inside three Protectorates.A total of 62 taxa and species were identified. At all sites,copepods were predominant in the standing crop with an averageof 1945 ind. M^–3 and formed {small tilde}75.5%, numerically,of the total zooplankton community. The meroplanktonic larvaeoccupied the second rank and they constituted {small tilde}19.7%of the total zooplankton. Seasonally, the main peak of zooplanktonabundance was recorded in winter (January) with an average of3510 ind. M^–3 while September was characterized by thelowest density (1906 ind. m^–3 The relatively higher diversityvalues were recorded at Ras Mohammed Protectorate and a progressivedecline in diversity was observed northward.     

The effect of hydrological and morphometric parameters of temporary waterbodies on the structure and abundance dynamics of crustacean zooplankton

The effects of hydrological conditions and morphometry of the temporary waterbodies on the structure, abundance, and biomass of crustacean zooplankton are described. This study was performed in the southeast of the European part of Russia. The existence duration (hydrological regime) of the temporary waterbodies has the most profound effect on the zooplankton patterns. A significant effect was observed for the number of dominant species, the zooplankton biomass, the calanoid-cyclopoid ratio, and the Shannon index. The brackish lagoons were characterized by the highest biodiversity and abundance and the lowest values of these parameters were found in the steppe puddles and waterbodies of terraces above the flood-plain in the river valleys.     

Associations between gelatinous zooplankton and hyperiid amphipods (Crustacea: Peracarida) in the Gulf of California

Hyperiid amphipods are pelagic crustaceans that live associated with gelatinous zooplankton including medusae, ctenophores, siphonophores, and salps. Standard plankton sampling disrupts natural associations, so the most reliable way to determine an association is through direct observation of the organisms in their environment. The planktonic fauna of the Gulf of California dwelling between 10 and 3000 m was surveyed using SCUBA diving and a remotely operated submersible (ROV) during March 2003. Here we report our observations on a total of 14 symbiotic associations found between the hyperiid amphipods and various taxa of gelatinous zooplankton. We found parental care behavior in a group of amphipods (Oxycephalidae) in which this phenomenon has not been previously reported. For two hyperiid species, Euthamneus rostratus and Vibilia australis, we present the first information on their symbiotic relations. Additional hosts were discovered for other well-known and widely distributed hyperiid species (i.e. Brachyscelus crusculum, Hyperoche medusarum). Photographic evidence of some of these interactions is included in this contribution. This is the first survey of these relationships in the Gulf of California, and many aspects of the ecology and biology of these symbioses remain to be studied.     

Relationships between leaf chlorophyll content and spectral reflectance and algorithms for non-destructive chlorophyll assessment in higher plant leaves

Leaf chlorophyll content provides valuable information about physiological status of plants. Reflectance measurement makes it possible to quickly and non-destructively assess, in situ, the chlorophyll content in leaves. Our objective was to investigate the spectral behavior of the relationship between reflectance and chlorophyll content and to develop a technique for non-destructive chlorophyll estimation in leaves with a wide range of pigment content and composition using reflectance in a few broad spectral bands. Spectral reflectance of maple, chestnut, wild vine and beech leaves in a wide range of pigment content and composition was investigated. It was shown that reciprocal reflectance (R lambda)-1 in the spectral range lambda from 520 to 550 nm and 695 to 705 nm related closely to the total chlorophyll content in leaves of all species. Subtraction of near infra-red reciprocal reflectance, (RNIR)-1, from (R lambda)-1 made index [(R lambda)(-1)-(RNIR)-1] linearly proportional to the total chlorophyll content in spectral ranges lambda from 525 to 555 nm and from 695 to 725 nm with coefficient of determination r2 > 0.94. To adjust for differences in leaf structure, the product of the latter index and NIR reflectance [(R lambda)(-1)-(RNIR)-1]*(RNIR) was used; this further increased the accuracy of the chlorophyll estimation in the range lambda from 520 to 585 nm and from 695 to 740 nm. Two independent data sets were used to validate the developed algorithms. The root mean square error of the chlorophyll prediction did not exceed 50 mumol/m2 in leaves with total chlorophyll ranged from 1 to 830 mumol/m2.     

Biodiversity in the Gulf of Guinea: an overview

Patterns of species-richness and endemism in the Gulf of Guinea reflect the region's biogeographic history. Bioko is a continental-shelf island that was recently connected to the African mainland, whereas Príncipe, São Tomé and Annobón are truly oceanic and have never been connected with each other or with the mainland. As a result, Bioko supports a much more diverse flora and fauna but with relatively low levels of endemism at the species level, whereas the oceanic islands are relatively depauperate because of their isolation but rich in endemic taxa. Species endemism is 0–3% on Bioko for angiosperms, bats, birds, reptiles and amphibians, compared with much higher values on Principe for these same taxa of 8% (plants) to 100% (amphibians), on São Tomé between 14% (plants) and 100% (amphibians), and on Annobón 0% (bats) to 71% (reptiles). On a global scale, for their size both Príncipe and São Tomé support unusually high numbers of single-island endemic species of birds, reptiles and amphibia. For its tiny size, Annobón is also notable for its endemic birds and reptiles. Among terrestrial molluscs the rates of endemism are in general higher than for plants and vertebrates, from ca 50% on Bioko to ca 80% on the oceanic islands. In contrast and as might be expected, only Bioko supports a rich freshwater fish fauna and it contains many endemic taxa, whereas the oceanic islands support only a few salt-tolerant species. The Gulf of Guinea islands are also important for their marine organisms, amongst which coral reef fish and marginellid molluscs show high levels of endemism, though they are not especially species-rich. The Gulf of Guinea islands are of great interest to conservationists and evolutionary biologists. Each island, of greatly differing size and degree of isolation, has acquired its unique sub-set of plants and animals separately from the neighbouring mainland, followed by adaptive radiations in situ. For this reason the conservation value of the archipelago as a whole is greater than the sum of the biodiversity contained in its individual islands. Conservation initiatives in the Gulf of Guinea should therefore ensure that representative terrestrial, freshwater and marine habitats and groups of organisms are targeted in a co-ordinated manner among the islands.     

Estuarine relationships between zooplankton community structure and trophic gradients

Zooplankton and water quality parameters were investigated ateight mesohaline stations in the lower Chesapeake Bay and ElizabethRiver from January through December 1994 to identify the changesof zooplankton community structure with increased eutrophication.The total micro- and mesozooplankton biomass decreased withthe increase of eutrophication. However, the relative proportionof microzooplankton increased with increased eutrophication.Within highly eutrophied waters, the small oligotrichs (<30µm) and rotifers dominated the total zooplankton biomass(as carbon). However, tintinnids, copepod nauplii and mesozooplanktonsignificantly decreased with the increase of eutrophication.These patterns were consistent throughout the seasons and hadsignificant relationships statistically. These results suggestzooplankton community structures characterize an increasingeutrophication of an ecosystem.     

Parasites of swordfish from the Gulf of Guinea

Ten parasite species were identified after a study carried out on 125 swordfish from the Gulf of Guinea waters. The samples were taken between August and November 1997; 3 of the parasite species, Caligus coryphaenae. Pelichnibothrium speciossum, and Sphyriocephalus viridis were recorded for the first time on this host.     

Diversity and endemism of angiosperms in the Gulf of Guinea islands

The richness of flowering plants (1666 native taxa) and the originality of the flora of the islands of the Gulf of Guinea are remarkable. The flora of Bioko shows the highest diversity in terms of families, genera and species of angiosperms but, due to its proximity to the mainland, the level of endemism is relatively low. The number of endemics in the four islands has suffered a decrease in the last years, due to taxonomic changes. Currently, 176 endemic taxa of angiosperms are recognized. Most of the endemic taxa are under-collected and information is lacking on their biology and distribution, hence the need for inventory work on the flora of the islands. A measure of the similarity between the floras of the islands can be given by determination of genera in common. The results are comparable to those obtained with Exell and Wild's quotient of affinity and show a great similarity between neighbouring islands. The presence of afromontane elements and several palaeoendemics in the mountain rain forest of the islands is notable and makes the study of its flora a priority for research.     

Size fractionation of algal chlorophyll, carbon fixation and phosphatase activity: relationships with species-specific size distributions and zooplankton community structure

Algal chlorophyll, carbon fixation and alkaline phosphataseactivity were net-fractionated using 22-µm, and 75-µmscreens in three lakes with contrasting zooplankton communities.Size distributions of algal biovolume were also determined throughmicroscopic examination. Relatively good correspondence wasfound between size distributions obtained through net fractionationand those determined by microscopic examination. Biovolume-specificcarbon fixation and chlorophyll decreased with increasing fractionsize but no differences were observed among fractions for chlorophyll-specificcarbon fixation. High algal standing stocks and low phosphorusdeficiency in Tuesday Lake were attributed to low grazing pressureby small, inefficient zooplankton and possible limitation bynutrients other than phosphorus. Algal standing stocks werelow and phosphorus deficiency was high in Peter and Paul Lakes,in which the zooplankton was dominated by large grazers. Differentalgal size fractions experienced differing degrees of phosphorusdeficiency. These size fraction differences in P-deficiencyin Peter and Paul Lakes were attributed to differences in algalspecies composition and to differing levels of zooplankton grazingpressure and nutrient regeneration. A unimodal relationshipbetween relative nanoplankton biovolume and zooplankton biomasswas found and reflects the positive (nutrient regeneration)and negative (grazing mortality) effects of zooplankton on thealgal community.     

Relationships between nonhyperbolic kinetics and dimeric structure in ribonucleases

Dimers of bovine pancreatic RNase A give nonhyperbolic saturation curves for the substrate of the second, rate-limiting step of the reaction. Under the same conditions, the monomeric native enzyme shows Michaelis-Menten kinetics. Naturally dimeric bovine seminal RNase, which has been found to give nonhyperbolic saturation curves, loses this property upon monomerization. It is proposed that when RNase monomers are arranged in a quaternary structure, they assume a conformation which enables them to be modulated in their catalytic activities. A correlation is suggested between this effect and the quaternary structure proposed for both of these dimeric ribonucleases, in which composite active sites are generated by the mutual exchange of the NH2-terminal ends of the two monomers.     

Water level and temperature and zooplankton population abundances in Lake Surinumu,Papua New Guinea

Lake Surinumu, an oligotrophic hydroelectric impoundment on the Laloki River in Central Province, Papua New Guinea, was sampled throughout 1982 for its zooplankton community composition, water level and surface temperature. The zooplankton community was observed to be normally dominated byEodiaptomus lumholtzi, Ceriodaphnia cornuta and theDiaphanosoma speciesD. sarsi andD. excisum, though the rotiferT. equatorialis became dominant toward the end of the sampling period. Nutrient levels, especially with regard to ionic nitrogen, were observed to decrease following the monsoonal influx. Close correlations were found between water level and surface temperature, and between water level and the relative abundances ofE. lumholtzi, diaphanosomids andT. equatorialis. The zooplankton community was observed to undergo the most significant changes during periods of monsoonal influx and lowest water level/highest water temperature. In the absence of significant interspecific abundance correlations, it is suggested that climatic factors are primarily responsible for the dynamics of the zooplankton community composition.     

Relationships between structure and function in streams contrasting in temperature

1. We studied 10 first-order Icelandic streams differing in geothermal influence in separate catchments. Summer temperature (August–September) ranged between 6 and 23 °C.
2. Macroinvertebrate evenness and species overlap decreased significantly with temperature whereas taxon richness showed no response. In total, 35 macroinvertebrate species were found with Chironomidae the dominant taxonomic group. Macroinvertebrate density increased significantly with temperature. Dominant species in the warm streams were Lymnaea peregra and Simulium vittatum . Algal biomass, macrophyte cover and richness were unrelated to temperature. Densities of trout ( Salmo trutta ), the only fish species present, reflected habitat conditions and to a lesser degree temperature.
3. Density of filter-feeders increased significantly with temperature whereas scraper density, the other dominant functional feeding group, was unrelated to temperature. Stable isotope analysis revealed a positive relationship between δ¹⁵N and temperature across several trophic levels. No pattern was found with regard to δ¹³C and temperature.
4. Leaf litter decomposition in both fine and coarse mesh leaf bags were significantly correlated to temperature. In coarse mesh leaf packs breakdown rates were almost doubled compared with fine mesh, ranging between 0.5 and 1.3 g DW 28 days⁻¹. Nutrient diffusion substrates showed that the streams were primarily nitrogen limited across the temperature gradient while a significant additional effect of phosphorous was found with increasing temperature.
5. Structural and functional attributes gave complementary information which all indicated a change with temperature similar to what is found in moderately polluted streams. Our results therefore suggest that lotic ecosystems could be degraded by global warming.