Biomass and estimated production rates of metazoan zooplankton community in a tropical coral reef of Malaysia

Quantitative research on composition, biomass and production rates of zooplankton community is crucial to understand the trophic structure in coral reef pelagic ecosystems. In the present study, micro‐ (35–100 μm) and net‐ (>100 μm) metazooplankton were investigated in a fringing coral reef at Tioman Island of Malaysia. Sampling was done during the day and night in August and October 2004, and February and June 2005. The mean biomass of total metazooplankton (i.e. micro + net) was 3.42 ± 0.64 mg C·m^?3, ranging from 2.32 ± 0.75 mg C·m^?3 in October to 3.26 ± 1.77 mg C·m^?3 in August. The net‐zooplankton biomass exhibited a nocturnal increase from daytime at 131–264% due to the addition of both pelagic and reef‐associated zooplankton into the water column. The estimated daily production rates of the total metazooplankton community were on average 1.80 ± 0.57 mg C·m^?3·day^?1, but this increased to 2.51 ± 1.06 mg C·m^?3·day^?1 if house production of larvaceans was taken into account. Of the total production rate, the secondary and tertiary production rates were 2.20 ± 1.03 and 0.30 ± 0.06 mg C·m^?3·day^?1, respectively. We estimated the food requirements of zooplankton in order to examine the trophic structure of the pelagic ecosystem. The secondary production may not be satisfied by phytoplankton alone in the study area and the shortfall may be supplied by other organic sources such as detritus.     

Rainfall downscaling in time: theoretical and empirical comparison between multifractal and Hurst-Kolmogorov discrete random cascades

Abstract

During recent decades, intensive research has focused on techniques capable of generating rainfall time series at a fine time scale that are (fully or partially) consistent with a given series at a coarser time scale. Here we theoretically investigate the consequences on the ensemble statistical behaviour caused by the structure of a simple and widely-used approach of stochastic downscaling for rainfall time series, the discrete Multiplicative Random Cascade. We show that synthetic rainfall time series generated by these cascade models correspond to a stochastic process which is non-stationary, because its temporal autocorrelation structure depends on the position in time in an undesirable manner. Then, we propose and theoretically analyse an alternative downscaling approach based on the Hurst-Kolmogorov process, which is equally simple but is stationary. Finally, we provide Monte Carlo experiments which validate our theoretical results.

Editor Z.W. Kundzewicz

Citation Lombardo, F., Volpi, E., and Koutsoyiannis, D., 2012. Rainfall downscaling in time: theoretical and empirical comparison between multifractal and Hurst-Kolmogorov discrete random cascades. Hydrological Sciences Journal, 57 (6), 1052–1066.     

Feeding habits of the ommastrephid squid Nototodarus sloanii on the Chatham Rise,New Zealand

The diet of the squid Nototodarus sloanii was determined from examination of stomach contents of 388 specimens of 14.3–41.0 cm dorsal mantle length sampled at depths of 211–760 m on the Chatham Rise, New Zealand. Prey items were predominantly mesopelagic fishes, with some crustaceans and cephalopods. The most important prey species identified was Maurolicus australis, followed by Lampanyctodes hectoris, and unidentified squids (Teuthoidea). Multivariate analyses using distance‐based linear models, non‐parametric multi‐dimensional scaling, analysis of similarities, and similarity percentages, indicated crustaceans were more important in the diet of smaller squid (83–480 g), the fish component of the diet was dominated by L. hectoris on the east Chatham Rise and M. australis on the west Chatham Rise, and there may be a difference in diet with sex, with crustaceans and cephalopods more important for females. The results indicated that N. sloanii, similar to other ommastrephid squids, foraged primarily in the mesopelagic layers.     

Leigh Marine Laboratory contributions to marine conservation

Abstract

The Leigh Marine Laboratory (LML) has taken full advantage of its location on the shores of one of the world's first no-take marine reserves. The foresight of the founders of the laboratory has enabled the pursuit of ecological studies that have been amongst the first to demonstrate the effectiveness of reserves as a tool for conservation and restoration. The insights flowing from this work at Leigh are important, not only for targeted marine species, but also at the ecosystem level, and have proven to be highly relevant to broader resource management issues. Novel methodologies have been employed in the pursuit of these aims, helping to popularise their wider use. More recent work has focused on understanding the processes underlying the variability in response to marine conservation in marine reserves across the spectrum of coastal marine habitats in New Zealand. The LML has probably exceeded the expectations of its founders, who hoped the laboratory might generate information of interest in the fields of ‘resource management, food web dynamics and natural fluctuations distinct from man-induced changes’, and its contribution in the field of marine conservation has been significant both within New Zealand and internationally. This has been a 50-year journey that has gone from a focus on local effects of conservation to the broader context, from direct effects of protection to indirect effects, and from small-scale spatial conservation management to ecosystem-based management.     

Adaptation of diet in a changed environment: Increased consumption of lobster krill Munida gregaria (Fabricius, 1793) by Argentine hake

A well‐replicated decadal‐term (2005–2014) stomach content data set was analysed in order to infer inter‐annual fluctuations in the diet of the Argentine hake, Merluccius hubbsi, an opportunistic predator in the San Jorge Gulf (SJG) ecosystem in the Southwest Atlantic. Ten research cruises were carried out each year during January from 2005 to 2014. A total of 18,461 specimens of Me. hubbsi was analysed, of which 6,777 (36.71%) contained food in their stomachs. The diet of Me. hubbsi changed markedly from 2011 onwards, with much greater consumption of the lobster krill Munida gregaria compared to the years before 2011. The frequency of occurrence (%F) of Mu. gregaria in the stomach contents of Argentine hake increased from the year 2009 onwards, most noticeably since 2011, and mostly over the southern region of the SJG. The main predators of Mu. gregaria in the SJG are two species of teleost fish (pink cusk eel, Genypterus blacodes, Argentine seabass, Acanthistius brasilianus) and three Rajidae skates (Zearaja chilensis, Psammobatis spp. and Sympterygia bonapartii), which exhibited decreased catches in the years analysed. The increased consumption of Mu. gregaria by Me. hubbsi, coupled with decreased trends in abundance of the main predators of the lobster krill during the last decade, indicate that top‐down trophic dynamic control occurs in the SJG ecosystem.     

Host‐dependent differences in resource use associated with Anilocra spp. parasitism in two coral reef fishes,as revealed by stable carbon and nitrogen isotope analyses

The role of parasites in trophic ecology is poorly understood in marine ecosystems. Stable isotope analyses (SIA) have been widely used in studies of trophic ecology, but have rarely been applied to study the role of parasites. Considering that some parasites are associated with altered host foraging patterns, SIA can help elucidate whether parasitism influences host trophic interactions. French grunt (Haemulon flavolineatum), an abundant Caribbean coral reef fish, contributes greatly to trophic connectivity. They typically depart the reef at dusk, feed overnight in seagrass beds, and return to the reef at dawn. The large parasitic isopod Anilocra haemuli commonly infects French grunt, and infected fish are less likely to complete their diel migration, and are in poorer condition than uninfected conspecifics. Brown chromis (Chromis multilineata) are diurnally feeding planktivores and infection by Anilocra chromis does not influence host condition. To determine if Anilocra infection influences host diet and foraging locality, we conducted stable carbon and nitrogen isotope analyses on scale, muscle, heart and gill tissues of infected and uninfected French grunt and brown chromis. We determined that all French grunt had δ¹³C values representative of seagrass habitats, but infected French grunt were significantly enriched in ¹³C and ¹⁵N compared to uninfected conspecifics. This suggests that compared to uninfected conspecifics, infected French grunt forage in seagrass, but on isotopically enriched prey, and/or are in poorer condition, which can elevate δ¹³C and δ¹⁵N values. For brown chromis, infection did not significantly influence any δ¹³C and δ¹⁵N values; hence they all foraged in the same environment and on similar prey. This is the first study to use SIA to examine differences in resource use by Caribbean coral reef fishes associated with parasitism and to evaluate how closely related parasites might have host‐dependent effects on host trophic ecology.     

Impacts of a bivalve mass mortality event on an estuarine food web and bivalve grazing pressure

Declines in bivalve populations have been quite common worldwide, often associated with coastal development, pollution and climate change. In addition to the impacts of these chronic stressors, occasional mass mortality events may have severe consequences on ecosystem services and biodiversity. In this study, we examined the impact of a mass mortality event of the clam (Austrovenus stutchburyi) on an estuarine food web and the grazing pressure exerted by the bivalve population. In February 2009, c. 60% of the clam population died in Whangateau Harbour, New Zealand. Population clearance rate calculations suggest that the clam population do not exert significant top-down control on phytoplankton biomass in the estuary, and thus the impact of the mortality event on bivalve grazing pressure was less severe than the reduction in abundance would suggest. A trophic model shows that phytoplankton play a limited role in the estuary food web, which is instead dominated by microphytobenthos and clams. This study highlights the importance of microphytobenthos in shallow estuaries, and the application of the trophic model is a useful tool that can identify key components of the ecosystem and could help inform monitoring programmes.     

The effect of abiotic environmental variables on the Danube macrozoobenthic communities

160 taxa of macrozoobenthos were recorded in the Danube River (R. km 1880-1704) riparian zone. Many typical Danubian and Pontocaspian representatives were found. The Slovak section of the Danube represents the border between its epipotamal and metapotamal stretches with different flow velocity and other environmental variables related to it. This paper characterises some abiotic ecological factors influencing the distribution of benthic taxa in five sampling sites along the longitudinal profile of the Danube. The benthic community composition was more strongly influenced by hydrological parameters than by oxygen and temperature regimes, as well as by the water quality conditions. In other words, the bottom substrate, flow velocity, water level fluctuation and discharge changes had the predominant effect on the taxocoenoses of macrozoobenthos. Three characteristic groups of macrozoobenthic organisms were recorded, as far as corresponding trophic guilds are concerned. Shredders and scrapers predominated in high flow velocity conditions with coarse substrate particles. Collectors of fine organic matter preferred slow-flowing conditions caused by damming or by a reduction of current due to the presence of bedrock. Filterers prevailed in the lower section of the Danube stretch monitored. Predators occurred independently of the environmental variables studied.     

Prognosis of the state （eutrophication and pollution） of freshwater ecosystems on the example of long-term research into Lake Baikal

Systematic （monthly） observations of changes in the components of trophic status in the pelagic zone of Baikal were carried out during years of spring blooms of almost pure cultures： Gymnodinium （1965）, Aulocoseira bai-calensis （1968）, Synedra acus （1969）, Nitzschia acicularis （1984 and 1987）, picocyanobacteria （2004-2005）. The research period coincided with various anthropogenic impacts on Baikal ecosystem： （1） the period of the natural state of the lake （until 1969）; （2） the period of weak anthropogenic impact （until 1985）; and （3） the period of acute anthropogenic impact. In the third period the following was found in the deep-water part of the lake： the episodic appearance of ammonium and nitrite nitrogen; change in the components of suspended matter （SM）; disturbed patterns of seasonal changes in SM content, chlorophyll-a, organic forms of carbon, nitrogen and phosphorus; the average annual concentrations of suspended organic carbon, nitrogen and phosphorus have increased considerably; the vertical distribution pattern of minerals and organic forms of nitrogen and phosphorus have been disturbed; finally, an observed inverse correlation between winter nitrogen content and the spring concentration of chlorophyll-a （1986-1989） would indicate the presence of toxins in the lake. This led to the study of POPs in Baikal and the Baikal region. Investigations undertaken during 2004-2005 in the pelagic coastal zones of the lake indicated the presence of toxic pollutants in southern Baikal （the correlation between winter nitrogen content and spring concentration of chlorophyll-a is inverse and equals 0.99 and 1.00 respectively）. Toxicants that enter the lake during the iced-over period mainly enter the trophogenic layer, as wastewaters are warmer than the lake waters, depress the development of endemic spring diatomic algae and lead to a rise in the trophic status.     

Seasonal variations of adsorption/desorption equilibrium concentrations of P at water-sediment interface in different trophic states of Taihu Lake, China

Sediment from three different trophic states （Meiliang Bay, Xukou Bay and Gonghu Bay） in spring, summer, autumn and winter were collected and analyzed in Taihu Lake. At the same time, seasonal variations in adsorption/desorption equilibrium were investigated with corresponding sediments from these three trophic states, including adsorption efficiency, adsorption/desorption equilibrium concentration and equilibrium adsorption quantity. Variations of TP and P fractions＇ concentrations in the initial and end of adsorption experiment were also documented in order to find the most active P fractions. The following conclusions were obtained： （1） Concentrations of total phosphorus （TP） and its fractions in the sediments were coincided with the trophic state of corresponding overlying water, Meiliang Bay〉Gonghu Bay〉Xukou Bay. The Meiliang Bay located in the north of Taihu Lake is in the eutrophic state and belong to alga-type lake; the Xukou Bay located in the northeast of Taihu Lake is relatively clean lake region; the Gonghu Bay is located in the east of Taihu Lake is in the meso-trophic state. Fe-P concentrations in the Meiliang Bay, Gonghu By and Xukou Bay account for 35.1%-70.9%, 19.6%-26.8%, 16.5%-34.3% of TP, Ca-P account for 20.6%-43.7%, 40.7%-45.0%, 23.0%-41.1% and OP accounts for 15.3%-20.2%, 28.4%-37.4%, 23.6%-54.3%, which changes obviously in different seasons. Fe-P is the major fraction in the eutrophic lake region, which is significantly correlated with the TP concentrations. （2） Adsorption and desorption processes in these three lake regions varied with season.