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.     

Inorganic nitrogen acquisition by the tropical seagrass Halophila stipulacea

The tropical seagrass Halophila stipulacea is dominant in most regions of the Indo‐Pacific and the Red Sea and was introduced into the Mediterranean Sea after the opening of the Suez canal. The species is considered invasive in the Mediterranean Sea and has been progressively colonizing new areas westward. Growth and photosynthetic responses of H. stipulacea have been described but no information is yet available on the nitrogen nutrition of the species. Here we simultaneously investigated the uptake kinetics of ammonium and nitrate and the internal translocation of incorporated nitrogen in H. stipulacea using ¹⁵N‐labelled substrates across a range of N_i levels (5, 25, 50 and 100 μm ). The ammonium uptake rates exceeded the nitrate uptake rates 100‐fold, revealing a limited capacity of H. stipulacea to use nitrate as an alternative nitrogen source. The uptake rates of ammonium by leaves and roots were comparable up to 100 μm ¹⁵NH₄Cl. At this concentration, the leaf uptake rate was 1.4‐fold higher (6.22 ± 0.70 μmol·g^?1 DW h^?1) than the root uptake rate (4.54 ± 0.28 μmol·g^?1 DW h^?1). The uptake of ammonium followed Michaelis–Menten kinetics, whereas nitrate uptake rates were relatively constant at all nutrient concentrations. The maximum ammonium uptake rate (V_max) and the half‐saturation constant (K_m) of leaves (9.79 μmol·g^?1 DW h^?1 and 57.95 μm , respectively) were slightly higher than that of roots (6.09 μmol·g^?1DW h^?1 and 30.85 μm , respectively), whereas the affinity coefficients (α = V_max/K_m) for ammonium of leaves (0.17) and roots (0.20) were comparable, a characteristic that is unique among seagrass species. No substantial translocation (<2.5%) of ¹⁵N incorporated as ammonium was detected between plant parts, whereas the translocation of ¹⁵N incorporated as nitrate was higher (40–100%). We conclude that the N_i acquisition strategy of H. stipulacea, characterized by a similar uptake capacity and efficiency of leaves and roots, favors the geographical expansion potential of the species into areas with variable water‐sediment N levels throughout the Mediterranean.     

Nitrogen uptake in light versus darkness of the seagrass Zostera noltei: integration with carbon metabolism

We conducted a study that shows that light and dark conditions do not affect the uptake rates of ammonium and nitrate by the seagrass Zostera noltei. This is an important advantage over some seaweed species in which these rates are severely reduced at night. In the light, the ammonium uptake rates were initially higher (15 and 20 μmol·g^?1·h^?1) and stabilized at a rate of 5 μmol·g^?1·h^?1 after 1 h, whereas in the dark the rates remained constant at a rate of 10 μmol·g^?1·h^?1 over the first 180 min of incubation. The rates of nitrate uptake in the light were high within the first 120 min of incubation (7.2–11.1 μmol·g^?1·h^?1) and decreased afterwards to lower values (0.8–3.9 μmol·g^?1·h^?1), whereas in the dark the rates fluctuated around 0.0–11.1 μmol·g^?1·h^?1 throughout the whole incubation time (7 h). The soluble sugar content of Z. noltei leaves increased significantly with both ammonium and nitrate incubations in the light, indicating the metabolic outcome of photosynthesis. In the dark, there was no significant variation in either the soluble sugar or in the starch content of leaves, rhizomes or roots in either the ammonium or nitrate incubations. However, the total starch content of plants decreased at night whereas the total soluble sugars increased, suggesting a process of starch catabolism to generate energy with the consequent production of smaller monosaccharide products. The starch content of rhizomes decreased significantly during the light incubations with nitrate but not with ammonium. These results suggest that carbohydrate mobilization is necessary for Z. noltei to account for extra energetic costs needed for the uptake and assimilation of nitrate. Furthermore, our results suggest that nitrate uptake, at least during the day, requires the mobilization of starch whereas the uptake of ammonium does not.     

Low calcification rates and calcium carbonate production in Porites panamensis at its northernmost geographic distribution

Porites panamensis is a hermatypic coral present in the eastern Pacific Ocean. Skeletal growth parameters have been reported, but studies of the relationship between annual calcification rates and environmental controls are scarce. In this study, we investigated three aspects of the annual calcification rates of P. panamensis: growth parameters among three P. panamensis populations; the sea surface temperature as a calcification rate control spanning a latitudinal gradient; and calcium carbonate production among three sites. Growth parameters varied among the sites due to the colony growth form. Massive colonies in the north showed a higher calcification rate than encrusting colonies in the south (mean: 1.22–0.49 g CaCO₃ · cm^?2 · yr^?1), where variations in calcification rates were related to growth rate (0.91–0.38 cm · yr^?1) rather than to skeletal density differences (overall mean ± SD, 1.31 ± 0.04 g CaCO₃ · cm^?3). Our results showed a positive linear relationship between annual calcification rates and sea surface temperatures within these P. panamensis populations. Differences were related to distinct oceanographic environments (within and at the entrance of the Gulf of California) with different sea surface temperature regimes and other chemical properties. Different populations calcified under different environmental conditions. Calcium carbonate production was dependent upon the calcification rate and coral cover and so carbonate production was higher in the north (coral cover 12%) than in the south (coral cover 3.5). Thus, the studied sites showed low calcium carbonate production (0.25–0.43 kg CaCO₃ · m^?2 · yr^?1). Our results showed reduced calcification rates, regional temperature regime control over calcification rates, different growth forms, low coral cover and low calcium carbonate production rates in P. panamensis.     

Protracted oogenesis and annual reproductive periodicity in the deep‐sea pennatulacean Halipteris finmarchica (Anthozoa,Octocorallia)

Halipteris finmarchica is one of the most common species of deep‐sea pennatulacean corals in the Northwest Atlantic; it was recently determined to act as a biogenic substrate for other species and as a nursery for fish larvae. Its reproductive cycle was investigated in colonies sampled in 2006 and 2007 along the continental slope of Newfoundland and Labrador (Canada). Halipteris finmarchica exhibits large oocytes (maximum diameter of 1000 μm), which are consistent with lecithotrophic larval development. Female potential fecundity based on mature oocytes just before spawning was ~6 oocytes · polyp^?1 (500–6300 oocytes · colony^?1); male potential fecundity was 16 spermatocysts · polyp^?1 (5500–57,400 spermatocysts · colony^?1). Based on statistical analysis of size‐probability frequency distributions, males harboured one cohort of spermatocysts that matured inside 8–11 months, whereas females harboured two distinct cohorts of oocytes; a persistent pool of small ones (≤400 μm) and a small number (~20%) of larger ones that grew from ~400 to >800 μm over a year. Despite this difference in the tempo of oogenesis and spermatogenesis, a synchronic annual spawning was detected. A latitudinal shift in the spawning period occurred from south (April in the Laurentian Channel) to north (May in Grand Banks and July–August in Labrador/Lower Arctic), following the development of the phytoplankton bloom (i.e. sinking of phytodetritus). Prolonged oogenesis with the simultaneous presence of different oocyte classes in a given polyp is likely not uncommon in deep‐sea octocorals and could hamper the detection of annual/seasonal reproduction when sample sizes are low and/or time series discontinued or brief.     

Reproductive traits of Euterpina acutifrons in a coastal area of Southeastern Brazil

We investigated the reproductive biology of the planktonic harpacticoid copepod Euterpina acutifrons, including morphometric data, egg production rates (EPR) and viability, and weight‐specific egg production. Experiments were carried out during 1 year in an inner‐shelf area off Ubatuba (SE Brazil), a site seasonally influenced by bottom intrusions of the relatively cold and nutrient‐rich South Atlantic Central Water (SACW). We hypothesized that E. acutifrons attain higher reproductive rates when SACW penetrates in this region. Live females were incubated individually in cell culture plates during two periods of 24 h each, under controlled temperature and light conditions. Euterpina acutifrons carried on average 16.9 ± 6.9 eggs·sac^?1, ranging between 10.8 ± 5.7 and 30.8 ± 7.4 eggs·sac^?1. Estimated EPRs ranged from 6.3 ± 3.4 to 13.6 ± 4.2 eggs·female^?1·day^?1, with mean weight‐specific egg production rates of 0.06 ± 0.04 and 0.17 ± 0.08 per day. Euterpina acutifrons was not directly influenced by SACW intrusions, but body length and clutch size were positively related to temperature and chlorophyll content. Egg hatching time was clearly dependent on water temperature, as a 2 °C increase resulted in a decrease of 15 h in egg hatching time. This shows that even a small variation in temperature may considerably affect E. acutifrons population dynamics. Reproductive traits of this pelagic harpacticoid seem, therefore, to be controlled by the trade‐offs between increased food supply and the metabolic demands at low temperatures associated with SACW bottom intrusions toward this coastal area.     

Enhalus acoroides responses to experimental shoot density reductions in Haad Chao Mai National Park,Trang Province,Thailand

The effect of self‐shading and competition for light in the seagrass Enhalus acoroides were investigated with a density reduction experiment in Haad Chao Mai National Park, Trang Province, Thailand. The study was carried out in a monospecific meadow with a natural density of 141.0 ± 8.7 shoots·m^?2. The intent was to determine the response of E. acoroides beds to loss of shoots and thinning, which often occur during typhoons and severe storm activity. Permanent quadrats were manipulated by clipping the seagrass shoots to 140, 72, 36 and 16 shoots·m^?2, to yield natural, 50%, 25% and 10% densities, respectively. Reducing shoot density in E. acoroides increased underwater light intensity below the canopy, generating increased leaf surface area and shoot weight. Seagrass leaf width, growth rate, and number of leaves per shoot also increased with greater light. The extent of flowering varied among treatments with no consistent trend. Our results demonstrate that increasing the available light to E. acoroides produces an increasing leaf size response as self‐shading in the bed is reduced.     

Copepod assemblages in a highly dynamic equatorial estuary on the Brazilian Amazon Coast

This study describes the spatial and temporal dynamics of the copepod fauna in the estuary of the Caeté River, a highly dynamic environment characterized by a unique set of hydrological and hydrodynamic attributes. This ecosystem is part of the Amazon Coastal Zone (ACZ), which sustains one of the world's largest continuous tracts of mangrove forest. In the present study, a predominance of high‐energy conditions characterized by macrotides and strong tidal currents was observed throughout the year. Salinity (0.03 ± 0.05–40.00 ± 0.84) and temperatures (26.43 ± 0.10–30.08 ± 0.43 °C) were higher than during the rainy season at all sampling stations. The highest chl‐a concentration (3.92 ± 1.47–17.63 ± 2.60 mg·m^?3) was recorded at the most oligohaline (innermost) station during the rainy season, while no spatial or seasonal pattern was found in dissolved nutrient concentrations, except for phosphates, which exhibited the highest concentrations during the dry season. A total of 22 copepod taxa was identified, of which the most abundant were Oithona hebes, Oithona oswaldocruzi, Acartia tonsa, Paracalanus quasimodo, Euterpina acutifrons and Pseudodiaptomus marshi. Copepodites and nauplii were also recorded. Mean total copepod abundance varied from 710.73 ± 897 individuals (ind.)·m^?3 at the inner station to 236,486 ± 398,360 ind.·m^?3 near the mouth of the estuary (outermost station). The results reflected rainfall‐influenced oscillations in hydrological variables, mainly salinity, which determined shifts in the distribution of copepods and their community structure within the study area. This pattern may be typical of estuaries in the ACZ with similar hydrodynamic and hydrological attributes that are not influenced by the Amazon River plume.     

Spatio‐temporal variation in density and size structure of the endangered sea cucumber Isostichopus fuscus in Huatulco National Park,Mexico

The brown sea cucumber Isostichopus fuscus (Ludwig, 1875) has been subjected to strong fishing pressure and is currently considered an endangered species by the IUCN Red List of Threatened Species. Spatial and temporal variations in density were analysed and population parameters of I. fuscus were estimated in three localities of the Southern Mexican Pacific. Density was estimated using circular transects covering a 300 m² area in each locality. Body length and weight were also measured. The mean density was 0.018 ± 0.013 individuals·m^?2, and was statistically significantly lower during summer. The mean length and weight were 22.4 ± 3.8 cm and 396 ± 130 g, respectively, and statistically significant differences were found among localities. The weight–length relationship was W = 0.28·L^1.32 and the mean relative condition index (Kn) = 1.04 ± 0.31. The von Bertalanffy growth equation was L_t = 38.7·(1–exp^(?0.4·t)). The lowest values of length, weight and age were found at Dos Hermanas, suggesting that this locality could be favorable for the settlement of larvae and recruitment and growth of juveniles. The present study is the second to estimate densities of I. fuscus and the first one to publish data on size structure and growth for the population at Bahias de Huatulco. The densities were so low in the three sampled localities that none of them would be able to support a fishery, even under a sustainable management scheme. The information collected in the present study could be helpful for management programs of the Huatulco National Park, as all the data used for these currently come mainly from the populations of I. fuscus in the Gulf of California.     

An experimental study of microflagellate bacterivory: further evidence for the importance and complexity of microplanktonic interactions

By simulating an upwelling event in a laboratory microcosm, it was possible to promote the development of a natural and diverse planktonic community. An initial bacterioplankton community which developed in response to phytoplankton growth was dominated by small coccoid forms (0,14–0,2 μm³) of the genera Vibrio and Pseudomonas. This group was heavily exploited by the heterotrophic microflagellate Pseudobodo sp. (30 μm³). Later, the bacterioplankton community was dominated by large rods (0,7 μm³) which the flagellates seemed unable to exploit. A Lotka-Volterra predator-prey model fitted to the observed data indicated that the flagellates consumed 2,4 times their carbon body mass per day or 19 bacteria·flagellate^?1·h^?1 when prey were not limiting. Clearance rates were inversely proportional to prey density and ingestion rate, ranging from 2 × 10^?3 to 20 × 10^?3) μ?·flagellate^?1·h^?1. At typical field densities of bacteria and heterotrophic flagellates in the southern Benguela region, between 5 and 30 percent of the water column could be cleared per day. Specific growth rates of the flagellates were positively related to prey density, the maximal rate being 0,84 · d^?1. Their initially faster growth rates allowed bacteria to increase in numbers despite predation. The growth yield of the flagellates (34–36 per cent) was also positively related to food density. Such low values suggest inefficient transfer of carbon to higher trophic orders but considerable nitrogen regeneration. Nitrogen excretion rates were approximately 6–7 μg N·mg dry weight^?1·h^?1, comparable to other flagellates but faster than ciliates. These rates are comparable with in situ measurements of NH⁺₄-N excretion in pycnoclinal regions based on ¹⁵N isotope studies but are only about 20 per cent of measured rates in surface waters. This is interpreted to mean that, in pycnoclinal regions where the relative input of "new" nitrogen is high, there are few regenerative steps and the model describes them satisfactorily. In surface waters, observed rates of excretion can only be accounted for by many regenerative steps in a highly complex food chain in which the cumulative total of nitrogen excretion at each step amounts to that based on ¹⁵N labelling studies.     

Nitrogen excretion by the Cape rock lobster Jasus lalandii and its possible contribution to the inshore Benguela System

The Cape rock lobster Jasus lalandii is a major predator in the inshore Benguela system. The mean density and biomass at Oudekraal is 0,48 individuals ·m^?2 or 49,75 g dry mass ·m^?2. The main component of its diet is Aulacomya ater, the ribbed mussel, which has a mean biomass of 1,15 kg dry mass ·m^?2. Daily consumption of carbon and nitrogen from this source reaches a maximum in summer and, when J. lalandii feed on mussels, 14,1 per cent of the flesh is lost to the environment as a result of "messy feeding". The absorption efficiency of ingested nitrogen is 86,2 per cent. Ammonia and urea excreted in the first 12 h after feeding represent 6,7 and 1,6 per cent respectively of the nitrogen ingested. Endogenous nitrogen excretion has a mean rate of 1,9 μg N·g (dry mass)^?1·h^?1 The range of estimates for combined figures of kelp and phytoplankton nitrogen requirements are 76,4 – 86,7 g N·m^?2·year^?1 J. lalandii returns 6,3 g N·m^?2·year^?1 to the system, accounting for 7,2 – 8,2 per cent of annual kelp and phytoplankton requirements. This could be of particular importance during downwelling when the supply of new nitrogen is limited.     

First insights into the demography of the rare gorgonian Spinimuricea klavereni in the Mediterranean Sea

We present the results of the first study to highlight the demography, morphometry and growth rates of Spinimuricea klavereni, a rare Mediterranean endemic gorgonian exceptionally common in shallow depths of the Northeast Marmara Sea. In the study area, this species forms vast populations on rocks, boulders and attached to pebbles/stones/shells on soft substrates between 20 and 45 m depth, with a total average density of 0.3 colonies·m^?2 but comprising patches up to 3 colonies·m^?2. Colonies, which are on average 42.9 (±20.1) cm in height, can reach up to 110 cm. Unlike other Mediterranean gorgonians, the colonies studied here showed fast growth rates that decreased with increasing colony height, between 1.5–11.1 and 4.96 ± 3.01 cm·year^?1 on average. The low necrosis and high growth rates displayed by this species in the Northeast Marmara Sea confirm the previously hypothesized opportunistic behaviour of the species. The unique community consisting of S. klavereni and other rare gorgonian/soft corals has limited distribution in this area and should be considered to be a vulnerable marine ecosystem. Therefore we recommend that some conservation measures are taken, including the prohibition of all fisheries and anchoring over these assemblages.     

Spatio‐temporal dynamics and biomass of Cymodocea nodosa in Bekalta (Tunisia,Southern Mediterranean Sea)

Leaf growth, biomass and production of Cymodocea nodosa were measured from October 2006 to September 2007 in Monastir Bay (Tunisia). Shoot density showed a clear seasonal pattern, increasing during spring and summer and decreasing during fall and winter. Monthly mean shoot density ranged between 633 ± 48 and 704 ± 48 shoots?m^?2. The monthly average total biomass ranged between 560 ± 37 and 646 ± 32 g dry weight (DW)?m^?2. Total biomass varied significantly among stations and sampling times but did not show seasonal variation. Leaf plastochrone intervals varied seasonally, with an annual average of 28–30 days. Leaf productivity was highest in August (2.61 g DW?m^?2?day^?1) and lowest in February (0.35 g DW?m^?2?day^?1). Annual belowground primary production varied from 263 to 311 g DW?m^?2?year^?1. Annual leaf production was approximately equal for all the stations (from 264 to 289 g DW?m^?2?year^?1). Variability in water temperature, air temperature and salinity explained the annual variability in biological characteristics. Changes in belowground and total biomass were not correlated with seasonal variability in the environmental parameters monitored. Additionally, a literature review was conducted of C. nodosa features at other Mediterranean sites, encompassing 30 studies from 1985 to 2014.     

Methane flux dynamics in relation to methanogenic and methanotrophic populations in the soil of Indian Sundarban mangroves

The dynamics of methane (CH₄) flux in relation to populations of methanogenic and methanotrophic bacteria was studied under the different biophysical conditions of the Indian Sundarban mangrove ecosystem. Soil depth profile analysis (up to 60 cm) in the lower littoral zone (LLZ) revealed that a methanogenic population of 6.45 ± 0.19 × 10⁴ cells/g dry weight (dry wt) of soil accounted for a CH₄ production rate of 6.23 ± 3.53 × 10³ µmol m^?2 day^?1, whereas in the surface soil, a methanogenic population of 3.34 ± 0.37 × 10⁴ cells/g dry wt of soil accounted for a CH₄ production rate of 31.6 ± 0.57 µmol m^?2 day^?1. The CH₄ oxidation rate at 60 cm depth in the LLZ was 24.42 ± 1.28 µmol m^?2 day^?1, with an average methanotrophic population of 1.33 ± 0.43 × 10⁴ cells/g dry wt of soil, whereas in the surface soil, the oxidation rate and average population were 3.38 ± 1.43 × 10³ µmol m^?2 day^?1 and 12.80 ± 2.54 × 10⁴ cells/g dry wt of soil, respectively. A similar soil profile in terms of CH₄ dynamics and the populations of methanogenic and methanotrophic bacteria was found in the mid‐littoral and upper littoral zones of the studied area. The results demonstrate that most of the produced CH₄ (approximately 60%) was oxidized by methanotrophic bacteria present in the soil, thus revealing their principal role in regulating the CH₄ flux from this unique ecosystem.     

Growth rates and ecology of coralline rhodoliths from the Ras Ghamila back reef lagoon,Red Sea

Rhodoliths are important marine carbonate producers that provide habitat for several marine organisms, and are threatened by ongoing global climate change. Meter‐sized sedimentary patches rich in living rhodoliths, interspersed among corals, were discovered in the back reef of Ras Ghamila lagoon, Southern Sinai, at less than 1 m water depth. In this shallow and relatively sheltered subtropical environment, rhodoliths were found to be monospecific or oligospecific, spheroidal, 3.5 to 9.4 cm in maximum diameter, with warty/lumpy or fruticose (protuberance degree IV) growth forms, and corresponded to the unattached branches or praline type. They grew in bright light under seasonal, moderate, wind‐driven water motion. The dominant rhodolith‐forming species recorded were: Lithophyllum kotschyanum, Porolithon onkodes, Hydrolithon sp. and three species of Neogoniolithon: Neogoniolithon fosliei, Neogoniolithon brassica‐florida, and an undescribed species noted in the text as Neogoniolithon sp. A total of 38 Alizarin‐stained rhodoliths was released in the field and collected after 1 year. They showed different banding patterns (alternating long and short cells) that revealed seasonal growth, with the lowest rates occurring in winter for all species, and an additional summer growth slackening in Neogoniolithon fosliei. Lithophyllum kotschyanum presented evidence of occasional growth cessation, possibly due to temporary burial. The observed annual growth rate of rhodoliths was unrelated to their size. The mean accretion rates were 1.08 mm · year^?1 in L. kotschyanum, 0.75 mm · year^?1 in P. onkodes, 0.49 mm · year^?1 in Hydrolithon sp., 0.85 mm mm · year^?1 in N. fosliei, 0.63 mm · year^?1 in N. brassica‐florida and 0.57 mm · year^?1 in Neogoniolithon sp. The annual mean marginal elongation rate for these taxa was respectively 8.74, 13.92, 3.59, 9.40 and 9.25 mm · year^?1, with the exception of Neogoniolithon sp., for which this parameter was not recorded. Maximum marginal elongation occurred in P. onkodes pointing out its greater ability as a space competitor in comparison with the other rhodolith species. The highest accretion rate and common presence of L. kotschyanum indicate its importance as carbonate producer in tropical reef.     

Yield and catch changes in a Mediterranean small tuna trap: a warming change effect?

Since the 17th century, the Tonnarella of Camogli, a small tuna trap, has been used to catch pelagic fish along the western coast of the Portofino Promontory (Ligurian Sea, Northwestern Mediterranean). The availability of long‐term datasets on fish yields (1950–1974 and 1996–2011), with information related to the seawater temperatures and the North Atlantic Oscillation (NAO), has allowed us to study the qualitative and quantitative changes in fish yields in the last decade and the possible relationships with the seasonal anomalies of temperature that have occurred in the Ligurian Sea. In 1950–1974, yields remained relatively constant over time (average of 35.6 ± 8.7 t·year^?1). From 1996 through 2011, yields were high (42.9 ± 15.9 t·year^?1) but inconsistent with strong annual variability in catches. The primary catches are Seriola dumerili, Auxis rochei, Trachurus spp. and Sarda sarda. Changes in species composition have occurred as well: S. dumerili, Sardinella sp. and Belone belone have appeared recently. Moreover, a significant decrease in the boreal scombroid (Scomber scombrus) and an increase of warm‐temperate carangids and other typically Southern Mediterranean species such as Coryphaena hippurus and Sphyraena viridensis, appear to be linked to the warming of the surface water layer, particularly evident in the Ligurian Sea, for the last 10 years. The analysis of this kind of trend may be a powerful tool for assessing structural changes of the pelagic fish community in the Ligurian Sea (Northwestern Mediterranean).     

Nitrification and the enumeration of marine nitrifying bacteria in a closed prawn-culture system

Nitrification in a closed prawn-culture system was well established and followed the classical oxidation sequence of ammonia via nitrite to nitrate. Ammonia levels were in the range 4,8–68,7 μg-at N·?^?1 nitrite 0,15–891 μg-at N·?^?1 and nitrate approached a maximum of 9 898 μg-at N·?^?1 after 22 weeks. Marine nitrifying bacteria were enumerated by the most probable number (MPN) technique. The maximum MPN estimate of either group of nitrifying bacteria in the filter was 1,73 × 10⁷·cm^?3 while the maximum MPN estimate of their counterparts in the culture water was approximately 500 times lower. To establish mean incubation times for the accurate enumeration of nitrifying bacteria, incubations were carried out over a period of 130 days. Maximum estimates of MPN of ammonia-oxidizing bacteria were obtained after an incubation period of 20 days with a mean of 15 days. Nitrite-oxidizing bacteria required a maximum of 65 days with a mean incubation period of 30,3 days.     

Anchovy spawning in relation to the biomass and the replenishment rate of their copepod prey on the western Agulhas Bank

Anchovy biomass and copepod standing stocks and growth rates on the Agulhas Bank were compared during the peak spawning period (November) in 1988 and 1989. In 1988, copepod biomass over the western Agulhas Bank was low (1,0 g dry mass·m^?2) relative to anchovy biomass there (14,7 g dry mass·m^?2). In November 1989 in the same area, fish biomass was much lower (5,7 g dry mass·m^?2), following a recruitment failure, and copepod biomass was higher (2,4 g dry mass·m^?2), possibly as a result of lesser predation by anchovy. By contrast, the eastern Agulhas Bank had a larger biomass of copepods (4–6 g dry mass·^?2) and a lower biomass of anchovy during both years. Knowing, from laboratory studies, that a prey biomass of 0,78 g·m^?2 is required for fish to obtain their daily maintenance ration, it is suggested that spawning on the western Agulhas Bank was food-limited in 1988. Copepods on the western Bank may be replaced by local growth or transport from the eastern Bank. Growth rates of copepods on the western Bank were 10–50 per cent of maximum in 1988, but total production (c. 100 mg dry mass·m^?2·day^?1) was low, primarily because biomass was low and less than the rate of consumption by anchovy (243 mg copepod dry mass·m^?2·day^?1). On the eastern Bank, copepod production exceeded anchovy consumption and it is concluded that the flux of copepod biomass onto the western Bank may be as important as local growth in replenishing copepod stocks there. Feeding conditions for anchovy on the western Agulhas Bank are often marginal compared to the situation on the eastern Bank, and it is suggested that the selection of the western Bank as the major spawning area is related more to the success of transport and survival of eggs and larvae on the West Coast recruiting grounds than to feeding conditions per se.     

Increased predation of juvenile European spiny lobster (Palinurus elephas) in a marine protected area

One of the aims of Mediterranean marine protected areas (MPAs) is to increase populations of exploited species, such as the European spiny lobster (Palinurus elephas), which is considered a key species for its commercial and ecological value. Monitoring of temporal patterns in abundance of early benthic stages of P. elephas indicated that predation may be higher inside the Medes Islands MPA relative to adjacent control sites. Tethering experiments were performed to test whether predation rates actually differed within and outside the MPA. Relative mortality of recently‐settled juveniles inside the MPA was much higher than in control sites in adjacent non‐protected areas. Treatments with and without shelter indicated that predation on recently‐settled juvenile spiny lobsters was moderated by the availability of suitable shelter. The decline or absence of fish predators in the fished area may be the reason why juvenile lobsters outside the MPA experience lower predation than within the MPA.     

Skeletal linear extension rates of the foliose scleractinian coral Merulina ampliata (Ellis & Solander, 1786) in a turbid environment

Skeletal linear extension rates of a foliaceous, IndoPacific, skiophilous, heterotrophic, scleractinian Merulina ampliata (Ellis & Solander 1786) were obtained along a sediment/nutrient load gradient at the southern islands of Singapore. Measurements were made during November 1999– November 2000 using the alizarin red‐S staining technique. Suspended particulate matter concentration (r²_adj = 0.76), turbidity (r²_adj = 0.59), the organic content of suspended sediments (r² = 0.50), and nitrite‐nitrate concentration (r²_adj = 0.50) were significant predictors of the skeletal linear extension rate of M. ampliata. Maximum linear extension growth rates of M. ampliata (mean ± SD: 1.43 ± 0.67–3.26 ± 0.59 cm·year^?1) were comparable to 15‐year‐old accounts at the same research sites, indicating adaptation to low‐light, high‐sediment waters.