Spatial and temporal pattern in seagrass community composition and productivity in south Florida

We document the distribution and abundance of seagrasses, as well as the intra-annual temporal patterns in the abundance of seagrasses and the productivity of the nearshore dominant seagrass (Thalassia testudinum) in the south Florida region. At least one species of seagrass was present at 80.8% of 874 randomly chosen mapping sites, delimiting 12,800 km² of seagrass beds in the 17,000-km² survey area. Halophila decipiens had the greatest range in the study area; it was found to occur over 7,500 km². The range of T. testudinum was almost as extensive (6,400 km²), followed by Syringodium filiforme (4,400 km²), Halodule wrightii (3,000 km²) and Halophila engelmanni (50 km²). The seasonal maxima of standing crop was about 32% higher than the yearly mean. The productivity of T. testudinum was both temporally and spatially variable. Yearly mean areal productivity averaged 0.70 g m⁻²day⁻¹, with a range of 0.05–3.29 g m⁻² day⁻¹. Specific productivity ranged between 3.2 and 34.2 mg g⁻¹ day⁻¹, with a mean of 18.3 mg g⁻¹ day⁻¹. Annual peaks in specific productivity occurred in August, and minima in February. Integrating the standing crop for the study area gives an estimate of 1.4 × 1011 g T. testudinum and 3.6 × 10¹⁰ g S. filiforme, which translate to a yearly production of 9.4 × 10¹¹ g T. testudinum leaves and 2.4 × 10¹¹ g S. filiforme leaves. We assessed the efficacy of rapid visual surveys for estimating abundance of seagrasses in south Florida by comparing these results to measures of leaf biomass for T. testudinum and S. filiforme. Our rapid visual surveys proved useful for quantifying seagrass abundance, and the data presented in this paper serve as a benchmark against which future change in the system can be quantified. Received: 30 January 2000 / Accepted: 24 July 2000     

Light and carbon balance in the seagrass Thalassia testudinum : evaluation of current production models

The production dynamics and carbon balance of Thalassia testudinum in the lower Laguna Madre, Texas, USA, were examined during the 1995 summer period based on in situ photosynthesis vs irradiance (PI) measurements and continuous measurements of underwater photon-flux density (PFD). The validity of applying the H _sat model, used to calculate production for Zostera marina as the product of the maximum rate of photosynthesis (P _max) and daily hours of saturating irradiance (H _sat) was assessed for T. testudinum by comparison with integrated production estimates derived through numerical integration. Gross integrated production values were combined with dark-respiration measurements of photosynthetic (PS) and non-photosynthetic (NPS) tissues and areal biomass to generate daily whole-plant carbon balance. Production and whole-plant carbon balance are discussed in relation to surface and underwater PFD measurements, biomass and other physical and chemical parameters collected during a 1 yr period from January to December 1995. The H _sat model significantly underestimated production during all summer months, averaging 70% of integrated production over the entire study period. Gross integrated production ranged between 11.5 mg C g⁻¹ leaf dry wt d⁻¹ in June (during a period of unseasonably low PFDs caused by a drift-alga mat covering the seagrass bed) to 26.7 mg C g⁻¹ leaf dry wt d⁻¹ in July. Modeled net carbon gain was highest in July at 454 mg C m⁻² d⁻¹ (1.4 g dry wt m⁻² d⁻¹), sufficient to account for measured rates of leaf production in the study area and representative of T. testudinum populations of low productivity. During part of the summer period, however, the population was in negative carbon balance. The relatively low productivity of this population and the periods of negative carbon balance are attributed to low net photosynthesis:dark respiration (P _net:R _d) ratios, sporadic low-light periods, the small fraction of PS tissue relative to whole-plant biomass (5 to 13%) and nutrient limitation. Production models are sensitive to both light availability and the proportion of PS tissue supporting NPS biomass as reflected in whole-plant P _net:R _d ratios. Received: 13 August 1997 / Accepted: 6 March 1998     

In situ net primary productivity and photosynthesis of Antarctic sea ice algal, phytoplankton and benthic algal communities

Primary production at Antarctic coastal sites is contributed from sea ice algae, phytoplankton and benthic algae. Oxygen microelectrodes were used to estimate sea ice and benthic primary production at several sites around Casey, a coastal area in eastern Antarctica. Maximum oxygen export from sea ice was 0.95 mmol O₂ m⁻² h⁻¹ (~11.7 mg C m⁻² h⁻¹) while from the sediment it was 6.08 mmol O₂ m⁻² h⁻¹ (~70.8 mg C m⁻² h⁻¹). When the ice was present O₂ export from the benthos was either low or negative. Sea ice algae assimilation rates were up to 3.77 mg C (mg Chl-a)⁻¹ h⁻¹ while those from the benthos were up to 1.53 mg C (mg Chl-a)⁻¹ h⁻¹. The contribution of the major components of primary productivity was assessed using fluorometric techniques. When the ice was present approximately 55–65% of total daily primary production occurred in the sea ice with the remainder unequally partitioned between the sediment and the water column. When the ice was absent, the benthos contributed nearly 90% of the primary production.     

The tunicate Salpa thompsoni ecology in the Southern Ocean. I. Distribution, biomass, demography and feeding ecophysiology

Distribution, density, and feeding dynamics of the pelagic tunicate Salpa thompsoni have been investigated during the expedition ANTARKTIS XVIII/5b to the Eastern Bellingshausen Sea on board RV Polarstern in April 2001. This expedition was the German contribution to the field campaign of the Southern Ocean Global Ocean Ecosystems Dynamics Study (SO-GLOBEC). Salps were found at 31% of all RMT-8 and Bongo stations. Their densities in the RMT-8 samples were low and did not exceed 4.8 ind m⁻² and 7.4 mg C m⁻². However, maximum salp densities sampled with the Bongo net reached 56 ind m⁻² and 341 mg C m⁻². A bimodal salp length frequency distribution was recorded over the shelf, and suggested two recent budding events. This was also confirmed by the developmental stage composition of solitary forms. Ingestion rates of aggregate forms increased from 2.8 to 13.9 μg (pig) ind⁻¹ day⁻¹ or from 0.25 to 2.38 mg C ind⁻¹ day⁻¹ in salps from 10 to 40 mm oral-atrial length, accounting for 25–75% of body carbon per day. Faecal pellet production rates were on average 0.08 pellet ind⁻¹ h⁻¹ with a pronounced diel pattern. Daily individual egestion rates in 13 and 30 mm aggregates ranged from 0.6 to 4.8 μg (pig) day⁻¹ or from 164 to 239 μg C day⁻¹. Assimilation efficiency ranged from 73 to 90% and from 65 to 76% in 13 and 30 mm aggregates, respectively. S. thompsoni exhibited similar ingestion and egestion rates previously estimated for low Antarctic (~50°S) habitats. It has been suggested that the salp population was able to develop in the Eastern Bellingshausen Sea due to an intrusion into the area of the warm Upper Circumpolar Deep Water     

Defecation by Salpa thompsoni and its contribution to vertical flux in the Southern Ocean

Measurements of the defecation rate of Salpa thompsoni were made at several stations during two cruises west of the Antarctic Peninsula in 2004 and 2006. Rates were quantified in terms of number of pellets, pigment, carbon and nitrogen for a wide size range of both aggregate and solitary salps. Measured defecation rates were constant over several hours when salps were held at near-surface conditions from which they had been collected. The defecation rate per salp increased with both salp size and the ambient level of particulate organic matter (POM) in the upper water column. The weight-specific defecation rate ranged between 0.5 and 6% day⁻¹ of salp body carbon, depending on the concentration of available particulate matter in the water. Carbon defecation rates were applied to biomass estimates of S. thompsoni to calculate daily carbon defecation rates for the populations sampled during the two cruises. Dense salp populations of over 400 mg C m⁻² were calculated to produce about 20 mg C m⁻² day⁻¹, comparable to other major sources of vertical flux of organic material in the Southern Ocean. Measured sinking rates for salp fecal pellets indicated that the majority of this organic material could reach deep sediments within a few days, providing a fast and direct pathway for carbon to the deep ocean.     

Phytoplankton production patterns in Massachusetts Bay and the absence of the 1998 winter–spring bloom

The seasonal productivity cycle and factors controlling annual variation in the timing and magnitude of the winter–spring bloom were examined for several locations (range: 42°20.35′–42°26.63′N; 70°44.19′–70°56.52′W) in Boston Harbor and Massachusetts Bay, USA, from 1995 to 1999, and compared with earlier published data (1992–1994). Primary productivity (mg C m⁻² day⁻¹) in Massachusetts Bay from 1995 to 1999 was generally characterized by a well-developed winter–spring bloom of several weeks duration, high but variable production during the summer, and a prominent fall bloom. The bulk of production (mg C m⁻³ day⁻¹) typically occurred in the upper 15 m of the water column. At a nearby Boston Harbor station a gradual pattern of increasing areal production from winter through summer was more typical, with the bulk of production restricted to the upper 5 m. Annual productivity in Massachusetts Bay and Boston Harbor ranged from a low of 160 g C m⁻² year⁻¹ to a high of 787 g C m⁻² year⁻¹ from 1992 to 1999. Mean annual productivity was higher (mean=525 g C m⁻² year⁻¹) and more variable near the harbor entrance than in western Massachusetts Bay. At the harbor station productivity varied more than 3.5-fold (CV=40%) over an 8 year sampling period. Average annual productivity (305–419 g C m⁻² year⁻¹) and variability around the means (CV=25–27%) were lower at both the outer nearfield and central nearfield regions of Massachusetts Bay. Annual productivity in 1998 was unusually low at all three sites (<220 g C m⁻² year⁻¹) due to the absence of a winter–spring phytoplankton bloom. Potential factors influencing the occurrence of a spring bloom were investigated. Incident irradiance during the winter–spring period was not significantly different (P > 0.05) among years (1995–1999). The mean photic depth during the bloom period was significantly deeper (P < 0.05) in 1998, signifying greater light availability with depth. Nutrients were also in abundance during the winter–spring of 1998 with stratified conditions not observed until May. In general, the magnitude of the winter–spring bloom in Massachusetts Bay from 1995 to 1999 was significantly correlated with winter water temperature (r ²=0.78) and zooplankton abundance (r ²=0.74) over the bloom period (typically February–April). The absence of the 1998 bloom was associated with higher than average water temperature and elevated levels of zooplankton abundance just prior to, and during, the peak winter–spring bloom period. Received: 3 July 2000 / Accepted: 6 December 2000     

Life cycle of <Emphasis Type="Italic">Oithona</Emphasis> <Emphasis Type="Italic">similis</Emphasis> (Copepoda: Cyclopoida) in Kola Bay (Barents Sea)

The annual population dynamics (nauplii, old copepodites CIV–CV and adults) and seasonal variations in reproductive parameters of the cyclopoid copepod Oithona similis were investigated on the basis of the data 1999–2006 in Kola Bay, a large subarctic fjord in the Barents Sea. Population density of O. similis ranged from 110 to 9,630 ind m⁻³ and averaged 1,020 ± 336 ind m⁻³. The relative abundance of adults was high during winter (~60%). At the end of winter (mid-March), the population included a large percentage of later-stage copepodites (stage CIV 23% and stage CV 57%). There were two periods of mass spawning, in late June and September. Autumn and summer generations strongly differed in abundance, average prosome length (PL), clutch size (CS), egg diameter (D), egg production rates (EPR and SEPR) and female secondary production. Average PL decreased with increasing water temperature, while D and CS were strongly correlated with PL but unaffected by temperature. Annual average EPR and SEPR were 0.55 ± 0.18 eggs female⁻¹ day⁻¹ and 0.0011 ± 0.003 day⁻¹, respectively. Female secondary production averaged 0.8 ± 0.3 μg C m⁻³ day⁻¹ (range 0.001–3.58). There were positive relationships between abundance, EPR, SEPR, production and water temperatures. Reproductive parameters appeared to be controlled by hydrological factors and food conditions.     

Life cycle of <Emphasis Type="Italic">Pseudocalanus acuspes</Emphasis> Giesbrecht (Copepoda,Calanoida) in the Central Baltic Sea: II. Reproduction,growth and secondary production

The population dynamics of Pseudocalanus acuspes in the Central Baltic Sea were studied from March 2002 to May 2003 on a monthly basis. All stages were present year round with a stage shift from nauplii to older copepodite stages over the course of the year. Biomass, estimated from prosome length, peaked between May and September with maximum recorded values of 594 and 855 mg C m⁻² in May 2002 and 2003, respectively. Differences in biomass between stations up to a factor of 20 were observed especially in April/May and October. Mean egg production rate (EPR) showed a seasonal course and was highest in April 2002 and 2003 with 3.6 and 2.1 eggs f⁻¹ day⁻¹, respectively, corresponding to a mean weight-specific egg production rate (SEPR) of 0.13 and 0.04. Egg production seems to be limited by food from May on. Stage durations determined from moulting experiments turned out to be extremely long. Maximum growth rates based on stage durations of 15–25 days at 4°C in May and July 2003 amounted for 0.03–0.05 day⁻¹ in CI-CIV. Comparing these rates with rates derived from temperature–development relationships for P. acuspes from the literature resulted in five times higher growth rates for the latter case. Secondary production reached values up to 9.1 mg C m⁻² day⁻¹ (method for continuously reproducing populations) and 10.5 mg C m⁻² day⁻¹ (increment summation).     

Population dynamics of Eudendrium racemosum (Cnidaria, Hydrozoa) from the North Adriatic Sea

Benthic suspension feeders in shallow waters develop in relation to the food availability and the variation of physical parameters giving rise to complex communities that act as a control factor on the plankton biomass. The aim of the work is to establish the role of the hydrozoan Eudendrium racemosum in the energy transfer from the plankton to the benthos in marine food chains of the North Adriatic Sea. This study highlighted that the hydroid biomass changed over time in relation to temperature and irradiance, and the highest abundance was observed during summer with about 400,000 polyps m⁻² (about 19 g C m⁻²). The population suffered an evident summer decrease in relation to a peak of abundance of its predator, the nudibranch Cratena peregrina, whose adult specimens were able to eat up to 500 polyps day⁻¹ and reached an abundance of 10 individuals m⁻². The gut content analysis revealed that the hydroid diet was based on larvae of other benthic animals, especially bivalves and that the amount of ingested preys changed during the year with a peak in summer when it was estimated an average predation rate of 13.7 mg C m⁻² day⁻¹. In July, bivalves represented over 60 % of the captured items and about 18 mg C m⁻² day⁻¹. Values of biomass of E. racemosum are the highest ever recorded in the Mediterranean Sea, probably supported by the eutrophic conditions of the North Adriatic Sea. Moreover, our data suggest that settling bivalves provide the greater part of the energetic demand of E. racemosum.     

Seafloor ecosystem functioning: the importance of organic matter priming

Organic matter (OM) remineralization may be considered a key function of the benthic compartment of marine ecosystems and in this study we investigated if the input of labile organic carbon alters mineralization of indigenous sediment OM (OM priming). Using ¹³C-enriched diatoms as labile tracer carbon, we examined shallow-water sediments (surface and subsurface layers) containing organic carbon of different reactivity under oxic versus anoxic conditions. The background OM decomposition rates of the sediment used ranged from 0.08 to 0.44 μmol C ml_ws⁻¹ day⁻¹. Algal OM additions induced enhanced levels of background remineralization (priming) up to 31% and these measured excess fluxes were similar to mineralization of the added highly degradable tracer algal carbon. This suggests that OM priming may be important in marine sediments.     

Feeding of Clausocalanids (Calanoida,Copepoda) on naturally occurring particles in the northern Gulf of Aqaba (Red Sea)

A total of 12 feeding experiments were conducted in the northern Gulf of Aqaba during spring (March/April) and autumn (September/October) 2002 at the Marine Science Station (MSS) in Aqaba. Females of three species of clausocalanids were selected: Clausocalanus farrani, C. furcatus and Ctenocalanus vanus. Natural occurring particle (NOP) larger than 5 μm were investigated as food source. The ambient chlorophyll a concentration at sampling depth (∼70 m) ranged between 0.15 and 1.00 μg chl a l⁻¹ and NOP concentrations ranged between 1.78 and 14.0 × 10³ cells l⁻¹ during the sampling periods. The division of particles into five size classes (5–10, 10–20, 20–50, 50–100 and >100 μm) revealed that most of the particles were found in the size classes below 50 μm (81–98%), while most of the natural occurring carbon (NOC) was concentrated in the size classes larger than 20 μm (70–95%). Ingestion rates were food density dependent rather than size dependent ranging between 0.02 and 1.65 × 10³ NOP ind⁻¹ day⁻¹ and 0.01 and 0.41 μg NOC ind⁻¹ day⁻¹, respectively, equivalent to a body carbon (BC) uptake between 0.4 and 51.8% BC day⁻¹. The share of the size classes to the total ingestion resembled in most cases the size class composition of the natural particle community.     

Effect of nutrient enrichment in the field on the biomass, growth and calcification of the giant clam Tridacna maxima

Nutrients were added separately and combined to an initial concentration of 10 μM (ammonium) and/or 2 μM (phosphate) in a series of experiments carried out with the giant clam Tridacna maxima at 12 microatolls in One Tree Island lagoon, Great Barrier Reef, Australia (ENCORE Project). These nutrient concentrations remained for 2 to 3 h before returning to natural levels. The additions were made every low tide (twice per day) over 13 and 12 mo periods for the first and second phase of the experiment, respectively. The nutrients did not change the wet tissue weight of the clams, host C:N ratio, protein content of the mantle, calcification rates or growth rates. However, ammonium (N) enrichment alone significantly increased the total population density of the algal symbiont (Symbiodinium sp.: C = 3.6 · 10⁸ cell clam⁻¹, N = 6.6 · 10⁸ cell clam⁻¹, P = 5.7 · 10⁸ cell clam⁻¹, N + P = 5.7 · 10⁸ cell clam⁻¹; and C = 4.1 · 10⁸ cell clam⁻¹, N = 5.1 · 10⁸ cell clam⁻¹, P = 4.7 · 10⁸ cell clam⁻¹, N + P = 4.5 · 10⁸ cell clam⁻¹, at the end of the first and second phases of the experiment, respectively), although no differences in the mitotic index of these populations were detected. The total chlorophyll a (chl a) content per clam but not chlorophyll a per cell also increased with ammonium addition (C = 7.0 mg chl a clam⁻¹, N = 13.1 mg chl a clam⁻¹, P = 12.9 mg chl a clam⁻¹, N + P = 11.8 mg chl a clam⁻¹; and C = 8.8 mg chl a clam⁻¹, N = 12.8 mg chl a clam⁻¹; P = 11.2 mg chl a clam⁻¹, N + P = 11.3 mg chl a clam⁻¹, at the end of the first and second phases of the experiment, respectively). The response of clams to nutrient enrichment was quantitatively small, but indicated that small changes in inorganic nutrient levels affect the clam–zooxanthellae association. Received: 2 June 1997 / Accepted: 9 June 1997     

Seasonal variations in the growth rates of euphausiids (<Emphasis Type="Italic">Thysanoessa inermis</Emphasis>, <Emphasis Type="Italic">T. spinifera</Emphasis>, and <Emphasis Type="Italic">Euphausia pacifica</Emphasis>) from the northern Gulf of Alaska

The euphausiids Thysanoessa inermis (Kroyer 1846), Thysanoessa spinifera (Holmes 1900), and Euphausia pacifica (Hansen 1911) are key pelagic grazers and also important prey for many commercial fish species in the Gulf of Alaska (GOA). To understand the role of the euphausiids in material flows in this ecosystem their growth rates were examined using the instantaneous growth rate (IGR) technique on the northern GOA shelf from March through October in 2001–2004. The highest mean molting increments (over 5% of uropod length increase per molt) were observed during the phytoplankton bloom on the inner shelf in late spring for coastal T. inermis, and on the outer shelf in summer for T. spinifera and more oceanic E. pacifica, suggesting tight coupling with food availability. The molting rates were higher in summer and lower in spring, for all species and were strongly influenced by temperature. Mean inter-molt periods calculated from the molting rates, ranged from 11 days at 5°C to 6 days at 8°C, and were in agreement with those measured directly during long-term laboratory incubations. Growth rate estimates depended on euphausiid size, and were close to 0 in early spring, reaching maximum values in May (0.123 mm day⁻¹ or 0.023 day⁻¹ for T. inermis) and July (0.091 mm day⁻¹ or 0.031 day⁻¹ for T. spinifera). The growth rates for E. pacifica remained below 0.07 mm day⁻¹ (0.016 day⁻¹) throughout the season. The relationship between T. inermis weight specific growth rate (adjusted to 5°C) and ambient chlorophyll-a concentration fit a Michaelis–Menten curve (r ² = 0.48) with food saturated growth rate of 0.032 day⁻¹ with half saturation occurring at 1.65 mg chl-a m⁻³, but such relationships were not significant for T. spinifera or E. pacifica.     

Phytoplankton growth and microzooplankton grazing rates in a restricted Mediterranean lagoon (Bizerte Lagoon,Tunisia)

Phytoplankton growth and microzooplankton grazing were investigated in the restricted Bizerte Lagoon in 2002 and 2004. The 2002 study, carried out at one station from January to October, showed significant seasonal variations in phytoplankton dynamics. High growth rates (0.9–1.04 day⁻¹), chlorophyll a (Chl a) concentrations (6.6–6.8 μg l⁻¹) and carbon biomass (392–398 μg C l⁻¹) were recorded in summer (July), when several chain-forming diatoms had intensively proliferated and dominated the carbon biomass (74%). In 2004, four stations were studied during July, a period also characterized by the high proliferation of several diatoms that made up 70% of the algal carbon biomass. In 2004, growth rates (0.34–0.45 day⁻¹) and biomass of algae (2.9–5.4 μg Chl a l⁻¹ and 209–260 μg C l⁻¹) were low, which may be related to the lower nutrient concentrations recorded in 2004. Microzooplankton >5 μm were mainly composed of heterotrophic dinoflagellates and ciliates. Microzooplankton biomass peaked during summer (2002 320–329, 2004 246–361 μg C l⁻¹), in response to the enhanced phytoplankton biomass and production. The grazer biomass was dominated by ciliates (71–76%) in July 2002 and by heterotrophic dinoflagellates (52–67%) in July 2004. Throughout the year and at different stations, microzooplankton grazed actively on phytoplankton, removing 26–58% of the Chl a and 57-84% of the primary production. In 2002, the highest grazing impact was observed on the large algae (>10 μm) during the period of diatom dominance. These results have a significant implication for carbon export to depth. Indeed, the recycling of most of the diatom production by the microbial food web in the upper water column would reduce the flux of material to the seafloor. This should be considered when modeling the carbon cycling in coastal environments and under conditions of diatom dominance. During both studies, ciliates had higher growth rates (0.5–1.5 day⁻¹) and a higher carbon demand (165–470 μg C l⁻¹ day⁻¹) than dinoflagellates (0.1–0.5 day⁻¹, 33–290 μg C l⁻¹ day⁻¹). Moreover, when grazer biomass was dominated by ciliates (in July 2002), herbivory accounted for 71–80% of the C ingested by microzooplankton while it accounted only for 14–23% when dinoflagellates dominated the grazer biomass (in July 2004). These results suggest that, in contrast to findings from open coastal waters, ciliate species of the restricted Bizerte Lagoon were more vigorous grazers of the large algae (diatoms) than were dinoflagellates.     

Production and biomass accumulation of periphytic diatoms growing on glass slides during a 1-year cycle in a subtropical estuarine environment (Bay of Paranaguá, southern Brazil)

Production rates, chlorophyll concentrations and general composition of periphytic diatom communities growing on glass slides were studied in relation to environmental parameters during one seasonal cycle in the Bay of Paranaguá, southern Brazil. Slides were routinely submersed at 1, 2 and 3 m depth and recovered weekly for microscopic examinations, analyses of chlorophyll, cell counts and in situ photosynthetic incubations using the Winkler titration method. Water samples were also collected at surface and bottom layers for determinations of temperature, salinity, nutrients and chlorophyll in the water. The periphytic community was mainly formed by epipelic and epipsammic species, dominated by Navicula phyllepta, Cylindrotheca closterium, Navicula spp. and Amphora sp. Weekly chlorophyll a and cell accumulations on slides varied from <1–32 mg m⁻² and up to 31 × 10⁸cells m⁻², respectively. Photosynthetic rates varied from <1 to 35 mg oxygen mg chlorophyll a ⁻¹ h⁻¹, with higher values in summer. Daily production varied from 5 to 3,600 mg oxygen m⁻² day⁻¹ (<0.01–1.4 g carbon m⁻² day⁻¹). Multiple regression analysis revealed that vertical differences in light conditions and grazing pressure jointly affected the influence of temperature on the seasonal patterns of cell densities and chlorophyll concentrations according to depth. Received: 27 April 2000 / Accepted: 16 August 2000     

Are monoalgal diets inferior to plurialgal diets to maximize cultivation of the calanoid copepod Temora stylifera?

Temora stylifera adult copepods were fed with four different monoalgal diets and six combinations of the same cultures for 15 days. Fecundity, hatching success, number of cannibalized embryos, fecal pellet production, adult mortality and naupliar recruitment were compared, in order to find the best diet for this species. Phytoplankton species tested were Prorocentrum minimum (PRO); Isochrysis galbana (ISO); Tetraselmis suecica (TETRA) and Rhodomonas baltica (RHO) which were supplied alone or in different combinations and at various concentrations ranging from a minimum of 1 mg C L⁻¹ day⁻¹ to a maximum of 66 mg C L⁻¹ day⁻¹. Of the ten diets tested, ISO was the worst and was unable to sustain egg production and adult survival possibly because adults were unable to ingest this alga due to its small size. TETRA was also a poor food since it negatively impacted egg production and adult survival, as well as egg hatching success, possibly due to the lack of essential compounds necessary for optimal embryogenesis. RHO and PRO were the best foods inducing highest egg production, hatching success and naupliar recruitment. Even if mean egg production rates were similar to those obtained with some mixed diets, carbon intake concentrations with mixed diets were from 3 to 33 and from 6.6 to 66 times higher than with RHO and PRO given alone, respectively. Mixed diets of ISO and PRO, especially when supplied at higher concentrations (66 mg C L⁻¹ day⁻¹), had a negative effect on egg hatching success and adult survival, with a corresponding reduction in naupliar recruitment. On the other hand, mixed diets of TETRA and PRO promoted high naupliar recruitment but values were similar to PRO offered alone. Our results indicate that a good monoalgal diet such as RHO and PRO can be as effective as a mixed diet to sustain the mass cultivation of T. stylifera.     

Food sources used by sediment meiofauna in an intertidal Zostera noltii seagrass bed: a seasonal stable isotope study

In an intertidal Zostera noltii Hornem seagrass bed, food sources used by sediment meiofauna were determined seasonally by comparing stable isotope signatures (δ¹³C, δ¹⁵N) of sources with those of nematodes and copepods. Proportions of different carbon sources used by consumers were estimated using the SIAR mixing model on δ¹³C values. Contrary to δ¹⁵N values, food source mean δ¹³C values encompassed a large range, from −22.1 ‰ (suspended particulate organic matter) to −10.0 ‰ (Z. noltii roots). δ¹³C values of copepods (from −22.3 to −12.3 ‰) showed that they use many food sources (benthic and phytoplanktonic microalgae, Z. noltii matter). Nematode δ¹³C values ranged from −14.6 to −11.4 ‰, indicating a strong role of microphytobenthos and/or Z. noltii matter as carbon sources. The difference of food source uses between copepods and nematodes is discussed in light of source accessibility and availability.     

Epibiosis on cerith shells in a seagrass bed: correlation of shell occupant with epizoite distribution and abundance

The cerith Cerithium atratum (Born 1778) is an abundant gastropod in the seagrass beds at Cabo Frio, Brazil. In order to estimate the ecological importance of cerith shells as a rare hard substratum in the seagrass bed, the abundances of C. atratum and of cerith shells occupied by hermit crabs were quantified. The mean densities of C. atratum and hermit crabs were 1887 and 100 individuals m⁻², respectively, and these provided 0.5 m² shell area m⁻² available for epizoite colonization. The tube-forming polychaete Hydroides plateni (Kinberg 1867) and oyster Ostrea puelchana Orbigny, 1841 were the dominant visible epizoites on inhabited cerith shells. These epizoite populations were compared in order to investigate whether the temporal and spatial patterns in the epibiotic community were related to ecological and behavioral aspects of the occupant species (cerith or hermit crab). Larger cerith shells had a greater abundance of epizoites. Each epizoite showed a preference for a different occupant of the shells (the oyster for C. atratum and the polychaete for cerith shells occupied by hermit crabs). The oyster showed a seasonal pattern in abundance on C. atratum, being more common in fall (March–April). The distribution of the epizoites on the shells depended on the shell occupant species and was probably related to their different foraging activity –C. atratum ploughs half buried through the sediment, while the hermit crab crawls on the sediment surface. In both cases, the activity of the shell occupant was considered to be beneficial to the epizoites, as empty shells and shell fragments did not support a macroepifauna. Received: 1 May 2000 / Accepted: 8 August 2000     

Strong variability in bacterioplankton abundance and production in central and western Bay of Bengal

With large influx of freshwater that decreases sea-surface salinities, weak wind forcing of <10 m s⁻¹ and almost always warm (>28°C) sea-surface temperature that stratifies and shallows the mixed layer leading to low or no nutrient injections into the surface, primary production in Bay of Bengal is reportedly low. As a consequence, the Bay of Bengal is considered as a region of low biological productivity. Along with many biological parameters, bacterioplankton abundance and production were measured in the Bay of Bengal during post monsoon (September–October 2002) along an open ocean transect, in the central Bay (CB, 88°E) and the other transect in the western Bay (WB). The latter representing the coastal influenced shelf/slope waters. Bacterioplankton abundances (<2 × 10⁹cells l⁻¹) were similar to those reported from the HNLC equatorial Pacific and the highly productive northern Arabian Sea. Yet, the thymidine uptake rates along CB (average of 1.46 pM h⁻¹) and WB (average of 1.40 pM h⁻¹) were less than those from the northwestern Indian Ocean. These abundances and uptake rates were higher than those in the oligotrophic northwestern Sargasso Sea (<7 × 10⁸ cells l⁻¹; av 1.0 pM h⁻¹). Concentrations of chlorophyll a (chl a), primary production rates and total organic carbon (TOC) were also measured for a comparison of heterotrophic and autotrophic production. In the WB, bacterioplankton carbon biomass equaled ∼ 95% of chl a carbon than just 31% in the CB. Average bacterial:primary production (BP:PP) ratios accounted for 29% in the CB and 31% in the WB. This is mainly due to lower primary productivity (PP) in the WB (281 mg C m⁻² d⁻¹) than in the CB (306 mg C m⁻² day⁻¹). This study indicates that bacteria–phytoplankton relationship differs in the open (CB) and coastal waters (WB). Higher abundance and contrastingly low bacterial production (BP) in WB may be because of the riverine bacteria, brought in through discharges, becoming dormant and unable to reproduce in salinities of 28 or more psu. Heterotrophic bacteria appear to utilize in situ DOC rather rapidly and their carbon demand is ∼50% of daily primary production. It is also apparent that allochthonous organic matter, in particular in the western Bay, is important for meeting their carbon demand.     

Effects of mussel (Perna canaliculus) biodeposit decomposition on benthic respiration and nutrient fluxes

Suspension-feeding bivalves increase the quantity and quality of sedimenting organic matter through the production of faeces and pseudofaeces that are remineralised in coastal sediments and thus increase sediment oxygen demand and nutrient regeneration. Bivalves are intensively cultivated worldwide; however, no bivalve biodeposit decay rates are available to parameterise models describing the environmental effects of bivalve culture. We examined sediment biogeochemical changes as bivalve biodeposits age by incubating coastal sediments to which we added fresh mussel (Perna canaliculus) biodeposits and measured O₂ and nutrient fluxes as well as sediment characteristics over an 11-day period. Biodeposits elevated organic matter, chlorophyll a, phaeophytin a, organic carbon and nitrogen concentrations in the surface sediments. Sediment oxygen consumption (SOC) increased significantly (P=0.016) by ∼1.5 times to 1,010 μmol m⁻² h⁻¹ immediately after biodeposit addition and remained elevated compared to control cores without additions for the incubation period. This increase is in the range of observed in situ oxygen demand enhancements under mussel farms. To calculate a decay rate for biodeposits in sediments we fitted a first-order G model to the observed increase in SOC. The significant model fit (P=0.001, r ²=0.72) generated a decay rate of 0.16 day⁻¹ (P=0.033, SE=0.05) that corresponds to a half-life time of 4.3 day. This decay rate is 1–2 orders of magnitude higher than published decay rates of coastal sediments without organic enrichment but similar to rates of decaying zooplankton faecal pellets. NH₄⁺ release increased rapidly on the day of biodeposit addition (P=0.013) and reached a maximum of 144 μmol m⁻² h⁻¹ after 5 days which was 3.6 times higher compared to control cores. During this period NH₄⁺ release was significantly (P<0.001 to P=0.043) higher in the cores with biodeposit additions than in control cores.