Benthic Fluxes of Dissolved Inorganic Nitrogen in a Coastal Lagoon of the Northern Adriatic Sea: an Interpretation of Spatial Variability Based on Sediment Features and Infauna Activity

Abstract. Dark respiration rates, dissolved inorganic nitrogen (DIN) fluxes and nitrification rates were measured at two sites in the microtidal Sacca di Goro lagoon in September 2000. DIN fluxes correlated with the biomass of the dominant macrofauna species (the amphipod Corophium spp. at station Giralda and the polychaete Neanthes spp. at station Faro). Respiration (> 6 mmol O₂ m⁻²h⁻¹) and ammonium fluxes (> 80μmol N m⁻²h⁻¹) were higher at station Giralda despite the lower organic matter content (4.5 %) and lower macrofauna biomass (4 g AFDW m⁻²). At both sites ammonium fluxes were significantly correlated with the biomass of the benthic infauna, but Corophium stimulated ammonium NH₄⁺ fluxes 3-fold compared to Neanthes. The amphipod also enhanced nitrification rates (> 300 μmol N m⁻²h⁻¹) due to the high density of its burrows, the higher NH₄⁺ regeneration rates and the enhanced oxygen supply to the bacteria.     

Chlorophyll in Copepod Faecal Pellets: Changes in Pellet Numbers and Pigment Content during a Declining Baltic Spring Bloom

Abstract. Zooplankton stock as well as faecal pellet numbers were monitored over 2 weeks during May in the central Baltic. Considerable changes in concentrations of chlorophyll and its derivates in copepod faecal pellets as well as in surface sediments were found during this period. The maximum concentration of 1.05 ngchl. a faecal pellet^-1, measured on 12 May, decreased by the end of the month to 0.08 ngchl. a faecal pellet^-1. This decrease was positively correlated with the disappearance of intact diatoms inside faeces. A flux of 1.53mgchl. a -m^-2-day^-1 via faecal pellets was calculated for the deep water layer (60–80 m) in mid May. This decreased to 0.005mgchl. a m^-2 day^-1 by the end of May. Chi. a accounted for up to 10 % of total pigments in samples from the top centimetre of the sediment surface. The means of transportation of faecal pellets as well as their function as a food supply to deeper ecosystems are discussed.     

Dispersal of Benthic Meiofauna by Wave and Current Action in Bogue Sound, North Carolina, USA

Abstract. Results from sediment trap experiments in Bogue Sound, North Carolina, indicate that meiofauna from a wide variety of taxa and benthic habitats are regularly suspended in the subtidal water column. Interstitial species are estimated to account for 10–30 % of the suspended meiofauna. Measurements of suspended nematode concentrations, when compared with wind and current velocity records, suggest that in Bogue Sound, shoaling and breaking waves are more important than tidal currents in controlling meiofauna erosion and deposition. Linear regression analysis indicates that 80% (r = 0.907) of the variation in suspended nematode density is correlated with changes in the mean onshore-offshore component of local wind velocity. Nematode turnover associated with spring and summer coastal wind patterns is estimated to be several hundred animals per m²per day. Once suspended, meiofauna may be carried up to 10 km per day by residual currents in the Sound. Although erosion, transport and deposition of benthic nematodes by wave and current action appears to provide an effective means of dispersal along continental coastlines, the high settling velocity of nematodes suspended in Bogue Sound (on the order of 10^-4m s^-1) suggests that net downward flux in shelf and slope waters probably prevents their dispersal across ocean basins by surface currents.     

Occurrence and distribution pattern of Palaemon spp. shrimps in a shallow submarine cave environment: a study case in South‐eastern Italy

The common shrimps of the genus Palaemon are often reported as living in Mediterranean submarine caves. The present study quantifies the distribution pattern of a Palaemon spp. populations throughout 1 year of observations in a shallow submarine cave in South‐eastern Italy, Ionian Sea. The cave was subdivided into six sectors from the entrance towards the inner portion of the ‘blind cave’ and 16 dives (four per season, during both day and night) were performed with SCUBA equipment. The population was estimated in situ using visual census. Four different species of Palaemon were identified. This study has shown that Palaemon spp. assemblages live throughout the year in submarine caves. Moreover, the results suggest submarine caves play an important role in the biology of Palaemon spp. populations, by providing refuge, juvenile recruitment and food resources.     

Colonization of mine tailings by marine invertebrates

An experiment was conducted to determine if a tailings substrate would inhibit recolonization of benthic macrofauna upon closure of a submarine tailings disposal (STD) operation. Trays of defaunated marine sediment, serving as a reference, and trays of tailings from a proposed gold mine were placed at 21 m depth on the ocean floor to allow colonization via settlement from the water column. Trays of reference sediment and tailings, and cores of ambient sediment were collected 9, 17, and 22 months after tray placement. Probable tray effects, which were desirable given the objectives of this study, precluded direct comparison of ecological succession in the tray sediments to the ambient assemblage. The ambient macrofauna assemblage was distinguishable from the reference sediment and tailings assemblages throughout the experiment and displayed more pronounced seasonality. Differences between the reference sediment and tailings assemblages were generally insignificant, including total abundance, total biomass, number of taxa, average size of individuals, numerically dominant taxa, abundance by ecological guilds, and overall community composition. Upon cessation of STD, recolonization of a benthic macrofauna community should not be inhibited by the presence of these tailings as a benthic substrate.     

Nutrients, Chlorophyll a and Phytoplankton in the İskenderun Bay (Northeastern Mediterranean)

Abstract. The monthly changes in chlorophyll a , phytoplankton abundance and nutrient concentrations at two stations, one at the inshore and the other at the deep waters of the northern part of İskenderun Bay, were investigated between 1994 – 1995. The vertical distribution of nutrients and phytoplankton biomass were also studied at the deep station. The concentrations of NO₃+NO₂-N, PO₄-P and SiO₄-Si of surface water at both stations were 0.31 – 1.63 µg-at · l^-1, 0.08 – 0.60 µg-at · l^-1 and 0.50 – 2.7 µg-at · l^-1, respectively. The highest concentrations were measured at the inshore station and clear differences were found between the inshore and deep-water stations. Chlorophyll a concentrations ranged from 0.17 to 2.78 µg · l^-1 and the highest value was measured in March. At the inshore station, which was affected by land run-off, phytoplankton abundance reached the highest value (21,308 cells · l^-1) in October 1995, with a marked dominance of Pseudonitzschia pungens (20,200 cells · l^-1). The nutrient and chlorophyll a concentrations at the inshore station were higher than those at the deep station. One reason for this is the land-based nutrient input into the coastal area here. In spite of these effects, the bay is not eutrophicated because of circulation events in the northeastern Mediterranean.     

Microbial Biomass Dynamics Along a Trophic Gradient at the Atlantic Barrier Reef off Belize (Central America)

Abstract. Recent findings indicate that heterotrophic bacteria and not phytoplankton are the most numerous biomass components even in the euphotic zone of oligotrophic, open oceans. In this study it was hypothesized that the microbial biomass components change within a few hundred meters as oligotrophic water flows across the reef and becomes enriched with nutrients. Along a trophic gradient, four stations at the Atlantic Barrier Reef off Belize (Central America) were sampled for microbial biomass components. Phytoplankton biomass (measured as chlorophyll a) ranged from the most oligotrophic station (St. 1) to the most eutrophic station (St. 4) from 6.9–415.5 μg CI"' (assuming a C:chl a ratio of 30): heterotrophic bacterial biomass increased 4-fold (from 10.1–46.4μg C 1^-1), heterotrophic nanoflagellate (HNAN) biomass increased from 4.6-19ug C 1^-1, and cyanobacteria from 0.9-4.5 μg C-1^-1. Production estimates derived from seawater cultures revealed a 5-fold increase in bacterial production from the oligotrophic station (3.7 ug C 1^-1 d^-1) to the eutrophic St. 4 (17.8ug C-1-d1^-1)- Cyanobacterial production rose from 1.1–3.5ug C-1–d^-1 and HNAN production from 0.65-1.13 μg C-1^-1 -d^-1. While cyanobacteria contributed between 13 and 20% to the autotrophic plankton component in the oligotrophic waters, their contribution dropped to about 1 % at the eutrophic stations.     

Biokarst on Limestone Coasts, Morphogenesis and Sediment Production

Abstract. Biokarst-forms on limestone coasts are developed and arranged according to the bionomic zonation. The development of biokarst is the result of bioerosion, a synergistic effect of biological corrosion by endoliths and biological abrasion by grazers.
The cumulative effect of biogenic carbonate destruction leads to coastal destruction with a resulting highly profiled morphology on the limestone surfaces along the coastal profile. Under the influence of environmental factors a zonation of organisms develops which brings in turn a zonation of erosion rates (0.1-1.1 mm a^-1) resulting in biokarst-forms such as rock holes, rock pools and notches.
Products of bioerosion on limestone coasts are dissolved carbonate (by biological corrosion, 10–30% of the decomposed limestone) and particulate carbonate (by biological abrasion, 70–90% of the decomposed limestone) both of which contribute directly or indirectly to nearshore sedimentation. Size and shape of the bioerosional grains are determined by the boring pattern of the endoliths. The fine-grained sediments (maximum within the fraction 20–63 μm) contribute 3–25 % to the nearshore sediments.
Drastic changes in the biological zonation (like the mass invasion of the sea urchin Paracentrotus lividus in the Northern Adriatic since 1972 which eliminated nearly the entire macrophyte zone) due to unknown factors or pollution can have a profound effect on the bioerosion rates, altering them by as much as a factor of ten.     

Macrofauna Communities in the Eastern Mediterranean Deep Sea

Abstract. During two expeditions with RV ‘Meteor’ in summer 1993 and winter 1997/98 the structural and functional diversity of the benthic system of the highly oligotrophic eastern Mediterranean deep sea was investigated. The macrofauna communities were dominated by polychaetes even at the deepest stations. The fauna at shallow stations was dominated by surface deposit feeders, whereas subsurface deposit feeders and predators generally increased with depth. A high percentage of suspension‐feeding Porifera was found in the Levantine Basin. Mean abundance and number of taxa of both expeditions were significantly correlated to depth and distance to the nearest coast as well as to the total organic carbon (TOC) content in sediments. Numbers of taxa and abundance decreased generally with depth, although lowest numbers were not found at the deepest stations but in the extremely oligotrophic Levantine and Ierapetra Basin. Biomass measured during the second cruise was extremely low in the Ierapetra Basin and comparable to other extreme oligotrophic seas. The significant correlations found for TOC contents and macrofauna with distance to coast during both expeditions apparently reflect the role of hydrographically governed transport of organic matter produced in coastal regions into greater and extreme depths of the Mediterranean Sea. Seasonal differences in macrofauna communities due to seasonal differences in food supply were not found. However, recent large‐scale hydrographic changes (Eastern Mediterranean Transient, EMT) might change the oligotrophy and, thus, the structure of the benthic communities in the Eastern Mediterranean deep sea.     

Freshwater Phytoplankton Bloom in Visovac Lake - A Possible Cause of Benthic Mortality in Krka Estuary (Adriatic Sea, Croatia)

Abstract. In late summer and early autumn of 1989 benthic mortality in the upper part of Krka estuary extended from the Skradinski buk waterfalls to approximately 5 km downstream. Dead benthic organisms were found on the bottom at depths of up to 4.5 m. During August, a freshwater phytoplankton bloom was recorded in Visovac lake (which supplies the Skradinski buk waterfalls). The green tide in the lake was composed of up to 11.9 million cells. 1^--¹, predominantly of Synedra acus and Dinobtyon sertularia . At that time the maximal total inflow of phytoplankton cells through the waterfalls was approx. 0.41 S^-I (38000 1. d^-1). Cells of these two species died after reaching the salt wedge and the cummulative effect of their decomposition apparently caused an oxygen demand sufficient enough to trigger the benthic mortality. Due to the water mass dynamics, the spreading of mortality downstream was slow (from August to October, approx. 5 km). Certain benthic fishes (like Gobius sp.) were observed on the bottom of the affected area in mid-October 1989.     

The Effect of Temporal Changes and Environmental Trophic Condition on the Isotopic Composition (ω13C and ω15N) of Atherina boyeri (Risso, 1810) and Gobius niger (L., 1758) in a Mediterranean Coastal Lagoon (Lake of Sabaudia): Implications for Food Web Structure

Abstract. ω¹³C and ω¹⁵N of organic matter sources and consumers were employed to analyse trophic differentiation between a benthic consumer, Gobius niger (L., 1758) (Pisces, Osteichthyes), and a pelagic consumer, Atherina boyeri (Risso, 1810) (Pisces, Osteichthyes) in a Mediterranean coastal lagoon (Lake of Sabaudia) in winter and summer 1999. Trophic differences between the two species throughout the two sampling periods were related to the environmental trophic condition (i. e. nutrient and phytopigment concentrations). Although these two fish have different habitats, they both exploited benthic organisms, above all in summer. When the nutrient and phytopigment concentrations were higher (summer), the most abundant benthic organisms were the main food sources for both species. In winter A. boyeri apparently shifted its feeding preferences to include zooplankton, confirming its opportunistic feeding strategy. Par-ticulate organic matter and algae seemed to play the main trophic role in the food web structure. Benthic invertebrates used both sources, while zooplankton seemed to rely exclusively on the particulate fraction. The overlapping and very depleted signatures of sedimentary and particulate organic matter highlights a strong link between sediments and water column, rarely observed in other aquatic ecosystems using stable isotopes. Such a finding further substantiates the importance of particulate organic matter as a food source in the study area.     

The Sponge Population of the Cabrera Archipelago (Balearic Islands): Characteristics, Distribution, and Abundance of the Most Representative Species

Abstract. The abundance, distribution, and species richness of the littoral sponges (0–55 m) from the Cabrera Archipelago (Balearic Islands) were studied along light gradients from the surface to the sea bottom and from cave mouths to their inner parts. A total of 98 species (11 Calcarea and 87 Demospongiae ) were recorded, 8 of which are new records for the Spanish coast.
Cluster and correspondence analyses enabled the identification of a sciophilous sponge group including three subgroups: sponges found only in semi-dark cave habitats, a subgroup common to the coralligenous, precoralligenous, and semi-dark cave biocoenoses, and a third subgroup exclusive to the coralligenous biocoenosis. A small number of photophilic species and other species having a wide bathymetric distribution made up another separate group. No species clusters for the different semi-sciophilous (either fleshy or carbonate) or photophilic seaweed communities were discernible. The number of sponge species was negatively correlated with the irradiance level.     

The Sponge Community of a Semi-Submerged Mediterranean Cave

Abstract. The sponge fauna of a semi-submerged cave from the Tremiti Archipelago (Adriatic Sea) was studied, and its distribution was analyzed in relation to abiotic (water-movement and light gradients) and biotic (algae and anthozoan substrate cover) ecological factors. Fifty-five species of sponges were recorded. The number of species and the abundance values of sponges increase in the first part of the cave, then progressively decrease, with a sharp fall at the end of the cave. The quick disappearance of algae along the light gradient allows sponges to thrive in the first portion of the cave. The subsequent, progressive decrement of sponges could be the result of food depletion phenomena due to a long persistence of the water body in this long cavity. A high water-turbulence, due to the peculiar morphology of the cave and indicated by the recorded values of water-movement, occurs at the end of the cavity and probably determines the sharp decrement of sponges in the inner portion of the cave. This turbulence may also explain the absence of typical still-water cave species and probably affects the type of development (shape, overgrowth) of the sponges in the community.     

Transport of no. 2 fuel oil between water column,surface microlayer and atmosphere in controlled ecosystems

No. 2 fuel oil hydrocarbons put into the bulk water columns of controlled estuarine ecosystems were found to accumulate in the surface microlayer at the air-water interface. The alkane hydrocarbons were disproportionately enriched in the microlayer compared with the aromatic hydrocarbons. A comparison of hydrocarbon boiling point distributions between bulk water, microlayer and air samples indicated that the oil hydrocarbons underwent extensive weathering by evaporation upon reaching the air-water interface. No evidence was found of increased biodegradation in the microlayer compared with that in the underlying water. A fraction of the high molecular weight alkanes, the least water soluble and least volatile constituents of the oil, appeared to be coated out from the microlayer onto the inner walls of the ecosystems.     

Role of Bacteria in the Carbon and Nitrogen Flow between Water-Column and Sediment in a Shallow Marine Bay (Bay of Piran, Northern Adriatic Sea)

Abstract. The interdependences between phytoplankton standing crop, bacterial biomass and the dissolved organic matter (DOM) pool in the water column were investigated and related to sediment parameters in a shallow marine bay (Bay of Piran, Northern Adriatic Sea) over an annual cycle. Bacterioplankton density varied between 1–10 × 10⁵ cells ml^-1, with lowest density observed in March corresponding to the low Chi a concentrations during this period. Generation times as determined by dialysis incubations ranged between 4h (June) and 82 h (March). Mean bacterial secondary production rates during summer were about 40 mg C m^-1 d^-1 and 5mg C m^-3.d^-1 during winter. With a short time lag, DOM concentrations followed the fluctuation in Chi a.
Sediment oxygen demand measurements revealed a mean mineralization rate of about 260 mg C m^-2 d^-1 during summer and 100–200 mg C m^-2 d^-1 in winter. Sediment bacterial density varied between 10⁸ - 10⁹ cells g (sediment dry wt)^-1 in the top 5 cm sediment layer or, in terms of biomass, 4.3 g C m^-l during summer and 0.6 g C m^-2 during winter. Highest concentrations of DOM in pore waters were measured in September, coinciding with high rates of sediment oxygen demand.     

The effect of a natural water-movement related disturbance on the structure of meiofauna and macrofauna communities in the intertidal sand flat of Rocas Atoll (NE, Brazil)

Rocas, the only atoll in the South Atlantic, is located 266 km off the northeast Brazilian coast. Spatial patterns in community structure of meiofauna, particularly nematodes, and macrofauna were examined along a transect through the sediment path from windward to leeward of the Rocas Atoll sand flat. Differences in benthic community structure between four zones of the sand flat were found to be significant and related to the major local processes of carbonate-grain transport and sedimentation. Both meiobenthic and macrobenthic assemblages were significantly more diverse and abundant within the sediment inflow zone (the initial part of the detrital path of Rocas sand flat) than in the other zones, where a clear impoverishment of benthic invertebrates occurred. This first study of the benthos of an intertidal sand flat over a reef island in the Atlantic showed that the meiofauna is numerically dominated by the nematodes Metoncholainussp. 1 (Oncholaimidae) and Epsilonema sp. 1 (Epsilonematidade), whilst the macrofauna is largely dominated by oligochaetes and large Oncholaimidae nematodes. Analysis of the species composition, trophic structure and abundance of both the meiobenthos and the macrobenthos revealed an impoverished community subjected to an intense water-movement disturbance.     

Study and Cartography of the Benthic Communities of Medes Islands (NE Spain)

Abstract. A bionomic study and cartography of the benthos of Medes Islands (NE Spanish coast, Catalan Costa Brava) is presented. From 1977 to 1980 the fauna and flora of the meso- and macrobenthos were sampled by a triple sampling procedure: standard, visual and photographic samples were simultaneously taken along underwater transects, yielding 124 punctual inventories, 176 visual inventories and some 1000 photographic "samples". These, together with the floristic and faunistic study of each algal and invertebrate group, served as the basis for the bionomic survey of the islands' bottoms. In a first approach, the hard substrata of the infra- and circalittoral Stages were studied, along with the Posidonia meadows, and their communities diagrammatically sketched along representative transects. Further work focused on the submarine caves and tunnels of the area, the supra- and mediolittoral communities and the coastal detritic soft bottoms. The bionomic survey of the Medes Islands has emphasized, with minor differences, the basic similarity between the archipelago's benthic communities and those described elsewhere in the Northwestern Mediterranean. The identified communities or groups of communities are the trottoir, the photophilic algae, the sciaphilic algae (precoralligenous), the coralligenous and cave communities on hard substrata, as well as the Posidonia meadow and the coastal detritic community on soft substrata. These have been used as the basic macro-units in the bionomic cartography of the islands, which has been plotted on a 1:2000 map. Their distribution, over a surface area of some 2 km² and to a depth of up to 60–70 m, follows that of the heterogeneous substrate, its slope and the hydrodynamical and illumination conditions of the area.     

A Comparison of Phytoplankton Biomass Estimators and Their Environmental Correlates in the Mali Ston Bay (Southern Adriatic)

Abstract. Phytoplankton biomass estimators – total cell number (CN), total cell volume (CV), chlorophyll a (Chl a ). phytoplankton organic carbon (PC), and their response to environmental variables, with a special emphasis on the vertical variability in the structure of the water column – were examined in the Mali Ston Bay (Southern Adriatic). Correlations among biomass estimators as well as with physical-chemical parameters varied according to hydrodynamic characteristics of the water column. The amount of Chl a per cell ranged from 0.28.06–10^-6μg during stratification to 0.7–2.0.10^-6μg during the mixing period. Most frequent values for PC/Chl a ratios and for Chl a /CV in mixed natural phytoplankton populations were 20–25 and 1–2, respectively.     

The Fauna of Floating Cyanobacterial Mats in the Oligohaline Eulittoral Zone off Hiddensee (South-west Coast of the Baltic Sea)

Abstract. The fauna — including macrofauna, meiofauna, and large ciliates — of floating cyanobacterial mats in a brackish shallow-water area was studied by analysing six 20 cm² pieces of mat. Although these microbial aggregations were scarcely 1 cm thick, their total meiofauna abundance was about five times as high as in the uppermost 4 cm of the adjacent sediment. The mat fauna was dominated by harpacticoids, although large ciliates, rotifers, nematodes, and oligochaetes were also markedly more abundant than in the sediment. All species occurring in the mats were members of the surrounding sediment fauna. Out of the 47 species found, only a few, among them predominantly the harpacticoid, Mesochra lilljeborgi B oeck , 1864, and the nematode Daptonema setosum ( bütschli , 1874), accounted for the majority of the individual abundance in the mats. Both are regularly found in sulphidic biotopes near Hiddensee. As SEM micrographs revealed, the oligochaete Paranais litoralis (O. F. M üller , 1788) and the harpacticoid Cletocamptus confluens (Schmeil, 1894) were apparently optimal substrates for dense lawns of cyanobacteria. This indicates possible close interactions between the meiofauna and these microbiota. The frequent predation of histophagous ciliates on nematodes and harpacticoids, which were probably weakened by oxygen deficiency and/or high sulphide concentrations, were not only a sign of a generally neglected pathway in the food chain, but also impressively emphasized the huge variety of interactions taking place between meio- and microfauna within this specific benthic microcosm. Because of their floating character, the mats can play an important role in the dispersal of benthic fauna.