Depth and spatial distribution patterns of transparent exopolymer particles (TEP) were measured during 2 east to west cruise transects across the ultra-oligotrophic Levantine basin, eastern Mediterranean Sea (SESAME, September 2008; ISRLEV, July 2009), and at 2 stations 20 and 50 km offshore (2008). TEP distribution was examined relative to chlorophyll a concentrations, bacterial production, and alkaline phosphatase activity (APA), taken as a measure of phosphorus (P) stress. During the stratified period, TEP levels were highest in a 5 m surface layer and correlated positively with APA as P concentrations decreased. On the transects, TEP concentrations from both surface and depth (1000 m) samples increased from west to east, corresponding to a pattern of increasing oligotrophy. In pelagic waters, maximal rates of bacterial production and TEP concentrations were consistently measured in surface samples. These contained abundant large (170 µm) TEP with numerous associated bacteria, possibly derived from algal or bacterial release or detritus. Lowest TEP concentrations were found in the deep chlorophyll maximum layer where TEP appeared as small (~4 µm) particles with only few attached bacteria. In deeper (300 to 1000 m) samples, both TEP concentrations and size increased, with most particles having associated bacteria. Our data augment previous studies on the formation of TEP and the subsequent utilization of this material by heterotrophic bacteria both in the euphotic zone and in deeper waters. Moreover, our study suggests that in ultra-oligotrophic environments such as the Levantine basin, TEP plays an especially important role in carbon cycling and transportation.

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, and photosynthetic rates concomitantly doubled from 15 to 35 µg C l -1 d -1 . Water transparency declined, as indicated by the vertical diffusion attenuation coefficient K d for photosynthetically active radiation (PAR), which increased from 0.076 to 0.090 m -1 and decreased the euphotic depth from 60 to 45 m. During this time, a significant increase in silica deposition by the diatoms was also detected. We attribute the mentioned changes in environmental characteristics to wind-generated surface currents. Strong winds (up to 10 m s -1 ) during the measurements enriched the surface layers with unusually high nutrient concentrations within <1 d. Hence, primary production rates were observed at a relatively eutrophic nearshore station (MP) and pelagic station (A 1 , 10 km towards the center of the Gulf). They were compared with rates measured on the subsequent day. Values measured were twice as high as those at the pelagic station during the previous calm day. Routine monitoring programs with monthly or semi-weekly sampling are thus likely to miss brief but significant injections of nutrients, leading to the underestimation of seasonal and annual primary production. Our results demonstrate the impacts of transient events on the function and annual yield of aquatic ecosystems.

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SUMMARYWave lensing produces the highest level of transient solar irradiances found in nature, ranging in intensity over several orders of magnitude in just a few tens of milliseconds. Shallow coral reefs can be exposed to wave lensing during light-wind, clear-sky conditions, which have been implicated as a secondary cause of mass coral bleaching through light stress. Management strategies to protect small areas of high-value reef from wave-lensed light stress were tested using seawater irrigation sprinklers to negate wave lensing by breaking up the water surface. A series of field and tank experiments investigated the physical and photophysiological response of the shallow-water species Stylophora pistillata and Favites abdita to wave lensing and sprinkler conditions. Results show that the sprinkler treatment only slightly reduces the total downwelling photosynthetically active and ultraviolet irradiance (~5.0%), whereas it dramatically reduces, by 460%, the irradiance variability caused by wave lensing. Despite this large reduction in variability and modest reduction in downwelling irradiance, there was no detectable difference in photophysiological response of the corals between control and sprinkler treatments under two thermal regimes of ambient (27°C) and heated treatment (31°C). This study suggests that shallow-water coral species are not negatively affected by the strong flashes that occur under wave-lensing conditions.

The Gulf of Aqaba (Red Sea) is characterized by seasonal plankton blooms which are driven by vertical nutrient upwelling during winter (Genin et al. 1995). In March 2009, following the seasonal upwelling, large numbers of the moon jellyfish (Aurelia aurita) were recorded at the local fringing reefs of Eilat, at depths of 2-20 m (Fig. 1a). During this event, several large (ca. 20-25 cm) solitary corals (Fungia scruposa) were observed to feed on these jellyfish (Fig. 1b, c). A. aurita is known to be eaten by a wide variety of relatively large predators, including fish, sea turtles and even sea birds; however, it has never been reported as a coral's prey. Despite the fact that hermatypic corals may feed heterotrophically on a broad variety of sources ranging in size from bacteria to mesozooplankton (up to 1,000 lm) (Houlbrèque and Ferrier-Pagès 2009), this is the first report of solitary corals feeding on large gelatinous plankton (ca. 12 cm in diameter) in their natural habitat. Other cnidarians, such as the sea anemone Entacmaea medusivora in Palau, have also been shown to feed on jellyfish (Mastigias papua). However, as opposed to F. scruposa, these sea anemones are constantly surrounded by their prey and they lack photosynthetic endosymbionts (Fautin and Fitt 1991). Our observations revealed that the large-mouthed solitary fungiids can consume relatively large prey organisms, which are not available to other corals, as an additional source of protein. It remains to be shown, however, how fungiid corals manage to capture these large jellyfish while overcoming their motility. This trophic opportunism and reproductive plasticity exhibited by fungiid corals (Loya and Sakai 2008) are suggested as an important asset in determining their evolutionary success.

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Variations in transparent exopolymer particles (TEP), bacterial biomass production (BP) and primary productivity (PP) were followed over 52 h at a deep water station in the Gulf of Aqaba (Eilat, Israel) during the spring, in April 2008. About 20 h after the start of the study, there was a short (~15 h) but intense storm event that probably caused a nutrient pulse and, subsequently, a brief outgrowth of diatoms in the euphotic layer. Concentrations of TEP and BP ranged from 23 to 228 µg gum xanthan equivalents l -1 and from 0.2 to 0.6 µg C l -1 h -1, respectively. Concentrations of TEP and BP were measured in unfiltered and in GF/C (1.2 µm)-prefiltered samples. Most of the TEP (59 ± 21% of total TEP, mean ± SD) were in the smaller (GF/C-filtered) size fraction (0.4-1.2 µm); however, after the crash of the diatom bloom, the majority of TEP were in the >1.2 µm size fraction. In the GF/Cfiltered fraction, BP averaged 59 ± 12% and 93 ± 5% of total BP in the upper water column and from 300 m, respectively. Significant correlations were observed between TEP and BP, suggesting that active heterotrophic bacteria may have been associated with these particles. During the 3 d of our study, PP and BP in the euphotic zone averaged 480 and 225 mg C m -2 d -1 , respectively, suggesting that about half or more of the primary produced carbon was metabolized by heterotrophic bacteria in the upper water column. Coincident with strong mixing caused by the storm, TEP concentrations decreased in the surface water and increased at depth. We suggest that TEP acted to link carbon flux between the primary producers and heterotrophic bacteria, and that the downward movement of TEP from the upper water layers may be an important process in transferring organic carbon to deeper waters of the Gulf of Aquaba. Sinking TEP could provide not only organic carbon substrates for associated bacteria but also form 'hot spots' of elevated microbial metabolism and nutrient cycling throughout the water column.