Dror Angel

Seaweed biofilters as regulators of water quality in integrated fish-seaweed culture units

Abstract The water-quality characteristics of a new system for the integrated culture of fish ( Sparus aurata L.) and seaweed ( Ulva lactuca L.) were examined. Seawater was recirculated between intensive fishponds and seaweed ponds. The seaweed removed most of the ammonia excreted by the fish and oxygenated the water. A model consisting of several tanks and a pilot consisting of two 100-m 3 , 100-m 2 ponds were studied. In both, the metabolically dependent water-quality parameters (dissolved oxygen, NH 4 + -N, oxidized-N, pH and phosphate) remained stable and within safe limits for the fish during over 2 years of operation. The design allowed significant increases in overall water residence time (4.9 days), compared with conventional intensive ponds, and produced a high yield of seaweed in addition to the fish. The design provides a practical solution to major management and environmental problems of land-based mariculture.

Hydrogen Peroxide Production Rates in Clean and Polluted Coastal Marine Waters of the Mediterranean, Red and Baltic Seas

Abstract The main aim of this study was to assess the hydrogen peroxide (HP) production rates (HPPR) related to anthropogenic pollution in coastal waters by laboratory and field experiments. HPPRs were assessed by simultaneous measurements of HP concentrations, cumulative solar UV irradiation and dissolved organic matter (DOM) fluorescence in the seawater samples at clean and polluted sites in the Mediterranean, Red and the Baltic Seas. The natural HP concentrations at all sites (8–100 nM) fall within the normal range recorded elsewhere, and follows a diurnal pattern. The polluted stations in the Mediterranean and Baltic Seas showed higher HPPR (3.2–16.6 nM m 2 W −1 h −1 ) than the clean stations, while in the Red Sea no significant differences were found because the station that was considered a priori polluted was actually rather clean (2–3 nM m 2 W −1 h −1 ). Laboratory experiments demonstrated that HPPR was positively linearly correlated to DOM fluorescence, however, this relationship was not found in the natural seawater samples examined in the field. The lack of relationship between HPPR and DOM in the field was attributed to enzymatic breakdown of HP as observed in dark decay experiments. HP dark decay rates were highest in polluted stations, probably due to larger bacterioplankton populations in these samples. Moreover, the HP dark decay rates were much lower in filtered than in non-filtered samples. Sun incubation of filtered (0.2 μm) seawater samples were performed to assess whether elimination of particles would yield higher HPPRs than in non-filtered samples. In the Baltic Sea (low UV irradiation) HPPR was higher in the filtered samples, while at sites with relatively high UV irradiation (Mediterranean and Red Seas), filtration of seawater did not stimulate HPPRs, probably due to UV-damage to planktonic microorganisms.

The impact of climate change on Mediterranean intertidal communities: losses in coastal ecosystem integrity and services.

As has been shown for other ecosystems, the ecological and socio-economic impacts of climate change on Mediterranean intertidal habitats are highly variable in space and time. We conducted field and laboratory measurements of cellular, ecophysiological and behavioural responses of selected intertidal invertebrates (mussels, gastropods and sponges) and completed a literature review to determine what is known of socio-economic consequences of these biological changes. Results suggest significant gaps in our knowledge that may impede a complete understanding of likely impacts (physical, biological and socio-economic) and that sufficient data for such an analysis are available only for mussels. Application of ecological models for native mussels Mytilaster minimus and invasive Brachidontes pharaonis bivalves indicates that the current distribution of these species is linked to the availability of food and local temperature. Choosing Israel as a case study, the study focused on the identification of ecosystem services and goods provided by the Mediterranean rocky intertidal and on the assessment of conservation approaches. Intertidal systems were poorly represented in the socio-economic literature, and there was low awareness of the value of these ecosystems among stakeholders. Subsequently, conservation efforts for intertidal communities were minimal. While climate change will very likely continue to impact these systems, our predictive capacity for the extent and locations of such impacts, and of any derived socio-economic consequences, remains limited.

In situ biofiltration: a means to limit the dispersal of effluents from marine finfish cage aquaculture

Net pen fish farms generally enrich the surrounding waters and the underlying sediments with nutrients and organic matter, and these loadings can cause a variety of environmental problems, such as algal blooms and sediment anoxia. In this study we test the potential of biofiltration by artificial reefs for reducing the negative environmental impacts surrounding fish farms in the Gulf of Aqaba, Red Sea. Two triangular-shaped artificial reefs (reef volume 8.2 m3) constructed from porous durable polyethylene were deployed at 20 m; one below a commercial fish farm and the other 500 m west of this farm in order to monitor the colonization of these reefs by the local fauna and to determine whether the reef community can remove fish farm effluents from the water. Both reefs became rapidly colonized by a wide variety of organisms with potential for the removal of compounds released from the farms. Within the first year of this study fish abundances and the number of species reached 518–1185 individuals per reef and 25–42 species per reef. Moreover, numerous benthic algae; small sessile invertebrates (bryozoa, tunicates, bivalves, polychaetes, sponges, anemones) and large motile macrofauna (crustaceans, sea urchins, gastropods) settled on the reef surfaces. Depletion of chlorophyll a was measured in the water traversing the artificial reefs in order to assess the biofiltration capacity of the associated fauna. Chlorophyll a was significantly reduced to a level 15–35% lower than ambient concentrations. This reduction was greatest at intermediate current speeds (3–10 cm s−1), but was not influenced by current direction. The reef structures served as a successful base for colonization by natural fauna and flora, thereby boosting the local benthic biodiversity, and also served as effective biofilters of phytoplankton.

Invasion Pathway of the Ctenophore Mnemiopsis leidyi in the Mediterranean Sea

Gelatinous zooplankton outbreaks have increased globally owing to a number of human-mediated factors, including food web alterations and species introductions. The invasive ctenophore Mnemiopsis leidyi entered the Black Sea in the early 1980s. The invasion was followed by the Azov, Caspian, Baltic and North Seas, and, most recently, the Mediterranean Sea. Previous studies identified two distinct invasion pathways of M. leidyi from its native range in the western Atlantic Ocean to Eurasia. However, the source of newly established populations in the Mediterranean Sea remains unclear. Here we build upon our previous study and investigate sequence variation in both mitochondrial (Cytochrome c Oxidase subunit I) and nuclear (Internal Transcribed Spacer) markers in M. leidyi, encompassing five native and 11 introduced populations, including four from the Mediterranean Sea. Extant genetic diversity in Mediterranean populations (n = 8, N a = 10) preclude the occurrence of a severe genetic bottleneck or founder effects in the initial colonizing population. Our mitochondrial and nuclear marker surveys revealed two possible pathways of introduction into Mediterranean Sea. In total, 17 haplotypes and 18 alleles were recovered from all surveyed populations. Haplotype and allelic diversity of Mediterranean populations were comparable to populations from which they were likely drawn. The distribution of genetic diversity and pattern of genetic differentiation suggest initial colonization of the Mediterranean from the Black-Azov Seas (pairwise F ST = 0.001–0.028). However, some haplotypes and alleles from the Mediterranean Sea were not detected from the well-sampled Black Sea, although they were found in Gulf of Mexico populations that were also genetically similar to those in the Mediterranean Sea (pairwise F ST = 0.010–0.032), raising the possibility of multiple invasion sources. Multiple introductions from a combination of Black Sea and native region sources could be facilitated by intense local and transcontinental shipping activity, respectively.

Exceptionally high abundances of microplastics in the oligotrophic Israeli Mediterranean coastal waters

Seasonal sea surface microplastic distribution was recorded at 17 sites along the Israeli Mediterranean coast. Microplastics (0.3-5mm) were found in all samples, with a mean abundance of 7.68±2.38particles/m3 or 1,518,340particles/km2. Some areas had higher abundances of microplastics than others, although differences were neither consistent nor statistically significant. In some cases microplastic particles were found floating in large patches. One of these patches contained an extraordinary number of plastic particles; 324particles/m3 or 64,812,600particles/km2. Microplastic abundances in Israeli coastal waters are disturbingly high; mean values were 1-2 orders of magnitude higher than abundances reported in other parts of the world. Light-colored (white or transparent) fragments were by far more abundant than all other microplastic colors and types. The results of this study underline the need for action to reduce the flux of plastics to the marine environment.

Impacts of climate change on biodiversity in Israel: an expert assessment approach

The Mediterranean region is both a global biodiversity hot spot and one of the biomes most strongly affected by human activities. Ecologists and land managers are increasingly required to advise on threats to biodiversity under foreseeable climate change. We used expert surveys to evaluate current understanding and uncertainties regarding climate change impacts on biodiversity in terrestrial, inland freshwater, and marine ecosystems of Israel. Finally, we propose a response strategy toward minimizing these changes. The surveys and the published literature indicated that the main climate change impacts in Israel include ongoing deterioration of freshwater habitats, decline of shrubland and woodland areas, and increased frequency and severity of forest fires. For the Mediterranean Sea, the surveys predict further introduction and establishment of invasive species from the Red Sea, accelerated erosion of coastal rocky habitat, and collapse of coastal rocky platforms. In the Gulf of Aqaba, Red Sea, corals may be resilient to foreseen climate change due to their high tolerance for rising water temperatures. Despite these predictions, science-based knowledge regarding the contribution of management toward minimizing climate change impacts on biodiversity is still lacking. Habitat loss, degradation, and fragmentation are presently the primary and immediate threats to natural ecosystems in Israel. Protection of natural ecosystems, including local refugia, must be intensified to maintain existing biodiversity under pressure from mounting urban development and climate change. This protection policy should include ecological corridors to minimize the consequences of fragmentation of existing natural habitats for species survival. A longer-term strategy should mandate connectivity across environmental and climatic gradients to maintain natural resilience by allowing reorganization of natural ecosystems facing climate change.

Local perspectives on regional challenges: jellyfish proliferation and fish stock management along the Israeli Mediterranean coast

Abstract The composition and abundance of marine biota in Israeli marine ecosystems are affected by natural and anthropogenic pressures, including blooms of non-indigenous jellyfish and overfishing. While overfishing is itself a major stressor of fish stocks, it appears that jellyfish may be outcompeting fish for scarce planktonic food resources. Beyond this direct impact on fisheries, jellyfish–ecosystem interactions are also important because of the disturbance they cause to multiple users of marine and coastal resources. This paper documents the concurrent changes in the composition of marine biotic communities, including jellyfish proliferation and dwindling stocks of endemic, commercially valuable fish and the rising rate of bottom trawling in Israeli fisheries. The capacity to deal directly with jellyfish is limited by lack of knowledge about their ecology. Therefore, we suggest that bolstering fish stocks and increasing their competitive advantage in the food web may be instrumental in limiting jellyfish blooms. Coordination of fishing and conservation policies is recommended, as are modifications to marine waste management and deployment of submerged artificial substrates.

Jellyfish blooms : new problems and solutions

Preface.- Identification key for young ephyrae: a first step for early detection of jellyfish blooms.- Blooms of the invasive ctenophore, Mnemiopsis leidyi, span the Mediterranean Sea in 2009.- Effects of pH on asexual reproduction and statolith formation of the scyphozoan, Aurelia labiata.- Effects of low salinity on settlement and strobilation of scyphozoa (Cnidaria): Is the lions mane Cyanea capillata (L.) able to reproduce in the brackish Baltic Sea?.- Effects of El Nino-driven environmental variability on black turtle migration to Peruvian foraging grounds.- Recurrence of bloom-forming scyphomedusae: wavelet analysis of a 200-year time series.- Behavior of Nemopsis bachei L. Agassiz, 1849 medusae in the presence of physical gradients and biological thin layers.- Avoidance of hydrodynamically mixed environments by Mnemiopsis leidyi (Ctenophora: Lobata) in open-sea populations from Patagonia, Argentina.- Response of Chrysaora quinquecirrha medusae to low temperature.- Use of respiration rates of scyphozoan jellyfish to estimate their effects on the food web.- Planktonic cnidarian distribution and feeding of Pelagia noctiluca in the NW Mediterranean Sea.- Bioenergetics and growth in the ctenophore Pleurobrachia pileus.- Degradation of the Adriatic medusa Aurelia sp. by ambient bacteria.- Identification of jellyfish from Continuous Plankton Recorder samples.- Separation and analysis of different types of nematocysts from Cyanea capillata (L.) medusae.- Characterisation of neurotoxic polypeptides from Cyanea capillata medusae (Scyphozoa).- Gill cell toxicity of northern boreal scyphomedusae Cyanea capillata and Aurelia aurita measured by an in vitro cell assay.

Dynamics in Microplastic Ingestion During the Past Six Decades in Herbivorous Fish on the Mediterranean Israeli Coast

Examination of the digestive tracts of two species of siganids (rabbitfish), collected in 2016 in the Mediterranean coastal waters of Israel, for the presence of microplastics (MP) revealed that 92% of the 88 fish examined had consumed between 1 and >500 MP per fish. A comparison of the gut contents of fish that had been collected from the 1960s to the present time showed that there was a temporal increase in the proportion of fish with MP, from ~10% in 1960–1970; ~80% in the 1990s; 92% in 2016. There was also a temporal change in the proportion of MP types ingested by these fish. Siganids may be valuable bioindicators of MP pollution in the sea.