Plastic pollution has been identified as a major threat for coastal marine life and ecosystems. Here, we test if the feeding behaviour and growth rate of the two most common cold-water coral species, Lophelia pertusa and Madrepora oculata, are affected by micro- or macroplastic exposures. Low-density polyethylene microplastics impair prey capture and growth rates of L. pertusa after five months of exposure. Macroplastic films, mimicking plastic bags trapped on deep-sea reefs, had however a limited impact on L. pertusa growth. This was due to an avoidance behaviour illustrated by the formation of skeletal ‘caps’ that changed the polyp orientation and allowed its access to food supply. On the contrary, M. oculata growth and feeding were not affected by plastic exposure. Such a species-specific response has the potential to induce a severe change in coral community composition and the associated biodiversity in deep-sea environments.

In August 2009, a blowout of the Montara H1 well 260 km off the northwest coast of Australia resulted in the uncontrolled release of about 4.7 M L of light crude oil and gaseous hydrocarbons into the Timor Sea. Over the 74 day period of the spill, the oil remained offshore and did not result in shoreline incidents on the Australia mainland. At various times slicks were sighted over a 90,000 km² area, forming a layer of oil which was tracked by airplanes and satellites but the slicks typically remained within 35 km of the well head platform and were treated with 183,000 L of dispersants. The shelf area where the spill occurred is shallow (100–200 m) and includes off shore emergent reefs and cays and submerged banks and shoals. This study describes the increased inputs of oil to the system and assesses the environmental impact. Concentrations of hydrocarbon in the sediment at the time of survey were very low (total aromatic hydrocarbons (PAHs) ranged from 0.04 to 31 ng g⁻¹) and were orders of magnitude lower than concentrations at which biological effects would be expected.

Macroalgal beds provide important habitat structure and support primary production for rocky reef communities, but are increasingly degraded as a result of human pressures. Various sources of pollution can have both direct and interactive effects on stressed ecosystems. In particular, interactions involving invertebrate grazers could potentially weaken or strengthen the overall impact of pollution on macroalgal beds. Using a paired impact-control experimental design, we tested the effects of multiple pollution sources (fish farms, marinas, sewerage, and stormwater) on translocated and locally established algal assemblages, while also considering the influence of invertebrate grazers. Marinas directly affected algal assemblages and also reduced densities of amphipods and other invertebrate mesograzers. Fish farms and sewerage outfalls tended to directly increase local establishment of foliose and leathery algae without any indication of changes in herbivory. Overall, pollution impacts on algae did not appear to be strongly mediated by changes in grazer abundance. Instead, mesograzer abundance was closely linked to availability of more complex algal forms, with populations likely to decline concurrently with loss of complex algal habitats. Macrograzers, such as sea urchins, showed no signs of a negative impact from any pollution source; hence, the influence of this group on algal dynamics is probably persistent and independent of moderate pollution levels, potentially adding to the direct impacts of pollution on algal beds in urbanised environments.

The availability of marine habitats maps remains limited due to difficulty and cost of working at sea. Reduced light penetration in the water hampers the use of optical imagery, and acoustic methods require extensive sea-truth activities. Predictive spatial modelling may offer an alternative to produce benthic habitat maps based on complete acoustic coverage of the seafloor together with a comparatively low number of sea truths. This approach was applied to the coralligenous reefs of the Marine Protected Area of Tavolara - Punta Coda Cavallo (NE Sardinia, Italy). Fuzzy clustering, applied to a set of observations made by scuba diving and used as sea truth, allowed recognising five coralligenous habitats, all but one existing within EUNIS (European Nature Information System) types. Variable importance plots showed that the distribution of habitats was driven by distance from coast, depth, and lithotype, and allowed mapping their distribution over the MPA. Congruence between observed and predicted distributions and accuracy of the classification was high. Results allowed calculating the occurrence of the distinct coralligenous habitats in zones with different protection level. The five habitats are unequally protected since the protection regime was established when detailed marine habitat maps were not available. A SWOT (Strengths-Weaknesses-Opportunities-Threats) analysis was performed to identify critical points and potentialities of the method. The method developed proved to be reliable and the results obtained will be useful when modulating on-going and future management actions in the studied area and in other Mediterranean MPAs to develop conservation efforts at basin scale.

Blooms of the moon jellyfish Aurelia coerulea frequently occur in coastal waters. The increased availability of substrates for the settlement and proliferation of polyps due to the expansion of artificial structures in coastal areas has been proposed as a possible contributing factor in jellyfish blooms. This paper investigates whether a marine artificial lake (Fenghuang Lake) provides additional substrates for A. coerulea polyps and contributes to jellyfish blooms. High densities of A. coerulea ephyrae were discovered in this lake, with a mean density of 41 individuals/m3 and a maximum measured density of 128 individuals/m3. Meanwhile, A. coerulea ephyrae were also found in the two emptying channels outside the lake, with a mean density of 13 individuals/m3. Underwater surveys revealed that dense colonies of A. coerulea polyps occurred mainly on biogenic reefs formed by a polychaete, which was identified as an invasive serpulid species Hydroides dianthus, based on the phylogenetic analysis of mitochondrial COI gene sequences. Our study highlights the potential modification of habitats by the alien polychaete H. dianthus, which might provide complex benthic habits suitable for the settlement and proliferation of A. coerulea polyps and may contribute to jellyfish blooms in the marine artificial lake and nearby coastal waters.

The dearth of long-time series hampers the measurement of the ecosystem change that followed the global marine climate shift of the 1980–90s. The sessile communities of Portofino Promontory reefs (Ligurian Sea, NW Mediterranean) have been discontinuously studied since the 1950s. Collating information from various sources, three periods of investigations have been distinguished: 1) 1950–70s; 2) 1980–90s; 3) 2000–10s. A cooler phase in time 1 was followed by a rapid warming in time 2, to stabilize at about 0.5°C higher in time 3. Human pressure grew impressively, especially after the establishment of a MPA in 1999. Multivariate analyses evidenced a major change of community composition in time 2. Some species disappeared or got rarer, many found refuge at depth, and among the newcomers there were recently introduced alien species. This study demonstrated the importance of descriptive historical data to understand magnitude and pattern of change in the long term evolution of marine ecosystems.

A new method based on photographic sampling coupled with in situ observations was applied to 53 stations along the French Mediterranean coast, to assess the integrity of coralligenous reefs affected by different levels of anthropogenic pressure. The conservation state of the assemblages characterizing these habitats was then assessed by an index – the INDEX-COR – that integrates three metrics: (i) the sensitivity of the taxa to organic matter and sediment deposition, (ii) the observable taxonomic richness, and (iii) the structural complexity of the assemblages. The sensitivity of INDEX-COR was tested and showed good correlation with the Level of Pressure calculated for each station according to expert judgment and field observations.

Oysters provide a critical habitat, are a food resource for higher trophic levels and support important commercial fisheries throughout the world. Oyster reefs can improve water quality by removing phytoplankton. While sediment denitrification may be enhanced adjacent to oyster reefs, little is known about nitrification and denitrification associated with living oysters and their shells. We measured nitrification and denitrification in living oysters (Crassostrea virginica and Crassostrea gigas) and empty oyster shells. Nitrification was similar between live oysters and empty oyster shells, however, denitrification was enhanced significantly on living oysters compared to shells. This is the first demonstration of nitrification and denitrification associated with living oysters and their shells. Our data suggest that loss of historic oyster reefs has likely affected the resilience of estuaries to eutrophication. The additional benefit of oyster mediated denitrification should be considered in restoration of oyster reefs as a tool for managing eutrophication.

Using long-term oceanographic surveys and a 3-D hydrodynamic model we show that localized peak winds (known as shamals) cause fluctuation in water current speed and direction, and substantial oscillations in sea-bottom salinity and temperature in the southern Persian/Arabian Gulf. Results also demonstrate that short-term shamal winds have substantial impacts on oceanographic processes along the southern Persian/Arabian Gulf coastline, resulting in formation of large-scale (52km diameter) eddies extending from the coast of the United Arab Emirates (UAE) to areas near the off-shore islands of Iran. Such eddies likely play an important role in transporting larvae from well-developed reefs of the off-shore islands to the degraded reef systems of the southern Persian/Arabian Gulf, potentially maintaining genetic and ecological connectivity of these geographically distant populations and enabling enhanced recovery of degraded coral communities in the UAE.

Coral colony size-frequency distributions can be used to assess population responses to local environmental conditions and disturbances. In this study, we surveyed juvenile pocilloporids, herbivorous fish densities, and algal cover in the central and southern Saudi Arabian Red Sea. We sampled nine reefs with different disturbance histories along a north–south natural gradient of physicochemical conditions (higher salinity and wider temperature fluctuations in the north, and higher turbidity and productivity in the south). Since coral populations with negatively skewed size-frequency distributions have been associated with unfavorable environmental conditions, we expected to find more negative distributions in the southern Red Sea, where corals are potentially experiencing suboptimal conditions. Although juvenile coral and parrotfish densities differed significantly between the two regions, mean colony size and size-frequency distributions did not. Results suggest that pocilloporid colony size-frequency distribution may not be an accurate indicator of differences in biological or oceanographic conditions in the Red Sea.