Aquatic Conservation-Marine and Freshwater Ecosystems最新文献

Hydrothermal vents are biodiversity hotspots on the deep seafloor powered by chemosynthetic primary production, inhabited by a specially adapted fauna whose composition varies between regions. Sumisu Caldera, located approximately 500 km south of Tokyo, hosts a hot vent with an unusual species composition among the Izu–Ogasawara Arc sites and has been suggested as a priority site for conservation in light of upcoming deep-sea mining for massive sulfides. However, this was based on just five species serendipitously recorded from geological surveys. Here, we carried out the first comprehensive biological sampling of Sumisu using two dives of the human-occupied vehicle Shinkai 6500. Together with literature records, we count a total of 54 animal species of which at least 25 are endemic to chemosynthetic ecosystems, drastically increasing the known faunal diversity—including three sponges, one cnidarian, 12 molluscs, 23 annelids, 13 arthropods, one echinoderm, and one fish. The presence of sediments facilitating the occurrence of burrowing species and three non-endemic predators contribute to the high species richness. Our findings make Sumisu the most species-rich vent community in the entire northwestern Pacific and our work serves as a prime example for detailed faunal surveys to obtain key piece of baseline data for future environmental assessments. Although the apparent lack of massive sulfide deposits means Sumisu is unlikely to be an immediate target of mining, its close distance to Bayonnaise Knoll with a major deposit and the possibility that it acts as a critical stepping-stone population for many species, as well as the presence of several endangered ones, presents a case for its protection.

In a time of ever-increasing pressure on the coastal ocean and rising costs, the development of effective and efficient methods for assessing the health of marine ecosystems is becoming essential for continued conservation efforts. Taking advantage of technologies such as remotely operated vehicles (ROVs) may be a way of achieving this, but a quantitative check on the quality of ROV-derived data is necessary. Here, using coralline algae reefs (maerl beds) as a model habitat, we compared 3D seabed reconstructions obtained from structure-from-motion photogrammetry surveys from diver-held and ROV-mounted camera systems. We found that both approaches achieved satisfactory alignment and mm-scale resolution, allowing small-scale features and individual organisms in the maerl bed to be resolved. The higher quality camera system available to divers resulted in generally lower modelling errors, but the spatial extent of surveys was highly restricted. In contrast, although associated with a slightly higher error, we show that much larger areas can be surveys by ROVs—we reconstructed 11,285 m² of seabed in just 400 min of ROV deployment time. Moving forward, we recommend that a hybrid survey approach is adopted: utilising ROV surveys for large-scale monitoring and diver surveys for higher detail insights that are informative for areas with highly complex and fine-scale morphologies (like coralline algae reefs). Here, even small changes in complexity can be indicative of habitat change, and associated species can be small in size so multiscale visual assessment is beneficial.

Information about reproductive habitat and migration pathways is of paramount importance to restore migratory fish species. This study assesses the availability of spawning and nursery habitats for the European sturgeon (Acipenser sturio) in the delta and lower Rhine (covering over 350 river kilometres) as part of a larger feasibility assessment for a future restoration of this critically endangered species. The general approach has three steps: (1) the identification of the species' specific habitat requirements, based on a systematic literature review; (2) the collection and preprocessing of data from two countries, including the 1D and 2D modelling of water depths and flow velocities; and (3) GIS-based mapping of spawning and nursery habitat. Based on a HSI score of 1, we identify a total of 0.75 km² as minimal spawning habitat, potentially suitable for approximately 2500 female European sturgeons (one spawning site would use ~300 m²). This is sufficient, as currently, only an estimated maximum number of 750 adults exist. Suitable spawning habitat is mainly located in the German state of North Rhine-Westphalia, whereas suitable nursery habitat is mainly located in the Netherlands. The availability is, however, significantly reduced by coastal infrastructure (damming) and inland navigation. The insights gained can be used to assess the current suitability of the river Rhine for the species' reintroduction and to identify opportunities for habitat restoration and protection for various life stages. The outcomes thus play an essential role in the conservation of the species. In addition, the modelling approach developed could be applied to other northwestern European rivers. This broader application would allow intercomparison and support decisions about which rivers are best suited for future reintroduction of the critically endangered European sturgeon.

As part of ongoing efforts to protect marine megafauna, especially cetaceans, in the NW Mediterranean Sea, a ‘Particularly Sensitive Sea Area’ (PSSA) was established in July 2023 by the governments of France, Italy, Spain and Monaco through the Marine Environment Protection Committee (MEPC) of the International Maritime Organisation (IMO). This is a legal instrument by which maritime traffic can be subject to advisories or controls to protect the natural environment. While the new PSSA is a significant step forward in terms of marine wildlife protection in the region, the current area only partially includes the waters that play a key ecological role for the conservation of Mediterranean sperm whales (Physeter macrocephalus) around the Balearics Archipelago. This isolated population is currently classified as endangered by the IUCN. Survey data from 2019 to 2022 show how the current area does not include portions of habitat in which calves are more likely to be encountered and risks displacing any maritime traffic that chooses to avoid the voluntary PSSA restrictions into habitat that is sensitive for calf survival. We argue therefore that this PSSA should be augmented to incorporate waters that are an important habitat for this endangered population.

The occurrence of rhodolith beds in the stratigraphic record from the Cretaceous to the Pleistocene was analysed from published papers. Most data refer to low–mid latitude records of rhodolith beds described in the Tethyan–Paratethyan–Mediterranean domain. The first putative rhodolith beds are from Albian (uppermost Lower Cretaceous) deposits. These rhodolith beds are made up mostly of unattached loose branching corallines as well as of nodular structures. From the Coniacian (Upper Cretaceous) to the Langhian (Middle Miocene), abundance of rhodolith beds shows a generally increasing fluctuating trend with two significant expansions in the Priabonian (late Eocene) and during the Aquitanian–Langhian (Early-Middle Miocene). After the Langhian maximum, rhodolith beds sharply declined to a minimum in the Zanclean (Early Pliocene). During the Pleistocene, they recovered to values similar to those reached in the Langhian. The general increase in rhodolith beds up the Langhian maximum correlates well with global temperature and pCO₂ declines and with an ocean pH increase. The tectonic activity leading to important palaeogeographic changes in the Tethyan–Parathetyan–Mediterranean realm might account for the Serravallian–Zanclean downfall of rhodolith-dominated deposits. The Cretaceous–Pleistocene record of rhodolith beds shows that these ecosystems withstood successfully a highly changing world. The rapid acclimation of particular taxa to environmental changes and the variable reaction of taxa distributed at different water depths can be crucial to understand their success. In this regard, it would be interesting to analyse how different taxa in modern deep rhodolith beds respond to changing oceanic conditions.