Distribution Of Jellyfish Research Articles

An evaluation of acoustic and video methods to estimate the abundance and vertical distribution of jellyfish

Four non-invasive methods (three acoustic and one video) were compared to estimate the abundance and vertical distribution of scyphomedusae, using the locally abundant coronate species Periphylla periphylla in Lurefjorden, north of Bergen, Norway, as the test organism. The acoustic methods included single-target quantification by, respectively, a hull-mounted 38 kHz split-beam echo sounder and a 675 kHz scanning sonar mounted on a remotely operated vehicle (ROV). Data from acoustic backscattering provided estimates of abundance and changes in the vertical position of scattering (= aggregation) layers. Vertical migration was also studied by acoustic target tracking, following single individuals as they ascended in the afternoon. The ROV-mounted scanning sonar missed an unidentified part in the lower size distribution of the target population. Vertical video profiles, conducted during ROV dives, provided the most detailed information on abundance and distribution, although uncertainties remained regarding the size distribution in the population.

In situ quantification and analysis of large jellyfish using a novel video profiler

Ecological studies involving large jellyfish have been limited by the inability of oceanographers to measure the abundance and distribution patterns of these highly aggregated ani- mals at local scales. Conventional plankton nets are undesirable in these applications because they cannot sample volumes large enough to accurately determine jellyfish concentration, nor do they have adequate spatial resolution to account for the ubiquitous patchiness of most large jellies. Nets are also notorious for damaging the watery bodies of jellyfish. To overcome these problems, we have developed a video system for use in the in situ study of large jellyfish. The design of our JellyCam is easily replicated since it incorporates commercially available components within a frame designed to hold hydrographic instrumentation available at most marine laboratories. We present data sets from 2 occasions as a demonstration of the utility of the JellyCam. On one occasion, a vertical profile of medusae of Pelagia noctiluca revealed intense layering of these jellyfish at the pronounced halo- cline/pycnocline. Most jellyfish in this layer were swimming toward the surface, and it was hypothe- sized that retarded forward-swimming velocity at the halocline, due to salt retention in jellyfish, caused this accumulation. A separate 800 m long horizontal transect of Phyllorhiza punctata medusae revealed distinct concentrated bands of jellyfish associated with increased chlorophyll concentration. Concomitant hydrographic data from the JellyCam showed that accumulation of both jellyfish and chlorophyll was associated with a hydrographic front. These data sets demonstrate that this system is capable of the desired 2 m 3 resolution, which is adequate for the observation and quantification of jellyfish distributions around small-scale physical discontinuities (e.g. fronts and pycnoclines). A series of side-by-side comparisons with a conventional plankton trawl resulted in comparable mea- surements of large jellyfish (Aurelia aurita) concentrations. Though in situ videography by itself is a powerful tool for investigating jellyfish, its use in conjunction with conventional nets or other technologies, such as acoustics and self-propelled vehicles (e.g. remotely operated vehicles and submersibles), will provide the most comprehensive view of jellyfish distribution in 3 dimensions.

Distribution and abundance of moon jellyfish ( Aurelia aurita ) and its zooplankton food in the Black Sea

The distribution of moon jellyfish (Aurelia aurita Linnaeus, 1758) in the Black Sea was determined from plankton samples collected above the anoxic zone (maximum depth 200 m) in the summer, winter and spring during 1991–1995. Distribution was patchy. Average biomass ranged from 98 to 380 g m−2, and abundance varied from 2 to 14 individuals m−2. Biomass and abundance peaked in late spring and summer. The distribution was correlated with hydrographic features in the Black Sea, with higher concentrations occurring at the peripheries of anticyclonic eddies. Centers of the two main cyclonic gyres generally had a low biomass of A. aurita. From July 1992 to March 1995, the populations were largely concentrated in offshore regions. A. aurita were confined to the upper part of the mixed layer. Smaller A. aurita (≤1 cm) were present in early spring (March), and individuals reached maximum size in the summer. Release of the epyhrae occurred in spring on the northwestern shelf of the sea when the seawater temperature was 11–12 °C. Microscopic analysis of stomach contents showed that copepods and mollusks form their main diet.

Distribution and relative importance of jellyfish in a region of hydrothermal venting

Net sampling to 3000 m depth at Endeavour Ridge in the northeast Pacific in July 1991–1994 shows that medusae in the immediate vicinity of the hydrothermal vent fields often make up a larger proportion of the total zooplankton abundance and biomass from mesopelagic to bathypelagic depths than in the surrounding waters. This was particularly evident in the dominant Trachymedusae, and least evident in the siphonophores. In addition, the large red Scyphomedusa Stygiomedusa gigantea was a major biomass component in the region of the deep (1000–1800 m depth) migrating scattering layers at the vent field, but was not found in any net tows greater than 10 km away from vents. There is no concurrent increase in relative or percent biomass of fish or chaetognaths, which are the other major predators in the community. We hypothesize that predaceous medusae respond opportunistically to the enhanced zooplankton biomass throughout the water column around vents in spring to early summer, in a way that other predators do not.

Implications of density driven currents for interaction between jellyfish (Aurelia aurita) and zooplankton in a Danish fjord

Abstract The distribution of Aurelia aurita in a shallow fjord with a local population of numerous small jellyfish was influenced by density driven currents created by frequent salinity changes in the adjacent open sea. When new water of either higher or lower salinity entered the fjord this gave rise to changes in the jellyfish distribution. Likewise, the presence and distribution of zooplankton was influenced. Incoming copepods disappeared simultaneously with the invasion of the new water mass by the jellyfish. The time it took for A. aurita to enter a new water mass of higher or lower salinity was dependent on the salinity difference. Laboratory experiments indicated that the adaptation time for equilibrium buoyancy and normal swimming of the jellyfish was directly proportional to the salinity difference. Osmoconforming times of2 to 4 h were found for salinity gradients of2 to 4 psu typically found in the fjord. The population filtration impact exerted by A. aurita was usually able to keep the zooplankton biomass low (mean residence time of a zooplankton organism varied between 10 and 20 h). Similar dynamics governed by density driven currents may be expected in other shallow waters influenced by frequently changing salinities. Such knowledge about the dynamic interactions between hydrography and biology, explaining otherwise unaccountable large variations in phyto- and zooplankton biomasses may be of importance for a general basic understanding of the dynamics in coastal ecosystems.

The Distribution of Jelly-fish

The Distribution of Jelly-fish