Spatial distribution and dietary overlap between Japanese anchovy <i>Engraulis japonicus </i> and moon jellyfish <i>Aurelia aurita</i> in the Seto Inland Sea, Japan

Abstract

SUMMARY: Biological and physical surveys were conducted in order to investigate the relationship between environmental conditions and the distribution of ichthyoplankton and jellyfish, and dietary overlap between the ichthyoplankton and jellyfish in the Seto Inland Sea (SIS), Japan. Ichthyoplankton, copepods, and jellyfish were collected during two cruises in July 2005 in the Sea of Hiuchi and in July 2006 in Hiroshima Bay within the SIS. Sea surface temperature (˚C), salinity, bottom-layer dissolved oxygen (mg l -1 ) and the abundance (no. m -2 ) of fish eggs and larvae were significantly higher in the Sea of Hiuchi. Japanese anchovy was most dominant (69.3% in number of eggs and 52.3% in number of larvae) among the ichthyoplankton. Mean jellyfish biomass (g m -2 ) in Hiroshima Bay was significantly higher (50-folds) than that in the Sea of Hiuchi. Moon jellyfish was the most dominant among the jellyfish collected, accounting for 85.6% in wet weight. Surface temperature had a significant effect on fish egg and larval distribution: abundance of fish eggs and larvae increased with increasing temperature. Jellyfish abundance was negatively correlated with the bottom-layer oxygen concentration. Stable isotope analysis indicated dietary overlap between the Japanese anchovy and the moon jellyfish in Hiroshima Bay. -Se realizaron campañas físico-biológicas a fin de investigar la relación entre las condiciones ambientales y la distribución del ictioplancton y las medusas, y el solapamiento de sus dietas en el Mar Interior de Seto (SIS), Japón. Durante dos campañas, en julio de 2005 en el mar de Hiuchi y en julio de 2006 en la bahía de Hiroshima (SIS), se recolectaron ictioplancton, copépodos y medusas. La temperatura superficial (°C), la salinidad, el oxíge-no disuelto en el fondo (mg l -1 ) y la abundancia de los huevos y larvas de peces (no. m -2 ) fueron significativamente mayores en el Mar de Hiuchi. La anchoa japonesa dominó el ictioplancton (69.3% en número de huevos y 52.3% de larvas). La biomasa media de medusas (g m -2 ) en la bahía de Hiroshima fue significativamente mayor (50 veces) que en el Mar de Hiuchi. La medusa Aurelia aurita fue la dominante entre las medusas recogidas, lo que representó el 85.6% en peso húmedo. La temperatura superficial tuvo un efecto significativo sobre la distribución de huevos y larvas de peces: su abundancia aumentó al aumentar la temperatura. La abundancia de medusas se correlacionó negativamente con la concentración de oxígeno en la capa del fondo. Los análisis de isótopos estables indicaron una superposición en la dieta de la anchoa japonesa y la medusa Aurelia aurita en la bahía de Hiroshima. KeywordsPalabras clave: ictioplancton, análisis de isótopos estables, mar de Hiuchi, bahía de Hiroshima.

Temporal and spatial patterns in the abundance of jellyfish in the northern Benguela upwelling ecosystem and their link to thwarted pelagic fishery recovery

“…As predators in the plankton, jellyfish have the potential to compete with (especially pelagic) fish for food (Purcell and Arai 2001), and this is exacerbated in situations where they overlap in time/space (Purcell and Sturdevant 2001, Brodeur et al 2008, Shoji et al 2009). Ramifications of this potential interaction are unknown, but can perhaps be presumed to be more negative for fish than for jellyfish, which are able to survive on a far broader range in prey diversity and size.…”

Jellyfish blooms in China: Dominant species, causes and consequences

“…E. japonicus is a major zooplankton feeder in the Yellow Sea ecosystem which mainly prey on copepods and their eggs and larval (Meng, 2003;Zhao et al, 2003). Previous studies showed that the Japanese anchovy might compete for the same zooplankton prey with moon jellyfish A. aurita or the giant jellyfish N. nomurai (Uye, 2008;Shoji et al, 2009b). Therefore, the large jellyfish species population increases might have been at least in part due to a decline in competition for food resources from the Japanese anchovy.…”

Jellyfication of Marine Ecosystems as a Likely Consequence of Overfishing Small Pelagic Fishes: Lessons from the Benguela

“…Despite the lack of direct information on jellyfish diet in the Benguela region, considerable evidence now suggests that the diets of many small pelagic fish species in other ecosystems overlap significantly with those of jellyfishes (see e.g., Purcell and Sturdevant 2001, Brodeur et al 2008, Shoji et al 2009), indicating the potential for competition between the two groups. Studies of trophic interaction between jellyfishes and pelagic fishes in the northern California Current ecosystem have documented the dietary overlap between jellyfishes and fishes, including sardines, anchovies, saury, and herring (Brodeur et al 2002(Brodeur et al , 2008, as well as the ecological consequences of the competition between those two groups (Ruzicka et al 2007, Brodeur et al 2011.…”