著者

SAWAMOTO SHOZO MATSUMOTO RUI

出版者

日本プランクトン学会、日本ベントス学会

雑誌

Plankton & benthos research (ISSN:18808247)

巻号頁・発行日

vol.7, no.4, pp.203-206, 2012-11-01

被引用文献数

14

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More than 50 specimens of the megamouth shark Megachasma pelagios have been reported so far, but biological observations on the species are still limited. We examined a female megamouth specimen that was captured by the bonito purse seine fishery in the Kuroshio Extension in July 2007 and donated to the Okinawa Churaumi Aquarium. The specimen was an immature female, 3,667 mm in total length and 361 kg in weight. The stomach contents measured 2,200 mL excluding the portion that was lost from the specimen before measurement. Detailed examination of a small part (14.6 mL) of the stomach contents revealed undamaged worm-like organisms, 10 partially damaged euphausiids and abundant fragmented pieces of euphausiids. The worm-like organisms were probably parasites such as tapeworms. The partially damaged euphausiids were identified as Euphausia pacifica except for one individual of Nematoscelis difficilis. Based on the number of fragmented right mandibles, which were less damaged than the other fragmented appendages, the total number of euphausiids in the stomach contents is estimated to be at least 18,000 individuals. The high abundance of euphausiids in the stomach contents suggests that the present specimen has fed on a swarm of E. pacifica in an oceanic area.

著者

Itoh Hiroshi Nishida Shuhei

出版者

日本プランクトン学会、日本ベントス学会

雑誌

Plankton & benthos research (ISSN:18808247)

巻号頁・発行日

vol.2, no.3, pp.134-146, 2007-08-01

参考文献数

48

被引用文献数

3 14

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A 17-month field survey and laboratory experiments were conducted to investigate the life cycle, seasonal population fluctuations, and salinity tolerance in the poecilostomatoid copepod Hemicyclops gomsoensis associated with the burrows of the mud shrimp Upogebia major and the ocypodid crab Macrophthalmus japonicus in the mud-flats of the Tama-River estuary, central Japan. On the basis of sample collections in the water column and from the burrows, it was revealed that H. gomsoensis is planktonic during the naupliar stages and settles on the bottom during the first copepodid stage to inhabit the burrows of U. major and, to a lesser extent, those of M. japonicus. While females carrying egg-sacs were present throughout the year, the copepods' reproduction took place mainly during early summer to autumn with a successive decrease from autumn to winter. Occasionally the copepod populations in the burrows suffered from severe flushes of river water that led to salinity decreases in the burrow water to fatal levels, but usually the salinity in the burrow was within optimal levels and permitted recovery and maintenance of the populations.

著者

Saito Shinsuke

出版者

日本プランクトン学会、日本ベントス学会

雑誌

Plankton & benthos research (ISSN:18808247)

巻号頁・発行日

vol.4, no.4, pp.160-166, 2009-11-01

参考文献数

15

被引用文献数

2

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Density and adult ratio of the symbiotic harpacticoid copepod, Idomene purpurocincta, living in the colony of the compound ascidian host, Aplidium yamazii, were investigated on the specimens taken from a boulder shore of Tosa Bay, western Japan, to know how these ecological parameters of the symbiont were related to the host size. Field collection of the host ascidian was carried out during the low tide in every spring tide from December 2004 to August 2006. All of the copepods isolated from the hosts using menthol were enumerated according to ontogenetic stages. The ascidian host colonies appeared from January to June 2005 and from December 2005 to August 2006. The symbiotic copepod was found in all of the hosts with few exceptions even at the initial appearance of the hosts in each season. These facts suggest that the copepod entered the host immediately after the colony formation. The density of the copepod in a host was usually >103 individuals per gram of host in dry weight. An exponential negative correlation was seen between the copepod density and the host size, and the density varied less as the host size increased. The adult ratio of the copepod also greatly varied in small hosts and tended to converge to about 25% with increase of the host size, and was negatively correlated with the copepod density. The reason for these host size-related copepod density and adult ratio may be explained by recruitment of nauplii in a host and migration of adults among hosts.