Life history of the copepod Hemicyclops gomsoensis (Poecilostomatoida, Clausidiidae) associated with decapod burrows in the Tama-River estuary, central Japan

Abstract

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.

Burrow association of Hemicyclops (Copepoda: Poecilostomatoida) as a possible strategy for predator avoidance

“…The abundances of Hemicyclops spp. in the burrows are expressed as individuals per burrow for the Macrophthalmus burrows and individuals per 1000 mL burrow water for the Upogebia burrows, because the water in the former was almost entirely sampled whereas for the latter the water was not entirely sampled due to the large volume of each burrow (Itoh & Nishida 2007).…”

“…The abundances of burrow-associating stages (CII-CVI) of Hemicyclops species were investigated monthly from April to September 2000 by sampling three to 10 burrows of M. japonicus in the Macrophthalmus-Area and U. major in the Upgebia-Area by the methods described in Itoh & Nishida (2007). The abundances of Hemicyclops spp.…”

“…The major benthic habitats of H. gomsoensis are the burrows of the mud shrimp Upogebia major (de Haan) and those of the ocypodid crab Macrophthalmus japonicus (de Haan). Hemicyclops spinulosus have been found from burrows of M. japonicus and those of the polychaete Tylorrhynchus heterochaetus (Quatrefages) (Itoh 2001, Itoh & Nishida 2007, 2008, while H. ctenidis occurs in the burrows of another polychaete Hediste sp. (referred to as Neanthes japonica (Izuka) in Ho & Kim 1990).…”

“…In the Tama-River estuary five species of Hemicyclops have been recorded from the burrows of invertebrates, among which H. gomsoensis Ho & Kim is the most abundant, followed by H. spinulosus Itoh & Nishida and H. ctenidis Ho & Kim which are much rarer (Itoh 2001, Itoh & Nishida 2007. These copepods are planktonic during naupliar stages, and shift from the water column to the mudflat substratum during the first copepodid (CI) stage to inhabit invertebrate burrows (Itoh 2001, Itoh & Nishida 2007.…”

“…These copepods are planktonic during naupliar stages, and shift from the water column to the mudflat substratum during the first copepodid (CI) stage to inhabit invertebrate burrows (Itoh 2001, Itoh & Nishida 2007. The major benthic habitats of H. gomsoensis are the burrows of the mud shrimp Upogebia major (de Haan) and those of the ocypodid crab Macrophthalmus japonicus (de Haan).…”