Phillips, D.G. (1976). The Biology of the Predatory Calanoid Copepod Tortanus discaudatus (Thompson and Scott) in a New Hampshire Estuary. Ph.D. Thesis, University of New Hampshire, Durham, New Hampshire, U.S.A. 152 pp.

108051

Phillips, D.G.

1976

152 pp.

Publication

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The biology of the predatory calanoid copepod Tortanus discaudatus (Thompson and Scott) was studied with field investigations of population fluctuations and with behavioral observations on feeding and reproduction in the laboratory. Plankton tows showed that JL discaudatus was most abundant during the winter, attaining greatest density in February at 85/m^, and was rare to absent during the summer. Its appearance coincided with decreasing temperature and seaward migration of planktivorous fish. An explanation is presented for the utilization of 1L discaudatus as a substrate for the benthic diatom Licmophora sp., via an intermediate host, Eurytemora affinis. Adult T_. discaudatus reacted to low salinity (to 14 o/oo) stress by increasing prey consumption. Below 14 o/oo prey consumption and egg production decreased. Loss of pigmentation and decreased mobility occurred at 12 o/oo. Salinities of 8 o/oo and lower were fatal. For attack initiation, T. discaudatus was dependent upon the movement of prey within an imaginary cone up to three body lengths ahead of the body and approximately 50° away from the body axis. The attack path extended to three body lengths in less than 1/30 second, and the prey was grasped by the extension and flexion of the Tortanus mouthparts. The degree and manner of consumption depended on the size of the prey. A prey wider than 0.4 mm was difficult to consume completely. Tortanus attacked those potential prey which displayed a fast, repetitive movement of the appendages. Copepods of the genera Acartia, Centropages, Temora, Pseudocalanus, Eurytemora, and Oithona were preferred as prey. Artemia, fish larvae, and Podon were accepted only under starvation at 10° C. Prey consumption by adult T_. discaudatus was determined in the laboratory using natural prey species of copepods (1.3 mm mean length, 12.0 pg dry weight). Males consumed fewer prey than females and lived for shorter periods. Both male and female subjects consumed approximately their own weight in prey daily. Females produced approximately 17 eggs per day to a maximum of 1624 eggs per female over 97 days. At 4° C T^. discaudatus consumed fewer prey per day and was more efficient in producing eggs per prey consumed than at 10° C. Females lacking sufficient sperm reserves to lay viable eggs consumed less prey per day than productive females. Isolated males consumed more prey per day than did males contained with females. The daily consumption by a pair of T^. discaudatus at 10° C was approximately 6 prey of the size indicated. At 4° C the rate was 4.5 prey per day. ]T. discaudatus males entered precopula by grasping the posterior margin of the female caudal furcae from below with the right geniculate antennule. The male immediately curled ventrally and grasped the base of the female caudal furcae with the chelate right fifth leg. In copula, the male urosome was bent sharply to the right with the caudal furcae placed under the female genital segment. After extrusion, the spermatophore was manipulated by the male left fifth leg and the male urosome. Males risked injury inflicted by the female if mating postures were not correct. Pairs remained coupled for 20 min to 24 hours. Elongate eggs were laid in clutches of 6 to 30. Eggs from females held at 10° C., were exposed to various combinations of temperature (4° to 20° C) and salinity '(0 to 38 o/oo). The hatching success was lower and development rate depressed at low salinity. Increased temperature shortened the development period. Some of the eggs held in distilled water for 60 days were able to mature and hatch after transfer to 32 o/oo seawater. It appeared unlikely that eggs of Tk discaudatus achieve a true resting state in the Piscataqua River within the normal geographic range of the adults.

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