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On the Life History of Nereis Grubei (Kinberg), a Polychaete Annelid from Californial

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On the Life History of Nereis Grubei (Kinberg), a Polychaete Annelid from Californial On the Life History of Nereis grubei (Kinberg), a Polychaete Annelid from Californial PAUL C. SCHROEDER2 RELATIVELY LITTLE INFORMATION is yet avail­ of February the animals are more abundant in able on the life histories of nereid polychaetes holdfasts of the highest specimens of the brown from the eastern Pacific. Johnson (1943) has kelp Egregia menziesii. In order to collect the raised some intriguing problems concerning animals from their burrows in the kelp the N ereis vexillosa, which have not been further holdfasts must be removed from the rock with explored, and Smith (1950) has reported de­ a hammer and chisel and carefully dismembered. tails of the life history of Nereis limnicola During the summer only a few, usually very (= Neanthes lighti) , an interesting viviparous, small specimens can be recovered from these euryhaline species. Information is also available holdfasts; this was tested by allowing summer­ for a southern Californian population of N el'eis collected holdfasts to stagnate in a pan until grubei, a species which reproduces more typi­ animals emerged from the inaccessible inter­ cally. The present paper deals with a central stices. It seems probable that the worms move Californian population of N. grubei from Pes­ into the kelp holdfasts for the winter, when the cadero Point, Monterey County. Interesting dif­ surf is most violent. Such seasonal habitat shifts ferences between these .two populations with are known in other intertidal animals from this respect to physiology and breeding season have area as well (e.g., the isopod Idothea monterey­ come to light during the course of an investiga­ ensis [see Lee, 1966]). tion of nereid metamorphosis (Schroeder, The habitat reported by Reish (1954b) for 1967) . the species at Point Fermin in southern Califor­ nia appears to be somewhat different. He found HABITAT N. grubei in algal tufts in or between tidepools scoured from a wide, flat rock ledge. The ledge At Pescadero Point, Monterey County, Cali­ is strewn with scattered boulders and sheltered fornia, N ereis grubei occurs on an exposed from the surf by offshore kelp beds. At Point coast where the surf can be quite violent, even Fermin the worm was found to be associated though offshore kelp beds are well developed. with a number of different species of algae, The intertidal region is composed chiefly of chief among which is Cladophora trichotoma. large boulders covered with abundant algae of This alga occurs in central California as well, many species. The worms may be found here in and a search through tufts of it near the Hop­ two different situations, in which their abun­ kins Marine Station, not far from Pescadero dance varies with the season. During the spring Point, failed to yield any specimens of N. grubei, and summer they are most readily found in the although the worm occurs beneath Gastroclo­ sandy substrate beneath the common red alga nittm in the same area. Although Reish surveyed Gastroclonium cottlteri. Some specimens may be the algal associates of the species at Point Fer­ found in this situation throughout the year, but min he mentions neither Egregia menziesii nor from the beginning of October until the middle Gastroclonium cottlteri, the two major algal as­ sociates at Pescadero Point. The former is not 1 A portion of a dissertation submitted to the Graduate Division of Stanford University in partial found south of Point Conception, but the latter fulfillment of the requirements for the degree of is recorded from as far south as San Diego Doctor of Philosophy. Manuscript received Septem­ (Smith, 1944). It thus appears that the more ber 26, 1967. northerly population favors Gastroclonium, de­ 2 Hopkins Marine Station, Pacific Grove, California. Present address: Department of Zoology, Washington spite the presence of Cladophora, and that the State University, Pullman, Washington 99163. opposite is true for the southern population 476 Life History of Nereis grubei-ScHROEDER 477 (although I do not know whether Gastroclo­ and sought, but not found.) Such nearly ma­ nium is abundant at Point Fermin). ture animals probably swarmed within a couple In an ecological study at the Hopkins Marine of days of being observed, although swarming Station, not far from Pescadero Point, small itself was never observed. numbers of N. grubei were found by Glynn The fact that maturing animals are found on (1965) in association with another alga, En­ separate occasions, and not in intervening pe­ docladia muricata. This alga is not included in riods, implies that specimens within the popula­ the list given by Reish for the southern Califor­ tion mature at different times. It should thus be nia population. possible, in midwinter population samples, to separate animals destined for different spring­ time spawnings. OOGENESIS AND METAMORPHOSIS Oocytes have been shown to grow at two dif­ N ereis grubei was collected every two weeks ferent rates, both in N. grubei (Schroeder, at Pescadero Point, Monterey, California, for a 1966) and in N. diversicolor (Clark and Rus­ period of 17 months. During the period of ton, 1963). Thus in N. grubei the oocyte oogenesis the average oocyte diameter was de­ growth rate (rate of diameter increase) seems termined for a number of specimens from each to accelerate when the oocytes are about 100"" collection; the number of specimens so deter­ in diameter, and it is at about this time that the mined varied with experimental requirements. first histological signs of metamorphosis can be All diameters were measured from fresh coelomic detected (Schroeder, 1967). This fact is utilized samples with a calibrated ocular micrometer and in Figure 1 in an attempt to follow the develop­ a compound microscope. Fixation in Bouin's ment of each monthly swarm within the popu­ fluid made up with picric-acid-saturated sea lation as a whole. The dotted lines are projec­ water was found to cause an irregular expansion tions based upon the apparent time of swarming, of the oocytes (Schroeder, 1966). In some ani­ estimates of the growth rate during the two mals, oocytes of considerably different diameters phases, and the recorded oocyte diameters. It is were present, but in most of these the recorded assumed that the oocyte growth rates are similar diameters fell into distinct size classes. In such in the component animals of successive spawn­ cases only the average diameter of the largest ings. Each month on the graph has been sub­ size class was utilized in the life history study. divided into 3-day periods, so that the positions In the few cases in which size classes were not of the points within a month are significant to evident, the diameters of all the oocytes from a within three days. It will be seen that during single animal were averaged together. It is the fall animals with oocytes of a wide range of probable that such figures are lower than the sizes are present, but that these are not separ­ value truly comparable to the others. The aver­ able into distinct groups until December, when age oocyte diameter was used as an index to most specimens can be assigned to a spawning the age of female animals. group, even though the oocytes are still small Oocytes could be found in at least a few ani­ and growing slowly. It is possible that the dif­ mals throughout the year. Oogonia and tiny ferent spawning groups are distinct from the oocytes appear in June, when very few matur­ initial moment of oogonial differentiation, but ing females remain from the previous year's the variability of oocyte sizes present in young spawning group. The oocytes probably reach animals prevents their recognition. maturity (about 200",,) in 7-8 months. The A number of animals was maintained in the young oocytes grow slowly through the fall and laboratory over a period of weeks and the growth early winter, and the population gives rise to of their oocytes was checked by repeated samp­ several swarms between mid-February and mid­ ling. These sampling points have also been in­ June. The occasions on which nearly mature cluded in Figure 1 and are connected with females were found in the field are indicated by heavy lines. It will be seen that all but two of the short vertical bars at the top of Figure 1. these animals were derived from the April (The 0 in mid-March represents a day on spawning group, while two others metamor­ which metamorphosing animals were expected phosed sooner and were closer to the March " i 01>­ OOCYTE DEVELOPMENT -...J AND METAMORPHOSISi IN NEREIS GRUBEI 00 AT PESCADERO POINT, MONTEREY CO. CAUFORNIA ~ 21 I i I, ~ II~I~ -i-I,·-/-- =t190 '. Wii, Ji I - / ,/ II11 !ll: /':. // i,SO / /. ,.: 11' 1/ ,:/ // // 130 / A:' . I J .M ',, ~ 110 ...-r:' J/ tj!-//J/i ~ o {~-:':>l:::lJ;>/ "!'j g90 . / ...... (') /xl~,> /l /'; /' en 70 ::~;-2tJj~~:~:::l' (') 50 II ! <: 30 r ii' 'j , .. i / i , ,::: ," i"· ii' .1 , ~ I~'; Jan; Feb Mar Apr May June July Aug SepfOcf Nov Dec Jan Feb Mar Apr MayJune July Aug ~~ f ~ 1965 MONTHS 1966 B ~...... ilf FIG. 1. Oocyte development and swarming in Nereis grubei at Pescadero Point, Monterey County, California. Each point in the 1966 series represents the average oocyte diameter of an animal collected on the date indicated. Dotted lines represent the postulated progress of several subgroups within the population o,.., toward their respective swarming dates. Solid lines represent growth rates from individual animals. The solid line on the left connects the largest oocyte S- diameters found in each collection. Days on which very mature specimens were found ,in the field are indicated by a vertical line through the delimited zone O"' ~ which includes the range of oocyte diameters found in swarming females.
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