THE LIFE HISTORIES AND POPULATION DYNAMICS OF THE POLYCHAETE$, NOTHRIA ELEGANS (JOHNSON) (ONUPHIDAE) AND MA.GELONA SACCULATA HARTMAN (MAGELONIDAE) IN MONTEREY BAY, CALIFORNIA
A Thesis
Presented to
The Faculty of the Department of Biological Sciences
San Jose State University
In Partial Fulfillment
of the Requirements for the Degree
Master of Arts
By
Cheryl Ann Hannan
May, 1980 ABSTRA..CT
The lychaetes Nothria elegans (Johnson) (Onuphidae) and
~1agelona sacculata Hartman (Magelonidae) were examined for several life history parameters (primarily size-frequency, size at maturity, breeding periodicity, fecundity, egg size and larval settlement) on a monthly basis for a year at three stations in the shallow
(14 m) subtidal sa7l.dflats in Monterey Bay, California. Both species exhibited seasonal spawning peaks in the winter and spring and peaks in larval settlement in thB spring and summer, but also had low levels of spavming year-round. Magelona reached maturity
in approximately two months and probably spavmed in its first year with death occurring at or shortly after spawning. This species had small eggs, high fecundities ~nd long-lived (at least two months) planktotrophic larvae. Abundance data on other populations
of Magelona in Monterey Bay indicated that densities were sometimes
extremely variable form year to year. Population densities of
Nothria also varied from year to year, but not as drastical as
Hagelona's. At the study sites Nothria had egg sizes twice and
fecundities half those of .Magelona and the lecithotrophic larvae
of Nothria have been reported to stay in the water column for only
sL'i: days. This species appeared to be i teroparous and thus more
than one year class may be contributing to the spawn each year. It
is probable that Nothria does not spa~l until its second year.
This, combined with the short planktonic life of the larvae and the
perennial nature of the species, contributes to its more stable
population densities compared to those of Magelona.
iii Although Nothria, Magelona and anotheT po aboundant at the study sites-,· Thalanessa spinosa (Hartman) spawned generally in the winter and spring with larval settlement in the spring and summer, the specific breeding cycles within this period varied with species" A single control mechanism for breeding act.ivity
(_e.g., temperature or food availability) is thus unlike I suggest that factors including coastal upwelling during late win ter and spring, food availability, species-specific predation, and the seasonal disturbance caused by wave surge affecting burro1ving and tube building may all be involved in producing the species specific breeding trends.
Unusual patterns of high larval settlement of Nothria and
low adult abundances of Magelona during the study period Here
correlated with the 1975 through 1977 drought in California.
During these winters considerably decreased river runoff may have
caus:ed changes in the supply of organic material to and salinities
in the bay.
Trends in larval settlement data as well as water character-
is·tics and circulation patterns in Monterey Bay suggest that lar
vae of both species are supplied to the bay from the south where
they settle first, leaving fewer larvae to settle in northern
areas of the bay. The north bay, however, may confer greater
survival to Nothria adults.
iv AC KNOWLEDGB-1ENTS
I begin by thanking Dr. John Oliver and Peter Slattery for sticking my head in the mud in the first place and Dr. James ken for agreeing that it should be there. This thesis resulted from a communal effort by many excellent folks at 'Moss Landing
Marine Laboratories. I especially thank my number one dive buddies,
Larry Hulberg and Jim Harvey, for their humor, curiosity and heroics.
Larry also identified the polychaetes and fed roe lunch. Mike Kelly,
Kathy Casson and Lynne Krasnow also gave their valuable dive time. l·iany fine people aided in the sieving, picking, egg measuring and egg counting of the worms, in sediment analyses and in data reduc tion; among them are; Jim Barry, Jane Dykzeul, Elaine Goepfert,
Monica Farris, Sandy Hawes, Signe Johnson, ~like Kelly, Jim Oakden,
Dan Reed, Teresa Turner and Bill Wright.
Though I learned something special from all the people with whom I worked, several provided especially good perspective and ideas: Bill Wright, Drs. John Oliver, Fred Nicnols, Ann Hurley,
Fred Grassle and Jim Carlton. Jim also gave generous editing assistance. Drs. William Broenkow, Ann Hurley, Greg Cailliet and
James Nybakken all made valuable comments on various drafts of this thesis. I especially extend my heartfelt thanks to Ann and
Dr. Nybakken for their encouragement and friendship.
Finally, I thank Kathy Casson for filling in all the gaps.
This research_ was supported by a grant fTom the California
State Water Resources Control Board awarded to Dr. James and Moss Landing Marine Laboratories.
v TABLE OF CONTENTS
Page
LIST OF TABLES. . vii
LIST OF FIGURES , . viii
INTRODUCTION. 1
Purpose . l Description of the study species. 6 Description of study sites. 8
JV!A TERIALS .A.ND METHODS • • . • • 16
Collection apparatus and procedures 16 Life history analyses 21
RESULTS ... 27
Abundance data. 27 ry') Size--frequency. :J~ Fecundity (_static) and egg size 41 Size at maturity and breeding cycle 56 Larval settlement ...... 66 Gut contents of Nothria . . . 72 A commensal relationship with Nothria 73
DISCUSSION.
Nothria elegans: reproductive biology and breeding cycle. 73 ~·1agelona sacculata: reproductive biology and breeding cycle-.-...... 86 Factors controlling breeding cycles and population densities. 97
SUMM.c\RY ••••• 110
LITERA~JRE CITED. 112
vi LIST OF TABLES
Table Page
1. Post--larvae size class distribution of Nothria elegans from February through May 1977 at the outfall, plume and windmill stations. . . 29
2. Monthly mean setiger number where eggs begin and end and mean total number of setigers, all ± two stan dard error$ for all Nothria elegans individuals for which these parameters were measured. . . 42-43
3. Relationship of number of setigers with eggs to mean fecundity, total number of setigers and time of year for Nothria elegans at the plume station ...... 44-45
4. Mean setiger number where eggs begin and end and total number of setigers, all ± t\vO standard errors for all Magelona sacculata individuals on which these parameters were measured . . . 50-51
5. Relationship of the number of setigers with eggs to mean fecundity, total number of setigers and time of year for Magelona sacculata at plume station ...... 52
6. The occurrence of Gyptis brevipalpa in the tubes of Nothria elegans in sieved, preserved and sorted samples...... 74
7. A comparison of densities (number per m2) of Nothria elegans from 1971 through 1977 at several stations in Monterey Bay...... 81-83
8. A comparison of densities (number per m2) of Magelona sacculata from 1971 through 1977 at several stations in Monterey Bay ...... 89-91
vii LIST OF FIGURES
Figure
1. Monterey Bay, California ..... 9
2. Watsonville study sites (outfall, plume and windmill), M-transect stations of Oliver et al. (1977) and Salinas River stations of ESI (_1979). • ...... 10
3. Cumulative percent of total species collected per replicate for Watsonville stations in September 1976 ...... 18
4. Rack holding jars to collect larvae and tubes to collect settling particulates. 19
5. Length and width measurement regions for Magelona sacculata (top) (from Hartman, 1969) and Nothria elegans (bottom) (from Hartman, 1968) 22
6. Plots of length times width of first nine setigers versus total length of Nothria elegans. 24
7. Abundances of Nothria elegans per macrofauna! core (area= 0.018 m~) at outfall (top), plume (middle) and windmill (bottom) ...... 28
8. Abundances of Magelona sacculata per macrofaunal core (area= 0.018 m2) at outfall (top), plume (middle) and windmill (bottom) ......
9. Size-frequency histograms for Nothria elegans collected at the outfall station. . . 33
10. Size-frequency histograms for Nothria elegans collected at the plume station. . . 34
lL Size-frequency histograms for Nothria elegans collected at the windmill station . . 35
12. Size-frequency histograms for Magelona sacculata collected at the outfall station ...... 36
Size--frequency histograJns for Magelona sacculata collected at the plume station ......
14. Size-frequency histogra.ins for Magelona sacculata collected at the windmill station ...... 38
viii LIST OF FIGURES, continued
Figure Page
15. Honthly graphs of fecundity versus size (.area of the first nine setigers) for Notfiria elegans. 46
16. Oocyte size-frequency distributions of all Nothria elegans individuals on wfiicfi fecundity- was estimated from the windmill station. • . . • . 48-49
17. Monthly graphs of fecundity versus size (area of the first nine setigcrs) for Magelona sacculata. 53
18. Oocyte size-frequency histograms for all }.iagelona sacculata individuals for which fecundity was estimated at the windmill station...... 54-55
19. Breeding cycle determination for Nothria elegans at the outfall station, graphing several parameters which may indicate periodicity of spawning activity...... 58
20. Breeding cycle determination for Nothria elegans at the plume station, graphing several parameters which may indicate periodicity of spawning activity...... 59
21. Breeding cycle determination for Nothria elegans at the windmill station, graphing several para~eters which may indicate periodicity of spawning activity...... 60
22. Breeding cycle determination for Magelona sacculata at the outfall station, graphing several parameters which may indicate periodicity of spawning activity. . . . ; ...... 61
23. Breeding cycle determination for Magelona sacculata at the plume station, graphing several parameters which may indicate periodicity of spawning activity...... 62
24. Breeding cycle determination for Magelona sacculata at the windmill station, graphing several parameters which may indicate periodicity of spawning activity ..•...... 63 LIST OF FIGURES, continued
Figure
25. Results of the larval jar, meiofauna core and quarterly macrofauna core (data from Hannan et al., 1978) collections of Armandia orevis at the outfall and windmill stations .. 67
26. Results of the larval jar, meiofauna core and quarterly macrofauna core (data from Hannan et al., 1978) collections of Capitella spp. at the outfall and windmill stations .. 68
27. Results of the larval jar, meiofauna core and quarterly macrofauna core (data taken from Hannan et al., 1978) collections of Prionospio pygmaea at the outfall and winmdill statlons. 69
28. Results of the larval jar, meiofauna core and macrofauna core collections of Nothria elegans at the outfall and windmill stations...... 70
29. Size-frequency histograms for Magelona sacculata collected at lvl-5 (from Hannan et al, 1978). 92
30. The reproductive timing of Magelona sacculata at M-5 (from Hannan et al., 1978) based on percentage of individuals which were ovigerous and immature each month ...... , . 93
31. Percent organic carbon values in core samples (lower lines) at outfall and windmill stations and in settling tubes (upper lines) at outfall and windmill stations ...... 103
X INTRODUCTION
f._~rpose
An understanding of the natural variability of marine benthic
communities is essential in elucidating the effects of man-induced
changes upon the marine environment. Listing species present
and grouping them into associations must be followed by ecological
analyses that ask questions about the variability and maintenance
of individual species populations.
The present s-tudy addresses the organization of the shallow
subtidal sandflats of central Monterey Bay, California through
examination of the life histories of two abundant polychaetes,
Nothria elegans (Johnson) (Onuphidae) (hereafter referred to as
Nothria) and :Magelona sacculata Hartman (Magelonidae) (hereafter
referred to as Magelona). Using specific life history data on
these two species, quantitative population data on other
co-occurring polychaetes, and physical environmental data, the
objectives of this study were: (1) to describe the life histories
and population dynamics of Nothria and Magelona, and to
ascertain factors important in determining the breeding periodicities
and resultant population fluctuations of these species. This work
was part a larger study that developed methods for doing life
history studies on benthic invertebrates (Hannan et al., 1978).
It is from this study that the community and sediment data are dravm.
The life history of a species covers a wide variety of
1 parameters, including feeding mechanisms, habitat preferences movement patterns, genetic characteris"tics, growth, and repro-
duction, to name a few. In the literature, however, especial
that concerning theoretical ecology, life history studies have
become synonymous with studies of reproductive biology (e.g.,
Stearns, 1976, 1977 ivho reviews this literature). In the present
study a discussion of life history characteristics will be
similarly limited mainly to reproductive parameters.
Little information exists regarding the life histories of
most polychaete species, including those in cen~ral California
and Monterey Bay. Life history studies in the subtidal sandflats
of Monterey Bay are limited to three studies. Oliver et al.
(1977) reported general life history characteristics of dominant
polychaetes, crustaceans and molluscs in their analysis of commun-
ity recovery following dredging and dredged spoil disposal in
Monterey Bay. Hannan et al. (1978) studied life history parameters
of benthic polychaetes, crustaceans and molluscs in .Monterey Bay
in preparation for their report on methodology to use in life
history studies for environmental assessment. The life histories
of several polychaete ~nd crustacean species were also examined in
a baseline study of a predisposal, predischarge sewer outfall site
in Monterey Bay (ESI, 1979).
Numerous laboratory studies of the lar1al development and
reproduction polychaetes have been done in California
1954, 1957, 1976, 1977; Woodwick, 1960, 1977; Dean and Blake, 3
1966; Richards, 1967; Blake, 1975a, l97Sb; Blake and Woodwick,
1975; Carr and Reish, 1977; Reish and Carr, 1978). However, field studies on California polychaetes in conjunction with or separate from laboratory work are few (Schroeder, 1968; Euerson, 1975).
Literature that addresses various aspects of the life histories of non-California polychaetes (see Schroeder and Hermans, 1975; also Hannan et al., 1978 for a bibliography of polychaete life history studies) is of limited value for comparative purposes.
There is some danger in inferring the life history of a species from data on the same species taken from a different connnuni ty, geographical location, or environmental setting, or studied at a different time of year.
Most marine invertebrate species demonstrate considerable variability in life history characteristics (see Hannan et al.,
1978); polychaetes are no exception. This variability may be attributable to the populationts biological and/or physical environment. Generalizations regarding life history characteris- tics cannot be made at the familial or generic level since repro ductive biology in polychaetes may vary markedly with species
(Richards, 1967) or with geographical location (Dean and Blake,
1966; Schroeder, 1968). For example, variations in development are knmm to occur within the spionid genera Polydora (Woodwick ..
1960; Blake, 1969} and Pseudopolydora (Blake and Woodwick, 1975).
Changes in development and modes of reproduction for a 1e species within its geographic range (poeci 1 have been 4 reported for the cirratulid. Cirriformia tentaculata (Montagu)
(George, 1967); the spionids, Polydora quadrilobata Jacobi
(Blake, 1969), !:: giardi Mesnil (Day a,'"ld Blake, 1979), Spio setosa Verrill (.Simon, 1967, 1968) and S. martinensis Mesnil (Hannerz,
1956). Differences in breeding periodicity at the same geographical location were reported for four species of cirratulid in one inter-. tidal area (_Gibbs, 1971). In different geographical locations, differences were reported in the breeding season of Nereis grubei
(Kinberg) (Nereidae) from northern and sourthern California
(;Jchroeder, 1968) and in the larval behavior of Boccardia hamata
(Webster) (Spionidae) from the east and west coasts of North
~~erica (Dean and Blake, 1966).
In all the above cases, the variation reported might be due to the single species studied actually b.eing a species complex
(e.g., Day and Blake, 1979). Such a species complex has been reported for the capitallid, Caoitella (referred to in most liter ature as the single species fapitella capi tat a [Fabricius]).
Grassle and Grassle (1976, 1977) reported six genetical distinct components of populations of this polychaete. Slight morphological differences in the larvae and varying life history traits were also reported. They termed these "sibling species.n Up to five of these sibling species occurred in a single area different abundances of each in polluted and non-p.olluted environments (see also Grassle and Grassle, 1974).
In summary, it is difficult if not impossible to generalize 5
about polychaete life histories either by taxonomic group or geographical location. Clearly there is a need in ecological work
for life histories to be studied concomitant with corn.muni ty studies o
Most studies describing the life histories and population dynamics of an organism have not attempted to relate reproductive strategies to enviro·nmental and biological phenomena. Several recent exceptions exist. Watling (1975), Boesch et al. (1976),
Holland and Polgar (1976) and Holland et al. (1977) used quali- tative life history characteristics (usually the degree of "oppor tunism" and/or the general time of spawning as delineated in
some other study) of numerically dominant species to explain
spatial and temporal differences in communities. lffiitlatch (19 used size-frequency and breeding cycle data of the numerical
abundant polychaete populations at Barnstable Harbor, !vlassachusetts
to explain seasonal trends in community stru.cture. Watling (1975),
working in Rehoboth Bay, Delaware, also used size-frequency data
of tl'i"O polychaete species at peak densities to chaTacterize
their spawning cycles. Grassle and Grassle (1974) and McCall (1
studied defaunated substTata to elucidate colonization patterns,
and interpreted theiT results relative to the life histories of the
abundant organisms in the newly-formed communities. A final example
of a study in which the population and enviro~~ental data on a
polychaete are co-related is that of Nichols (1977). Nichols
demonstTated that wide yearly population fluctuations of the
polychaete Pectinaria koreni (Malmgren) in Kiel Bay, Germany were 6
due to the presence or absence of henthic oxygen deficient con ditions in shallow subtidal areas of the bay.
Description of the study snecies
Nothria elegans is a large (to 16 em at the study sites), jawed tubiculous polychaete of the family Onuphidae. It has been repor ted from the intertidal zone to 200 ~ in mud and sand from western
Canada to southern California (Hartman, 1968). Within the super family Eunicea, the family Onuphidae is one of the best repre sented in deep water (Fauchald, 1977). Jumars and Fauchald (1977) descrihe the feeding strategy of the Onuphidae as "surface deposit feeding, sessile or discretely motile, jawed" (p. 4). Nothria is probaoly an omnivore and will capture and ingest swimming brine shrimp (Artemia) and barnacle nauplii in the laboratory (Blake,.
1975a). The permanent parchment tube is affixed with sand grains and may oe a meter long. The ani~als may be able to choose the sand grain s·izes they use in tube construction (Blake, 1975a).
The reproductive and developmental biology of the Eunicea is relatively well-.documented (see review by Richards, 1967). There is a dearth, however, of comprehensive population and life history studies·, and only on~ such study is available for a California onuphid, that of Emerson (1975) on Diopatra ornata Hartman,
Developmental studies of California Eunicea are limited to the larval development of Nothria elegans from Tomales ake,
1975a} and tlie reproduction and development of Stauronereis _ru_d_o__ .___
(Pelle Chiaj (J)or;illidae) from Los Angeles harbor (Richards, l 7
Magelona sacculata belongs to the fai'Ilily Magelonidae charac- terized as "surface deposit feeding, dis.crete motile, tentaculate" forms by Jumars and Fauchald (1977, p. and reaches a maximum length of six em at the study sites. It lives in a "flimsy tube structure" (Fauchald, 1977, p. 26) in a well-sorted sand envirorunent selectively feeding on microscopic organic debris, diatoms and small animals and plants which collect at the bottom of ripples (Jones,
1968). The burrow wall is probably maintained by mucous secretions
(Jones, 1968}. The tentacles can extend from the burrow 15 to 20 m.m in the overlying water column; when a food particle is contacted, the tentacle forms: loop after loop on its papillated surface to pass the food dovm to the mouth. A free-fall of the food into the mouth afte.r it gets beyond this papillated region of the tentacle has been suggested (,Jones, 1968), Though Jones has studied the morphology, feeding and f:Jehavior of Nagelona sp. in detail, v;ith the exception of a study of the breeding cycle of Magelona sacculata in Monterey Bay reported by Oliver et al. (1977) and Hannan et al.
()978}. there are no accounts of Magelona reproduction. Magelona sacculata has· been reported from southern California in 10 to 40 m on silt oottom (Bartman, 1969) as well as in the shallow subtidal of Monterey Bay (J-lodgson and Nybakken, 1973; ERC, 1976; Oliver and
Slattery, 1976; Oliver et al., 1977; ESI, 1979).
Magelon2:_ taxonomy was under revision during this and proolems· arose in identifying juveniles (Jess than t:wo :mm in total
length}. At least three species of f.~agelona occur in Monterey
Nagelona sacculata, M. pitelkai Hartman and 1'-L hartmanae Jones, 8
Jones (1978) recently described the latter species and redescribed
M. Ditelkai. Though Jones clearly separates all three species as adults, juvenile identification is tenuous and sometimes impossible,
Description of study sites
Three s~upling sites were established in central Monterey Bay in the vicinity of the Watsonville Sewer Outfall (Figures 1 and
The outfall is located 1. 2 km seaward from the community of Paj aro
Dunes at a depth of 14m (MLLW) at 36°50.8 N, 121°49.4 1 W,
Stations established along the 14 m contour at the outfall terminus,
50 m north, and about 400 m north of the outfall were designated
"outfall," 11 plume, !l and "windmill" respectively (Figure 2), and were marked by permanent buoys. The latter two stations are referred to as control stations. However, the element that dis tinguished the outfall station from the controls appeared to be the pipe structure itself, a11d not the effluent as a source of pollution. This is discussed later in this section. Sampling began in September 1976 and continued through December 1977.
Central Monterey Bay is characterized by high energy beaches that have a gentle seaward slope and a distinct winter berm. Pre vailing wind direction ~id wave arrival are from the northwest from February to September, during the upwelling period, and from the southwest from November through January. Winds diminish from
September to November (Bolin and Abbott, 1963). Wave refraction along the Monterey Submarine C&!ycn concentrates wave energy on the beaches north of Moss Landing and disperses wave energy in the can- 9.
:· --~~---- ;:~;; ----=:-~ ~- ll . .:·_. . >_ FRANCISCO ',>· .. II -;· ·.• · · ·:· .. ·. BA'f '': .. .I ' ·... ·=·~:-::,h ·:::'·> l .... ::.';>G;~·) I
... ~ ~ ! • • . • Nau fi:oi Mii ••'e ~:r:0<:::·.: PT. ANO NUEVO Monterey 4 zo' l22.. W Figure l. }.lontercy Bay, California. Rectangular is enlarged in Figure 2. 10 DSPTH CONTOURS IN MEiERS Figure 2. Watsonville study sites (gutfa11, phmw and windmill), M-transect location and M-5 station of Oliver et al. 9771 Salinas River stations (1181, 1183, 1185, 11861 of ESI (1979). Note that distance between the latter stations is not to scale on this map; each station is approximately 0.95 k.JTI from the adjacent station, 1181 is accurate placed. 11 yon head at the entrance to Moss Landing Harbor and along the adjacent southern sand flat. The width of the breaker zone and wave height increase dramatically north of Moss Landing. Thus, the study sites were generally characterized by high energy waves and physical reworking of the sediments. The physical reworking of sediments in the shallow offshore zone is often intense and undoubtedly is a major factor controlling faunal distributions and population dynamics of the infauna (Oliver et al., in press). Average monthly surface water-temperature ranges from l0°C to l7°C, mean monthly river run-off for the Salinas River alone ranges from 0 to 100m3/sec and the influx of organic carbon ranges from 0.01 to 0.16 g organic carbon per settling tube (diameter = 3.4 em, height = 30 em; collection over two week intervals); all parameters exhibit marked seasonal patterns (Oliver et al., 1977). The variations in temperature and river run-off over a period of several days are often nearly as great as during the entire year. The Salinas and Pajaro Rivers are the largest sources of sediment to the bay in the winter rainy season. During summer months, the mouths of both rivers are usually closed, but at peak winter discharge highly turbid water extends several kilometers offshore, reducing water visibility and light penetration to zero below a few meters. The flow from year to year is, however, highly variable. The present study was done in the second year of a drought in California and the Pajaro 12 River not flow into the ocean the course of this study. The hydrography of Monterey Bay in the vicinity of the study areas is described by Broenkow and McKain (1972), Broenkow and Benz (1 and Lasley (1977). 1ne outfall consists of a diffuser pipe which discharges primary-treated doemstic sewage from the Watsonville area. Approx imately 5.5 million gallons (mg) of waste are discharged per day, increasing to 8 to 9 mg/day during canning season (August through October). Chlorine and anionic polymers to enhance sedimentation are the only additives to the effluent. The major industrial input is from the canneries, and from Pacific Extrusions, which dumps hydroxides and acids into its waste disposal system (personal communication from Watsonville Wastewater Treatment Facility). The outfall terminus lies in a shallow,..sloping sandflat lope of about 0.03 m vertical per 42 m horizontal) characterized by weak currents (generally less than one knot) parallel to the coast line (ERG, 1976). ERG (1976) reported that the currents from May 1975 to March 1976 offshore of the Pajaro River (Figure 2) around the outfall were dominated by the tides. The submarine canyon has a profound effect on these tidal currents. The incoming tides travel faster in the canyon than on the adjacent shallow shelves; thus, water flows up the canyon, diverges at the canyon mouth and flows north and south parallel to the coast. On the ebb tide, the water flows off the shelves into the canyon, but in a much more diffuse fashion. There is a net northerly current flm¥ l3 1976; ESI, 1979; Lasley, 1977). There is also an onshore-offshore flow of the currents, the onshore component predominating 1976). At least in June, currents south of the submarine canyon are slightly stronger than those north (Lasley, 1977). Sediments are fine to very fine sand with a thin layer (about 0.25 em) of mud at the sediment-water interface (ERC, 1976). The mud layer is deposited by t.he Pajaro River discharging just south of the outfall. This river normally flows during the rainy months (December through March) and the predominant norther currents carry the flocculent material to the outfall area. During the present study, however, the river never broke through the sand dunes to flow into the bay. When the river again broke through the dunes in the winter of 1977-1978, fine mud was observed on the bottom as well as in the water column making water clarity zero about a meter below the surface and at all depths to 14 m for most of the winter and early spring (December through March, personal diving observations). Sediment chemical analyses were done in April to May and in November 1975 by ERC (1976). Though total organic carbon in the sediment was reported_to increase slightly from April to November, and no substantial changes in the trace metal and chlorinated hydrocarbon concentrations between these two samplings were the ERC samples do not constitute an adequate assessment of the chemical nature of the sediment nor the temporal variations in these parameters during 1975 due to the infrequency of sampling. 14 During the study to demonstrate the feasibility of using life history studies as a tool for assessing marine pollution, the Watsonville outfall was used as the lluted site" (Hannan et al., 1978). However, as they admit, neither organic carbon contamination in the sediments, nor a biologically demonstratable pollutant effect in the organisms could ever be detected at the outfall station when compared with the control stations and other areas in Monterey Bay of similar depth and grain size (Hannan et al., 1978). A func tional distinction between "pollutant" and "contaminant" is used here, i.e., the former is "any substance introduced into the envi ronment in amounts sufficient to cause biological damage" (SCCWRP, 1978, p. 4 ), whereas the latter term refers to "an increase above the natural range of values in the amount of some substance .. , [and] ... does not necessarily result in adverse effects" (SCCWRP, 1978, p. 4 ). Percentage of organic carbon and grain size were the principal parameters measured to discern the presence of con taminants, although the number of the colon bacteria, Escherichia coli colonies in the sediment \ (Hannan, unpublished data). Because this outfall is almost exclu sively discharging domestic waste, I feel that organic carbon values as an index of enrichment are a good assessment for the presence of sewage contamination. Sediment sampling methodology and site locations are described in detail elsewhere (Hannan et al., 1978). In sediment samples taken year-round at all three stations 15 and during two periods of more extensive sampling to 100 m north, south and west of the pipe, all organic carbon values were between 0.04% and 0.20% with an occassional patch of higher organics (maximum= 0.56%). These are low values for marine sediments (e.g., Pearson, 1970; Rashid and Reinson, 1979) and do not approach values recorded in organically contaminated and polluted sediments, usually values greater than 2.0% (Reish, 1960; Pearson, 1971; Rosenberg et al., 1975; see also review by Pearson and Rosenberg, 1978) and are within the range of values in other areas of similar depth in Monterey Bay (e.g., Oliver et al., 1977). This suggests that the outfall does not cause an increase in organic carbon in the sediments within a 100 m radius of the pipe. Biological data taken at the three study sites were also remarkably similar between stations. Results of analyses of the polychaete component of the com~unities showed that the stations •N"ere more similar to each other in each quarterly sample than they were to samples from other sampling dates (see results of Bray Curtis similarity index and Jaccard Coefficient of Community Sbnilarity in Hannan et al., 1978). Individual density data of abundant polychaete species also showed temporal variability but no spatial variability for most of the species studied. The few differences seen between stations were not readily lained by a pollutant stress a."'1d were most like a result of natural patchiness in the animal's distribution, or a samp It can thus be concluded that there is no pollutant effect exhibited 16 at the Watsonville study sites using the polychaete component of the community as a biological index. Physical characteristics of the Watsonville area are probably inhibiting settlement of effluent particulat'es near the outfall and are enhancing diffusion and dispersion of the effluent as soon as it leaves the pipe. The diffuser ports along the pipe discharge at an upward angle. This lower density fresh water rises and appears to be almost immediately mixed with surrounding waters by turbulent seas and subsequently carried away by tidal currents. Only during periods of especially calm seas (sUmmer and early fall) were effluent particulates evident in the water colTh~n at the outfall compared to control areas. During such calm periods, the increased turbidity may have an important effect on settling lar;ae leikov~ sky, 1970; Rosenberg, 1977). However, the residence time of settl organics on the bottom appears to be very short and resuspension of the top few centimeters occurs even during very small swell personal diving observations, also sediment analyses in Hannan et: al., 1978). MJHERIALS AND METHODS Collection apparatus_ and procedures Macrofauna! (herein defined as organisms retained by a 0.50 mm sieve) collections at all three study sites coa~enced on 24 ember 1976 and continued at monthly intervals through 21 August 977. All collections were done by SCUBA divers using hand-held 17 ... ; devices consisting of three pound coffee-can cores (surface area = 2 2, 0. 018 m ; volu..'Tie = 0. 0027 m 1 • Each core was carefully worked into the sediment to approximately 15 em, capped with a snap-on plastic lid, dug out by hand, inverted and the other end capped. 2 coffee-can cores (total area = 0.288 m) and two sediment cores were collected monthly at each station concurrent \llith macrofauna! collections (see Hannan et al., 1978 for description and results). At twelve cores a plot of cumula·tive percent of total species collected versus replicate number (Figure 3) levels off and thus the polychaete species present are probably well-represented by sixteen co:res. Sediment in the coffee-can cores was sieved through a 0.50 mm screen using running sea water, the animals rel~xed in 0.15% propylene phenoxetol, fixed in 10% formalin and stained with rose bengal. The samples were sorted for polychaetes under a dissecting microscope and both the left over s&~ple residue and the sorted worms were placed into 70% ethanol plus 5% glycerin. All individuals of Noth:ria and Magelona were separated monthly for life history analyses. Collections of larvae and settling particulates at the outfall and windmill stations began on 26 October 1976 and continued through December 1977 at biweekly intervals. The collection apparatus consisted of a rack holding jars one meter above the bottom attached to a fence anchor screwed into the sediment (Figure The rack held two wide-mouth (10 ern diameter) 3.8 1 plastic jars for 18 - WINDMILL ~PLUME .,...... ,..OUTFALL 8 12 REPLIC~TE 'NUMBER Figure 3. Cumulative percent of total species collected per replicate for Watsonville stations in September 1976. Twelve replicates collect 90 to 100% of all species col lected in sixteen replicates. tube larval I.~ Jiar :::1m offshore s I wI l I: I i l! sediment ! I I' Figu1·e 4. Rack holding jars to collect larvae and tubes to collect settling particulates. 20 collecting larvae and three 36 em long butyrate tubes (3.5 em dia meter) for collecting settling particulates. Plastic screening (0.63 em mesh) covered the jars to prevent entry of predatory crabs and fish. A one to two em layer of sediment collected at the study sites, air dried or oven dried at low heat and sieved through a 0.25 mm mesh screen, was placed in each jar to provide a substrate for settling larvae. The two larval collecting jars were oriented in a line parallel to the swell and perpendicular to the longshore currents so as not to interfere with each other. The jar's contents were sieved through a 0.25 mm screen and pro cessed as described for the macrofaunal samples. All specimens of Nothria and !v!agelona and the other abundant post-larvae were identified in each sample. The material deposited in the settling tubes was frozen as quickly as possible, thawed for processing, dried, weighed and analyzed for percentage by weight of organic carbon (see Hannan et al., 1978). Concomitant with the biweekly collections of larvae with jars, 1Ileiofauna (herein defined as animals passing through a 0.50 TlllTI, but being retained by a 0.25 nun sieve) samples were taken from March_ 1977 through December 1977. Two three pound coffee-£:an cores were inserted approximately seven em (such cores are hereafter referred to as nhalf cores") into the sedi!nent and removed as described for the macrofauna! cores. These Nere sieved on a 0.50 m:m screen overlying a 0.25 min screen and processed. Post-larvae in the latter residue were identified and en~merated as in the jars. 21 Life historv analyses Each individual of Nothria and Magelona from the monthly macrofauna! collections was measured and inspected for the presence of eggs in the coelom. Length times width (area) of an anterior body region was determined to be a more accurate estimate of size than either length or width alone in preserved polychaetes., After preservation, polychaete individuals of the same size (estimated when alive) are in various states of contraction such that they may have widely disparate length and width measurements for the same number of setigers. By using area to estimate size, these problems diminish (see Hannan et al., 1978). An anterior region was measured because often well over 50% of the collected worms in a single sample were broken in the collection and sieving process. Fecundity and egg size were estimated on selected individuals. The general region of egg occurrence for both species was determined prior to the onset of this study and thus worms broken anterior to this general region were noted when they were measured and were excluded from the breeding analysis. Methods used for egg analyses varied with species. Magelona was measured under a dissecting microscope equipped with an ocular micrometer from the beginning of the first setiger to the end of the ninth setiger. A small constriction occurs anter ior to the tenth setiger which has lateral sacs. Therefore, the first nine setigers are a well-defined region (Figure Width was measured at the midpoint of the ninth setiger, excluding para- 22 LENG H (setig ers l-9) % lateral sacs)} .,'!,-.___ -~ \VID H slightly large~~ (at 9thsetiQer posterior segments (excluding parapodia) Nothria at 9th setiger (inc\. parapodial bases) Figure 5. Length and width measurement regions for Magelona sacculata (top) (from Hartman, 1969) and Nothria elegans (bottom) (from Hartman, 1968). -- podia. Total length was also measured on whole specimens. A milli- meter ruler or, for very small specimens, a dissecting microscope equipped with an ocular micrometer was used to measure total length from the tip of the scoop-shaped prostomium to the end of the pygidium. Eggs were never found before the sacs and therefore, worms missing setigers beginning a few setigers posterior to the sacs were excluded from the br~eding data. Eggs, if present, were extruded when the body wall was ripped with forceps in several places beginning a few setigers posterior to the sacs. The first nine setigers of Nothria were measured as described for Magelona except that width of the ninth setiger included para- podial bases. Total length was measured from the tip of the pro- stomium (excluding antennae) to the end of the pygidium. Because. eggs in Nothria do not appear until setiger 50 to 60 (Table 2, pp. 42" 43), fragmented individuals with heads missing portions beginning in the 20 to 30 setiger region were excluded from the breeding data because it could not be determined whether or not they contained eggs. The presence of eggs was determined as described for Magelona. The occurrence of Nothria larvae, some with less than nine , larvae with the ninth setiger being the pygidium, and the ity in general of very small individuals when held with forceps for measuring necessitated recording only total length for worms less than 2.6 mm long. Plots of juvenile total length versus area T<::ovealed.that 2.6 mm individuals reached a maximum area of 0.60 6). These animals fall into the smalles·t size class when 24 WINDMILL 2. 4 ~ • X 18 March 1977 - • 2.8 9 June 1977 • • * l E • • • - , •t ~ 3 1.6 - • •• . • ::::: • )I.. •• • 1- ~ (..!) • .l< • • - • • • ffi 1. 2 - • • • ...J ••• ...J - !-< aa 0 !- - a. 4 - - a. a ~. N CT') ~ Lti "'. ~ -cs5 cs5 cs5 cs5 cs5 s v 1\ ~IDTH Cmm sauared) LENGTH I WINDMILUPLUME ...... 12. B - • X 23 June 1977 ( i~indrnilD X 1a. B * 22 Mai"'ch 1977 (Plume) • e - -e - S.B f. 1-== (...!:) :z: w 6. B ~ ....J X X • X • ....J X • - •• X .. .. < 4. B X 1- 1- • Jf X ... 0 .. • 1- • • ~· ..~ f' ~·.. • • X • •X 2.B • • • X ... l- X • • - ae lS:I. N . ~. "'. CD . ~. N . tS:I ~ ..... s ~ s - LENGTH X WIDTH Cmm souared) I Figure 6. Plots of length times width of first nine setigers ver sus total length of Nothria elegans. Animals were measured were from meiofauna cores (top) and macrofauna cores (bottom). 25 2 0. 75 mm areal size classes are used (see results of s:LZe- analysis, Figures 9, 10 and 11). Fecundity was estimated in most cases, for five whole individuals per station per month for Nothria and on all whole ovigerous individuals of Magelona. Individuals of Nothria were not chosen randomly 'for fecundity estimates, All whole ovigerous worms were arranged by size class and individuals representing a range in sizes selected for estimates. There appeared to be a rather constant relationship between the proportion of ovigerous individuals in a sample and the proportion of broken worms and a random relati:onship ·between breakage and size. Fecundity was estimated in the following way. All eggs were removed from the individuals under a dissecting microscope by ing the body wall open with forceps and removing as much of the extraneous tissue as possible. The eggs were spread in a gridded ivatch glass and estimated to be either more or less than 1,000. If less than 1,000 eggs were present, then all eggs were counted directly. Larger numbers were estimated by counting the eggs in twenty squares down the middle of the dish, mixing up all of the eggs, and recounting the same twenty squares; this was repeated a third time. When replicate counts differed by 500 eggs or more (35 of the 141 estimates where replicate counts were taken most individuals with 4,000 to 12,000 eggs), one or two one case three and in another seven) more replicates were counted, Mean total number of eggs and standard errors were then calculated. Wnen 26 eggs in more than three replicates were counted, usually an anomalously high or low estimate was identified in the first three replicate counts due either to a counting error or to clumping of the eggs. Thus, beyond three replicate counts the mean did not significantly increase or decrease (because the largest range in values occurred in the first three replicates), however, standard errors were reduced due to the increased sample size in estimating the mean. Also recorded were the setiger number where eggs began and ended, the total number of setigers, and egg size (based generally upon 50 and in a few cases upon 100 eggs selected haphazardly). Eggs were measured in a dish under a dissecting microscope; they were not squashed on a microscope slide. Gut contents of four large Nothria were examined from t~e windmill and outfall collections in March, April and May. These months constitute the period of peak larval settlement for Nothria; gut contents of adults were examined for the presence of Nothria post-larvae since cannibalistic activity has been reported in the closely related Diopatra ornata (Emerson, 1975). Gut contents were removed under a aissecting microscope and examined under a compound microscope. ; l l 27 RESULTS Abundance data Major pulses in macrofaunal numbers of small Nothria (Figure 7; see also size-frequency Figures 9, 10 and 11) indicate that larval settlement began in March at the outfall and plume and in April at the windmill. Densities from September through December 1977 (Figure 7) were from the 0.50 ~ screen residues of the half cores taken for meiofauna and may be a poor estimate of actual faunal densities if patchiness exists. The between-core variability at a given sample date was much greater in March and April showing that initial larval settlement was patchier than expected from adult distributions othermonths. One or two replicates containing large numbers of post-larvae (45 to 85 per 0.018 m2) were collected at the outfall and plume in March. When post-larvae were collected at the windmill in April, large clumps of post larvae were not found (Figure 7). Large discrete patches of post larvae were either missed altogether at the windmill in March or did not occur. A higher percentage of large post-larvae occurred in the April settlement peak at the windmill than at any other station in March and .April (Table 1). High densities of Nothria also occurred at the outfall in September and May (Figure 7, top). This was not, however, due to an abundance of post-larvae, but to an unusually high abundance of mature adults (Figure 9, p. 33). Between-core variability for these adult densities was low compared to the high between-core variability 28 ea )J, @ s N J M J s H J > ____.., ----~·*~...,.._, g Bil i J s N j "" "" ""m Ooy~ from s~pt3mtor 1975 Figure 7, Abundances of Nothria elegans per macrofaunal core (area= 0.018 m2) at outfall (top), plume (middle) and windmill (bottom). Dots represent a total of 16 cores taken per station per month from September 1976 through August 1977, with the exception of Septemher (outfall'l, April (windmill) and June (plume), h'hen 15 cores were collected. Lines connect mean densities per month. 29 Table 1. Post-larvae size class distribution of Nothria elegans from February through May 1977 at the outfall, pl~~e and windmill stations. Size is recorded as length times width of the first nine setigers and 0,50 mm squared size classes are used. Numbers recorded are the number per square meter. ') Size classes (mm~) Month 0.00 to 0.50 o. 51 to 1. 00 1.01 to 1.50 OUTFALL February 17 0 0 March 431 0 ,:; ?1 April 10 --"- 3 May 0 21 17 PLUME February 7 3 3 March 663 52 3 April 118 73 3 May 0 49 21 WINDMILL February 0 0 7 March 128 21 0 April 296 263 4 May 17 76 17 30 during settlement. Except for the two exceptions mentioned, density of Nothria adults was fairly constant spatially and temporally. Abundance of Magelona (Figure 8) v,ras consistently low from September through April but rose continually during larval recruit- ment from May through October 1977. Mean densities of Magelona from September through December 1977, estimated from the 0.50 ~Tt residue of the cores taken for meiofauna biweekly (Figure 8), v:ere at least twice the fall 1976 densities. These high densities may also reflect patches of settled larvae, Again, estimating density from two replicates is not reliable unless faunal distributions are . ,. un:u:orm. Initial larval settlement may have been earlier in the year for both Magelona and Nothria if the sieve screen size (0. SO :m.<1l) used in the macrofauna! cores was too large to retain newly settled forms (see Buchanan and Warwick, 1975; Whitlatch, 1977). For Nothria, this possibility was examined by comparing size- frequency histograms of post-larvae in the 0.25 mm meiofauna residue with histograms of post-larvae in the 0.50 mm macrofauna residue 7 using 0.10 mm- size classes. Although the meiofauna cores rarely 2 . 1 1 co 1 lecte d post- 1arvae greater t h an 0 . So mm , an~ma ... s were con1mon y '") collected even in the 0.10 to 0.20 ~~~ size class in the macro- fauna cores. Small animals were probab lodged on larger animals or debris suggesting that: (1) meiofauna cores probab under- estimated larval settlement, and (2) macrofauna! cores probab 31 J Maqelona sacculala ~ 29 OUTFALL C> <> ~ 24 c:o ;si 20 ~ 16 CD a 12 () i 8 ~ 0 "" & "" li) N ~ ~ ~ ...,. Days from Septe:.;ber 1976 ~ 28 PLU!I.E Ql ~ ~ 24 c:o s 2tl csi ~ 16 Ql a 12 (,) i 8 ~ ~ 4 c ~ tl L_~!~-·~~======~====~~~--~~~--~~~__] lSI tSl rn. G ""(T) lSI0'> r- (T) 0'> i N N (T') ,.,., Days from September 197fi 1 36 .-S~~-N--~_j _____M__ ~-M~---J~~-S~~--N~~~J 0 ~32 "' • WINDMILL ~ 28 r ~0: ~4' ~ CD s Ztl ~ 1 r~-~ 0 L.:..~_;•:..==::::....;•:....._:=::::!::'.. ='==.!:,_::;_...:.._ . ! ~. j 5 "" c:s> "" a __..:.._.,.;..... --.,~_.:....~-~-1& ;2 m m ~ N ~ fri ~ ?j ~ Days from 1 September 1976 Figure 8. Abundances of Magelona sacculata per macrofaunal core (area= 0.018 m2) at outfall (top), plume (middle) and windmill (bottom). Dots represent a total of 16 cores taken per station per month from September 1976 through August 1977, with the exception of September (outfall), April (windmill) and June (plume), when 15 cores were collected. L 32 missed some small larvae but likely collected the bulk of settling larvae. Because Magelona larvae were only rarely collected in meio- fauna cores, there was a dearth of small animals to measure in order to analyze the collection efficiency of macrofauna! cores for larvae of this species. Size-frequency Size-frequency histograms (Figures 9 through 14) were con- structed for Nothria and Magelona using length times width of the first nine setigers as an index of size. In all histograms the largest size class contains individuals of that size and larger. Frequencies are divided into 0.75 rnm2 size classes for Nothria, 0.122 mm2 size classes for Magelona, and are standardized to individuals per square meter. The actual number collected monthly (N) is given in the upper right-hand corner of each histogram. Sixteen cores were taken monthly (total area = 0.288 m2) except in September at the outfall, April at the windmill, and June 2 at the plume when only 15 cores were taken (total area= 0.270 m ). Regions filled in on the histograms indicate the frequency of individuals with eggs- in their coeloms. Size-frequency histograms for Nothria at all stations (Figures 9, 10 and 11) indicate that the animals had a bimodal size distri- bution from September through February with larval recruitment constituting a new mode from March through August. Variability in these general trends was probably due to patchiness in the 33 ,-No!/Jr/a e/e ons ,....,.------,OUTFALL l97r:. :;EPT llQ'I jfl! 1< 0 189 N= !55 ! 197'1 DEC JAN N•l02 :,•110 431 I k Figure 9. Size-frequency histograms for Nothria elegans collected at the outfall station. See text for details. 34 Noll;da elegans f );b SfYT t;'l60 r 1977 ' DEC JAN n:& 'i•95 N•l14 N•S9 I[ 174 APR --:1 N= 180 cl= 100 ] j I I I ~1't JUt!\~ ""I C/9 I 1 j I ::1....---l 0 "" Figure 10. Size-frequency histograms for Nothria elegans collected at the plume station. See text for details. 35 Noll?rio elegans \NI 1916 srpr OCT ''"I '6 !1•158 1977 JI\N N= 115 N-<89 150 ' j I ::22 JUt A1oqe/cna sacculala OUTFALL I I ~ rja o;::c N=25 l f~.....~o...i-..!...1.0 .wll~-·~-JI w... n"----J..,;:r~::;;:::;IIU::JL.--...~ ..~L..-J.l l f l MAR APR MAY l N-7 t WII l In i'F45 f j' f ' l I ~ l' j \, ~ l 1 I Il I I H' 1 I t C! al:h !Ill Cl ..,...,...., lLL__~ c L I "' ~ l Figure 12. Size-frequency histograms for Magelona sacculata collected at the outfall station. See text fer details. !vfagelona socculota PL 1976 r HCV ll 1<• I I l I , I l I l...... r_~~-~..-..---..~l l." = . 11!..U...-0.. n a r~JJ ------l l ! 1977 1 DEC JA'\ FEB ~17 l N=l:l l N= 12 I ,..-...... I --~ MAR APR M~Y N= 10 -I N= 13 rt"'JO l I I I f I J i l 1 r~---., Ld"i ..,.;.;Jr;b~ l~ 0 a_!;l "' l JUNE S:JI n 11=.1;5 N~ 60 I; ~ •o ~ ~ 201.-\.-1~....;,______j , LE;iVJth X wIdth !mm .. i 1-lgure 13. Size-frequency histograms for 1'-iagelona sacculata collected at the plume stations. See text for details. 38 l,·l/oqelona sacculata !NOM!LL r- ; 1976 I SET' r OCT I()V N•3S N-2~ N•l ~ I r ! l i f i . rlU ,..J1.Cl I c 1!11 I f1 LD l 1 1977 DEC JAN FEB I N•21S N•IB NOilH l kr" ~-:fli J -1 l MAR r MJIV H:;:7 I N= II N=50 II l ~ l ~~i l L I 1 ~ Cl J I~~ ' ~ J 100 r "l ! l !~9 1 80 t IZ2 : o; AUG s JUNE JULY ' : l N= 1 ~2 ••=68 I tJz:;49 t ' I I I 1 ' • 60 ~ ~ 1 ·;" 40 I i ~ J1 ~~ l lj I ! 20 I r I l I l lir· LJL I I! J t n 1 tO'k- I :J ... ' .J .,. OJ 0 r-; - "" ": ...;"' I~0 o - - ~ N "'N Length X W!ath {i'fffl7 ~ Figure 14. Size-frequency histograms for lv!agelona sacculata collected at the windmill station. See text for details. 39 animal's distributions and/ or to sampling artifacts, The postions of the modes were approximate 3. 5 and 6. 5 mm 2 at all stations during these months. It appears that little growth occurred. Bimodality of mature (ovigerous) individuals generally became less pronounced a month prior (February) to larval recruitment. Unimodality predominated through August indicating, perhaps, that smaller individuals were growing more than larger ones. In addition, individuals may have died after spawning as suggested by the low density of mature animals from May through August. Strong larval settlement began at all stations in March and continued sporadically through August. Because settlement of larvae continued over an extended period (six months), it is difficult to follow growth by following changes in size of this new "yearn class. The histograms reveal pulses months apart of strong larval settlement suggesting an extended breeding season and, again, patchy larval settlement and/or the periodic sampling of these patches. The size classes that comprised the anomalously high densities of animals at the outfall (Figure 9) in May were mature animals and not settling larvae. In September only half of the individuals were mature (the second mode), and those individuals in the first mode were juveniles rather than newly settled larvae, All ~ populations sampled experienced high post-larval mortality (Figures 9, 10 and 11; Table 1). In August 1977 the size class structure was approaching that of the previous September; 40 two modes with no mature individuals in the first mode and approx- 2 imate positions of the modes at 1.5 and 6.5 mm • However, absolute densities in August 1977 were nearly half those of September 1976. In contrast to the decreasing Nothria populations, all popu- lations of Magelona increased over time (Figures 12, 13 and 14). Extremely small sample sizes prior to May 1977 make histogram interpretation difficult. Furthermore, errors which may have occurred in identifying ~1agelona sacculata post-larvae (see pp. 7-8) make it impossible to determine absolute nmnbers of settling larvae of this species. However, the planktonic larval lives, extended breeding seasons and patchy larval settlement patterns for both Nothria and Magelona make discussions of absolute recruitment and mortality rates an unrealistic objective anyway. Therefore, I address only general trends in larval settlement and recruitment, Larger size classes (Figures 12, 13 and 14) of Hagelona populations were best represented from February through April, Two pulses of larval settlement occurred (May and August). Post- larval mortality was high in this species also. Post-larvae appeared to grow quickly to Jnaturity; again, actual growth cannot be estimated because some larval settlement occurred throughout the summer. Minimum growth of the new recurits could be at 0.,~2'7" mm 2 or six size classes in three months (assuming larval settlement occurred as early as April, immediate fol macrofaunal collections that month), Trends in size-frequency 41 histograms were extremely similar between stations suggesting little large scale spatial patchiness of this species between the study areas. Fecundity (static) and egg size With few except~ons, eggs in Nothria first occurred between setigers SO and 60 and continued through setigers 110 and 150 (Table 2). The setiger where eggs first occurred varied little among individuals whereas the number of the last egg-bearing setiger increased with total number of setigers. The number of setigers containing eggs has no obvious relationship to the mean fecundity of the animal, nor to its total n~~ber of setigers (Table 3). Fecundity (defined here as brood size, not having a time factor dir·ectly associated with it) of Nothria varied from less than a hundred to almost 7, 000 eggs per individual. Most fecun dities were less than 1,000. Fecundities greater than 1,000 eggs were essentially absent from the su.rnmer months (Figure 15) and comprised aobut 50% of the fecundity estimates from December through May. A positive relationship of fecundity to animal size ·for fecundities greater than 1,000 clearly existed from December through April (Figure 15), being the most pronounced in March. However, this relationsip between fecundity and size did not appear throughout the entire year for animals with less than 1,000 eggs. Animals with greater than 1,000 eggs will be termed 11 ripe" and those \'ii th less than or equal to 1, 000 eggs "unripe" in Table 2. Monthly mean setiger number where eggs begin and end and mean total nwnber of seti gers, all ± two standard errors (S,E.) for all Nothria elegans individuals for which these parameters were measured. N :::: number of estiJnates used in calculating the mean and S.E. -~·~~·---~Mean setiger Mean Month no. where 2 S.E. N 2 S.E. N no. 2 S.E. N eggs setigers begii}______·------OUTFALL September 40.5 25.88 4 134.0 11.20 4 278.8 6.75 4 October 59.0 3.63 5 135.2 24.29 5 259.6 30.74 5 November 55.5 1. 73 4 149.3 17.91 4 277.3 30.64 4 December 55.3 4.78 6 142.8 23.72 6 252.8 38.76 6 January 56.8 2.87 4 146.5 17.41 4 248.3 32.47 4 February 52.0 3.52 5 116.6 22,36 5 221.4 35.58 s March 53.0 2.28 5 138.2 24.43 5 233.7 22.10 3 1 56.0 3.46 5 115.4 31.56 5 226.2 22.86 5 May 57.5 2.38 4 127.8 22.46 . 4 240.7 29.49 :'i June 60.8 4.12 6 113.2 20.80 6 258.8 19.45 4 July 55.5 1. 73 4 149.3 17.91 4 277.3 30.64 4 August 55.3 4.78 6 142.8 23.72 6 252.8 38.76 6 PLUME September 69.0 22.01 2 146.5 3.00 ,.2 289.5 19.01 2 October 60.8 6.74 5 144.8 27.87 ,) 266.6 43.55 5 November 59.2 9.23 5 142.4 46.37 5 272.3 43.45 4 December 57.0 6.00 2 128.0 1.99 2 287.0 1 51.5 l. 73 4 117.6 24.61 5 202.3 42.94 4 55.4 5.60 9 125.3 21.33 9 230.1 24.23 9 March 56.1 2.14 26 132.6 6.63 26 259.1 8.38 25 1 53.1 2.06 7 132.1 22.87 7 254.3 24.48 7 56.2 2.14 5 144.4 33.36 5 250.0 38.16 3 60.5 6.96 6 131.8 26.56 6 251.0 22.81 6 .j:., .58.3 2.67 6 125.5 17.73 6 258.2 10.17 6 h) 51.0 6.05 2 117 .. 9 26.88 '),. 243.9 32.47 2 , Table 2. Continued. Mean setiger setiger Mean Month no. where 2 S. E. N no. where 2 S.R. N no. 2 S. fL. N eggs eggs setigeTs beg_in end WINDMILL September 53.6 12.13 5 112.6 29.91 5 246.2 22.33 s October 56.=) 4.65 26 125.2 9.67 25 246.1 13.10 24 November 52.8 3.12 6 138.7 8.34 6 265.5 15.02 6 December 58~6 4.08 5 121.2 16.80 5 230.0 23.94 4 r- January 52.8 1. 94 s 116.4 13.38 ;:) 217.3 20.97 4 February 54.0 3 .. 65 6 124.7 15.51 6 196.2 52.98 6 !\larch 52.7 3.57 7 119.3 12.75 7 227.4 32.13 7 April 52.2 5,30 5 125.0 34.25 5 221.6 68.60 5 May 55.5 3.09 6 129.8 25.52 6 147.0 --- l June 51.0 6.51 6 119.3 25.39 6 239.3 23.37 4 July 59.5 7.00 2 126.0 38.00 2 252.0 22.01 2 54.8 1. 60 5 126.0 11.52 5 248.7 56.66 3 ------ .f.>, td 44 Tahle 3. Relationship of number OI~ setigers with eggs to mean fecundity, total numher of setige1·s and time of year for Nothria elegans at the plume s-tation. Each entry represent.s one individual. Number of Total setigers Mean number Month with eggs fecundity setigers Sampled 23 196 210 Aug. 30 61 248 Oct, 34 667 221 Feb. 35 263 214 June 36 62 225 June 38 301 235 Apr. 40 97 254 July 41 3618 206 Feb. 42 544 May 44 487 181 Feb. 47 316 250 July 47 349 234 Nov. 47 245 222 Mar. 50 1038 152 Jan. 52 115 252 Mar. 53 828 257 Mar. 56 898 215 Apr. 57 355 278 }1ar. 57 650 213 Feb. 58 490 271 Aug. 58 393 230 Mar. 61 392 272 June 61 4884 248 Mar. 62 291 248 Aug. 63 114 249 Mar. 64 105 243 Mar. 65 264 275 June 65 82 299 Sept. 65 1482 228 Feb. 65 1975 208 Jan. 66 275 234 May 67 1062 287 Dec. 68 436 l'-iar. 68 2846 276 Apr. 68 137 232 Aug. 69 343 238 Aug, 69 659 241 Nar. 71 848 275 July 71 806 200 Oct. '7" I l 991 271 Mar. 72 1805 216 Feb. 73 673 236 Nov. 45 ~ Table ,:), Continued. Number of Total setigers l>lean number 1-1onth with eggs fecundity setigers Sampled 74 1028 218 Mar, 75 859 233 Aug. 75 602 Mar. 75 913 263 Mar. 75 2311 Dec. 75 815 Nov. 77 778 Mar. 77 1158 253 Mar. 78 509 27'"', :;:, Aug. 79 679 286 June 79 1390 260 Apr. 80 1047 248 June 81 651 241 Mar. 82 715 302 Nov. 83 1336 May 85 604 278 Mar. 86 258 254 July 86 555 256 Oct. 90 678 280 Sept. 90 1607 273 Apr. 90 2036 256 Jan. 91 1264 Nar. 91 2564 295 Mar. 92 1978 253 Mar. 94 3899 219 Apr. 95 2796 285 Mar. 96 793 279 Mar. 97 951 254 Mar. 97 6857 Jan. 98 416 244 July 98 4116 279 Feb. 108 3574 280 Mar. 109 5426 298 Feb. 109 5946 229 Feb. 113 2658 269 Mar. 113 540 315 Oct. 116 818 288 120 1025 .314 Oct. 133 1247 258 134 2618 228 139 2563 317 Nov. 46 ,------?----~-1 r·- ~- --- -~ ---- ~- ~'J.,._) r 1 o e:t¥"\".:ll Nolhrio 'elegons : :!=~:l i. l I l r I f '' I • I . , l ~ ~ ..., '! J f. • • ! 8 "' " .. lll ~ 1 f.t .. ., . ' t~ -·-~- SS'To"3fil !97t ,~~.-!J~~ ~~-~--~ f :w I 1 I ,,. j i f j l I f j ' I I j l 1 'I j f t ' 1 f ! .. ! L~~------'1 ; L_..____~~_j J,\1'1.1\R1' \911' 1 Ij i j .1 1 • J ! •• •• I ~ ~ ~ ~ ~ ~ ~ ~ ~ N ~ ~ ~ g ~ ~ ~ ~ MAY' J'.J.Y SlZt: (oreo 10 mm') Figure 15. Monthly graphs of fecundity versus size (area of the first nine setigers) for Nothria elegans. Vertical bars represent single individuals on which more than one estimate of fecundity '.vas made and show the range of the values. Single points represent individuals for Nhich all eggs i'<'ere counted. 47 subsequent discussions (justification this will be discussed later, pp. 76-77). Individuals in the oocyte size-frequency histograms (Figure 16) are arranged by increasing size (area of the first nine setigers), moving from left to right, each month. Size classes of 13 ~ are used. Fecundity of the individual appears in the upper left-hand corner of each histogram. Unless otherwise noted, 50 eggs were measured (N) per individual. Histograms for Nothria (Figure 16) showed no change in size frequency with animal size, season or fecundity. Mean oocyte diameter over all time was 195.8 11 ·for 241 fecundity estimates. Eggs generally first occurred in Magelona between setigers 10 and 20, except at the plume where eggs began more posteriorly, between setigers 30 and 70 (Table 4). Eggs were found to within 10 to 15 setigers of the end of the worms and in the most fecund individuals eggs extended to the last setiger. There was a slight trend at the phune of higher fecundity being correlated with greater number of setigers with eggs and a larger total number of setigers (Table 5). However, the small sample size of whole fecund animals hinders the detection of any consistent trends. Fecundity varied from 8 to 12,000 eggs with most fecundities being of 2,500 eggs and less (Fi5ure 17), approximate those of Nothria. Oocyte size-frequency histograms (Figure 1 are arranged as for Nothria; they showed essentially the same ,, ... ,,,., ., OCTOBER (CONT.> Notma eleqans [i3J w~U! lll tlJlll [lJ~l"'l Ul ~~TIL!.~$.1R till 1.11 []]U]] []1] Q ~~~~- ~ . HI · Ul Ul 161 1.11 i.11 Ld:JQ 1111 Ul Lru~!I ~ .. ~tDJ LJlJ L] ~ LIJ Q1J Ul! ill 'll US U Ul . OCTO!lf.R EJ. Qlli'11 . Ir;--l N· !.Iii 111 lif 1,'.; i, l...... I.....-..L.....JLJ~~ L~ L_~ L2U111 l~ 1. l. +->· 00 []"' [jJ .....__,__ __ _u Ul til Ul Ul Ul l~ l6. distributions of aU ~---'-'-~~ inidviduals on wh.i fecundi was windmi 11 station. See --··-·-.. ·- s .. 49 Table 4. Mean setiger number where eggs begin and end and mean total number of setigers, all ± two standard errors (S.E.) for all Magelona sacculata individuals on which these parameters were measured. N = number of estimates used in calculating the mean and S.E. ------Mean Mean setiger setiger Mean Month no. where 2 S.E. N no. tv here 2 S.E. N no. 2 S.E. N eggs eggs setigers begin end OUTFALL September 14.4 6.51 5 60.8 4.70 5 65.0 3.16 4 October 12.3 3. 71 3 60.0 6.00 3 62.7 5.69 3 November 15'. 5 11.00 2 64.0 0.00 2 70.5 1.00 2 December 11.0 1. 99 2 6:5.0 10.00 2 66.7 4.80 3 January 11.0 10.00 2 64.0 0.00 2 72.5 3.00 2 February. 14.5 2.38 4 68.0 2.94 4 77.0 2.83 4 March 16.0 -- 1 55.0 -- 1 70.0 --- 1 April no \~Thole ovigerous worms May no whole ovigerous worms .June 18.0 6.00 2 ss.o 10.00 2 68.5 5.01 2 July 18.1 1.63 8 34.8 3.13 8 59.7 3.51 7 18.8 4.40 5 47.0 7.29 s 68.6 2.41 5 PLUME September 29.5 19.01 2 60.5 13.00 2 73.5 3.00 2 October 36.0 --- l 51.0 --- 1 75.0 -- 1 November 23.0 -- l 47.0 -- 1 66.0 -- l December 24.5 7.00 2 44.0 0.00 2 66.7 2.91 3 19.3 2.50 4 64.0 4.69 4 76.5 6.03 4 23.8 9.00 4 55.0 9.42 4 73.0 8.29 Lj March 18.0 l. 99 2 58.5 19.()1 2 73.0 6.00 2 l 22.0 12.01 2 58.0 4.00 2 71. s 3.00 2 ,__ 16.0 1 55.0 -- 1 67.0 - ·- 1 June 18.0 ,_ ~· 1 58.0 ·-- 1 60.5 23.00 2 tn 19.5 3.00 2 44.5 8.99 2 64.5 3.00 2 0 17.0 1. 5 3 44.0 12.22 3 64.0 6. 11 5 Table 4. Continued. ---~an-- Mean setiger setiger Mean Monthly no. tvhere 2 S.E. N no. where 2 S.E. N no. 2 S.E. N eggs eggs setigers ---- begin end WINDMILL September 16.0 12.01 2 63.0 14.00 2 70.0 -- 1 October 17.3 5.69 3 71.3 l. 77 3 72.7 0.67 3 November no whole ovigerous worms December 12.0 8.00 2 63.5 3.00 2 66.0 4.00 2 14.7 8.11 3 70.3 9.95 3 75.0 6.00 3 17.8 2.87 4 58.0 7.12 4 69.0 6.38 4 March 20.0 -- 1 61.0 -- l 75.0 -- l April 17.0 -- 1 66.0 - - 1 76.0 -- l f\1ay no whole ovigerous worms June 15.3 3.10 4 42.3 6.13 4 61.4 2.73 5 July 18.4 2.06 s 38.0 6.23 5 59.3 3.45 6 19.6 4.04 8 50.7 4.57 9 65.9 2.73 10 ------ lll I-' 52 Table 5. Relationship of the number of setigers with eggs to mean fecundity, total nui·nber of setigers a.'"ld time of year for Magelona sacculata at plume station. Each entry represents one individual . Number of Total setigers Mean number Month with eggs fecundity setigers sampled 12 212 68 Feb. 14 44 60 Aug. 15 420 75 Sept. 15 683 75 Oct. 16 176 64 Dec. 19 583 63 July 21 421 67 Feb. 23 317 67 Dec. 24 540 66 Nov. 28 1412 70 30 166 70 Mar. 31 2014 66 July 32 8 21 62 Aug. 35 1630 70 Aug. 39 2504 67 May 40 3123 72 June 41 2052 72 Feb .. 42 697 68 Jan. 43 2170 79 Jan. 44 1784 7-. I Jan. ~., 47 1439 /.:. Sept. T ...,. n 50 2748 82 v c&..~.l"' 51 2818 85 Feb. 51 1050 76 Mar. 56 7924 7~,.) Apr. 53 ... - .. ~- -...---- -'>'"------.... - ...... i i i "' ovt'oi [ li! p;V'l', !vfo9elono sac cu!o/o 'lll~U!l [ I i i t . . ~ I f t I • j ~ : : L~~~~---~' L..:.'-'-' ~~~~--' ~?rE~;;E;; OCGOoR i'GV(Maf.R '9715. ~~l j j I I 1 I i j It 'I!I 1 ij j [ ~i l • I j • j i I ' I j I l j .. -~..___._j I Fr:B.' 12ii:il; r f ~-l r li I f l l t l -r I ;: I t ~ ~! t f .... f l 1 ' I ~l l ! f l 2ii:ill t I I'· I)*! l t r [.. _, _ _j ~~~----~~~ L...-_..-~-~~_._j ; ~ ~ ~ ~ ~ £ ~ ~ ~ ~ W ~ ~ ~ ~ ~ ~ N N N N MAt .m:: .ltU SIZE (01~a "' mm'l Figure 17. Monthly graphs of fecundity versus size (area of the first nine setigers) for Magelona sacculata. Vertical bars represent single individuals on which more than one estimate of fecundity was made and show the range of values. ~1ngle points represent indivi duals for which all eggs were counted. 54 r-- 1 I 97 4 ~ i rl I i i ) I ,J l..., ! Moge!ono ' L J !. i5 OCTOBER ...... ----~ I l2lil I 1 n 1 I _, L I _j I I 11!<4 I U1J JAN:JARY 1977 lj ''.f.RCH Figure 18, Oocyte size-frequency histograms for all Magelona sacculata indiYiduals for which. fecundity was esti.'11ated at the lllinci.TJlill station.~- 55 .\PF IL Mcrck:;no 1-,E~---~' ' '1 ; I' : ' l I I I -·.lJ 1.74 I m ! 13!1· I I ~ .i LrLII. 74 !.Sf 1.64 3.79 I!. OS ll.g" i~ I d 1 1 lr1lI I ! J ii.SS !1.02 lliJ!.82 ~stn. {JilJt.:'f..K:;iJ llil ;;: "' :;,J =n~ i5 1 llJJ~e L, 3 ' 1.1\'! Figure 18. Continued. 56 distribution of egg sizes year-round with most eggs being between 80 and 130 ]J (mean = 90.5 for 96 fecundity estimates). Fecundity data versus size relationships (Figure 17) are difficult to interpret, again due to the small sample size of fecund worms. Lowest fecundities (less than 2,500 eggs) occurred in the fall; however·, animals with these low fecundities also occurred year-round. There is insufficient evidence to justify the creation of a "ripen category for Magelona. A 1,000 egg cut-off, and the use of thi~ category f~r breeding cycle determination below, were used only in order to contrast Magelona data with Nothria data. Fecundities of less than 1,000 eggs in Magelona may be more direct related to animal age and size than these low fecundities in Nothria. Size at maturity and breeding cycle Size at maturity is defined here as the smallest size class containing more than one individual with eggs, and serves as a maturity estimate for intra-population comparisons. Data were obtained from ovigerous-frequency histograms superimposed over size-frequency histograms (Figures 9 through 14). The breedingcycles of the worms was determined using five parameters plotted over time, each measuring different phenomena: (l) percentage of ovigerous individuals of mature worms and percentage of immature individuals, (2) number of ovigerous number of mature animals, (3) fraction of the ovigerous indivi- duals that are "ripe," ) mean fecundity, and (5) oocyte 57 diameter. The percentage of ovigerous individuals per month was calculated as the number of mature ovigerous animals divided by the number of mature animals minus the individuals fragmented before the region of egg occurrence. The fraction of ripe individuals (Figures 19A through 24A) and the pooled ~ean fecun- dity of individuals (Figures 19C through 24C) are Eased on esti- mates from ovigerous worms which were subsampled from whole ovig- erous individuals collected each month for Nothria and are based on estimates from all whole ovigerous 1viagelona collected monthly. The number of individuals for which fecundity was estimated appears above the graphs (Figures 19C through 24C). All determinations of the breeding cycles of these WOlTIS are indirect. Wtihout information on gametogensis and spermatogenesis in a population over time, spah~ing times can only be inferred by a period of reproductive maxima measured by one or more of the parameters mentioned above. Using the peak period of larval set- tle.ment as an indirect estimate of when spa1ming occurred in the Watsonville populations is of limited value because larvae are prob~- ably recruited from elsewhere in Monterey Bay, and possibly from even greater distances along the California coast. This is espe- dally a problem with Magelona whose larvae could have a very long (up to two months· J, Blake, personal co~munication) larval life. The lower limit of the smallest mature size class of Nothria 7 at all stations was 2.0 JDID- (Figures 9, 10 and 11). The animals appeared to spawn over a four to five month period in late Hinter Nothr/a elegans 0 TFALL 40 - ~-v--...,------r-- --r--r-- ~--- ,--~.------r-----w---r-- LDBf~--~ ~~- ll40 .. ,11! B lil.75 30 II o.u. FJ'.. •....-! •.-1 I > i ::: , I oo> .,~ C) ""N 80 ~;- kl. 50 20 X X 6 4k X IllL •• - (!) (l) (" (L (L 60 \ 0 ~ -~ fl n::: a:: ~·g (!_ 25 ~ llil u u L 0 ,) L L ~- r U- U. ~~ ::1 ~~- _J;x 1 .~ l 1 ~·::. ' ...A------L--.1!...-._..;.__.._.,__,L...... _._-!,_ 0 ~~-~-_] 0~ 013 t~---'------ A S 144000 J J -,---,----~- D J F 't..~ • ---~--A ~ ' ---,----~-~ 321il -~~---.-----.----~~ ~ -----.-- r: 0 N - -·---~--~ --~ s l I 1~0 l 300£1 __ 5 :; 5 4 b ,, i 120000 ::__,__:-~~~~~~\ c o. D ~- .... \1) > 256 L 0 _..,:l 9 " \ j ~- '"" ft \ 96~00 N 0 :::£ X u. 50 '0 ~,, '"" r , ~ . IX 72000 ::h --t:i l5fl0 ~ c > 40 ° 48000 I N -..,0 .. m 0 IUO' 1-- t > '~ ' ';::'\~- 20 " / 0 I c" . "-" 24000 ~OJ "" ~/~ X if ::J -~=-- ~ E u_ 0 ~-A---A-----JI--.....-lc ...... --4-----"------"- ""- -- 0 0 Iii ·-· r::J ISl 1$1 ~ m ~ IX ~ ... M m 1n ~ ~~ m (".fl N N m P1'"" ~n from I !976 00 Figure 19. Breedi cycle determination for 3t the outfall station, several parameters may indicate odic act 11'1!>',,, !iothr/a e/egoos PLUME 1.011 r-~~- \ ~-~.,-.-A~~---.--l40 ··-r--"1!-·-.,------,-_,.,..-.- -~--v- ll40 ;;Ill ~ L1! A B II "-' 120 13. 75 30 ,_,.(j) ~ ll rhm I 5 .....,. •1'"'11,. ..t b 100 ~I 00 E 1'\ I (;) E (j) ""N. 6-· 80 v~" X>< L'*' !:-0.50 20 (j) 0:: w w m .• c \l 0.. 0.. \ 0 31 60 ...., 0.::0.::-·- 'U: ~ 41ii .-, ·- 10 0 d g 0.25 0 Q (I) L L I.A.. L L ::J LL -.____-// u= b 20 :;;;:: ~l iil. 0~ l ---~---~~-~--"-----'-~~ __.... 0 ""' 0 ... ~ -~~ s 0 0 J F M A M J J A s 320 31/1?,0 l442i8i2l I ~~-1100 f 5 5 2 5 9 26 7~ 5 b 6 1 ' !h (I) 12~000 D --> 255 80 ~ 0 ~ c 0 '"'" t ~ ~ :;;;:: 2Z00 ,· I 95000 X T 4- u.. ~ !92 60 ° IX L u. 72000 ..n'I) ~)c l500l .. E ::J J 40 c5 u z 128 N (j) LL ! 00(1 48030 I -··0 c ,.., 0 ch 0 on -~ r- (r) Ol IX "' ""';q m "' (}1 fron• '" l 1976 \.0 Fjgure at the plume stat on, g several indicate activitv. See text for Jetai1s. VJ!NDMILL ~-.--..--, 40 I ::: ·_:\~~ _,_ --· . ~~ . A 8 ''f1~ 3fil . . ~ Ol \_ ...... 01 01 > > 1~ 100 -·\ C) Cl '~ H 90 0) aJ ~\, .~0.5:1 2fil X X 0:: ill (' J A ;.) l , SONOJFMAMJ 144000 320 ,.---r----v--~-y·~r 100 ""' 3vti~ ~-"-T'-----r-...... _v----r--~---r----r---~-v----r- m '] •M I! 31 ll 5 5 6 5 6 6 2 c 5 > D l 0 25&\0 !20000 Q) N 256 80 L ...,:l >< 0 I zmm 960(10 LL ::!£ IX T ~ 192 50 '0 >--. .. L +' (j) .:u 1500 72000 .J) ch t: E - J :l 0 I z 128 413 3 Jl N 4G02liil ~ Ll. HJI)kJ ....m ..0, .. c > 0 0 0 1- II) 64 ::E: 24000 20 1 ~'-0... ::~· l --· "" >< fl LL 0 :: 0 L.--~-~·-·--·--'-~----'-~---~-JIL..__.___j flJ !X 0 .... ro a rtl rn ...... rn "" "" ""(\J ""N ""m m -··''"' "' ()'\ f ,-·om 1 1976 0 21. Breeding cycle determinat for Nothria el s at the 11 station several which may indicate --~----- act See text for details. Magelona socculata OUTFALL 1.0 .--.,-T---~--,-T--.---...... ,.---,-, 70 " ~ +~·· r~~-~ -~r1 0. 8 - 56 f. i '--' I]) ---1 ::!"' -~") .. I~ .3 80 >. > 0 42 0 0 '" E :..1t: ·N E U) ,_, 60 :: 2~~ \ §.- ll4 . 28 -~ .~ ~,.,..::- -- (' ·rl \ 0:: 0:: ... 40 . ~ > 1 "E '·' ~ \j 14 .~ "~ ~ ~ '" . · /!-~~~ ' '~m/ ill _() S ll N fJ j F M A M J J A (J~l~M ~j ~l :f :f li0Vl I :Ill 5 3 2 2 2 !J IIJ 2 ncs ,., ,.-.., N (j) L 7200 4g'ggg .---.. ::> 80 !Sl. • tSl N C'J I~..z• • -t • ; T'·' q 3 >< >< L 0 60 ~"i4mJ (I) ;,~ ~ (I) Ql __ n •rl E rh ·o 0 '{; ::> ·d c 0 0 :z > J 2 ~ 1.-(~ 0 ~ 36Vl0 40 _.,0~~ LL \ \ I r I c 0 0 ~-] :£_ 1800 loa 2eJ ~1::: N > ,.-.. 100 ' ,: :~~~~· --r--1...-----r- .--.. I i B l 56+ Q) '-' 80 .m .._, 1 . {\ j m· ..... Ts0 ...., E "-"' 0. 6 42 ·;c?; E ( ) 0 00,_, 60 c ;.U::N ::J ' Q'lt 0: >< >< L (J) 6 0. 4 28 it it .~j' ..... •.-4 ·ril 40 ~ a::: a::: > ~ o ..... ;...o "'t: u 0 (!) 14 0 0 L L L ::l 20 Ll_ Ll- +' tl :::;;:: l::~L~~~~ 0 'It 0 900(:1 -~-r_f!_,... N 0 J __ F M A ~1...-~-~--~ 5 ...... ---.-.---,-.-r----r---~ -y-~ ' 100 1:'1 tl ~/ 2 2 4 4 2 2 2 2 3 ~ ~::) II""..,!>::;) ([I c 4CSIQ 7200 CSl • "" 5 80 CSl!'Sl • C:;J -g CSl ...... 1 :::;;:: I ""' 4- >- 5400 fu 0 60 ...,:5 3 >< .Dem • <:J :J •rf c zcS ~' - 0><·- 0 0~ 3fl'~" ~• u ~ -· 40 ~ oN +' 0 •• ,J_ '"" /~ \/ 2 CJ ~ [ rr:: .n. r-J E \, E '-~J"i ~ ~~~~'X X ~~-'--~~~ -~.....1...... _.__1~-....· --'il 1 0~LL.. IX IX -· <1'-t (";.' Q <'5l t';;J IS) lSl ~ N ~--· 6!3 (L0 0.6 ~ •M 0~ 0::: > r.-~ I 9303 S 0 N 0 J F M AM J J A S s'f --.---.--r--~ -,---~-,.- -;--;-;--;-~--~--.-~~;r-~7,~-.--1 ~ gg ! Hllil I c t'Sl Q (!) : 4LS)csi 7200 '!" s 80 -~ ~·0 X>< ....,_.:::<: I L ,.._ 3 ~ (!) 0 5490 o~ _] 60 u 0 E • !I) 0 :J ITI 'Tl ,__. ~o 5,. 3500 2 ch 3N 40 LA_ ' t ; ch 0 1\ D ·~ c > 1-- •• 0 'it: C:J I ~ 1800 lxN 1 20 '~ ~.~..x !:< l~. ~ E (l ~-----~-----'----.~-~·-I 0 '" 0 ·~-~-~-~-~-~-~..__.____..L.~-~~ IS! ISl ~ Q s ~ ~ N Q\ M \'¥} m tn ...... ~ li rn (;-l -~-~lYIN N ('r) (Y} September· 1976 Figure cycle deteTminat:lon for windmill station, ing scvera l may indicate ci tv. See text foT details. 64 and early spring (January through April at the outfall and ume; January through May at the windmill) with larval settlement having occurred sporadically from March through Au~ust (Fi6ures 19, 20 and 21). The best evidence for this appears in the compari son of the fraction of ripe individuals, and the mean fecundity of the individuals, over time (Figures 19A, 19C, 20A, 20C, 21A and 2 Because the percentage of ovigerous individuals rose only slightly in the winter months, because this percentage stayed between 20 and 40 year-round, and because the number of ovigerous individuals oscillated little on a monthly basis, using these parameters as multipliers for the fraction of ripe individuals and mean fecm1dity of individuals created the same trends as using either of the latter parameters alone. Nothria appears to be a perennial species. The proportion of ripe and unripe worms varied throughout the year and was apparently independent of size class (Figure 15). Only individuals with less than 1,000 eggs occurred in the summer (Figures 19A, 19C, 20A, 20C, 21A and 21C); these were distributed through all size classes (Figure 15) and the distribution of oocyte diameters was similar during these months to the rest of the year (Figure 1 These may thus be partially spent worms which will probably not spm;m again this season, as further evidenced by the lack larval recruitment in the fall and 1,'linter (Figures 9, 10 and 11) . Several year classes may have contributed to the breeding at ion and/or individuals may spaym several times over the breeding season, '65 phenomena that cannot be distinquished in the present study. Oocyte size-frequency histograms for ani.'llals of increas size and varying fecundities at the windmill station (Figure 16) showed an overall mean of 195.8 ~ during the year; all other stations were similar. There was little variation in oocyte size-frequencies with either animal size or fecundity; thus, either animals with small developing eggs were not detected, or eggs were continually added to these stable egg size distribu- tions and retained until a certain fecundity was reached and/or spawning occurred. Some onuphids possess nurse cells in chains which have a nutritive function as food for oocytes (Schroeder a~d Hermans, 1975), and are absorbed as they are used by the egg. Such a chain was observed once while estimating fecundity in this study (E. Goepfert, personal communication). Thus, the smaller gonial cells which were always present in the worms may be nurse cells and larger oocytes may be those eggs which have absorbed varying amounts of nurse cell material. With few exceptions, the lower limit of the smallest mature ") size class of Magelona was 0. 732 nun- (Figures 12, 13 and 14). From the estimated minimum growth of a settled larvae (p .40), it appears that an individual can grow to maturity in about three months. Analysis of breeding periodicity using the five para~eters used for Nothria is inappropriate for Magelona due to the very small sample sizes for all stations most of the year (September ~ through 1 J (>::.1gures • """~~. ')';;~-an d A4)L • 66 The breeding cycle of this species can be best inferred from juvenile settlement. Number and percentage of immature individuals increased consistently bet;.;een stations in May, June and August (Figures 22B, 22D, 23B, 23D, 24B and 24D); larval settlement thus occurred in two summer pulses following late winter and spring spa;.;ning. Alternatively, differential juvenile survival during s~~er months may have occurred. Again, inferring that the settlement of juveniles at a site of a given species directly relates to the breeding cycle of the population at that local may be erroneous for taxa with long-lived planktonic larvae. The breeding cycle of the Watsonville population is not necessari the same as the breeding cycle of the animals which spawned the settling larvae. Oocyte size-frequency histograJns (Figure 18) showed that essentially all oocytes were from 80 to 130 ]J (mean= 90.5). appears to be no relationship between oocyte diameter, fecundity and time of year. Larval settlement Larval abundances (Figures 25 through 28) are standardized 2 to the number per 0.018 m . The distance between data points reflects the actual number of days in which the jars were collecting larvae except l'>~here noted by an arrow, indicating the date jars were put down, preceeding the data point. Jars were first put down on 26 October 1976. Vertical bars represent the range of two replicates for the larvae jars (solid lines, solid circles], 67 Armond;(; brevis OUTFALL 90 . !20 150 180 210 240 270 300 330 360 A M J J A s 0 N D JULIAN DATE 10•000 f Armond/o brev/-s WINDMILL +/ \ \ i 129, 150 180 2!0 240 270 3&J '" J J A s 0 ~,/(/!_/A lv' 0.4 T£ Figure 25. Results of the larval jar, meiofauna core and macrofauna core (data from Hannan et al., 1978) collections of Armandia brevis at the outfall and windmill stations. See text for details. 68 10,ooo~r Cop/!e//o OUTFALL ·~ ~ l t'\j r, --r t2 1,000~ \ ~ E , ~ t \ ~ too[ \ ! ~\ ~I1\ 10 \ i 0 0 0 () ()00000500 0 05 1916 1911 298 328 1 30 60 90 l20 150 180 210 240 270 300 3?JJ 360 N 0 J F M AM J J AS 0 N 0 JUL/4/V DATE 10'000[ Copt!ello spp. ~ WINDMILL 1 ,J ~ ~ ~ J_, ! 1\ •;1 r "' I i ~~ , ;;3~ rL \ • I \J'l ~ 10-. \ I I ' ~ +I I I vi \ 'I ;t I I 1 + r 1 I L \ I !\ 1 I ~ ~ 1... :__ 1.0 .. '<=.~- _;- .,.-~....,.....,;~/J... \,..,..,J_o_l_u ;l\o_l_,, __ 0 e_i_~\ _j 1916 o,~,J o o o o.s o o o oo o o o o c o o o~o 298 328 1 30 60 9U 120 150 180 210 240 270 360 N 0 ,J F M A M J J !-\ S 0 c/t/LIAN DATE Figure 26. Results of the larval jar, meiofauna core and quarterly macrofauna core (data from Hannan et al., 1978) collections of Capitella spp. at the outfall and windmill stations. See text for details. 69 Prioaospic pyqmoeo OUTFALL ~ \ I \~ I ~ i} I «:20 . j11'. 1 l I ~ I r\' I /.-./I+ f \ I I If\! ~~~I \ . ~ ~ 101 ' ..,. .I x'~~ \ . ,. l!l· \i\ r / 1\.,,- _ l +/i\1·-·-·t-·-~-·-· t \ ~ \ /\ tjfi , \til " 1 \I I I \ "' ' 0L ~__./11 .' 1 L..:.~ ..~....-I_ 1----L¢ h-. · · tL-~_j 0 0 0 0 00 1976 1977 298 328 1 30 60 90 120 150 180 210 240 270 300 N D J F M AM J J AS 0 N JULIAN OATE 9Q 120 150 180 210 240 270 300 33{) 360 A M J J A s 0 N D /ULIAN DATE Figure 27. Results of the larval jar, meiofauna core and quarterly macrofauna core (data taken from Hannan et al., 1978) collections of Prionospio uygmaea at the outfall and Hindmi 11 stations. See text for details. 70 90 120 150 180 2!0 240 2?0 300 330 360 AM J J AS 0 N D JUL/I!N 04rE 100- ltollirio1 elegons so WINDMILL 90 120 lSO 180 210 240 27C AM J J AS 0 JUL/;1/v· OAr£ Figure 28. Results of the larval jar, meiofauna core and macrofauna core collections of Nothria elegans at the outfall and windmill stations, See text for details. ·- 71 and the meiofauna cores (dotted lines, open circles). Means are connected between sample dates. One jar only was collected on 18 March 1977 at the outfall and on 7 January 1977 at the windmill. Vertical bars represent two standard errors for sixteen macro- faunal cores (5iot-dash lines, solid triangles); means are connected between sample dates. Nothria and Prionospio pygmaea Hartman, the most abundant po chaetes in the macrofauna at the Watsonville stations ivere a very minor component of the larval jar collections (Hannan et al., 1978). Instead, two opportunistic (_sensu Grassle and Grassle, 1974) po chaetes, Armandia brevis Moore and Capitella spp. * >.Jere collected abundantly during the spring and summer months (Figures 25 and From March through December 1977, however, !::_. brevis and Capitella spp. were absent or minor components of the benthos in the areas surrounding the larval jars. More Capitella spp. settled at the outfall than at the windmill station. This genus was also collected in the fall in large numbers at the outfall. Prionosuio pygmaea >vas more abundantly collected in the meiofauna cores (Figure Nothria was collected in both the larval jars and in the meio- fauna cores during the spring and summer months (Figure 28). ·~< The species formerly knowTl as Capitella capi tata has been shovm to be a complex of a number of sibling species that may occur sympatrically (.Grassle and Grassle, 1976) 0 These species have not been formally described, so the Ca:oitella collected in this are referred to as Capitella spp. This takes into account the fact that the relative abundances of the different species change radically spatial and temporally depending on enviYonmental factors and on life history characteristics of the different 72 Magelona was almost never collected in the jars, hut occas sionally a few larvae were collected in the meiofauna cores throughout the year. Gut contents of Nothria Gut contents of Nothria were examined during peak larval settlement (March, April and May} at the outfall and windmill stations in order to determine if the worms were showing cannibalistic activity as previously reported for another onuphid, Diop~ ornata (Emerson, 1975). However, neither worm parts, setae, nor jars were found in the individuals examined. Results for the fev1 worms examined indicated that Nothria ingested crustaceans (a.mphipods, ostracods, harpacticoid copepods and barnacle nauplii), algae and sand grains. The algae may have· been ingested inadvertently with sand grains druing burrowing. In one case a tiny bivalve (Macorua sp.?) was found in the gut contents. Examination of one individual under the scanning electron microscope revealed that numerous species of planktonic diatoms (?.g., Coccinodiscus, Skeletonema) and fora.'Tlinifera le,g,, Globigerina) were also present in Nothria's guts. These were probably ingested with the sediment when burrowing, Most of the guts were nearly empty probably due to fast digestion, infrequent prey capture and/or handling technique. Food .material was located in the most posterior segments of the digestive tracts in all case but one. Regurgitation of r 73 I contents in formalin preserved specimens has als.o been previously suggested (_Buchanan and Warwick, 1974). ~ commensal relationship with Nothria Tubes of Nothria contained single individuals of the hesionfd worm, Gyptis brevipalpa (Hartmann-Schraeder) (}'able 6) at all three stations year-round. The infrequent but steady presence of Q. brevipalpa in Nuthria tubes may be significant, as hesionids have been previously reported in commensal rela- tionships (Pettibone, 1956). DISCUSSION Nothria elegans: reproductive biology and breeding cycle Several lines of evidence indicate that Nothria in central Monterey Bay has at least two year classes present in the population at one time, that it is a perennial species, and that it breeds seasonally over a period of about five months, from January through May with a very low level of spawning and recruitment year-round. Peak larval settlement occurred in Harch and April wi.th "bursts" of settlement continuing through August. Because this species has lecithotrophic larvae which spend only about six days in the water column (Blake, 197Sa), larvae settling in the sample area are probably recruited from elsewhere. Death of one of the year classes or a portion of both year classes may occur at, or shortly after, spawning. Furthermore, very high post--larval mor- tality is evident. Emerson (1975) suggested that adult Diopatra 74 Table 6. The occurrence of Gyptis b.revipalpa in the tubes Nothria ~egans in si~ved, preserved and sorted samples. Month Station Number of "u. brevinalna in tubes o! N. elegans October Outfall one Windmill one November Outfall four December Plume one January Outfall one Plume one Windmill one February Windmill two April Plume one Windmill two May Outfall one Plume two July Outfall one ~·· ornata ate their settling young. Gut analysis of Nothria adults during larval settlement (March, April and May) revealed no Nothria jaws, setae or worm parts as a portion of their diet at this time. However, the small sample size (four worms per station per monthJ and the possibility that gut contents may have been regurgitated during the preservation process, make results of the gut analysis inconclusive. Patches of unusually high adult densities were twice sampled (in September and May) at the outfall station. Areas where these dense clumps of adults occurred may have been areas of organic accumulation which could support a large number of individuals. Such a situation has been reported for another onuphid, Diopatra ornata, which. congregates at the seaward edge of kelp beds where organic matter accw~ulates and in other clumps of high organic matter on sandflats based on observations of Catalina Island and Monterey Bay populations (Emerson, 1975). Larvae may also be able to detect areas of high organic content and, in these areas, settle more abundantly and experience greater survival. Emerson (1975} has also demonstrated that, in the laboratory, Q_. ornata selected sediments conditioned by the presence of Macrocystis algae, the adult's major food source. In the present study dense clumps of adults occurred only at the outfall station i\lhere clumps of organic matter are more like to occur. .,_, Peak larval settlement was detected one month later at ~,.,ne most northern station (windmill) than at the southern sites (outfall 76 and plume). Furthermore, larvae were larger and more even distributed at the winmdill station in the April collection compared with March collections at the outfall and p1Ul1le stations. These data indicate either that conditions were better for short- term post-larval survival at the windmill than at other stations (supporting the hypothesis that patches containing large numbers of newly settled individuals were missed in the March sampl at the windmill) or that some larvae settled initially at a larger size in April at the windmill. The windmill station is the most northern site sampled and correlations between the predominate northerly currents and a south/north settlement gradient in larvae will be discussed later. Perhaps due to differential post- larval survival and/or to migration of post-larvae and juveniles away from their settlement clumps, the post-larvae collected in April at the windmill were more evenly distributed throughout the cores than at the other two stations in March. In some estimates of the breeding cycle of Nothria in this study, fecund individuals were broken into two categories: "ripe" and 11 unripe11 worms (see po 41). I suggest that individuals with less than 1,000 eggs (unripe) are recently spaw11ed individuals,_ are at various stages of recovery from spawning and undeTgoing subsequent egg proliferation and/or are individuals too young to spawn. The 1,000 egg lm 1. 1,000 eggs was the upper limit of brood size in all but three fecundity estimates taken during the summer months (June, and August) following the peak period of larval settlement (March and April) (see fecundity data, Figure 15). 2. The m.L'Tiber of fecund worms with greater than l, 000 eggs increased from September through April reaching anaximum during the peak period of larval settlement (Figure 15). 3. There appears to be a linear relationship of fecundity to worm size only in worms with greater than 1,000 eggs. This relation ship becomes increasingly pronounced during the proposed spawning season (January through May) and especially during peak larval settlement (Figure 15). 4. Worms in the proposed unripe category are not smaller than the ripe worms; they occur in all mature size classes (Figure 15). 5. The unripe worms do not have eggs of smaller sizes than the ripe worms (Figure 16). Supporting my designation of an unripe category which includes spent worms, Emerson (1975) reported that 11 a few" oocytes remain in the coelomic cavity of Diopatra ornata after spmming and thus mature females could be identified year--round; the breeding cycle of D. ornata had to be based on the maturity of the oocytes. Emerson collected coelomic content samples from live individuals on a monthly basis and did not quantify brood size, and thus his reference to a "fewn oocytes is unclear. Emerson (_1975) studied Dionatra ornata at a depth of 20 m at 78 Catalina Island, California, a depth only six meters different from that of the present study. Diopatra ornata and Nothria, as well as being closely related taxonomically, are extreme similar in many aspects of their reproductive biology (mature egg size, larval type, peak breeding period and period of larval settlement) as well.· Thus, comparisons of their developmental biology may be fruitful. Emerson suggested a twelve month mat.ur ation period for an oocyte of 25 11 (egg size when released from gonads into coelomic cavity) to grmv to 235 }.l (spawning egg size) in Q. ornata, but he lacked estimates of the period of develop ment in the gonad prior to release of eggs into the coelom. I suggest that this 12 month estimate may be a low estimate if applied to Monterey Bay populations of Nothria since the water temperature at 20m in Emerson's southern California sites can be above 20°C from July through October, but rarely reaches l8°C at the surface in I-1onterey Bay at any time of year; bottom temperatures are colder still. Higher water temperatures have been associated with increased metabolic rates; thus, egg development in southern California D. ornata may be faster than for central California Nothria. Applying the 12 month estimate of egg development time to size-frequency (.Figures 9, 10 and 11) and fecundity (Figure 15) data, I suggest that Nothria probably first spawns in its second year of life. ,Juveniles recruited in the spring of 1976 1vere first discovered carrying eggs in November 1976 (Figures 9, 10 and 11). If 25 JJ eggs were released into the coelom at this time, 79 individuals would not have had mature eggs until November 1977. However, eggs less than 26 y were rarely detected in this study (Figure 16), possibly the result of specimens being examined only under a dissecting microscope compared to Emerson's (1975) examination of live coelomic contents under a compound microscope. fu< alternative hypothesis is that eggs are released into the coelom at a larger size in Nothria. Egg size--frequency histograms in the present study showed peaks near spawning egg si:e (182 to 234 y) in most invididuals (Figure 16). These spaw11ing egg sizes agree with Blake (l97Sa) who reported 230 y as the spaw11ing egg size of Nothria elegans in a laboratory study of Tomales Bay, California populations, Emerson's (l975) egg size-frequencies for D. ornata also showed a year-round peak in eggs of 201 ]J and greater (without nurse- cell chains). He concluded that eggs grew to a mature size and were held until spawning. If eggs are proliferated from the gonads into the coelom year-round, and held until a cue or cues induce (s) spawning, the individuals of Nothria 1vhich were recruited in spring 1976 would be unable to spaw-n until the late winter and spring of 1978. Some individuals in the second mode of the size-frequency histograms (Figures 9, 10 and 11) evidental spawned in the late winter and spring of 1977. At this time approximately S09o of the fecund individuals were in the ripe and SO% 11ere in the unripe conditions. The unripe worms appear to be a mixture of the spring 80 ll 1976 recruits and spaw11ed animals since a 4 ~ size classes were represented in the unripe category (Figure 15). Some or all of the spawning individuals evidentally died at or after spawning as evidenced by the decreased numbers· of individuals in the second mode from September 1976 to August 1977 (Figures 9, 10 and 11). If all of the 'spawning individuals died, those worms with eggs in the summer of 1977 may represent spring of 1976 recruits that will spawn in the winter and spring of 1978. Without know- ledge of growth and spawning frequency in Nothria, however, it is impossible to know if the second liJode in the size-frequency histo"" grams represents one year class or a composite of several. The possibility that the worms are large enough, but have not acquired a spawning threshold egg number cannot be discounted. Previous studies of the breeding cycle of Nothria elegans in Monterey Bay also indicated seasonal spa•ming activity. Studies done along a depth transect from 10 to 26.5 m (''Ivl-transect 11 , Figure 2) over four years (July 1971 through June 1975) revealed ovigerous individuals of Nothria exclusively in the winter and spring months (Hannan, unpublished data). Peaks in larval settlement occurred from March through August during these years but never reached the extreme larval settlement peaks of the present study (Table 7: maximum density = 734/m2 at M-5 in July 1974 compared to maximum density= 1115/m2 at plume in March 1977}. Another study, over- lapping tfie present one, at 26.5 m depth offshore of the Salinas River mouth (_Figure 2) s-howed larval settlement of ~ from Table 7. A comparison of densities (number per m2) of Nothria e1egans from 1971 through 1977 at several stations in Monterey Bay. Data are taken from Oliver and-slatte:ry (1976) and Oliver et al. (1977) for M-transect, from ESI (1978) for Salinas River, and from the present study for the Watson ville stations. Blank spaces indicate that no samples were taken. All samples \vere sieved over a 0.50 rnm screen. ------· Station Year and month sampled (Depth in M) 1971 1972 1973 1974 July Sept Nov Jan Mar June Sept Dec Apr May July Aug Oct Dec Mar transect M-2 (10) 325 290 85 184 297 205 134 191 141 f\1-4 (20) 129 304 23:~ 304 452 410 148 311 240 379 177 192 1 113 219 M-5 (26.5) Watsonville Outfall (1 Plume (l Windmill (14) -----·---Salinas River 1181 (26.5) 1183 .5) U85 (26.5) CXJ 1186 .5) f<-·" -··-----~---"~-~'-·~··~--~------~--~--·------...... ~~-·~------.. -~--~····-~·~·------·--~----~·---··-·~-.,---- Table 7. Continued. Station Year and month sampled (Depth in m) 1974 1975 1976 July July Aug Sept Oct Dec Dec Jan Mar Apr May June July Sept Oct ··------·------·~----- M-transect M-2 (10) 331 141 M-4 (20) 318 M-5 (26.5) 73c1 607 558 332 210 282 304 228 381 289 381 233 345 Watsonville Outfall ( 700 359 Plume (14) 556 417 Windmill (14) 521 521 Salinas River 1181 (26. 1183 (26.5) 1185 (26.5) 1186 ·---··--·------·------·· 00 h) Table 7. Continued ------Station Year and month sampled (Depth 111 m) 1976 1977 Nov. Dec Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec ·------M-transect M-2 (10) M-4 (20) ~1-5 (26.5) -----Watsonville Outfall (14) 669 354 382 309 701 330 792 267 420 358 Plume (14) 382 330 396 309 1115 625 375 404 379 337 Windmill (14) 379 399 309 333 389 904 267 455 292 295 ------Salinas River 1181 (26. 120 63 143 108 462 357 268 62 42 28 35 1183 .5) 103 128 692 163 768 735 405 68 67 30 30 1185 .5) 133 1133 1893 168 447 420 149 62 33 32 33 1186 (26.5) 150 117 1505 682 667 743 342 106 23 33 18 --~ .. ----~------·--~------~------··~------~- 00 tN 84 February or March 1977 to July or August 1977 (Jable 7: maximum 7 density= 1893/m- in April 1977), but approximately 90% of the juveniles died by December 1977 (ESI, 1979). Ma.--dmum sizes of individuals in the resident populations, and average densities of Nothria in the Salinas River study, were half those of the worms in the present study at the Watsonville sites. No bimodality in size-frequencies was discovered by ESI. They found a maximlim of nine ovigerous worms per square 1neter during their sampling year while I found a maximum of 65 ovigerous ivorms per square meter in the present study. Thus, moving north from the Salinas River to the Pajaro River (see Figure 2) between 10 and 26.5 m depth, Nothria populations are larger with more mature individuals and are more persistent in the northern parts of central Monterey Bay than in southern aTeas. Even though the Salinas River populations experienced higher maximum larval settlement than the Watsonville study sites, mortality >lias more extreme and thus year classes were never able to develop. It ~ay be that these populations continually decrease in size as older individuals spawn and die each year (population densities at all four stations of ESI [1979] decreased by 75% from February 1977 to December 1977). The low nu~ber of mature individuals in the Salinas River populations suggests that this population probab contributes 1i ttle spawn compared with the more noTthern populations at M-5 and in the Watsonville area. Although larval settlement for Nothria is patchy in 85 Bay and survival -'-·""· variable from year to year 1 the population densities at the M-transect and the Watsonville stations did not change markedly from year to year (Table 7). There is a seasonal increase in population densities in the spring and summer (which drops in the fall each year) owing to the perennial nature of this species and its probable one year delay to first spawning. Because several year classes may be contributing to the spawn each year (with only the oldest individuals dying after spm~ning) a buffer adult population remains after the spa~T.ing season. Poor recruitment or high post-larval mortality in any one year decreases, but does not demolish the population. Post-larval mor tality was high in the Watsonville populations in the spring and summer of 1977; this, coupled with death in the older individuals after spawning, decreased adult faunal densities by approximate half from fall 1976 to fall 1977. A similarly small population size existed in 1971. Sa.111pling in November of 1971 at the outfall and a station 500 meters north of the outfall (near the windmill station), using methods almost identical to those of the present study, yielded densities approximately 3QS6 lower than the November 1976 densities (Panietz, 1973). However, these popula tions. increased in size by the time I began sampling in 1976. Several sequential years of poor recruitment appear to be necessary to cause a marked population decline in Nothria populations to numoers as low as those at the Salinas River stations (Table The lack of development of larger size class individuals and the 86 high mortality in 1977 produced population numb.ers almost 109,; smaller than the Watsonville populations. by December 1977. A comparison of Nothria to Diopatra ornata in southern Calif- ornia (Emerson, 1975) suggests many similarities in their breeding cycles. Diopatra ornata spa1ros at a 10\v level year~-round, with a period of increased spawning from April through August. Recruitment similarly occurs year~-round, with highest levels from early May to September. Emerson suggests that a single individual can spawn four times in its; life at approximately 12-month intervals, but gives no estimates: of time to first spawning. I suggest that Q_. ornata may also delay spawning until its second year as argued earlier for Nothria (pp. 78-80). Diopatra ornata, like Nothria, is a species characterized hy relatively stable population densities and I sug- gest that its· perennial nature -may, in part, account for this. Magelona sacculata: reproductive biology and breeding cycle The presence of low population densities (until larval recruitment began in May 1976) -makes it difficult to interpret-the reproductive biology and b.reeding cycle of the Magelona populations in the present study. Nonetheless, reliable conclusions include the . .., . following: Cll ovigerous worms occurred in size classes 0. 732 mm'" and greater, (_2). larval recruitment occurred from May through August and population densities. increased by a factor of five from Spetember 1976 to August 1977 and remained relatively high (9ouble and triple the prevous year's values) through December 1977 even though post--larval mortality was high, (3) egg 87 size data indicate a planktotrophic larvae according to the defin ition of Dales (1967), 1-.rho states, "i\lost planktotrophic larvae develop from small eggs (100 ]J) which hatch quickly. Development from larger eggs (250 V) is carried further before hatching and such larvae often enter the plankton or swim freely for only a short time" (p. 171 )'. This definition is in agreement with the findings of Blake (1975a) who e:x:perimentally determined that mature egg sizes of 235 ]J in Nothria elegans represent a short lived, lecithotrophic larval form. Woodwick (1977) also reported planktotrophic larvae developing from 100 11 eggs for the spionid Boccardia hamata in Elkhorn Slough (see Figure 2), while, in the same location, 150 ]J eggs of the same species produced lecitho trophic larvae. Larvae of Magelona may spend two months or more in the water column (J. Blake, personal communication), suggesting that this species spaivns in the winter and early spring (i.e. , larval recruitment occurs in the late spring and su:miner). Thus, with long-lived planktotrophic larvae, local recruitment is probably from areas far removed from Monterey Bay rather than from local populations. The complex and dynamic water circulation and temporal current regime in Monterey Bay make it nearly impossible to predict from where the larvae originated. Based on a detailed study of water characteristics during t1110 t•.;o-week sampling periods in June and July of 1976 in Monterey Bay, Lasley (1977) concluded that there is a net northerly flow of water through the Bay with a nine 88 residence time of the water mass. However, current patterns and wind direction vary seasonally (Bolin and Abbott, 1973). Further more, drift card studies have shown that surface cards generally follow the wind direction while bottom drift cards move more shoreward and northward with the currents (Blaskovich, 1973). The position of larvae in the water column is thus· important in assessing the origin of recruited individuals. No doubt worms recruited over the four month recruitment period (May through August) originated from several different adult populations outlying or inside Monterey Bay dependent on the exact time of spawning. Data on populations of Magelona sacculata along the M-.transect (Oliver et al., 1977; Hannan, unpublished data) and Salinas River area (]:SI, 1979) in Monterey Bay also support a winter and early spring spawning followed by spring and summer recruitment (Table 8; Figures 29 and 30). In February and March 1977 macrofaunal densities of Magelona were remarkably similar at the Salinas River and Watsonville sites ('fable 8). Larval settlement was detected in April at the Salinas River areas and not until May in the Watsonville populati~ns. This one month lag time in settlement between the southern and northernportions of central Monterey Bay suggests that larvae may arrive from the south and/or may reflect the inadequacy of one month sampling intervals to pin-point precise periods of larval settlement. An annual life history with seasonal spawning activity in Table 8. A comparison of densities (number per m2) of Magelona saccul from 1971 through 1977 at several stations in Monterey Bay. Data are taken from Oliver and Slattery (1976) and Oliver et al. (1977) forM-transect, from ESI (1978) for Salinas River, and from the present study for the Watsonville stations. Blank spaces indicate that no samples were taken. All samples were sieved over a 0.50 mm screen. Station Year and month sampled (Depth in m) 1971 1972 1973 1974 July Sept Nov Jan Mar .June Oct Dec Apr May July Aug Oct Dec Jan H- M-2 (1 1018 727 544 92 487 55 M-4 (20) 1041 1229 1278 678 2576 2323 600 134 1010 1114 551 215 473 557 480 M-5 (26.5) Watsonville Outfall (14) Plume (14) Windmill ( 4) Salinas River 1181 . 5) 1183 1185 (26.5 00 1186 \0 v>_···~~ Table 8. Continued. ------· ------Station Year and month sampled (Depth in m) 1974 1975 1976 !11ar July ,July Aug Sept Oct Dec Dec Jan Mar Apr May June July M-transect M-2 (10) M--4 (20) 5388 282 !11-5 (26.5) 1398 1208 607 395 202 162 184 172 134 304 1172 1462 3185 Watsonvi lie Outfall (14) 148 Plume ( 87 Windmill (1 132 Salinas River 1181 .S) 1183 (26.5) 1185 .. S) tD 1186 . 5) 0 Table 8. Continued. ----·------~-·- Station Year and month sampled (Depth in m) 1976 1977 Oct Nov Dec Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec -- !vi-transect M--2 (1 M-4 (20) M-5 (26.5) ------Watsonville Outfall ( 42 46 87 69 56 24 38 156 257 135 427 Plume (14) 28 38 59 45 42 35 45 104 241 149 441 Windmi 11 (14) 83 49 90 63 38 24 41 174 236 170 458 Salinas ---River 1181 .5) 38 53 132 187 500 193 230 365 322 257 286 1183 (26.5) 42 30 133 158 178 363 2~53 418 298 242 277 1185 30 27 218 198 413 253 350 =~46 348 435 285 1186 (26 0 5) 17 13 147 148 30:~ 205 230 480 280 627 353 .._,~0 92 Mogelono socculata -5 19it:. 6 Jt:LY 3n Jrt"': :~ 3•1 SEPT 3! OCT H..,-44 ~·24 l L = ,J~:J ""J 1975 l 30 DEC 26 J A •; 2 >;AR ~~21 :;-2 3 N•!R 1 l I ' [ 1 l •j 1 l==~ L = -~ fii=J = Iii..,- w:aJ :!50.------....-, Figure 29. Size-frequency histograms for f\!agelona ~lata collected at M-5 (from Hannan et al., 1978). Histograms are constructed as for Figures 9 through 14, except that only 8 cores were taken monthly (total area= 0.144 m2) for all months but July when 4 cores were taken (total area = 0. 072 m2) and October \vhen 7 cores were taken (total area = 0.126 m2). 27 31 II 15 3 2 7 10 17 3 4 13 #ovigerous 112 63 38 18 20 18 19 17 5 13 31 mature 55 15 3 5 I 3 I 2 31 144 174 #immature 0 94 171 83 44 24 22 21 23 i8 37 158 206 N= fatal I r---r--~1 I I I -T r: I \ __,18 ...... N \ 0 ... . X--> Magelona is supported by size-frequency (Figure 29) and breeding cycle (Figure 30) data collected at M-5 from June 1974 to July 1975 (Oliver et al., 1977; Hannan et al., 1978). The population of :.Magelona was abundant enough (Table 8) to premit a confident estimate of the breeding cycle. The percent of ovigerous indivi- duals oscillated between 15 and 40 until February 1975, peaking at 100% in March (Figure 30). Larval settlement followed this peak by one month and remained high through June 1975. 1\~ost of the pop ? ulation was: in the mature size classes (0. 603 wn~ and greater in this study) from August through March with all large individuals completely absent from the population oy June 1975 (Figure 29). This· strongly suggests death at or shortly after spawning, follm.,;- ing the growth and spawning of a single year class. The number of mature worms increased in July and August in the present study following initial larval settlement by one month (figures- 22, 23 and 24). ESI (1979) similarly found that the numlJer of ovigerous worms peaked in August and September. These data suggest a very rapid growth of spring immatures to summer adults· (~SI:, 1979}. Some individuals may spawn as early as s·eptemher as evidenced by a few individuals with fecundities 5000 to 8000 eggs at this time (figure 17), but most of the ··rngl · h . fecun, di.t)' individuals: occurred iB ·r:eb:ruarv" .__ ~.- . There also appears: to be some larval settlement year-round in all of the studies done in J1onterey Bay (Oliver et aL, 1977; ESI, 1979; and the present study). 95 Magelona is clearly an annual species in Monterey with seasonal spawning activity occurring as early as the fall and extending into the early spring months, depending on the location of the population and year of sampling. Peak larval recruitment always occurs in the late spring and s~~er months, reflecting the long larval life ·of this species. Growth to maturity is rapid (pne to two months). Death at or shortly after spawning is evident in the population at M-5 (Oliver et al., 1977; Hannan, unpublished data). Juveniles recruited largely from one settlement event (.lasting days to weeks) may have been responsible for the clear annual cycle displayed in the M-5 population during 1974 to 1975 while the Salinas River and Watsonville popultions in 1977 demon strated several recruitment periods lasting months. The high fecundity (ma:dmum of 12,000 eggs in the present studyl of Magelona compared with Nothria appears to be effective in carrying a population through a year of poor rec~Jitment to repopulate in the next spawning season. Poor recruitment ',vas evidently a widespread phenomena in Monterey Bay in 1976 because the >vinter populations of adults at both the Salinas River and Watsonville areas were extreme low (see Table 8). Though enough larvae were spawned in the winter and spring of 1977 to repopulate and sustain population levels up to 10 times higher than in the previous year, there were clearly fe;ver larvae available to settle during the SUi1JIDer 1977 recruitment season (J'able 8, the thousands of larvae settling in 1975 at M-5 versus the hundreds settling in 96 1977 at both the Salinas River and Watsonville areas). These differences in numbers of settling larvae could, however, reflect some larval settlement preference or physical phenomena that attracts larvae to the M-transect stations more than to the other areas sampled. Unfortunately, theM-transect populations were not sampled in 1976 to 1977 for comparison with the Salinas River and Watsonville areas. Oliver et al. (1977) suggested that Magelona leads an ephemeral existence at shallow depths (10m and shallower). They suggested that massive winter die-offs of the shallow populations of this species were due to the disturbance caused by wave activity. If this is true, then the low population densities of Magelona at the Salinas River and Watsonville study sites in the winter of 1976 to 1977 may have been due to unusual storm activity reaching these greater depths. However, diver observations during sampling indicated that this was, on the contrary, a very calm winter compared to earlier winters and that of 1977 to 1978. In contrast to the relatively stable temporal abundances of Nothria, Magelona populations are capable of nboom and bust11 years of abundance. The extremely low population densities of f\lagelona in the winter of 1976 to 1977 reflect this. Perhaps an annual life history facilitates the bloom and bust syndrome. Because there is probably only one year class present in the population at a time, population densities reflect the recruitment success of the previous year. With Nothria, several years of poor recruitment are necessary 97 to produce the drastic density changes (five to 10 fold) seen m only one year with Tvlagelona. Maximum fecundities in 1vlagelona are about two times those of Nothria and such high fecundities may in- deed be required to insure some larv·al recruitment even when the abun- dance of ovigerous individuals contributing to the spawn is low. Factors controlling breeding cycles and population densities I have suggested that the breeding cycles of Nothria and Mage lana exhibit seasonality with winter and early spring spawning and larval settlement in the spring and summer months. A clear case of seasonal spawning activity has also been demonstrated for another subtidal polychaete, Thalanessa spinosa (Hartman) in the Salinas River area in Honterey Bay (ESI, 1979). Ovigerous individuals occurred exclusively from March through June 1977 while larval settlement began in July and continued through October 1977. I h·ave also suggested that the differences in the temporal var- iabi1ity of population densities exhibited by Nothria and Magelona may be due to their perennial and annual life cycles respective however, I have not yet indicated why settlement success may vary from year to year. I also noted spatial variability in population densities and larval settlement on a south/north gradient between 10 and 26.5 m in depth in central Monterey Bay. I will now hypoth- eisze factors that may be important in producing the temporal and suatial variability observed in the breeding cycles in populations . . of Nothria and 1v!agelona in Monterey Bay. The actual importance of these factors in determining the events described will requi:re testing by future experimental manipulation. 98 Clark (1965), Dales (1967), Clark and Olive 973) and Schroeder and Hermans (1975) have reviewed the relationship of temperature and food abundance to sperm and oocyte development and spawning cues in polychaetes. Emerson (1975) has discussed the literature relating these two factors to marine invertebrates which breed continuously with a period of increased spawning activity. Polychaete reproduction literature is profuse with references to temperature and food abundance as primary controllers of their breeding cycles (e.g., Thorson, 1946; Southward and Southward, 1958; Olive, 1970; to name a few). While correlations have been made of breeding cycles with field conditions, and labor atory experiments involving the raising or lowering of water tem perature and food abundance have induced successful spawning in adults, this does not necessarily mean that these factors control spaw11ing in the field. Schroeder and Hermans (1975) point out that in none of the studies where temperature has been correlated with spawning activity have the authors been able to show that it is the "immediate cause of gamete release" (p. 87 ) . Likewise, Schroeder and Hermans stress that "there have been fe1.; attempts to correlate field nutritional conditions with a population's repro ductive perfonnance" (p. 99 ) . Though drastic changes in temperature and food availability in highly seasonal environments provide a gratifying correlation with highly seasonal spawning cycles (e.g., data on boreoarctic invertebrates provided by Thorson, 1946 and Barnes, 195 , there is a steady accwuulation of breeding cycle data which cannot be 99 simply explained by these means (e.g., Duncan, 1960; Schroeder, 1968; Gibbs, 1971; Whitlatch, 1977). Most breeding cycle studies have been limited to a single species in a single environment. Physical factors as controls of observed breeding periodicity are sought, perhaps because biological data suggestive of such controls are completely lacking. As breeding cycle data are acquired on more than one population of a species (closely or widely spaced geo graphically) and on several species in one location, it becomes more apparent that simple physical factors alone cannot explain the patterns observed. For example, Whitlatch (1977) found four distinct breeding cycles in macrofauna of an intertidal mudflat in Barnstable Harbor, Massachusetts and he evoked latitudinal distributional patterns of the species, some being at the northern and some at the southern boundaries of their ranges, while some species were cosmopolitan, to explain the results. Differences in breeding periodicity at the same geographical location were also reported for four cirratulid species in one intertidal area in Plymouth, England (Gibbs, 1971). Two species spawned very seasonal but at different times: Tharvx marioni (St. Joseph) in late October/ early November and Cirriformia tentaculata (Montagu) in late June/ early July. Caulleriella cauut-esocis (St. Joseph) spawned over a three-month period (August to October) and Cirratulus cirratus (Muller) spa~~ed year-round. These data suggest biological or an integration of several biological and physical properties to explain the breeding cycles because simple physical phenomena 100 may be unable to account for the observed diversity. What the adults and larvae feed on, how much food they require versus how much is available, the mobility and position of the species in the sediment, the individual tolerances of the species to various physical stresses, the endocrine control of the species reproductive cycles and biological interactions between species may be factors important in controlling the breeding cycles of the worms. Breeding cycle control has likely been oversimplified in the past; alternative hypotheses must be posed and tested regarding the relationships between breeding periodicity and physical and biological environ- ments of the populations. Staggered spawning and larval settlement are evident in the three species studied in detail during 1976 and 1977 in Monterey Bay (Nothria elegans and Magelona sacculata at the Watsonville study sites and the Salinas River stations and Thalanessa spinosa at the Salinas River area, also an abundant member of the Watsonville communities). All exhibited seasonal spawning and larval settlement, but at different specific times. Magelona may have spmmed as early as September 1976, but probably spawned primarily from January through March 1977. Nothria probably spawned from January through May and 1:: spinosa from March through June (ESI, 1979). Larvae of Nothria settled first in !'larch and continued settling through August· ~1agelona larvae settled from April through September (Salinas and May through August (}vatsonville); T. spinosa larvae settled from July through October (ESI, 1979). Both Nothria and Magelona_ 101 settled at a low level year·-round and ovigerous individuals occurred continuously throughout the year. Thalanessa .:;J2inosa exhibited more distinct breeding periodicity; ovigerous individuals and larval settlement occurred only during the periods mentioned above. Although the peak breeding periods for the species are not simultaneous, all spawn during the winter and spring. Water temper atures decrease beginning in February due to coastal upwelling. Spawning in invertebrates has been correlated with maximum and minimum >vater temperatures (Kinne, 1970) as well as with magnitude of temperature change (Orton, 1920; Thorson, 1946; Giese, 1959). Decreasing water temperature is not usually associated with increasing food sources (Emerson, 1975); however, in the case of coastal upwelling nutrients surface with the deep, cold water and, combined with sunlight, produce large phytoplankton blooms. Even minor temperature fluctuations may be important in reproductive cycles (Giese and Pearse, 1974), but, iiihen these fluctuations occur year round their influence as a spmming stimulus is hard to interpret· From 1971 through 1975 the average monthly water temperature along the M-transect varied between 10° and 16 °C; the largest monthly change in water temperature was only 5°C (Oliver et al., 1977) · Oliver et al. further report that "short term variations .e., several days) were often nearly as great as that during the entire year11 (p. 18). Because theM-transect sites were located offshore of the mouth of Elkhorn Slough and near the head of the submarine canyon (Figure 2), they were more influenced by the sl 102 ocean tidal exchange. During upwelling warm, shallow slough waters are mixed with cold, upwelled, oceanic water at ebb tide. The Salinas River and Watsonville study areas are not as affected by this tidal exchange and thus may experience continuously colder water during upelling. Phytoplankton blooms resulting from coastal upwelling may, in turn, effect blooms of grazing and predaceous zooplankton. Seasonal organic enrichment of the water column was detected in particulates analyzed from s.ettling tubes (see pp. 17-20; Figure 31). Organic carbon values were high in particulates collected from March through june and occassional large fluxes of organic material occurred in the fall of 1977 as well (Hannan, unpublished data). Percentage of organic carbon in bottom sediments changed little over time (Figure 31). A seasonal increase in food abundance in the water column would be advantageous to the planktotrcphic larvae of Magelona and Thalanessa spinosa. Emerson (1975) suggested that bottom sediments may be organically enriched by phytoplankton blooms, thus increasing settlement success in the lecithotrophic larvae of Diopatra ornata which feed several days after settlement. Settling larvae of Nothria may also experience increased survival in organ- ically enriched sediments. Although seasonal enrichment of bottom sediments was not detected in the monthly sediment analyses (Hannan I et al., 1978; Figure 31), clumps of organics may have been missed in sampling. Upwelling in the early spring also corresponds with very rough waters, thus resuspension of fine organic-laden sediments .600 r-~r--,·---T---~---r--~--·~--~--~~-· .600 s·ettling tubes 0:: (x, n =3) u ~-outfall u -;;r ~---·~ w indmi II ?Q •'- sedime cores (5{ n=2) ::::::::--- ' .. , . ____ _,_____-..-~~~-..--..-., 31. Percent organic carbon values in core samples (lower U nes) at 1 and windmill (- - - -) stations and in settling tubes (upper lines) at outfall and windmill stations akcn from !Iannan ct al,, 1978). Data points are connected straight lines and represent the mean of h1o samples for the sediment ,..... cores and of three samples for the settling . SettLing tubes were ically 0 v' not at the \vindmi 11 station due to rough bottom conditions, 104 may have prevented collection of high. organics in the bottom samples. Adult animals feeding directly on an increased supply of dia- toms has also been suggested as a "hatching stimulus" (Crisp, 1956; Barnes, 1957; Crisp and Spencer, 1958) for some barnacles. Nothria and Magelona do not feed directly on the plankton as adults; they are deposit feeders. Benthic food increasing with plankton enrich- ment during upwelling may indirectly trigger spawning in adults; however, this would not account for winter spawning activity. If all species are responding in some way to upwelling condi- tions, why then are their breeding cycles so different within this period of time? I here present three hypotheses to explain the staggered spawning and larval settling periods. Firstly, develop- mental time from larval settlement to mature adult and from initial gamete formation to oocyte release varies with species. Thus, time of initial larval settlement in an annual species (Magelona) and time of last spawning in perennial species (Nothria and Thalanessa spinosa) may determine exact time of gamete release due to develop mental times. Though conditions may be "right" for spawning to occur, the individuals must be physiologically capable of doing so. Secondly, the availability of larval food may be important in determining when adults spawn. In addition, larval survival has 1 been clearly related to variations in predation pressure and this may directly affect larval collections (Whitlatch, 1977). For i. i 105 example, prey refuges in size from various predators have been reported (Paine, 1976; J. Oliver, personal communication). Larvae of certain preferred prey could settle early enough to grow to a non-preyable size before predators increase in abundance or migrate into an area. Nothria and Hagelona are eaten by several species of benthic perch and flatfish (Nybakken et al., 1977). Seasonal increases in the perch populations at the outfall during the spring were noted in the present study (Hannan, personal diving observations). Data on infaunal predators in the study areas is unavailable; however, preliminary evidence sugge-sts that at least part of the diet of Thalanessa spinosa consists of polychaetes (S. McCormick, personal communication). It is interesting that larvae of this species are the last to settle of the three species considered here and may, thus., be maximizing their food intake by feeding on other polychaete larval forms. The gut data on Nothria indicate that Crustacea made up a major po!tion of its diet from March through May. Seasonal cycles in crustacean species in Monterey Bay have been reported at shallow depths \.,..i th peak reproductive activity in the spring (e.g., the amphipod, Paraphoxus epistomus at 10 m, Oliver et al., 1977). Again, feeding larvae may reach the sediment in time to take advantage of this food resource. Predation effects by other organisms on planktonic or settling larvae of Nothria, Magelona and/or Thalanessa spinosa may mask ac- tual timing of larval availability and settlement. Patchiness in lar- val settlement was observed for all species due to differential settle- 106 ment of larvae and/or differential survival of post-larval formso Sample areas may have been too small and sampling intervals for the macrofauna (one month) and even for the larvae (two weeks) too infrequent to accurately reflect the periods of larval settlement for these specieso Thirdly, the seasonal disturbance caused by wave surge in the winter and early spring may be an important factor. Of the three species, Nothria lives in the most permanent structure, a parchment tube affixed with sand grains. Larvae begin tube building almost immediately after settlement (Blake, 1975a). There is also some evidence that larvae may be able to choose the sand grains they use in tube construction (BLake, 197Sa). Winter and early spring sediments are better sorted due to resuspension of the finer fractions by '\..rave surge (Hannan et al., 1978). Thus, the Nothria larvae may be aided in tube construction by the availability of prefered sand grain sizes during this time. Furthermore, with the protection of a tube, the species may be more equipped to settle earliest in the spring than the other two species and may, thus, confer higher recruitment success at this time by exploiting food resources and space "t?efore other larvae settleo Mag~ is the second most sedentary animal, living in a mucus-lined burrow. It settles after Nothria and before Thalanessa spinosa. Thalanessa spinosa, the most motile of the species 11 nestlesn (that is, lies in a shallow impression) in the sediment (ESI, 1979). By settl in July, it avoids the winter and early spring Have energy, 107 and thus escapes excavation by waves illhich ivould lead to more intense predation by visual predators. It is doubtful that any one of these three hypotheses will account for the trends observed. I suggest many factors are probably responsible for breeding cycle control and larval settle- ment trends. Two phenomena revealed in the present study may be related to California's drought which occurred from 1975 through 1977: ( 1~J ' Nothria's extremely high larval settlement in 1977 versus data on settlement in previous years (Table 7), and (2) ~1agelona 1 s extremely low adult densities in 1976 compared with previous years (Table 8). The Pajaro and Salinas Rivers and Elkhorn Slough normally supply nearshore waters with organically enriched water · and sediments from agricultural runoff. The increased fresh water mass also tends to decrease nearshore water salinities Hhen the rivers are flowing. A pronounced seasonal flux of river flow is 3 evident; Salinas River mean monthly flow increased from 0 m /sec in 3 3/ December 1972 to 100 m /sec in February 1973, from 5 m 1 sec in 3 3, December 1973 to 75 m /sec in· January 1974, and from 5 m 1 sec in 3 ·December 1974 to 60 m /sec in February 1975 (numbers reported in, but not collected Oliver et al., 1977). Highest river flows are normally experienced from January through MardL Hm'l'ever, during these months in 1976 and 1977, neither the Salinas nor the Pajaro Rivers broke through the sand dunes to flow into the ocean, and flow from Elkhorn Slough was greatly reduced. Waters of 108 areas probably e.xperienced higher winter salinities and loHer nutrients during these drought years. If nearshore populations 1vere adapted to the normal seasonal flux of river water, the dis tinct absence of this flow may have affected the life histories of the organisms; for example, in 1976 the triggering of gamete release in Magelona or settlement and survival of lVlagelona 1 s planktotrophic larvae. Drought conditions might also be responsible for the poor development of older and larger size classes of Nothria at the Salinas River stations. The Salinas River normally supplies three times as much discharge as the Paj arc River (Oliver et aL, 1975) and thus populations at the former sampling sites may be affected more by a lack of river runoff. ESI (1979) haye further suggested that the unusually large bloom of Nothria larvae in 1977 might be a response to the drought conditions. A south/north gradient is evident in several population phenomena: (1) Density of larval settlement of Nothria >vas higher in southern areas. Larval settlement of Nothria was greater at the Salinas River stat:ions than in the Watsonville area and, of the Salinas River stations, the southern-most stations received the highest settlement (.l::S:r, 1979; Table 7 and Figure 2), (2) Persistence of larger, presumablly older size classes of Nothria occurred only in northern populations (Table 7). Nothria individuals were largest at the windmill stations (Figures 9 to 11), (;))_ Larvae of Magelona first appeared earlier in the year in 109 southern regions compared to northern areas. Larvae of Magelona appeared a month earlier at the Salinas River stations than at the Watsonville stations (Table 7). As earlier mentioned, these trends may reflect infrequency of sampl or patchiness of settling larvae. However, another hypothesis to explain these data involves water circulation patterns. Lasley's (1977) detailed study of water characteristics during June and July of 1976 revealed \vater masses entering from the south bay and circulating north. He also found that, in general, the south bay showed higher or equal l~vels of nutrients (reactive phosphate, nitrate and silicate) and higher chlorophyll-a concen~ trations c01llpared with central and northern Honterey Bay. However, the north hay showed less variability and greater stability of temperature and oxygen than the south bay. ESI (1979) also found that the percentage of organic carbon in bottom sediments was greater at their southern stations than at their northern ones during 1 1977. Thus, larvae may first approach south bay sediJnents and settle there. The higher nutrient and organic carbon values in the south bay may further enhance its attractiveness to settling larvae. The more stab.le temperature and oxygen regime of the north bay, however, may be favorable to Nothria adults. Lack of development of larger size-classes of Nothria in southern regions due to the absence winter and s.pring flow of the Salinas River during the drought years has already been suggested. Biological interactions resulting in the s.outh/north differences could also occur. 110 SUr4MARY The breeding cycles of Nothria elegans and Magelona sacculata have been delineated for three essentially replicate study areas around the Watsonville se\ver outfall in central Monterey Bay, California. Both species exhibited seasonal spa\ming peaks in winter and spring, and larVal settlement in the spring and sTh~er, with a low level of spawning year-round. Magelona reached maturity in two months and probably spa\ffiS the first year with death occurring at or shortly after spawning. This species had small eggs, high fecundities and long-lived (at least two months) planktot:rophic larvae. Population densities were sometimes extremely variable from year to year, Population densities of Nothria also varied from year to year, but not as drastically as Magelona's. Nothria had egg sizes twice and fecundities half those of Magelona and the lecithotrophic larvae of Nothria stay in the water column for only six days (_Blake, 1975aJ , This species appeared to be i teroparous and thus more than one year class may be contributing to the spawn each year. It is probable that Nothria does not spawn until its second year. This, combined with the short planktonic life of the larvae and the perennial nature of the species, contribute to its more stable population densities compared with those of 1>1agelona, Hypotheses were proposed providing factors may be control- ling the breeding cycles and population fluctuations of Nothria, Nagelona and another Monterey Bay polychaete abundant at the Watson ville study sites, Thalanessa spinosa. All three species spaHned 111 sometime in the \-'_inter and spring with larval settlement in the spring and summer; however, the specific breeding cycles varied with species and larval settlement times were staggered over the settlement season. Although coastal upwelling beginning in the late winter which pro- vides nutrients and decreases water temperatures may effect spawning activity, it is unlikely that a single factor (~.g., temperature or food availability) controls these cycles. Biological hypotheses were suggested to account for the observed species-specific breeding cycles.. These included: species-specific developmental times, food availability versus larval food preferences, predation effects and the physical disturbance caused by seasonal wave surge affecting burrowing abllities of and tube construction by newly settled larvae. It was suggested that California's drought from 1975 througl!. 1977 may have effected the unusually high larval settlement of Nothria in 1977 and the unusually low adult densities of Magelona in 1976 compared to previous years. Reduced river flow into Mon terey Bay during the drought may have affected the infauna and/or planktonic organisms. For example, organic enrichment may have b.een unusually low and salinities unusually high during these winters. Larval settlement in Magelona and Nothria and the size-class structure of Nothria demonstrated gradients from the southern portions of central Monterey Bay to more northern regions. I proposed, from water characteristics and circulation patterns, that larvae mayhave first approached Monterey Bay from the south and settled there lea ving fewer larvae to colonize northern r.egions. However, Nothria adults appeared to experience greater survival in north central areas. LITERUURE CITED Barnes, H. 1957. 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