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Spring 1980 THE FUNCTIONAL ROLE OF ASTERIAS VULGARIS VERRILL (1866) IN THREE SUBTIDAL COMMUNITIES ALAN WILSON HULBERT
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Recommended Citation HULBERT, ALAN WILSON, "THE FUNCTIONAL ROLE OF ASTERIAS VULGARIS VERRILL (1866) IN THREE SUBTIDAL COMMUNITIES" (1980). Doctoral Dissertations. 1252. https://scholars.unh.edu/dissertation/1252
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H u lbert , Al a n W ilson
THE FUNCTIONAL ROLE OF ASTERIAS VULGARIS VERRILL (1866) IN THREE SUBTIDAL COMMUNITIES
University of New Hampshire Ph.D. 1980
University Microfilms Intern ât ions! 300 N. Zeeb Road, Ann Arbor, MI 48106 18 Bedford Row, London WCIR 4EJ, England
Copyright 1980
by Hulbert, Alan Wilson
All Rights Reserved
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. THE FUNCTIONAL ROLE OF ASTERIAS VULGARIS
VERRILL (1866) IN THREE SUBTIDAL COMMUNITIES
by
ALAN W. HULBERT B.S., University of Lowell, 1968
DISSERTATION
Submitted to the University of New Hampshire in Partial Fulfillment of the Requirements for the Degree of
Doctor of Philosophy
in
Zoology
May, 1980
i Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ALL RIGHTS RESERVED © 1980
Alan W. Hulbert
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. This dissertation has been examined and approved.
DissertaÆ ^ director, Larry G. Harris AssociateTrofessor of Zoology
Edward N. Francq, A ssistant Prc 'essor of Zoology
David J. Hàrœbaim, /Adjunct Professor of Zoology
Arthur C. Mathieson, Professor of Botany
enneth P. Sebens, Assistant ProfeSaar of Zoology
Janes T. Taylor, A s^stant Professor of Zoology
Date
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS
I am thankful to Dr. Larry G. Harris for his friendship and
continuous support as my major advisor. Stimulating discussions with
faculty and students helped me throughout my research program and
have considerably improved the thesis. Discussions with Jonathan
Witman, Terrence Gosliner, Luther Black, Clair Buccanan, Mark Mattson,
Barry Spracklin, Wayne Lord and Alan Kuzirian have been particularly
helpful. Many people helped in the study and I am especially indebted
to Douglas Denninger, Larry MeEdward, and John Duclos for the laboratory
work and without Dr. Larry Harris, Jonathan Witman, and the crew of
the Jere A. Chase the field work would not have been possible. Captains
Ned McIntosh and Paul P ellitier and Diving Safety Officer Paul Lavoie
always maintained a positive attitude even on the most "Moderate" Gulf
of Maine days.
Theodore Donn helped with the statistics and his insights and
Clayton Penniman's computer programs helped enormously in the data
a n a ly s is .
I wish to further thank Dr. Mathieson who allowed the use of
the facilities at the Jackson Estuarine Laboratory. Research support
has been provided by the National Marine Fisheries Service, the American
Museum of Natural History, the Dryfus Foundation, the ÜNH Sea Grant
Program, the UNH Central University Research Fund, and the UNH Zoology
Department which provided the necessary boat time.
The many talents of my wife, Kathy, helped in all aspects of
this study, and for her continued patience, confidence, and much more
I am very grateful.
IV
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS
Acknowledgements ...... iv
List of Tables ...... v i i
List of Illustrations ...... ix
A b s t r a c t ...... x i
Chapter Page
I. Introduction ...... 1
P urpose ...... 4
II. Site Descriptions ...... 6
L o c a tio n ...... 6
Communities ...... 9
8m community ...... 11
Transition Zone ...... 12
18m community ...... 13
30m community ...... 13
Seasonality ...... 17
Physical Seasonality ...... 17
Biotic Seasonality ...... 22
Summary o f S ite D e s c rip tio n s ...... 23
III. Materials and Methods ...... 26
Population Structure ...... 26
Feeding A ctivity ...... 28
Flux R a te s ...... 29
C a g e s ...... 31
Predation Effects on A. vulgaris ...... 33
Natural History ...... 34
a Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I
IV. Results ...... 35 i Population Structure ...... 38
Seasonality ...... 38
■ i other Locations ...... 39 y Feeding Activity ...... 65
i Field Results ...... 65
Laboratory Results ...... 68 3 Flux R ates ...... 82
Predation of A. vulgaris ...... 85
A s t e r o i d s ...... 85
Non-Asteroids ...... 90
Natural History ...... 97
V. D iscu ssio n ...... 108
Population Structure ...... 109
Feeding Biology ...... I l l
Size Selective Predation ...... 112
M igration ...... 118
P red a to rs ...... 119
Summary ...... 120
Literature Cited ...... 124
Appendix A ...... 134
Appendix B ...... 144
Appendix C ...... 154
Appendix D ...... 158
Appendix E ...... 162
Appendix F ...... 169
Appendix G ...... 171
VI
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF TABLES
II-l Abundance of dominant invertebrate groups at the
research site ...... 14
II-2 Organisms associated with the Modiolus clumps at 18 m. . . 15 2 IV-1 Abundance of A. vulgaris and Leptasterias sp. from .25m
q u a d r a t s ...... 40
IV-2 Size structure of A. vulgaris and Leptasterias sp.
from .25m quadrats ...... 41
IV-3 Biomass of A. vulgaris and Leptasterias sp. from 2 .25m quadrats ...... 42 2 IV-4 Abundance and size structure of A. vulgaris from 10m
t r a n s e c t s ...... 43 2 IV-5 Biomass of A. vulgaris from 10m tran sects ...... 44
IV-6 Abundance and size structure of A. vulgaris at Gosport
Harbor and Malaga Gut, the Isles of Shoals, N.H., and
Nubble Light, York, Me ...... 45 2 IV-7 Multiple regression analysis of .25m quadrat abundance. . 46 2 IV-8 Multiple regression analysis of .25m quadrat size
s t r u c t u r e ...... 47 2 IV-9 Multiple regression analysis of 10m transect abundance. . 48 2 IV-10 Multiple regression analysis of 10m transect size
s t r u c t u r e ...... 49
IV-11 Multiple regression analysis of the relationship of the
size of the disc to the length of the arm in A. vulgaris . 50
IV-12 Feeding data summarized and expressed as percentages
for A. vulgaris ...... 70
I vii
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. IV-13 Feeding data summarized and expressed as percentages
for small (< 1 cm) A. vulgaris and Leptasterias sp. . . . 71
IV-14 The 15 categories of prey and the mean sizes of A.
vulgaris that utilize them ...... 72
IV-15 ANOVA of the 15 categories of prey relative to the mean
sizes of A. vulgaris that utilize them ...... 73
IV-16 Feeding percentages per size class of A. vulgaris at
dm, 18 m and 30 m ...... 74
IV-17 Laboratory prey preference of A. vulgaris ...... 75
IV-18 Laboratory prey consumption rates of A. vulgaris ...... 76
IV-19 Mytilus edulis consumption rates of A. vulgaris ...... 77
lV-20 Rate of A. vulgaris movement at 8m, 18m and 3 0 m ...... 84
IV-21 Size and abundance of A. forbesi at 8m...... 86
IV-22 Potential predators and competitors of A. vulgaris. . . . 95
IV-23 Population parameters of asteroids that do not directly
a f f e c t A. v u l g a r i s ...... 101
IV-24 Abundance of Henricia sanguinolenta at 8m, 18m, and 30m . 1Q2
IV-25 Size structure of Henricia sanguinolenta at 8m, 18m
and 3 0 m ...... 103
I viii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF ILLUSTRATIONS
II-l Map of the Isles of Shoals, indicating the research site. . 7
II-2 Temperature range at 8m, 18m and 30m ...... 18
II-3 Ambient temperatures at 8m, 18m and 30m from November,
1974 to February, 1980 ...... 20
II-4 A rtist's rendition of 8m, 18m and 30m communities ...... 24
IV-1 Abundance of A. vulgaris and Leptasterias sp. for 9
complete sampling d a te s ...... 51
IV-2 Size structure of A. vulgaris and Leptasterias sp.
for 9 complete samping dates ...... 53
IV-3 Biomass of A. vulgaris and Leptasterias sp. for 9
complete sampling d a te s ...... 55
IVs-4 Biomass of A. vulgaris and Leptasterias sp. at 8m,
18m and 30m ...... 57
IV-5 Mean abundance of A. vulgaris and Leptasterias sp.
from October, 1976 to January, 1979 ...... 59
IV-6 Mean size structure of A. vulgaris and Leptasterias
sp. from October, 1976 to January, 1979 ...... 61
IV-7 Mean biomass of A. vulgaris and Leptasterias sp.
from October, 1976 to January, 1979 ...... 63
IV-8 The 15 categories of prey plotted against the mean
sizes of A. vulgaris that utilize them ...... 78
IV-9 Pie diagrams of the percentages of A. vulgaris feeding
on the 15 prey categories, by size class and community. . .80
IV-10 Abundance of Henricia sanguinolenta at 8m, 18m and 30m. . 104
ix
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. IV-11 Size structure of Henricia sanguinolenta at 8m, 18m
and 3 0 m ...... 106
V-1 Major components of the food web relative to A.
v u lg a r is ...... 122
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT
THE FUNCTIONAL ROLE OF ASTERIAS VULGARIS
VERRILL (1866) IN THREE SUBTIDAL COMMUNITIES
by
ALAN W. HULBERT
University of New Hampshire, May, 1980
The functional role of Asterias vulgaris has been investigated
in three subtidal communities at the Isles of Shoals, New Hampshire,
U.S.A., from 1975 to 1980. The three communities are located at depths
o f 8 m, 18 m, and 30 m along a transect from the intertidal to a depth
of 35 meters on rocky substrate of an exposed shore.
Components of the study based on in-situ observations included
an analysis of population structures, feeding biology, flux rates,
predators and natural history of Asterias vulgaris in the 3 communities.
The feeding data shows a series of prey specializations by size such
that a progression of specializations on increasingly larger prey seems
to be required for the species to grow larger (i.e. ectoprocts to hydroids
to small gastropods to echinoids . . . to bivalves for the largest
individuals). The communities at 8 m and 30 m contain a variety of
prey that are utilized, and normally distributed population structures
of asteroids are found. The middle community at 18 m is anomalous in
several ways; fewer asteroids are feeding at 18 m, a small species of
Leptasterias is present in high densities which may be a direct com
petitor for food as well as a predator upon Asterias vulgaris, especially
I
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at the most critical small sizes, and the resulting population structure
is strongly skewed to very small individuals, 90% of which are Leptasterias
sp. The giant Asterias vulgaris, found only at 18 m feed almost exclu
sively on large Modiolus modiolus, and are probably migrants into the
community from deeper, soft-substrate communities.
Asterias vulgaris is a generalist species found in a wide range
of communities, consuming the prey available in a community in relation
to its size-limited abilities. Its role in the 3 communities is not
that of a major structuring or controlling factor, but rather it is
itself controlled by the characteristics of the community. Most of the
species in the low diversity Gulf of Maine are opportunistic in nature
and not competitive dominants. Therefore concordance to recent community
models is in terms of which community is more (8 m) or less (30 m)
opportunistic. The 8 m community is a shallow subtidal continuation
of the intertidal into a highly productive algal zone. The 30 m
community is much more physically stable, but has lower productivity
than the shallower areas. The 18 m community is transitional between
the geographically more extensive 8 m and 30 m communities and is an
area of ecological release for some species and stress for others.
The functional role of Asterias vulgaris in three adjacent sub
tidal communities showed differences in the feeding biology, population
structure, and rates of movement of this species in each community.
The observed differences in the populations can be related to differences
in ecological aspects of each community. The important potentially
controlling factors for Asterias vulgaris appear to be: 1. physical
disturbance at 8 m due to temperature changes and wave action; 2 .
decreased food availability at 18 m due to a Leptasterias sp. predator
x i i I Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. and competitor exaggerating low food potential; and 3 . decreased primary
productivity at 30 m, Asterias vulgaris is a foraging predator which
takes prey as encountered and its population structure and feeding
biology reflect a dynamic equilibria with the community.
x i i i
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t-s CHAPTER I
i INTRODUCTION
Competition, predation and disturbance have been widely used
in considerations of the important aspects governing the structure of
various communities (Birkeland, 1970; Buss & Jackson, 1979; Connell, g 1961a & b; Dayton, 1970; Dayton et al, 1974; Rolling, 1973; Jackson,
1972, 1973, 1975; Lubchenco & Menge, 1978; Menge, 1976, 1978a & b,
1979; Osman, 1978; Woodin, 1974, 1978). Community diversity
invariably becomes an aspect of the literature concerning these
parameters and several attempts have been made to synthesize the
relationships (Connell, 1972, 1976, 1978; Paine, 1966, 1974; Pianka,
1966, 1974; Sanders, 1968). Menge and Sutherland (1976) proposed a
model stating that in systems of low diversity, competition would be
an important structuring force at the level of primary space occupiers.
In a system with greater diversity, more trophic levels are added
and predation becomes an important aspect of the communities. With
still greater diversity competition again becomes an important aspect,
but only between the predators as they compete for food. The model
would suggest that in the low diversity communities of the Gulf of
Maine, competition at the primary space occupier level should be the
most important structuring force. Models proposed by Connell (1976,
1978), Paine and Vadas (1969), and others attempt to incorporate the
effects of disturbance, as well as predation and competition on species
diversity. The models suggest an intermediate amount of disturbance
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. is necessary if the highest level of diversity is to be maintained over
time. Disturbance maintains a mixture of competitive dominants and
colonizing species within the communities. Too much, as well as
too little, disturbance leads to a reduction in diversity and either
colonizing species or competitive dominants, respectively, w ill
dominate the system. Wiens (1977) has pointed out that care must be
exercised in the application of data to these theoretical considerations.
Specific results, for example high food overlap, can mean decreased
competition in the real world instead of the reverse due to a release
from competitive pressures.
Much has been written about asteroids and the important effects
they can have on benthic marine communities. A large part of this
literature deals with the commercial importance asteroids may have,
especially relative to their destructive predatory effects on commercial
oyster beds (Burkenroad, 1946; Galtsoff and Loosanoff, 1939; Loosanoff,
1961, 1964; Loosanoff et al, 1955).
Recent literature has dealt with asteroids on a more theoretical
or ecological level. Asteroids are often community dominants, in size,
abundance, biomass or impact, and are often upper level predators (Feder,
1959, 1963, 1967; Landenberger, 1968; Mauzey et al, 1968; Rosenthal and
Chess, 1972). They have been shown to have a major impact on structuring
benthic communities (Connell, 1966; Dayton, 1970, 1972; Dayton et al,
1974, 1977; Menge, 1972, 1976, 1979; Paine, 1966, 1969, 1974, 1976, 1977).
The concept of a "keystone predator" developed by Paine (1966) is based
on the predatory effect of Pisaster ochraceus. on intertidal communities.
Experimental manipulations showed how Pisaster can have a great impact
on benthic communities by selectively preying upon the most abundant prey.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Il
maintaining a higher diversity by not allowing the compeitive dominants
to exclude other species. In other geographic localities various workers
have shown the effects of asteroids on a variety of marine communities
(Annala, 1974; Dayton et al, 1974; Hancock, 1955, 1958, 1963, 1965, 1974;
Keough & Butler, 1979; Menge, 1979; Moitoza et al, 1979.
An organism adapts to its total environment (Kinne, 1963) rather
than to any specific factor, such as temperature. However, Hedgepeth
(1957) and Hall (1964) state that ambient temperature is the single
most important factor influencing the distribution and reproduction of
marine invertebrates. Feder and Christensen (1966) stated that
temperature tolerance is a decisive factor governing the horizontal
and vertical distribution of sea stars, although as a group they
experience the entire range of temperatures encountered in the sea.
L ittle information exists on the ecology of N.W. Atlantic
asteroids. The Ph.D. thesis of Annala (1974) on A. vulgaris foraging
activity and the papers by Smith (1940) and Menge (1976, 1979), constitute
the bulk of the literature. All of these reported results are for rocky
intertidal areas only. In the Gulf of Maine there are only two dominant
species of asteroids in the rocky intertidal, Asterias vulgaris V errill
(1866)^ and Asterias forbesi Desor (1848). The two species of Asterias
are very sim iliar ecologically. A. vulgaris is a colder water species
generally more abundant north of Cape Cod, and A. forbesi is a warmer
water species more abundant to the south. Restricted populations of
either species can be found where local conditions permit from Newfound
land to at least Virginia. A. vulgaris tends to be found deeper to
^Asterias vulgaris V errill (1866) may be a junior synonym of Asterias rubens Linnaeus (1758), (Tortonese, 1937, 1963).
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the south and A. forbesi is often found only at shallow depths to the
north (Ernst, 1967; Gosner, 1971; Hyman, 1955; Miner, 1950; V errill, 1866,
1873). Huntsman and Sparks (1924) found that A. forbesi could with
stand higher temperatures than A. vulgaris and later Smith (1940) showed
that A. vulgaris regularly dies when the temperature is above 25°C.
Zinn (1937) found that A. forbesi did not feed below 5.2°C in the spring,
although MacKenzie (1969) later reported that the rate of feeding slowed
substantially in cold water (3°C) but that the animals were still feeding.
Both species feed on similar benthic invertebrates, including
barnacles, mussels, urchins, and gastropods as well as a number of other
species (Galtsoff and Loosanoff, 1939; Hancock, 1955, 1958, 1963, 1965,
1974; Menge, 1979; personal observations AWH). A behavioral difference
exists in that A. vulgaris shows a well developed escape response to
contact with A. forbesi and in fact A. forbesi w ill chase and prey upon
its congener.
Crossaster papposus Linnaeus (1780), a circumboreal sun star
(Hancock, 1974; Hyman, 1955; Mauzey et a l., 1968; Miner, 1950; V errill,
1866) is commonly found in deeper (> 30 m) rocky communities in the
Gulf of Maine (personal observations AWH). Crossaster has been shown to
also prey upon other asteroids and in fact may specialize on A. vulgaris as
its preferred food (Hancock, 1955, 1958, 1974; personal observations AWH).
Purpose
The purpose of this study was to investigate the functional
role of A. vulgaris in 3 adjacent rocky subtidal communities. I define
the functional role similar to that of Sutherland (1978) as the effect
of this species on the distribution and abundance of other species
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. in the community. The role of A. vulgaris can then be considered as
its relative importance to the other members of the community.
In the study I analyzed in detail the population structure,
feeding biology and predator-prey relationships of A. vulgaris in three
very different communities. The community comparisons were then used
in ascertaining the functional role of the asteroid. The evidence
was also used to evaluate current models of predation, competition,
and disturbance in the context of the factors regulating A. vulgaris
populations and the effects of the asteroid on the benthic communities.
The questions asked were: 1. What are the population structures
and how permanent are they, for all of the asteroid species in each
community? 2. What are the asteroids feeding on, to what extent,
and are any feeding specializations (either behavioral, mechanical or
by size) apparent in each community? 3. What are the predators of
A. vulgaris and their potential effect on the asteroid populations?
I considered it especially important to include the full range of
sizes in the analyses. Many studies neglect the very small individuals
and as a result there is a big gap in our knowledge. Subtidally
small individuals make up the bulk of the populations and in many
instances appear to be critical (a weak link) to the populations as
well as the communities. I believe the careful consideration of the
ecological role of the very small (< .5 cm) asteroids is one of the
most significant and unique contributions of this study.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. B W
CHAPTER 2
SITE DESCRIPTIONS
L ocation
The study was conducted at the Isles of Shoals, a group of
seven principle islands, and many ledges, located 10 kilometers off
the coast of New Hampshire, USA (Fig. II-l). The islands are
glacially eroded granite and the surrounding bottom is level sedimented
deeps and rocky outcrops. The islands present massive outcrops and
faults at various slopes and angles to the ocean.
A single, permanent transect was established in September,
1975 extending from the intertidal to a depth of 35 meters on the
exposed southeastern side of Star Island as a continuation of the
Shoals Marine Laboratory (located on Appledore Island) intertidal
transect #10 into the subtidal (See Kingsbury, 1976).
The subtidal substrate of Star Island is granitic, mostly
in the form of large smooth expanses of bedrock, but large outcrops,
c re v ic e s , and b o u ld e rs a re common. The slo p e av erag es ap p ro x im ately
10° to a depth of 35m, but is quite variable with large steps and
f l a t s common. Below 35m th e bottom c o n s is ts o f a c o a rse co b b le, sand
and shell fragment matrix frequently exhibiting .5m standing waves
(see Bloomshield, 1975; Fowler-Billings, 1977; Kingsbury, 1976; and
Nouak, 1971 for more geological details).
Currents around the Isles are relatively strong and variable.
The currents are associated with the CCW rotation of the Gulf of Maine
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure II-l. Map of the Isles of Shoals, N.H., showing location
of the research site.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. MAP of ISLES of SHOALS and TRANSECT STATIONS
Appledore Is.
N . I
Smuttynose Is. >42°59' Malaga Is.
Gosport Harbor 70° 38' Cedar Is.
Lunging Is. Star is.
"•••Zone1 Station (8ml X-. ■••Zone 2 Station HSml
X Zone 3 Station (30m) White Is. a
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. gyre and the tides, as well as fresh water runoff and wind. Normandeau
Associates, Inc. (1974) who have done most of the oceanography around
the Isles of Shoals, have measured currents of .02m/sec. to .5m/sec.
(max = 1 knot). Personal observations indicate currents of 1 knot
are common with spring tides at the research site.
The Gulf of Maine is a comparatively stormy and foggy area
with high winds and waves possible any time of the year and on very
short notice (see Kingsbury, 1976, for a review of the weather
statistics). The mid-winter months are the most severe with gale
force winds common. The southeastern point of Star Island, where
the study was done, is the most exposed location of the Isles of
Shoals. Oceanic swells generated by offshore storms fetch unimpeded
against this shore and impact strongly, even if the storm passes well
offshore (Kingsbury, 1976; personal observations AWH).
Communities
The intertidal flora and fauna of the exposed areas of Star
Island are similar to other exposed rocky intertidal areas in the Gulf
of Maine. The relatively gentle slope and large swells create a
dilated intertidal region. Ice cover and scraping in winter are quite
severe. The well-known intertidal zonation (Connell, 1972; Hutchins,
1947; Lewis, 1964; Southward, 1958; Stephenson and Stephenson, 1972)
obtains. Note that my definition of zonation comes from that of Chapman
et al (1953); "definite belts which possess horizontal continuity with
well marked upper and lower lim its". Blue-green algae are found very
high in the intertidal with barnacles (Balanus balanoides) slightly
lower and the mussel, Mytilus edulis below the barnacles in the mid to
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 10
low intertidal. In the low intertidal a variety of algae become dominant
including Ascophyllum nodosum. Fucus vesiculosus, Gigartina stellata,
and Chondrus crispus.
The intertidal zonation continues into the subtidal as a
series of communities delineated by depth. I define a "community"
as a group of co-occurring interacting species at all trophic levels
in a particular habitat (per Dayton, 1972).
Subtidal zonation is a world wide phenomenon (Golikov &
Scarlato, 1973; Goreau, 1959; Harris, 1973; McLean, 1962) but the
causal factors are not as well known as in the intertidal (see Connell,
1972 for a review of intertidal dynamics) and some controversy exists
concerning definitions of zonation (Clausen, 1965; Daubenmire, 1966;
Sears and Wiltce, 1975; Whittaker, 1956, 1970). At the transect
location on Star Island the communities are differentiated by sharp
discontinuities with depth. The differences between communities can
be quantified using two criteria: 1) the presence or absence of species,
o r 2 ) a difference in the composition of the species present if these
differences are significant and stable over time. A number of species
fall into these categories. For example, urchins are present in all
communities but the abundance and size structure they exhibit differ
considerably with depth and these differences are maintained over time.
Laminaria settles out on the substrate to at least 25 m, but rarely
can survive below 12 meters deptl^ probably because of herbivore
activity (A. Mathieson, personal communication, personal observations AWH).
A number of species are unique to deeper depths (> 30m) in the Gulf of
Maine. For example the asteroids, Crossoster pappasus, Hippasteria
phirygiana, Porania insignis, Pteraster m ilitaris, and Stephanasterias
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 11
albula are generally only found on hard substrate below 30 m. Asterias
forbesl is usually only found above 10 m.
Physical factors have been implicated in various schemes of
faunal and floral distributions (Connell, 1972; Clausen, 1965;
Daubenmire, 1966; Sanders, 1968; Setchel, 1922; Whittaker, 1970). A
list of potential physical factors that might affect subtidal
communities include ; substrate, light, temperature, salinity, and
water movement. At the Isles of Shoals light is probably the most
important factor because of its direct attenuation effect on the macro
algae depth distribution (Norall, 1976). Temperature varies dramatically
over the year, but its effects are also attenuated with depth (Fig. II-2
& II-3; Norall, 1976). Water movement (surf and currents) is fairly
im p ressiv e a t tim es (5m sea s common, 15m n o t uncommon), b u t ag ain th e se
effects show a gradient with depth. The result of the physical factors
is that shallow communities receive more light (Norall, 1976) and are
more productive, but the organisms located there must survive highly
variable conditions, whereas deeper communities are more stable, but
less productive. Golikov and Scarlato (1973) implicated light and
temperature as the most important factors on subtidal communities
and zonation, but they did not elucidate the causal factors.
Three research sites were chosen for investigation along the
permanent transect at depths of 8 m, 18 m and 30 m (Datum level = NHW).
The sites were chosen because they were considered representative of
3 major community zones found along the transect.
The communities present at the three study sites can be briefly
described as follows:
8 m community. The shallow community is essentially a continuation
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of the intertidal down into the shallow subtidal. The dominant algae
are Chondrus crispus and Laminaria saccharina as well as a number of
ephemeral species. The algae provide the physical structure of the
community and a refuge to a large number of organisms, in terms of
physical shelter and also as surface area (secondary substrate) for
encrusting species to grow upon. The dominant macroinvertebrates are
crabs (Cancer irroratus, Cancer borealis, and Cancinus maenas), lobster
(Homarus americanus), urchins (Stronglyocentrotus droehbachiensis) ,
a large predatory whelk (Buccinum undatum), sea stars (Asterias vulgaris,
Asterias forbesi, and Henricia sanguinolenta) and fish (Tautogolabrus
adspersus, Psuedopleuronectes americanus) . Population estimates from
10 m X Im band transects are given in Table II-l for the dominant
invertebrates except for the sea stars that are considered in detail
below. The thick algal covering provides a great deal of secondary
substrate and the algae is heavily encrusted with epifauna (Bryozoans
and Spirorbis spp.). The mat of algae provides protection to many small
crabs, urchins, amphipods, snails and asteroids which utilize it as a
refuge. The 8 m community is highly productive comprising large
numbers of individuals within the three dimensional structure provided
by the algal canopy.
Transition Zone. At approximately 12 m, the depth varies
seasonally, a sharp discontinuity is found, defined by the upper grazing
lim it of the urchin, Strongylocentrotus on the lower lim it of the
Laminaria (see Prentice & Kain, 1976 for a similar situation). During
winter when the urchins are feeding in herds (see Seasonality below)
on the lower populations of Laminaria they cause a sharp demarcation of
the end of the shallow algal zone into an area dominated by crustose
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coralline algae. The change of communities usually occurs in less
than .5 m, but the depth of the boundary changes seasonally as the
algae recruit in and the urchins change their foraging behavior.
18 m community. From the abrupt end of the erect algae at
12 m to approximately 25 m the substrate is 85% covered by crustose
coralline algae. The horse mussel. Modiolus modiolus arranged in
discrete clumps, occupies the remaining 15-20% of the primary substrate
(J. Witman, personal communication). Only two species of erect algae
are commonly found, Agarum cribrosum and Ptilota serrata, both of which
are very low on the preference hierarchy as urchin food sources (Harris
and Hulbert, in preparation). Large urchins, snails and giant (< 20 cm)
sea stars are found on the open substrate between mussel clumps. The
Modiolus clumps themselves trap sediment and thus provide a refuge
(virtually the only refuge) and secondary substrate for a wide range
of infaunal and epifaunal species (Table 11-2). Small asteroids,
snails, urchins and many other species utilize the refuge and the
Modiolus clumps become very complex three dimensional communities.
30 m community. The 30 m site is representative of a deeper
sessile, suspension-feeding community (essentially a fouling community,
Sutherland, 1974), which is common on deeper community substrates in
the Gulf of Maine. The deep community has a high density and diversity
of attached, suspension-feeding forms (e.g. brachiopods, cnidarians,
sponges and tunicates). The substrate is covered with a matrix of
polychaete tubes and soft coral stolons which trap and hold detritus
providing a thin infaunal habitat and secondary substrate for many
small invertebrates. Modiolus clumps are still present but they tend
to be much smaller and more cryptic, such that by 42 m there are only
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i
es o r» \0 O 1—1 \0 en O O 00 I-) sr m ON en o o 0 . 0 o es vo o o o o iH 0) >> iH 60 4J (B cd -H <- H M (0 es 0) (U S rS 00 o vo
es es es es es es g •H es O iH 00 (U (U dJ (U M O 0 \ r4 m ON 00 O W K w (B (B B) (B sr es I o I WWW o w
/-s \ \ /—s XS /—» X es 00 rW es r» sr 00 n o W z fH rH rS w w 3 N-/ s»» 3 CO W (S_ a 43 E es sr es en en en ON 3 3 O ON rH O'- O iH o o o O b • • • w es ON en ’ o o o o o o o o a "3 43 / m N^ '--- u 3 G •H 3 3 M 3 es 3 O U G es 00 3 es r~ r-» en m 4J 3 O vO
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Table 11-2.^ Most Common Invertebrates Associated with Modiolus clumps 2 S p ecies Mean #/m
Modiolus modiolus 209 Ishnochiton alba 167 Hiatella arctica 100 Buccinum undatum 18 Acmaea testudinalis 10 Onchidoris fusca 6 Ophiopholus aculeata 786 Asterias vulgaris 218 Strongylocentrotus droehbachiensis 80 Cucumaria frondosa 50 Henricia sanguinolenta 15 Amphipholus squamata 5 Psolas fabricii 2 Amphitrite spp. 61 Pectinaria gouldii 23 N ereis p e la g ic a 20 Lepadonotus squamatus 6 Harmathoe imbricata 6 Amphiporus angulatus 8 B o lte n ia e c h in a ta 20 Boltenia ovifera 4
Total X = 1809/m within Modiolus clumps
1 2 Results from 5 X 1/4 m Modiolus clump samples 2 (Taken from: Hulbert et al, 1976)
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a few scattered, small individuals in cracks and crevices.
Benthic fish predation can be very heavy during summer and fall
especially from cunner and flounder. Estimates of 200 cunner per
25 m^ are not uncommon and they are voracious bottom feeders, picking
small invertebrates directly from the substrate.
Gut contents and field observations of cunner, flounder,
cod, haddock, eel pout and wolffish show that all are benthic inverte
brate predators consuming large numbers of urchins, b rittle stars,
and worms (Richard Langton, NMFS, personal communication, personal
observations AWH). Several red algae are found at 30 m, mostly Ptilota,
but they are near their extinction depth in the Gulf of Maine and are
not community dominants. As the algae become sparser with depth,
the vertical communities tend to come up on to the horizontal surfaces,
almost in a direct inverse relationship, possibly suggesting an
interference effect of the aglae on vertical community species. By
35-42 meters in the Gulf of Maine no macro algae are found (Mathieson,
1979;. Sears.& Cooper, 1978^personal observations AWH). Coralline algae
dominates any open, rocky substrate shallower than 25 m. Deeper they
no longer dominate primary substrate, although they are still present
underneath. They are replaced by the polychaete tube - soft coral
matrix as the primary space occupier. Productivity at 30 m is relatively
low compared to the 8 m shallow algal zone with most of the energy being
imported, but the physical conditions are much more stable. Many
animal species are found only at 30 m or deeper in the Gulf of Maine.
The community has a higher diversity than 8 m and 18 m because of a
large number of rare species.
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Seasonality. There is marked seasonality in both the physical
and biotic components of the communities.
Physical Seasonality.
1) Light ; The amount of light received by the communities
is highly variable. In the summer when day length is longest often
there is a dense fog cover and the water is quite turbid from plankton.
In the winter and spring there is no fog and the water is quite clear
(18-25 m visib ility ), but the day length is much shorter and storms
are common. The skies are often overcast and the sea is rough, both
of which decrease the amount of light that might be received by a sub
tidal community (see Norall, 1976).
2) Salinity; Salinity appears to be quite constant, both
throughout the water column and seasonally at Star Island. Salinity
readings are generally 31%. year round, although they may be slightly
less during a period of heavy rain or strong spring runoff.
3) Water movement: Water movement due to tidal currents
and storm surge are both highly variable at Star Island. The amount
of tidal current ranges from zero to greater than 1 knot with spring
tides and usually extends from top to bottom. Storms are relatively
rare during the summer, and the norm during fall, winter and spring,
but gale force winds can occur almost instaneously at any time of
year and readily produce 8-12 m waves. During winter 20 m waves
are regularly reported in the Gulf of Maine. Thus the amount of water
movement encountered by these communities is substantial and highly
v a r ia b le .
4) Temperature : Temperature varies seasonally and also ver
tically, (Fig. I I - 3 ) . There is a considerable lag time between
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Figure II-2. Annual temperature range at 8 m, 18 m, and 30 m
at the research site.
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<0 ^ 01 w M M (0o)3yniya3dU3i
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Figure II-3. Temperatures at 8 m, 18 m, and 30 m from November,
1974 to February, 1980 at the research site.
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(N»^ocDoop^(Din^cocN^oa)oor^ C3o] 3dniyd3dU31 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 22 terrestrial temperatures and the temperatures at the three subtidal sites but the same seasonal periodicities are exhibited. The surface and 8 m temperatures are very similar and quite variable, being the warmest in summer and coldest in winter. A 21°C summer temperature on I one day can become a 12°C temperature on the next day due to a strong wind overturning the water column. The deeper water in the Gulf of Maine is relatively stable (2-6°C) year round and provides a cold water temperature sink. The surface waters can warm up in summer, but an overturn of the water column has the effect of cooling every thing down quickly to the deeper water temperature. In winter we have had sea ice forming on our apparatus at 8 m. The range o f temperature decreases (Fig. II-2) and the overall temperature stability, (temp, change/time) increases as one goes below 8 m. O v e ra ll, th e temperature is highly variable, but it becomes more stable with depth. Biotic seasonality. At Star Island there are both winter and summer guilds of organisms (a guild is a group of organisms at the same trophic level. Root, 1967; Menge and Sutherland, 1976). Snmmer. Fish, crabs, lobster and asteroids are active in the warmer months of the year. They generally reproduce in the late spring and forage actively until the water cools down in winter. In winter the fish either hibernate (cunner - Green & Farwell 1972) or presumably migrate deeper. A downward tendency has been observed every fall as well as a sequential deep to shallow appearance of fish in the spring. The crabs and lobster hibernate or become inactive and the asteroids become inactive at temperatures below about 4°C. Chondrus and many other ephemeral algae grow especially well in the warmer months as do benthic diatoms, which often are 3-4 mm deep in a surface layer at the 30 m community. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 23 Winter» Nudibranchs, urchins, ectoprocts and tunicates are the most obvious cold water activists. They usually reproduce in the winter months. The nudibranchs and tunicates are present in low numbers in the warmer months but their populations virtually explode in the winter. The urchins change their foraging behavior in the winter (see Breen. & Mann, 1976, for a sim ilar situation) from a behavior of hiding in crevices in summer to open foraging in hugh packs on the upper surfaces. All sizes of urchins (from 2-3 mm to 100- 120 mm diameter) voraciously eat everything in their paths down to coralline algae and bedrock in winter. The change in urchin behavior coincides well with the decreased activity of their major predators; fish, crabs and lobster. The large brown kelps Laminaria and Agarum grow well in the colder months. Summary o f S ite D e sc rip tio n s The study was done at an offshore, relatively pristine location which exhibited a large amount of physical and biotic, temporal and spatial heterogeneity. Three permanent research sites were established a t 8, 18, and 30 m depths along a single transect. The sites were representative of a shallow algal dominated community, a deep sessile- suspension feeder dominated community and a transitional area, between the 2 more geographically extensive areag, dominated by Modiolus clumps I and crustose coralline algae. The physical factors of light, temperature I and wave action all decrease with depth. Figure II-4 summarizes these I I communities. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 24 Figure II-4. A rtist's rendition of the three subtidal communities at the Isles of Shoals, N.H. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 25 Key -Cunner '" -Ascerias 2 ^ -LepCaacerlas sp. -Crossaster 3m communlcy -Coralline -Modiolus -Urchins -Polychaete matrix Æ, -Brachiopods f -Anemones 18m communlcy -Stalked ascldlans I v l -Crabs TP—. -Ptilota -Chondrus -Agarum -Laminaria 30m communlcy Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. i CHAPTER 3 MATERIALS AND METHODS All asteroids were sampled at the 3 research sites to obtain information on abundances, diets, sizes, population flux rates, lairval recruitment, and predatory activities. All subtidal observa tions were made using SCUBA and only horizontal rocky surfaces were considered. Whenever possibly all 3 sites were sampled on the same day to minimize extraneous variables. 1. Population structure Data on the size and abundance of all asteroids were collected 2 2 utilizing disruptive .25m and Im quadrats and 10m X Im band transects. 2 2 Photographic .25m and .Im quadrats were also taken utilizing an 2 underwater quadrapod system. The .25m disruptive quadrats were the main sampling units for all sizes of asteroids. The 10m transects were used to more accurately estimate the larger individuals. Only indivi duals greater than 3 cm were used in the transect analysis. The quadrat and transect were deployed in a haphazard manner by a swim and toss method. The technique was used rather than a true random technique because of bottom time considerations and the need to maximize data per unit effort. Asteroids were measured from the tip of the longest arm and across the disc to the opposite interradii, a method necessitated by many small (2 to 3 mm) individuals and a large number of regenerating arms. I consider the longest arm to be most representative of the true size of the animal. The measuring method, necessary for the small and 26 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 27 regenerating individuals, was standardized to all individuals. Biomass estimates were obtained by utilizing a random collection of 150 indivi duals in a range of sizes from smallest to largest, measuring blotted wet weight, and then fitting a regression line to the data. The more easily measured sizes could then readily be expressed as biomass by using the regression equation. Throughout the study a number of small (< .5 cm) asteroids were collected, especially at 18 m. Taxonomic features for identifica tion of small asteroids are difficult at best, largely because with growth, new spines, pappulae, tube feet etc. are added. For example A. vulgaris adds the third and forth rows of tube feet between the first and second rows at .4 to .5 cm. For lack of any evidence to the con trary the small asteroids were considered A. vulgaris. It became apparent in the winter that at least some individuals were decidedly not A. vulgaris because they began brooding embryos, and this species is a broadcast spawner. Subsequent investigation revealed a species of Leptasterias that is similar to Leptasterias literalis, but has several conservative traits. In the remainder of this paper the species is con sidered to be Leptasterias sp. Ecologically this species appears very similar to small A. vulgaris with the reproductive strategy difference noted above. Leptasterias sp. is generally < .8 cm s iz e (1 .1 cm max a t transect), broods from early December to late March and makes up < 1% of the population at 8 m and 30 m, but > 90% at 18 m. I have developed a suite of characters to distinguish the two species, but the sim ilarities of <.5 cm individuals are such that definitive classification is impossible unless they are brooding. For this reason I have considered A. vulgaris and Leptasterias sp. together in most analyses, unless Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 28 otherwise stated, to allow the best qunatification of the data. The reader may then use the above proportions to obtain species specific population estimates. The two species are specifically considered 2 together in the .25m quadrat size and abundance results. Areas that differed in location or exposure were sampled for comparative population estimates on a one-time basis, at the same depths as the transect locations. The areas included; 1) Gosport I Harbor: The harbor on the protected side of Star Island was sampled k to compare the effects of exposure and soft substrate (Fig. II-l). ; f; 2) Malaga Gut: An exposed, rocky location on the NE side of the I island was sampled for potential differences (Fig. II-l). 3) Jeffries Ledge: An offshore, very exposed pristine area that comes up from a soft bottom at 125 m. was sampled. The area is located at the south Î central portion of Jeffries Ledge at a pinnacle called Pidgeon Hill, [: located 37 kilometers off Cape Ann, Mass. (Lat. 42° 46.5' N, Long. 70° I 14.5' W). 4) Nubble Light, Maine: An inshore exposed location was ! sampled for comparison with the offshore tmasect locations. [ 2. Feeding Activity [ A. vulgaris was the most common asteroid. It feeds mainly by tr everting the stomach and extraorally enveloping the prey. Damage to fI the prey can usually be readily determined and feeding by Asterias ÊI ascertained. Feeding data was obtained in-situ by observing each I asteroid encountered, its feeding state, the prey, and the size of the asteroid. For rare species of asteroids, feeding data were recorded whenever they were encountered throughout the study. The data were recorded on an underwater clipboard with paper, or on an underwater Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 29 tape recorder developed for the purpose. For asteroids less than 1 cm a different technique was used due to a lack of resolution of their prey in the field. Small asteroids were collected, as encountered, put individually into clean vials with forceps and later examined under a microscope for prey remains. The prey usually had hard parts and identification was positive. In this manner I obtained data on diet, predatory behavior, prey selection and size of the asteroids that were feeding in all three communities. The methods have been shown to have some bias (Peterson and Bradley, 1978) due to the size of prey and the time it might take a predator to consume it. Basically the method underestimates rapidly consumed prey. I consider the bias to be minor in this case, since comparisons between the three communities were done with the same techniques. I am confident that I am presenting an accurate picture I of asteroid feeding. The methods have been used by many other workers b i (Birkeland, 1974; Mauzey et al, 1968; Menge, 1979; Paine, 1966) and I it is important to have comparable data. r 3. Flux Rates The available data on asteroid migration varies greatly from miles per year to no movement at all (see Feder and Christensen, 1966 for a partial review). Information on the permanency of the three populations of asteroids and the relative amounts of movement were y .: considered essential aspects of the study. Asteroids were tagged utilizing neutral red and methyl blue chloride dyes concentrated to a b paste-like consistency, sim ilar to that used by Sebens (1976) and Feder S (1959, 1970). Tagging was accomplished by dipping arms into the dyes I Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 30 and blotting for several minutes before returning them to sea water. The procedure allowed numerous combinations of red and blue arms for coding purposes. The technique worked well for asteroids and lasted a t l e a s t 6 months in the tube feet and ambulacral groove area, and it did not appear to effect the animals. Two types of tag and recapture studies were accomplished. Experiment #1: Approximately 100 asteroids in a range of sizes were collected from the three locations, dyed with a descriptive code of red and blue arms, and returned to their in itial locations where they were released from a specific point. On succeeding days tagged individuals were monitored for rate of movement, directionality of movement, and size of the asteroid relative to its movement. The asteroids were observed on consecutive days after release and left where they were found. An average rate of travel over several days was determined which I consider more accurate than one day estimates. The procedures were conducted simultaneously at all three locations to allow comparison of the results. Two replications of this experiment were done. Asteroids were tagged and released on 17 July, 1978 and monitored on 18, 19, 21, 23, and 26 July. The experiment was repeated with asteroids tagged and released on 12 June, 1979 and monitored on 13, 14, 15, 19, 21 June. Experiment #2: On 12 June, 1979 asteroids from 8m were tagged and approximately 100 were transplanted to 18 m and 30 m. The transplants were observed on 13, 14, 15, 19, 21 June, but due to logistical considerations (i.e. no decompression lim itations) only qualitative data were obtained from this experiment. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 31 B The tagging experiments were designed to provide information I on the amount and directionality of asteroid movement in each community I and by transplantation, the community imposed (or environmental) extent I of the movement. I 4 . Cages I:P Caging experiments provide an opportunity to alter the natural I I balance of a community by adding or substracting known components fe; I in a controlled manner. Cages have been used successfully in the inter- I ( tidal and the application of the methodology to the subtidal seemed Straight forward. For a valid experiment I believed that in consideration of the size, mobility and patchiness of the community components, a cage 2 size of at least .25m was necessary. For example, mussels can be 8-10 cm, u rc h in s 7-8 cm, s n a ils 7-8 cm, crabs 10 cm, a m odiolus clump i s 2 usually at least .25m in surface area and the algae are often 30 cm or more in height depending on the species. To minimize physical interference in the community large cages are optimal for the experiments. Unfortunately large cages are difficult to secure in exposed locations with granite substrate. An experimental design for an asteroid exclusion caging experiment was thus set up as follows: Irsatmenls. 8m 18m 30m C o n tro l 1 1 1 Cage effect control 1 1 1 I: ri Exclusion (asteroids) 2 2 2 I Four experiments were attempted: 1) Im^ (x 40 cm high) cages and appropriate controls were set up in September, 1975 using fabricated Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ,32 cement blocks (4 x 20 kilograms/cage) and ropes to hold down the array. The cages were totally destroyed during the winter and most have never 2 been found. 2) 0.5m (x 30 cm high) cages were set up in October, 1976 in the proper arrangement, using slightly protected microhabitats, cement blocks and ropes for attachment. The cages survived better than the preceeding year, but they were moved around sufficiently enough to damage the benthic communities being studied, and half of the cages were again lost. 3) A third attempt at the same experimental design 2 was set up in October, 1977, utilizing .25m (x 15 cm high) cages. Underwater cement was used to attach eyebolts in crevices and the cages were tied down to the eyebolts using resilient dacron lobster pot line. In February, 1978 the Gulf of Maine experienced a once in a hundred years winter hurricane, complete with 35 m seas and associated "stress". 3 The result was that the surge was able to move boulders of over 1 m . Incredibly, all of the cages were in place after the storm, but the wire mesh was stripped from the metal frames, leaving a bare framework where an exclusion cage had been. 4) The cages and controls from attempt #3 were rebuilt and replaced in the summer of 1978. The cages have survived to date, but the results are difficult to interpret. Little if any community difference could be attributed to the experimental exclusion cages. Small fish, crabs and a number of other species utilized the cages as a nursery, rather than being excluded from the areas underneath. I believed some resilience was necessary in the system of ropes and frames so that some wave impact could be absorbed, rather than destroying the cages. The flexibility of the system probably allowed entry to the small animals found in the cages; although a wire skirt was used to prevent access, possibly the skirt was too rigid. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 33 Ephemeral algae settled out on top of the cages and survived much longer than the same species on the surrounding benthos, but eventually small hermit crabs and snails cleaned the algae from the cages. To summarize my caging experiments, much effort was expended and no reliable results were obtained. I feel an area of at least 2 .25 m must be included in a caging design for these communities. A system of underwater cement, pitons and rope w ill work to hold them in place, but after observing the cage's effect as a nursery, in damaging the communities being observed, and generally being unreliable, I I would suggest that for exposed rocky areas caging experiments are I probably not the most efficient experimental method to utilize and results from such studies must be carefully interpreted. 5. Predation Effects on A. vulgaris Field observations and laboratory tests and observations were conducted on predators of A. vulgaris. Laboratory tests were conducted by undergraduates under my supervision and included binary choice experiments and limited consumption rate analysis of the major predators (Hulbert et al, 1976; Lull et 1979). The predators fall into two main groups: 1) Asteroids; Asterias forbesi, Leptasterias sp.. Crossaster papposus, Solaster endeca; 2) A guild of other predators: crabs ; Carcinus maenas Linnaeus, Cancer irroratus Say, Cancer borealis Stimson; Lobster; Homarus americanus Milne-Edwards; Fish; cunner, Tautogolabrus adspersus Walbaum; Cod, (Morhua callaris Linnaeus); Eel Pout, (Macrozoarces americanus Walbaum); Wolf Fish, (Anarchichas lupus Linnaeus). All of these species have been personally observed either eating or having A. vulgaris in gut contents. I attempted to determine Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 34 the extent of predation on the A. vulgaris populations at the three transect locations by quantifying abundances, field behavioral obser vations, communications with National Marine Fisheries biologists, and lab tests conducted by undergraduate special project students. 6 . Natural History Qualitative observations were made on all dives at both the community and asteroid population levels. Notes were made of predator- prey interactions, escape responses, feeding biology, community component growth, health and activity, prey availability, algal species dynamics, and presence or absence of seasonal species. i Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER IV RESULTS The following standard practices were followed with all of the results of the study, unless otherwise stated. All asteroid measurements are expressed in cen tim eters and measured as s ta te d 2 previously, all abundance and biomass results are given for a .25 m area, all depths are given in meters below MHW, * signified P < .05, ** signifies P < .01, *** signified P < .001, all error estimates are standard errors, and all data are for the three research sites at the Star Island transect. 1. Population Structure Quantitative population estimates of all asteroid species were accomplished monthly from October, 1976 to August, 1977, in June, 1978, and January, 1979. Asterias vulgaris was the dominant asteroid throughout the study, except in the small size classes at 18 m, where Leptasterias sp. was important. Abundance, size, and biomass estimates for A. vulgaris and Leptasterias sp. are given in Tables IV-1 through IV-6 , Figures IV-1 through IV-7 , and Appendices A through E. Abundances and sizes were measured directly from the samples while biomass was estimated from the regression formula Log wt. = -1 + 2.74 Log Length 2 (r = .938, P <.001, 150 d.f.). Error estimates are given for all I sizes and abundances, but not for biomass since the latter are extra polated values. I have compared the results of my biomass analysis against the actual blotted wet weight of samples nearly equivalent to 35 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 36 the mean values for each depth and the estimates concur very closely I with the actual estimates. The results published by Menge (1979) for biomass of A. vulgaris are an order of magnitude too high for this speciesJ see Appendix F for a comparison of results. The size and abundance data were analyzed utilizing a multiple regression formulation of the general model: Y = 3 q + + ggXg + ggXg + . . . + + E where 3 's are the regression coefficients to be estimated from the I independent variables X^, Xg, Xg . . . X^. The three research stations I and seasons were coded as dummy variables for the analyses (Kleinbaum I and Kupper, 1978). The analyses were accomplished utilizing the f multiple regression programs of the MINITAB II statistical package (Ryan, 1976), as adapted to the DEC 1090 computer system. 2 kI An analysis of sampling efficiency of .25 m quadrat size I 2 g: was accomplished early in the study by comparing the results of 1 m ______. . . ,._2 I samples to included .25 m samples utilizing a regression analysis. 2 The results showed that .25 m quadrats give the same results for the 2 2 asteroids (P < .001, r = 77%). As a result .25 m quadrats were used for the duration of the study. The size and abundance data were consistant over the study period, showing highly signifient differences of both mean size and mean abundance between the three populations (Tables IV-7 through IV-10, Figures IV- 8, IV-9). Size classes were never ascertained in the field or in the data; possibly the absorptive capabilities of the animals during degrowth and reproduction blur any size class differences by increasing the variability and overlap among individuals. Size data were recorded for each individual in each quadrat Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 37 or transect, a mean size/sample calculated and this value was used while abundance data were recorded for each sample and used as input to the analyses. Thus, n for size is the number of individuals whereas N for abundance is the number of samples. As mentioned above, A. vulgaris and Leptasterias sp. were considered together, due to the taxonomic problems relative to the many small individuals. Winter was considered as the period from November to April and summer from May to October for the purpose of the analyses. The periods correspond to ambient sub- I tidal water temperatures, not calendar seasons. 't'i 2 I The results of the .25 m quadrats show a relatively large 5: population with a range of sizes at 8 m giving a high biomass; a large ; population of very small individuals at 18 m (> 90% = Leptasterias sp.), with very low biomass; and a small population with a range of sizes at 30 m with low biomass. The 10 m transects (to estimate large individuals ) show a number of mid-sized individuals at 8 m, a few giants at 18 m and a few larger sized individuals at 30 m. The populations of A. vulgaris and Leptasterias sp. are thus quite different in the three adjacent communities in terms of mean abundance, mean size and biomass. The differences in population structure are significant (Tables IV-7 through IV-10) and have been observed throughout the study: 1: 8 m has a large I number of a range of sizes of individuals and by far the highest biomass, I 2. 18 m has a very large number of small (< .5 cm) individuals, most F ! of which are Leptasterias sp., thus there are few A. vulgaris but the I giants (> 20 cm) only occur at 18 m and, 3: 30 m has a low number of I (; small and mid sized A. vulgaris. i'i A number of individuals were always found regenerating arms in each community. Large individuals were more often found missing Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 38 arms, but no trends could be discerned in the numbers or sizes of regenerating individuals. The percentages of individuals with missing 2 arms from the .25 m quadrat samples were 16.7% at 8 m, 3.7% a t 18 m, and 6.2% at 30 m. A number of factors can cause A. vulgaris to autotomize an arm, notably a predator such as the lobster noted below. The percentage of the population regenerating arms may be an indication of predation pressure on the asteroids. Seasonality. Seasonality differences were observed in abundance but not in size of A. vulgaris and Leptasterias sp. (Tables IV-7 through IV-10). There are fewer individuals in the winter than summer, but the size structure remains the same, probably because they tend to seek shelter (i.e. they become harder to find in winter), although some always remain active. Seasonal differences were also observed in the relationship of disc and arm measurements (Table IV-11). Although [ the relationship of the disc to arm size was highly significant, the I proportions were different in each population and they varied seasonally. L The a s te r o id s a t 8 m and 18 m had longer arms relative to the disc than t those at 30 m, and in summer the arms were longer than in winter. Possibly i the differences are due to nutritional levels in the three populations t and the yearly reproductive cycle in which the gonads are greatly enlarged I:'- in late winter. I Recruitment by A. vulgaris appeared to be quite variable each ¥ year. Plankton tows and algal collections were regularly taken to look I: for larvae, but none were seen. Stable populations over the period of the study suggest that recruitment was occurring each year, at least nearby such that they were able to migrate into the areas, or in some microhabitat not sampled. In 1979 small A. vulgaris were seen for the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 39 first time on the buoy lines to the three sites which clearly showed recruitment, since lines were replaced in the preceeding spring. I believe the species recruitment success is highly variable, both spatially and temporally. Other areas. The results at the rocky substrate areas of Nubble Light and Malaga Gut showed sim iliar population structures to the Star Island research site (Table IV-6 and Appendix E). Both areas showed larger and more abundant asteroids at 8 m than deeper. Neither area had many Leptasterias sp. Thus the results portray only A. vulgaris and potential comparisons of areas with and without Leptasterias sp. are possible. The population structures observed at the soft substrate Gosport Harbor location differed considerably from all of the rocky substrate areas (Table IV- 8, and Appendix E). On soft substrate the mean sizes are small at 8 m (.49 cm) and large at 18 m (4.55 cm). The 18 m community in the harbor is dominated by bivalves (Cardium sp. Arctica islandica and Mercenaria mercenaria) and sand dollars (Echinarachnius parma) , hence a very different community from the rocky areas. Feeding results (below) showed that bivalves were a highly preferred prey of large A. vulgaris. Thus a community of bivalves where large A. vulgaris are found may be a cause and effect relationship. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 40 Table IV-1. Abundance of A. vulgaris from .25 m quadrats, at the research sites. Date 8 m 18 m 30 m 2 2 2 Mean/.25m Mean/.25m Mean/.25m X SE (N)l X SE (N) X SE (N) Oct '76 6.05 .930 (5) 32.0 4.25 (2 ) 1.61 .59 (5) Nov '76 21.25 2.998 (2 ) 35.25 12.99 (2 ) 4.50 .877 (3) Dec '76 23.00 3.686 (6 ) NT? ND ND ND Jan '77 4.14 1.007 (8) 13.5 5.37 (4) ND ND Feb '77 3.96 .716 (12 ) 26.75 • 9.28 (4) 5.50 .749 (2 ) A p ril '77 7.00 1.55 (3) 53.00 4.99 (2 ) 5.33 1.85 (3) May '77 11.33 2.402 (3) 52.00 19.99 (2) ND ND June '77 7.66 1.662 (3) 42.00 19.15 (3) 3.80 1.59 (5) July '77 14.66 5.48 (3) 57.00 32.95 (2 ) 8.57 1.19 (7) Aug '77 10.30 1.04 (15) 37.00 15.48 (2 ) 12.25 .855 (4) June '78 13.10 1.65 (10) 20.80 3.16 (10) 11.40 2.06 ( 10) Jan '79 8.30 1.26 (10 ) 21.50 3.41 (10) 15.50 .502 (2 ) O v erall 9.95 8 .2 2 (80) 29.33 3.099 (40) 8.33 .946 (41) 1 N = The number of .25m^ quadrats samples 2 nd means no data were collected due to weather complications I Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 41 Table IV-2. Size structure of A. vulgaris from .25m quadrats at the research sites.t D ate 8 m 18 m 30 m Mean S ize (cm) Mean S ize (cm) Mean S ize (cm) X SE (n )l X SE (n) X SE (n) Oct '76 2.62 .084 (121) .57 .001 (256) 1.35 .095 (31) 1 Nov '76 1.83 .093 (170) .91 .017 (282) 1.18 .026 (54) 2 ïi Dec '76 1.48 .018 (138) ND ND Jan '77 2 .1 1 .111 (29) .84 .041 (54) ND Feb '77 2.24 .046 (163) .69 .016 (107) .77 .006 (44) A p ril '77 2.95 .218 (21) .55 .003 (106) 1.19 .119 (16) May '77 1.90 .053 (34) .69 .029 (104) ND 1 June '77 1.80 .150 (23) .53 .004 (126) .99 .120 (19) Ju ly '77 1.90 .086 (44) .53 .009 (114) 1.06 .069 (62) ; Aug '77 2 .1 0 .014 (146) .41 .007 (75) .89 .020 (49) June '78 1.84 .036 (108) .45 .004 (208) .90 .036 (114) ' Jan '79 2.08 .090 (83) .53 .006 (215) .58 .028 (31) (1080) : O v erall 1.961 .045 .588 .013 (1647) .964 .0 3 9 (4 2 0 ) 1 (n) = The number of individuals measured from .25m quadrats 2 ND = means no data were collected due to weather complications Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 42 Table IV-3. Biomass of A. vulgaris from .25m quadrats at the research sites. All values are in grams blotted wet weight from the Regression Equation Log wt = -1 + 2.74 Log Lth (see text), Date 8 m 18 m 30 m Mean Biomass Mean Biomass Mean Biomass (grams) (grams) (grams) X/.25m? X/indiv. X/.25m^ X /in d iv . X/.25mf X/ind: Oct '76 8.47 1.40 .70 .02 .38 .23 Nov '76 11.13 .52 2.71 .08 .71 .16 Dec '76 6.72 .29 NE?- ND ND ND Jan '77 3.19 .77 .84 .06 ND ND Feb '77 3.61 .91 .97 .04 .27 .05 A p ril '77 13.56 1.94 1.03 .02 .85 .16 May '77 6.58 .58 1 .8 8 .04 ND ND June '77 3.83 .50 2.64 .06 .36 .10 Ju ly '77 8.51 .58 1 .0 0 .02 .89 .10 Aug '77 7.86 .76 .31 .01 .89 .07 June '7 8 6.96 .53 .23 .01 .86 .07 Jan '79 6.17 .74 .38 .02 .35 .02 O v erall 6.73 .68 .69 .02 .92 .11 ^ND - Means no data were collected due to weather complications Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 43 2 Table IV-4. Abundance and size of A. vulgaris from 10m transects at the research site for individuals over 3 cm (see text). Abundance Date 8m 18 m 30 m 2 2 2 (Mean/lOm ) Mean/lOm Mean/lOm X SE (N)l X SE (N) X SE (N) Aug '77 m ? 3.16 .576 (11) ND Dec '77 38.50 5.33 (4) 10.75 3.82 (4) 2.92 .55 (4) June '7 8 26.10 3.63 (10) 4.92 1.25 (12) 3 .90 .72 ( 10) Jan '79 11.60 2.69 (10) 4 .60 .90 (10) 4.75 2.49 (4) Overall 22.13 2.860 (24) 4.86 .712 (37) 3.91 .657 (18) Size Date 8m 18 m 30 m Mean S ize (cm) Mean S ize (cm) Mean S ize (cm) X SE (n)3 X SE (n) X SE (n) Aug '77 ND? 10.63 .122 (95) ND Dec '77 3.90 .008 (154) 5.98 .070 (129) 4.32 .128 (35) June '78 4.52 .035 (227) 5.77 .345 (59) 3.81 .062 (39) Jan '79 4.86 .078 (116) 5.72 .190 (46) 4.24 .112 (19) O v erall 4.55 .032 (497) 7.13 .155 (329) 4.01 .056 (93) 1 2 9 N = number of 10m band transects sampled; ND = no data were collected 3 2 n = the number of individuals measured from 10m transects Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 44 Table IV-5. Biomass of A. vulgaris from 10m transects for large individuals (> 30 cm) at transect locations. All values are in grams blotted wet weight from the regressioq equation Log wt = -1 + 2.74 Log Lth (see t e x t ) . Date 8 m 18 m 30 m Mean Biomass Mean Biomass Mean Biomass (grams) (gram s) (gram s) X/lOmf X/indiv. X/lOmf X/indiv. X/lOmf X /in d iv . Aug '77 nd J- ND 205.9 64.97 ND ND Dec '77 160.88 4.18 144.40 13.43 15.37 5 .50 June '7 8 162.82 6.23 59.88 12.18 15.21 3 .90 Jan '79 88.27 7.61 54.81 11.91 24.80 5 .2 2 Overall 140.58 6.35 105.70 21.75 17.57 4.49 1 = No data were collected I Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 45 T able IV-6 . Size structure and abundance of A. vulgaris from .25m quadrats at areas other than the research sites. 8 m 18 m 30 m L ocation Mean S ize (cm) Mean S ize (cm) Mean s iz e (cm) X SE X SE X SE Malaga Gut Isles of Shoals S ize (n^ = 211) 2 .3 9 .078 1.16 .084 4 .8 4 .091 Abundance (.25 (N^ = 35) 5 .5 0 .411 4.4 3 .259 1 .4 0 .150 Nubble Light, Maine S ize (n = 420) 2.36 .036 1.57 .031 NiP Abundance (.25 m^) (N = 40) 12.43 1.358 6 .5 0 .697 ND Gosport Harbor Isles of Shoals S ize (N = 156) .49 .015 4.55 .099 ND Abundance (N = 26) 15.60 4.58 .99 1 .0 2 ND In = Number of individuals measured from .25m quadrats 2 2 N = Number of .25m quadrats collected. 3 = ND = No data were collected due to bottom topography Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 46 Table IV-7. Multiple regression analysis of .25m quadrat abundance data. ^ The analysis shows a significant effect of season on mean abundance and significant differences in mean abundance at 8m and 18m as compared to 30m. Mean abundances are significantly higher at 8m and 18m. Model; Y = 3q + + ggXg + 63 X3 + E 2 Where: Y = Abundance/.25m X. = 1 = 8 m ^ 0 ^ X. = 1 = 18 m 0 f X- = 1 = summer ^ 0 9^ Results: loe (y + 1) = .780 + .115 X^ + .566 Xg + .110 X^ Variable Coefficient STD. DEV. of Coef. T-RATIO (coef./S.D.) Y .7799 .0605 .1152 .0584 1.97* ='1 .5656 .0666 8.50*** .1101 .0479 2.30* ANOVA Table Source d.f. SS MS = SS/d.f. F R^ Regression 3 7.8238 2.6079 30.01*** 35.0% Residual 167 14.5097 0.0869 T o tal 170 22.3335 * = P < .05; *** = P < .001 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 47 T able IV-8 . Multiple regression analysis of .25m quadrat size data. The analysis shows no effect of season on mean size of the asteroids, and' significant differences in mean sizes a t 8m and 18m as compared to 30m. The mean sizes of asteroids are smaller at 18m and larger at 8m. Model; Y = + B^X^ + + E 2 Where; Y = size (cm.) from .25m quadrats X., = 1 = 8m ^ 0 f X_ = 1 = 18m 0 i X, = 1 = summer ^ O f Results: log (y + 1) = .308 + .168 X^ - .105 Xg - .0097 X. Variable Coefficient STD. DEV. o f Coef. T-RATIO (C o e f./S .D .) Y .3079 .0165 .1678 .0158 10.62 *** ^1 -.1 0 4 8 -5 .8 8 *** ^2 .0178 -.0 0 9 7 .0131 -0 .7 4 NS s ANOVA T able Source d.f. SS MS = SS/d.f. F R^ R egression 3 2.26208 0.75403 119.88*** 69.2% Residual 160 1.00677 0.00629 T o tal 163 3.26885 *** = P < .001; NS = not significant I t a Log (y + 1) transformation was used with all data to eliminate heteroscedasticity of the variances and the residuals were plotted to graphically check conformance to this assumption of the tests. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 48 Table IV-9. Multiple regression analysis of 10m transect abundance data. Transect analysis pertains only to large individuals (> 3 cm.). The analysis shows no effect of season on mean abundance of the asteroids, no significant difference in mean abundance at 18m relative to 30m, and a significant difference of mean abundance at 8m r e l a t i v e to 30m. The mean abundances are higher at 8m. Model: Where; Y = abundance/lOm^ X = 1 = 8m ^ 0 f X_ = 1 = 18m ^ 0 f X, 1 = summer 0 f Results; log (y + 1) = .611 + .634 X^ + .0634 Xg + .0049 X^ Variable Coefficient STD. DEV. of Coef. T-RATIO (Coef./S.D.) Y .6106 .0865 Xl .635 .101 6.28*** .0634 .0929 0.68 NS ^2 .0049 .0741 0.07 NS ANOVA T able Source d.f. SS MS = SS/df F r 2 Regression 3 5.899 1.966 18.90*** 43.0% R esidual 75 7.812 0.104 T o tal 78 13.711 NS = Not significant, *** = P < .001 t a Log (Y + 1) transformation was used for all data to eliminate heteroscedasticity of the variances and the residuals were plotted to graphically check conformance to this assumption of the tests. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 49 2 t Table IV-10. Multiple regression analysis of 10m transect size data. Transect analysis pertains only to large individuals (< 3 cm). The analysis shows no effect of season on mean size of the asteroids and no significant difference in mean size a t 8m relative to 30m. The mean size at 18m is larger than 30m. Model; Y = + g^X^ + g^X^ + E Where; log (y + 1) = .678 + .0490 X^^ + .186 X^ + .0362 X^ X., = 1 = 8m ^ 0 f X_ = 1 = 18m ^ 0 f X- = 1 = summer O f Results; Y = .678 + .0490 X^ + .186 X^ + .0362 X^ V ariab le Coefficient STD. DEV. of Coef. T-RATIO (Coef./S.D.) Y .6777 .0306 .0490 .0352 1.39 NS \ *** Xz .1856 .0326 5.70 .0362 X3 .0253 1.43 NS ANOVA Table Source d.f. SS MS = SS/d.f. F r 2 R egression 3 .5344 0.1781 15.22*** 38.7% Residual 72 .8457 0.0117 Total 75 1.3801 NS = Not significant, *** = P < .001 t a Log (y + 1) transformation was used for all data to eliminate heteroscedasticity and the residuals were plotted to graphically check conformance to this assumption of the tests. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ~ r 50 Table IV-11. Multiple regression analysis of disc and arm proportions of A. vulgaris. The analysis shows a significant relation ship of disc size to am size, but the proportions differ in each population and by season. Model; Y = 0Q + * 3X3 + B^X^ + E Where; Y = disc size X^ = am size X. = 1 = 8m ^ 0 f X_ = 1 = 18m 0 ^ I X, = 1 = summer 0 ^ Results; Log (Y + 1) =-.0257 + Log .639 X^ + .0334 + .0120 X_ + .0409 X, V ariab le C o e ffic ie n t STD. DEV. o f Coef. T-RATIO (C o e f./S .D .) Y -.02568 .00329 .63892 .00530 120.57 *** ^1 .03340 .00284 11.74 *** ^2 .01203 .00259 4 64 *** ^3 .04089 .00095 43.04 *** ^4 ANOVA Table Source d . f . SS MS = S S /d .f. F R^ R egression 4 8.96479 2.24120 4980.4*** 97.6% R esidual 495 .22344 .00045 T o tal 499 9.18823 *** = P < .0 0 1 t a Log (Y + 1) transformation was used for all data to eliminate heteroscedasticity and the residuals were plotted to graphically check conformance to this assumption of the tests. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 51 Figure IV-1 Abundance of Asterias vulgaris and Leptasterias sp. at 8m, iSm and JO ra for 9 complete sampling dates. Data points are mean values with standard error bars. 1 = Oct. 1976 2 = Nov. 1976 3 = Feb. 1977 4 = April 1977 5 = June 1977 6 = July 1977 7 = Aug. 1977 8 = June 1978 9 = Jan. 1979 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 52 »ii|niHiiiifriii|iin|ini|iin|iiiipiiip m TnnTnfiTrrn p in |m n ini|iiii|nu|iim iiii CM Jiiilimliiiiliiiiliiii iliiiiiimliniliinliinlHiHuiiliuüuiiiiUilmjlimJim oinoinoinotnoinoinoinoiooinoino CgWSZ'] A1ISN30 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 53 Figure IV-^ Size structure of Asterias vulgaris and Leptasterias sp. at 8m, iSm and 30m for 9 complete sampling dates. Data points are mean values with standard error bars. 1 = Oct. 1976 2 = Nov. 1976 3 = Feb. 1977 4 = April 1977 5 = June 1977 6 = July 1977 7 = Aug. 1977 8 = June 1978 9 = Jan. 1979 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 54 œ 2 €0 11 CD 0 LU in I- co (N in m CM CU3D azis Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 55 Figure IV-3 Biomass of Asterias vulgaris and Leptasterias sp, a t 8m, 16m and 30m for 9 complete sampling dates. 1 = O ct. 1976 2 = Nov. 1976 3 = Feb. 1977 4 = A p r il 1977 5 = June 1977 6 = J u ly 1977 7 = Aug. 1977 8 = June 1978 9 = Ja n . 1979 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 56 O GO i CE O in UJ û . z= - 5 co CM in^cocM»-*oo)ooi^©in^cocM^o c gWsz"/suv^s] ssbuoia Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 57 F ig u re IV - 4 Biomass of Asterias vulgaris and Leptasterias sp. a t 8m, iBm and 30m, Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 58 CL LU Q ON O M CO in T 0) (N o c jUS3‘/suyasD ssyuoia Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 59 F ig u re IV - 5 Mean abundance of Asterias vulgaris and leptasterias sp . a t 8m, l 8m and 30m from October, 1976 to January, 1979* Data points are mean values with standard error bars. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 60 « M m o » m N o w M W W W O w Qg W o k- LÜ C e T CL N W — Q •H « p H «0 . Il II N O W o V) O m m « w N M C g U S Z '] AHSW3Q L Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 61 Figure IV-6 Mean size of Asterias vulgaris and Leptast(?rias sp. at 8 m, 18 m and 30 m from October, 1976 ho January, 1979» Data points are mean values with standard error bars (inside the symbols). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 62 I CD 0^ 111 I- k— CL o ID o o ID o » CUOD 3Z IS Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 63 FigureIV“7 Mean tiomass of Asterias vulgaris and Leptasterias sp. at 8m, iSm and 30m from October, 1976 to January, 1979■ Values are estimated from the regression equation log weight = -1.66 + 2.74 log length (see text). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 64 O UJ Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 65 2. Feeding Activity Field results. The data on prey eaten (Tables IV-13, IV-14) show that A. vulgaris is a generalist in its feeding behavior, consuming a wide variety of species at all three sites, however the data does |ï show differences between the communities. A striking result of the analyses in both Tables IV-13 and IV-14 is that fewer individuals are feeding at 18 m, while similar proportions are found feeding a t 8 m and 30 m. The differences have been consistent over the period of the study and are probably related to the prey availabilities of the three communities, as discussed below. Table IV-13 for all K A. vulgaris and Table IV-14, for the small sizes show that the depressed : (' feeding at 18 m obtains for the range of sizes, but may even be inten- l I sified for the smallest individuals. I'' There are a number of prey that are taken in relatively large amounts at one depth only, including: Mytilus edulis, barnacles. Lacuna vincta, and tunicates at 8 m. Modiolus modiolus and chitons at 18 m, and detritus, Colus spp., and hydroids at 30 m. All of the noted differences in prey eaten per area reflect the prey availabilities in those communities. Other prey are relatively ubiquitous in dis tribution and the feeding data reflect the general distribution of ectoprocts, amphipods, isopods, Spirorbis spp., other polychaetes, bivalve spat, and hydroids. Overall A. vulgaris is a generalist taking prey in close approximation to prey availability. When the feeding results are analyzed according to the size of A. vulgaris and the prey eaten by that size, a series of prey speciali zations emerges (Fig. TV -8 ^ Table IV-14). Comparing the 15 common prey categories to the size of A. vulgaris eating them, significantly Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 66 (Table IV-15) different prey are consumed by the small, mid and large asteroids. Categories 1 through 6 are commonly found as epifauna, I ■and invariably the small asteroids are on the secondary substrate consuming them. The range of prey categories available to the smallest asteroids is not as wide as it appears in Fig. IV- 8 , and Table IV-15, because not every category is available in each community. Bivalve spat are available in every community, but they are highly ephemeral, available only in late spring and summer. Detritus is a catch all term that includes the many small algae, diatoms, radiolarians, foraminiferans, bivalves and pseudofeces that are common as a substratum covering in places in all communities, but especially common at 30 m, within the polychaete tube and soft-coral matrix. Larger size asteroids can always physically consume the same prey as asteroids of smaller sizes and this is the reason for most of the variability in the results. A comparison of Figure IV- 8 showing what small A. vulgaris eat, and Table IV-13 showing the community differences in feeding suggest strong limitations of small A. vulgaris in a given community, as a result of both the spatial and the temporal prey availability differences. Thus, bivalve spat are heavily preyed upon when seasonally available in all communities, ectoprocts are abundant at 8 m and heavily taken as is the detritus matrix at 30 m. There appears to be no good prey species available at 18 m for the smallest sizes. Mid-sized A. vulgaris (categories 7-13, Fig. IV- 8 ) e a t a wide variety of prey probably because they have the mechanical ability to do so. The prey for this group also occur in a range of sizes, for example urchins and snails, and the combination of various sizes of prey and asteroid Is largely responsible for the variability. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 67 Again the actual specificity per community is greater than shown in F igure IV - 8 and Table IV-15, because the prey categories for the mid sizes are not equally available in each community (Table IV-13 gives a close estimate of prey availabilities). A unique foraging behavior is commonly observed for the mid-sized asteroids. Frequently they feed in groups of 4-10 individuals in which they attack a large, solitary prey including Modiolus. crabs, or urchins. Often the prey is larger than they would normally be capable of attacking and consuming. Buccinum undatum, a large predatory whelk, is invariably associated with the group feeding A. vulgaris. Buccinum has been reported (Nielson, 1975) to be a bivalve feeder utilizing the lip of its shell to open prey. The effect of the behavior may be to allow predation of larger prey than mid-sized individuals would normally be functionally able to successfully attack. The largest individuals prey almost exclusively on bivalves and barnacles, however, the latter are not available in high densities in the subtidal. Barnacles are virtually absent on horizontal surfaces at the deeper sites in this study. At 8 m the bivalve most available is Mytilus edulis, whereas at 18 m and 30 m Modiolus is the only common large bivalve. The giant A. vulgaris (> 20 cm) found only at 18 m are exclusively (> 99%) eating large Modiolus, a prey which has an escape in size from all but these asteroids and possibly large lobsters. To summarize the field feeding results, A. vulgaris is a generalist predator, preying upon many species that are available in each community. Availability is considered in terms of presence or absence of prey species, as well as whether or not the asteroid can mechanically eat it. There are fewer asteroids feeding at 18 m, in Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 68 all sizes, relative to the surrounding areas. The results of the analysis of prey eaten by all size classes of A. vulgaris show a series of specializations on specific prey/community. The specializations are tightest at the smallest and largest sizes. Table IV-17 and Figure IV-9 summarize the feeding data for all size classes in the three areas and demonstrates the differences between size classes as well as between areas. Laboratory Results. Laboratory studies were done on the feeding of A. vulgaris by students in a Sea Grant sponsored projects course under my direction. Larry McEdward (Hulbert e^ ad, 1976) investigated the prey preferences and consumption rates of A. vulgaris on a variety of prey. John Duclos (Lull et al, 1979) investigated the size preference and consumption rates of A. vulgaris on Mytilus edulis. Both studies were done in the UNH Zoology Dept, environmental control, sea water room at 12-14°C. Binary choice experiments for prey preference showed that the three bivalve species were highest in preference of the potential subtidal prey (Table IV-17). Barnacles and Mytilus were found to be highly preferred and would be taken unequivocably over all other prey listed in Table IV-17. The next four prey were preferred with no difference between them as a group in preference. The categories from number 7 to 15 were consumed only if there were no other choice. Con sumption rate experiments in 1976 showed (Table IV-18) A. vulgaris consumed an average of 1-2 barnacles, mussels or limpets per day, with a high variability in feeding rates. Barnacles were eaten faster by small individuals, while mussels and limpets were eaten slightly faster by large individuals. More specific experiments in 1979 of consumption rates on mussels utilized three size classes of mussels (Table IV-19) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 69 and 4 to 5 cm asteroids. The largest size class (7-8 mm) of mussels was rarely completely consumed in the laboratory, in a process which took 3-5 days. The smallest mussels (1-2 cm) were completely consumed in about five hours. The smallest sizes were very highly preferred in the choice experiments over the large individuals which were never I touched in the same experiments. In a number of instances A. vulgaris chipped the shells of the small mussels to gain entry. The laboratory experiments showed that there was a direct relationship between mussel size and size of asteroid predator; A. vulgaris is limited in maximum prey size by its mechanical feeding abilities. It was predicted that larger predators would take larger prey, which is bom out by the field observations. Thus, the laboratory results showed a strong preference for barnacles and bivalves as prey and functional lim itations to feeding related to the size of the asteroid. The field results showing pack feeding of mid-sized individuals may be a behavioral adaptation to circumvent the functional lim itations of the size class. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 70 Table IV-12. Feeding Data Summarized and Expressed as Percentages 1 for A. vulgaris. Prey (8 m) (18 m) (30 m) Bivalvia (total) 25 .4 31.2 9 .8 Hiatella arctica <1 5 .3 0 Modiolus modiolus 4 .6 14.7 <1 Mytilus edulis 12 .3 0 0 O ther 7 .1 11.3 9 .3 Cirripedia 8.6 <1 1 .5 C rustacea 2.8 4 .9 1 .7 D e tritu s 1.0 <1 36.2 Echinoidea 9 .1 4 .2 <1 Ectoprocta 12.7 9.5 7 .1 Gastropoda (Total) 10.5 1.7 10.5 Lacuna vincta 8.6 0 0 Colus spp. 0 0 2 .3 Hydrozoa 2.2 2.8 10.9 Ophiuroidea 3.5 3 .2 <1 Polychaeta (Total) 7 .6 18.1 12.6 Spirorbis spp. 3 .4 13.7 6 .5 Other 4 .2 4 .4 6.1 Polyplacophora <1 5 .6 <1 T unicata 7 .4 <1 2.5 Unidentified and 7.4 17.5 5 .5 m isc. T o tal % feeding 5 1.9 33.7 54.3 Total obser v a tio n s (N) 1632 847 876 % Overlap? 68 . 0% 47.2% 52.4% 1 - Number of Feeding Observations/Prey „ ^ Total Feeding Observations 2 = Overlap is the sum of the lower percentages of each overlaping prey and is essentially a sim iliarity index (Whittaker and Fairbanks, 1959). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 71 Table IV-13. Feeding data summarized and expressed as percentages^ for small A. vulgaris and Leptasterias sp.l (< 1 cm). Prey 8 m 18 m 30 m A. v u lg a ris Leptasterias sp. B iv alv ia (SPAT) 31.8 44.9 34.2 15.3 C rustacea 0 6 .4 4 .9 3 .0 D e tritu s 0 0 0 35.1 E chinoidea 7 .0 1 .3 0 0 E cto p ro cta 39.4 12.8 18.2 8.9 Hydrozoa 12.7 6 .4 21.8 22.8 Polychaeta (Total) 5 .6 19.2 17.8 12.9 Spirorbis sp. 3.5 19.2 14.7 9.4 Unidentified and misc. 3 .5 9 .0 3 .1 2.0 T o tal % 89.3 39.0 61.0 84.9 Feeding Total Observations (N) 159 200 369 238 Small A. vulgaris and Leptasterias sp. have 93.9% overlap in prey utilization from these data. ^Number of feeding observations/prey ^ Total Feeding Observations Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 72 Table IV-14. The categories of common prey and the sizes of A. vulgaris that feed upon them. Prey Mean S ize (cm .) X SE (N): B iv alv ia (SPAT) .80 .047 (129) Hydrozoa 1.01 .154 (78) E ctoprocta 1.13 .120 (132) Spirorbis sp. 1.36 .172 (88) D e tritu s 1.47 .138 (123) C rustacea 1.73 .154 (44) Gastropoda 2.31 .124 (79) T unicata 2.39 .139 (42) P olychaeta 2.46 .169 (63) Ophiuroidea 3.10 .188 (30) A stero id ea 3.14 .394 (11) Echinoidea 3.24 .205 (87) Polyplacophora 3.41 .307 (16) B iv alv ia 4.34 .228 (105) C irrip e d ia 4.74 .392 (29) * N = The number of observations in each prey category. g Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 73 Table IV-15. One way ANOVA of Size of Asterias vulgaris relative to prey category. The analysis shows a significant difference in size of the asteroid relative to prey c a te g o ry . ANOVA T able: Source d . f . SS MS = SS/d.f. F Among 14 1464.270 104.591 47.2*** R esid u al 1041 2306.081 2.215 T o tal 1055 3770.351 *** = P < .001 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table IV-16. Feeding Percentages.Per Size Class of A. vulgaris at 8 m, 18m and 30 m showing the differences of feeding by size and by community. Size Classes of A. vulgaris (cm) 30m 1 3m Prey (%) w Bivalve (SPAT) Hydrozoa 00 w ui Ectoprocta VI 00 Spirorbis spp CD Detritus W VO o Crustacea 3 0 wi 00 Gastropoda w jTunlcata CO Polychaeta N3 VI VC VI 0 0 vO w Ophiuroidea CO Asteroidea oa Echinoidea UI VI 00 w Polyplacephora Bivalvia VI VI cirripedia Reproduced with permissionof the copyright owner. Further reproduction prohibited without permission. 75 Table IV-17. Prey preference of A. vulgaris from binary choice laboratory experiments* P referen ce Prey I High 1. Balanus balanoides (Barnacle) I 2. Mytilus edulis (Bivalve) 3. Hiatella arctica (Bivalve) 4. Acmaea testudinalis (Limpet) 5. Modiolus modiolus (Bivalve) 6 . Strongylocentrotus droehbachiensis (U rchin) 7. Electra pilosa (Ectoproct) 8. Lacuna vincta (Gastropod) 9. Ophiopholis aculeata (Brittle star) 10. Cucumaria frondosa (Sea cucumber) 11. Asterias vulgaris (Asteroid) v: 12. Littorina littorea (Gastropod) r: 13. Ischnochiton alba (Chiton) 14. Isopoda sp. Low 15. Amphipoda sp. *From: Hulbert, et al, 1976, Page 36, experiments were done by Larry McEdward. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 76 (U (U Q) u Ü § s s )4 s (U (U iî tw tw tw (U (U (U u ' w w w «W 0) A o . ex CI un w lU (U 0) Oh N N N •H -H 4 4 on o r 4 CO u T> I k M ►. on 2 o C\ o n on cr> 1-4 en h cl SJ 00 iH 8 + -F a I u O m m o i n A O m m > w to o « on n r n r on n r on n r 4J 4 4 < u 1 1 1 1 3 ) 4 N m o m o m t*5 T3 0) 4 4 w CO r 4 r 4 on 1-4 on § 2 en w PU < Pu Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 77 3 >1 > "3 in m •H 0 0 I I I "3 3 o o o 5 2 CO 44 •Hg 44 on a 3 on IM 1 5 o . g u CO iH 3 CO 0 ë 4J o \ 0 4 r 4 r 4 v C y H I 3 3 § P Ü 3 .5 P 0 (d "3 D •H 3 >> td 2 P bsi 3 3 3 3 3 43 3 > 44 O 0 3 •3 3 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 78 F ig u re IV -8 Size of Asterias vulgaris plotted against prey categories. Data points are mean values with standard error tars. 1 = Bivalvia (Spat) 2 = Hydrozoa 3 = Ectoprocta 4 = Spirorbis sp. 5 = Detritus 6 = Crustacea 7 = Gastropoda 8 = Tunicata 9 = P o ly ch aeta 10 = Ophiuroidea 11 = A ste ro id e a 12 = Echinoidea 13 = Polyplacophora 14 = Bivalvia 15 = Cirripedia Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 79 I I I I I I ' I in CO CM I O i CO ^ > LÜ in CO CM CUOD siauG inA ’ u do b z is Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 80 Figure IV-9 Pie diagrams of the percentages of Asterias vulgaris feeding on the 15 major prey categories, by size class and community. 1 = Bivalvia (Spat) 2 = Hydrozoa 3 = E c to p ro c ta 4 = Spirorbis sp. 5 = Detritus 6 = Crustacea 7 = Gastropoda 8 = T u n icata 9 = Polychaeta 10 = Ophiuroidea 11 = Asteroidea 12 = E chinoidea 13 = Polyplacophora 14 = Bivalvia 15 = Cirripedia Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 81 I SIZE CIASSES Small (0-2 cm) Mid (2-4 cm) large (a- cm) I Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 82 3. Flux Rates The results of the tagging experiments initiated 17 July, 1978 and 12 June, 1979 to determine the rate and directionality of movement of A. vulgaris that were tagged and returned to their home community are given below. There was no apparent trend for A. vulgaris to move in any I direction preferentially in any of the three communities. They tended to move until a shelter was found, mostly under rocks and crevices, ) and a t 8 m they tended to follow a shallow 5 cm. by 5 cm. crack. ' Once a shelter was found they tended to stay there and not move, j e sp e c ia lly a t 30 m. I The data on rate of movement per depth are given in Table IV- 20. The rate of movement was significantly different at each depth (P < .05). A. vulgaris was most active at 8 m, but the activity was of a protean nature such that there was considerable back and forth movement of the animals, and after three days, 56% were recaptured. At 18 m most of the released asteroids disappeared very quickly, and on the third day only 26% were recaptured. At 30 m they moved slowly, most not moving at all, and after three days 58% were recaptured within a 10 m C: i; radius of the release point. Tagged individuals at 30 m were seen f ■ in the same area regularly for 6 months after the experiments, whereas I they diffused much more rapidly at 8 m and 18 m. •I The results of the transplantation experiments, in which individuals from 8 m were tagged and released at 18 m and 30 m, were only qualitatively recorded. The results showed that the 8 m individuals behaved very actively at first, much like they would in their home community. After about 3 days, however, they appeared to take on the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 83 characteristics of the new community, which was especially obvious at 30 m where transplants were active at first, then settled down and I a number of them could be found for weeks afterward in the same places. At 18 m the animals disappeared very quickly as did the home individuals when they were tagged and replaced in the previous experi- ment. The largest individuals moved the greatest distances (for example, a 28.0 asteroid moved 400 cm/day), and small individuals moved very little giving a trend that was significant (P < .001) mainly because of the 673 degrees of freedom involved. However, the 2 trend was not of a predictable nature because of an r of 28.6%. About all I can conclude by comparing the size and distance moved by the asteroids (Table IV-20) is that larger individuals have a greater potential to move farther than small individuals. Thus the tagging experiments showed no preferential direction of movement or different rates of movement/area. The tagged individuals quickly disappeared at 18 m and hardly moved at 30 m. Transplants quickly assumed the behavior of the new community, and the largest individuals had the potential of moving the farthest distances/day. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 84 Table IV-20. Rate of Asteroid Movement in Each Community. Distances are I mean rates per individual per day. A. Overall Rates Depth Mean Distance moved/individual X S.E . 8 109.44 cmL 5.70 18 71.645 cm 5.24 30 37.944 cm 4.97 iThe 95% confidence lim its do not overlap, therefore the rates are different at P < .05. B. Rates per size class of Asteroid. Depth Mean Distance/Size Class sm all (0-2 cm) med (2-4 cm) la rg e (4-oc cm) X SD X SD X SD 8 33.0 cm 34.2 90.5 cm 80.1 119.5 86.3 18 29.5 cm 40.2 70.1 cm 77.1 133.5 130.1 30 30.3 cm 61.0 35.9 cm 66.4 77.9 130.9 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 85 4. Predators of A. vulgaris There are 4 sympatric asteroids, 3 crabs, 1 lobster and at least 5 fish species that have been observed to eat A. vulgaris. A s te ro id s . 1. Asterias forbesi. Observations in the field and lab show conclusively that A. forbesi will chase and prey upon A. vulgaris and that A. vulgaris has a well developed escape response to its con gener, implying an historical aspect to the confrontation as a selective agent for the response to evolve. A. vulgaris was observed cannibalizing its own species, but was never observed preying upon A. forbesi. A. forbesi was found (with 2 exceptions after storms) only above the summer th e rm o d in e a t th e 8 m site. Presumably warm water adaptations allow it to survive effectively when the ambient water warms up in the summer (F ig . 1 -3 ) . In th e w in te r i t was d i f f i c u l t to fin d A. fo rb e s i although several were active even at 0°C. A 2°C increase in ambient temperature invariably brought out many more individuals (of large size) in the spring, implying a hibernation technique. A. forbesi eats virtually identical prey to its congener, preferring mussels over all else, but also taking gastropods and ophiuroids, and when present, almost all other invertebrates. Size and abundance of A. forbesi are given in Tables IV-21 and IV-22. A. forbesi is present in similar sizes to its congener at 8 m, but its abundance is very low year round (Table IV-21), showing up in samples on only 5 sampling dates. Thus, although this species has the potential of affecting the I; A. vulgaris population at 8 m, because of low abundance, its impact is m inim al. ! . Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 86 Table IV-21. Size structure and Abundance of Asterias forbesi from 2 + .25m quadrats at the 8 m research site. Date Mean S ize (cm) Mean Abundance /.25m^ X SE (n>*- X SE (N f Oct *76 4.55 .55 (2) .10 .10 (5) f Nov *76 nd '*' 0.0 0.0 (2) Dec *76 ND 0.0 0.0 (6 ) Jan *77 ND 0.0 0.0 (8) Feb *77 1.8 .60 (2) .17 .11 (12) A pril *77 ND 0.0 0.0 (3) May *77 1.7 0.0 (1) .33 .33 (3) June *77 ND 0.0 0.0 (3) July *77 2.0 .50 (2) .67 .66 (3) Aug *77 1.8 0.0 (1) .07 .07 (15) June *78 ND 0.0 0.0 (10) Jan *79 ND 0.0 0.0 (10) O verall 2.37 .43 (8) .11 .02 (80) 2 — 2 +10m transects at 8m give results of Abundance X = 1.42/lOm , BE = .16 N = (24), Size X = 3.44, SE = .07, n = (29) (for individuals > 3.0 cm) 2 in = number of individuals measured from .25m quadrats 2 2 N = number of .25m quadrats collected tND = No data were collected on size because no A. forbesi were collected in samples. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 87 2. Leptasterlas sp. Occurring in high densities (up to 2 200/m ) a t 18 m, b u t in reduced numbers a t 8 m and 30 w, the small (< 1 cm)asteroid has several possible interactions with A. vulgaris. On two occasions I observed Leptasterlas sp. (.7 cm and .8 cm) preying upon small (.5 cm) A. vulgaris but I never observed the opposite inter action. Small A. vulgaris occurred on the buoy line at one meter off the bottom at the 18 m sit% implying that they do settle and meta- morphase at 18 m, although they are rare on the bottom. Possibly this is due to Leptasterlas sp. predation on the small A. vulgaris, thus acting as a larval filter. The diet of Leptasterlas sp. is very similar (Table IV-14) to small A. vulgaris (93.9% overlap). In vertical communities, I regularly observed Leptasterlas sp. preying upon brachiopods (Terebratulina septentrionalis). Very little is known of brachiopod biology and I believe this is one of the few recorded observations of a brachiopod predator (see also Mauzey et ^ 1968 for Evasterias troschelii). Leptasterlas sp. is a brooder. Individuals can be found brooding 10-18 embryos from November to late March. Only a few members (< 30%) appear to be brooding at any time. The 1 mm juveniles crawl away from the adult after absorbing the yolk stalk. At 3 mm a number I- of these small sea stars develop gonads, which are yellow and can be seen through the body wall. At 3-4 mm they may produce 3 to 5 large ! yolky eggs, and by 5-6 mm they appear fully mature and can produce 15-18 eggs. The eggs are easily seen and counted through the body wall. Often 5 mm animals have not yet developed gonopores. I have observed eggs within the stomach, suggesting a body wall rupture to release the eggs, although I have no firm evidence of this. When brooding embryos. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 88 Leptasterlas sp. appears to follow the standard developmental format as seen in Chia (1964) for Leptasterlas hexactis. Leptasterlas sp. is present in high densities, eats the same food, and there is depressed feeding at 18 m (Table IV-13) suggesting i I a prey limitation. To some extent it will also prey upon A. vulgaris. There is thus considerable evidence for a potential controlling effect of the Leptasterlas sp. population on A. vulgaris at 18 m. The effect would be most strongly felt on the smallest sizes of A. vulgaris, as they settled into the community where Leptasterlas sp. was already well established. The brooding reproductive strategy is geared to main taining the population in the immediate vicinityj thus once the species established itself, it could potentially exclude small A. vulgaris either by direct competition for food or as a larval filter. Nubble Light and Malaga Gut populations at 18 m in sim iliar communities provide natural comparisons with Leptasterlas sp. being absent. At both areas the abundance and size of A. vulgaris is higher (Table IV- 6 , Appendix E) than the estimated population of A. vulgaris alone at the research site (Figure IV- 8), again suggesting a suppressive effect due to Leptasterlas sp. 3. Crossaster papposus. It was only encountered in the 30 m community (Table IV-22) as part of the deeper fauna in the Gulf of Maine. Hancock (1974) has shown this species to be a specialist on Asterias rubens, a very sim ilar species to A. vulgaris, in England. On the West Coast of the U.S. Crossaster is an opisthobranch predator (Birkeland, 1974, Mauzey et al. 1968). I have observed predation by Crossaster on A. vulgaris, but I have also observed it preying upon urchins, bivalves, ophiuroids, hydroids, and other asteroids. A. vulgaris Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 89 shows a well developed escape response to Crossaster Implying that predation pressure has existed historically as a selective force. In the Gulf of Maine, Crossaster is not a specialist on A. vulgaris ; less than 20% of the feeding observations were on asteroids. The feeding data is inconclusive however, because Crossaster is relatively 2 rare (< 1/30 m ) and less than 100 feeding observations were made during the study. Thus, although Crossaster has the potential to affect A. vulgaris populations as a predator, it does not specialize on asteroids as prey and it is relatively rare in the community. 4. Solaster endeca. I have observed Solaster preying upon A. vulgaris on 2 occasions at 18 m and 30 m (Table IV-22). Both prey were 6-8 cm and were almost as large as the Solaster. Solaster feeds primarily on sea cucumbers (> 95%), predominantly Psolas fab ricii, but also Cuc"maria frondosa. Psolas is found abundantly on vertical and horizontal substrates, between 18 and 30 meters and the distribution of Solaster follows the prey closely. Solaster appears to eat only 1 Psolas at a time and takes several days to complete its meal. In general they don't move much in a given area; I have been observing two large individuals that haven’t moved more than 10 meters in over 2 years at the 18 m site. It appears that when Psolas are not available, Solaster forages within the Modiolus clumps for Cucumaria and A. vulgaris. Solaster occurs in a range of sizes, including a number of large 20-25 cm individuals. Between 18-30 m depth they are most common, averaging 1-2/30 m^. While Solaster has the potential to affect A. vulgaris popula tions, they prey predominantly upon sea cucumbers. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 90 Non-Asteroids. .1. Crabs. All 3 common crab species, Carcinas maenas, Cancer irroratus and Cancer borealis (Table IV-22) have been observed I; eating A. vulgaris (personal observations AWH). Laboratory studies 6'' (Harris, personal communication; Hulbert et al, 1976) showed that |;I mussels and urchins were highly preferred as food by all 3 species, BÏ while asteroids were not preferred. Crabs are especially common I I a t 8 m, utilizing the Chondrus as an effective refuge, while at 18 m f I and 30 m individuals are rare (Table II-l). The crabs are highly f seasonal, being active only in the warmer months. In winter they burrow into small sand deposits between boulders and in crevices where they I [■ appear to hibernate for the winter. At 8 m the crabs (there are many 5 small individuals) are active during both day and night, while at 18 m i; and 30 m they are primarily nocturnal, possibly due to the Chondrus Ë I shelter at 3 m and behavioral differences of the larger individuals t:- found at 18 m and 30 m. Crabs may play an important role at 8 m in i V ' controlling the urchin populations, which would otherwise clear the I Chondrus and eliminate the refuge. Although they will eat asteroids, f-. they don’t prefer them and probably don’t prey upon them to any extent, i Gut contents from the 8 m site showed that urchin and bivalve prey are Ï. ingested by the crabs, both of which overlap with the prey of mid-size j: A. vulgaris (Table IV-14 and Figure IV-11), but prey don’t appear to be I a limiting resource at 8 m. I Crabs do occasionally prey upon A. vulgaris and there is definite prey overlap. However, prey density does not appear limiting at 8 m, where most of the crabs are, so it does not appear likely that competi tion OT predation from crabs is an important factor affecting A. vulgaris Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 91 populations. The strongly seasonal and diurnal activities of the crabs compound on a n a ly s is o f t h e i r long term im pact on th e com m unities. X 2. Lobster. Homarus americanus is rare at all 3 sites (Table IV-22) but the area is prime lobster habitat. The Isles of Shoals support a large lobstering industry and thus the rarity of lobsters is probably directly related to the intense fishing pressure (> 40,000 lobster pots around the islands). Homarus is a large and efficient predator which appears to have a strong preference for urchins, bivalves and crabs (L. Harris, personal communication ; Hulbert et al, 1976). The interactions of lobster and urchin are well documented by Breen and Mann (1976) and appear to hold at the Isles of Shoals. Lobsters are apparently capable of controlling urchin populations, allowing a kelp forest to develop resulting in higher productivity. With such heavy fishing pressure on lobsters, the urchins are increasing in both size and abundance. At some areas of the Isles of Shoals they have stripped former kelp forests to bedrock and crustose coralline algae, which is a very dramatic shift in community structure. I have observed Homarus eating both large and small A. vulgaris in the field and lab. A 2 cm sea star can be consumed in less than 30 seconds, while larger (7-8 cm) prey take longer and usually autotomize the limb before the whole animal is eaten. A. vulgaris is a preferred prey of lobsters in the laboratory, but at times they did coexist for long periods. When urchins, crabs or bivalves are present, Homarus appears to prefer them over all other choices, although in the laboratory none of the prey offered were found to be unacceptable to the lobster. |i Homarus is predominantly a nocturnal animal, capturing large invertebrates I at night and bringing them back to its den for later consumption. They Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 92 are rare at all 3 sites during the winter. Whether they migrate or hibernate is not known, although it is suspected they move into deeper waters in the winter. Thus, the lobster is an important potential predator on A. vulgaris, They are also potential competitors because they eat similar prey to the large asteroids (mostly bivalves); however, large bivalves and urchins are abundant. If the lobsters are affecting the populations of asteroids it is as a predator, but I have seen little evidence of this in th% field. Most of the remains around lobster dens are bivalve, crab, and urchin parts, and although asteroid parts wouldn’t show up, the r other remains indicate predation on other species. Lobsters are 2 relatively rare (< 1/500 m ) even in the summer months, so its potential effect on A. vulgaris is strongly attenuated by its seasonality, low abundance, and eating of alternate prey. r- 3. Fish. As mentioned earlier a large number of species of bottom feeding fish are present at the 3 research sites (Table IV-22). The fish are highly seasonal in occurrence. In the late spring they begin an upward migration and can be tracked at 30 m, then 18 m, and one to two weeks l a t e r a t 8 m. Larger individuals are usually found a t 30 m and th e sm all a t 8 m of all fish species. In late November ; when the ambient water temperature drops, a downward migration of the r ; fish is apparent. During the coldest months they are absent from the 3 sites. Small fish appear to utilize the algal canopy at 8 m much like the invertebrates, as shelter and for foraging. During the warmest parts of the year (Figure II-3) high densities of fish may occur I especially at 18 m and 30 m. Gunner are the most abundant fish with 2 average densities of 200/25m being recorded at 18 m and 30 m. Gunner I Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 93 are extremely voracious when most abundant, picking at anything stirred loose on the bottom. I have observed them picking invertebrates from the substrate and I have fed them small A. vulgaris which they readily accept. When less abundant they are not as likely to take small a s te r o id s . Gut contents of cunner taken from the research site show a wide range of small invertebrates are taken. Cunner pick at the bottom in a head down position, using the projecting front teeth to pluck invertebrates from the substrate. The honey and very rough pharynx then macerates most prey. In this manner cunner eat limpets (L. Harris, personal communication) small snails, crabs, urchins, brittle stars, polychaetes and almost anything small sitting on a horizontal substrate. The potential effect of this one species on the communities is substantial, considering its abundance and high metabolic rate (D. C. Edwards, personal communication). Its effect on A. vulgaris is probably minimal, since asteroids are not acceptable as prey in laboratory tests (Hulbert ejt al, 1976) and appear to be taken only incidentally to the preferred prey. The other fish present, winter flounder, eel pout, cod, and wolffish all act similarly to the cunner, but they are not present in as high densities. Eel pout are present year-round and are the only large fish consistently observed in the winter. Stomach contents of all the bottom feeding fish contain large numbers of invertebrates, predominantly ophiuroids, urchins, and polychaetes. Asteroids are commonly present in low numbers in the gut contents of all of the fish, but are probably taken incidently to the intended prey. Flounder pick at the bottom and suck in prey somewhat selectively, whereas the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 94 other fish suck in larger quantities of animals at a time. Codfish especially scrape and suck in substantial quantities of indiscriminate horizontal community as they plow into an area. Small fish are usually much more selective in feeding than larger individuals (R. Langton, personal communication), implying a possible functional lim itation to feeding by size. Large fish quite often are specialized as individuals, in that their guts w ill be full of one type of prey, whereas another individual may be full of another. The specialization may simply be a function of the type of community where they feed, representing the prey availability of that community. Thus, the fish have a great potential for directly affecting A. vulgaris populations as predators, but they appear to take asteroids only incidentally. Fish most certainly affect the community structure, which in turn secondarily affect the asteroid populations within the communities. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 95 Table IV -22. Summary D ata on th e P re d a to rs o f A. v u lg a r is . I Species Community Density Size Comments (Relative to S.D. S.D. A. v u lg a ris ) A steroids Asterias forbesi 8 m .142/mT .78 4.00 2.60 -High food o v erlap -Summer -E ats A. v u lg a ris -Low d e n sity Leptasterlas sp, 18 m 2 3 .4 / .25m .5 -High food o v e rla p -year-round -larval filter -high density C ro ssaster 30 m (< l/30m ^) 5.95 3.95 -High food papposus o v erlap -Year-round -E ats A. v u lg a ris -Low density Solaster endeca 18 m (l-2/30mi ) 15.262 11.50 -Prefers sea 30 m cucumbers (99%) -Year-round -E a ts A. v u lg a ris Crabs Carcinus maenas 8 m ( * .30/m^) a l l s iz e s -High food Cancer irroratus 18 m o v erlap Cancer b o re a lis 30 m -nocturnal -Summer -Not acceptable prey Lobster Homarus am ericanus 8 m (< 1/500 m'") all sizes -High food 18 m o v e rla p 30 m -nocturnal -Summer -Preferred prey -Low d e n sity F is h l Tautogolabrus 8 m up to 200/25m all sizes -Summer adspersus 18 m attracted by -Not acceptable (cunner) 30 m activity prey -High densities Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 96 Table IV-22 (cont. ) Species Community D ensity S ize Comments X S.D. X S.D. Morhua c a ll a r i a s 18 m attracted by Large -Eats urchins. (codfish) 30 m a c t i v i t y ophiuroids & polychaetes -Summer Macrozoarces 8 m rare ( Psuedopleuronectes 8 m attracted by Large -Eats ophiuroids americanus 18 m a c t i v i t y & polychaetes (flounder) 30 m -Summer Anarchichas 8 m rare ( 1 All of the fish appear to take A. vulgaris only incidentally to the intended prey. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 97 5. Natural History Several other species of asteroidsare present in the 3 communities that do not either prey upon or compete with A. vulgaris (Table IV-23). Henricia sanguinolenta, Hippasteria phyrigiana, Leptasterlas litto ralis, Porania insignis, Pteraster m ilitaris and Stephanasterias albula do not appear to be important to A. vulgaris. Brief descriptions of each are given below for completeness in describing the asteroids of rocky communities at the Isles of Shoals. Henricia. Henricia is common at all 3 sites and is the only asteroid other than A. vulgaris which occurs in most samples (Table IV-24, IV-25). An analysis of its size and abundance by multiple regression methods, as described earlier, revealed no significant differences due to depth or season on the population structure. It appears to be homogeneously dispersed throughout all 3 communities with no significant trends observed in the results (Fig's IV-10, IV-U). There was a highly significant correlation between the size of the disc to arm in Henricia (Log S ize D isc = .0729 + 0.511 Log length arm, P < .001, r^ = 76.8%, d.f. = 55). Henricia has been a subject of some controversy in the literature. Observations and laboratory tests have shown (Anderson, 1960; Rasmussen, 1965) that it is a suspension feeder and is well adapted functionally for ciliary feeding. Other observations (Vasserot, 1962) have shown that is a carnivore, actively consuming macro-invertebrate prey (sponges). I have recorded many feeding observations of Henricia at the 3 research sites. Many individuals were undoubtedly suspension feeding, as they were located upon algae or other exposed points with their arms extended to the water currents. However, I have also noticed at least Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 98 2 other feeding behaviors. Henricia was often found clearly associated with sponges; they have the same pigmentation and are found within cavities, which appear to have been eaten into the sponge. The sponges Halichondria sp. and Haliclona sp. appear to be most often utilized. Also, in gut contents of 12 one cm. individuals, I have found sponge spicules in all. It appears that Henricia eats sponges, and does not just utilize its currents as a commensal as Rasmussen suggested (1965). I also observed it eating other invertebrates. For example, in the winters of 1978 and 1979 numerous Henricia were preying upon 2-4 cm. diameter urchins, usually in packs of 3-4 individuals/urchin. Year-round they can be found eating ectoprocts, Spirorbis, and small bivalves. In all cases there was convincing evidence of damage to the prey that could be attributed directly to Henricia. Unpublished results from Monterey Bay, Ca. where I was able to quantify the feeding of Henricia spp. showed approximately 36% were feeding on ectoprocts and tube worms (Hulbert, in prep.). Thus, Henricia appears to have the simultaneous potential to suspension feed or to attack larger prey. Recruitment in Henricia appears to be very patchy. I have observed them brooding in mid-summer in different locations in different years. The only year I observed brooding at the research site was during 1979. Leptasterlas litteralis is found shallow on vertical walls and is often in narrow crevices (Table IV-23). Its distribution is patchy, missing from whole localities^ and quite common at others (i.e. Nubble Light). L. litteralis consumes small bivalve spat, gastropods, and urchins. It broods in mid-winter within small cracks of vertical walls. I: The remaining 4 species of asteroids observed during the study are all relatively rare and occur only below 30 m at the Isles of Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 99 Shoals (Table IV-23). All were found only on hard substrate. Hippasteria phyrigiana has been observed eating soft corals (Gersemia) and sea anemones r,- (Metridium). I collected only 3 specimens from 1976 to 1980 at the 30 m I site*, they measured 15.0, 8.4, and 7.5 cm. The species is more abundant B in other deep local communities. An explanation for their absence at the : 30 m site is lacking, since soft corals (Gersemia and Clavalaria) and I anemones (Metridium and Tealia) are abundant. Porania insignis was also rare at the 30 m site. A total of 6 I'- individuals were observed from 1976 to 1980. Two of these were collected (10.5 cm weighing 162.1 grams wet weight and 12.5 cm weighing 185.5 grams wet weight). One 16.4 cm individual was observed at Jeffries Ledge. Two of the Porania were eating a mounding sponge on horizontal substrate (possibly a Craniella sp/) / The species is not regularly reported from other areas in the Gulf of Maine by divers or from fishermen’s nets, and the center of its distribution is unknown. Pteraster m ilitaris was often seen (once/month) on boulders and vertical walls at the 30 m site. Six typical individuals were collected (4.0, 4.0, 2.7, 2.5, 3.3, 2.3 cm) of the approximately 30 observed. All of the individuals were small, which made feeding observations difficult. :- However, they appeared to be direct deposit feeders. Pteraster at Eastport, Maine and on the West Coast of the U.S. eats sponges (Larry Harris, personal observation). ; Stephanasterias albula. The species is very rare at the 30 m E |b s ite (2 observations), but is is an important component of other deep sub tidal rocky communities. At Jeffries Ledge it is the most common asteroid at 30 m and 42 m(averaging 6.9/.25m with a mean size of .65 cmj, feeding on small bivalves. I suspect it is more common at the Isles of Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 100 Shoals in deeper water. Stephanasterias is interesting because it is a fissiparous asteroid, and gonads have never been discovered in the species. It reproduces entirely by regenerating arms, and virtually every individual has 2, 3, or 4 different sizes of arms in different stages of regenera tion. Individuals have 1-8 arms with no consistent pattern. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 101 Table IV-23. Asteroids Species Community D ensity Size Comments X H enricia 8 m .69 / .25m 1.07 cm -No trends to dis- sanguinolenta 18 m 1.12/.25m2 .85 cm tribution 30 m .37/.25mt 1.72 cm -Suspension feeder and predator -Broods young Hippasteria 30 m rare 10.3 cm - -Deep water species p h y rig ian a -Preys on soft- bodied inverte b ra te s Leptasterlas 8 m p a tch y - 2—3 cm - -Shallow water l i t t e r a l i s r a r e sp ec ie s v e r t i c a l -Preys on small w a lls bivalves and gastropods -Broods young in crevices Porania 30 m r a re 1 3.1 cm - -Deep water in s ig n is sp ec ie s -Preys on sponges Pteraster 30 m ra re 3 .1 cm - -Deep water m ilita r is sp ec ie s -Probably a direct deposit feeder S tep h an asterias 30 m r a re .6# -Deep water species alb u la -Preys on small b iv a lv e s -fissiparous i; I' 1 data from Jeffries Ledge not Isles of Shoals, I Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 102 Table IV-24. Abundance of Henricia sanguinolenta from .25m quadrats at research sites I Date 8 m 18 m 30 m 2 Mean/.25d^ Mean/.25m^ Mean/.25m X SE (Nf- X SE (N) X SE (N) Oct ’76 1.00 .52 (5) 1.75 1.24 (2) .50 .05 (5) Nov ’76 0.0 0.0 (2) 3.50 1.50 (2) .25 .14 (3) Dec ’76 .17 .17 (6) ND 2 ND Jan '77 .25 .16 (8) 1.75 1.10 (4) ND Feb ’77 .13 .04 ( 12) .33 .28 (4) .13 .13 (2) A pril ’ 77 1.33 1.32 (3) 1.50 .50 (2) .33 .40 (3) May ’ 77 .67 .33 (3) .50 .50 ( 2) ND June '77 1.0 .57 (3) 0.0 0.0 (3) .50 .26 (5) July '77 2.0 .57 (3) .50 .49 (2) .71 .18 (7) Aug '77 1.06 .42 (15) .50 .49 (2) .50 .50 (4) June '78 0.0 0.0 ( 10) .50 .27 ( 10) .40 .22 (10) Jan '79 .70 .39 ( 10) 1.50 .45 (10) .50 .49 (2) O verall .69 .07 (80) 1.12 .16 (40) .37 .03 (41) I n = Number of .25m quadrats collected 2 ND = No data were collected Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 103 Table IV-25. Size structure of Henricia sanguinolenta from .25m q u a d ra ts a t th e re s e a rc h s i t e s (cm) Date 8 m 18 m 30 m 1, Mean/.25m Mean/.25m Mean/.25m X SE (N) 1 X SE (N) X SE (N) Oct '76 .92 .10 (19) .88 .01 (14) 2.6 0.0 ( 1) Nov '76 ND^ .76 .02 (27) 1.66 .33 (3) Dec '76 .17 0.0 ( 1) ND ND Jan '77 1.05 1.50 (2) .95 .12 (7) ND Feb '77 1.03 .24 (3) 1.30 0.0 (1) 2.2 0.0 (1) A pril '77 1.02 .21 (4) .87 .09 (3) 1.7 0.0 (1) May'77 1.45 .25 (2) .70 0.0 (1) ND June '77 2.13 .39 (3) ND 2.20 1.2 (2) July '77 .78 .06 (6 ) 1.00 0.0 (1) 1.02 .26 ( 8) Aug '77 .97 .04 (16) .50 0.0 (1) 1.15 .91 (2) June '78 ND .90 .08 (5) 2.16 .64 (6 ) Jan '79 1.21 .19 (7) .69 .05 (15) .80 0.0 (1) O verall 1.07 .06 (63) .85 .02 (75) 1.72 .12 (25) % = Number of individuals measured from .25m^ quadrats ND = No data were collected Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 104 # FlgioreIV-10 Abundance of Henricia sanguinolenta at 8m, iBm and 30m for 9 complete sampling dates. Data points are mean values with standard deviation bars. 1 = O ct. 1976 2 = Nov. 1976 3 = Feb. 1977 4 = April 1977 5 = June 1977 6 = J u ly 1977 7 = Aug. 1977 8 = June 1978 9 = Jan. 1979 I Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 105 0» 2 2 - 00 2 00 O CO (O ■ u II II 0 □ (D LU lO h- 00 (N (O in 00 CN o CM I c 2 ^0 2 - 3 AlISKiaa Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 106 FigureIV-11 Size structure of Henricia sanguinolenta at 8m, 18m and 30m for 9 complete sampling dates. Data points and mean values with standard deviation Tsars. 1 = Oct. 1976 2 = Nov. 1976 3 = Feb. 1977 4 = April 1977 5 = June 1977 6 = July 1977 7 = Aug. 1977 8 = June 1978 9 = Jan. 1979 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 107 LU I- «o CUOD 3 ZIS Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER V DISCUSSION The purpose of this study was to investigate the population I structure, feeding biology, rates of movement, and predator inter actions of A. vulgaris, a common local asteroid, within selected sub- tidal communities at the Isles of Shoals, N.H. Three communities at 8 m, 18 m and 30 m on the exposed SE side of Star Island were chosen as typical of subtidal zones in the Gulf of Maine. All of the aspects investigated were found to maintain stable differences in the three communities during the period of the study. The 18 m community appears anomalous for several reasons relative to the surrounding 8 m and 30 m communities: 1. The population density of A. vulgaris is depressed, but giant individuals (> 20 cm) are only found at 18 m; 2. The proportion of the population feeding is lower at 18 m; 3. Tagged and released individuals leave the area much more quickly at 18 m; and 4. A small species of Leptasterias is present at 18 m in high density. What is controlling the A. vulgaris populations to maintain the observed differences, and what is the role of the species in the three communities? Previous studies of asteroids have been mostly limited to laboratory observations, intertidal species or dredged specimens. In contrast, r. I field and subtidal populations are poorly known. The major subtidal I asteroid surveys are those of Birkeland (1974), Dayton et ^ (1974), Dayton e^ ^ (1977), and Mauzey et ^ (1968). These surveys were 108 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 109 t conducted over â broad range of locations and depths. Others have i investigated A. vulgaris in similar communities but have only dealt with the intertidal and shallow subtidal (Annala, 1974; Menge, 1976, 1978a, 1978b, 1979). Such studies are limited to what is probably the most successful habitat of A. vulgaris in terms of abundance, size, biomass, feeding activity, rate of movement and lack of predators. Deeper populations appear to be much more stressed for food and from potential competitors and predators. The present study is unique in the coverage of all sizes of all asteroids at three adjacent subtidal locations over a period of five years. Population Structure Almost nothing is known of population lim itations in A. vulgaris. I agree with van Valen’s statement (1973) that most evolutionary strategies are related to body size. Body size in A. vulgaris is directly related to reproductive output; the larger the animal, the higher its fecundity (C. Walker, in press; personal communication; Smith, 1940). Body size also sets limits to predation, that is, it sets a threshold beyond which a prey species is safe from further predation-caused m ortality. This applies to predation on A. vulgaris as well as its effects on prey species (see Schoener 1969a). As an indeterminate grower, A. vulgaris body size may reflect local conditions. The observed population differences in size can be considered as dynamic equilibria. The average local size reflects a complex interdependence between size-related metabolic neëds, population density, characteristics of the prey, the predators, and the physical environment. Paine (1976) believes Pisaster ochraceus also adjusts Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 110 its size and growth to local resources in the intertidal area of Washington, and he suggests that the constant starfish densities he has observed are related to great longevity and low mortality. There is virtually no field data available on longevity of asteroids. I Although they are probably capable of long life, this is not what I would predict for field populations in rigorous environments. However, the sparse recruitment I observed, the lack of size classes and the I stable populations suggest long-lived individuals. Paine (1976) has noted that where Pisaster is uncommon, relative I to its resources, it attains a larger body size, while at higher densities it is smaller. The same pattern appears in A. vulgaris. At 18 m, where there are the fewest A. vulgaris, those that are present are the largest (> 20 cm). However, resources have to be considered relative to size classes, since A. vulgaris is a size-limited predator, and large prey are abundant in this community. Clearly the argument could become tautological. The smallest Pisaster are generally 4-7 cm, which corresponds to the large size class of A. vulgaris. Very little is known of the small sizes of Pisaster; what is known is only for intertidal areas (Paine, 1976). The large number of small asteroids which constitute the majority of the starfish in this study are apparently unique in ^ comparison to other communities. The small body sizes observed in an indeterminate grower suggest lim itations to growth, keeping the average ?'■ local sizes small. Biomass measurements of most marine invertebrates tend to be highly variable both between and within species and populations. The differences in asteroid biomass measurements are due to many factors. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 111 especially water content, reproductive state, number of regenerating I arms, amount of calcification, and amount of stored nutrients. A separate estimate should be obtained for each population studied since many of the above variables are community imposed. Paine (1976) has shown that intertidal Pisaster populations are different in biomass, but a given population remains remarkably constant over time. This I is probably the result of the dynamic equilibrium size obtained by an f indeterminate growth species in a given community. Menge (1979) has published biomass estimates for A. vulgaris which are much too high, even when the inherent variability is considered (see Appendix F). The regression formula I have presented is for all three depths and suffers from the variability mentioned above, as well as the seasonal differences in A. vulgaris proportions. However, actual measurements of biomass are close to my predicted values (Appendix F). Feeding Biology There is little data on asteroids in the subtidal where con tinuous feeding is possible. A. vulgaris has a catholic diet, con suming a wide variety of sizes and species of prey. In feeding, at least, it is an r strategist on the r and K continuum (Pianka, 1970). The evolution of a generalist can occur for at least three reasons (Schoener, 1969b, 1971): 1. Differences in the abundances of prey between areas; 2. Differences in the clumping of prey; or 3. The prey have large fluctuations in abundance within areas. All three evolu tionary pressures have certainly been imposed upon A. vulgaris, when its geographic and depth distributions throughout almost all fully marine benthic communities in the Gulf of Maine are considered. The general unpredictability of prey, both temporally and spatially, has undoubtedly I Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 112 been a strong selective force toward predation on a wide variety of prey. All models of foraging predict that unreliable prey abundances lead to an increase in the range of prey taken. A feeding generalist by definition (Schoener, 1969b, 1971) has; 1. a wide range of food types; 2. a wide variance of food types; and 3. a wide range of behavior in feeding. A. vulgaris is a foraging predator, feeding primarily on sessile prey. The asteroid appears to be limited in its feeding activity only by physical factors and prey availability to the different size classes. It stores excess energy in the pyloric caecae and gonads (Walker, in press); the more that it eats, the higher its fecundity. The species conforms to the Schoener model (1969b, 1971) of an Energy maximizer where time is lim iting, in this case due to wave action and temperature disturbance. Many asteroids appear to be Energy maximizers that pursue or search for prey and evaluate it only after capture (Dayton e_t al, 1977; Mauzey e£ a l, 1968; Menge, 1972). The field feeding results of this study at 8 m and 30 m show sim ilar feeding proportions of the populations to other studies (most literature feeding rates are approxi mately 50%). The feeding proportions are low at 18 m, apparently due to locally low food availability. Size-Selective Predation Asteroid prey almost always have a size-refuge beyond which they are too large to be killed by an individual predator. Many studies have investigated the size relationships of asteroids and their prey (Birkeland, 1974, Dayton et al, 1974; Mauzey et al, 1968; Menge, 1972; Paine, 1974, 1977; Rosenthal and Chess, 1972), but to my knowledge, no Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 113 i study has included the full range of asteroid sizes. The smallest sizes are usually not found and cannot be effectively considered, or they are I neglected due to the sampling difficulties involved. The differences in prey o f A. v u lg a ris a t 8 m, 18 m and 30 m (Figure IV-11) reflect the environmentally induced selectivity (see Murdock, 1969) that body size sets to predation, creating a threshold beyond which the prey is safe I from predator-caused m ortality. A prey individual can become too large to be killed by an individual predator. Laboratory choice experiments show a strong preference by A. vulgaris for mussels, and Landenburger (1968) has shown a sim ilar strong pre ference by Pisaster for mussels. Pisaster has the ability, by associa tive learning, to increase both its selectivity and rate of consumption of mussels (Landenburger, 1966, 1968). Prey preferences, specializations and learning can only occur in the large sizes which have the functional ability to consume a variety of prey. Smaller sizes are limited by size-selectivity to very few prey. The strong selectivity observed in the field results of this study (Figure IV-11) are a result of the many small individuals, and the relatively few prey in each community available to a specific size asteroid.’ The largest individuals invariably prey upon bivalves subtidally, suggesting close correlation of the laboratory and field results, for those individuals that were not size-lim ited. Large Pisaster have a minimally acceptable size of mussel (Paine, 1976), while my laboratory experiments on A. vulgaris (Lull e^ 1979) show they prefer the smallest sizes of mussel, no matter how big they get. It is possible that tests of still larger individuals would yield similar results to Pisaster. but it is also possible that A. vulgaris Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 114 may not energetically be able to reject any prey encountered, due to the unpredictable nature of the prey and the environment. I I Schoener (1969a) has suggested that larger animals should eat a greater variety of prey. This prediction holds true only for small and mid-sized A. vulgaris. which are strongly size-lim ited. However, the largest individuals have behavioral modifications, shown as feeding preferences, which narrow the prey variability. Both the size of the predator and the size of the prey are important sources of variability. Feeding in packs by mid-sized individuals (2-4 cm) may be a behavioral adaptation to alleviate the foraging restrictions of size normally associated with this size class. Schoener (1971) has suggested and many have shown (see Klieman, 1966, for dogs) that in many cases increased group size may allow an increase in the size of the prey cap tured. A. vulgaris commonly displays pack feeding behavior at 18 m on Modiolus, where there is little prey available for all but the largest sizes (> 20 cm), which can eat Modiolus. Group feeding has been regularly observed at other locations on large urchins, mussels, sand dollars and crabs. Invertebrates do not possess the elaborate communication systems that higher animals usually employ for such behavior. Asteroids have a very simple nervous system, few environmental receptors, fewer transm itters, and should not be capable of what is a ,i complex behavior. They may simply be following a chemical gradient to an injured prey and congregating upon it. Further studies to elucidate i' I; the mechanism of this behavior certainly appear warranted. f': I Menge (1972) and others have found that different prey of a single species of asteroid in different areas were related to prey Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 115 availabilities. Prey availability is difficult to quantify and presents many sampling problems. Subjective impressions of availability may be highly anthropomorphic, while quantification may lead to firmer estimates which are just as unrealistic. The sampling procedures can be extremely time and energy intensive. It appears that A. vulgaris consumes prey related to availability for each size class in each community, according to my "subjective" impressions. Size-limited predation can lead to a coexistence of prey and predator in the same area. The large surviving prey often have a high fecundity and may seirve as the most important reproductive component of their populations. Paine (1976) has suggested that a sure sign of a size-limited predator is a population of large prey which add to the vertical structure of the community, and he considers some Mytilus califomianus beds as indicative of such predation by Pisaster. Mussels appear to have an escape in size from almost all A. vulgaris, but even they cannot escape predation from packs and giant individuals. Size- limited predation should lead to locally large size differences in components of communities. The observed nature of the 18 m community where there are large mussels in clumps, forming the vertical structure, large A. vulgaris, and small Leptasterias sp. support this prediction, but th e 8 m and 30 m communities do not. A coexistence of predator and prey based on disproportionate sizes may only function in areas of limited prey availability. Simply observing size differences within a community says nothing of the development or dynamic nature of the system; for example, it is not possible to tell whether large Modiolus led to large A. vulgaris or vice versa. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 116 A small Leptasterias sp., observed to be an important component of the 18 m community, has not previously been reported in the Gulf of Maine. Leptasterias are generally arctic species and, as such, can probably tolerate more extreme winter conditions than A. vulgaris. At 18 m Leptasterias sp. was very abundant in an area that I consider transitional between a shallow algal zone and a deep sessile suspension feeder zone; both of the latter zones are extensive in the Gulf of E Maine. The transitional area varies in vertical extent between locations, depending on physical and biotic factors, and is an area of ecological release for some species and an area of stress for others. Modiolus, Leptasterias sp., Buccinum, Agarum, Ptilota and the urchins do well in the area, while most algae, crabs and A. vulgaris appear stressed, as indicated by low densities. The only vertical structure in the area for refuge, foraging, epifauna and sediment accumulation is that of the Modiolus clumps, since the urchins keep the remaining substrate bull dozed down to the coralline algae. Paine (1976) found that Leptasterias hexactis uses the vertical structure of the mussel beds as an apparent refuge and is only abundant where mussel beds of large individuals of Mytilus califomianus are present. The situation he describes appears analogous to the association of Leptasterias sp. and Modiolus clumps of large individuals at the Isles of Shoals. The densities of both Leptasterias species are sim ilar within the mussel clumps on both coasts of the United States. Paine (1976) believes that Leptasterias enhances the probability for its own persistence by simplifying the mussel bed structure. I believe Leptasterias is enhancing its survival by both decreasing the food available to young Asterias and by preying upon the recruits of Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 117 Other species, effectively excluding them from the local area. Paine ti suggests that Leptasterias is important in maintaining the mussel clump, as an alternate stable state (Paine, 1966, 1976; Sutherland, 1974). The mussels grow by chance escapes from a series of potential predators until they attain a refuge in size. The resultant clumps are less attractive to other predators, partly due to the action of Leptasterias. Nothing is known about how Modiolus clumps develop, but their biology is similar to Mytilus califomianus. It seems plausible that similar interactions could lead to the development of Modiolus clumps. If the system functions sim ilarly for the development of Modiolus clumps and Leptasterias sp. is functioning to enhance the survival of the the clumps, then possibly the results of this study could explain why there are so few small Pisaster in the intertidal of the West Coast. Leptasterias sp. appears to effectively exclude A. vulgaris, where Modiolus clumps are present at 18 m, by decreasing food availability and by direct predation on the young stages. Possibly Pisaster young cannot do well in sim iliar communities, because Leptasterias hexactis is limiting food and preying upon them. A. vulgaris fecundity is much h ig h er a t 8 m outside the mussel clump area based on the biomass and increased fecundity with size. Also, the 8 m area appears to be a nursery area (C. Walker, personal communication; personal observations AWH). Pisaster may have subtidal nursery areas outside of the mussel clumps, in addition to the limited intertidal nursery areas (Paine, 1976). Menge (1974) has shown the antagonism of Pisaster on Leptasterias, but he did not test size differences in the experiments. It is possible that small Pisaster are preyed upon by Leptasterias, as small A. vulgaris a re . Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 118 Leptasterias is a brooder and would be likely to have a greater segregation of local demes because of restricted gene flow. A relatively fast selective response to favorable local conditions, such as at 18 m at the Isles of Shoals, would be possible. Menge (1974) has shown that II with increased exposure, the fecundity of Leptasterias hexactis decreases. g: |; The wave a c tio n a t 8 m may be too great for Leptasterias sp. to effectively reproduce, limiting it to 18 m or deeper. K; Migration I The results of the tagging experiments suggest that movement is related to metabolic rate and foraging activity. Temperature directly f ' E affects metabolic rate and at least partially is responsible for the I slow rates observed in the colder water at 30 m. Movement at 8 m was I - I very fast and non-directional and probably represents foraging behavior I' in the warm, shallow area where there are many prey. At 18 m movement was rapid, but most of the asteroids left the area, possibly because no prey were available for most of the sizes released. Foraging I activity in A. vulgaris can be considered kinesis with prey availability i:' ' (■ as the nondirectional stimulus. Individuals more randomly, within '■ g physiological constraints, until food is found. Paine (1976) has found little exchange between adjacent intertidal populations of Pisaster, as t a result of long term tagging studies. I suspect there is some exchange I between A. vulgaris populations due to the apparent random foraging I. I activity. Based on observed prey availability one would expect large A. vulgaris to remain in the transition zone and smaller size classes to accumulate or remain in the 8 and 30 m communities. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 119 P red ato rs Non-asteroid predators probably have a minimal effect on î A. vulgaris » Fish may have some effect at 30 m because of their high metabolic rates and densities. Even if asteroids are taken only # incidentally by fish at 30 m, there is the potential for a significant p effect. The low densities of A. vulgaris at 30 m, relative to 8 m, 0 could be due to fish predation pressure but may also be due to low 1 recruitment, for which no information exists. 0 I' Dayton (1977) has suggested that often the only controls on I" asteroids are other asteroids. At the Isles of Shoals, predation I from other asteroids is probably not controlling A. vulgaris populations, I' Ë although there are potential different asteroid predators at each i: I depth. Asterias forbesi. Crossaster papposus, and Solaster endeca I I'; are relatively rare and eat alternative prey most of the time. I;- Leptasterias sp., by preying upon the young of A. vulgaris, is enhancing k: its own survival in the local area. Leptasterias is probably a larval fc filter, preventing A. vulgaris recruitment into the area. !'■ Menge (1979) states that A. vulgaris is a predator of A. forbesi, I g the opposite results of this study. I have observed cannibalism of I; A. vulgaris and predation by A. forbesi on A. vulgaris, but never the reverse interaction. In the laboratory there is no question of the results; the two species w ill not coexist, and eventually only A. forbesi rem ains. Cannibalism has frequently been observed in the field, although it occurred in less than 1% of the quantitative feeding observations. Eating a conspecific is intriguing from the perspective of the population. The energy is maintained in the population, and there may not be a Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 120 decrease in fecundity as a result of the larger size of the consumer. The adults of a population may prey upon the young and act as density- dependent controls on their own populations. Many starfish have been observed to consume their own species, and the resultant energy transfers are interesting to consider (Paine, 1965). Partial escapes mean an increased energy expenditure to the population for the regenera tion of an arm, or the loser may be chased out of the population and its contribution to fecundity lost. Dayton (1977) suggests cannibalism may be both a functional and numerical response (see Rolling, 1959) of an asteroid population for self-control. I' Summary The observed differences in population structure and feeding at 8 m and 30 m probably reflect the productivity of the two areas. A high primary productivity at 8 m supports a high asteroid biomass. The 30 m area, where most energy needs are important, supports lower asteroid biomass. Leptasterias sp. as a competitor for food and 1 predator on small sizes may lim it A. vulgaris to a low biomass at (; 18 m. A. vulgaris appears to be reflecting in its population structure and feeding biology a dynamic equilibrium in response to community factors, indicative of the average capacity of the environment to support them. A. vulgaris has local potential for controlling prey populations and structuring communities. Frequently many individuals move into shallow Mytilus edulis beds and decimate them. The ability of predators to control prey has been shown conclusively by Elton (1977), MacArthur (1955), and Paine (1966). Larger individuals which have the functional ability to switch prey may specialize on a preferred prey L Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 121 when available, and later switch back to a generalist life style. In this manner they could locally control preferred prey populations. Since the sizes of preferred prey that can be eaten are only found in abundance in shallow communities, A. vulgaris may not be able to control prey in deeper areas. The food web diagram (Figure V-1) summarizes many of the predator- prey interactions relative to A. vulgaris in the three communities. The observed relationships are highly overlapping and interconnected, reflecting the resilient nature of the subcomponents of the communities. Specific feeding relationships are usually due to size-related lim ita tions, rather than behavioral specializations. Relative to published results for similar communities, the observed trophic structure is simple and the species are highly flexible. The highly overlapping nature of the predator-prey interactions is the predictable evolutionary consequence of a physically demanding and unpredictable environment. The most important controlling aspecis of A. vulgaris populations appear to be prey availability to the various size classes, distur bance as it lim its foraging time, and temperature and its effect on metabolic activity. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 122 Figure .V-1 Schematic representation of the major food web interrelationships as they pertain to Asterias vulgaris in the three communities at the Isles Shoals, N.H. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 2 3 ca •H g a 3 CO O o o a-g o 0> 0 0 M •P M ^ ~ ~ ~ r = r - i •H \ \ Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LITERATURE CITED ï':' Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 125 Anderson, J.M. I960 Histological studies on the digestive system of a starfish, Henricia. with notes on Tiedemann's pouches in starfishes. Biol. Bull. Vol. 119, No. 3, pp. 371-398. M' Annala, J. 1974 Foraging Strategies and Predation Effects of Asterias rubens and Nucella lapillus. Ph.D. Dissertation. Univ. of N.H. 145 pp. Birkeland, C.E. 1970 Consequences of Differing Reproductive and Feeding Strategies for the Dynamics and Structure of an Associa tion Based on the Single Prey Species Ptilosarcus gumeyi (Gray) Univ. of Washington. Ph.D. Thesis. 99 pps. Birkeland, C.E. 1974 Interactions Between a Sea Pen and Seven of its Predators. Ecol. Monogr. 44, 211-232. Bloomshield, R.J. 1975 Superposed deformations on the Isles of Shoals, Maine, New Hampshire. M.S. Thesis, Univ. of N.H. 57 pp. Breen, P.A. and K.H. 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Woodin, S.A. 1978 Refuges, Disturbance, and Community Structure: A Marine Soft-Bottom Example. Ecology 59: (2), pp. 274-284. Zinn, D.J. 1937 The Growth and Development of Starfish in Narragansett Bay in Relation to Temperature and Food Supply. Masters Thesis, Univ. of R.I. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX A ABUNDANCE OF ASTERIAS VULGARIS AND lEPTASTERIAS SP. V FROM 25 QUADRATS AT 8M, 18M AND 30M. DATA POINTS ARE MEAN VALUES WITH STANDARD ERROR BARS. r". Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 135 APPENDIX A .2jm^ quadrat abundance for October, 1976. r 11111 i 11 n I n I n 11 [ 11111 FT r i 1111111111 Q. o Uj Q o o ? (0 N c gwsz") Aiiswaa Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1.36 APPENDIX A (C o n t.) .Z^nr quadrat alsundance for Novem'ber, 19?6 O LÜ o o o o o o USZ-D A1ISN3Q Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 137 APPENDIX A (C o n t.) .25m^ quadrat abundance for February, 1977 N « » r O UJ C,US2*D A1ISW30 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 138 APPENDIX A (Cont.) .2jm^ quadrat abundance for April, 1977» (M to N ...... C 7US3*D A1ISW30 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 139 APPENDIX A (Cont.) quadrat abundance for June, 1977. N O LU o o o o o o o o 00 v> M CgWSZ"] AiISN3Q Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 140 APPENDIX A (Cont.) .2jm quadrat abundance for July, 1977- w (0 o m o w o w N W W o w OD X V* 1- Q. •> ÜJ Q *4 M w O «4 00 o o OOOOOOOQOOOO <-«ooi»rsonTcoM«^ CgWSZ'] A1ISM3Q Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 141 APPENDIX A (Cont.) .2jm^ q.uadza,t abundance for August, 1977• 4" iiininnniMim|TnnTTir|rn n m i|niiiirn|inm ni O M CO o m 00 N o N M M M O w 00 X k— 0 _ o w Q V# w «-< o CO o ' t w tiiinnilintiiiiilniiuiiiliiiiiiminiininltiiiiiiiiJ o o o 0 O O O o ID ? m M CgWSZ") A1ISW3Q L Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 142 APPENDIX A (Cont.) .25ni2 quadrat abundance for M&y, 1978. H CO O CO » M o (W 4" M N M O (W 2£ Q. O UJ - Q o- N «■* o 00 o 4- M 4 t I I I II t ill I .4 _ U _ L jj_ L L L l.l I I L o ? CO CM C gWSZ"] A1ISN30 I Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 143 APPENDIX A (Cont.) ,25ni^ quadrat abundance for January, 1979 o o o o C gUSZ'] A1ISN30 W: Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX B SIZE STRUCTUEE OP ASTERIAS VULGARIS AND LSPTASTERIAS SP. FROM .25m2 quadrats AT 8M, 18M AND 3OM. DATA POINTS ARE MEAN VALUES WITH STANDARD DEVIATION BARS. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 145 APPENDIX B .25m^ quadrat size structure for October, 1976 . X (L W O CUOD 3ZIS Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 4 6 APPENDIX B (Cont.) .2jm^ quadrat size structure for November, 1976. W UJ CU03 3ZIS Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 147 APPENDIX B (Cont.) .2jm^ q.uadrat size structure for February, 1977* 2Ï CL o u i a Iv ïr.' CU03 3ZIS Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 148 I APPENDIX B (Cont.) .25^ quadrat size structure for April, 1977. S: CL O u Q CUOD 3ZIS :: i I Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 149 APPENDIX B (Cont.) quadrat size structure for June, 1977- CUOD 3ZIS I Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 150 APPENDIX B (Cont.) .25m^ q.uadxat size structure for July, 1977 O Ui 0> w o CUOD 3ZIS Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 151 APPENDIX B (Cont.) .2jm^ quadrat size structure for August, 1977 CU3D 3ZIS Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 152 APPENDIX B (Gont.) .2 3 n r quadrat size structure for May, 1978 O U J M n o CU3) 3ZIS I Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 15.3 APPENDIX B (Cont.) .2^m^ quadrat size structure for January, 1979. I m CM m o CO 0 0 CM K > CM M- CM CM CM O CM CO z «4 J— Q. o W « 4 O #4 CM #4 o #4 m ( 0 M* CM j i I ■ I O m CM CWO] 3ZIS Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX G ABUNDANCE OF ASTERIAS VULGARIS FROM lOM^ TRANSECTS AT 8M, 18M AND 3OM. DATA POINTS ARE MEAN VALUES WITH STANDARD DEVIATION BARS. I Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 155 APPENDIX G lOm^ transect abundance for December, 1977• Be m f N 0 o < 0 CO CM o CM M- CM CM CM O CM 0 9 X 1 - Q. O UI O CM #4 o m» 0 9 O I t CM 111 II n III III H i III II m m u t HI H IM I I n i n m i I il 11 HI O O o o O ? (l> w C ^UOTD A1ISN30 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 156 APPENDIX G (Cont.) lOm^ transect abundance for June, 1978. rT T i r i 11111 III III III Til III III 111 III III III III III II 00 fS o N 't w M N i I LI 11 I I I I I I I I I I i I I I I i I I I I I I i I I I I I I I I I ...... I n O o o V) CO M c ^uon AiiSNaa I Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 157 APPENDIX G (Gont.) lOm^ transect abundance for January, 1979. 0 9 U J CjUOTD A1ISW3Q Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX D SIZE STRUCTURE OF ASTERIAS VULGARIS FROM lOM^ TRANSECTS AT 8M, 18M AND ]0M. DATA POINTS ARE MEAN VALUES WITH STANDARD DEVIATION BARS. g I Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 159 APPENDIX D lOm^ transect size structure for December, 1977• I I I CWO ‘ 0'8 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 160 APPENDIX D (Gont.) lOm^ transect size structure for June, 1978. Ë;, I: k I CU0'0’ 8 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 161 APPENDIX D (Cont.) lOm^ transect size structure for January, 1979. — r - — r - — r — —T“ —T" — r ~ — r ~ —T“—T" 09 — (M - • 09 O 09 - 09 t N O - - M M - - W M - O - N 09 X 1 - Q. - - O UJ Q - N - - O - - 09 - - O * - w 1 1 1 1 1 1 1 1 1 o 3 o « o in ♦ (0 N w o cuo "o'eo 3ZIS i? Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX E ABUNDANCE AND SIZE STRUCTURE OF ASTERIAS VULGARIS FROM .25 m2 quadrats AT GOSPORT HARBOR AND MAIAGA GUT, THE ISLES OF SHOAIS, N .H ., AND NUBBLE LIGHT, YORK, ME. DATA POINTS ARE MEAN VALUES WITH STANDARD DEVIATION BARS. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 163 APPENDIX E Abundance of Asterias vulgaris at 8m and l8m at Gosport Harbor, the Isles of Shoals. ( 0 m o m c s N o w ' t CM M CM O CM CO X 1 - Q. o W a m4 CM «« O to e CM A I i_L l I I i I I I H > I I I H I H i i I I I I , I I I I I I I H > i , I , i I i I n t I > I 1 O tn o in o in N M #4 w C gWSZ"] A1ISKI3Q Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 164 APPENDIX E (Cont.) Size structure of Asterias vulgaris at 8m and 18m at Gosport Harbor, the Isles of Shoals. m CUOD 3ZIS Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 165 APPENDIX E (Cont.) Abundance of A sterias vulgaris at 8m, l 8m and 30m at Ifelaga Gut, the Isles of Shoals. TTT T T T T T CQ CM CO o CO 00 CM 40 CM CM CM CM d CM Q. 4 0 U J o CM O W 00 4 0 ♦ CM O <0 CM C SZ" ] AIISM3Q Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 166 APPENDIX E (Cont.) Size structure of Asterias vulgaris at 8m, iSm and 30m at Ifelaga Gut, the Isles of Shoals. 1 1 1 1 1 1 1 1 1 1 «0 N TO O TO TO TO TO TO TO TO TO O TO TO X —« F— • * CL TO UJ a Q TO o t - 4 - - TO - - TO - - - # - TO 1 1 1 !___ L__J ___ J____ L L l _ _J ____ TO m m M (MO) azis I Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 167 APPENDIX E (Cont.) Abundance of A sterias vulgaris at 8m and 18m at Nubble light, York, Me. , 1 , , , , ' t r r i-T T 'r i 1 1 T.T r m - - TO TO • • o <0 .. - 1 1 • 1 1 I • • t 1 I 1 1 O n o w O V) o w TO C j U S Z - D A i I S N 3 0 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 168 APPENDIX E (Cont.) Size structure of Asterias vulgaris at 8m and 18m at Nubble Light, York, Me. I I I CUOD BZIS Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I APPENDIX F I COMPARISON OF BIOMASS ESTIMATES OF ^ VULGARIS FROM THIS STUDY AND FROM MENGE (1979) I Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 170 APPENDIX F Comparison of biomass estimates of ^ vulgaris from t h i s stu d y and from Menge (1979). Based on the data of this study, a regression formula of lo g . w eight = - 1 + 2 .7 4 Log Length was obtained to estimate biomass of A. vulgaris. The regression formula of Menge (1979)* of Ln. weight = 1T66 + 2.0 Ln arm length was also used to obtain biomass estimates for ^ vulgaris. The results obtained by Menge's formula are an order of magnitude too high for this s p e c ie s . A. Biomass estimates based on the results of this study, for observed sizes and abundance of ^ vulgaris at the research s i t e . Depth X Size X Abundance Biomass est. P r2 8m 2.01 cm 9.93/.25m Z 6.7 7 0 9 g/.25m 2 .001 9 3 .8 I I8m .59 cm 29.33/.23mf .6894 g/.25m ^ I 30m 1.04 cm 8.33/.25m 2 .9250 g/.25m 2 -X B. Biomass e stim a te s based on th e form ula o f Menge f o r th e & same sizes and abundance of A. vulgaris. Depth X Size X Abundance Biomass est. p R^ 8m 2.01 cm 9.95/.25m2 212.18 g / . 25m2 .001 n o t 18m .59 cm 29.33/.25m^ 5 3 .6 2 g/.25m 2 g iv en 30m 1.04 cm 8.33/.25m2 4 7 .3 1 g/.25m 2 C. Actual blotted wet weights from selected samples Depth X S ize X Abundance Biomass 8m 2.02 cm 9 .2 /. 2 5 4 1 .4 9 g/.25mZ 1 .9 0 cm 3 . 6 / . 25m 3 .0 2 g/.25m ^ I8m .49 cm 21.8/.2$m 2 .88 g/.25m2 .69 cm 54.0/.25m 2 3 .2 0 g / . 25m2 30m .50 cm 10.0/.25m 2 .51 g/.25mZ .77 cm 12.0/.2$m 2 1.20 g/.25m2 * There is some question of the measurement used by Menge. His states that a ll measurements were from the madreporite to the opposite arm; the latter is a near measure to that used in this study. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX G MULTIPLE REGRESSION ANALYSIS WITH INTERACTION TERMS Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 172 2 2 APPENDIX G The .25m abundance data and the .25 m size data were also (see Tables IV-7 and IV-8) analyzed with a multiple regression model f which included interactive terms. The analyses presented here (Appendix g G) are identical to the analyses of Tables IV-7, and IV-8 with the addition of interactive variables. Independent variables can interact to affect a dependent variable and often the interactive effects overwhelm the total regression model. The result of large interactions may be to mask or decrease the significance of the relationships between . the prime inde pendent variables. In this study the results of the regression analysis with and without the interactive terms are essentially the same. The interactive variables do not add to the predictive value of the resultant regression equation 2 since the r values are similar. Non-Interactive Model Interactive Model .25m^ abundance r^ = .350 r^ = .359 .25m^ s iz e r^ = .692 r^ = .700 The resultant T-values for the comparisons between variables change slightly when the interactive variables are added to the model, but the changes are small and can easily be explained biologically as the results of winter temperatures on population abundance and size (see also Table IV-11). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. X/J appendix g (cont.); Multiple regression analysis of .25m quadrat abundance of data with interaction variables. M o d e l : Y = 8q + 3^x^ + GgX? + G 3X3 + 813X1X3 + 623 * 2X3 G R e s u l t s ! Log Y + 1 = .908 - .0353X^ + .444 X^ - .0441 X^ + .203 X-X_ + .40 XgX. Variable Coefficient STD. DEV. of Coef. T-RATIO (c o e f./S .D .) Y .908 .111 -.0 3 5 .119 -.30 NS *1 .444 .128 3.47*** *2 -.0 4 4 .122 -.3 6 NS *3 .203 .138 1.48 NS I *1*3 .140 .152 .92 NS *2*3 ANOVA Table Source d . f . 85 MS = S S /d .f. F R^ Regression 5 8.0162 1.6032 23.58*** 35.9% Residual 165 14.3174 .0868 Total 167 22.3335 *** = P < .001 ; NS = n o t significant a Log (Y + 1) transformation was used for all data to eliminate heteroscedasticity of the variances and the residuals were plotted to graphically check conformance to this assumption of the tests. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 174 appendix g (cont.)î Multiple regression analysis of .25m quadrat size data with interaction variables.^ Model: Y = 3q + + 62 X2 + ^3X3 + 813X1X3 + 323X2%3 + B Results: Log Y + 1 = .270 + .203X^ -. 0504X2 + . 0359X3 -. 0399X^X3 -.OSOlXgXg Variable Coefficient STD . DEV. o f Coef. T-RATIO (c o e f./S .D .) I Y .270 .0298 .203 .0324 6.25*** "1 -.0 5 0 .0340 -1 .4 8 NS "2 .036 .0327 1.10 NS S -.040 .0372 -1.07 NS % -.0 8 0 .0404 -1 .9 8 * % P. ANOVA Table Source d.f. SS MS = SS/d.f. F Regression 5 2.28787 .45751 73.68*** 70.0% Residual 158 .98098 .00621 Total 163 3.26885 *** = P < .001 ; NS = not significant ^a Log (Y + 1) transformation was used for all data to e lim in a te heteroscedasticity of the variances and the residuals were plotted to graphically check conformance to this assumption of the tests. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.