MARINE ECOLOGY - PROGRESS SERIES I Vol. 1.81-89. 1979 1 Published July 30 Mar. Ecol. Prog. Ser. I l

The Marine Life of an Offshore Oil Platform*

A. Wolfson', G. Van Blaricom2, N. Davis3 and G. S. Lewbe14

' International Biological Consultants, 819 DeWitt Avenue, Encinitas, California 92024, USA U.S. Fish and Wildlife Service, Piedras Blancas Station, San Simeon. California 93452. USA Chambers Consultants and Planners, 10557 Beach Blvd., Santon, California 90680, USA L G L, Ltd., 1122 Silverado Avenue, La Jolla, California 92037, USA

ABSTRACT Our research at Union Oil Platform EVA, off Huntington Beach, California, USA, was aimed at understanding how man-made offshore structures function as artificial reefs and how they modify the surrounding marine environment Underwater surveys were conducted to detern~lne (1) the distribution, standing stock and productivity of attached fouling organisms, (2) the density, size-structure, and biomass of eplbenthic populations beneath the platform, and (3)the abundance, species composition and distribution of eplfaunal and infaunal benthos as a function of distance away from EVA The platform substructure is overgrown with dense clumps of sea mussels An estimated cubic meter of mussels falls from the platform each day, supporting extraordinary densities (29 m-') of sea stars on the bottom Sea stars are prevented from climbing up onto the platform by bands of stinging sea anemones on EVA s base The adjacent sand community is strongly influenced by EVA s presence with densities of some species greatly enhanced and others significantly reduced by proximity to the structure A trophlc model of dominant fauna1 elements in the oil platform ecosystem indicates high productivity and turn-over rates for the attached community

INTRODUCTION underlying benthic ecosystem has received relatively little attention. Our interest in extending research in Permanent offshore structures for oil and natural gas this direction was motivated by the discovery of an production are an expanding feature of the coastal extraordinary congregation of sea stars beneath Union marine environments of the world. These installations Oil's production platform EVA in southern California, are a focus of intensive public interest and concern, USA. A general review of oil effects on marine organ- particularly since the blowout and oil spill at Platform isms will appear in Volume V of 'Marine Ecology'. 'A' in the Santa Barbara Channel, California, in 1969. Our study at Platform EVA (three km offshore of The soaring rates of petroleum consumption by indus- Huntington Beach, California; latitude 33"401N, lon- trialized nations have stimulated exploration and plat- gitude 118"93' W) had two primary goals: (1) to form construction in remote and physically hostile describe and explain distributional patterns in benthic locations such as the North Sea and Beaufort Sea, populations on and near the platform, and (2) to illus- while existing production fields in southern California trate the potential utility of platforms such as EVA for and the Gulf of Mexico are being rapidly expanded. quantitative biological research. We describe here the Most offshore platforms are placed on soft-sediment animal community attached to EVA, the sea stars on bottoms, forming artificial reefs which provide attach- the platform, the assemblage of large echinoderms ment sites for marine life and vertical relief attractive living below the platform, and the epifaunal and to fishes. Algal spores and invertebrate larvae rapidly infaunal communities of the adjacent soft bottom. colonize submerged portions of platform structures, Descriptive data are used to estimate the standing establishing a 'fouling' assemblage which provides stock and productivity of the fouling community and to food and shelter for associated fishes. Previous studies model trophic relationships between the attached com- of oil platform ecology have concentrated on describ- munity and the benthic echinoderm aggregation. ing these fouling communities and fish populations (Carlisle et al., 1964; George and Thomas, 1975; Meams and Moore, 1976; Sonnier et al., 1976; Wolfson, MATERIAL AND METHODS 1976). The influence of platform presence on the Platform EVA, constructed in 1964 on a fine sand ' A contribution from International Biological Consultants, bottom (depth 18 m), is typical of offshore oil platforms 819 DeWitt Avenue, Encinitas, California 92024, USA. in southern California. Production facilities are located 82 Mar. Ecol. hog. Ser., 1, 81--89, 1979

on several steel decks supported by 12 vertical legs Estimates of echinoderm standing stock were made bridged by horizontal, oblique, and vertical cross in the following way. Large random samples of ani- members. Oil well encasement shafts descend from the mals were collected from beneath EVA, drained, western half of the platform into the bottom. The weighed, and measured to derive size/weight rela- exposed surface area of all submerged legs (0.84 m tionships for each species. Using these relationships, mean diameter), cross braces (0.32 m dia.), and well size-frequency histograms produced from transect cen- casings (0.51 m dia.) totalled about 4600 m2 at installa- sus data were converted to weight-frequency histo- tion. grams, from which standing stock biomass estimates All data and samples were collected by the authors were computed for the total population of each species during a series of SCUBA dives in December 1975 and under the platform. June 1976. The volume of fouling bivalves (mostly sea Finally, the thickness of the accumulation of mussel mussels Mytilus spp.) on the support structure was shell debris on the sea floor was estimated by compa- estimated by measuring circumferences of columns ring readings of diver-held depth gauges on the bot- and braces. Twenty-five measurements were made at tom under EVA with similar readings on adjacent sand various depths on legs, cross braces, and well encase- bottoms and with charted bathymetry at the EVA site ment shafts. Net volume of sea mussels was computed prior to its installation. by subtracting the volume of the support columns at installation from the estimated total volume derived from our circumference measurements. RESULTS AND DISCUSSION Sea stars living on EVA were censused in randomly selected areas, including four vertical legs (242 m2 The Fouling Community surface area) and 28 horizontal braces (402 m') at various depths. From roughly the mean tide level to within a few Species abundance and size-frequency distributions meters of the sea floor, the submerged support struc- of epibenthic biota were assessed in band transects ture and well casings of EVA were thickly fouled by located: (1) directly beneath EVA, (2) beginning at the the mussels Mytilus californianus and M. edulis, in an edge of the platform and extending away from EVA, approximate ratio of abundance of 1:4 (respectively). and (3) in a comparison area 300 m east of the platform. All size classes, ranging from 0.2 cm to 25.0 cm maxi- Transect surveys were made by placing a weighted, mum valve length, were represented. The complex marked line on the bottom and censusing animals matrix of shells and byssal threads formed by the within either 0.25 m or 0.5 m of the line. In every case, mussel clumps provides an important source of secon- counts and size measurements were made on each side dary space and shelter for other fouling species on of the line. EVA (Wolfson and Parr, 1975). The degree of encrusta- Core samples were collected along a 100 m transect tion of mussel shells by other fouling organisms which began 10 m east of the edge of the platform, at appeared to increase with depth. the point where debris from EVA's fouling community The space dominance by Mytilus spp, ends a few no longer covered the sand bottom. At eight stations meters above the bottom. The remaining primary along this transect running eastward from the platform, space is covered by densely-packed individuals of a two cores were collected, along with two (ca. 100 ml) small sea anemone Corynactis californica. This band of sediment samples for analysis of grain size distribution anemones at the base of the platform legs may be and organic carbon content. The coring device was a important in maintaining the structure of the mussel- diver-manipulated metal cylinder which sampled to a dominated community above it. Our data (see below) depth of 12 cm, with a surface area of 0.018 m2. Core show that densities of Pisaster spp. (asteroids which contents retained by a 0.5 mm mesh sieve were fixed in feed voraciously on mussels) are markedly lower on formalin, then stored in -40 "0 isopropanol. Infauna the platform itself than on the bottom beneath it. The were separated from debris, identified, and counted mussel populations on EVA include high densities of under a dissecting microscope. Sediment grain size size classes which Pisaster spp. are able to consume distributions were determined by passing dried sub- (Landenberger, 1968; Feder, 1970; Paine, 1976a). We samples of sand through a graded series of sieves, then believe that the band of anemones prevents migration weighing the fraction retained by each sieve. Sedi- of sea stars from the bottom onto the structure. This ment parameters were determined from these data by could explain the unexpectedly low density of sea stars graphical techniques (Inman, 1952). To measure orga- up on the platform, and account for the spatial domi- nic content, sediment subsamples were treated with nance by Mytilus spp. of subtidal areas from which 0.1 N HC1 to remove carbonate, then burned in a Leco they might normally be removed by Pisaster spp. pre- induction furnace carbon analyser. dation (Paine, 1966, 1974). Similar patterns of subtidal Wolfson et al.: Offshore 011 platform marine life 83

dominance by mussels occur on natural rock substrates cucumbers (Parastichopus parvirnensis and Parasticho- which lack the necessary recruitment habitat for pre- pus californicus) during the initial survey (December datory sea stars, or are exposed to heavy wave shock or 1975). Resurveys of selected transects in June 1976 strong tidal currents which restrict sea star foraging suggested that the December data were representative (Chan, 1973; Paine, 1976b). The anemone C. califor- of long-term densities of epibenthic animals. nica, plays a comparable role in influencing structure and zonation of pier piling communities near Santa Table 1. Echinoderm density and biomass estimates for ben- Barbara, California (Landenberger, 1967), and in an- thic populations below Platform EVA. Density estimates for other bivalve-dominated (Charna pellucida) commu- the two most abundant sea stars are based on average density nity at Santa Catalina Island, California (Vance, 1978). in two 0.5 X 5.0 m transects located on the bottom below the eastern and western halves of the platform. Estimated popula- The mechanism of Pisasterspp. repulsion by C. califor- tion densities for the other echinoderms are based on counts nica has not been demonstrated, but appears to involve from a 1.0 X 27.0 m transect which covered more of the area sensitivity of the sea star's tube feet to the stinging below the platform, providing better estimates for less com- nematocysts of the anemone. mon species Only two species of asteroids were present on the support structure of EVA: Pisaster ochraceus (average Species Density Total Biomass density 0.25 m-'), and Pisaster giganteus (0.1 m-2). (No m-2) number (kg) Their numbers are probably limited by dislodgement during storms and by the anemone barrier to immigra- Pisaster brevispin us 18 11.500 10.275 tion by benthic populations. Some of the sea stars on Pa tiria rninia ta 9 6,000 750 EVA may have settled onto the platform as larvae, and Pisaster ochraceus 1.5 1,000 4.000 Pisaster gigan teus 0.4 250 1.500 have grown to large sizes feeding on the essentially Pycnopodia helianthoides 0.3 200 200 unlimited supply of mussels. These two asteroids Demasterias imbricata 0.03 20 showed marked vertical stratification on EVA; P. ochraceus predominated in the upper three to five Total asteriods: 29 18,970 16,725 meters, while P. giganteus was more common below, Parastichopus spp.: 8 5,000 1,075 corresponding to the natural situation in rocky areas Total echinoderms: 37 23,970 17,800 where P. ochraceus is mostly intertidal and P. gigan- teus is almost exclusively subtidal. The general features of the subtidal fouling commu- In our combined research diving experience in nity of EVA are comparable to those of other artificial coastal habitats of Pacific North America (3000 dives marine habitats, including pier pilings (Landenberger, total), we have observed no asteroid aggregation even 1967), jetties (Haderlie, 1968), and other oil platforms approaching the density (29 m-') under platform EVA. (Carlisle et al., 1964; Shinn, 1974; Mearns and Moore, Pisaster giganteus is the most common asteroid of the 1976). rocky subtidal zone of southern California (Hopkins and Crozier, 1966). We have recorded maximum densities for this species of 0.23 individuals m-2 in La Benthic Epifauna Jolla, but a more typical density is 0.01 m-2 beneath kelp beds (Rosenthal et al., 1974). The density of P. The substrate beneath and adjacent to EVA has been giganteus under EVA (0.4 m-') represents a two to completely altered by biological 'fallout' from the plat- forty-fold increase over reported natural abundances. form's fouling community. The bottom was covered The aggregation of P, brevispinus is particularly with mussel shells, barnacle tests, and other biologi- dramatic. The highest density of P, brevispinus we had cally derived material. This pile of debris was occu- previously recorded occurred on an artificial reef at 14 pied by extraordinary numbers of sea stars, which were m depth off Torrey Pines State Park, California, where feeding on mussel clumps containing live individuals heavy recruitment of this species apparently occurred that had apparently fallen from above. Sea star densi- in July 1975. Densities on this reef (0.68 m-2) were 30 ties were so high that animals often were literally arm- times less than those found under EVA (18 m-2). Pisas- in-arm, completely obscuring the underlying sub- ter ochraceus is not commonly found subtidally in strate. Near freshly-fallen mussel clumps, sea stars southern California, making its high density (1.5 m-*) were regularly found piled several animals deep. quite remarkable. The presence of approximately 200 Extrapolation from transect data (Table 1) indicates Pycnopodia helianthoides below EVA is also notewor- that roughly 19,000 asteroids (wet weight 16.8 metric thy. This carnivorous, multi-armed sea star, an abun- tons) were concentrated in the 24 m by 27 m area dant and important component of nearshore rocky bot- beneath the platform, along with about 5000 sea tom ecosystems in the northwestern United States 84 Mar Ecol. Prog. Ser., 1, 81-89, 1979

(Mauzey et al., 1968), is seen only rarely elsewhere in prefer rocky bottoms (Hopkins and Crozier, 1966), southern California, and small individuals (common although P. brevispinus and Patina miniata will read- under EVA) are even more unusual to find in natural ily cross soft substrates. Pisaster ochraceus and Pisaster situations. giganteus occasionally traverse soft bottoms but Platform EVA is located approximately 10 km from appear to do so with reluctance. Colonization of the the nearest natural hard substrate. All asteroid species platform area by these last two species may have taken under the platform, with the possible exception of place by larval settlement and/or transport of adults on Pisaster brevispinus and Pycnopodia helianthoides, mats of dislodged algal material moved across the bottom by surge and currents (Fager, 1971). pp~pPISASTER BREVISPINUS Another unusual feature of EVA's sea star aggrega- 1 N= 106 tion was the presence of individuals of each species spanning a wide range of size classes (Fig. 1). Paine (1976a) reports that Pisaster ochraceus populations in different areas of the rocky intertidal of Washington are characterized by one dominant size class and that at higher densities, the mean individual size is smaller. Under EVA, we not only observed a high density of sea stars with a wide size range within each species, but SlZE (cm) unusually large individuals of each species of asteroid were present. Results from 0.5 m by 50 m band transects directed away from the edges of the platform (Fig. 2) indicated "[ PISASTER OCHRACEUS 15 -- N=65 m that the bat star Patiria miniata was the dominant asteroid on the bottom adjacent to EVA. Bat star density declined rapidly with distance from the plat- form edge, approaching zero at 40 to 50 m. Unlike other asteroids associated with EVA, bat stars will consume detritus and are therefore able to feed on particulate organic matter falling from EVA's support complex. The other sea stars under EVA probably SlZE (cm) require direct access to live mussel clumps, relatively few of which fall beyond the platform perimeter. None of the large echinoderms observed under or near the platform was found along the 1 m by 25 m comparison area. The only asteroid present was the sand star Astropecten verrilli (21 individuals in 25 m'), a common resident of nearshore sand bottoms in south- ern California.

1111~111111111In summary, these data on benthic echinoderm 0 3 6 9 12 15 18 21 24 27 30 33 36 39 populations beneath EVA indicate that sea star SlZERANGE (cm) densities are approximately three orders of magnitude 60 - greater than natural levels in the surrounding area, PATlRlAMlNlATA and that platform-associated species are not typical N=185 residents of the sand substrate upon which EVA was 45 - -- >0 constructed. z :m- - B E The Sand Community 15 - The mean grain diameter of sand samples declined 0111 I1 0123456789101112 from a high value of 170 microns at the edge of the SlZE (cm1 shell pile below EVA to 88 microns at 20 m from the shell accumulation, beyond which the grain size com- Fig. 1. Size [arm radius]-frequency distribution of asteroid species below Platform EVA. Size range only shown for the position remained essentially constant (Fig. 3). The two least abundant species samples from the shell pile edge and 5 m distant W.2 tn: 0 2 6 W> '- m E 0, .E B ,- z g P E z gg m .$! E" 2 2 tn- S 2 .2 0 EC ;Z 4 2 >; m '=',Q) E 'G; !$ .g $5 8 ,; g cam

C)m>a 2 .S .G 55ig .- Q) > 3 X -4 - 4 tn 4- .z 2 .k! c :q'$8 4 ;.g :Em .2 z 0E'

FQ)Q) 0 mu 5 E .M 5 a 2 3 2 0 3m% 8 5 .Mui .S !$ 2 -z m E tS 2 2 a 8 Q) S V] a c4 2

Wolfson et a1 : Offshore oil platform marine life 87

pulchrum, is also suspected to occasionally feed on distribution are evident from these data: (1)an appa- sand stars. During dives at EVA we observed groups of rent positive response to the presence of platform EVA, P. furcatus and P. nebulifer foraging on the sand bot- (2) an apparent negative response to platform pre- tom as far as 45 m from the edge of the platform. All sence, and (3) no discernible response. Among three species of fish were abundant among the sub- polychaete species found at all eight sampling sta- merged legs and braces of EVA. Predation by these tions, the seven most abundant were tested for correla- fishes may be responsible for the reduced densities of tion of abundance with distance from EVA (Kendall's sand stars near the platform. Tau). Three species exhibited a significant (p 0.01) Infauna collected in the core samples included a negative correlation, while one species showed a sig- total of 106 species, with numerical dominance by nificant positive correlation. polychaetous annelids (47 species). The remainder Positive and negative responses were not confined to were primarily peracarid crustaceans and bivalve and the polychaetes. For example, the pelecypod mollusc gastropod molluscs. Most of the infaunal species found Tellina modesta is rare near EVA, but showed a sig- in the core samples were deposit feeders, but other nificant increase with distance (Tau =-0.49, groups (suspension feeders, scavengers, carnivores) p < 0.01). An unidentified brittle star (family were also represented. A full description of the com- Amphiuridae, all individuals too small for generic plex abundance patterns of these species would be identification) was the most abundant of all the lengthy and is, therefore, not included here. Using infauna at the edge of the shell pile (mean density selected polychaetes as an example, summary data are 3100 m-2), but its numbers declined sharply along the presented which illustrate the prominent patterns dis- transect (400 m-2 at 100 m) (Tau = + 0.511, p < 0.01). played by species in all taxa (Table 2). Three types of It is likely that at least some of the positive and nega-

Table 2. Presence (+) of selected polychaete species in benthic core samples as a function of distance from Platform EVA

Species Distance (m) 0 5 10 20 30 50 75 100

Capitita ambiseta Hartman, 1947 Pherusa neopapillata Hartman, 1961 Eteone californica Hartman, 1936 Eteone dilatae Hartman, 1936 Armandia bioculata Hartman, 1938 Dorvillea articulata (Hartman, 1938) Asychis disparidentata (Moore, 1904) Ampharete labrops Hartman, 1961 Amaeana occidentalis (Hartman, 1944) Anaitides spp. Goniada brunnea Treadwell, 1906 Diopatra ornata Moore, 1911 Mediomastus spp. Nereis spp. Chaetozone setosa Malmgren, 1867 Lumbrineris sp. Spiophanes bombyx (Claparede, 1870) Haploscoloplos elongatus (Johnson, 1901) Chone gracilis Moore, 1906 Harmothoe sp. Aricidea neosuecica (Hartman, 1965) Gyptis arenicola glabra (Hartman, 1961) Glycera sp. Nephtys cornuta franciscana (Clark, 1955) Paraprionospio pinnata (Ehlers, 1901) Nothria elegans (Johnson, 1901) Tharyx sp. Axiothella rubrocincta (Johnson, 1901) Laonice sp. Glycinde sp. Thalenessa spinosa (Hartman, 1939) Pista sp. Typosyllis armilaris (Miiller, 177 1) 88 Mar Ecol. Prog. Ser , 1, 81-89, I979

tive responses to platform presence relate to higher- since dead shells compact, occupying less volume than order competitive, predatory, and larval recruitment live animals, and significant mussel fallout probably interactions whose results are sensitive to the proxim- did not begin for at least a year after EVA's emplace- ity of a large structure such as platform EVA. Control- ment. If a compaction of 20 "/" is assumed, and a delay led field experiments would be required to determine of one year is allowed before commencement of sig- the relationship between such physical and biological nificant fallout, the resulting productivity estimate factors and observed distributional patterns. increases to 96.8 kg wet mussel biomass day-', which is within a factor of two of the productivity estimate by the first method. The volume of live mussels equiva- A Trophic Model lent to 96.8 kg and 167 kg of wet tissue biomass is calculated to be 1.07 m3 and 1.85 m3, respectively. The The benthic animal communities associated with volume of live mussels on EVA is approximately platform EVA have organizational features which 617 m3. The annual loss of mussels via fallout to the facilitate modelling of quantitative trophic relation- bottom is thus estimated by the two computation

ships. The primary consumer biomass is dominated by methods at 63 O/O and 109 V,,of the standing crop on the two species of mussels which remain fixed in time and platform. To maintain steady state, then, the attached space. Virtually all of the export of primary consumer mussel population must replace itself every 11 to 18 biomass occurs in a known direction (downward to the months. bottom) where it is consumed by primary carnivores While recognizing the simplifying assumptions with few available alternative sources of nutrition. inherent in this model, we believe the energy budget Beyond metabolic loss, there is probably little export of derived for platform EVA represents a good first carnivore biomass away from the platform area. Thus approximation of rates of turnover and consumption in the oil platform associates at EVA form a trophic sys- this system. Certain key interactions may be of para- tem which is relatively simple, physically localized, mount importance in determining these rates. For and has few pathways for energy loss and material example, the repulsion of Pisaster spp. by Corynactis transport. californica, a simple behavioral interaction which The high densities of sea stars under EVA are evi- requires little energy transfer, probably prevents sig- dence of an impressive primary consumer productivity nificant reduction of the mussel populations by preda- 11y the attached mussels. We have estimated fouling tion. If the anemones were not present, the major community productivity in two ways. First, we have pathway of energy transfer would probably shift from determined that the five most abundant asteroid consumption of fallen mussels on the bottom to direct species on the bottom form 16,725 kg of wet live predation by sea stars on the platform support struc-

biomass. Assuming a mean sea star feeding rate of l "/D ture. This hypothesis could be readily tested by con- of body weight day-' (Feder, 1970), the sea star popu- trolled field experiments involving manipulation of lation will require about 167 kg of wet (tissue) Mytilus anemone densities. spp, biomass day-'. If mussel fouling biomass is We have found the offshore oil platform environment assumed to be at steady state (as it has appeared well-suited to the study of marine benthic ecosystems. visually on repeat visits to EVA), 167 kg wet biomass These structures harbor a variety of community types, day-' becomes the estimate of primary consumer pro- in close proximity, which appear in many cases to ductivity. The second method involves an extrapola- constitute closed, virtually self-contained systems. In tion based upon the volume of the shell pile beneath the brief duration of our field work at platform EVA, the platform. The mean depth of the shell pile is 3 m, we have found a number of interesting distributional tapering to zero at a distance of 16 to 21 m from the patterns which seem amenable to analysis by field platform perimeter. From these data the volume of the experiment. To the extent that the results of such pile is estimated at 3115 m". If steady state conditions programs can be applied to natural ecosystems, have existed since installation, the mean accumulation research on offshore platforms holds the promise of rate has been 283 m3 year-', or 0.78 m3 day-'. This contributing to the advancement of ecological theory. daily rate is equivalent to 12 kg Mytilus spp. dry In response to ovenvhelming economic pressures, the weight, excluding shells (Harger and Landenberger, numbers of offshore production facilities are likely to 1971), or 70 kg wet weight (Menge, 1972). This last increase dramatically. in the near future. Marine estimate involves two assumptions: (1) One m3 of live ecologists should c~nsideroil platforms as a useful mussels produces one m3 of shell debris, and (2) no resource for the study of patterns and interactions time was required following the construction of EVA among marine plant and animal populations. for the fallout rate to stabilize at its average value. These assumptions are overly conservative, however, Wolfson et a1 . Offshore oil platform marine llfe 89

Acknowledgements. This research was sponsored by the Landenberger, D. C. (1968). Studies on selective feeding in International Biological Consultants Research Fund. Struc- the Pacific starfish Pisaster in southern California. tural information and logistical support on EVA were gra- Ecology, 49, 1062-1075. ciously provided by K. Guziak and E. J. Schmidt, Union Oil Mauzey, K.P.. Birkeland. C. and Dayton, P. K. (1968).Feeding Company of California. behavior of asteroids and escape response of their prey in the Puget Sound region. Ecology, 49, 603-619. Mearns, A. J. and Moore, M M. (Eds.) (1976). Biological Study of Oil Platforms Hilda and Hazel, Santa Barbara Channel, California, Final Report. Institute of Marine LITERATIJRE CITED Resources, Scripps Institution of Oceanography, La Jolla, California. Carlisle. J. G. Jr., Turner. C. H. and Ebert, E. E. (1964). Menge, B. A. (1972). Foraging strategy of a starfish in relation Artificial habitat in the marine environment. Bull. Dep. to actual prey availability and environmental predictabil- Fish Game St. Calif., 124, 1-93. ity. Ecol Monogr., 42, 25-50. Chan, G. (1973). Subtidal mussel beds in Baja California, with Paine, R. T (1966). Food web complexity and species a new record size for Mytilus californianus. Veliger, 16, diversity. Am. Nat., 100, 65-75. 239-240. Paine, R. T (1974). Intertidal community structure: experi- Davis, N. D. (1978). Studies of the southern California near- mental studies of the relationship between a dominant shore sand bottom community. Ph. D. thesis, University of competitor and its principal predator Oecologia, 15, California, San Diego. 93-120. Emerson, R. R. (1976).The biology of a population of Diopatra Paine, R. T (1976a). Size-limited predation: an observational ornata at Santa Catalina Island, California. Ph. D. thesis. and experimental approach with the Mytilus-Pisaster University of Southern California. interaction. Ecology, 57, 858-873. Fager, E. W. (1971). Pattern in the development of a marine Paine. R. T. (197613). Biological observations on a subtidal community. Limnol. Oceanogr., 16, 241-253. Mytjlus californianus bed. Veliger, 19, 125-130. Feder, H. M. (1970). Growth and predation by the ochre sea Rosenthal, R., Clarke, W and Dayton, P. (1974). Ecology and star, Pisaster ochraceus, in Monterey Bay, California natural history of a stand of giant kelp, Macrocystic pyri- Ophelia, 8, 161-185. fera, off Del Mar, California. Fjsh. Bull. U. S., 72, 670-683. George. R. Y and Thomas, P. J. (1975). Aspects of fouling on Shinn, E. A. (1974). Oil structures as artificial reefs. In L. offshore oil platforms in Louisiana shelf in relation to Colinga and R. Stone (Eds), Proceedings of an Interna- environnl.enta1 ~mpact.Gulf University Res. Consort. Off- tlonal Conference on Artificial Reefs. Texas A and M. shore Ecological Investigations. G.U.R.C. Contract University (SA - 74-103). pp. 91-96. NO. 853.1-12. Sonnier, F., Teerling, J. and Hoese, H. D. (1976). Observations Haderlie, E. C. (1968).Marine fouling and boring organisms on the offshore reef and platform fish fauna of Louisiana. in Monterey harbor Veliger, 10, 327-341. Copeia, 1, 105-111. Harger, J. R. E. and Landenberger. D. E. (1971). The effects of Vance. R. R. (1978). A mutualistic interaction between a storms as a density dependent mortality factor of sea sessile marine clam and its epibionts. Ecology, 59, mussels. Veliger, 14, 195-201. 679-685. Hopkins, T. S. and Crozier, G. F. (1966). Observations on the Wolfson, A. (1976). Submerged platform structure com- asteroid echinoderm fauna occurring in the shallow water munities. In A. J. Mearns and M. M. Moore (Eds), Biologi- of southern California. Bull. Sth. Calif. Acad. Sci., 65, cal Study of Oil Platforms Hilda and Hazel, Santa Barbara 125-145. Channel, California, Final Report, Institute of Marine Inman, D. L. (1952). Measures for describing the size distribu- Resources, Scripps Institution of Oceanography, La Jolla, tion of sediments. J. sedim. Petrol., 22, 125-145 California. pp. 3844. Landenberger, D C (1967).A study of predation and predat- Wolfson, A, and Parr, T. (1975) The marine life of offshore oil ory behavior in the starfish, Pisaster. Ph. D. thesis, Uni- drilling platform EVA. Marine Ecological Consultants of versity of California, Santa Barbara. southern California. Tech. Rep. No. 75-11

This papel was presented by Dr. N. D. Holland, it was accepted for printing on May 21, 1979