Erect Bryozoans Research Articles

Sediment accumulation in a shallow-water meadow carpeted by a small erect bryozoan

Abstract A marine meadow covered 80–90% by a turf of the erect bryozoan Cellaria occurs over an area >104 m2 west of Banjole Island (Croatia) in the northeastern Adriatic Sea. Surrounding areas are bare to patchily covered by isolated clumps of bryozoans, sponges, and ascidians attached to scattered shell and rock debris. Silt and clay comprise >90% of the mass of sediment within the meadow, and Cellaria branch fragments are the next-most-abundant component. From 13-cm to at least 25-cm depth in the meadow sediment coralline algal branch fragments are abundant, and silt and clay comprise over 50% of the sediment's mass. In contrast, sediment accumulated in the bare area adjacent to the meadow is predominantly coarse carbonate sand composed of diverse skeletal grains. Mud comprises Concentration of mud in the sediment below the meadow apparently is due primarily to baffling by the erect bryozoans and earlier by the coralline algae, because composition and texture of the muds and fine sand are identical within and outside the meadow. The proportion of bryozoan skeletal fragments to mud in the upper sediment is similar to that of erect delicate bryozoans to sediment in shallow ramp buildups of Late Ordovician age in the southern Appalachians and of fenestrate bryozoans to mud plus cement in bryozoan-rich cores of Carboniferous mounds. The Paleozoic mounds also are surrounded by coarser sediment. By analogy with the Cellaria meadow, trapping and deposition of muds by erect bryozoans can be inferred for many of these Paleozoic mounds, even though bryozoans are a relatively small proportion of the total sediment.

Macrofouling community structure in Kanayama Bay, Kii Peninsula (Japan)

An investigation on the macrofouling community in Kanayama Bay, Kii Penin­ sula, Japan was undertaken from June 1994 to May 1995 by exposing fiber reinforced plastic (FRP) panels at subsurface and bottom (2.2 m) depths. The composition and abundance of fouling organisms were monitored at monthly intervals. Fortnightly variations in hydrogra­ phic parameters were also noted simultaneously. The fouling community at this bay was a complex assemblage of bryozoans, ascidians, polychaetes and barnacles comprising more than 40 species. The faunal elements exhibited distinct seasonal trends in abundance closely associated with fluctuations in temperature, i.e. maximum abundance was recorded in summer and the reverse in winter. Greater faunal abundance was generally observed on the subsurface panels. Significant depth wise variation in abundance seems to be the result of predation, competition and the effect of residents on recruits. Succession in the community was divided into three stages by dendrogram analysis. First stage was characterized by polychaetes (Protohydroides elegans and Dexiospira foraminosa) on panels from both depths. The encrusting bryozoan, W atersipora subtorquata dominated on the subsurface panels and a mixed dominance of W. subtorquata, barnacles, P. elegans and the ascidian, Polyclinum constellatum, on bottom panels in second stage. Third stage was characterized by a mixed dominance of W. subtorquata, Bugula neritina (an erect bryozoan) and P. constellatum at the subsurface and B. neritina at bottom depths.

Do life patterns differ between two Scotia Arc localities? A preliminary investigation of three erect Antarctic bryozoan species

Erect bryozoans are extremely abundant and diverse in polar waters and individual species may span a wide range in latitude and bathymetry. A number of aspects of lifestyle, including polypide recycling, embryo production, distribution, growth form and epibiosis were compared in three species of erect byozoans. These were collected from two locations; Signy Island (60°S) and Rothera Point, Adelaide Island (68°S) and a variety of depths. All three species were in similar stages of polypide cycling within and between the two sites. In the species Isosecuriflustra rubefacta and Nematoflustra flagellata the rate of brown body production (polypide generations) was slower at Signy Island than at Rothera Point. There was little difference between localities (within species) in the pattern of embryo production and no change in embryo size with depth. Embryos of I. rubefacta, however, were significantly larger at Rothera Point than at Signy Island. The proportion of the community occupied by each species changed with depth, but all three species occurred in shallower water at Rothera Point than at Signy Island. Fouling by epibionts decreased with increasing depth and from Signy Island to Rothera Point, both in terms of per cent cover and number of colonizing taxa. Possible trends with depth and latitude are compared with other studies involving bryozoans. The literature on Antarctic benthic taxa, in general, is also considered to determine whether trends within the Bryozoa are reflected in other groups.

Biomechanics and mass mortality of erect bryozoans on a coral reef

The bryozoan Cigclisula sp., is a heavily calcified erect species which occurs abundantly in the shallow sublittoral coral reef at Quilaluia Island, Quirimba Archipelago, northern Mozambique. It grows in an arborescent bilaminate form termed adeoniform on the undersides of coral heads or other available bioconstructed hard substratum. The geography and bathymetry of the area results in periodic high and complex current regimes often carrying water borne debris. If this periodic force overcomes the structural integrity of Cigclisula sp. either the outermost branches break or the colony topples at the base. The local population was dominated by young individuals: nearly 40% of the sample population had ten branches or fewer and less than 10% had more than 50 branches (these could be ascertained as young due to the lower proportion of damaged colonies with ≤10 branches; Figure 1). The only size group with no damaged specimens (branch breakage) were those with ≤5 branches. The mean proportion of branches broken significantly increased with increasing colony size. After one year a population of Cigclisula sp., initially comprising 30 colonies (encompassing the entire size spectrum of colonies), consisted of just one small specimen.

Seasonality of polypide recycling and sexual reproduction in some erect Antarctic bryozoans

The seasonality of polypide cycling has been investigated for three species of erect bryozoans from Antarctica: Isoseculiflustra rubefacta (Kluge, 1914), Nematoflustra flagellata (Waters, 1904) and Himantozoum antarcticum (Calvet, 1905). Approximately ten colonies of each species were collected monthly by SCUBA divers over a 14 mo period during 1992/1993, and the status of each individual zooid was classified as differentiating/regenerating, active (feeding autozooids), degenerate (brown body) or sexually reproductive (ovicells present, or zooid containing a larva). Polypide cycling in all three species was distinctly seasonal. New zooids formed at the growth margin and typically contained actively feeding polypides for ≃9 mo before these polypides degenerated into brown bodies in the austral winter (June). Very few polypides were active in the period from June to August, when water-column food levels were at their lowest; after this period new polypides differentiated. Individual zooids typically underwent a total of five (I. rubefacta and N. flagellata), or at least four (H. antarcticum) complete polypide cycles before becoming senescent. Polypide lifetimes generally became shorter as the age of the zooid increased. Sexual reproduction was also distinctly seasonal in these species, with bands of ovicells or sexually reproductive zooids being formed each year in late summer once a given colony had grown to a threshold size (or age). Larvae were then brooded for ≃10 mo before being released in January/February (N. flagellata) or February/March (H. antarcticum). The seasonal patterns of polypide cycling are related clearly to the variations in food availability, and these species appear to have the longest zooid lifetime (≃5 yr) and the slowest polypide cycling (once per year with polypide lifetimes up to 10 mo) reported for any bryozoan so far.

Epibiont communities: Recruitment and competition on North American Carboniferous brachiopods

Shell-encrusting assemblages have uniquely high ecological fidelity among paleocommunities because adjacent epibionts coexisted in ecological time, and the abundances and spatial relationships of the various members are accurately preserved. This study presents a quantitative reconstruction of communities on brachiopod shells (Composita and alate spirifers) from the Carboniferous of North America. Thirty-one epibiont communities, comprised of a total of 1180 encrusted brachiopods, are analyzed in terms of epibiont abundance (e.g., percent areal cover), ecological diversity (e.g., Shannon-Wiener Index), and the role of larval recruitment and spatial competition in structuring the communities.Mississippian epibiont communities contain from seven to 14 encrusting taxa that occupy up to 25 percent of host shell surfaces. These communities are spatially dominated by trepostome bryozoans, but also include common lower Paleozoic epibionts, such as encrusting ctenostome bryozoans, hederellids, cornulitids, and edrioasteroids. Pennsylvanian epibiont communities contain between eight and 16 epizoan taxa that occupy up to 34 percent of shell surfaces. They are dominated by fistuliporoid or trepostome bryozoans and increasing proportions of erect bryozoans (e.g., fenestellids), encrusting foraminiferans, and articulate brachiopods.Carboniferous epibionts, like their modern counterparts, exist in loosely organized ecological communities that vary widely in abundance and composition in space and geological time. There is little evidence for tight controls on community structure. Much of the variation is attributed to vagaries in the magnitude and selective nature of larval recruitment. Evidence of competition between community members is rare, except where a high percentage of the shell surface is covered. In these cases, sheetlike bryozoans are usually most abundant. Solitary epibionts are surprisingly successful competitors in one-on-one encounters, but apparently lose areal cover to longer-lived colonial encrusters during ecological succession.

Epibiota and attachment substrata of deep-water brachiopods from Antarctica and New Zealand

Prevalence (proportion of host organisms covered) and cover of encrusting epibiota were investigated for four Antarctic and two New Zealand species of deep-sea brachiopods. All epibiota was identified to the lowest possible taxonomic level, such that prevalence and dominance of each taxon could be assessed on different brachiopod species. Punctae had no detectable influence on fouling, whereas valve architecture and ornamentation were probably a major influence. Prevalence and percent cover of epibiota were found to decrease with depth (from 50-600 m) in the Antarctic terebratulidLiothyrella uva. A maximum of 5 % epibiotic cover was recorded on the punctate terebratulids from beyond 160 m (Liothyrella uva,Magellania fragilisandMagellania joubinifrom Antarctica andNeothyris lenticularisfrom New Zealand). Epibiotic cover significantly increased with valve area to over 40 % in the Antarctic inarticulateNeocrania lecointeiand the New Zealand impunctate rynchonellidNotosaria nigricans. Bryozoans, foraminiferans and polychaetes were the most abundant colonizers, but there were also representatives present from seven other phyla. The epibiotic community structure of the terebratulidsLiothyrella uva,Magellania joubiniandNeothyris lenticularis, and the inarticulateNeocrania lecointeiwere broadly similar, suggesting a cosmopolitan nature to deep-sea brachiopod epibiota. The community onMagellania fragiliswas notably different, in being almost entirely dominated by foraminiferans, but the reasons for this are unknown. Analyses of attachment substrata for the Antarctic terebratulid brachiopods indicated erect bryozoans were most commonly used, but that sponges, rocks and even echinoid spines were used. The substratum used by the majority of the New Zealand specimens was unknown, but this is possibly becauseN. lenticularishas been described as degenerating its attachment and becoming free-living with age.

Encrusting organisms on co-occurring disarticulated valves of two marine bivalves: comparison of living assemblages and skeletal residues

Study of the assemblage of encrusting organisms on co-occurring disarticulated valves of the bivalvesCrassostrea virginicaandMercenaria mercenariain Bogue Sound, North Carolina, indicates that there is little or no substrate specificity among the encrusting organisms but that the shape of the shells has an important influence on how extensively members of each higher taxon collectively inhabit the shells. Encrusting bryozoans, a dense low mat composed of many species from diverse phyla, and a unicellular film cover most of the area of both exterior and interior surfaces. The encrusting bryozoans most extensively cover both surfaces ofC. virginicabut are in second place behind the multispecies mat on exterior surfaces ofM. mercenariaand behind the unicellular film on its interior surfaces. These differences are inferred to result from different physical stability of valves of the two bivalve species, which exhibit different frequencies of circumrotatory growth.Degradation of the assemblage by sodium hypochlorite, to simulate loss of organic matter during fossilization, results in the complete loss of encrusting sponges, erect hydrozoans, erect bryozoans, and ascidians. Loss of these taxa results in overexposure and more apparently uniform distribution of skeletal taxa with respect to their surface representation in living assemblages and also in complete loss of the higher tiers present in the living assemblage. However, indications of the original structural organization of the living assemblage is indicated by preservation of the most abundant taxa in the lower tiers and by the retention in the reduced treated assemblage of thepatternsof distribution that characterized the living assemblage.

Sublittoral epifaunal communities at Signy Island, Antarctica. II. Below the ice-foot zone

Photographic samples were taken every 5 m along two 40 m transects on mostly rock face at Signy Island, Antarctica, during the austral winter of 1991. Dense and taxonomically rich communities of benthos occurred at most of the sublittoral study locations. These communities, however, varied significantly with substratum type, substratum profile and depth. Algae were generally the largest occupiers of space, but the area of substratum colonised by animal taxa increased whenever the profile approached vertical. Shallower than 15 m, disturbance effects, largely from ice, restricted community development to a high degree, but the frequency of disturbance at 25 m appeared to maintain high diversity by preventing domination of the assemblage by a few competitively superior taxa. Bryozoans, and to a lesser extent sponges, were the most abundant animal phyla. Among the bryozoans, species with an encrusting growth form occurred at the shallowest depths followed by encrusting massive/folaceous species and, at 40 m, the erect flexible forms. The ratio of encrusting to erect bryozoan species changed rapidly over the 0 to 50 m depth zone, from exclusively encrusting at 0 to 5 m to approaching 1 at 50 m. The erect bryozoans studied, from the shallow sublittoral to 290 m, could be classified as encrusting massive (foliaceous), erect flexible or erect rigid forms. There was some suggestion, despite the overlap between groups and considerable intra-group variation, that encrusting massive forms were abundant in the shallowest water, followed by erect flexible forms and then erect rigid forms with increasing depth. Some species which occurred as encrusting massive/foliaceous forms in deeper water occurred mostly in encrusting form only in shallow water (<15 m).

Larval settlement in hard substratum epifaunal assemblages: a manipulative field study of the effects of substratum filming and the presence of incumbents

Natural larval settlement on black Perspex settlement panels was analysed for two experiments (1 and 2) conducted amongst epifaunal assemblages beneath pier pilings at Williamstown, Victoria and one experiment at Mornington, Victoria, in southeastern Australia. The overall objectives of this manipulative study were to distinguish experimentally the effects of “filming” of the substrata and the presence of previously settled incumbent invertebrates on subsequent larval settlement in the sublittoral. Filming of substrata, whilst largely excluding larval settlement, was permitted by the enclosure of settlement panels within tightly-fitting pouches of plankton gauze of 150 and 236 μm mesh size. Williamstown 1 and Mornington included only fine-mesh treatments and Williamstown 2 included both coarse and fine mesh-sizes and also an additional treatment in which panels were initially filmed intertidally and then deployed sublittorally. Each experiment was conducted over periods of ≈2 wk. For Williamstown 1 filming generally enhanced larval settlement, with the exception of various ascidian species and the erect bryozoan Bugula neritina. Inhibitory effects of incumbents were found for Bugula dentata, the colonial ascidian Trididemnum spp. and Total Settlement: this effect was possibly attributable to Didemnids (excl. Trididemnum spp.). For the repeat of the first experiment (Williamstown 2), Bugula dentata and Serpulins all showed enhanced settlement in response to films developed on panels screened with both mesh sizes. Incumbents inhibited the settlement of Didemnids (excluding Trididemnum spp.) (cf. Williamstown 1) and Encrusting Bryozoans were facilitated. There was no significant difference in sublittoral settlement during the second week of the Williamstown 2 experiment between panels upon which the initial filming was developed either intertidally or sublittorally: settling larvae apparently responded simply to whether or not a substratum was filmed and not to the source of the film, although the possibility remains of rapid modification of the intertidal film to one typical of the sublittoral. At Mornington, Arborescent Bryozoans, Tricellaria occidentaux, Slime Sponges and Spirorbins all showed enhancement of their settlement by filming of the substrata, whereas incumbents significantly inhibited settlement of Didemnids, Microporella sp., Encrusting Bryozoans and Tricellaria occidentalis. The results show clearly the importance of repeating experimental analyses such as these at a given site and of undertaking experiments at different sites. One striking outcome was the marked inhibitory effect on other settlers of Didemnids (excluding Trididemnum spp.) at Williamstown 2. Those ascidians were themselves subject to high levels of post-settlement mortality and, although the cause of their mortality remains unknown, it is possible that the bacteria and ciliates attacking the ascidians were the source of the inhibitory effects on other settlers: these micro-organisms might therefore themselves provide adaptive biological cues indicative of otherwise unfavourable substrata to settling larvae.

Larval behaviour and choice of settlement site: Correlation with environmental distribution pattern in an erect bryozoan

This paper concerns the preferred environmental conditions for settlement and metamorphosis of larvae of the erect, rigidly calcified cheilostome bryozoanSchizotheca serratimargo and compares the settlement preferences with in situ distribution of adult colonies. A review of bryozoan larval behaviour and responses to environmental parameters is given in order better to understand larval settlement and metamorphosis in this species. Release of larvae ofS. serratimargo (Hincks) was induced so that each travelled down a path with a limited set of microenvironments in which it could choose to settle. Four different flow velocities, three different depths below the water surface, two different light intensities, three different orientations of plexiglas surfaces, and subdivision of distance of travel into three segments, yielded 216 microenvironments. 466 larvae successfully settled and metamorphosed within the experimental chamber. They metamorphosed in significantly higher numbers in microenvironments with low flow velocity, in the shallowest of the three possible depths, in darker areas, and on nonoverhanging surfaces with little or no sediment. The most important stimulus for settlement was darkness, especially where there was a strong gradient in light intensity.S. serratimargo grows as erect bilaminate bushes on protected flanks of boulders, in small caves, and just within the entrances of larger caves at depths of 5–30 m, as well as on hard debris on open muddy sand floors at 30–35 m depth in the Adriatic and Mediterranean Seas. The experimentally-determined settlement patterns suggest that recruitment is more important than post-settlement interactions or exposure to physical damage in determining local distribution of the species.

De possibles Crisiidae (bryozoa-articulata) dans le néocomien du Jura franco-suisse

In several localities of the “Marnes à bryozoaires”, in Northern French and Swiss Jura, were found very slender erect bryozoans. These bryozoans differ completely of the other Neocomian bryozoans, by the slenderness of their uni or biserial stems. The greatest similarity is with Crisiidae. So, though the articulate nature of the colony is impossible to prove in the fossils, we attribute them to this group. Two new species are described: Filicrisia (?) neocomiensis nov. sp. and Crisia (?) nozeroyensis nov. sp. The age of localities being Upper Valanginian and Lower Hauterivian, these bryozoans would be the oldest known Crisiidae.

Population density and demography of a fouling community amphipod

Tube-building amphipods are abundant members of fouling communities but are not major space competitors. Their ecology and relationships with the dominant fouling species are poorly understood. This study documents the population dynamics and demography of the amphipod Jassa marmorata Holmes in a New York fouling community. Large recruitment peaks were used to track age cohorts over time. Growth was exponential beginning in March, with high but variable densities through the summer, declining to winter low levels in November. Of the 5 overlapping cohorts yr −1, 3 were present between May and September. Survivorship and mortality curves differed between overwintering vs. summer cohorts. Life spans of the former were 6–8 months but <3 months for the latter. Adult body size varied inversely with water temperature and was a major determinant of fecundity. The density of gravid females varied inversely with body size. Thus, water temperature indirectly determined recruitment rates by affecting body size, fecundity, and cohort life spans. The summer population explosion was correlated with expansive growth of hydroids, Ulva, and especially, the erect bryozoan Bugula turrita (Desor), all provided living space for Jassa. Mortality rates of adults in the short-lived summer cohorts limited population growth in summer. Multiple cohorts confer flexibility for the Jassa population by facilitating recruitment onto newly developing ecospace in a rapidly fluctuating community. Water temperature, as a determinant of body size and lifespan, is a major regulatory factor affecting density and demography in this population.

Erect Bryozoans Are More Than Baffling: Enhanced Sedimentation Rate by a Living Unilaminate Branched Bryozoan and Possible Implications for Fenestrate Bryozoan Mudmounds

Feeding colonies of the branched cheilostome bryozoan Bugula nertina trap sediment more effectively from sediment-laden water flowing at velocities of a few cmls than do dead colonies, which in turn collect more sediment than bare, smooth substrata. The enhanced sedimentation immediately downstream of live colonies is due apparently to cilia-generated currents. These currents draw water, sediment and organic material, that would otherwise pass by unimpeded, through the colonies and into the stagnant region below and leeward of them. Ancient colonies with organization generally similar to Bugula (such as the Paleozoic fenestrate bryozoans) may also have generated higher sedimentation rates where slightly turbid water passed over them than passive baffling or production offeces or pseudofeces alone would generate. This potentially could have contributed to enigmatic mudmound buildups, such as the Carboniferous Waulsortian mounds, and other muddy facies.

Evolution of Erect Marine Bryozoan Faunas: Repeated Success of Unilaminate Species

Twice, over era-scaled lengths of time, the relative diversity of branched unilaminate species among the erect bryozoan fauna increased by a factor of 10. In this duplicate natural experiment, a colonial form that offers the least resistance to the outflow of filtered water apparently replaced all the others. The data suggest long-term progressive evolution by an increase in the number of species and lineages that are hypothesized to be more hydrodynamically efficient in eliminating filtered water. Except for the Late Permian extinction event, the increase in the proportion of unilaminate species continued through, and perhaps was enhanced by, periods of mass extinction.

Historical record of erect bryozoan growth forms

Information compiled from literature on marine bryozoans suggests that erect taxa have had a limited range of repeatedly evolved growth forms, each with characteristic branch widths or surface morphology, through the nearly 500 Ma history of the phylum. The range of erect growth forms among the Bryozoa has been limited to six (with only rare exceptions) that have co-occurred constantly throughout the history of the phylum. Ciliated tentacles of bryozoan lophophores are located just above the surface of colonies and draw a flow of food-bearing water. Outflow of the filtered water is confined to the space between the tentacles and the colony surface, until some point of escape is reached. In almost all erect bryozoans, lophophores are closely spaced and, in extant species, feed simultaneously. Therefore, for broad surface areas to develop, colony margins must be supplemented by other points of outflow (chimneys), commonly situated on surface disruptions, to keep local volume and velocity within manageable bounds. Presence of chimneys apparently permits branch widths to increase beyond certain size limits into less tightly constrained morphospace, and branch widths have been narrowly limited in the various growth forms except where regularly spaced chimneys can be demonstrated or reasonably inferred. It is hypothesized that the observed limits on form, size and surface morphology are derived primarily from the phylogenetic constraint of byrozoan lophophore size and attendant limitations on flow of filtered water across colony surfaces.

New species of Hippothoidae (Bryozoa) from Chile, Antarctica and New Zealand

Abstract Six austral hippothoan species—Celleporella antarctica n.sp., C. bougainvillei (d'Orbigny), C. patagonica (Busk), C. yagana n.sp., Plesiothoa australis n.sp. and P. coquimbana n.sp.—are described. Of the new species, P. coquimbana, P. australis and C. yagana occur along the coasts of northern, central and southern Chile respectively, and C. antarctica along the Antarctic Peninsula and Ross Sea area. Plesiothoa australis is also in New Zealand. Celleporella yagana has been segregated from C. patagonica, which actually comprised two separate, but similar, species. Celleporella antarctica, which is similar to C. bougainvillei, typically occurs on reduced surfaces such as erect bryozoans and hydroids.

Benthic Community Development in Limestone Beds of the Waynesville (Upper Dillsboro) Formation (Cincinnatian Series, Upper Ordovician) of Southeastern Indiana

ABSTRACT Vertical and lateral changes in composition occur within 13 individual limestone beds of the Waynesville (Upper Dillsboro) Formation (Upper Ordovician) near Brookville, Indiana. Fossil allochems formed approximately 40%. and carbonate ooze 60% of the original carbonate sediment, with later conversion of most of the ooze to microspar and pseudospar. The relative abundances of individual constituents, however, vary between the top, center, bottom, and margins of each limestone bed. The centers of the beds are distinguished from the tops, bottoms, and margins of beds using certain variables and discriminant function analysis. Variables important in separation include neomorphic sparry calcite and echinoderms within the bed centers, and micrite, bryozoans, and brachiopods within the tops, bottoms, and margins of beds. An increase in faunal diversity from the bottoms to the centers of beds indicates rapid community succession. A decrease in faunal diversity from the centers to the tops of the limestone beds indicates community degradation. The writers propose that a subtidal, terrigenous mud substrate was colonized by thin, flat, brachiopods (Onniella). The accumulation of these valves provided a pavement upon which erect bryozoans could grow. Further stabilization of the substrate allowed crinoids to become established. A wave-current baffle was produced in the denser parts of the community by the abundant growth of bryozoans and crinoids creating low energy conditions favorable for the simultaneous accumulation of unsorted allochems and ooze. The community spread laterally as skeletal debris swept from atop the growing centers stabilized the peripheral muds. Carbonate accumulation terminated when mobilized, muddy, bottom sediment, thrown into suspension under storm conditions, settled and smothered the community. The model proposed for the accumulation of the carbonate sediments is independent of bottom topography and conditions of accumulation of terrigenous mud.

Succession of a wharf‐pile fauna at Lyttelton, New Zealand

Summary A 31/2‐year succession of wharf‐pile fauna is described from communities of different known ages on piles at Lyttelton, New Zealand. Intertidal regions of the piles were initially colonised by the barnacle Elminius modestus; these populations developed to form a subclimax community which was subsequently replaced by a climax community of the mussel Modiolus neozelanicus after 21/2 years. The stability of this climax is discussed. In the infratidal region initial settlement of the tubicolous amphipod Corophium acherusicum and an erect bryozoan Bugula sp. was followed after 5 months by colonisation by solitary tunicates. These tunicates became dominant only after H years and provided numerous niches for superficial foulers, crevice dwellers, and motile organisms. This succession is compared and contrasted with a terrestrial succession of plants. Four vertical zones were recognised: supralittoral zone, midlittoral zone, in‐fralittoral fringe, and infralittoral zone. Species additional to those record...