Low Intertidal Regions Research Articles

Biodegraders of Large Woody Debris Across a Tidal Gradient in an Indonesian Mangrove Ecosystem

There has been limited research on the breakdown, recycling, and flux of carbon from large woody detritus (LWD) in mangrove forests. The breakdown of LWD is caused by guilds of terrestrial and marine biodegrading organisms that degrade wood at a range of rates and efficiencies. Spatial variations in environmental factors within mangroves affect the distribution and community of biodegrading organisms, which, in turn, impacts carbon flow and sequestration. We reveal the role of biodegrading organisms in LWD breakdown and the environmental factors that influence the distribution of biodegrading guilds within a mangrove forest in South East Sulawesi that supports a diversity of mangrove species typical of Indonesian mangrove forests, which constitute 20% of Global mangrove cover. Within the high intertidal regions, terrestrial biodegradation processes dominated upon LWD. After 12 months exposure on the forest floor, experimental wooden panels in these areas remained unchanged in mass and condition. In the low intertidal region, marine wood-boring animals belonging to the family Teredinidae were the dominant biodegraders of LWD, and their activity reduces LWD volume and speeds up the loss of LWD volume. More than 50% of the experimental wooden panels’ weight in these areas was lost after 12 months exposure on the forest floor. Although different biodegrading guilds occupy the same LWD niche, their distribution throughout the mangrove forest is influenced by inundation time. The change of biodegrading guilds within LWD between the terrestrial and the marine organisms was distinct, creating a biodegradation boundary in a distance as narrow as 1 m on the mangrove forest floor. These results are important, as rising sea levels have crucial implications for biodegrading guilds. A full understanding of factors affecting the biodegradation processes of LWD in mangrove forests is critical to accurately assess mangrove carbon stores and the fate of mangrove derived carbon.

Intertidal Zonation of the Suminoe Oyster Crassostrea ariakensis and the Kumamoto Oyster Crassostrea sikamea on the Coast of the Northern East China Sea

The Suminoe oyster Crassostrea ariakensis and the Kumamoto oyster Crassostrea sikamea coexist and are habitat-forming ecosystem engineers in the Yangtze River estuary and its adjacent coasts. To date, little quantitative information is available on the intertidal zonation patterns of these two oysters within their native range or on the related mechanisms generating these spatial patterns. This study first carried out field surveys and laboratory experiments to explore the vertical zonation patterns of the two oysters in the intertidal habitats of northern Hangzhou Bay, assess the roles of abiotic (aerial exposure stress) and biotic (larval distribution, recruitment, and competition) factors in regulating vertical zonation and understand their driving mechanisms. At the study site, C. sikamea dominated the higher intertidal zone (approximately 6.7 h and 56% emersion/12 h tidal cycle), whereas C. ariakensis occupied the three deeper intertidal zones (mid, mid-low, and low intertidal). Mean aerial exposures of 56% and 42% represented the optimal growth zones and the lower limits of C. sikamea, respectively. The growth boundary of the two oysters was located in the intertidal zone that was exposed 42% of the time. The area with the highest C. ariakensis densities (the optimal growth zone) was the mid-low intertidal (mean: 3.0 h and 25% emersion/tidal cycle). In a laboratory 72-h aerial exposure experiment, the percentage of water loss was significantly greater for C. ariakensis than for C. sikamea after 24 h (P 0.05). Twenty-two individuals among the 30 oyster recruits (73%) in the high intertidal region were identified as C. sikamea, and six recruits (20%) were identified as C. ariakensis. All 36 recruits (100%) in the low intertidal region were identified as C. ariakensis. It was concluded that the differential larval distribution, settlement, and post-settlement mortality along the intertidal elevation gradients served as a mechanism for vertical zonation of these two oyster species.

Influence of waves and currents on the growth rate of the kelp Laminaria digitata (Phaeophyceae).

The kelp Laminaria digitata growing in the low intertidal region along energetic coastlines are exposed to a range of hydrodynamic environments. Macroalgae in the intertidal zone can experience both waves and currents independently, but it is unknown how they influence growth rate. Relative growth rate of the meristematic region and the entire blade of L.digitata were measured to assess the influence of wave and current motion from three hydrodynamic environments: low current and low wave (LCLW), high current and low wave (HCLW), and high wave and low current (HWLC). Alongside hydrodynamic data, seawater nutrient concentrations and temperature were also collected and analyzed. Results suggest that differences in L.digitata relative growth rates were not attributed to the seawater nutrient concentrations or temperature, but attributed to the hydrodynamic environments. At the high current condition, kelp growth rate of the meristematic region was enhanced by 45% compared to the high wave condition. When including the entire blade growth rate, an average increase of 25% was observed between the high current and high wave condition. Potentially, the division in growth rate observed between the wave and current motion is related to the frequency and magnitude at which the hydrodynamic forces act. These findings highlight the complexity ofthe hydrodynamic environment and that forces associated with waves and currents may have a significant role on the productivity of kelp.

A larval-settlement assay method for the gregarious serpulid polychaete, Galeolaria caespitosa

Static settlement assays are considered the standard tool for determining the settlement preferences of marine invertebrates. Often used to assess and evaluate the properties of a given substrate or biofilm cues for colonisation, the static assay format is technically simple, rapid, and inexpensive. Galeolaria caespitosa is a sessile, filter-feeding polychaete worm that inhabits mid to low intertidal regions of exposed rocky shores. Mature adults of G. caespitosa are fertile throughout the year, easy to spawn and rear to settlement competency, and their gregarious settlement behaviour enables easy collection making them an ideal test species. Here we report an optimised protocol for larval settlement assays with G. caespitosa. Unlike other serpulid polychaetes, a bacterial biofilm alone was not sufficient to consistently induce settlement. Instead, a conspecific cue was required for reliable settlement under assay conditions. Yet empty tubes and a homogenate of crushed adult worms had no significant impact on settlement compared to a control, and both treatments showed high variance, inducing <5% of larvae to settle. Only the presence of live conspecific worms consistently induced settlement to the extent necessary for useful assays. In this case, after 48h the proportion of larvae to have successfully settled reached 44%. On average, live conspecific worms increased settlement by 87% compared to the presence of a biofilm alone. The static settlement assay protocol developed in this study provides a reproducible tool for assessing invertebrate settlement with G. caespitosa. Guidelines are provided for adapting this approach to other species.

Population structure of the burrowing crab Neohelice granulata (Brachyura, Varunidae) in a SW Atlantic salt marsh

Neohelice granulata inhabits estuarine and protected coastal areas in temperate regions, and is the most dominant decapod crustacean in the Bahía Blanca estuary. The population structure was studied during a year in a SW Atlantic salt marsh located in the Bahía Blanca estuary, Argentina. Crabs were sampled monthly from August 2010 to July 2011. The maximum observed density was 39 crabs/m2 in February and 70 burrows/m2 in May. The maximum carapace width (CW) in males was 32 mm and 27.5 mm in females. Medium size crabs were between 16 and 20 mm CW. Significantly smaller sized crabs were observed at the lower intertidal regions (p

Macrobenthos of the nearshore Aleutian Archipelago, with emphasis on invertebrates associated with Clathromorphum nereostratum (Rhodophyta, Corallinaceae)

In the Aleutian Islands, Alaska, crustose coralline algae can be widespread in the low intertidal and shallow subtidal regions, and cover most available hard substrates. The longevity and slow growth-rate of coralline algae make them vulnerable to major disturbances, including anthropogenic disturbances and ocean acidification. Subtidal habitats dominated by crustose coralline algae are often associated with sea urchin-barren grounds and regarded as supporting limited invertebrate communities, especially compared with the adjacent kelp forests. Clathromorphum nereostratum is one of the most abundant crustose coralline algae found in the Aleutian Islands. Although the surface of this crustose alga exhibits little structural complexity, it can develop into crusts half-a-meter thick (2-10 cm in this study) that provide microhabitats for a variety of cryptic invertebrates. Despite the omnipresence of this alga throughout the nearshore Aleutians, very little is known about its associated faunal community. In the summers of 2006 and 2007, a benthic survey was conducted at 50 sites throughout the shallow (<20 m), nearshore Aleutian Islands as part of the Alaska Monitoring and Assessment Program. The habitat encountered at each site was categorized as soft sediment, macroalgae-dominated, or crustose coralline-dominated. At each site, scuba divers sampled three 0.06-m2 quadrats. Invertebrate communities associated with thick crustose coralline algae were compared with soft-sediment and macroalgae-dominated communities based on faunal abundance and diversity. Despite the depauperate appearance of crustose habitats, this study revealed that crustose environments support faunal communities as diverse and abundant as those found in rich macroalgal habitats.

HABITAT AND HOST SPECIFICITY OF TREMATODE METACERCARIAE IN FIDDLER CRABS FROM MANGROVE HABITATS IN FLORIDA

Fiddler crabs (Uca spp.) are common inhabitants of temperate and tropical coastal communities throughout the world, often occupying specific microenvironments within mangrove and salt marsh habitats. As second intermediate hosts for trematodes, we investigated patterns of host distribution and parasitism for 3 species of sympatric fiddler crabs in mangrove habitats adjacent to the Indian River Lagoon, Florida. Fiddler crab distribution varied among species, with Uca speciosa dominating the low and mid intertidal regions of mangrove banks. This species also exhibited higher prevalence and abundance of Probolocoryphe lanceolata metacercariae compared with Uca rapax, which is relatively more abundant in the high intertidal zone. We conducted a field experiment to test whether U. speciosa was more heavily parasitized by P. lanceolata as a result of its habitat distribution by raising U. speciosa and U. rapax under identical environmental conditions. After exposure to shedding cercariae under the same field conditions, all individuals of U. speciosa became parasitized by P. lanceolata, whereas no U. rapax were parasitized, suggesting that differences in parasitism were driven by host selection.

Coupling between sedimentary dynamics, early diagenetic processes, and biogeochemical cycling in the Amazon–Guianas mobile mud belt: coastal French Guiana

Coastal French Guiana lies within the vast mobile mudbelt that characterizes much of the S. American inner shelf downdrift of the Amazon River. Approximately ∼15–20% of the Amazon sediment outfall moves NW along the Guianas, in part as a series of 20–25 coastal mud waves. Seasonal studies of a representative migrating mudwave located between Kourou and Sinnamary, French Guiana demonstrate that diagenetic properties and biogeochemical cycling are closely coupled to sedimentary dynamics and the refluxing of reduced components between the seabed, coastal facies, and well-oxygenated overlying water. An unsteady two-zone diagenetic regime is typically present in the shallow subtidal and low intertidal regions. A surficial layer, usually ∼0.5–1 m thick, is nonsulfidic, highly reactive, and dominated by Fe, Mn cycling. This suboxic layer unconformably overlies more consolidated sediment in which net SO 4 2− reduction is often observed, and contracts shoreward toward the mangrove fringe as sediments stabilize and become bioturbated. The relatively stable intertidal flats are also sites of significant benthic primary production. Despite suboxic conditions over extensive intervals, anaerobic remineralization rates are high (ΣCO 2∼0.2–0.6 mM day −1), and often show little evidence of attenuation with depth. Integrated ΣCO 2 fluxes are ∼20–235 mmol m −2 day −1 (wet/dry season average ∼120), far exceeding diffusive O 2 fluxes into the bottom. High reactivity (∼0.08 day −1) and low C/N remineralization release ratios (∼5.3) of decomposing material imply fresh substrate of marine origin. Most reduced solid phase Fe is present as nonpyritic authigenic Fe minerals (<20% Fe(II) is in pyrite), and low sedimentary C/S ratios (∼6–8) reflect the generally nonsulfidic conditions. A broad range of tracers (e.g. 234Th ( t 1/2=24 days), 210Pb ( t 1/2=22 years), seasonal Cl − profiles) and nonsteady state diagenetic models of pore water concentrations and oxidant–reductant relationships demonstrate that the upper 0.1–1 m of deposits are reworked and exchanged with overlying water on timescales of <10 days to seasonally. Thus, the seafloor acts as a massive suboxic batch reactor, entraining and processing reactive marine plankton, regenerating Fe, Mn oxides, exchanging metabolites and nutrients with the oxygenated water column, and generating suites of nonsulfidic authigenic minerals. The apparent paradoxical properties of high remineralization rate, low reductant content (C org∼630 μmol g −1), and dominance of suboxic metal cycling are a direct consequence of frequent entrainment of highly reactive organic substrate and simultaneous regeneration of the major Fe oxidants in oxygenated water. The Amazon–Guianas mobile mudbelt is a zone of extraordinarily intense sedimentary and biogeochemical recycling, greatly exceeding stable coastal systems, such as salt marshes, in material exchange with the sea.

Population dynamics and potential yield of three species of giant winkles in the Western Cape, South Africa

Of the southern African intertidal and shallow subtidal trochid and turbinid gastropods, Turbo sarmaticus , T. cidaris and Oxystele sinensis , are the most abundant large species, and therefore obvious targets for a winkle fishery. T. sarmaticus is harvested by recreational snorkel divers, and an application has been made for a permit to experimentally harvest the other two species commercially. This study involves four major aspects, namely morphometrics and flesh yield, shore-based abundance estimates, subtidal abundance estimates, and an estimate of the potential yield for each of the three species off the South-Western Cape, South Africa. Abundance and biomass of the winkles increased from west to east, highest densities being recorded in the low intertidal regions to 2 m depth. Low biomasses of the three species were recorded west of Cape Hangklip and are unlikely to support a fishery there. East of Cape Hangklip, invasion of rock lobsters Jasus lalandii has had a considerable impact on T. cidaris and O. sinensis populations. Consequently, a boat-based fishery with an estimated annual total allowable catch of 75.5 tons for T. cidaris , with a bycatch of 9.9 tons for O. sinensis , can only be considered in the easternmost fisheries-management area between Kleinbaai and Quoin Point. Because previous studies on the harvesting potential of T. sarmaticus off the Western Cape concluded that it was not commercially sustainable, a total allowable catch for that species was not considered. Management options deserving considerations before the commencement of a giant winkle fishery are discussed. Keywords: commercial exploitation, Oxystele sinensis , stock assessment, Turbo cidaris , Turbo sarmaticus , yield African Journal of Marine Science 2002, 24: 161–183

Abundance and distribution of sessile invertebrates under intertidal boulders (São Paulo, Brazil)

The encrusting communities under two boulder fields (Praia Grande and Ponta do Baleeiro) were monitored monthly during 1990 and 1991, in São Sebastião, on the northern coast of São Paulo State, Brazil. Two sizes of boulders were chosen: small (20-30 cm² underside area) and larger ones (160-220 cm²) located on the middle and lower levels of the intertidal. The community's components were mainly sessile animals either compound ones such as Bryozoa, Ascidiacea, Porifera and Cnidaria, in this order of abundance, or simple ones such as Polychaeta and Bivalvia, also in this order of abundance. All groups, except by serpulids (Polychaeta), had higher percent cover in the low intertidal region and under large boulders. Diversity was higher at Ponta do Baleeiro, and in the low intertidal region and on large boulders for both shores.

Abundance and distribution of sessile invertebrates under intertidal boulders (São Paulo, Brazil)

The encrusting communities under two boulder fields (Praia Grande and Ponta do Baleeiro) were monitored monthly during 1990 and 1991, in Sao Sebastiao, on the northern coast of Sao Paulo State, Brazil. Two sizes of boulders were chosen: small (20-30 cm² underside area) and larger ones (160-220 cm²) located on the middle and lower levels of the intertidal. The community's components were mainly sessile animals either compound ones such as Bryozoa, Ascidiacea, Porifera and Cnidaria, in this order of abundance, or simple ones such as Polychaeta and Bivalvia, also in this order of abundance. All groups, except by serpulids (Polychaeta), had higher percent cover in the low intertidal region and under large boulders. Diversity was higher at Ponta do Baleeiro, and in the low intertidal region and on large boulders for both shores.

Algal recruitment and the maintenance of a plant mosaic in the low intertidal region on the Oregon coast

The role of recruitment of turf-forming algae in maintaining a low rocky intertidal plant mosaic on the central Oregon coast was investigated. Monthly samples suggested that spore release by one of the most abundant turf-forming red algae at wave-exposed sites ( Constantinea simplex Setchell) occurred only in spring. In contrast, spore release by the two most abundant wave-sheltered red algae [ Odonthalia floccosa (Esper) Falkenberg, Neorhodomela larix (Turner) Masuda] occurred at all times but winter. At wave-exposed sites, the turf-dominant colonized clearances frequently. At wave-sheltered sites, one dominant colonized frequently and the other turf-dominant colonized clearances infrequently. Experiments evaluated the rates of recruitment of these algae to manually cleared plots with respect to distance and direction from spore source, species of colonist, presence or absence of early colonists, wave turbulence (wave-exposed or wave-sheltered), and location. We also tested the effect of grazing at wave-exposed but not at wave-sheltered sites (where grazers were scarce). At one wave-exposed site, but not the other, recruitment of Constantinea within 1 sx 2 m cleared areas responded differently to distance depending on its direction from the propagule source. Significant variation also occurred between clearances and sites. The effects of preemptive competition and grazing were not significant. At wave-protected sites, recruitment of Odonthalia but not Neorhodomela varied significantly with several factors. These included presence of early colonists, blocks (one site only), and sites. However, no variation in recruitment of either species occurred with respect to direction or distance from propagule source. Compared to Odonthalia, recruitment of Neorhodomela was extremely low suggesting that the high abundance of the latter depends on vegetative growth and long persistence. We conclude that recruitment processes can contribute to the maintenance of a high diversity mosaic at wave-exposed sites, but are of minor importance at wave-sheltered sites.

Macroalgal assemblages in New Zealand: structure, interactions and demography

Quantitative descriptions of macroalgal distributions from low intertidal regions to a sublittoral depth of 20 m are presented for rocky reefs from several localities ranging over 16° latitude in New Zealand. These include the northern and southern main islands as well as the Chatham Islands and the sub-antarctic Auckland Islands. Fucalean algae are dominant in the shallow sublittoral regions throughout NZ. Laminarian species are rare and generally reach their greatest abundances at 7–17 m depth. The colder waters in central and southern NZ tend to have different dominant species from those in northern NZ. Sea urchins form a characteristic zone devoid of kelp at 5–8 m in the north, but tend to occur only in patches on reefs in southern localities. Summaries of experiments in the north show that strong interspecific effects occur among algal species, particularly due to canopy shading, and between sea urchins and algae. Much of the patchiness in algal assemblages, however, is not accounted for by these effects. A knowledge of the demographic processes of individual species is necessary to understand assemblage organization; life histories, phenology and biogeography significantly affect distributions and interactions.

Distribution of carbonic anhydrase in British marine macroalgae.

Thirty-four species of marine macroalgae from around St. Andrews, Scotland, have been assayed for their external activity and thirty-three species for their total activity of carbonic anhydrase. Activity was detected in all the Rhodophyta tested apart from Chondrus crispus, but was absent in Codium fragile, Enteromorpha sp. and Monostroma fuscum (Chlorophyta), and Alaria esculenta, Laminaria digitata, L. saccharina and L. hyperborea (Phaeophyta). Total activity of carbonic anhydrase per unit fresh weight tended to be higher in the Rhodophyta than in the Chlorophyta or Phaeophyta. External activity was present in two of the six Chlorophyta, four of the twelve Phaeophyta and four of the sixteen Rhodophyta tested. On average, when present, external carbonic anhydrase activity represented 2.7% of the total activity. A relationship was found between total carbonic anhydrase activity and habitat. Species from the high intertidal and the low-light subtidal habitats had significantly higher activity than species from the mid and low intertidal, rockpools, or high-light region of the subtidal. External carbonic anhydrase activity did not vary significantly with habitat. There appeared to be no strong relationship between carbonic anhydrase activity and the ability of a species to use HCO -3 in photosynthesis under water.

Epiphytic diatoms of the inshore marine area near Davis Station

Collections of macrophytic algae from the subtidal and lower intertidal regions were processed to observe the diatom epiphytes both by light and scanning electron microscopy. For the purpose of comparison some samples of the sub-ice assemblage were also collected and processed similarly. The standing crop of epiphytes was high throughout the winter as well as the summer but the community composition varied depending upon the collection site and the morphology of the host macrophyte. The genus Cocconeis was ubiquitous achieving densities approaching 105 cells cm−2 and surpassed only by Nitzchiawith a density of twice that amount on one sample.

The importance of form: Differences in competitive ability, resistance to consumers and environmental stress in an assemblage of coralline algae

Competitors, consumers, and environmental stresses are everpresent factors that most organisms face during their lifetime. On the Pacific northwest coast of North America there are three forms of coralline algae (Rhodophyta, fam. Corallinaceae) differentially distributed within and around large tide pools in the mid and low intertidal region. Observations and experiments were conducted to test whether species of three different forms (finely branched, coarsely branched, and encrusting forms) were differentially susceptible to consumers, competitors and environmental stress. The results indicate that the distributions of these three forms are distinctly different. Although no single factor appears to be controlling this zonation during the time scale of this study, the three forms are differentially susceptible to these potential selective agents. The finely branched coralline ( Corallina vancouveriensis Yendo), found immediately outside of the pools on emergent substrata, is the most resistant to desiccation. This is apparently because its bushy structure holds more water than the other forms preventing drying during times of emersion. The coarsely branched coralline, Calliarthron tuberculosum (Post. & Rupr.), is the most resistant to consumers; it was not eaten by any of four moliuscan herbivores tested. Again it appears to be the structure of the plant that provides this protection. When this species is ground and placed in agar, it is readily eaten by all four herbivores. The encrusting corallines (approximately six species) appear to be the best spatial competitors, occupying the majority of the space within the pools, and were the winners of all overgrowth encounters with articulated coralline species.

Intraspecific variation in the population dynamics and growth of the limpet, Cellana tramoserica.

Populations of the limpet Cellana tramoserica (Sowerby) from high, mid, and low intertidal regions, and from a subtidal zone, were studied at Cape Banks (N.S.W.), Australia. Individuals from the subtidal population had the largest mean and maximum shell size, the low and high shore populations were intermediate, while the midshore population had both the smallest mean and maximum size. The density of adults showed the reverse trend: the midshore region had the greatest adult population density while the subtidal population had the smallest density. The density of juveniles and recruits was negatively correlated with tidal height in the intertidal areas, but the density of both age-classes was smallest in the subtidal region. The rate of growth of individuals was negatively correlated to the adult density of a site; individuals from the subtidal population grew the fastest, while those from the midshore region grew the slowest. The level of adult mortality of the four populations was similar, with an annual rate of between 50-60%. Juvenile mortality did, however, differ among populations; reduced percentages of juveniles reached adult size in the mid and low shore populations than in the highshore and subtidal populations.The expected lifetime fecundity of individual females differed among the four populations. Subtidal individuals were expected to spawn 40 times the amount of gonad material during their life than were individuals from the midshore population. Individuals from the high and low populations probably spawn 10 times more than those from the midshore region. Differences in the fecundities of individuals were not likely to be the result of genetic differences because experimental transplants and manipulations of density showed that individuals from all the intertidal populations could increase their growth rate to match that of subtidal individuals. The implications of the difference in lifetime fecundity among populations are discussed.

Reproductive strategies in intertidal populations of two co-occurring seagrasses (Zostera spp.)

Reproductive strategies were analyzed in intertidal populations of two seagrasses of the genus Zostera to test the application of r–K selection theory to a novel habitat. Zostera americana has appeared in the study area recently and is spreading rapidly. It grows in the mid to upper intertidal regions and is an r-strategist; i.e., a rapidly growing, essentially annual plant that uses a large proportion (up to 25%) of its resources for flowering. Zostera marina, the native eelgrass, grows in the mid to low intertidal regions and is a K-strategist; i.e., a perennial that uses a large proportion of its resources for maintenance via rhizomes and roots. Considering that the environment becomes less predictable for marine plants on a gradient from the lower to the upper end of the intertidal zone, then the two seagrasses behaved as predicted by the theory.

The effects of emergence and submergence on the photosynthesis and respiration of marine macrophytes

Respiration and gross and net photosynthesis were measured for three species of intertidal algae growing at 10 and 18°C when they were submerged and emerged. Evidence that the high intertidal alga, Fucus distichus is physiologically well adapted for its position in the intertidal zone comes from the following observations: (1) maximum gross and net photosynthesis were greater for emerged than submerged thalli; (2) net photosynthesis for emerged thalli was a maximum at 20% desiccation; (3) only above 50% desiccation did net photosynthesis steadily decrease. The representative of the low intertidal region, Iridaea cordata, appears to be better adapted for submergence than emergence since values of maximum gross and net photosynthesis for submerged thalli were always greater than when emerged. When this alga was emerged, respiration was greater than when submerged. Ulva fenestrata, a low to mid-intertidal alga, exhibited an intermediate response to submergence and emergence, in terms of net photosynthesis, when compared to Fucus and Iridaea.

The ecology of Mytilus edulis L. in exposed rocky intertidal communities

Information is given to show that Mytilus edulis L. is an important component of exposed rocky coast communities of the Western Hemisphere. It is abundant on the exposed coast of Washington State with a potential distribution extending from + 10.6 ft ( + 3.2 m) down to at least 10 m depth: it is not continuous along this entire gradient. It dominates a band from +10.6 ft down to +9.6 ft ( + 3.2 to + 2.9 m) tidal height where it usually intergrades with its congener M. californianus Conrad. Its upper limit appears to be determined by desiccation stress and the lower probably by competition and or predation. In the mid-intertidal zone, from + 5.6 to + 9.6 ft ( + 1.7 to 2.9 m), where M. californianus is dominant, M. edulis occurs in patches of cleared space which usually form in the M. californianus bed matrix in winter months. Here, it acts as an opportunistic species by colonizing quickly and growing rapidly to reproductive size. It is preyed upon by Thais spp. which prefer it to Mytilus californianus and eventually is eliminated from these patches. It also occurs, sometimes abundantly, in tufts of the red alga Endocladia muricata (Postels & Ruprect) J. Agardh at high and mid-intertidal heights. In low intertidal and subtidal regions, to ≈ 10 m depth, Mytulis edulis can be found in refuges of filamentous or intricately arranged substrata which generally offer protection from predation. These are represented by a wide variety of forms such as hydroids. bryozoans, filamentous algae, coralline algae, and kelp with convoluted holdfasts or complex stipes.