Mass brooding of the blue octocoral,Heliopora coerulea on a sedimented equatorial reef

The octocoral Heliopora coerulea is a gonochoric surface brooder. Although the species is common on shallow Indo-Pacific coral reefs, information on its reproductive biology is limited and spawning timings have only been reported from four locations. We report the first observations of surface brooding in H. coerulea on a sedimented equatorial reef. In April 2014, 46 and 26 brooding colonies were recorded, respectively, from reefs fringing the islands of Kusu and Lazarus in Singapore. The brooded coral larvae were tightly bound to inflated coral polyps, forming a dense white mat which blanketed the brown coral tissue. The inflated polyps also protruded from layers of sediment, which accumulated in colony crevices, such that the brooded larvae were elevated above the settled sediment. Our observations supplement existing knowledge on the reproductive timing of H. coerulea and highlight the adaptations that improve survival of this species on sediment-impacted reefs.     

Population dynamics of the mushroom coral Heliofungia?actiniformis in the Spermonde Archipelago, South Sulawesi, Indonesia

The fungiid Heliofungia actiniformis is one of the most popular coral species in the Indonesian aquarium trade, yet information on the biology of this species is limited. H. actiniformis growth rates, population size–frequency distributions and the seasonality of recruitment rates were measured at three replicate sites in the Spermonde Archipelago, South Sulawesi. Growth and population models were applied to estimate coral ages, mortality rates and the size of maximum yield. Growth decreased linearly with polyp size. High numbers of attached polyps budded from clusters of stalks attached to the reef, with each cluster originating from the settlement of a sexually produced larva. Neither the settlement of sexual recruits, nor their asexual budding, showed seasonality. The overall population structure reflected the high mortality rates of young, attached polyps (Z = 0.5–0.6 yr⁻¹), and the much lower mortalities of free-living individuals (Z = 0.05–0.08 yr⁻¹). There were no statistically significant differences in overall mortality rates and the age–frequency distributions of polyps aged 0–15 years between the sites. Differences in the abundance of large H. actiniformis polyps at the three replicate sites were correlated with percent cover of coral rubble. The application of the Beverton and Holt model revealed the highest biomass per H. actiniformis recruit was 12 cm, corresponding to a polyp age of 20 years.     

Manganese‐Rich layers in calcareous deposits along the Western shore of the Dead Sea May have a bacterial origin

Spore formers were detected in samples of calcareous crust with manganiferous laminations and in water from the Dead Sea in Israel. They were able to grow in media made with fresh water but not with synthetic Dead Sea water. Some of these spore formers were also able to oxidize Mn (II) in fresh water. No other bacteria capable of both growth and Mn(II) oxidation in hypersaline media prepared with synthetic Dead Sea water were found in the samples. However, bacteria capable of growth and Mn(II) oxidation in fresh water media were detected in water and sediment from fresh water springs at Ein Feshkha and in lake water and sediment from the beach near Wadi Kidron. Both sites are located on the western shore of the lake. These findings suggest that the manganiferous laminations in calcareous crusts and concretions in the Dead Sea along its western shore may have originated, at least in part, from manganese oxide formed by bacteria in fresh water environments on shore and washed into the lake in runoff, with subsequent incorporation into the crusts and concretions.     

On natural metamorphosis inducers of the cnidarians Hydractinia echinata (Hydrozoa) and Aurelia aurita (Scyphozoa)

 Hydractinia echinata and Aurelia aurita produce motile larvae which undergo metamorphosis to sessile polyps when induced by external cues. The polyps are found at restricted sites, A. aurita predominantly on rocks close to the shore, H. echinata on shells inhabited by hermit crabs. It has been argued that the differential distribution of the polyps in their natural environment largely reflects the distribution of the natural metamorphosis-inducing cues. In the case of H. echinata, bacteria of the genus Alteromonas were argued to meet these conditions. We found that almost all substrates collected in the littoral to induce metamorphosis in H. echinata, and several bacterial strains isolated from the sea, including the common E. coli, induce metamorphosis efficiently. In A. aurita metamorphosis may be induced by the water–air interface, whereby metamorphosis precedes (final) settlement. Received: 7 December 1998 / Accepted: 8 July 1999     

Seasonal growth patterns of Saccharina latissima (Phaeophyceae,Ochrophyta) in a glacially‐influenced subarctic estuary

Global climate warming is exacerbating the melting of glaciers in Arctic and subarctic nearshore regions. Glacial discharge causes increases in sedimentation, abrasion of organisms, and sand/silt cover along with lowered light intensity, salinity, nitrate and hard substrate cover. These effects can have deleterious consequences on foundation species, such as the kelps that provide important habitat structure and support tightly‐linked food webs. The purpose of this study was to determine if the kelp, Saccharina latissima, from a glacially‐influenced and an oceanic shore in a subarctic Alaskan estuary exhibits differing seasonal growth patterns in response to its environment. Reciprocal in situ shore transplant studies examined seasonal patterns in growth, physiological competence (as maximum quantum yield), morphology and storage product levels (mannitol) of S. latissima. In situ growth was seasonally different at the two shore locations, with a shorter growing season at the glacially‐influenced shore. During the glacial melt season, the thalli at the two shore locations were morphologically distinct. Mannitol levels were typically higher in thalli from the oceanic site, with generally low mannitol levels at the end and the beginning of the growing season on both shores. Maximum quantum yield was consistently high (≥0.7) at both shore sites and did not vary seasonally. Growth rates of glacially‐influenced transplants to the oceanic shore suggest that the glacially‐influenced population has a different seasonal growth pattern from that of the oceanic shore site, which seems to be genetically fixed or based on differences in gene expression. It appears that S. latissima is a highly resilient species, partly due to high phenotypic plasticity, which may have led to genetic fixation under persistent glacial conditions.     

Size-structures of populations of the mushroom coral<Emphasis Type="Italic"> Fungia fungites</Emphasis>: the role of disturbance

Changes in the size-structure of populations of the mushroom coral Fungia fungites were quantified at two reefs during four annual surveys. Exposure to disturbance was predicted to affect the size and frequency of life history stages of polyps at each reef and their variability through time. The Mainland reef experienced frequent and intense disturbances, primarily as exposure to cyclones and substantial sedimentation, which were comparatively absent from the East Lewis reef. Disturbance to the Mainland reef was evident in the smaller size of polyps, and the many parent polyps, asexual buds, and polyp skeletons, which were all absent from the East Lewis reef. Over three years, the number and area cover of polyps at the Mainland reef decreased to 9% and 3% of their initial values respectively, compared with 73% and 36% at East Lewis. The size-structure of polyps at East Lewis remained comparatively stable; whereas, the abundance of all life history stages at the Mainland reef had high but variable rates of decline each year. Changes in the size-structure of polyps at the Mainland reef indicated it was exposed to levels of disturbance that it had not experienced, and would not recover from, for many years.     

Influence of species richness and environmental context on early survival of replanted mangroves at Gazi bay, Kenya

Mangrove reforestation projects often suffer from low sapling survival, especially after transplanting saplings from nurseries to reforestation areas. This may be due to the sediment conditions at the target site, the planting strategy or failure to re-establish ecosystem processes. We examined experimentally the influence of environmental context, species richness and identity, sapling height and position on sapling survival and environmental variables linked to ecosystem functioning at deforested sites in Gazi Bay, Kenya. At site 1, a high shore location, 32 plots (36 m²) were planted with 8 treatments: all possible combinations of Avicennia marina, Bruguiera gymnorrhiza, and Ceriops tagal and an unplanted control (total: 3390 saplings; 4 plots/treatment). At site 2, a low shore location, the influence of sapling height, sapling position and sediment depth were tested by planting with 697 Sonneratia alba in a single monospecific plot (341 m²). After ∼2 years, there were significant differences in survival among the three species at site 1 with Bruguiera gymnorrhiza recording the lowest survival rate (29%). Survival was correlated with salinity (a strong effect) and height above chart datum (a weaker effect) at site 1. Sapling position did not significantly affect survival at either site. There was thus no evidence that early survival of transplanted saplings is influenced by the species mix in which they are grown, or by their position in the plot. Rather the tolerance of individual species to salinity was the key to their survival at the high tidal site. Species mix also had no significant effects on environmental variables in the plots. The former presence of a species at a site does not guarantee it will succeed there again if environmental degradation has exceeded species’ tolerance. Handling editor: T. P. Crowe     

Using short-term growth of enclosed 0-group European flounder, Platichthys flesus, to assess habitat quality in a Danish bay

Instantaneous growth rates of 0‐group European flounder, Platichthys flesus, obtained from two 9‐day enclosure experiments were used to assess the relative quality of three eelgrass and three bare sand habitats in the Bay of Aarhus, Denmark. Measurements of temperature, dissolved oxygen, salinity, sediment structure and biomass of benthic macrofauna were made during the experiments. Gut content analysis was performed after retrieval of the fish. Growth rates of flounder at two bare sand sites were higher or equal to growth rates at the three eelgrass sites, and at a muddy bare sand site in both experiments. The variation in gut fullness of flounder between vegetated and bare sand sites followed the pattern observed in growth rates, but diverged from the spatial variation in prey abundance, which indicates that there were differences in the feeding efficiency between sites. Overall, habitat complexity, i.e. the presence or absence of vegetation seems to be the most important factor determining the growth rates and, by corollary, habitat quality for juvenile European flounder in the Bay of Aarhus.     

Caesium-137 and lead-210 dating of recent sediments from Mondsee (Austria)

Mean annual sedimentation rates over the last 20–30 years were determined in the pre-alpine Mondsee (Upper Austria) using Cs-137 and Pb(Po)-210 profiles for sediment core dating and two natural sediment markers. Lower sedimentation rates of about 2–3 mm yr^–1 were observed in the central part of the lake near the shore at 18–20 m and in the southern part at 30 m depth. Higher sedimentation rates of 4–7 mm yr^–1 were found in the central part of the lake at 47 and 65 m and in the northern bay at 18 and 41 m depth. At both these sites the Pb-210 profiles were strongly disturbed in the upper zone of the sediment cores, whereas the Cs-137 pattern remained intact. The higher annual sediment accumulation rates can be explained only partly by deposition of allochthonous material discharged by the streams, enhanced eutrophication in these parts of the lake, erosion and sediment focusing by turbidity currents being also probable.     

Seagrass recovery in the Northern Wadden Sea?

Aerial surveys on seagrass (Zostera spp.) indicate a three to fourfold increase in bed area from 1994 to 2006 with up to 100 km² or 11% of intertidal flats in the Northfrisian Wadden Sea (coastal eastern North Sea), observed at seasonal maximum in August when flying during low tide exposure 300 to 500 m above ground. When viewed from the air, difficulties in distinguishing between seagrass and green algae and a lack of contrast on dark-coloured mudflats are sources of error in areal estimates. Particularly the positioning of beds remote from shores was imprecise. However, the consistency in method over time gives confidence to the inferred positive trend which is opposite to the global pattern. Both, the spatial pattern and a recent decrease in storminess suggest that sediment stability is the key factor for seagrass dynamics in this tidal area. On exposed sand flats, high sediment mobility may be limiting and along the sheltered mainland shore land claim activities with high accretion rates may cause a scarcity of seagrass. The potential area of seagrass beds may be twice as large as the realized maximum in 2006 but eventually the rising sea level will reverse the observed seagrass expansion.     

Release rates and potential fates of nitrogen and phosphorus from sediments in a eutrophic reservoir

1. Nutrients released from lake sediments can influence water column nutrient concentrations and planktonic productivity. We examined sediment nutrient release [soluble reactive phosphorus (SRP) and ammonia (NH)] at two sites in a eutrophic reservoir (Acton Lake, OH, U.S.A.) that differed in physical mixing conditions (a thermally stratified and an unstratified site). 2. Sediment nutrient release rates were estimated with three methods: sediment core incubations, seasonal in situ hypolimnetic accumulation and a published regression model that predicted sediment phosphorous (P) release rate from sediment P concentration. All three methods were applied to the deeper stratified site in the reservoir; however, we used only sediment core incubations to estimate SRP and NH release rates at the shallow unstratified site because of the lack of thermal stratification. We also compared the total P concentration (TP_S) of sediments and the concentration of P in various sediment fractions at both sites. 3. Anoxic sediments at the stratified site released SRP at rates more than an order of magnitude greater than oxic sediments at the shallow unstratified site. However, P accumulated in the hypolimnion at much lower rates than predicted by sediment core incubations. In contrast, NH was released at similar rates at both sites and accumulated in the hypolimnion at close to the expected rate, indicating that P was ‘lost’ from the hypolimnion through biogeochemical pathways for P, such as precipitation with inorganic material or biological uptake and sedimentation. 4. TP_S was significantly greater at the deeper stratified site and organically bound P accounted for >50% of TP_S at both sites. 5. We examined the magnitude of SRP fluxes into the study reservoir in 1996 by comparing the mean summer daily SRP fluxes from anaerobic sediments, aerobic sediments, stream inflows and gizzard shad excretion. While the SRP release from anaerobic sediments was high, we hypothesise that little of this SRP gained access to the epilimnion in mid‐summer. SRP flux to the reservoir from aerobic sediments was less than from gizzard shad excretion and streams. Large interannual variability in thermocline stability, gizzard shad biomass and stream discharge volumes, will affect SRP loading rates from different sources in different years. Therefore, construction of P budgets for different years should account for interannual variation in these parameters.     

Spatial distribution of algae and invertebrates in the rocky intertidal zone of the Strait of Magellan: are patterns general?

Spatial variability in the distribution of macroalgae and invertebrates was examined at a number of sites in the Strait of Magellan. Two main predictions of models of zonation were tested in this study: (1) consistency in patterns of vertical distribution among sites one to tens of kilometers apart, and (2) homogeneity between areas at the same level on the shore, tens to hundreds of meters apart. Two types of habitat were considered: continuous rocky shores and blocks of rock in gravel beaches. In the former habitat, percent cover estimates of sessile organisms (algae and mussels) were obtained from three replicated plots (0.5 × 0.5 m) sampled non-destructively in each of three random areas (stretches of shore about 20 m long) at each of three levels on the shore: high, middle and low intertidal zone. This procedure was repeated at six different sites along the Chilean coast of the Strait of Magellan. Blocks of rock were sampled at two sites about 1 km apart. Estimates of the abundance of sessile (barnacles and mussels) and mobile (limpets) organisms were obtained for six blocks at each of two levels on the shore (high and low intertidal zone) at each site. At each level on the shore, three blocks were sampled on the top and three on the vertical sides. A single plot was sampled on each block. This design allowed a test of the null hypothesis of no interactive effects between position on the blocks and level on the shore. Both the predictions were falsified: (1) there were large between-site differences in the vertical structure of assemblages and (2) variability between areas at the same level on the shore was large for some of the most common algae. In contrast, the null hypothesis of no interactive effects of position on the blocks and level on the shore was retained. The results of this study show that vertical position on the shore alone is not a good predictor of the structure of assemblages of benthic organisms in the rocky intertidal of the Strait of Magellan. Received: 9 December 1996 / Accepted: 2 May 1997     

Population structure, recruitment, and succession of the brown alga, Padina boryana Thivy (Dictyotales, Heterokontophyta), at an exposed shore of Sirinart National Park and a sheltered area of Tang Khen Bay, Phuket Province, Thailand

The brown algal genus, Padina, has a worldwide distribution in tropical and subtropical climate zones. Padina individuals are common and sometimes dominant in both the intertidal and shallow subtidal regions associated with coral reefs. We investigated the population structure and recruitment of two populations of Padina boryana at an exposed shore in Sirinart National Park (SNP) and a sheltered shore of Tang Khen Bay (TKB), Phuket Province, Thailand. From September 2005 to August 2006, the number of released spores and the height and radius of fronds were measured monthly. New recruits were recorded and monitored on manipulated permanent plots 0.25 m². The experiment was carried out monthly over a year. We found Padina recruits 1 month after the plots were cleared at both sites. There was a significant difference in percentage cover by new individuals between the two locations (P < 0.05) and also at the shore levels within the sites. At SNP, the highest recruitment was found in the uppermost zone, while at TKB high recruitment occurred at all shore levels except at 80-100 m from the shore. The factors influencing recruitment of P. boryana include wave motion, competition with other earlier successional species and sediment. The high availability of reproductive spores throughout the year, the successful recruitment and the Dictyerpa stage promote the successful establishment of Padina populations.     

Variation in the population dynamics of the intertidal pulmonate gastropod Salinator solida Martens (Gastropoda: Amphibolidae) at Towra Point,NSW, Australia

This paper describes variation in the population dynamics of the intertidal pulmonate gastropod solida among mangrove and saltmarsh habitats at Towra Point, NSW, Australia over a two-year period. In general, this paper describes the degree to which the density of the populations fluctuated and the size structure of the populations varied among heights on shore. The density of individuals in the upper mangrove forest was most variable through time and their population size structure was dominated by smaller individuals. The density of populations in the Sarcocornia high on the shore fluctuated least through time and were dominated by large individuals. Those populations found on the mid-shore in the Sarcocornia had population characteristics intermediate to those populations in the upper mangrove forest and the Sarcocornia high on the shore. Analysis of size frequency data indicated that the growth rates of individuals and their annual mortality decreased with increasing height on shore.     

Aspects of the ecology of an exposed shore population of dogwhelks Nucella lapillus (L.)

Summary Up to the third year of life Nucella lapillus (L.) could be aged in the laboratory and in the field using shell characters. Monthly counts along transects on an exposed rocky shore have shown that the age groups behave differently, dogwhelks in their first year migrating upshore, and returning to lower levels in the second year. Adults (three years or older) lived and laid egg capsules in the low shore. The most favourable situation for subsequent hatching of these capsules was where they were permanently submerged in sea water.The first requirement of recently hatched young was probably protection from water movement, but they soon gegan feeding on small mussels. The shell height attained by the end of the first winter was related to winter temperatures, but the main growing season was June to November. Adult size was attained in two years, after which the individuals did not usually grow, but those which did grow during the third or succeeding years may have been nonbreeders or have been castrated by the trematode Parorchis acanthus.The age structure of the population suggested that mortality rate decreased with age, and this was confirmed by calculating annual mortality rates for the first three years of life. Heavy mortality in the low shore during the first winter was due mainly to predation by purple sandpipers. In succeeding winters mortality was low, and predation, the main mortality factor, was restricted to the summer months. At this time Cancer pagurus was the most voracious predator, but it was active mainly in the low shore, and the upshore distribution of second year dogwhelks, which were preferred to other age groups, age groups also led to a more economical use of environmental resources, namely food, winter aggregation sites and breeding sites.     

Stimulation of sulfate reduction rates in Mediterranean fish farm sediments inhabited by the seagrass <Emphasis Type="Italic">Posidonia oceanica</Emphasis>

Sulfate reduction rates and biogeochemical parameters of fish farm sediments across the Mediterranean were investigated in the order to evaluate the potential effects of organic matter inputs on habitat quality for the common seagrass Posidonia oceanica. Four study sites were selected in Spain, Italy, Greece and Cyprus to represent the Mediterranean basin. P. oceanica was found in immediate vicinity of all the farms, which were located at physically exposed sites about 1 km from the shore lines. Organic matter accumulation, sulfate reduction rates and sulfur pools were measured in depth profiles along transects from the farms in both bare and vegetated sediments. Results show that although the organic matter accumulation was minor at the sites (POC < 2.8% DW), the sulfate reduction rates were high, in particular at the largest farm in Italy (up to 212 mmol m⁻² d⁻¹), similar to rates found at shallower, temperate fish farm sites, where higher sedimentation rates can be expected. Sulfate reducing bacteria in these low-organic, carbonate-rich Mediterranean sediments respond strongly to organic matter loadings and cause habitat degradation. Sulfate reduction rates measured in the P. oceanica sediments were among the highest recorded (7.8–42.0 mmol m⁻² d⁻¹) similar to rates found in degrading meadows impacted by organic matter loadings. As sulfate reduction rates were correlated with the sedimentation rates along the transects rather than organic matter pools this suggests mineralization processes were controlled by organic matter loading in fish farm sediments. The vegetated sediments near the net cages were more reduced due to accumulation of sulfides compared to control sites, which is a possible contributing factor to the observed seagrass decline in the farm surroundings. It is recommended that Mediterranean fish farms are placed in areas with rapid dispersal of particulate waste products to minimize organic matter loading of the sediments and thereby preserve habitat quality for benthic fauna and flora.     

Functional indicators of stream health: a river‐basin approach

1. The efficacy of leaf‐litter decomposition, sediment respiration, biofilm biomass, growth, chlorophyll a concentration and the autotrophic index (biofilm ash‐free dry mass/chlorophyll a) and fungal biomass for detecting human‐induced change was evaluated using 24 references and 15 disturbed stream sites located in central Portugal. 2. Decomposition rates of alder (Alnus glutinosa) and oak (Quercus robur) leaves and sediment respiration rates were effective in discriminating impairment. Decomposition was negatively correlated with abiotic factors, such as ammonium and nitrite concentrations, connectivity and alterations in the hydrological regime, and positively correlated with nitrate concentration and oxygen concentration. Sediment respiration rates were correlated with organic contamination, land use and morphological changes. 3. Growth rates of biofilm, concentration of chlorophyll a and the autotrophic index, although 41–73% higher at disturbed compared to reference sites, were not significantly different. These three variables were significantly correlated with total organic carbon, oxygen concentration, pH, nitrite and the presence of dams. Fungal biomass on leaves and biofilm biomass on natural substrata did not differ between reference and disturbed sites. 4. Our findings lend support to the use of functional variables like decomposition and sediment respiration in monitoring and when used together with structural variables should give a more holistic measure of stream health.     

Fatal errors in set as a cost of dispersal and the influence of intertidal flora on set of barnacles

Summary Cyprid larvae of Balanus cariosus settle preferentially on slate plates with a biota characteristic of the lower intertidal shore, and the cyprids also prefer plates with more algae. Cyprid larvae of Balanus glandula had the same preferences in two out of three experiments. We conclude that some component of the flora guides both species during settling and metamorphosis. Data on vertical distribution and fecundity of B. glandula show that the preference for the lower shore decreases fitness of B. glandula at the site of the settling experiments and at most other sites sampled in or near the San Juan Islands, though in some restricted habitats in the San Juans and extensive areas in the adjacent regions of Puget Sound a preference for the lower shore is appropriate. Extensive dispersal among sites is possible in the planktonic period of 2 to 4 weeks. This example supports the hypothesis that a cost to large scale dispersal is lower fitness at many sites within a species' range. In this case the cost is through poorer correlation between stimuli guiding choice of habitat and favorability of habitat.     

Sediment-Associated Phototoxicity to Aquatic Organisms

Phototoxicity is a two to greater than 1000-fold increase in chemical toxicity caused by ultraviolet radiation (UV), which has been demonstrated in a broad range of marine and freshwater fish, invertebrates, and other aquatic organisms in water column exposures. Field collected sediments containing polycyclic aromatic hydrocarbons (PAHs) and other contaminants are phototoxic to sediment-dwelling organisms in laboratory tests, but in situ or field investigations of phototoxicity have not been reported. Sediment provides a pathway for the bioaccumulation of phototoxic chemicals through contact with and ingestion of bedded and suspended sediment, and maternal transfer, but risks are uncertain. Risks from sediment-associated phototoxicity will be greatest in areas of both high contaminant exposure (e.g., surficial and suspended sediments in harbors, outfall areas, and spill sites), and high UV exposure (e.g., high optical clarity or shallow depths). Organisms and life-stages most at risk will be those translucent to UV that inhabit the photic zone and near shore areas, but benthic organisms may have generally low UV exposure because of life history and morphological characteristics. Site-specific assessments are needed to characterize risks both spatially and temporally because of heterogeneous sediment contamination and large differences in species sensitivity and exposure pathways.     

Effect of wave exposure on vegetation abundance, richness and depth distribution of shallow water plants in a New Zealand lake

SUMMARY 1. The effects of physical disturbance in terms of wave exposure, shore slope and substrate mobility on the presence, species richness, cover and depth limits of the low‐growing, shallow water macrophyte community (called the low mixed community) were examined at 41 shore sites in Lake Wanaka, South Island, New Zealand. 2. Wave exposure at a site was described by the previous year's maximum depth of sediment motion and maximum vertical extension of waves, determined from a computer wave model. Shore slope at each site was recorded from ?1 to 0 m depth, and sediment stability was assessed as the cover of small gravel. 3. The low mixed community was only present on sites where the previous year's maximum depth of sediment motion was <8 m, maximum wave run‐up was <0.3 m, shore slope <0.12 m m^?1, and small gravel cover <78%. 4. Species richness, cover and depth limits of the low mixed community decreased with increasing disturbance on the sites. Sixty‐two percentage of the variation in species richness could be explained by physical disturbance variables when all sites were included (N=41). When only sites with a low mixed community were included (N=22), only 18% of the variation was explained. Species richness within sites supporting a low mixed community is thus poorly explained by physical disturbance, whereas presence or absence is better explained. There was no evidence to support the intermediate disturbance hypothesis in this study. 5. Disturbance as a result of waves explained 86% of the variation in cover among sites with a low mixed community and accounted for 68 and 58% of the variation in upper and lower depth limit of the low mixed community, respectively. 6. The models obtained in this study can be used as predictive models for the low mixed community in New Zealand lakes in relation to natural physical disturbance on the shore. By integrating these results with previous studies on the effect of water level fluctuation, we describe a generalised optimum physical habitat for the low mixed community in New Zealand lakes.