Epiphytic Macroalgae Research Articles

Epiphytic diatoms associated with red mangrove (Rhizophora mangle) prop roots in Bahía Magdalena, Baja California Sur, Mexico

The first floristic inventory of benthic diatoms is provided for the Bahia Magdalena-Bahia Almejas lagoon system. Samplings were carried out during November of 1999. The oxydized samples were mounted permanently. Eighty six diatom taxa were identified, out of which 59 are new records for the Bahia Magdalena area, and 12 taxa are new for the Baja California peninsula. Taxa recorded previously as rare in other substrata are common or abundant on the epiphytic macroalgae of mangrove prop roots. Other species are mainly epipelic forms, while 24 are commonly found as tychoplankton in the area. Certain taxa appear to be characteristic of mangrove systems in general.

한국산 진두발, Chondrus ocellatus의 생장과 질병에 대한 연구

동해안의 3개 정점(삼척, 영덕, 포항)과 서해안의 2개 정점(학암포, 만리포)에서 여름철(7, 8월)에 진두발을 채집하여 생장, 성숙, 배우체와 사분포자체 비율 및 질병에 대한 연구를 실시하였다. 진두발의 체장은 개체군별로 평균 6.10~9.69 cm였으며 만리포에서 최소였고 포항에서 최대로서 동해안 개체가 서해안 개체에 비해 큰 것으로 확인되었다. 개체가 서해안 진두발에 비해 큰 것을 확인하였다. 진두발 개체군의 영양체 비율은 26.7~66.7 %였으며, 영양체를 resorcinol 방법으로 구분한 후 배우체:사분포자체 비율은 동해안에서 1.7:1로 배우체가 우점하였고 서해안에서는 학암포에서 1:1.1, 만리포에서 1:2.3로서 포자체가 번무하였다. 본 연구에서 한국산 진두발은 다양한 질병(백색증과 녹반증 등), 내생조류와 착생조류를 가지고 있었으며, 여름철의 진두발은 건강한 조체는 20~40 %로서 많은 개체가 질병을 가지고 있었다. 진두발은 현재까지 동정되지 않은 사상형 녹조류인 내생하는 Ulvella sp.를 가지고 있었다. 이러한 내생조류는 유럽과 캐나다의 주름진두발에서 관찰되는 감염성 병원체로서 보다 많은 관심과 연구가 요구된다. The growth, reproduction, gametophyte(G)/tetrasporophyte(T) ratio, and diseases of Chondrus ocellatus populations were examined at 3 sites (Samcheok, Youngduk, Pohang) of East coast and at 2 sites (Hakampo, Manripo) of West coast in between July and August, 2013. Average plant lengths were 6.10~9.69 cm and it was minimum at Manripo and maximum at Pohang population. In general, average plant length and weight of C. ocellatus were greater on East coast than West coast populations. The proportion of vegetative plant was between 26.7~66.7 %, and G/T ratio of total plants including vegetative plants after testing resorcinol method was 3:2 on the East coast where is gametophyte dominant area. However, G/T ratio was 1:1 at Hakampo and 1:2.3 at Manripo representing tetrasporophyte dominance. In the present study, Korean C. ocellatus have various diseases (white colour and green colour), an endophytic alga(Ulvella sp.), and many epiphytic macroalgae and diatoms. Healthy C. ocellatus plants were about 20~40 % in summer population and most of plants had disease. Chondrus ocellatus had a filamentous green alga, endophytic Ulvella sp. which was not identified. The endophyte is easily observed in C. crispus growing in Europe and Canada and it is recognised as a pathogen destroying population and reducing yield of C. crispus. Thus more interest and research on the endophytic algae and disease of C. ocellatus are required.

Distribution of epiphytic macroalgae on the thalli of their hosts in Cuba

We investigated the distribution of epiphytic macroalgae on the thalli of their hosts at eight localities along the southeastern coast of Cuba between June 2010 and March 2011. We divided he epiphytes in two groups according to their distribution on the host: those at the base of the thallus and those on its surface. We determining the dissimilarity between the zones and the species involved. We identified 102 taxa of epiphytic macroalgae. There were significant differences between the two zones. In 31 hosts, the number of epiphytes was higher on the surface of the thallus, whereas the number of epiphytes was higher at the thallus base in 25 hosts, and the epiphytes were equally distributed between the two zones in five hosts (R=−0.001, p=0.398). The mean dissimilarity between the two zones, in terms of the species composition of the epiphytic macroalgae, was 96.64%. Hydrolithon farinosum and Polysiphonia atlantica accounted for 43.76% of the dissimilarity. Among macroalgae, the structure of the thallus seems to be a determinant of their viability as hosts for epiphytes.

Epiphytic macroalgae from Boa Viagem Beach, Recife, Pernambuco state, Brazil

The aim of this study was to carry out a taxonomic survey of epiphytic seaweeds that occur on reefs of Boa Viagem Beach, located in the metropolitan region of Recife – Pernambuco state, Brazil. The samplings were performed in the dry season (December 2009) and rainy season (April 2010) at intertidal reefs using 625 cm2 squares. Voucher specimens are deposited at the Herbarium of the Instituto de Botânica, São Paulo, Brazil (SP). A total of 48 taxa were recorded of which 20 were Chlorophyta, 27 Rhodophyta and one Heterokontophyta. The most representative orders were Ceramiales and Cladophorales, with 17 and 10 taxa respectively. Nine species are new additions to the flora of Pernambucan coast. Gelidium pusillum (Stackh.) Le Jol. 1863 and Chondracanthus saundersii C. W. Schneid. and C. E. Lane 2005 had the highest number of epiphytic macroalgae. The majority of species was collected in the rainy season and on wave-exposed sites.

<strong>Additions to the epiphytic macroalgae flora of Bahia and Brazil</strong>

The northeastern coast of Brazil is one of the richest and most diverse areas for the marine algae, but there are still many gaps in our knowledge about the flora, especially in terms of deep-water taxa and small epiphytic macroalgae. Studies of the epiphytic algae on Acetabularia crenulata from the coastal waters along the beaches of Barra Grande and Penha, Vera Cruz, Itaparica Island, Bahia State, Brazil, revealed the occurrence of the genus Chroodactylon and the species Chroodactylon ornatum in the South Atlantic Ocean. The red algae Chondria collinsiana and green algae Phaeophila dendroides expanded its geographical distribution to the northeastern coast of Brazil; the green algae Ulva clathrata and U. flexuosa subsp . paradoxa are new records for the coast of Bahia. The vegetative and reproductive structures are described in detail and a comparison with similar species is provided.

Planctomycetes diversity associated with macroalgae

Planctomycetes associated with 12 macroalgae from the north coast of Portugal were isolated, using an improved method. A total of 138 isolates were found to comprise 10 operational taxonomic units (OTUs), with 65% of the strains being closely related to the species Rhodopirellula baltica. The other strains are probably new species or genera related to Rhodopirellula, Blastopirellula and Planctomyces. Some of the OTUs isolated are unique and have never been found before in previous studies. Catalyzed reporter deposition-FISH confirmed the presence of Planctomycetes on macroalgal surfaces. This study provides the first report of the cultured diversity of Planctomycetes on the epiphytic macroalgae community and presents clear evidence of their nutritional and intimate relationship.

Dietary Segregation of Pelagic and Littoral Fish Assemblages in a Highly Modified Tidal Freshwater Estuary

AbstractEstuarine food webs are highly variable and complex, making identification of their trophic pathways difficult. Energy for the food web of the San Francisco Estuary is thought to be based largely on in situ phytoplankton production, but little attention has been paid to littoral habitats, where other energy sources may be important. We analyzed the stomach contents of over 960 juvenile fishes and the stable carbon and nitrogen isotope ratios of these fishes and their potential food resources in pelagic and littoral habitats from the tidal freshwater area of the estuary. The mixing model IsoSource was used to examine energy sources important to consumers. Our results show evidence of two predominant food web pathways. Pelagic fishes and some littoral fishes showed strong dependence on a zooplankton–phytoplankton trophic pathway. However, the majority of fishes in littoral habitats had diets and carbon isotope ratios consistent with energy arising from submerged aquatic vegetation and epiphytic macroalgae. IsoSource revealed that the overall majority of nutrition of littoral fishes originated from consumption of grazer amphipods. Examining both stable isotopes and stomach contents allowed us to identify a food web with contributions to resident fishes that had been previously underestimated in the estuary. This study provides insight to how estuarine food webs have changed over the last few decades and highlights why the functions of habitats must be understood for effective restoration planning.

Variations in Posidonia oceanica meadow structure along the coast of the Dugi Otok Island (eastern Adriatic Sea)

Although the anthropogenic impact on Posidonia oceanica meadows in the Mediterranean Sea has been studied over the last few decades, the data about the status of this endemic magnoliophyte are scarcer from the Adriatic Sea. Samples of P. oceanica meadows were collected in June and July 2004 using SCUBA diving at 8 sites in the area of the Dugi Otok Island, all at depths of 10 m. The meadow's shoot density was measured, and shoots were collected to be examined and compared through number of leaves per shoot, leaf surface per shoot, leaf area index, number and biomass of taxa of epiphytic flora. Significant differences in P. oceanica meadow structure were found among investigated sites, especially between sites in the vicinity of the fish farm and the other sites. Meadow density decreased at sites in the Dugi Otok channel and the main impact factors seem to be the input of organic matter, originating from the fish cages and sewage input. These human activities are a source of nutrient pollution and stimulate blooms of phytoplankton and higher algae. The sea grass meadow vitality seems to be more negatively affected in the channel. The highest values of shoot density were recorded at investigated sites VR and ME at the outer part of the Dugi Otok Island. The shoot density was very low at site FU, situated in the channel. Biomass of the epiphytic algae exhibited the highest values at the site FU, while at the other investigated sites the values were significantly lower. Concerning the epiphytic macroflora, a total of 55 taxa of epiphytic macroalgae were identified and the class Rhodophyta dominated in all samples. The present study shows the high differences in morphological and structural characteristics of Posidonia oceanica meadows among various sites with and without anthropogenic influence.

Retrospective analysis of epiphyte assemblages in relation to seagrass loss in a eutrophic coastal embayment

This is a retrospective study of shifts in species composition of epiphytic macroalgae that occurred during a period of seagrass loss in Cockburn Sound, Western Australia. Detailed analysis of data on relative abundances of 108 epiphytic taxa collected over 2 yr from 27 widely dispersed sites around Cockburn Sound showed differences in epiphyte composition between sites with loss of sea- grasses (Loss sites) and those with no loss in the the long-term (No Loss sites). Future seagrass losses, however, were not predicted by shifts in species composition. Most species were rare and varied with season of sampling. Hence, varying assemblages of species contributed to differences on each sam- pling occasion. Only 6 of the 108 species were strong, consistent contributors to differences between Loss and No Loss sites (Sphacelaria sp., Laurencia sp., Enteromorpha intestinalis, E. prolifera, Ulva lactuca, Acrochaetium sp.) and could be considered as 'indicator species'. Only 2 species (Sphacelaria sp. and Laurencia sp.) were present consistently in high abundances at No Loss sites. Foliose green algae (Ulva sp., Enteromorpha spp.), commonly considered to signal eutrophication, were found con- sistently in higher abundances at Loss sites. Shifts in epiphyte species composition correlated with patterns of nutrient loading and seagrass decline, in addition to the increases in biomass reported earlier, but did not predict future seagrass loss.

Seasonal and bathymetric variations of epiphytic macroflora on Posidonia oceanica (L.) Delile leaves in the National Marine Park of Zakynthos (Greece)

A survey on the epiphytic macroalgae growing on Posidonia oceanica leaves was conducted along a depth transect in Laganas Bay (National Marine Park of Zakynthos, Greece). Samples were collected using scuba diving at depths of 5, 10 and 15 m in July 2001 and January 2002. The meadow’s density was measured at each depth and shoots were collected to examine and/or calculate: number of leaves per shoot, leaf surface per shoot, Leaf Area Index (m 2 AEm )2 ), number of epiphytic taxa and their coverage. Meadow density decreased at deeper sampling sites. Total leaf number was relatively constant at different depths in both summer and winter. Maximum leaf surface per shoot occurred at 15 m for both sampling periods. Leaf Area Index decreased from shallow to deep stations because of the decrease in the meadow’s density. Concerning the epiphytic macroflora, a total of 30 taxa, at specific and infraspecific rank, were identified. Filamentous and crustose macroalgae were abundant in summer, and crustose forms dominant in winter. The number and coverage of identified macroalgae varied between seasons, with higher values being observed during summer. Macroalgae taxa and coverage decreased from the shallowest to the deepest station during both seasons. The present study shows that many parameters play an essential role in epiphytes settling, among them leaf features, depth, and light intensity.

Community structure and food web based on stable isotopes ( δ15N and δ13C) analysis of a North Eastern Atlantic maerl bed

Maerl beds are highly biodiverse biogenic substrata that have been receiving increasing attention in the last decade. Although maerl beds represent important nursery areas for commercial fishes and molluscs, little is known on the trophic web of their communities. Community structure parameters of maerl bed of the Bay of Brest (species richness, abundance, biomass and dominating species) were studied in parallel with the carbon and nitrogen isotopic composition of their main benthic species (macrofaunal, and megafaunal organisms) in order to assess the trophic levels and differences in the potential food sources of maerl inhabitants. The major potential sources of energy were identified to originate either from epiphytic macroalgae and microphytobenthos both growing on maerl thalli, together with sedimenting (sedimentary) particulate organic matter (POM) originating from the water column. The majority of the macro- and megafaunal organisms investigated were filter feeders, selective-deposit feeders and predators/scavengers. Filter feeders fall into three different groups representing different trophic pathways (i) sponges feeding directly on POM (water column filter feeders I), (ii) ascidians and holothurians feeding on POM and probably captured pelagic preys (water column filter feeders II), and (iii) filter feeding molluscs and crustaceans were hypothesised to feed on microphytobenthos or on decaying sedimented POM (Interface filter feeders). Selective deposit feeders were also divided into two subgroups. Carnivores were also distinguished between those with scavenging habits and true predators. Coupling of the trophic levels observed with the community biomass structure revealed that most of the benthic biomass derives its food from detritic sedimented POM and/or microphytobenthos, with interface filter feeders (23% of the biomass), selective deposit feeders (12%). Carnivores made up to 14% of the total biomass. Generally stable isotopes ratio mean values overlap and cover a large range within feeding types, indicating a strong overlap in food sources and a high degree of complexity of the food web presumably due to the diversity of the potential food sources.

δ15N and δ13C analysis of a Posidonia sinuosa seagrass bed

Potential food sources and dominant invertebrates and fishes were collected for the examination of variability in 13C/ 12C and 15N/ 14N to determine the sources of carbon available to consumers within a Western Australian Posidonia sinuosa-dominated seagrass bed. Autotrophs showed a wide distribution of δ 13C values, with P. sinuosa at −11.3 ± 0.8‰ and macroalgae ranging from −16.6 to −31.7‰. This variation allowed us to successfully identify macroalgae as the main contributor of carbon to the trophic structure, although no distinction could be made between epiphytic macroalgae on seagrass, or allochthonous macroalgal sources. The range in δ 15N ratios among potential food items at the trophic base was too small to make it useful as tracer of nitrogen flow pathways, but it consistently increased from macrophytes and detritus (4.1–6.8‰), to invertebrates (5.7–7.4‰) located near the middle of the food web, to fishes (8.3–11.9‰), with piscivorous species such as Leviprora inops generally having a higher 15N. δ 13C of seston (−12.8‰) and sedimentary organic matter (−8.7‰) indicate that seagrass material is the main contributor to these two carbon pools, and that very little of it contributes to animal biomass.

Structure of Diatom Assemblages Living on Prop Roots of the Red Mangrove (Rhizophora mangle) from the West Coast of Baja California Sur, Mexico

ABSTRACT Samples of epiphytic diatom assemblages found on prop roots of red mangrove (Rhizophora mangle) from four sites were collected at two tidal levels of exposure on two different dates from the cool season (autumn, spring). The overall floristic analysis yielded 171 diatom taxa, including 16 new records for the Baja California peninsula. Diversity estimates were among the highest ever measured for benthic diatoms using Shannon's (mean H′ = 4.89) and Simpson's (0.945) indices. Many species scored high on the Biological Value Index (BVI), thus reflecting their numerical importance within the assemblages. According to diversity values and overall species composition, all sampling sites represented a similar habitat consisting of three types of substrates: prop roots, epiphytic macroalgae, and sediments. These values are considered to represent stability in the diatom assemblages living on red mangrove prop roots. Thus, the conditions determined by periodic tidal exposure are not to be considered extrem...

Phosphorous dynamics in a temperate intertidal estuary

Conservation and management of aquatic systems require detailed information of the processes that affect their functioning and development. The objectives of the present work were to describe the phosphorus dynamics during a complete tidal cycle and to quantify the relative contribution of the most common estuarine areas (e.g. seagrass beds, salt marshes, mud- and sand-flats without vegetation) to phosphorus net internal loading in a temperate intertidal estuary. Results show that phosphate efflux rates were higher during the first hours of tidal flood, and that phosphate concentrations were lowest at high tide. During tidal ebbing, ephemeral tide pools may cover a considerable percentage of the intertidal area. In these tide pools, water shallowness combined with enhanced temperatures stimulate the occurrence of high phosphate effluxes. The effluxes to the main water body during high tide contributed 57% of dissolved inorganic phosphorus and efflux during low tide contributed 43% to the net internal loading. Calculations of the phosphate net effluxes (kg P) indicate a strong contribution of the bare bottom mud-flats to the whole system internal phosphate loading, especially during the warmer periods. As a consequence of eutrophication, perennial benthic macrophytes are commonly replaced by fast-growing epiphytic macroalgae. Calculations showed that for a hypothetical intertidal estuary in a temperate region, management programs considering an eventual re-colonization of mud-flats by seagrasses or salt marsh plants may reduce the P-efflux by 13–16 kg ha −1. For example, in the small Mondego estuary, eutrophication has contributed to a reduction of the Zostera noltii meadows, leading to an increase in 190 kg of phosphorus net internal loading.

Reefs as contributors to diversity of epiphytic macroalgae assemblages in seagrass meadows

The links between macroalgae-covered reefs and diversity and biomass of epiphytic algae assemblages in adjacent seagrass meadows were investigated. Algae assemblages were sam- pled in 3 habitats: on-reef, seagrass meadow near-reef ( 3000 m), off the coast of Fremantle, Western Australia. We interpreted differences among these habitats as evidence that proximity to reefs influences epiphytic algae assemblages. Propagules in the water column, epiphytes recruiting onto artificial seagrass units (ASU) and assem- blages on natural Posidonia sinuosa were sampled in each habitat. For propagules, ASU and natural P. sinuosa, there were significant differences in the structure of algae assemblages near and distant from reefs, while assemblages near reefs tended to resemble those found on reefs. Multivariate analysis (ANOSIM) confirmed that propagule assemblages near reefs and on reefs were similar, but those distant from reefs differed from those on reefs. Near-reef habitat recorded the highest total number of algal taxa growing on ASU (53), followed by on-reef (44) and distant-from-reef (37) habi- tats. ANOSIM again confirmed that assemblages at on- and near-reef sites were not significantly dif- ferent, but both differed from those at sites distant from reef. We identified 59 species of algal epi- phytes growing on mature P. sinuosa leaves at near-reef and distant-from-reef sites, with only 19 species being common to both habitats, and multivariate analyses were suggestive of differences in assemblage structure. Biomass was only recorded for the ASU epiphyte assemblages and was great- est in the near-reef habitat (0.63 ± 0.11 g shoot -1 ) followed by the on-reef habitat and the distant- from-reef habitat (0.18 ± 0.04 and 0.11 ± 0.01 g shoot -1 , respectively). Our results demonstrate that diversity and biomass of macroalgae epiphytes in seagrass ecosystems differ between habitats of varying proximity to reefs.

Biomass response and changes in composition of ephemeral macroalgal assemblages along an experimental gradient of nutrient enrichment

Most conceptual marine eutrophication models predict that ephemeral and epiphytic macroalgae will become substantially more abundant with increasing nutrient richness. This expectation is based on the fact that most of these fast-growing algae possess high requirements for inorganic N and P and, therefore, suffer from nutrient limitation under nutrient poor conditions. We tested the hypothesis that nutrient enrichment will stimulate the abundance of ephemeral macroalgae by studying the abundance and species composition of these algae on several types of substrata along an artificial nutrient gradient. The total biomass of ephemeral macroalgae differed considerably among different types of substrata. The total ephemeral load was significantly higher on consolidated substrata than on large perennial algae, but we were unable to detect any systematic increase in the abundance of these ephemerals with increasing nutrient richness. We found, however, indications that the composition of the ephemeral assemblage changed with nutrient richness. Hence, corticated filamentous algae (mostly red algae) were more abundant at low nutrient richness while thin foliose algae (mainly green species) tended to become more abundant with increasing nutrient richness in most of the surveyed assemblages.

Epiphytic macroalgae on the introduced brown seaweed Sargassum muticum (Yendo) Fensholt (Phaeophyceae) in Norway

The invasive brown alga Sargassum muticum was first observed growing attached in Norway in 1988. Since then, the species has spread rapidly and is now an established member of the algal community in sheltered areas along the entire Skagerrak coast. In 1999, one population in the outer Oslofjord was investigated for epiphytic macroalgae, and evidence was found of a rich macroalgal community on S. muticum. A total of 82 different algal taxa were identified: 34 rhodophytes, 23 phaeophytes and 25 chlorophytes. The epiphytes found on S. muticum included more than 25% of the total number of algal species found in the Oslofjord area. A summary of all species recorded is given, with floristic notes on particular taxa.

Seasonal and vertical distribution of marine epiphytic algae in the Evoikos Gulf (Aegean Sea, Greece)

The subtidal epiphytic communities of both macroalgae and microalgae of the Aegean Sea have been inadequately investigated. In this paper epiphytic algal assemblages thriving on different hosts [i.e. the phaeophyte Padina pavonia (L.) LAMOUROUX, the chlorophyte Halimeda tuna (ELLIS et SOLANDER) LAMOUROUX and the seagrass Posidonia oceanica (L.) DELILE], were studied in a typical oligotrophic site of the Aegean Sea (Dikastika, Attica Peninsula) during the course of one year (June 1997-May 1998). A total of 47 taxa of epiphytic macroalgae were identified, with Hypnophyceae and Ephemerophyceae being the dominant life forms. The major algal groups (rhodophytes, phaeophytes, chlorophytes) showed a distinct seasonality, with rhodophytes predominating on all hosts. The majority of epiphytes favoured a certain position on the host thallus or blade. A distinct vertical zonation pattern was found, with epiphytes covering only certain host areas (upper-, middle-, lower parts of the plant), and further differentiated between the frond edge and blade's lamina. A total of 175 taxa of diatoms were identified and the diatom assemblages bear great resemblance to typical epiphytic floras, with dominant genera Mastogloia, Amphora, Nitzschia, Diploneis, Navicula and Cocconeis. Mass development of epiphytic diatoms on certain hosts implies host preference, but no host-specificity could be ascertained. The total epiphytic species composition seems to be affected by the seasonal alteration of abiotic factors. Epiphytic macroalgal species abundance and diversity was the highest during spring, having a possible competitive influence on the epiphytic diatom growth, whereas higher species abundance of diatoms during summer might furthermore be attributed to the surface increase of macroalgae.

A comparison of spatial and temporal patterns in epiphytic macroalgal assemblages of the seagrasses Amphibolis griffithii and Posidonia coriacea

Studies of patterns in assemblages of epiphytic macroalgae growing on seagrasses have largely focussed at the scale of leaves or shoots. Few have examined patterns at larger spatial scales or the influence of host seagrass type on these patterns, despite interest in monitoring changes in epiphyte composition that can lead to the death of seagrasses. We studied spatial pat- terns in assemblages of epiphytic macroalgae on 2 seagrass species with different morphologies and longevity, Amphibolis griffithii and Posidonia coriacea, which co-occur on Success Bank, West- ern Australia. Epiphyte assemblages were described for each species at a hierarchy of spatial scales (sites separated by 10s, 100s and 1000s m) in summer and winter. At all locations and at both times, A. griffithii supported a higher species richness. A total of 91 taxa were recorded on A. griffithii and 70 on P. coriacea. Both seagrass species showed strong temporal patterns in their epiphyte macro- algal assemblages, but this was stronger in P. coriacea. For A. griffithii spatial variation was the dominant pattern. Epiphyte assemblages of the 2 seagrasses displayed striking differences in pat- terns of dissimilarity at different spatial scales. For A. griffithii, Bray-Curtis dissimilarity (D) among pairs of samples progressively increased with increasing spatial scale (D = 0.31, 0.37 and 0.47 at scales of 10s, 100s and 1000s m, respectively). For P. coriacea, the differences among samples sepa- rated by 10s m or 100s m were relatively small (0.29 and 0.32, respectively), but the differences among samples 1000s m apart were much greater (0.52). We suggest that the differences in spatial and temporal patterns between species of seagrass may reflect an interaction of timescales of seagrass longevity with timescales of algal reproductive biology and the dispersal ranges of algal propagules. Due to the high turnover of P. coriacea leaves, the assemblages present at any given time are strongly influenced by recent recruitment events. The epiphytic assemblage of long-lived A. griffithii integrates a much longer period of recruitment, so that recent events may produce comparatively smaller shifts in composition. The longevity of A. griffithii may also permit local reinforcement of existing assemblages, so that differences in assemblage structure increase with spatial scale. The high turnover of P. coriacea leaves results in less opportunity for an assemblage to reinforce its presence, so patterns at the smaller scales are comparatively weaker. Strong patterns across km are more likely to be the result of environmental gradients. Patchiness within these gradients leads to complex, many layered spatial patterns.

Macroalgal communities of the Suez Canal after the recent improvement of marine habitats

The macroalgal communities of the Suez Canal were seasonally investigated at 16 sites during 1996 and 2000. A hundred and twenty eight taxa including 15 new records were identified. The recent reduction of navigation and urbanization works resulted in an increase in species richness (42 species) and algal forms. Distribution pattern, seasonal variation, and algal zonation were also examined. All were intensely regulated by substrate, space, depth, light, and water movement during the passage of ships. Sites were clustered, on the basis of species co-occurrence, into five groups, suggesting division of the Suez Canal into four biological sectors. The hard substrata supported distinct algal zones. Cladophoropsis zollingeri and Bangia fuscopurpurea characterized the littoral zone. A rich algal community dominated the infralittoral at a depth of 30-150 cm, while a few red species with Caulerpa racemosa were found deeper. Competition for space in some sites was evident by presence of 61 epiphytic macroalgae. A half of these were also found on hard substrata when the space was available. Algal succession in the canal during the past century was also discussed in the light of environmental changes. Algal succession could have passed through four stages; including the establishment of pioneers until 1924, the maturity to a climax sometime before1953, degradation of the climax due to navigation and urbanization constructions, and the reestablishment of the climax with the recent improvement in algal habitats.