Volume 45, Issue 2

Infralittoral benthic biocoenoses and their patterns of zonation on exposed shores north of the Ría de Muros (northwest Spain)were studied. Atotal of 84 surveys allowed the characterisation of 11maincommunities, which differ mainly due to depth and substrate. These communities develop in broad belts, with awell marked zonation: communities of Cystoseiraceae at the infralittoral fringe, communities of Laminariales down to 15m deep, sciophilous communities at deeper levels, and infralittoral communities on sandy bottoms. Although variations with depth were noted, the main number of species is rather similar in all communities except for those on sandy bottoms. Numbers of Rhodophyta stand out in all communities except for that of Halidrys siliquosa . Thenumber of animals is high in all communities, but animal cover is only high in this last community. Cover of Phaeophyceae stands out among the algal cover, except for communities of sandy bottoms. Hemiphanerophyceae are the algae with highest cover on rocky bottoms, and cover is more variable on sandy bottoms. The presence of upwelling in this area explains the presence of 9 of the 11 communities characterised as being typical of northwestern Europe, while only 2 ( Phyllariopsis purpurascens and Cystoseira usneoides communities) show meridional affinities.

Caulerpa , a coenocytic marine macroalgae, is a genus characterized by having a prostrate indeterminate axis (stolon) with rhizoids and vertical axes that are potentially independent units as Caulerpa can withstand fragmentation and regenerate after a lamina or stolon are cut. This is similar to clonal growth described for vascular plants. A morphometric study was conducted comparing two morphologically distinct populations of Caulerpa prolifera growing in contrasting light environments of a coral reef lagoon. Morphometric measurements and dry weight partitioning were analyzed. Results of this study show that significant morphological differences exist. In a shaded environment C. prolifera had a higher dry weight (mg/cm 2 ) than in sunny areas, distance between ramets was longer in shade areas, resulting in an open growth similar to the ‘Guerrilla’ growth form compared to the ‘Phalanx’ growth form of sunny sites. In shaded areas the population had fewer lamina per ramet and longer stipes. Morphological differences were analyzed in relation to light intensity. Compact growth, highly branched and thick, small laminas are morphological traits associated with plants in bright habitats. In contrast, thin and longer laminas are more efficient in the capture of light and typify shaded populations. Differences were found at all three levels: clonal fragment, ramets and modules. This suggests that C. prolifera has a clonal plant morphology and behavior.

In this study, we examined the qualitative changes in macroalgal assemblages during the climatic phenomena of drought and rainy season in 45 sampling stations along Estero de Urías in the Gulf of California. The lagoon has a mouth that connects it to the ocean, but there is no continuous supply of fresh water, and physico-chemical characteristics are highly influenced by the contrasting weather in this region. The ratio of green algae versus total species per sampling station was used as an indicator of change in organic enrichment. The ratio was high during both seasons, and the nutrient concentration averaged 14.8 μg at N/L and 1.0mM dissolved-P during the drought and 12.4 μg at N/L and 1.7 μM dissolved-P during the rainy season, showing that the estuary has constant high levels of nutrients in both seasons. However, the average number of species per sampling station, and the number of stations with macroalgae were both larger during the drought season, mainly with Ulva lactuca , U . lobata and Enteromorpha clathrata . In contrast, during the rainy season the assemblages in some parts of the estuary are dominated by red seaweeds such as Gracilariopsis sjoestedtii and Caloglossa leprieurii . Moreover, in spite of the drought season (when it is not possible to observe clear assemblages), during the rainy season four main groups of stations were established by means of a classification analysis based upon the number of species that occur in the different stations. It seems that during the drought the system is environmentally more homogeneous than during the rains, when there is a slight improvement of water conditions, and different environmental zones are established.

Since the last century, the richness of the Canary Islands marine flora has attracted many botanists. Børgesen's seminal papers have been the main reference source for anyone interested in this flora. The first checklist of the marine macroalgae from the Canary Islands was published by Gil-Rodríguez and Afonso-Carrillo (1980a) with 434 macroalgal species being listed together with some dubious records. In recent years, the research efforts of local phycologists and the output of some scientific expeditions have yielded some new species and a large number of new records to the Canarian seaweed flora. The aim of this contribution is to compile an up-to-date catalogue of the marine plants for the Canary Islands (including cyanobacteria, macroalgae, seagrasses and fungi). The review of all published records of these marine plants takes into account the present taxonomic status and nomenclatural changes of the taxa concerned and rejects old and dubious records. After a careful review of the pertinent references and revision of live and preserved material, only valid records published before July 2001 are included in this checklist. Besides, each species is quoted for the islands in an east-west fashion to illustrate the distributional pattern of the species concerned. The marine flora of the Canary Islands is composed of 711 species, which are distributed as follows: 59 Cyanophycota, 385 Rhodophycota, 125 Chromophycota, 117 Chlorophycota, 3 seagrasses and 22 fungi. Compared to nearby regions, the Canarian archipelago comprises a much larger number of species. This high diversity appears to be the result of the combined effects of its geographic location, paleoclimatic events and the prevailing oceanographic conditions.

The aim of this paper was to improve the knowledge of the primary producers living in the Venice Lagoon by studying the composition and the distribution of the benthic diatom communities populating subtidal surface sediments. The upper 5mm of sediment from four areas distributed between the Malamocco inlet and the mainland north of Venice were collected and analysed. Sampling was carried out monthly for one year (1998–99). Species composition, cell abundance and carbon content were determined by light microscopy after separation of cells from the sediment particles using hydrogen peroxide. A total of 147 taxa were identified, mostly pennate diatoms (Bacillariales) belonging to the genera Amphora , Cocconeis, Navicula, Nitzschia and Pleurosigma . Cell abundance ranged from 0.7 x 10 6 cells cm −3 , near the Malamocco inlet (Station A), to 10.46 10 6 cells cm −3 near the mainland (Station C). Diatom carbon content was between 28 and 380 μg cm −3 . Seasonal trends were slight, except at Stations D and C where the lowest abundance was found in October–November and the highest one in summer. Significant relationships between benthic diatoms and macrophyte biomass, sediment grain size, underwater light transmission, sediment fluxes and the salinity gradient were found.

The critical contents of nitrogen and phosphorus for sorus formation in Laminaria angustata , L. japonica , L. ochotensis and L. religiosa were measured using cultured discs cut from the sporophytes. In L. japonica , fertile sporophytes were also used. Discs were cultured in Provasoli's enriched seawater or nutrient-poor seawater at 10 °C under 100 μmol photons m −2 s −1 of irradiance (12L:1̅2̅D̅). Regardless of the nutrient conditions in the culturemedia, the contents of nitrogen and phosphorus in the sorus part of discs and sporophytes of L. japonica were above 1.78 mgN cm −3 and 0.19 mgP cm −3 respectively, showing these values are critical for sorus formation in this species. Discs of L. angustata , L. ochotensis and L. religiosa in PES had higher contents of nitrogen and phosphorus in sorus parts than in L. japonica . The sorus area increased with accumulation of nitrogen or phosphorus in all species, but in L. angustata it was small despite the high contents of nitrogen and phosphorus, showing that this alga has a high nutritional cost in reproduction that might be a physiological adaptation to cold and nutrient-rich habitats.

Measurements on vegetative and reproductive structures from plants of the genus Batophora J. Agardh were made. Plants possessed spherical or ovoid gametophores, corresponding to Batophora oerstedi and B. occidentalis species, respectively. Both species coexist in the Chetumal Bay estuarine system. The species present different vegetative and reproductive characteristics compared to Batophora species from other parts of the world. The two species have different positive relationships between gametophore area and number of gametangia, and between reproductive thalli distance and number of gametophores. Gamete release was assayed applying two treatments to gametangia. Gamete release was significantly greater in B. occidentalis than in B. oerstedi. Both species showed the highest percentage of gamete release at between 100 and 150 μmol m − 2 s − 1 radiation. Reproductive potential per plant was estimated in July 1999 to be similar for both species; however, the difference in the number of reproductive plants per unit area of the Bay provided a greater total reproductive potential for B. occidentalis than for B. oerstedi . The reproductive differences may permit the two Batophora species to coexist in sympatry in Chetumal Bay. The reddish-brown pigmentation of gametophores exhibited by both species invalidates the diagnosis of B. occidentalis var. largoensis , a variety that has been separated on the basis of its color.

The physiology of nitrogen acquisition was determined for Gracilaria gracilis (Stackhouse) Steentoft, Irvine et Farnham in a series of perturbation experiments with the aim of examining uptake kinetics in response to transiently variable N. Experiments were designed to determine how variables such as history of exposure to nutrients, NO 3 − -N and NH 4 + -N concentrations and interactions, temperature and water motion affect parameters of linear and Michaelis-Menten models. A third ‘Michaelis-Menten parameter’ (α) is introduced here and used to extract additional ecological relevant information from the model. Ammonium-nitrogen uptake was best described by a linear, rate-unsaturated response, with the slope increasing with N-limitation, indicating that Gracilaria is more efficient at acquiring nutrients when internally stored N pools were impoverished. Temperature also affected the slope of the linear regression in the case of N-repletematerial. Nitrate-nitrogen uptake was suppressed by approximately 38 % in the presence of NH 4 + -N at concentrations above 5 μM, and the seaweed displayed a higher affinity for NH 4 + -N than for NO 3 − -N at low temperatures. Nitrate-nitrogen uptake followed a rate-saturating mechanism best described by the Michaelis-Menten model. Increased temperature enhanced the affinity for NO 3 − -N only in N-limited thalli, while nutrient limitation enhanced affinity irrespective of temperature. The maximal velocity of uptake ( V max ) and the half saturation constant ( K s ) appeared to vary with experimental conditions, but these differences were not statistically significant. Water motion was shown to reduce ‘diffusion transport limitation’ experienced by the alga under conditions of low external dissolved inorganic nitrogen (DIN) concentrations, so that the rate of N uptake responds with a 4.5-fold increase under conditions of enhanced water motion. All results suggest that Gracilaria gracilis is well suited to remain productive in an upwelling environment dominated by the transient availability of DIN through the use of a high affinity system for NO 3 − -N and non-saturable uptake of NH 4 + -N. Water motion interacts strongly with nutrient concentration, and may alleviate N limitation by reducing boundary-layer resistance to diffusion. Practical application of the results of this study is discussed in terms of significance to mariculture.