Band 47, Heft 4

Severe outbreaks of the crust-forming European bryozoan Membranipora membranacea in northwestern Atlantic waters have caused extensive losses of kelp canopy through a process of defoliation. Here, we report how these crusts may negatively impact kelp beds by reducing spore release from fertile blades. In the laboratory, fully and partially encrusted sori of Laminaria longicruris released significantly fewer spores than bryozoan-free blades. Through field observations, we quantified the potential ecological impact of the encrusting mechanism. Unlike previous years, infestation was minimal in 2002 when only 4% of kelp surface areas were covered with bryozoan colonies (with a maximum of 72% of kelp individuals infested). This indicates strong interannual variability in the scale of impact on kelp spore release. In years when Membranipora encrustation impact is high and coincides with invasion by other nonnative species and/or elevated levels of sea urchin grazing, there is the potential for conversion of the rocky subtidal benthos to a new, possibly stable community state.

Phosphorylated fractions in tissues of starved and fresh plants of Porphyra purpurea, a representative of the Bangiophyceae, were analyzed over a 48 h incubation period in pulse-enriched seawater (15 uM phosphorus and 25 uM nitrogen). Compared to Chondrus crispus, a representative of the structurally and reproductively more complex Florideophyceae, P. purpurea takes up phosphorus much more actively, with a higher turnover rate, in which the orthophosphate fraction is predominant and acid-soluble and acid-insoluble polyphosphates are less significant as storage pools. Presence of cytoplasmic acid-insoluble polyphosphate granules was confirmed by transmission electron microscopy and energy dispersive X-ray microanalysis. The granules in P. purpurea were much smaller (20–110 nm in diameter) than those in C. crispus (around 1 um, but some larger than 2 um). Larger granules (290–310 nm) were observed in P. purpurea. They were more uniformly electron-opaque, without the reticulated/globular appearance of typical polyphosphate granules. Energy dispersive X-ray microanalysis demonstrated they were siliceous granules. To our knowledge, this is the first report in algae of such structures whose occurrence and metabolic role remain enigmatic.

A detailed vegetative and reproductive study of the little known species Spatoglossum solieri, using both fresh material and herbarium specimens, showed that the reproductive structures hitherto described as oogonia in S. solieri correspond, in fact, to undivided sporangia. Oogonia of S. solieri are reported and described for the first time in the present paper. They can be distinguished from undivided sporangia by their shape, the presence of a pedicel consisting of 1–2(3) basal flat cells and because they protrude up to half their length above the blade surface. Sporangia appeared as sessile structures, although they sometimes show a single lenticular stalk cell laterally placed. Likewise, and contrary to the published data, this study showed that antheridia are pedicellate structures.

The biomass and morphometric features of subtidal eelgrass (Zostera marina) beds were examined in Kwangyang Bay on the south coast of Korea. Benthic samples were collected from four sites at 2-month intervals, and various environmental parameters were simultaneously monitored. Shoot density increased from 15.7±1.4 (mean±SE) in November 1998 to 65.0±6.0 m -2 in May 1999 and gradually decreased during July–September 1999. Total biomass (shoot and rhizome-root) ranged from 20.2±5.5 in September 1999 to 188.5±19.1 g dry weight m -2 in May 1999. Shoot biomass and density were positively correlated, showing a spring peak on an annual cycle. Significant differences in leaf number per shoot, shoot length, third youngest leaf length, leaf width, leaf surface area index, internode length, root length and root number per node were observed among the sampling times. Shoot length and third youngest leaf length were positively correlated with leaf width, but poorly correlated with the leaf number per shoot. Seasonality of eelgrass beds and morphological traits of Zostera marina at Kwangyang Bay were compared to those in other temperate regions of the northern hemisphere.

We examine here the annual variation in leaf photosynthesis and nutrient status of four temperate seagrass species: Posidonia oceanica, Cymodocea nodosa, Zostera noltii, and Zostera marina. We also examine the relationship between leaf photosynthesis and seasonal plant growth and productivity. The four seagrass species examined co-occurred in a shallow protected cove on the NE Spanish Mediterranean coast. The results presented give evidence of large annual variation in the leaf physiological status of these four seagrasses, as well as the occurrence of significant differences in the seasonal pattern among species. We found two contrasting seasonal patterns characterized by optimal leaf photosynthesis in summer (represented by C. nodosa), and winter-autumn (represented by P. oceanica and Z. noltii). These contrasting patterns corresponded with a differential plant dependence on climate fluctuations (described by temperature and irradiance) vs. speciesspecific nutrient status (described by leaf nutrient content). As plant nutrient status results from speciesspecific differences in nutrient requirements, nutrient uptake efficiency, and internal nutrient economy, we conclude that the variation among species found in leaf nutrient content derives from species-specific responses to environmental forcing. Consequently, we can infer that an important fraction of the seasonal variability that seagrasses show may be related to species-specific responses. We also found significant differences among species in the coupling between leaf photosynthesis and plant growth and productivity. Both aspects, speciesspecific responses to environmental forcing and speciesspecific coupling between leaf photosynthesis and plant growth may result in differential seasonal patterns of growth and productivity among seagrass species.

To assess the effects of shading by epiphytes on the carbon balance of the seagrass Posidonia oceanica, we examined the patterns of within-shoot epiphyte abundance on leaves, and their variability with season and depth. Epiphyte biomass was found to depend on leaf age (larger epiphyte load on older tissues), leaf side (more epiphytes on the inner face than on the outer) and depth (more epiphytes in deep meadows). Depth differences were maximum in spring and disappeared in late summer. Percent light absorbed (absorptance) by epiphytes was measured; light absorptance followed an exponential- saturated model with epiphyte biomass. Combining these data of percent light absorbed, within-shoot epiphyte biomass distribution and an existing carbon balance model, we conclude that reduction in carbon gains caused by epiphyte shading is relatively small, and greater in deep meadows (8.8% on average, with values up to 14.2% in May) than that in shallow water (4.7% on average with maximum values of 7% in August). This is mainly due to the accumulation of epiphytes on old tissues, which contribute only marginally to the carbon gain of the plant. Using the same procedure, we modelled the effects of a doubling in epiphyte biomass, conserving the observed within-shoot distribution. The result was a very small additional carbon loss. However, using the same biomass but modifying the distribution (shifting the same abundance towards younger leaf age classes), the reduction in carbon gains was dramatic, particularly in deep meadows (between 21% and 41%, depending on the shift used). Therefore, it is the epiphyte growth timing rate rather than the final biomass reached which seems to be a key control for Posidonia oceanica survival, especially near the deep limit of its distribution.

We studied seasonal prevalence of dinoflagellates and of cyst production in relation to hydrological factors in Bahía Concepción, Mexico. In situ production of dinoflagellate cysts was recorded for the first time in Mexico. The resting stage of toxic Gymnodinium catenatum, potentially toxic Alexandrium pseudogonyaulax, and other red tideforming dinoflagellates were collected in traps. Cyst associations were linked with the composition of vegetative stages in the water column, and production yields (128 to 1.465×10 6 cysts m -2 d -1 ) were comparable with other reports in areas around the world. Seasonal abundance of major meroplankton dinoflagellates and relationships with yields of newly-formed cysts coincides with hydrographic transitional periods in the water column in spring and early fall. From factor analysis, the physico-chemical variables that correlate with the presence of the major meroplanktonic species are, in descending order of importance: temperature, phosphates, dissolved oxygen, silicate, nitrite, and nitrate. In Bahía Concepción, Gonyaulacales and Scrippsiella trochoidea cysts are present during declines in algal blooms as a mechanism to counteract adverse conditions, and to secure an inoculum for blooming when favorable conditions return. In contrast, G. catenatum cysts maintain the motile stage over prolonged periods with recurrent germination.

Archeospore germlings of five strains of Porphyra suborbiculata from tropical to sub-tropical (Ilocos Norte, Philippines and Shangwei, China, respectively) and warm-temperate waters (Kagoshima and Enoshima, Japan and Tongyoung, South Korea) were cultured under two photoperiod regimes (14L:10D and 10L:14D) and different temperature conditions (5, 10, 15, 20, 25, and 30°C) at 60–80 umol m -2 s -1 photon flux density in the laboratory. The blades of the Philippines and China strains grew at 15–30°C with optimum growth at 20–25°C under both photoperiods, while the strains from Japan and Korea tolerated a temperature range of 10–25°C under both photoperiods and grew best at 10–20°C under SD conditions. The specimens from the Philippines and China had varying blade shapes in culture while the Japanese and Korean strains had prominent round to ovoid blades and linear to lanceolate blades under long and short day-length conditions, respectively. Archeospore liberation was observed earlier in higher temperatures for all strains, regardless of photoperiod. Sexual reproduction occurred within the optimum growth conditions (20–25°C for the samples from the Philippines and China, and 10–20°C for the warm temperate samples) of all strains under both photoperiods. The Philippines specimens had blade spores that developed directly into ‘‘spoke-like conchosporangia’’ restrictively at 30°C, without observed fertilization. The appearance of 2–3-celled marginal denticulation generally occurred earlier at higher temperature under longday conditions. The Chinese strain had a smooth-edged shape, denticulate cell margin and contrasting cell number (4–5 cells) at 25°C. Porphyra suborbiculata exhibits wide geographic distribution, and the temperature and photoperiod tolerance shown here could imply adaptation and differentiation within a species to varying environmental conditions.

Ten species of benthic algae, principally associated with coral reef habitats, are newly reported for the Puerto Rican marine flora. These include eight Rhodophyta: Renouxia antillana, Lithophyllum congestum, Lithothamnion occidentale, Metapeyssonnelia corallepida, Maripelta atlantica, Pihiella liagoraciphila, Antithamnionella graeffei, and Myriogramme prostrata; one Heterokontophyta: Dictyota pfaffii; and one Chlorophyta: Caulerpa nummularia. Maripelta atlantica and Myriogramme prostrata are additionally reported for the Cayman Islands and from Venezuela, respectively.

The taxonomy of the genus Minidiscus, whose generic name refers to its small size and shape, is revised. The various species previously described are almost impossible to differentiate without electron microscopy. And even so, some confusion remains in their delineation. During a Phaeocystis survey in March and April 2002 in the eastern English Channel and Southern Bight of the North Sea, specimens of Minidiscus were collected and examined by scanning electron microscopy. We confirm that Minidiscus trioculatus has different morphotypes, ranging from 2.5 um to 6.8 um in diameter, with a small morphotype showing a valve surface with irregular openings of areolae, and a large morphotype with very small exterior openings of areolae arranged in almost linear rows. These extreme morphotypes, as well as intermediate specimens are illustrated here. We report for the first time the presence of Minidiscus chilensis along the French Atlantic coast and the eastern English Channel, and we describe a new marine species of this genus, Minidiscus decoratus, previously illustrated and identified as M. trioculatus by Aké-Castillo et al. in 2001 (Species of Minidiscus (Bacillariophyceae) in the Mexican Pacific Ocean. Cryptogam. Algol. 22: 101–107). A formal description of the new species is given, and a key for species identification is provided.

Phytoplankton samples were collected along the north coast of the Antarctic peninsula, the Weddell Sea and the Gerlache Strait, in different seasons in 1985, 1986, 1999, and 2000–2002. Chaetoceros castracanei Karsten, a fairly rare species was present in the samples; its morphology, taxonomy and distribution have not been recently investigated. This species occurred mainly from January to April, and was recorded with relatively high abundances in the Weddell Sea (up to 9.5=10 4 cells l -1 ). C. castracanei forms straight or slightly curved, short to long chains, with the terminal and intercalary setae pointing in the same direction. The apertures are very reduced, centrally constricted, and there are numerous chloroplasts in the cells including the setae. Electron microscopy studies showed that valves are randomly perforated by round poroids, costae on the valve are absent, and an excentric rimoportula is present in every valve of the chain; the setae are circular in cross section at the base, but become four-sided distally. Setae have perpendicular rows of elongate poroids, spines are arranged in spirals along the setae and the tips are very pointed. The intercalary setae are fused together in sibling valves. Chaetoceros impressus Jensen et Moestrup, recently described from Danish waters, appears to be conspecific with C. castracanei, and consequently we propose it as a synonym of the latter. The known distribution of Chaetoceros castracanei may be broadened to include Antarctic, subantarctic and Danish waters, and also possibly more temperate regions.