Volume 56, Issue 1

No abstract available.

Several large kelp species are capable of long-distance dispersal via rafting. However, seasonal changes in environmental conditions at the sea surface may variably affect the physiological status of the floating thalli; challenging conditions during summer may accelerate disintegration and cause rapid sinking. We used the bull kelp Durvillaea antarctica from northern-central Chile (30°S) to test seasonal variation in floating persistence. Experiments with tethered specimens were conducted in all seasons to assess how variable environmental conditions influence the morphology and photosynthetic characteristics of floating D. antarctica . Floating specimens stayed afloat at the surface for more than 1 month during moderate environmental conditions that prevailed in winter, spring, and fall. However, higher water temperatures and intense solar radiation in summer resulted in significant biomass losses and rapid disintegration of the floating kelps; consequently, they sank within <1 month. These strong seasonal effects were reflected in decreasing maximal quantum yield as well as in maximum relative electron transport rates of photosynthesis. Understanding physiological responses of floating algae is important because increasing global temperatures and shifts in solar radiation may strongly affect the survival of floating algae, potentially reducing the distances and frequencies of rafting dispersal.

Recent DNA sequencing studies have demonstrated that many widespread species consist of species complexes with high genetic diversity. The brown alga Colpomenia sinuosa is a suitable candidate for studies into cryptic diversity because of its cosmopolitan distribution in the world’s oceans. To examine the genetic diversity within the species and the relationships of the genetic lineages to current distribution, we analyzed a total of 134 cox 3 sequences from C. sinuosa specimens collected in 19 countries; we also examined 16 rbc L from a subset of the specimens for comparative purposes. Phylogenetic trees and haplotype analyses of cox 3 and rbc L revealed high cryptic diversity comprising three genealogical groups within C. sinuosa. Two groups overlapped in the Indo-Pacific and Atlantic regions, one was confined to the tropics, while the remaining group was localized in the Red Sea and western Mediterranean Sea. Thus, the current distribution of C. sinuosa may well result from a mixture of modern anthropogenic introductions and ancient relicts.

On the basis of morphological and molecular studies, we identified the Australian endemic green alga known as Caulerpa distichophylla along the coasts of Sicily (Italy, Mediterranean Sea). The slender Caulerpa previously reported as C. taxifolia from southeastern Turkey (Gulf of Iskenderun) also belongs to C. distichophylla . Morphologically, C. distichophylla clearly differs from C. taxifolia in its slender thallus and the lack of large rhizoidal pillars. However, genetic data do not provide undisputed evidence that the species are distinct. Sequences of the tuf A cpDNA gene and of the cp 16S rDNA intron-2 sequences separated the two taxa by only one single nucleotide mutation, whereas ITS rDNA sequences did not clearly distinguish them. The new combination Caulerpa taxifolia var. distichophylla is therefore proposed. Western and eastern Mediterranean populations of C. taxifolia var. distichophylla are probably the result of introduction events from southwestern Australia. Although the vector of primary introductions remains unknown (aquarium trade or shipping), maritime traffic appears to be the most likely vector of secondary dispersal. C. taxifolia var. distichophylla is closely related to C. taxifolia , hence interbreeding with the other C. taxifolia strains in the Mediterranean Sea might be expected to occur.

Polysiphonia morrowii , a species native to the North Pacific, is believed to have been introduced to Chile, Turkey, Italy and France. This species was first recorded from New Zealand in 2011, based on collections made in 2004 from two sites on South Island, but no commentary was provided in the distribution or characteristics of the material collected. In 2009, as part of a study on macroalgae associated with soft sediment habitats in New Zealand, several samples of P. morrowii were collected from Otago Harbour, a location already known to host 17 non-indigenous macroalgal species. However, this species has gone unnoticed in New Zealand. We present the current understanding of the distribution of this species in New Zealand, and the distinguishing features of the specimens collected, to assist with biosecurity and monitoring programmes. Including this report of P. morrowii , there are now seven species of Polysiphonia and Neosiphonia that are regarded as non-indigenous in New Zealand.

We studied variations through 1 year in concentrations of several macronutrients (C, N, P, Na, K, Ca, Mg, S) and micronutrients (Fe, Mn, Cu, Zn) and water content in tissues of the brown seaweeds Ascophyllum nodosum , Fucus vesiculosus and Fucus spiralis at two sites in a coastal embayment in northwest Spain. The annual mean concentrations of the nutrients in A. nodosum were very similar at both sampling locations. There were no significant differences between sites in the concentrations of N, P, Na, K, Ca, S, Fe, Mn or Cu, the C:N or N:P ratios or in the water content, whereas the chemical composition of this species was notably different at the site where it coexisted with F. vesiculosus (the only parameters that were not significantly different were concentrations of Ca, Cu and the N:P ratio). The C:N:P ratios and the clear seasonal variability in N in all species, with minimum values in summer, suggest limitation by this element. Along with N, K was the only other element that varied throughout the seasons in all of the species, and this was most notable in F. vesiculosus . Minimum concentrations of K were also observed in summer, which might indicate limitation by this element. Seasonal variations in C were only observed in the Fucus species; they followed a reverse trend from those of N and K, as the highest levels occurred in summer. The highest concentrations of P and Zn in F. vesiculosus were also observed in spring. No obvious seasonal trends were observed in the remaining minerals.

In natural environments, marine biotas are exposed to a variety of simultaneously acting abiotic factors. Among these, temperature, irradiance and CO 2 availability are major factors influencing the physiological performance of marine macroalgae. To test whether elevated levels of CO 2 may remediate the otherwise reduced performance of uncalcified seaweeds under the influence of other stressful abiotic factors, we performed multi-factorial experiments with the red alga Chondrus crispus from Helgoland (North Sea) with two levels of CO 2 , temperature and irradiance: low and high p CO 2 levels were tested in combination with either (1) optimal and low irradiances or (2) optimal and sub-lethal high temperatures for growth. Performance of C. crispus was evaluated as biomass increase and relative growth rates (RGR), gross photosynthesis and pigment content. Acclimations of growth and photosynthesis were measured after 4 and 8 days. Acclimation time was crucial for elucidating single or combined CO 2 effects on growth and photosynthesis. Significant CO 2 effects became evident only in combination with either elevated temperature or reduced irradiance. Growth and photosynthesis had divergent patterns: RGR and biomass significantly increased only under a combination of high p CO 2 and elevated temperature; gross photosynthesis was significantly reduced under high p CO 2 conditions at low irradiance. Pigment content varied in response to irradiance and temperature, but was independent of p CO 2 .

Zostera japonica is a non-indigenous seagrass that is expanding along the Pacific Coast of North America. The ecophysiology of this seagrass is poorly studied and management of the species is fragmented. This split-plot mesocosm experiment was designed to evaluate the response of Z. japonica to chronic, extreme temperature and salinity stress to facilitate development of models to predict potential Z. japonica colonization. We collected Z. japonica plants from Padilla Bay, Washington and Yaquina Bay and Coos Bay, Oregon and exposed them to a constant water temperature of 15°C or 35°C at three different salinities (5, 20 and 35). After 7 days exposure, shoot survival ranged between 6% and 42%; after 9 days exposure, only a few plants from the Yaquina Bay population survived. At a ambient temperature (15°C), no differences were detected among the three salinity treatments. However, at a temperature of 35°C, the survival of plants grown at a salinity of 5 was significantly lower than at higher salinities (20 and 35). Although the effect of population was weak, the northern population appeared to be more susceptible to the combined effects of heat stress and low salinity than the southern populations. We suggest that Z. japonica will continue to spread southward along the Pacific coast of North America until it reaches systems that regularly exceed the temperature tolerances of this non-indigenous seagrass.

We describe the taxonomy and species diversity of 35 taxa of the diatom genus Thalassiosira from a series of net plankton collected quarterly or monthly from eight locations off the Guangdong coastal waters in the South China Sea. Field samples and 14 cultured Thalassiosira clonal strains were studied by light and electron microscopy. A total of 35 Thalassiosira species were recorded, including nine new records for China, namely T . cedarkeyensis , T . densannula , T . duostra , T . hendeyi , T . nanolineata , T . nodulolineata , T . punctigera , T . tubifera and T . visurgis , and eight new records for Asia (taxa as above, except for T . punctigera ). The morphological features of these Thalassiosira species are described and compared with previous illustrations. Some morphological variations are reported and discussed. This study was the first attempt to describe Thalassiosira species diversity in the South China Sea and Asian tropical waters. The results highlight a higher species diversity of Thalassiosira in the Guangdong coastal waters than in other studied regions.