Mapping 3D structure of a Sargassum forest with high-resolution sounding data obtained by multibeam echosounder

Sargassum forests play an important role in coastal waters as habitats for marine organisms, including commercial species. However, human activities have negatively affected their distribution causing a worldwide decline of Sargassum forests. Mapping and monitoring the distribution and biomass of these habitats using acoustic remote sensing techniques is key for their conservation. Nonetheless, most researches based on acoustic remote sensing methods focus on estimations of macrophyte area and its canopy height, and less researches reporting 3D visualization of these habitats. This study demonstrates the use of high-resolution multibeam echosounder (MBES) bathymetric data to visualize the 3D structure of Sargassum forests. Comparing acoustic data and underwater camera photos collected in field surveys, we identified Sargassum individuals as vertical clusters of contiguous sounding points with a base close to the sea bottom in the sounding data of the MBES. Using this criterion, we could distinguish Sargassum echoes, visualize the 3D structure of Sargassum forests and estimate the number of Sargassum individuals in the survey area. Using the relation between thallus length and dry weight of sampled Sargassum plants, standing stock and biomass could be estimated assuming the thallus length was the height of Sargassum plants identified with the MBES.

Gastropod communities associated with different morphologies of the intertidal seaweed Hormosira banksii

Hormosira banksii is an important intertidal habitat-forming seaweed in southern Australia that shows large variation in morphology. We examined the relationship between morphological variation in Hormosira and associated gastropod community structure, abundance and diversity in Tasmania, southern Australia. We sampled both Hormosira and gastropods from sites in two habitats (coast and estuary), two times (February–March and October–November) at two regions (northern and eastern Tasmania). There were distinct Hormosira morphs on the north coast (small individuals), east coast (intermediate sized individuals) and in estuaries (large individuals). Multivariate analysis showed that gastropod communities varied among the different algal morphologies, and suggest an influence of morphological traits, specifically thallus length, vesicle number and size, on the distribution patterns of gastropod species. Despite the finding of distinct gastropod communities associated with the different Hormosira morphs, because the different morphs occur in different locations with different physical conditions, we cannot unequivocally attribute the differences in gastropod communities to seaweed morphology per se. Nonetheless, our results confirm that H. banksii is an important foundation species in the intertidal zone and suggest a habitat-specific effect of algal morphological traits on gastropods.

Heading northward to Scandinavia: Undaria pinnatifida in the northern Wadden Sea

The kelp Undaria pinnatifida, native to East Asian shores, was unintentionally introduced with Pacific oysters into the Mediterranean in 1971. Intentional introduction from there to the French Atlantic coast 12 years later led to a gradual spread to the British Isles and the North Sea. Here, we report on the northernmost established population in continental Europe, and suggest a further spread into Scandinavian waters to be almost inevitable. In 2016, several thalli were found washed ashore at the eastern side of the island of Sylt in the northern Wadden Sea (German Bight, Eastern North Sea). Most specimens bore fertile sporophylls and thallus lengths of >1 m were common. In June 2017, 91 sporophytes were found attached to a mixed bed of Pacific oysters and native blue mussels, located just below low tide level in a moderately sheltered position. Mean thallus length was 0.2 m and the longest 0.7 m. Most had distinctive sporophylls and released spores in the laboratory. From sporophylls collected in the previous year, we successfully reared a new generation, demonstrating the kelp’s potential for further spread by natural means or human vectors.

Growth of Gracilaria under Different Planting Distances in Pond

<p>The use of non-productive shrimp ponds for cultivation of <em>Gracilaria</em> is one of the strategies that can be performed to achieve production target of seaweed. This study was conducted to determine the influence of different planting distances on growth of <em>Gracilaria</em> cultivated in pond. <em>Gracilaria</em> was separately planted in distant of 20x20 cm; 25x25 cm; 30x30 cm and 35x35 cm in pond for 45 days cultivation. Relative growth rate and thallus length increment were measured to obtain an optimal planting distance. The results of study showed that 25x25 cm planting distance resulted in a higher relative growth rate (137.8%) and increment of thallus length (15.3%) compared with other treatments. Thus, cultivation of <em>Gracilaria</em> in an unproductive pond with 25x25 cm planting distance may improve production.</p> <p>Keywords : non-productive ponds, planting distance, <em>Gracilaria</em></p> <p> </p> <p>ABSTRAK</p> <p>Pemanfaatan tambak udang yang tidak produktif untuk budidaya <em>Gracilaria</em> merupakan salah satu strategi yang dapat dilakukan untuk mencapai target produksi rumpul laut. Penelitian ini dilakukan untuk mengetahui pengaruh jarak tanam yang berbeda terhadap pertumbuhan <em>Gracilaria</em> di tambak. Gracilaria ditanam terpisah dengan jarak 20x20 cm; 25x25 cm; 30x30 cm dan 35x35 cm di tambak selama 45 hari pemeliharaan. Pertumbuhan relatif dan panjang thalus diukur untuk memperoleh jarak tanam yang optimal. Hasil penelitian menunjukkan bahwa jarak tanam 25x25 cm memberikan pertumbuhan relatif (137.8%) dan pertambahan panjang thalus (15.3%) tertinggi dibandingkan dengan perlakuan lainnya. Dengan demikian, budidaya <em>Gracilaria</em> di tambak tidak produktif dengan jarak tanam 25x25 xm diduga sangat membantu untuk mencapai target produksi rumput laut.</p> <p>Kata kunci : tambak non-produktif, jarak tanam, Gracilaria</p>

14C/C measurements support Andreev's internode method to determine lichen growth rates in Cladonia stygia (Fr.) Ruoss

Growth rates and the ability to date an organism can greatly contribute to understanding its population biology and community dynamics. 1n 1954, V. N. Andreev proposed a method to date regularly branched members of Cladonia, a fruticose lichen, using total thallus length and number of internodes. No research, however, has demonstrated the reliability of this technique or compared its estimates to those derived by other means. In this study, we demonstrate the utility of 14C/C ratios to determine lichen age and growth rate in Cladonia stygia (Fr.) Ruoss collected from north-western Alaska, USA. The average growth rate using 14C/C ratios was 6·5 mm yr−1, which was not significantly different from growth rates derived by Andreev's internode method (average = 6·2 mm yr−1); thus, suggesting the reliability of Andreev's simple field method for dating lichens.

Litter fall of epiphytic macrolichens in two old Picea abies forests in Sweden

The seasonal and annual variation in the litter fall of epiphytic lichens and tree litter was studied over a period of 2 to 3 years at two forested hills in the eastern part of central Sweden. Litter fall was measured using traps and for one species, Usnea longissima, by collecting specimens present on the ground. Total litter fall amounted to 2.5 and 2.8 tons ha−1 year−1 of which lichens constituted 4.6 and 5.7% at the two sites. Lichen litter fall was highest during the period from late autumn to the beginning of summer. Both the lichens and the tree litter showed significant between-year differences. Usnea longissima had an annual turnover of 7.0 and 10.0% of the standing crop at the two sites. The thallus length distribution of U. longissima was positively skewed. It is concluded that dispersal of thallus fragments by wind evidently plays an important role for many of the filamentous lichens studied. It is suggested that U. longissima disperses over a much shorter distance than Alectoria sarmentosa and Bryoria spp. within a forest stand.