Volume 50, Issue 5-6

Ulva pertusa Kjellman (Ulvales, Chlorophyta), which is widely distributed in the Pacific Ocean, has been detected on the NW Atlantic coast of the Iberian Peninsula (Galicia, Spain). The material has lobed and perforated blades, without marginal teeth, and with characteristic wrinkling at the base; it has an average thickness of 150 μm in the upper basal zone. Cells have a single chloroplast with (1-) 2 (-3) pyrenoids and, in surface view, show only local ordering. In transverse sections, cells are squarish or oblong, with rounded corners. Blades have a wide fertile margin with cells containing up to 28 gametes. The species-level identification as U. pertusa was confirmed by molecular studies ( rbc L sequence analysis). This is the first report for this opportunistic species from the Iberian Peninsula. Its introduction is probably attributable to the importation of biological material for shellfish culture.

The lunar day differs in length from the solar day so that times of low tide vary from day to day. Thus, aerial exposure of intertidal seaweeds may be during the day or during the night. We measured photosynthetic CO 2 assimilation rates of the intertidal green macroalga Ulva lactuca during exposures of varied daily timings during sunny days of summer to establish how photosynthetic performance responds to emersion timing under varied CO 2 levels [at ambient (360 ppmv) and 2× ambient (720 ppmv) atmospheric CO 2 concentrations]. There was an increase in net photosynthetic rates following some duration of exposure when the initial timing of exposure occurred during early morning (06.30 h) and late afternoon (17.15 h). In contrast, net rates exhibited a sharp decline with exposure duration when the initial timing of exposure occurred at 09.30 h, 15.30 h and especially at noon (12.30 h), implying the occurrence of a severe photoinhibition resulting from mid-day insolation. Doubled atmospheric CO 2 concentration significantly enhanced the emersed photosynthetic rates, indicating that the emersed photosynthesis is CO 2 -limited at ambient CO 2 levels. However, increasing CO 2 barely stimulates the emersed photosynthetic rates during mid-day insolation.

Seaweeds in the offshore waters of Isla Mujeres, in the western Caribbean Sea on the east coast of the Yucatán peninsula, were sampled using SCUBA. Three species of Cyanophyta, 90 Rhodophyta, 21 Ochrophyta and 41 Chlorophyta were identified. New records and earlier accounts of the shallow-water flora around the island indicate a rich flora of 400 taxa. Five localities around the island were sampled and each had a distinctive community of seaweeds. Over two-thirds (104) of the 155 taxa identified were present at only one of the five localities, and only one species was present in all five localities.

Dictyota dolabellana De Paula, Yoneshigue-Valentin et Teixeira is a new species of Dictyotaceae from the South Atlantic Ocean and the first denticulate species in which dolabellane diterpenes have been found. The major compound found in this species is the 4-hydroxy-7,8-epoxy-2-dolabellene. Until now, all populations of thalli containing dolabellane diterpenes had smooth margins and all species with denticulate margins produced prenylated guaiane and xeniane diterpenes. In addition, Dictyota dolabellana differs from other species by the presence of an inconspicuous denticulation irregularly located in the central to upper portions of the frond. Morphological and chemical data and comparison with type materials of other species clearly indicate the presence of a new species.

A Lulworthia -like species with affinities to Lulworthia opaca (= Halophiobolus opacus ) and L. longirostris (= H . longirostris ) was discovered on driftwood collected along the Danish coast and from the northwestern coast of the USA. Examination of the type material of L. opaca and L. longirostris leads to the conclusion that the two species are different at the generic level. Lulworthia longirostris shares several characters in common with the Lulworthia -like species collected in Denmark. A detailed study of the Lulworthia -like species has provided evidence for the erection of a new genus Rostrupiella to accommodate it. The new taxon is characterised by large ascomata that are deeply seated within the wood, with long necks extending through the wood to the surface, a bell-like structure protruding into the centrum, large, melanised bladder cells present in the wood cells and formation of inhibition zones in the host tissue. Partial nuclear LSU ribosomal RNA gene of Rostrupiella was sequenced to determine its phylogenetic relationship with other genera in the Lulworthiales.

Ascoma initials in the marine ascomycete Corollospora gracilis (Halosphaeriales) are formed from a coiled ascogonium following antheridium-ascogonium conjugation. Dikaryotic ascogenous initial cells derived from the distal end of the ascogonial coil produce ascogenous hyphae that then form the hymenium. Basal regions of the ascogonial coil and the initial investing hyphae form the sterile centrum tissue including the plug, separation layer, and centrum pseudoparenchyma. Pit-connections of the centrum pseudoparenchyma are normal ascomycetous septa. Thick-walled, non-melanized plug cells and a thin melanized separation layer form at the base of the ostiolar canal to delimit the centrum from the external environment. The subiculum that attaches the ascomata to sand grains is comprised of aggregated hyphopodia and mucilage.

We studied the chemical structure and yield of low-molecular-mass carbohydrates (LMMC) and soluble polysaccharides produced by green and red morphs of Gracilaria domingensis . Red plants had higher amounts of the LMMC floridoside than green morphs (324.4±8.1 and 220.1±6.0 μmol g -1 dry biomass, respectively). The yield of polysaccharides was similar between morphs (46.3±5.8% for the red and 41.4±8.3% for the green) as was the monosaccharide composition. The same agaran (6- O -methylated and sulphated) was isolated from both morphs, as determined by 13 C NMR spectroscopy analysis. The floridean starch content (mg g -1 dry biomass) for the green morphs (116.2±1.7) was lower than that of the red morphs (143.9±1.8). This study showed that green and red morphs of G. domingensis are similar in their polysaccharide composition, but differ in the short-term storage compounds, starch and floridoside. These differences may be related to light and shade photosynthetic strategies, which lead to different storage accumulation.

Macroalgae are a significant component of historic and modern invasions, with association to a wide variety of transport mechanisms. These transport mechanisms pose specific constraints on the ways by which species can be taken up, transported and released into a new environment. Currently operating transport mechanisms for marine macroalgae are either associations with intentional introductions (translocations for aquaculture, aquarium or live seafood trade) or accidental introductions (mainly as hull-fouling). A number of potential management options exist, including the development of international instruments and regional agreements. The development of treatment options for hull fouling, the most significant and poorly managed transport mechanism for macroalgae, is of urgent need. Our current ability to identify which species are likely to invade next is limited. However, an examination of the synergies between species' functional traits, transport constraints, and recipient community attributes will likely provide possible options in the future.

The two main drivers for intentional introductions of commercial macroalgae are (1) increasing global demand for macroalgae and macroalgal products, and (2) increasing need for alternative and sustainable livelihoods among coastal communities in less-developed countries (particularly to reduce degradation of coral reefs) and in the less-developed rural areas of more-developed countries. The macroalgal species that form the basis for commercial aquaculture (mainly Saccharina japonica (J.E. Areschoug) C.E. Lane, C. Mayes, Druehl et G.W. Saunders, Porphyra species, Undaria pinnatifida , Kappaphycus alvarezii , and Gracilaria species) are thus the ones most likely to be intentionally introduced to other places. The highest-profile cases of “invasive” macroalgae have mainly resulted from unintentional introductions, particularly via shipping. Two cases are species important commercially for aquaculture, U. pinnatifida and K. alvarezii , although the global spread of U. pinnatifida beyond Asia has been caused mainly by shipping. K. alvarezii has been intentionally introduced to many countries for aquaculture and has been reported as invasive in one locality in Hawaii; however, more recently it has emerged that Eucheuma denticulatum is in fact the main culprit at this locality. While environmental problems from intentional introductions have been few compared with those from unintentional introductions, it does not appear that commercial species are, as a group, inherently any more or less risk-prone than most unintentionally introduced species. Only a minority of alien species may ever become invasive, but it is difficult to predict which will become pests. In principle, international norms allow states to intentionally introduce exotic species for commercial purposes, provided that environmental threats can be avoided. In practice, the burden of proof and duty of care about environmental threats and protection of biodiversity is nowadays much higher than before. States cannot take it for granted that alien species may be introduced; new proposals should follow formal risk assessment and monitoring processes that are science-based, and should be strongly justifiable in terms of ability to provide expected economic benefits.

Understanding the mechanisms that facilitate or inhibit invasion of exotic seaweeds is crucial in assessing the threat posed by their incursion and to define control options. In this paper, we consider how life history characteristics of the invading species and properties of the recipient environment influence the likelihood of invasion, giving particular emphasis to how disturbance influences the establishment, spread and persistence of introduced seaweed populations. Very few commonalities in key life history traits emerge since each species possesses a unique set of traits that confers a high capacity for invasiveness. Consequently, for seaweeds at least, predictions of invasibility based on life history characters alone are unlikely to be useful. In contrast, it is clear that disturbance is an important process in the establishment of these invasive species. With the possible exception of Caulerpa taxifolia , disturbance appears to be a critical factor that is either a key requirement (e.g., Codium fragile ssp. tomentosoides , Sargassum muticum and Undaria pinnatifida ), or which accelerates (e.g., Fucus serratus ) establishment and spread. The role of disturbance in the persistence of the invaders is more complex and depends on the species concerned. In several cases there is substantial evidence for positive feedback mechanisms that enable introduced species to persist in the absence of the disturbance factor that facilitated establishment in the first place. These circumstances define examples of ecological hystereses that pose particular challenges for management and control. The evidence suggests that, in several cases, preventing anthropogenically mediated disturbance to canopies of native seaweeds should be considered as a potential control option to minimise the risk of establishment of exotic species at high densities. However, for these kinds of introduced species, once they are established, control options that primarily target the disturbance are unlikely to represent viable management options.

At least since Elton's work in the 1950s it has been argued that properties of recipient communities influence invasion rates. The widespread view, initiated by Elton and later supported by both empirical and modelling studies, is that species-rich communities are more resistant to invasion than species-poor communities in otherwise identical habitats. However, the dynamics of some empirical systems do not support this idea, but reveal instead a positive relationship between species richness and invasion, reflecting the particular attributes of component species and their interactions. These findings cannot be explained solely by Shea and Chesson's (2002) attempt to reconcile divergent observations of both positive and negative relationships between invasion rates and richness of the recipient community. Here, based on the behaviours of several models, we develop an alternative view that invasion success is related positively to variability in resource availability. This variability can arise in many ways, dependent in part on the life history features of component species, the nature of interactions among species, and the spatial arrangement of individuals on a landscape. Our overall conclusion is that the ability of a community to resist the establishment of new populations comes not from species richness, diversity or the average connectivity of the system per se , but from the ability of established species to utilise the maximum amount of resources in the long term and realise the smallest amount of variability in resource availability. We argue that seaweed communities adhere to this principle.

Tracking macroalgal invasions relies on a variety of approaches and techniques, including random sampling, active tracking near sources of introduction, and identification of alien species and their vectors of introduction using both classical means (based on taxonomical and biogeographical knowledge) and molecular tools. To identify the invaded ecosystems, and to describe the rate of spread and invasion dynamics, other approaches must be used, including mapping techniques and public awareness campaigns. In these endeavours, standardisation of geographical and density data is important. The tracking of alien species before eradication or control measures are instigated requires special cartographic techniques. This paper provides a general overview of these different approaches and the specific strategies adapted to the biological and ecological characteristics of particular species.

A wide range of vectors is currently introducing a plethora of alien marine species into indigenous marine species assemblages. Over the past two decades, molecular studies of non-native seaweeds, including cryptic invaders, have successfully identified the species involved and their sources; we briefly review these studies. As yet, however, little research has been directed towards examining the genetic consequences of seaweed invasions. Here we provide an overview of seaweed invasions from a genetic perspective, focusing on invader species for which the greatest amount of information is available. We review invasion processes, and rationalize evolutionary and genetic consequences for the indigenous and invader species into two main groups: (1) changes in gene-pool composition, in population structure and allele frequencies; and (2) changes in genome organization at the species level through hybridization, and in individual gene expression profiles at the levels of expressed messenger RNA and the proteome (i.e., all proteins synthesized) and thus the phenotype. We draw on studies of better-known aquatic and terrestrial organisms to point the way forward in revealing the genetic consequences of seaweed invasions. We also highlight potential applications of more recent methodological and statistical approaches, such as microarray technology, assignment tests and mixed stock analysis.

We analyzed 69 publications on the impacts of introduced seaweeds. The predominant impacts were changed competitive relationships in the recipient habitat, indicated by high abundances of invaders, resultant space monopolization, and reduced abundances/biomass of native macrophytes. Changes in biodiversity, effects on fish and invertebrate fauna, toxic effects on other biota, and habitat change were also identified. The mechanisms underlying the manifestation of impacts are uncertain and inferences about common patterns were hampered because impact studies were available for only a few introduced seaweeds, covered only a fraction of their introduced distribution and generally were conducted over short time scales. There was no information about evolutionary effects or changes of ecosystem processes. Knowledge of socio-economic impacts of invasive seaweeds is poor. We collated costs associated with control/eradication activities and for national spending on marine biosecurity in Australia, New Zealand and the United States. Prevention of impacts is the driving force for costly surveillance, eradication and control programs. Until we are able to understand, predict and measure impacts of introduced seaweeds, the management of species incursions needs to remain focused on early detection, rapid response and control to reduce the likelihood of negative impact effects.

Seaweeds have invaded ecosystems along the coasts of many countries where they can displace native algae and seagrasses, reduce biodiversity and impair habitat of fish and invertebrates. The most widespread and notorious cases have been introductions of Caulerpa taxifolia , which now infests over 20,000 ha of Mediterranean subtidal zones. Few attempts to control seaweed invasions have been successful, due to often harsh and highly variable physical conditions in marine environments, and the lack of efficacious methods. Use of heat, copper, chlorine, salt, freshwater and various mechanical (removal) approaches have been successful in reducing or eradicating some infestations. Biological control by herbivorous mollusks and sea urchins has been investigated, but has yet to result in any operational programs. Nutrient inputs from near-shore sources have exacerbated the spread of some species (e.g., off the Florida coast). To counter the increase in seaweed introductions and the spread of these species, it will be useful to adapt, where feasible, methods that have proven successful in controlling freshwater weeds. New methods will need to be developed as well. This will require better communication among researchers and managers working to reduce introductions and negative impacts of these seaweeds.

We consider law and policy responses to invasive seaweeds at global and regional levels. Key global regimes considered include the 1982 United Nations Convention on the Law of the Sea, the Convention on Biological Diversity, the Ramsar Convention and the Bonn Convention on Migratory Species. Contributions from the Food and Agriculture Organization and the International Maritime Organization are also considered in the global context. At a regional level, examples of efforts in North America and Europe are offered to illustrate challenges and opportunities for regional responses to invasive seaweeds. We conclude with law and policy recommendations, most notably the need to approach the issue of invasive seaweeds in a manner consistent with the precautionary principle.

In the introduction of this special issue of Botanica Marina , we established the scope of this topic around a series of questions, which also provided a framework for integrating the different contributions and a means of highlighting deficiencies in knowledge and understanding (Johnson and Chapman 2007). In defining challenges for the future and suggesting how those challenges might best be tackled to optimize returns on research investment, it is useful to revisit those questions under four main headings dealing with species introductions per se , the invasion process, consequences of invasions and human responses to the threat and occurrence of invasion.