Phytomyxea (plasmodiophorids) is an enigmatic group of obligate biotrophic parasites. Most of the known 41 species are associated with terrestrial and freshwater ecosystems. However, the potential of phytomyxean species to influence marine ecosystems either directly by causing diseases of their hosts or indirectly as vectors of viruses is enormous, although still unexplored. In all, 20% of the currently described phytomyxean species are parasites of some of the key primary producers in the ocean, such as seagrasses, brown algae and diatoms; however, information on their distribution, abundance and biodiversity is either incomplete or lacking. Phytomyxean species influence fitness by altering the metabolism and/or the reproductive success of their hosts. The resulting changes can (1) have an impact on the biodiversity within host populations, and (2) influence microbial food webs because of altered availability of nutrients (e.g. changed metabolic status of host, transfer of organic matter). Also, phytomyxean species may affect their host populations indirectly by transmitting viruses. The majority of the currently known single-stranded RNA marine viruses structurally resemble the viruses transmitted by phytomyxean species to crops in agricultural environments. Here, we explore possible ecological roles of these parasites in marine habitats; however, only the inclusion of Phytomyxea in marine biodiversity studies will allow estimation of the true impact of these species on global primary production in the oceans.

Wetland depressions without surface channel connections to aquatic systems are substantial sinks for nitrogen (N), phosphorus (P) and organic carbon (org. C). We assessed accretion, N, P and org.-C accumulation rates in 43 depressional wetlands across three ecoregions of the USA (Erie Drift Plain, EDP; Middle Atlantic Coastal Plain, MACP; Southern Coastal Plain, SCP) using caesium-137 (Cs). The mean sediment accretion rate in minimally affected (reference) sites was 0.6 ± 0.4 mm year and did not differ among ecoregions. Accumulation rates for N and org. C averaged 3.1 ± 3.1 g N m yearand 43.4 ± 39.0 g org. C m year respectively, and did not differ across minimally affected sites. Phosphorus accumulation rates were significantly greater in EDP (0.10 ± 0.10 g P m year) than MACP (0.01 ± 0.01 g P m year) or SCP (0.04 ± 0.04 g P m year) sites. Land-use modality and wetland-type effects were analysed in SCP, with few differences being found. Depressional wetlands sequester substantive amounts of nutrients and C; their cumulative contributions may significantly affect landscape nutrient and C dynamics because of the abundance of wetland depressions on the landscape, warranting further investigation and potential watershed-scale conservation approaches.