Laminaria abyssalis and rhodolith beds
The endemic Brazilian deep kelp L. abyssalis is strongly associated with rhodolith beds along its range . Rhodolith beds are communities dominated by free-living calcareous algae which develop in the form of nodules [2,3,4]. These structures are considered “carbonate biofactories” due to their fundamental importance in the biogeochemical cycle of carbon, especially in regions with little occurrence of coral reefs . The Brazilian rhodolith beds are regarded as the largest in the world, occurring also continuously from the Amazonian River mouth (5°N) to Santa Catarina State (27°S) . They harbor an associated biota comparable (considering the richness of vertebrates, invertebrates and macroalgae) to that of rocky or coral reefs .
The increase in structural complexity promoted by rhodolith beds provides shelter and food resources for diverse and abundant nekto-benthic communities and result in megahabitats of high biodiversity [6, 7]. Moreover, the structural complexity provided by rhodolith beds also subsidizes a diverse ichthyofauna inhabiting these environments for foraging, reproduction and/or shelter against predation . Watch a video showcasing some of these rocky reefs’ biodiversity here.
L. abyssalis evolution and distribution
In 1967 Joly and Oliveira Filho described two species of Laminarian kelps for the Brazilian coast (Laminaria abyssalis and Laminaria brasiliensis). In 1978, Oliveira Filho described the life cycle of L. brasiliensis. Thirty-four years later a taxonomic study revealed that L. abyssalis and L. brasiliensis are, in fact, only one species: L. abyssalis [8, 1]. The populations of L. abyssalis described for the Brazilian coast are rare relicts of shallow-water populations that existed during glacial periods of cooler oceanographic climate [8, 9], and originated from northern laminarian populations at ~ 1.34 myr .
These laminarian beds have been found in a small portion of the Brazilian coast, in tropical latitudes, where suitable conditions for cool-water microhabitats exist (e.g., coastal upwellings and deeper cooler water with sufficient light) , , , . The kelp L. abyssalis habitat extends over 33,000 km². It occupies a very specific biotope characterized by depths ranging from 40 to 120 meters, temperatures ranging from 15°C to 19°C, low light intensity (5-8 m Em-1 s-1) and grows over a substrate formed by nodules of calcareous algae (rhodolith beds) , , . The South Atlantic Central Water (SACW) is directly related to the tropical kelp distribution due to its high nitrate (10-15 μM) and phosphate (0.8 μM) concentrations . Moreover, L. abyssalis’ populations tend to vary seasonally, with higher biomass productivity during the austral summers .
A threatened ecosystem
The common reports of L. abyssalis brought aboard by Brazilian fishermen indicate that these kelp beds are important fishing grounds. In the past five years, trawling fishermen from Espírito Santo have been reporting frequent fragments or entire individuals as bycatch, pointing towards an escalating trawling activity on kelp beds , . The increase in trawling activities on L. abyssalis beds, oil mining, CaCO3 mining, global warming, and a sequence of environmental catastrophes mediated by human activities , can erode the Brazilian deep kelps to a rapid extinction, faster than the species is able to “adapt” to a novel environment. According to Casado-Amezúa (2019) , kelps, which sustain critical ecosystem services in coastal habitats, are suffering strong populational declines and distributional shifts worldwide directly attributed to anthropic activities.
L. abyssalis and the RESTORESEAS project (Federal University of Espírito Santo partner)
The role of the Restoreseas project regarding L. abyssalis and its ecosystem is to access the ichthyofaunal diversity associated with L. abyssalis habitat using molecular tools (e-DNA); compare environments where L. abyssalis occur and does not occur, aiming to develop an effective management initiative for the conservation and restoration of top priority areas along the effective niche of the deep kelp. The results obtained will close some of the gaps regarding the ecological aspects of marine fish assemblages associated to L. abyssalis and will identify top-priority sites for the conservation and implementation of restoration initiatives of this biological component. The project will also generate scientific and educational material (e.g., scientific papers, presentations, classes and lectures), participation in events (e.g., national and international congresses), management tools to be shared with politicians, stakeholders, Brazilian educational institutions and the general public. Conservation strategies and research initiatives are crucial to understand the environment and preserve the rare and endemic Brazilian deep kelp.
Written by Anderson Antônio Batista
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