Guilherme H. Pereira-Filho

Rhodolith Beds Are Major CaCO3 Bio-Factories in the Tropical South West Atlantic

Rhodoliths are nodules of non-geniculate coralline algae that occur in shallow waters (<150 m depth) subjected to episodic disturbance. Rhodolith beds stand with kelp beds, seagrass meadows, and coralline algal reefs as one of the worlds four largest macrophyte-dominated benthic communities. Geographic distribution of rhodolith beds is discontinuous, with large concentrations off Japan, Australia and the Gulf of California, as well as in the Mediterranean, North Atlantic, eastern Caribbean and Brazil. Although there are major gaps in terms of seabed habitat mapping, the largest rhodolith beds are purported to occur off Brazil, where these communities are recorded across a wide latitudinal range (2°N - 27°S). To quantify their extent, we carried out an inter-reefal seabed habitat survey on the Abrolhos Shelf (16°50′ - 19°45′S) off eastern Brazil, and confirmed the most expansive and contiguous rhodolith bed in the world, covering about 20,900 km2. Distribution, extent, composition and structure of this bed were assessed with side scan sonar, remotely operated vehicles, and SCUBA. The mean rate of CaCO3 production was estimated from in situ growth assays at 1.07 kg m−2 yr−1, with a total production rate of 0.025 Gt yr−1, comparable to those of the worlds largest biogenic CaCO3 deposits. These gigantic rhodolith beds, of areal extent equivalent to the Great Barrier Reef, Australia, are a critical, yet poorly understood component of the tropical South Atlantic Ocean. Based on the relatively high vulnerability of coralline algae to ocean acidification, these beds are likely to experience a profound restructuring in the coming decades.

Extensive Rhodolith Beds Cover the Summits of Southwestern Atlantic Ocean Seamounts

Abstract PEREIRA-FILHO, G.H.; AMADO-FILHO, G.M.; MOURA, R.L.; BASTOS, A.C.; GUIMARÃES, S.M.P.B.; SALGADO, L.T.; FRANCINI-FILHO, R.B.; BAHIA, R.G.; ABRANTES, D.P.; GUTH, A.Z., and BRASILEIRO, P.S., 2012. Extensive rhodolith beds cover the summits of southwestern Atlantic Ocean seamounts. Calcium carbonate production by marine organisms is an essential process in the global budget of , and coralline reefs are the most important benthic carbonate producers. Crustose coralline algae (CCA) are well recognized as the most important carbonate builders in the tropical Brazilian continental shelf, forming structural reefs and extensive rhodolith beds. However, the distribution of CCA beds, as well as their role in mineralization in mesophotic communities and isolated carbonate banks, is still poorly known. To characterize the bottom features of several seamount summits in the Southwestern Atlantic (SWA), side-scan sonar records, remotely operated vehicle imagery, and benthic samples with mixed-gas scuba diving were acquired during two recent research cruises (March 2009 and February 2011). The tops of several seamounts within this region are relatively shallow (∼60 m), flat, and dominated by rhodolith beds (Vitória, Almirante Saldanha, Davis, and Jaseur seamounts, as well as the Trindade Island shelf). On the basis of abundance, dimensions, vitality, and growth rates of CCA nodules, a mean CaCO3 production was estimated, ranging from 0.4 to 1.8 kg m−2 y−1, with a total production reaching 1.5 × 10−3 Gt y−1. Our results indicate that these SWA seamount summits provide extensive areas of shallow reef area and represent 0.3% of the worlds carbonate banks. The importance of this habitat has been highly neglected, and immediate management needs must be fulfilled in the short term to ensure long-term persistence of the ecosystem services provided by these offshore carbonate realms.

Reef fish and benthic assemblages of the Trindade and Martin Vaz Island group, southwestern Atlantic

The Trindade and Martin Vaz island group (TMVIG) is located at about 1,120 km off the Brazilian coast. Despite its importance, highlighted by the presence of several endemic fish species, the TMVIG lacks detailed information on the structure of fish and benthic assemblages. Presented here is the first quantitative assessment of reef fish and benthic assemblages of the TMVIG in a depth gradient ranging from 5 to 45 m. Additional qualitative information on reef assemblages between 45 and 100 m was obtained using advanced gas diving techniques (TRIMIX) and a remotely operated vehicle (ROV). Similarly to other Brazilian oceanic islands, the TMVIG possesses depauperated fish and benthic assemblages, possibly due to its isolation and small size in comparison to the mainland. Depth was the most important factor affecting the structure of fish assemblages, with the density of most fish species declining with depth. Deep reefs (> 45 m) were characterized by the presence of extensive rhodolith beds and rocky reefs sparsely covered with crustose coralline algae, black coral (Cirripathes sp.) and a few massive or plate-like reef corals. Part-time or obligatory planktivorous fishes (e.g. Cephalopholis furcifer and Clepticus brasiliensis) also dominated deep reefs. Similar characteristics were recorded in mesophotic reef ecosystems across the Western Atlantic. Evidence of overfishing (obtained here and in other recent studies), the presence of four endemic and restricted range fish species, as well as the increase in number of new (and still undescribed) endemic taxa, indicates that the adoption of precautionary conservation measures are urgently needed in order to maintain the fragile and unique ecosystems of the TMVIG.

The Farther the Better: Effects of Multiple Environmental Variables on Reef Fish Assemblages along a Distance Gradient from River Influences.

The conservation and management of site-attached assemblages of coastal reefs are particularly challenging because of the tremendous environmental variation that exists at small spatial scales. In this sense, understanding the primary sources of variation in spatial patterns of the biota is fundamental for designing effective conservation policies. We investigated spatial variation in fish assemblages around the windward and leeward sides of coastal islands situated across a gradient of riverine influence (13 km in length). Specifically, relationships between rocky reef fish assemblages and benthic, topographic and physical predictors were assessed. We hypothesized that river induced disturbances may overcome local habitat features in modeling spatial patterns of fish distribution. Fish assemblages varied primarily due to the strong directional gradient of riverine influence (22.6% of the estimated components of variation), followed by topographic complexity (15%), wave exposure (9.9%), and benthic cover (8%). The trophic structure of fish assemblages changed from having a high abundance of invertebrate feeders in macroalgae-dominated reefs close to river mouths to a high proportion of herbivores, planktivores and invertebrate feeder species in reefs with large boulders covered by epilithic algal matrices, as the distance from rivers increased. This gradient led to an increase of 4.5-fold in fish richness and fish trophic group diversity, 11-fold in fish biomass and 10-fold in fish abundance. Our results have implications for the conservation and monitoring of assemblages patchily distributed at small spatial scales. The major role of distance from river influences on fish assemblages rather than benthic cover and topographic complexity suggest that managing land-based activities should be a conservation priority toward reef restoration.

Seasonal changes in population structure of the tropical deep-water kelp Laminaria abyssalis

Tropical kelp populations are rare and anomalous relicts of shallow‐water populations that existed during glacial periods of cooler oceanographic climate. The endemic Brazilian tropical kelp, Laminaria abyssalis Joly and Oliveira Filho, occurred at depths below 40 m. The seasonal variations in biological aspects of L. abyssalis sporophyte populations and local variations in seawater nutrients and temperature were evaluated. A population was sampled four times between the austral spring of 2005 to winter 2006. Seasonal variations in the population structure and in the tissue content of nitrogen (N), carbohydrate and pigments were observed. Higher density (6.3 individuals m−2), biomass (7.3 kg m−2) and blade area (13 221 cm2) were observed in summer, while the highest percentage of tissue total N (1.6%), carbohydrates (32.9%) and photosynthetic pigments (chlorophyll a = 1.9% and chlorophyll c = 0.4%) were observed in spring. The highest surface area of fertile tissue in L. abyssalis sporophytes (2.36%) was recorded in winter, indicating winter as the season when more investments are made in reproduction. The highest concentrations of total N (6.3 μM) and phosphate (0.6 μM) in seawater were observed in spring and summer, respectively. Seawater temperatures lower than 20°C, which are characteristic of upwelling waters, occurred every month and were most frequent in spring and summer. We show that L. abyssalis invests more in growth in spring and summer and reaches the greatest thallus size and population density in summer. The lower abundance during winter may be related to the lower frequency of temperatures below 20°C and the local seasonal storms that cause turnover of rhodoliths, the main substrate for L. abyssalis.

Evaluation of the stocks of Hypnea musciformis (rhodophyta: gigartinales) on two beaches in Bahia, Brazil

Hypnea musciformis occurs widely in the northeast coast of Brazil, and it is one of the most important natural sources of k-carrageenan, which is used in food and cosmetic industries. Despite its potential for exploitation little is known about its ecology. The aim of this study was to investigate the biology and ecology of H. musciformis in Brazil through analyses of biomass stock and accompanying flora. Two populations of H. musciformis were analyzed: those on the beaches of Stella Maris and Itacimirim (Bahia, Brazil). Eight samplings were conducted between 2007 and 2009 during the dry and rainy seasons. The algae were sampled along transects (20 m) using quadrats (0.04 m2) in three different hydrodynamic regions of the reefs (TP, PRR and FRR). The t-Test, Dunns Test and parametric and nonparametric ANOVA were used for statistical analyses. 17 host species and 41 associated species were identified. The highest biomass stock was observed during the dry season. On Stella Maris, the region with the highest biomass stock was FRR; on Itacimirim, TP had the highest biomass value. This study permits the assumption that seasonality, microhabitat, hydrodynamic and micro scale factors contribute to variation in biomass stock in H. musciformis populations.