Seabed Morphology and Sedimentary Regimes defining Fishing Grounds along the Eastern Brazilian Shelf

Abstract

Shelf morphology and sedimentary regimes are influenced by processes operating at different temporal and spatial scales and are important records of sea level changes and sediment supply and/or carbonate production. The northern continental shelf of Espírito Santo (Brazil) contains evidence of different sedimentary regimes that distribute diverse and complex marine habitats. Herein, seabed morphology, acoustic images of the seafloor (side scan sonar and sub-bottom profiler), and sediment samples were used to investigate the influence of sedimentary regimes on physical marine habitat distribution. Seabed mapping is also integrated with available data on fisheries to understand the influence of shelf morphology and sedimentology in the usage of distinct fishing gears. The results indicate five morpho-sedimentary facies: terrigenous mud, terrigenous sand, rhodolith beds, carbonate gravel with rhodoliths, and hardground. Through an integrated analysis of the geomorphology and sedimentary distribution, two morpho-sedimentary domains were identified: a sediment-fed shelf adjacent to the Doce River associated with a major mud depocenter and a delta front morphology characterized by gentle slopes and low terrain ruggedness, and a sediment-starved shelf dominated by carbonate sedimentation showing an irregular morphology associated with higher slopes and terrain ruggedness. These contrasting morpho-sedimentary domains are a result of sedimentary responses to sea level fluctuation during Late Quaternary, specially, during the deglaciation processes after the Last Glacial Maximum. The morphological and sedimentary contrasts along the area define the physical habitat distribution. The sediment supply regime area is associated with a terrigenous fine/muddy sedimentation bed, which control the local morphology and favors coastal and delta front progradation. This physical habitat is a well-known shrimp-fishing ground where intense trawling takes place, as well as gillnet fisheries targeting weakfish and croakers. The accommodation regime or low sediment influx area is characterized by carbonate sedimentation associated with hardgrounds and rhodolith beds. In contrast, this physical habitat with scarce sediment supply, facilitates extensive benthic colonization by crustose coralline algae (CCA), which is primarily associated to line fisheries, longlines, and spearfishing. Rhodoliths show a high diversity of CCA and the occurrence of an endemic kelp species. Long-term processes such as relative sea level fluctuations and sediment supply are a legacy for the distribution of benthic

Marine Habitats in Conservation Units on the Southeast Coast of Brazil

“…Dias (2000) reported that the maerl and Lithothamnium alga banks are better developed in the 8 to 60m depth interval, where the algae take better advantage of light intensity and penetration, providing the ideal conditions for their development. The records and distribution of maerl and Lithothamnium coralline algae in the study site corroborate the findings of Dias (2000) and other studies (Albino, 1999;Bourguinon et al, 2018) in this area. The maerl and Lithothamnium banks associated with fragments of rhodoliths and biolitoclastic sediments occur from 40 to 60 m deep in the submerged channels of the Costa das Algas EPA, forming the Bioclastic sand (Bs) sedimentary facies and the soft unconsolidated marine habitats with gravel sediment and gravel sediment wave, besides the Biolitoclastic Sand (BLs) sedimentary facies and the soft unconsolidated marine habitats of sand and gravel sediment, and sand and gravel sediment wave, the latter as intermediaries between the terrigenous and marine sedimentation environments.…”

Charting the Course for Future Developments in Marine Geomorphometry: An Introduction to the Special Issue

“…Zimmermann and Prescott [23] accomplished the feat of combining 18 million data points from more than 200 individual sources to produce the best bathymetric model to date of the Eastern Bering Sea, enabling them to study 29 canyons in the area and to confirm the legendary status of some pinnacles. Bourguignon et al [24] used single-beam echosounders data and chart data to produce a 200-m resolution DBM by interpolating more than 150,000 points.…”

“…A geomorphological analysis was used to provide insight into the geological and ecological processes that have influenced the formation of these shelves around the two islands. Bourguignon et al [24] examined the use of seabed geomorphology and sedimentology to study the influence of sedimentary regimes on physical marine habitat distribution. They then used that information to define potential fishing grounds and predict fishing activities.…”

Reef Mapping Using Different Seabed Automatic Classification Tools

“…The increasing interest and necessity for seabed habitat mapping in marine spatial planning initiatives has forced the industry of sonar makers, software developers and scientific research institutions to invest in new technology capable of producing seabed classification over regional areas [6]. Fisheries, oil and gas exploration, offshore engineering, as well as shallow and deep sea mining are examples of industries that are requiring seabed classification to support environmental risk assessments and spatial planning [6][7][8].…”