Distribution, threats, and management of submerged reefs in the north of the reef corridor of the Southwest Gulf of Mexico

The Saya de Malha Bank (SMB) is one of the largest and least studied marine banks on the Mascarene Plateau. This study aimed to examine the diversity and distribution of the main benthic habitats in the shallow waters of the SMB (23 to 50 m). The survey was carried out in May 2018 during the EAF-Nansen Indian Ocean Research Expedition using a Remotely Operated Vehicle (ROV) deployed at 15 stations. Four main benthic habitats were investigated and their relative abundance determined during the survey. The 143,110 m2 surveyed area revealed proportional benthic habitat cover of 43.6 ± 22.4, 24.5 ± 21.9, 21.2 ± 27.8, and 10.5 ± 12.6 % for seaweed, abiotic substrate, seagrasses and corals, respectively. The seaweed habitat (43.6 %) was mainly composed of Halimeda spp. It represented up to 77 % of the habitats observed at SS34 (4553 m2). Even though seaweeds are considered seasonal, their dominance at all stations creates an important habitat structure for many organisms. The seagrass habitat (21.2 %) was dominated by Thalassodendron ciliatum. This habitat covered up to 93 % of the area investigated at SS38 (5950 m2) and was found mainly on the eastern side of the bank. The live hard coral habitat (10.5 %) was the highest at SS36-2 (35% of 9819 m2) and was more homogenously spread within the shallow areas. The unstable and the stable bare bottom substrate habitat (24.7 %) characterized as abiotic habitat was mainly composed of bedrock, sand, and rubble. It dominated at SS42 where it constituted 72.5 % of the 5114 m2 investigated and was recorded at all stations. Further research is warranted to better understand the diversity and the distribution of benthic habitats within the shallow waters of the SMB, along with collection of targeted benthic organisms for identification at higher taxonomic levels, to better formulate conservation and management measures and strategies.

The influence of geomorphology and sedimentary processes on shallow-water benthic habitat distribution: Esperance Bay, Western Australia

Distribution and extent of benthic habitats in Puck Bay (Gulf of Gdańsk, southern Baltic Sea)

With the increasing human activities in the marine environment, such as fisheries, dredging, coastal protection or construction of marine infrastructure, seabed sediment and habitat mapping have become highly relevant for the development of sustainable marine management strategies. Compared to traditional mapping methods, primarily based on bed sampling, multibeam echosounding belongs to the cutting-edge technology to time-efficiently acquire high-resolution bathymetric and backscatter (BS) data over large areas. Using classification methods to combine the acoustic data with ground-truthing, large-scale maps can be automatically and objectively produced, that enables to describe the distribution of benthic habitats or quantify marine resources. However, acoustic sediment classification still does not allow to discriminate between the entire heterogeneity of the seabed and is generally applied to a single multibeam echosounder dataset by means of revealing the seabed state only at a given time instant. Two challenging issues addressed within the scope of this thesis are summarized as: (1) Investigation on the applicability of repetitive multibeam (single-frequency) BS measurements for monitoring the seabed; and (2) Evaluation of the potential of multispectral BS to increase the acoustic discrimination between different seabed environments.

The benthic biodiversity-rich but degradation-prone coastal waters of Pombo Island, Maluku, were mapped using high-resolution PlanetScope (3m) satellite imagery and field data through a random forest approach. The results showed the dominance of inner reef flat (54%) and sand substrate (39.62%), with 22.31% coral cover, while geomorphological analysis revealed a strong correlation between sheltered reef slope (18.78%) and benthic habitat distribution (85% classification accuracy). These findings not only prove the effectiveness of remote sensing technology for tropical ecosystem monitoring but also recommend zoning-based conservation strategies, particularly reef crest protection and seagrass rehabilitation, as a contribution to sustainable environmental management in line with SDG targets.

The oceanography around Mauritius (in the Western Indian Ocean) remains largely unstudied, hence there is an acute scarcity of marine environmental data for management purposes. Rigorous water depth and current measurements were made on a system of grids inside Le Morne lagoon (in the south western part of Mauritius) in March–April 2000 to generate semi-quantitative models of general flow pattern in the form of contour maps using SURFER 6 computer programme. A simultaneous survey on composition of bottom cover was conducted to examine possible relationships with current speed. A separate investigation recorded surface and bottom currents prevailing amongst various habitat types to demonstrate the nature of the resulting damping effect on surface current speed. Significant correlations generated from data analysis were discussed as a basis for real biophysical relationships. Some of the limitations in the current analysis and some of the seemingly contradictory results are acknowledged and addressed in the light of the general assumption that the structure of the lagoon is conditioned by current speeds. Much stronger current speeds just outside the reef (e.g. >0.5 m s−1) than inside the lagoon (e.g. <0.32 m s−1) indicated a substantial slow-down of water current by the reef barrier. Inshore bottom currents were weaker than at the surface and current speed correlated well with water depth. Bottom and surface current directions were generally similar, i.e. going northward during flood tide and southward during ebb. The lagoon would be classified as ‘restricted’, exhibiting well-defined tidal circulation, which is modified by wind forcing. Dense fields of branching Acropora corals slowed down surface current speed by as much as 87%, but the relationship between current speed and bottom cover appears to be variable, depending on the specific location within the lagoon under consideration. The contour plots of the flow pattern model generated reasonably high qualitative modelling of spatial current speed pattern in the lagoon, with stronger currents generally along the reef areas, at the reef passes and in the deeper zones. However, these plots did not match closely those displaying distribution of bottom cover, thus confirming results obtained from pair-wise correlation tests, namely the lack of a significant relationship between current speed and bottom cover. Most of the correlations would appear to represent biological relationships, with different types of communities enabling or excluding other types. Thus, the biophysical structure of the lagoon would be driven a priori by the distribution and abundance of corals rather than current speeds, which contradicts the above hypothesis. Recurrent natural hazards subject the benthic communities to a state of ‘perpetual knock-down and recovery’. Recovery, however, can be seriously impaired by the chronic ongoing degradation of the coastal marine environment of Mauritius. An urgent review of its coastal zone management and protection strategy would be desirable for the island.

Shallow coastal ecosystems are the interface between the terrestrial and marine environment. The physical and biological composition and distribution of benthic habitats within these ecosystems determines their contribution to ecosystem services and biodiversity as well as their connections to neighbouring terrestrial and marine ecosystem processes. The capacity to accurately and consistently map and monitor these benthic habitats is critical to developing and implementing management applications. This paper presents a method for integrating field survey data and high spatial resolution, multi-spectral satellite image data to map bathymetry and seagrass in shallow coastal waters. Using Quickbird 2 satellite images from 2004 and 2007, acoustic field survey data were used to map bathymetry using a linear and ratio algorithm method; benthic survey field data were used to calibrate and validate classifications of seagrass percentage cover and seagrass species composition; and a change detection analysis of seagrass cover was performed. The bathymetry mapping showed that only the linear algorithm could effectively and accurately predict water depth; overall benthic map accuracies ranged from 57–95%; and the change detection produced a reliable change map and showed a net decrease in seagrass cover levels, but the majority of the study area showed no change in seagrass cover level. This study demonstrates that multiple spatial products (bathymetry, seagrass and change maps) can be produced from single satellite images and a concurrent field survey dataset. Moreover, the products were produced at higher spatial resolution and accuracy levels than previous studies in Moreton Bay. The methods are developed from previous work in the study area and are continuing to be implemented, as well as being developed to be repeatable in similar shallow coastal water environments.

The new found ability to measure physical attributes of the marine environment at high resolution across broad spatial scales has driven the rapid evolution of benthic habitat mapping as a field in its own right. Improvement of the resolution and ecological validity of seafloor habitat distribution models has, for the most part, paralleled developments in new generations of acoustic survey tools such as multibeam echosounders. While sonar methods have been well demonstrated to provide useful proxies of the relatively static geophysical patterns that reflect distribution of benthic species and assemblages, the spatially and temporally variable influence of hydrodynamic energy on habitat distribution have been less well studied. Here we investigate the role of wave exposure on patterns of distribution of near-shore benthic habitats. A high resolution spectral wave model was developed for a 624 km2 site along Cape Otway, a major coastal feature of western Victoria, Australia. Comparison of habitat classifications implemented using the Random Forests algorithm established that significantly more accurate estimations of habitat distribution were obtained by including a fine-scale numerical wave model, extended to the seabed using linear wave theory, than by using depth and seafloor morphology information alone. Variable importance measures and map interpretation indicated that the spatial variation in wave induced bottom orbital velocity was most influential in discriminating habitat the classes containing canopy forming kelp Ecklonia radiata, a foundation kelp species that affects biodiversity and ecological functioning on shallow reefs across temperate Australasia. We demonstrate that hydrodynamic models reflecting key environmental drivers on wave exposed coastlines are important in accurately defining distributions of benthic habitats.

The influence of geomorphology and sedimentary processes on benthic habitat distribution and littoral sediment dynamics: Geraldton, Western Australia

Since research on soft-seabed macrozoobenthic community, including polychaetes, of Mediterranean and in particular Italian Saes still display a lack of data concerning taxonomic aspects and species distribution patterns, and the pre-existing information are frequently outdated, further studies and revisions of data are a primary necessity. These habitats are widely common in coastal areas all over the world and host most of sensitive and protected benthic habitats, species and typical biocoenoses as well as most of the human activities. At the same time, in a framework of an ecological sustainability of human activities, such as sand dredging extraction, upon the marine environment, it is important to understand the extent of their effects on marine ecosystem, to protect the environment itself and to develop management strategies. In Italy, the use of marine relict sands, to repair the effects of the increasing coastal erosion, has become more common in the last decades. The efficiency of biodiversity and environmental monitoring studies in marine environments is strongly influenced by the selection of the spatial and temporal scale. Investigations at regional as well as at adequate temporal scale allow to analyse the comprehensive variability of biological systems, strongly influenced by the interactions of numerous environmental factors (depth, geographic position and sediment types). To display the variability of polychaetes diversity patterns in space and time, and to investigate how this variability is related to the habitat characteristics and human impacts, this research, is aimed to:1) identify diversity distribution patterns of polychaete assemblages and species at a regional (Latium Continental Shelf) related to depth, sediment grain size, latitude and longitude; 2) compare information, concerning the spatial distribution and ecology (related to sediment composition and depth range) of a number of selected soft-sediment polychaetes species, obtained at regional (Latium Continental Shelf) and national scale (Italian Continental Shelf); 3) assess the effects of human activities (sand dredging) on marine ecosystems at a local scale through the analysis of biological diversity variation over time. The amount of pre-existing studies, carried out in Mediterranean and in particular along the Italian Seas, concerning macrozoobenthos species, polychaetes, and their spatial distribution as well as the role of macrozoobenthic community for the environmental assessment, contributes to be the background of this research focused on the assessment of ISPRA multidisciplinary data-set, from environmental monitoring programmes, as a source of valuable scientific data. Results from PERMANOVA, CCA, BIOENV and Spearman rank correlation analyses, have pointed out that the three main categories explaining the drivers of biodiversity patterns in the Tyrrhenian continental shelf are: bathymetric gradients, geographical features, responsible for the north-south gradient in environmental conditions, and environmental heterogeneity (i.e. grain size distribution, habitat complexity). ISA analysis showed that some species distribution is significantly associated to definite sediment grain sizes and depth ranges confirming or updating the ecological characteristics of the investigated species as emerged from the comparison of results of this study with pre-existing knowledge. Moreover, the species distribution patterns as well as the assemblages composition observed along the Latium continental shelf (tested with PERMDISP analysis), confirm results obtained in previous studies carried out in neighbouring areas along Tyrrhenian Sea. A continuum of species distribution along Tyrrhenian continental shelf can be expected and represented by means species diversity maps (by Universal Kriging interpolator) able to represent comprehensive species diversity distribution patterns at the regional scale; despite polychaetes have been demonstrated to be able to respond quickly to changes in their environment as a consequence of dredging activities, the assessment of the effects of these activities upon benthic organisms is quite complex to define.

Multibeam echosounders (MBES) are increasingly becoming the tool of choice for marine habitat mapping applications. In turn, the rapid expansion of habitat mapping studies has resulted in a need for automated classification techniques to efficiently map benthic habitats, assess confidence in model outputs, and evaluate the importance of variables driving the patterns observed. The benthic habitat characterisation process often involves the analysis of MBES bathymetry, backscatter mosaic or angular response with observation data providing ground truth. However, studies that make use of the full range of MBES outputs within a single classification process are limited. We present an approach that integrates backscatter angular response with MBES bathymetry, backscatter mosaic and their derivatives in a classification process using a Random Forests (RF) machine-learning algorithm to predict the distribution of benthic biological habitats. This approach includes a method of deriving statistical features from backscatter angular response curves created from MBES data collated within homogeneous regions of a backscatter mosaic. Using the RF algorithm we assess the relative importance of each variable in order to optimise the classification process and simplify models applied. The results showed that the inclusion of the angular response features in the classification process improved the accuracy of the final habitat maps from 88.5% to 93.6%. The RF algorithm identified bathymetry and the angular response mean as the two most important predictors. However, the highest classification rates were only obtained after incorporating additional features derived from bathymetry and the backscatter mosaic. The angular response features were found to be more important to the classification process compared to the backscatter mosaic features. This analysis indicates that integrating angular response information with bathymetry and the backscatter mosaic, along with their derivatives, constitutes an important improvement for studying the distribution of benthic habitats, which is necessary for effective marine spatial planning and resource management.

Information on community structure and spatial distribution of benthic habitats are important in marine conservation and management. Coral areas, often monitored by trained scuba divers, are of importance for the ecosystem goods and services they provide. The data gathered may, however, be limited due to cost and time constraints. These restrictions and the continuing decline in coral reef health contribute to the need to develop rapid methods to efficiently document the distribution and status of coral reefs. A Rapid Assessment Instrument for Coastal Benthic Habitats (ARAICoBeH) System was developed to enable large-scale but low-cost coastal benthic habitat characterization and mapping without compromising accuracy. Inquiries on community structure and status in coral-dominated areas are also possible with the data collected using the method. The instrument, as well as the data processing and mapping algorithm are described in detail in this paper. A comparative study was conducted between ARAICoBeH and the frequently used underwater photo transect method. Variables compared were percent coral cover, functional group diversity, community structure as well as time and monetary requirements. There were no significant differences in estimates of percent coral cover and diversity of benthic functional groups for majority of sites while estimates of community structure were very similar. ARAICoBeH is cheaper and requires less time to gather the same amount of data as that of the photo transect method. The spatial distribution of coastal benthic habitats and community structure of coral-dominated areas in El Nido, Palawan, Philippines, are included to illustrate the application of the method.

Chapter 30 - Submerged reefs in the Abrolhos Shelf: morphology and habitat distribution

The ocean covers about seventy percent of the planet. The ocean provides many economic activities that include fisheries, tourism, and marine transport. Two-thirds of the value of all natural services is in the world is provided by the ocean. Fisheries related activities alone support the livelihood of approximately 200 million people in the world. As an island Sri Lanka is heavily depend on the ocean for economic development and food security. The coastal zone contains 62% of the industries and 70% of infrastructure related to tourism. Sri Lanka has a coastline of about 1620 km. The continental shelf covers about 30,000 km2. It is relatively narrow, averaging 22.5 km, width and the mean depth is approximately 75 m. The exclusive economic zone is about 517,000 km2. The marine environment around the country is governed by the northeast and southwest monsoons. The tidal range is low; the maximum spring tide is less than 1 m. The country is endowed with highly productive marine ecosystems; mangroves, sea grass meadows and coral reefs. In addition there are many coastal wetlands including salt marshes. The majority of mangroves are associated with coastal lagoons and the sea grass meadows are in the Gulf of Mannar and the Palk Bay where the sea is relatively shallow and calm. Coral reefs occur around the island with the largest shallow-water coral banks in the Gulf of Mannar. There are 40 species of mangrove and mangrove associated plants, 15 species of sea grasses and 208 species of corals recorded for Sri Lanka. There may be more than 1500 species of marine fish in Sri Lanka’s marine waters. The charismatic marine mega fauna include 5 species of sea turtles and twenty eight species of marine mammals. Although some groups have been studied relatively well, there is a general lack of information on marine biodiversity, especially the marine invertebrates. Sri Lanka depends heavily on marine resources both in coastal and offshore areas. Fishing is main economic activity supporting nearly 1.25 million people. The coastal waters provide about 65% of the marine fish production. Extraction of hydrocarbons may become one of the most important economic activities in the future. The marine environment around the country is heavily influenced by human activities including unsustainable resource exploitation and the use of destructive fishing methods. It is widely accepted that the coastal waters have been overfished as the populations of many large fish species have been reduced drastically. Many land-based activities have contributed to high levels of pollution in the coastal environment. Poor garbage disposal, agricultural runoff and industrial and domestic waste have polluted several coastal lagoons, beaches and inshore waters. More recently Sri Lanka has experienced negative impacts of global warming and climate change. Coral reefs have indicated this rapid environmental change through extensive coral bleaching events. Sri Lanka lost much of its shallow water coral reefs in 1998 during the unprecedented coral bleaching event in the Indian Ocean. A similar bleaching event has occurred in 2016 where many shallow water corals have been affected. However, adaptive management is lacking in Sri Lanka. Although several marine protected areas and fisheries management areas have been established, there is little or no management of human activities in these declared areas. In general there is a lack of implementation of laws and regulations which result in the continuous degradation of the marine environment. Keywords: Marine environment, Coastal, Resources, Management

The significance of coral disease epizootiology for coral reef conservation