Underwater Video as a Tool to Quantify Fish Density in Complex Coastal Habitats

Habitat loss is a serious issue threatening biodiversity across the planet, including coastal habitats that support important fish populations. Many coastal areas have been extensively modified by the construction of infrastructure such as ports, seawalls, docks, and armored shorelines. In addition, habitat restoration and enhancement projects often include constructed breakwaters or reefs. Such infrastructure may have incidental or intended habitat values for fish, yet their physical complexity makes quantitatively sampling these habitats with traditional gears challenging. We used a fleet of unbaited underwater video cameras to quantify fish communities across a variety of constructed and natural habitats in Perdido and Pensacola Bays in the central northern Gulf of Mexico. Between 2019 and 2021, we collected almost 350 replicate 10 min point census videos from rock jetty, seawall, commercial, public, and private docks, artificial reef, restored oyster reef, seagrass, and shallow sandy habitats. We extracted standard metrics of Frequency of Occurrence and MaxN, as well as more recently developed MeanCount for each taxon observed. Using a simple method to measure the visibility range at each sampling site, we calculated the area of the field of view to convert MeanCount to density estimates. Our data revealed abundant fish assemblages on constructed habitats, dominated by important fisheries species, including grey snapper Lutjanus griseus and sheepshead Archosargus probatocephalus. Our analyses suggest that density estimates may be obtained for larger fisheries species under suitable conditions. Although video is limited in more turbid estuarine areas, where conditions allow, it offers a tool to quantify fish communities in structurally complex habitats inaccessible to other quantitative gears.

A CFD Analysis of Decommissioned Oil Platforms Jackets on the Brazilian Coast

Every facility reaches the last phase in its life cycle, which is decommissioning. Since the last decade, this subject has been gaining importance in Brazil’s offshore oil and gas companies. For jacket type rigs, one of the methods widely applied after idling the production is the conversion of these structures into artificial reefs (ARs). There are several critical aspects for choosing the best strategy for cutting and sinking a platform jacket, ensuring the success of an AR from a biological point of view. One of them is the influence of marine currents and their fluid-structure interaction which, by maximizing local upwelling and back vortex effects, favours the growth of aggregated flora and fauna. This study consists in the application of computational fluid dynamics (CFD) techniques for studying the marine flow around a disassembled and sunk jacket in the seabed for the purpose of converting it into an artificial reef. An FVM (Finite Volume Method) from a commercial software (most recent version of ANSYS FLUENT®) is applied with the upwind scheme. A k-ε turbulence model on steady state is chosen. Field data about Brazilian coastal currents are collected and analysed from the amount of information available on a Brazilian Navy's meteoceanographic program. Next, different combinations of cutting and sinking a jacket are studied, always keeping a minimum 55m free water column. The objective is to verify where the formation of local upwelling regions - that is, where the vertical velocity component reaches values equal or greater than 10% of the magnitude of the free flow velocity - is more significant, without decreasing back eddy formation. It is observed that the dismemberment of the jacket with the positioning of its parts in an increasing height sequence in the direction of the prevailing current is favourable to generate local upwelling while tipping the structure at 90° to the prevailing current results in the most voluminous back eddy region.

Enhancing reef fish diversity using artificial reef-building: A case study of coral reef rehabilitation on Nyamuk Island, Anambas Islands

CCMRS-IPB conducted coral reef rehabilitation at damaged coral reefs around Nyamuk Island. Those artificial reef buildings for rehabilitation gave shelter spaces for reef fish. This research aims to calculate the effect of coral reef-building, which enhances rugosity to the reef fish diversity around the rehabilitation sites. The study was conducted on Nyamuk Island in the Anambas Islands. Reef fish were sampled annually from 2014 to 2019 using the underwater visual census. The Diversity index and non-Metric Multidimensional Scaling were built to discover reef fish diversity, and reef fish species were affected the most. Yearly data shows an escalation number of reef fish abundance and richness at the end of 2019. The major reef fish group is found to have constant diversity throughout the year compared to other functional groups. The target reef fish group came to this rehabilitation ecosystem primarily attracted by nourishment availability. There is a shift in the reef fish diversity from the early year to the project end. Generally, major reef fish groups will be refuged first around the rehabilitation sites, especially territorial types. Target fish groups from herbivorous and carnivorous types will mostly come along after their food availability and location to get around.

Effects of seasonal changes and depth on growth parameters of the Mediterranean mussel (Mytilus galloprovincialis) on a shipwreck in the Eastern Mediterranean Sea

The study was conducted between July 2018 and May 2020 to compare seasonal changes in growth parameters of the Mediterranean mussel (Mytilus galloprovincialis) at different depths in two different areas of the Northeastern Mediterranean Sea (Aegean Sea). In a preliminary study, mussels were placed in cages at different depths of an artificial reef (AR – shipwreck) and natural reef (NR). Temperature, salinity, pH, and dissolved oxygen were determined seasonally at both sites at a depth of 37 m (deepwater) and 25 m (midwater). Linear increases in length and width of mussels at the AR site were recorded, while no consistent changes were observed for mussels at the NR. There was negative correlation between the specific growth rate (SGR) and salinity (r2 = 0.5098) and temperature (r2 = 0.1470) at the AR site. Negative correlations were also recorded between pH and the commercial condition index (CCI) at both the AR (r2 = 0.3869) and NR (r2 = 0.3600) sites. Our findings show that depth had a significant effect (p < 0.05) on the CCI of mussels at the NR site, while its effect was insignificant for this index at the AR site (p > 0.05). This study indicates that natural reefs provide more suitable conditions for the growth of Mediterranean mussels than shipwrecks used as artificial reefs.

Improving Biological Reefing Viability Index as a Predictive Tool for Assessment of Potential Reefing Site in the Tropical Shallow Offshore Environment

The current study improved the predictive capability of the biological reefing viability index (BRVI) calibrated using local data. The prediction capability of the BRVI improved from 61% to 76% accuracy out of the 181 locations where the underwater videos available for verification. The BRVI includes corals larvae density, age of larvae at site, sea current, sea temperature, chlorophyll-a, water depth and sediment type to predict biological productivity of an area. Among the parameters, corals larvae density and age of the larvae are the most critical parameters that influent establishment of new biological ecosystem. The BRVI uses settlement of corals larvae as the precursors for the establishment of new habitats in the offshore environment because scleractinian corals is known to be able to form backbone of a new habitat in the environment. In this approach, the BRVI focuses on habitat creation instead of just being a fish aggregating device (FAD) when an artificial reef is deployed in an area. The BRVI can be used as a rapid screening tool to identified potential area for deployment of artificial reefs. The BRVI could reduce the chances of artificial reefs deployment that failed to address its objectives and intended outcomes.