New Challenges in Marine Aquaculture Research

Marine aquaculture has witnessed remarkable growth in recent decades, contributing significantly to global food security and economic development. As the world population continues to expand and dietary preferences shift towards healthier, protein-rich options, the demand for seafood, particularly from aquaculture, is expected to rise significantly [1,2]. However, the sector faces numerous hurdles to ensure its continued success and sustainability. One of the most pressing challenges is the increasing pressure on natural ecosystems. The expansion of aquaculture operations can lead to environmental impacts such as water quality and habitat degradation, and competition with wild fish populations [3]. Moreover, the industry partly relies on wild-caught fish for feed ingredients [4]. Climate change poses another significant threat to marine aquaculture. Rising sea temperatures, ocean acidification, and changes in ocean currents can have detrimental effects on aquaculture species, leading to diseases, increased mortality rates, reduced growth, and altered reproductive cycles [5,6]. In addition, the marine aquaculture industry also faces economic and social pressures. Market fluctuations and regulatory hurdles can significantly impact the profitability and sustainability of operations, whereas ensuring fair labor practices and the well-being of workers in the aquaculture sector remains a critical challenge [7]. To address these complex challenges and ensure the long-term sustainability of marine aquaculture, innovative and collaborative research and development are essential. This Special Issue of the Journal of Marine Science and Engineering presents a comprehensive collection of research papers spanning a wide range of topics. It includes studies focused on environmental, ecological, and sustainability aspects (contributions 1 to 5) as well as innovative approaches to feed and growth performance optimization (contributions 6 to 13). It addresses critical challenges such as species diversification, animal growth efficiency, and the impact of climate change, while also focusing on alternative feed sources, natural resource conservation, and minimizing environmental impacts. This Special Issue offers valuable insights and solutions for promoting a more sustainable and productive future in the field. The research topics and key findings featured in this Special Issue include the following.

Hengjie et al. (Contribution 1) presented a systematic review examining the effects of ocean acidification (OA) on seaweed aquaculture, analyzing studies from 2001 to 2022. The review explored how seaweeds acclimate to increasing CO₂, focusing on the effects of OA on photosynthesis and nutrient uptake, while identifying knowledge gaps in mitigation strategies. The findings revealed that while certain seaweed species may experience enhanced productivity, others could suffer reduced growth and economic losses if critical biological systems are compromised. The review highlighted the need for future research to focus on actionable mitigation strategies and to assess the economic impacts of OA on seaweed farming.

Deen et al. (Contribution 2) investigated the effects of coastal shellfish aquaculture on benthic–pelagic systems in Onagawa Bay, Japan, through monthly field surveys conducted in 2023. The study demonstrated that shellfish farms significantly influence both the water column and the seafloor by consuming phytoplankton and depositing organic matter as biodeposits, which alter sediment characteristics and the local benthic community. The surveys revealed that polychaetes dominated the benthic macrofauna (86.3%). Additionally, biomass and biodiversity were higher near the aquaculture sites, while chlorophyll-a concentrations and sediment organic matter were lower. However, the combination of global-warming-induced water column stratification and excess organic input may result in hypoxic conditions, presenting new challenges for the sustainability of aquaculture.

Slobodskova et al. (Contribution 3) addressed the increasing mass mortality of cultured seaside scallops (Mizuhopecten yessoensis) in the Sea of Japan, proposing a rapid diagnostic method utilizing DNA damage and oxidative stress markers for the early detection of health threats. The study revealed a correlation between elevated DNA damage, malondialdehyde accumulation in tissues, and the mortality of older scallops. This predictive approach offers aquaculture farms a valuable tool for mitigating losses and improving scallop farming management practices.

Lee et al. (Contribution 4) explored the potential of utilizing offshore wind farms (OWFs) for scallop aquaculture, focusing on the growth of Zhikong scallops (Chlamys farreri) and bay scallops (Argopecten irradians) in South Korea. The results indicated that scallop growth, in terms of shell size and weight, was significantly lower at OWFs compared to traditional farming sites, though consistent growth patterns were observed. Additionally, species-specific differences in mortality rates were noted, with temperature identified as a key factor affecting scallop growth. This study offers valuable insights into the feasibility of farming marine bivalves, such as scallops, in underutilized OWF areas, providing guidance for future aquaculture practices in these environments.

Castilla-Gavilán et al. (Contribution 5) examined the carbon footprint of various land-based marine aquaculture systems, focusing on strategies to reduce emissions and enhance sustainability. Key approaches include polyculture, the use of low-trophic-level species, and improvements in waste and energy management. Systems such as Recirculating Aquaculture Systems (RASs), Biofloc Technology (BFT), and Integrated Multi-Trophic Aquaculture (IMTA) were identified as offering significant environmental benefits, with IMTA considered the most eco-friendly option, though its carbon footprint remains challenging to quantify. The study emphasized the need for further research to optimize these methods and improve their sustainability.

Basto et al. (Contribution 6) explored the effects of replacing fishmeal (FM) with defatted Tenebrio molitor larvae meal (dTM) on the stress response of European sea bass. Three diets were tested: a control diet with FM, and two others where 50% and 100% of FM was replaced by dTM. After a 16-week feeding period, the fish were exposed to an acute stressor (1 min air exposure). The study found that seabass exhibited a clear stress response, shown by increased hemoglobin, hematocrit, and various plasma metabolites, regardless of diet. While partial FM substitution did not affect stress responses, full FM replacement led to higher liver antioxidant enzyme activity, particularly in total peroxidase and superoxide dismutase. Despite this increase in antioxidant activity, insect meal remains a promising sustainable alternative in aquafeeds.

Claessens et al. (Contribution 7) evaluated the use of mussel meal (Perna perna) as a feed additive for whiteleg shrimp (Litopenaeus vannamei) to improve growth and cold resistance. Five diets, containing varying levels of mussel meal inclusion (0–4%), were tested over an 8-week period. Shrimp fed diets with 1–2% mussel meal exhibited significantly better growth performance and a lower feed conversion ratio compared to other groups, while no differences in cold resistance were noted. The optimal inclusion level for enhancing growth was identified as 1.73–2.00% based on quadratic regression models.

Vale Pereira et al. (Contribution 8) compared alternative feed formulations for rainbow trout, demonstrating improved growth performance and higher consumer acceptance for diets without processed animal proteins. Long-term predictions suggest that some of these alternative diets could also be economically viable for trout farming, offering a sustainable option for the industry.

Rajendran et al. (Contribution 9) explored the anti-inflammatory properties of the acetone extract from the lichen Parmotrema austrosinense using a zebrafish model. The study demonstrated that P. austrosinense possesses significant anti-inflammatory potential, making it one of the most comprehensive in vivo analyses using zebrafish for modeling inflammation.

Soares et al. (Contribution 10) developed FEEDNETICS, a nutrient-based model designed to aid fish farming decisions by simulating individual fish growth and scaling the results to population levels. The model was validated across key aquaculture species, including gilthead seabream, European seabass, Atlantic salmon, rainbow trout, and Nile tilapia. FEEDNETICS helps optimize aquaculture by converting data into actionable insights, supporting experimental design, and assessing the nutritional and environmental impacts on fish farming systems.

Hotos et al. (Contribution 11) assessed the salinity tolerance of two copepod species, Tigriopus sp. and Tisbe holothuriae, from the Messolonghi Lagoon in Greece. Both species demonstrated strong resilience across a wide salinity range. Tetraselmis suecica was identified as the most effective feed for Tigriopus nauplii, while Rhodomonas salina and Dunaliella salina were optimal for T. holothuriae. However, high salinity levels negatively impacted reproduction. These copepods show significant potential for use in ecological research and as live feed in marine hatcheries.

Luís et al. (Contribution 12) investigated the effects of different microalgal diets and dietary proportions on the larval development, growth, and survival of the sea urchin Sphaerechinus granularis at the premetamorphosis stage. Three diets were tested: Dunaliella tertiolecta, Rhodomonas marina, and a combination of both, with varying cell densities (low, medium, and high dietary proportions). The results showed that lower cell densities and a combined microalgae diet positively influenced larval survival. This approach is expected to enhance larval production and provide valuable insights for future research in sea urchin aquaculture.

Matias et al. (Contribution 13) evaluated the impact of long-term day/night temperature oscillations on gilthead seabream (Sparus aurata) juveniles. Fish were exposed to two thermal regimes: a constant temperature of approximately 19 °C and a daily temperature cycle oscillating between 19 °C and 13 °C for a 67-day period. The results showed that temperature fluctuations negatively impacted fish growth efficiency, reduced fatty acid levels in tissues, and altered blood parameters. In contrast, maintaining a constant temperature of ~19 °C optimized both fish growth and health. Therefore, a constant temperature is recommended for gilthead seabream production, although the choice of heating energy source should align with operational conditions and business strategy.

This Special Issue showcases groundbreaking research that sheds light on the pressing challenges confronting marine aquaculture and highlights the innovative solutions being developed to address them. By focusing on species diversification, improving production efficiency, mitigating climate change impacts, exploring alternative feed sources, and adopting sustainable practices, the marine aquaculture industry can continue to grow and thrive while minimizing its environmental footprint. These topics remain critical areas for future research, which is the focus of New Challenges in Marine Aquaculture Research—2nd Edition.