The research team, led by Halley E. Froehlich of the University of California, Santa Barbara, together with colleagues at UC Santa Cruz, UC Berkeley, Cal Poly San Luis Obispo, California Sea Grant, and the Hog Island Oyster Company, introduces and formalizes a concept they call secondary extensive aquaculture, or SEA. The idea is deceptively simple: seaweeds such as Ulva, Gracilaria, and Pyropia naturally recruit and grow on infrastructure built for a different primary species, typically oysters or clams. Instead of treating that growth purely as a maintenance problem, farmers could cultivate, harvest, and sell it as a co-product. Because the seaweed arrives on its own, the approach requires no seeding, no hatcheries, and no additional gear beyond what the farm already deploys.

The authors are careful to argue that SEA genuinely qualifies as aquaculture under the definitions used by the Food and Agriculture Organization of the United Nations and the European Union, both of which require some intervention in the rearing process and ownership of the stock. The placement and maintenance of longlines and bags, they contend, constitute the intervention: the infrastructure provides artificial hard substrate and alters local water flow, structuring where and how much seaweed recruits compared with an unmanaged wild population. Ownership is satisfied because the recruiting seaweed spends its entire rearing period on privately leased and actively managed infrastructure. The researchers draw an analogy to traditional Hawaiian fishponds, or loko i’a, which have long been recognized as aquaculture despite relying on tidal recruitment of wild fish through sluice gates rather than active stocking.

To test whether the concept could survive contact with economic reality, the team built a scenario-based bioeconomic model coupling logistic seaweed growth and sustainable harvest with a simple profit function. The framework borrows from fisheries science: because extensive aquaculture resembles harvesting from the wild, the researchers applied a surplus-production model of the kind routinely used to estimate maximum sustainable yield. Biomass dynamics were simulated at a daily time step over a 20-year horizon, with harvest rates linked to a profit function accounting for market price, variable costs, labor inputs, and fixed operating costs. Oyster production was treated as a fixed baseline — roughly $100,000 in revenue and $80,000 in costs per hectare per year — so that seaweed profitability could be read as an incremental gain or loss from diversification. Crucially, the model assumes that the labor once spent clearing biofouling is redirected into harvesting it, rather than disappearing.

The model was parameterized with literature-derived ranges for seaweed growth rates and carrying capacities, and grounded in real-world data from a pilot harvest conducted in April 2025 on the roughly 65-hectare Hog Island Oyster farm in Tomales Bay, Northern California. During two harvest events, crews pulled Gracilaria, known commercially as ogo, from bottom bags and Pyropia, the nori used in sushi restaurants, from suspended gear and lines. The first harvest, performed by three people, produced about 22.7 kilograms of wet nori in 19 minutes; the second, with six people, yielded roughly 104 kilograms of total wet biomass. The material was processed for Hog Island’s restaurant operations, giving the team an unusually direct measure of what SEA actually costs in labor.

The simulations revealed a clear hierarchy of what matters. Profitability increased with farm size, growing season length, and the intrinsic growth rate of the seaweed, with viable scenarios typically requiring more than 50 to 100 hectares and more than 60 growing days under conservative market assumptions of $400 per ton of wet weight. Strikingly, the intrinsic growth rate exerted a stronger influence on profitability than carrying capacity: the maximum possible profit under the fastest growth scenario was more than 500 percent higher than under the highest carrying capacity. That finding has practical consequences, because it points to fast-growing fouling species — Ulva, Gracilaria, and Pyropia among them — as the most suitable SEA candidates, and it means a farmer’s first diagnostic step is simply identifying which algae are colonizing the farm. Under very slow growth and low carrying capacity, profits were negative regardless of farm size, showing that some ecological conditions preclude feasibility altogether.

Labor emerged as the decisive bottleneck. The pilot harvests required roughly 50 to 60 labor-hours per ton for harvesting and between roughly 140 and 200 labor-hours per ton once processing was included — figures that dwarf the approximately 10 labor-hours per ton needed to break even at California’s minimum wage of $16.90 per hour. Doubling the crew from three to six people cut labor hours by about 30 percent, but that was nowhere near enough. The team’s modeling of efficiency improvements showed that technological and knowledge-driven gains matter far more than adding workers: with an 80 percent reduction in labor-hours per ton, breakeven became achievable with a crew of roughly eight people, while a 50 percent improvement required around 15. Those improvement targets are conservative by historical standards — Maine’s seaweed sector documented a roughly 14-fold increase in labor efficiency between 2017 and 2022, equivalent to about a 41 percent annual reduction in labor-hours per unit harvested.

Despite the labor challenge, the yield numbers were encouraging. The pilot SEA harvests produced between roughly 0.66 and 1.10 tons per hectare per year, and the model’s estimated maximum sustainable yield came in at about 0.94 tons per hectare per year — figures that sit near the lower bound of global seaweed aquaculture production but remain within plausible commercial ranges. The pilot yields were two to three times higher than the single lowest yield documented in a global systematic review of dedicated seaweed producers, a Gracilaria monoculture in China. Under modal ecological conditions on a 65-hectare farm, or at a higher seaweed price of $1,200 per ton typical of restaurant-grade nori, SEA could account for 4 to 11 percent of total farm profit — enough to recoup the 5 to 10 percent losses that unharvested biofouling typically inflicts.

The authors are candid about the caveats. Many parameters rest on limited pilot observations and model assumptions; seaweed markets remain emerging and volatile; and the analysis treated SEA as a standalone revenue stream, leaving out indirect benefits such as improved primary crop production from more thorough fouling removal. Because SEA depends on natural recruitment rather than seeding, farmers have limited control over which species colonize their gear, meaning farm suitability rather than species selection is the relevant management lever — and species composition may shift over time, complicating market strategy. A biostimulant market, where marine soil additives sell for roughly $0.22 to $0.66 per kilogram, may be more resilient to that variation than a nori-only market, and the researchers suggest smaller-scale, local-regional supply chains may be the ideal pathway for SEA harvests.

What emerges is a concept that is ecologically feasible but economically constrained — a promising complementary strategy for diversifying revenue and enhancing circularity in aquaculture systems, contingent on sufficient scale, favorable biological productivity, labor efficiency gains, and supportive policy frameworks that clarify permitting for co-harvested species. For the small farms that dominate the U.S. seaweed landscape, the message is sobering but precise: simply removing the fouling seaweed is likely the better financial option, unless family or voluntary labor changes the calculus. For larger operations in productive waters, the nuisance growing on the oyster lines may be quietly waiting to become a second harvest — provided the industry can learn to pick it fast enough to make the arithmetic work.

Subject of Research: Bioeconomic viability of harvesting naturally recruiting seaweed as a secondary crop on shellfish aquaculture farms

Article Title: Defining and finding the profit for seaweed secondary extensive aquaculture

Article References: Froehlich, H. E., Campbell, R. S., Miller, K. A., Johnson, K. M., Fleener, G., & Kroeker, K. J. (2026). Defining and finding the profit for seaweed secondary extensive aquaculture. Frontiers in Aquaculture, 5, Article 1844314. https://doi.org/10.3389/faquc.2026.1844314

Image Credits: AI Generated

DOI: 10.3389/faquc.2026.1844314

Keywords: seaweed aquaculture, secondary extensive aquaculture, biofouling, oyster farming, bioeconomic modeling, maximum sustainable yield, Ulva, Gracilaria, Pyropia, labor efficiency, blue economy, California

Researchers led by Cecilia Martin of Red Sea Global tagged 96 mature Avicennia marina trees across 12 sites spanning the northern Saudi Red Sea coastline. On each tree, three permanent terminal branches were marked and monitored monthly from August 2021 to October 2022, with the team counting bud clusters, flowers and propagules at every visit. The trees, averaging just 2.2 meters in height, reflect the naturally dwarfed growth habit that characterizes mangroves in this nutrient-poor, freshwater-starved region, where a one-meter tree is already considered reproductively mature.

The monitoring revealed a striking seasonal choreography. Buds and flowers increased in abundance during the hot summer months and declined through winter, while propagules followed the exact opposite pattern, peaking when temperatures fell. Using Generalized Additive Models, the team confirmed that these patterns were statistically significant rather than random fluctuations. Cross-correlation analysis showed that rising air temperatures prompted bud and flower production with a lag of about one month, while falling temperatures triggered propagule formation with a lag of zero to one month. Solar radiation also played a role, with buds and flowers responding positively to increased irradiation after a three-month delay, and propagules showing a negative correlation with a two-month lag.

Perhaps most surprising was what did not matter. Precipitation showed no significant correlation with any reproductive phase, and sea surface salinity showed no link to propagule abundance. In a hyper-arid environment where annual rainfall is less than 50 millimeters and fell almost entirely in just two months of the study period, this makes ecological sense. The species’ renowned salt tolerance appears to render sea surface salinity irrelevant to its reproductive timing, although the authors caution that soil pore-water salinity, which can reach far higher levels during hot, dry summers when evaporation concentrates salts in the sediment, may still suppress propagule development and germination.

When the team normalized propagule counts across sites to remove the influence of naturally more productive forests, a second, previously hidden reproductive season emerged. Beyond the dominant winter season running from December to April and peaking in February, a secondary flush of propagule production occurs at the end of summer, around August to October. Cluster analysis then revealed a clear latitudinal gradient: the three northernmost sites peaked around September, the five central sites peaked from February to March, and the three southernmost sites peaked earliest, from December to January. This south-to-north progression mirrors patterns documented across Australia, New Zealand and Papua New Guinea, where mangrove reproduction is consistently delayed at higher, cooler latitudes.

The ecological logic behind this temperature-driven schedule is compelling. Studies of the related species Avicennia germinans have shown that high temperatures inhibit propagule rooting and germination, suggesting that mangroves maximize recruitment success by releasing their offspring during cooler months. In the northern Red Sea, where winter temperatures can drop low enough to threaten less hardy species, Avicennia marina’s well-documented cold tolerance allows it to exploit this window. The correlation between propagule production and seawater level further supports the idea that higher water levels aid the floating dispersal mechanism by which mangrove propagules spread.

These findings arrive at a critical moment. Saudi Arabia has made mangrove restoration a centerpiece of its Vision 2030 strategy and the Saudi Green Initiative, with Red Sea Global committing to plant or enhance 50 million mangrove trees in the region. Until now, propagule harvesting has been based on local observations at a handful of forests. The new study provides the region-wide, quantitative foundation needed to plan harvesting operations scientifically, identifying exactly where and when propagules can be collected at their peak abundance across the entire study area.

The latitudinal gradient offers a practical advantage: by targeting different forests during their respective peak months, harvesters can spread collection across multiple months of the year, reducing pressure on any single stand while maximizing the genetic diversity of collected propagules. To safeguard natural regeneration, the researchers applied a Maximum Sustainable Yield framework, capping harvests at 50 percent of mature propagules per tree. Under this framework, the 12 assessed forests, which together represent roughly one third of the region’s total mangrove area of 2,400 to 2,700 hectares, could sustainably supply around 680,000 propagules per year during peak season, or an estimated 2 million across the full region. Including shoulder months, availability could reach approximately 4 million propagules annually, meaning the 50-million-tree goal could theoretically be met in about 13 years, though the authors stress this idealized scenario ignores accessibility constraints and germination failures.

The dual-season reproductive pattern carries an additional operational bonus for nurseries. Avicennia marina propagules germinate within days of harvesting and seedlings are typically grown for six to eight months before reaching the roughly 50-centimeter size suitable for outplanting. Propagules collected in December would therefore be ready to leave the nursery just as the second propagation season begins in August, allowing nursery space to be reused twice a year and minimizing the physical footprint of propagation operations.

The study also sounds a note of caution for a warming world. Rising temperatures could extend the flowering season at this northern range limit, potentially improving reproductive completion, yet the same warming is expected to impair propagule germination and early recruitment, which favor cooler conditions. Conversely, milder winters may boost seedling survival where cold damage currently constrains regeneration. These opposing feedbacks make the fate of range-edge mangrove populations genuinely uncertain. What is clear is that understanding the fine-grained, site-specific reproductive biology of these remarkable trees is no longer an academic luxury. As mangrove ecosystems worldwide continue to decline, losing roughly 3.4 percent of their extent between 1996 and 2020, the success of the restoration projects meant to reverse that trend will depend on precisely this kind of ground-truthed ecological knowledge, harvested one tagged branch at a time.

Subject of Research: Reproductive phenology of the grey mangrove Avicennia marina at its northwestern range limit in the northern Red Sea

Article Title: Understanding the reproductive phenology of Avicennia marina at its northwestern range in the Arabian Peninsula supports improved afforestation planning

Article References: Martin, C., Rossbach, S., Alansari, A., & El-Bana, M. (2026). Understanding the reproductive phenology of Avicennia marina at its northwestern range in the Arabian Peninsula supports improved afforestation planning. Discover Oceans, 3(1), Article 22. https://doi.org/10.1007/s44289-026-00135-3

Image Credits: AI Generated

DOI: 10.1007/s44289-026-00135-3

Keywords: mangroves, Avicennia marina, Red Sea, phenology, propagules, afforestation, restoration, Saudi Arabia, hyper-arid climate, temperature, Maximum Sustainable Yield, coastal ecosystems

The research team, led by Steven Saul and including scientists from The Nature Conservancy, Yayasan Konservasi Alam Nusantara, Indonesia’s Ministry of Marine Affairs and Fisheries, and the University of Rhode Island, confronted a core dilemma of tropical fisheries science: most of these fisheries are too poorly documented for conventional assessment. Data-limited methods, which squeeze advice from sparse catch records and fish length measurements, are the only realistic option, but they vary widely in the estimates they produce from the same data. Rather than relying on any single model, the team combined five different fishing mortality estimators, including length-based spawning potential ratio methods, the LIME framework, Beverton-Holt total mortality estimation with bias correction, catch curve analysis, and a solution of Baranov’s catch equation. Biomass was estimated with the catch-only Catch-MSY approach, wrapped in four sensitivity scenarios around catch history and depletion assumptions.

Uncertainty was layered even deeper. The analysts paired these biomass and mortality models with five alternative life history parameter sets, drawn from FishBase, from the FishLife predictive database, from the study’s own length data, and from calculations five percent above and below those data-derived values. Every permutation of model, life history scenario, and biomass scenario — which the authors call “states of nature” — was carried through the entire workflow to reconstruct population demographics and forecast numbers at age forward in time. The result is an assessment in which both model uncertainty and data uncertainty flow directly into the confidence bounds reported for every stock status estimate, a deliberate design choice meant to communicate honest ranges rather than false precision.

The findings, presented in Kobe plots and boxplots pooled across management areas, are sobering despite their uncertainty. Most model scenarios indicate that fishing is occurring above the target reference point, defined as the fishing mortality that maintains a stock at a spawning potential ratio of 40 percent. Approximately 60 percent of the assessed species have biomass below their limit reference point, the biomass corresponding to a 20 percent spawning potential ratio. Snappers, drums, croakers, and some emperor species fell below the limit, while groupers and grunts were estimated to remain above it. Across all Fisheries Management Areas, roughly half of the assessed species had biomass under the limit benchmark and about three-quarters were being fished harder than the target rate, although the authors caution that substantial uncertainty surrounds these figures.

What distinguishes the study is its translation of stock status into decision-relevant trade-offs. The team evaluated six management alternatives: continuation of current fishing mortality, and managing each stock at fishing rates sustaining spawning potential ratios of 20, 30, and 40 percent, maximum sustainable yield, or maximum economic yield. For each option, they estimated rebuilding times, equilibrium catches, profit, and nutritional composition of the catch. Rebuilding is fastest, within roughly five to 10 years, if fishing is held to the F@SPR40 percent benchmark, while continuing to fish at the SPR 20 percent or maximum sustainable yield levels would delay recovery to about 15 to 20 years for stocks currently below their limit.

Equilibrium catches once stocks recover are remarkably similar across benchmarks, ranging from about 70,000 to 88,000 metric tons per year. The species composition of that future catch also changes little between scenarios. The economics tell a sharper story: fishing at current mortality rates is projected to produce a financial loss, driven largely by the Malabar snapper, Lutjanus malabaricus, the fishery’s primary target species, which is being fished above its target while its biomass sits below the limit. Managing the fishery at any of the sustainability benchmarks turns profit positive once depleted stocks rebuild, with the largest profits realized at maximum economic yield and at the SPR 30 percent benchmark.

Nutritional outcomes, calculated by applying the Nutracast model to forecast catch composition, show little difference across management scenarios once stocks are rebuilt, because the species mix of the equilibrium catch is fairly consistent. But the authors warn that this stability cannot be taken for granted. If costs continue to exceed revenues and stocks remain below their limits, catches could decline in future years, eroding the fishery’s contribution to food security. About 80 percent of Indonesia’s snapper and grouper production is sold domestically, and it remains unclear how much of the retained harvest reaches Indonesian consumers versus the tourism sector, or how it divides between subsistence use, market purchases, and low-grade fish parts retained by fishers and processing workers.

The socioeconomic dimension adds further nuance. Recovering overfished stocks requires reducing fishing pressure, which imposes near-term costs on fishing communities in the world’s second-largest wild-capture fish producing nation. The authors recommend a slow, phased approach with very small, incremental reductions, giving fishers time to adapt by changing target species, gear configuration, or livelihoods. They also explore the hypothetical consequences of restricting landings of Lutjanus malabaricus alone, noting that the species could act as a “choke” constraint: fishers might switch to other species, discard regulated catches and cause discard mortality, or exit the fishery, potentially leaving healthy stocks underutilized. Because the other main species, Pristipomoides multidens and P. typus, overlap spatially with Malabar snapper, managing the dominant species would inevitably affect the rest of the catch.

The study is candid about its limitations. Length samples and landings were assumed to be uniformly distributed within each management area, yet sampling is shaped by where vessel captains choose to fish, with GPS trackers from participating vessels showing repeated visits to the same locations. Local depletion and targeting of plate-sized fish can bias mortality estimates, and gear selectivity in this mixed-gear fishery is only partially modeled. The catch-only biomass method rests on strong assumptions, including the use of a length-based spawning potential ratio as a proxy for depletion, which the authors acknowledge is not strictly equivalent. Trophic-level analysis found no correlation between a species’ position in the food web and its stock status, hinting that exploitation spans all trophic levels rather than progressing from top to bottom, though the sampled species covered only trophic positions three to five.

Ultimately, the study’s contribution is methodological as much as substantive. It demonstrates that even where formal assessments are impossible, a carefully combined ensemble of data-limited models with systematic sensitivity testing can deliver tactical management advice, complete with quantified uncertainty and explicit trade-off tables, suitable for structured decision-making. The authors emphasize that the results are shared to inform, not dictate, policy: decisions rest with Indonesian resource managers and stakeholders through the country’s legally established processes. The analysis code is publicly available on GitHub, and the underlying data collection system, the Crew Operated Data Reporting System, relies on commercial fishers themselves recording the lengths of their catch — a partnership the study’s authors say is essential to building the data streams that will steadily narrow the uncertainty surrounding one of the world’s most important tropical fisheries.

Subject of Research: Biological, economic, and nutritional trade-offs of management reference points in Indonesia's data-limited tropical demersal snapper and grouper fishery

Article Title: Biological, economic and nutritional trade-offs in tropical information limited fisheries: Indonesia's demersal finfish

Article References: Saul, S., Carrella, E., Carroll, G., Satria, F., Sadiyah, L., Mous, P., Perdanahardja, G., Ekawaty, R., Ananthanarayanan, A., Bailey, R., Dorsett, C., Drexler, M., Humphries, A., & Wibisono, E. (2026). Biological, economic and nutritional trade-offs in tropical information limited fisheries: Indonesia's demersal finfish. Environmental and Sustainability Indicators, 32, Article 101492. https://doi.org/10.1016/j.indic.2026.101492

Image Credits: AI Generated

DOI: 10.1016/j.indic.2026.101492

Keywords: data-limited fisheries, Indonesia, snapper, grouper, stock assessment, demersal finfish, spawning potential ratio, maximum sustainable yield, maximum economic yield, food security, fisheries management, Lutjanus malabaricus