Diversity of marine benthic algae from Cantabria (Eastern Cantabrian, Spain): a historical overview of research and publications

The macroalgal flora of Cantabria (north of Spain) has attracted the interest of many researchers on past occasions. Currently published information only reflects occasional collections from sporadic field visits to this region of the Spanish Atlantic coast. To overcome this, a historical overview of research and publications, encompassing collections and presence data recording, has been undertaken. This work lists the resultant taxonomic records and provides information about macroalgal flora of Cantabria. A total of 425 species (25 Cyanobacteria, 55 Chlorophyta, 81 Ochrophyta, and 264 Rhodophyta) were identified. The number of specific, infraspecific taxa, and stages is 437: 25 Cyanobacteria, 57 Chlorophyta, 89 Ochrophyta, and 266 Rhodophyta. The floristic character of flora from the Cantabrian coast is compared over time and with nearby regions applying Cheney’s ratio [(Rhodophyta+Chlorophyta)/ Ochrophyta, or (R+C)/O]. The present paper aims to provide an overview of the research that has been conducted in the Cantabrian coast, not only found in international publications but also in local publications as well as unpublished theses.

Effects of Climate Change and Anthropogenic Activities on Algivorous Cichlid Fish in Lake Tanganyika

Over the last century, water temperatures in Lake Tanganyika have risen due to climate change, which increased thermal stratification and reduced the magnitude of nutrient availability. A rise in temperature increases the C:N:P ratio resulting in a poor algal diet. In addition, lake littoral habitat is experiencing increased sediment load due to deforestation of the watershed caused by anthropogenic activities. Sediments cover benthic algae and reduce its nutritional value, consequently affecting the foraging behavior, distribution, and growth performance of algivorous fish. Algae and algivorous fish are an important link in the lake food chain; therefore, if the rise in temperature will continue as predicted, then this may have a cascading effect for the rest of the community in the food chain including human being. This, in turn, may contribute to food insecurity at local and regional levels. To counteract this adaptation and mitigation measures such as environmental monitoring systems and creating new opportunities should be considered.

Confirmation of fishers' local ecological knowledge of ciguatoxic fish species and ciguatera-prone hotspot areas in Puerto Rico using harmful benthic algae surveys and fish toxicity testing

Ciguatoxin fish poisoning (CFP) is caused by the consumption of tropical and subtropical fishes and other marine species with high levels of ciguatoxin (CTX) in their tissues. CTX is a polycyclic neurotoxin produced by single-celled, photosynthetic dinoflagellates in the Gambierdiscus and Fukuyoa genera which are found in close association with benthic autotrophs. CTX enters the food web when these dinoflagellates are inadvertently consumed by herbivores grazing on their preferred substrates. The toxin biomagnifies up the food chain to the top predators and if humans consume seafood with high levels of CTX it can cause a variety of flu-like symptoms. The best way to avoid CFP is to avoid toxic fishes. However, CTX is undetectable by physical inspection. This study investigated local fishers knowledge of ciguatera hotspots and coldspots along Puerto Rican coral reefs using toxic-dinoflagellate cell counts and by estimating fish toxicity in those sites using a cell-based Neuro-2a cytotoxicity assay. The fishers identified regions of high and low risk for CFP based on their local ecological knowledge (LEK) which were deemed hotspots and coldspots, respectively. There is a 35-fold difference in dinoflagellate cell counts of low-toxicity Gambierdiscus species in samples in the identified hotspot compared to the coldspot. Also, higher trophic level fishes (>3.4 ETL) had higher median estimates of CTX in their tissues at the hotspot than the same species in the coldspot. This study shows the effectiveness of LEK in identifying potential problem areas for ciguatera.

Ecological ramifications of adaptation to size-selective mortality

Size-selective mortality due to harvesting is a threat to numerous exploited species, but how it affects the ecosystem remains largely unexplored. Here, we used a pond mesocosm experiment to assess how evolutionary responses to opposite size-selective mortality interacted with the environment (fish density and light intensity used as a proxy of resource availability) to modulate fish populations, prey community composition and ecosystem functions. We used medaka ( Oryzias latipes ) previously selected over 10 generations for small size (harvest-like selection; small-breeder line) or large size (large-breeder line), which displayed slow somatic growth and early maturity or fast somatic growth and late maturity, respectively. Large-breeder medaka produced more juveniles, which seemed to grow faster than small-breeder ones but only under high fish density. Additionally, large-breeder medaka had an increased impact on some benthic prey, suggesting expanded diet breadth and/or enhanced foraging abilities. As a consequence, increased light stimulated benthic algae biomass only in presence of large-breeder medaka, which were presumably better at controlling benthic grazers. Aggregated effect sizes at the community and ecosystem levels revealed that the ecological effects of medaka evolution were of similar magnitude to those induced by the environment and fish introduction. These findings indicate the important environmental dependency of evolutionary response to opposite size-selective mortality on higher levels of biological organizations.

Role of nearshore benthic algae in the Lake Michigan silica cycle

Si cycling is linked with processes from global carbon sequestration to community composition and is especially important in aquatic ecosystems. Lake Michigan has seen dramatic fluctuations in dissolved silica (dSi) over several decades, which have been examined in the context of planktonic processes (diatom blooms), but the role of benthic organisms (macroalgae and their epiphytes) in Si cycling have not been explored. To assess significance of nearshore benthic algae in Si dynamics, we assembled dSi data from an offshore site sampled since the late 1980’s, and sampled off three Milwaukee beaches during 2005–19. Using colorimetric assays and alkaline digestion, we measured dSi, biogenic silica in particulate suspended material (pSi) and biogenic silica in benthic macroalgae (Cladophora) and epiphytic diatoms (bSi). Offshore, dSi increased about 1 μM per year from 25 μM in the late 1980’s to nearly 40 μM in 2019. Nearshore dSi fluctuated dramatically annually, from near zero to concentrations similar to offshore. Both Cladophora and its epiphytes contained significant bSi, reaching up to 30% of dry mass (300 mg Si g dry mass-1) of the assemblage in summer. Microscopic analyses including localization with a Si-specific-stain and X-ray microanalysis showed bSi in epiphytic diatom cells walls, but the nature and localization of Si in macroalgae remained unclear. A simple model was developed estimating Si demand of algae using the areal macroalgal biomass, growth rates inferred from P-content, and bSi content, and comparing Si demand with dSi available in the water column. This indicated that 7–70% of the dSi in water overlying nearshore benthic algal beds could be removed per day. Key elements of the Si cycle, including which organisms sequester bSi and how rapidly Si is recycled, remain unclear. This work has implications for coastal marine waters where large macroalgal biomass accumulates but bSi content is virtually unknown.

Cross-Ecosystem Linkages: Transfer of Polyunsaturated Fatty Acids From Streams to Riparian Spiders via Emergent Insects

Polyunsaturated fatty acids (PUFAs) are essential resources unequally distributed throughout landscapes. Certain PUFAs, such as eicosapentaenoic acid (EPA), are common in aquatic but scarce in terrestrial ecosystems. In environments with low PUFA availability, meeting nutritional needs requires either adaptations in metabolism to PUFA-poor resources or selective foraging for PUFA-rich resources. Amphibiotic organisms that emerge from aquatic ecosystems represent important resources that can be exploited by predators in adjacent terrestrial habitats. Here, we traced PUFA transfer from streams to terrestrial ecosystems, considering benthic algae as the initial PUFA source, through emergent aquatic insects to riparian spiders. We combined carbon stable isotope and fatty acid analyses to follow food web linkages across the ecosystem boundary and investigated the influence of spider lifestyle (web building vs. ground dwelling), season, and ecosystem degradation on PUFA relations. Our data revealed that riparian spiders consumed considerable amounts of aquatic-derived resources. EPA represented on average 15 % of the total fatty acids in riparian spiders. Season had a strong influence on spider PUFA profiles, with highest EPA contents in spring. Isotope data revealed that web-building spiders contain more aquatic-derived carbon than ground dwelling spiders in spring, although both spider types had similarly high EPA levels. Comparing a natural with an anthropogenically degraded fluvial system revealed higher stearidonic acid (SDA) contents and Σω3/Σω6 ratios in spiders collected along the more natural river in spring but no difference in spider EPA content between systems. PUFA profiles of riparian spiders where distinct from other terrestrial organism and more closely resembled that of emergent aquatic insects (higher Σω3/Σω6 ratio). We show here that the extent to which riparian spiders draw on aquatic PUFA subsidies can vary seasonally and depends on the spider’s lifestyle, highlighting the complexity of aquatic-terrestrial linkages.