The life cycle of sessile marine invertebrates relies on a successful transition from a free-swimming larval stage to a benthic adult form. Gaining a deeper understanding of this transition is essential, as this transition often serves as a bottleneck in the life cycle of marine invertebrates and shapes the marine communities, particularly in diverse ecosystems like coral reefs. Recent studies focusing on various marine invertebrate model organisms have shed light on how ciliated larvae navigate their environments, detect essential cues, and activate their specialised sensory nervous systems to initiate larval settlement and metamorphosis. This chapter synthesises current knowledge on the sensory abilities of larvae, the role of peptidergic and classical neurotransmitter signalling in neural control, the influence of environmental cues, and the evolution of intracellular pathways that underpin settlement processes. It focuses on the early-branching metazoans, such as sponges (phylum Porifera) and cnidarians. Despite lacking a true nervous system, sponges show coordinated sensory responses, illustrating that fundamental molecular elements of sensory functions predate the emergence of neural complexity. Cnidarians, as one of the oldest extant phyla with a nervous system, provide crucial insights into the early evolution of neural organisation.
Coral reef ecosystems are inherently dependent on their surrounding ocean. Mounting evidence reveals that oceanographic processes deliver pelagic subsidies that shape coral reef food webs and influence reef persistence following disturbance. These findings are challenging the classical view of reefs as 'self-sustaining' ecosystems in oligotrophic seas. Yet our observations of these biophysical interactions are limited, and we lack a fundamental understanding of how ocean-reef interactions structure shallow reef dynamics. As climate change continues to alter fundamental physical processes within our ocean, the impacts of ocean-reef interactions on reef futures remain unknown. In this review, we offer a forward-looking perspective to catalyze our understanding of ocean-reef connections through interdisciplinary studies and more standardized approaches to data collection and validation. We provide a primer for ecologists on some of the foundational physical processes structuring subsurface temperature dynamics and resource supply to coral reef ecosystems and synthesize the available evidence on how these biophysical interactions influence reef food webs, from microbes to sharks and ultimately humans. Lastly, we emphasize how climate change is restructuring vital biophysical processes in the ocean and on reefs and identify practical solutions for improving our ability to more critically evaluate ocean-reef interactions across scales. Achieving this will be crucial to improve our projections of coral reef futures and to help inform strategic management to support and promote reef persistence under climate change.
The phylum Echinodermata is a familiar constituent of almost every marine environment and a predominant portion of the fauna in some regions. As with most marine taxa, the clade is currently threatened by a range of human mediated threats ranging in scale from the global consequences of climate change to local extinctions driven by disturbance, pollution and overfishing. In part due to their evolutionary and life history traits, echinoderms are often subject to dramatic swings in population size in the face of these threats, with knock on effects for their genetic diversity and population viability. Proper conservation of species and regional populations requires accurate taxonomic assessment to define species statuses and range size parameters, yet despite being the largest exclusively marine phylum, with more than 7000 accepted species, the Echinodermata have been comparatively understudied amongst marine clades. Herein we show the lack of taxonomic activity across the phylum has been dominated by a small number of experts and is unusually low for such a large clade. We discuss the ways in which the lack of taxonomic certainty and the over-application of names across cryptic or misidentified diversity has, in part, contributed to conservation pressures and complicated conservation measures, with discussion of invasive species, echinoderm fisheries and the complex biodiversity of the Southern Ocean.
Amid the current global biodiversity crisis, understanding and conserving marine invertebrates is more urgent than ever. Marine invertebrates are key components of biodiversity in benthic ecosystems, however, in Australia they remain underrepresented in biodiversity data and conservation planning. Australia's coastline extends from the tropics to subpolar environments and the surrounding waters comprise the Australian Territorial Seas and the Exclusive Economic Zone (EEZ). Currently there are 60 Australian Federal and 98 State Marine Parks which by law must ensure the sustainable management of their biodiversity. Polychaetes are dominant in benthic communities both in terms of species richness and diversity and play a critical role in the functioning of marine ecosystems. Polychaetes are also sensitive to environmental disturbance and change and must be considered in developing marine park zoning and monitoring plans. Here we review the history of species discovery (1791-2025) in shallow (0-300 m) and deep waters (300-5,000 m) within Australia. We highlight that many species remain undescribed, especially in the deep sea, and vast areas in Australian waters have little or no data on the polychaetes that occur there. Finally, we propose what can be done to ensure that polychaetes are included in management plans, including (1) increased availability of information for benthic ecologists from museums, (2) the development of reference DNA barcode libraries by museums, (3) increased tertiary education opportunities and (4) increased philanthropic funding sources.
This volume of Advances highlights not only the importance of marine benthic diversity in several regions of the world but also the impediments to describing this fauna. Taxonomy is the science of classifying organisms and is the bedrock of marine biodiversity research and conservation, yet it faces significant decline in Australia. Thus, it is critical that the scientific community understand why taxonomy is so important. This paper underscores the foundational role of taxonomy in marine ecology, using case studies that highlight its critical relevance to species management, conservation policy, and international trade regulation. Despite extensive research and funding, unresolved taxonomies continue to affect our management of ecologically and economically important taxa, including crown-of-thorns seastar (Acanthaster spp.), exploited sea cucumbers (Holothuroidea), and invasive Cassiopea jellyfish. These ambiguities hamper accurate species identification, hinder effective conservation strategies, and complicate regulatory listings under frameworks such as CITES and the IUCN Red List. Key challenges include dwindling taxonomic expertise, reduced funding, lack of university training, and limited career pathways, all of which contribute to Australia's inability to adequately explore and manage its vast marine jurisdiction. The paper advocates for immediate systemic reforms through a series of 11 recommendations related to revitalizing taxonomic education, fostering museum-university partnerships, supporting early career researchers, and investing in infrastructure to enable species discovery. Taxonomic rigor is also essential to validate modern tools like eDNA, metagenomics, and image-based analysis. Without it, efforts to safeguard biodiversity and to foster a sustainable blue economy risk failure.
Benthic marine macroinvertebrates are one of the main components of the marine ecosystem. Proper management of these animals is therefore crucial to maintain sustainable ecosystem functions and services. However, information on the diversity of these phyla in the ASEAN (Association of Southeast Asian Nations) countries has been patchy. This study aimed to determine the current status of benthic marine macroinvertebrate identification in the ASEAN countries and its implications for effective marine resource management and conservation. Regional data on identified species and authors were analysed to determine the species diversity, as well as local and foreign taxonomists and ecologists. A total of 18,084 benthic marine macroinvertebrate species from six phyla (i.e., Annelida, Arthropoda, Cnidaria, Echinodermata, Mollusca, and Porifera) were documented. The Philippines has the highest marine benthic macroinvertebrate species recorded (11,685 species), followed by Thailand and Indonesia, while Cambodia has the lowest recorded species. Indonesia, Malaysia, the Philippines, and Thailand exhibited the highest species similarity. Notably, the number of local taxonomists in the Southeast Asia region was lower than that of their foreign counterparts. Several ASEAN countries, such as Brunei, Cambodia and Myanmar, relied more on either foreign taxonomists or ecologists in identifying their local species, although species identification by the latter workers potentially leads to misidentifications. Possible causes and improvements are discussed.
Seasonal upwelling events have a significant impact on the Mauritanian waters, which are a component of the Canary Current Large Marine Ecosystem (CCLME). These events frequently provide nutrient-rich waters to Mauritania's coastal waters. This influx of nutrients supports some of the most productive fish stocks in the Atlantic and sustains the development of a rich and diverse marine biodiversity. Despite its ecological and economic importance, a significant part of Mauritania's marine fauna remains insufficiently investigated, with significant taxonomic gaps spanning over a variety of taxa. A comprehensive understanding of regional biodiversity is essential for the implementation of sustainable fisheries management and the effective protection of marine ecosystems. Such understanding depends on accurate taxonomic knowledge, which forms the basis for assessing species distributions, ecological interactions and trophic networks. This review provides a synthesis of past research initiatives and campaigns conducted along the Mauritanian coast and identifies key coastal ecosystems of particular ecological relevance. It further highlights current gaps in taxonomic knowledge and points out the importance of an integrative approach to biodiversity research that combines classical morphological taxonomy with modern genetic species identification techniques. Additionally, the review advocates for the establishment and maintenance of a scientific reference collection of the Mauritanian marine fauna as a foundational resource for ongoing and future biodiversity assessments. Ultimately, this article proposes an integrative and interdisciplinary biodiversity research strategy for Mauritania's unique marine environment, thereby contributing to long-term conservation efforts and the sustainable use of marine resources at times of climate change and overexploitation of biological resources.
The world is facing a double crisis of climate change and biodiversity erosion. Global environmental changes have sparked an unprecedented and ongoing loss of biodiversity. To minimize this alarming trend, a deeper understanding of biodiversity is essential for effective conservation and management strategies. However, major taxonomic knowledge gaps remain, particularly in remote and understudied regions such as the Southern Ocean. Without knowledge on the marine biota living within these ecosystems, it becomes challenging to assess the success of existing marine protected areas or to design new ones that can address both current and future threats. This paper aims to highlight the critical role of taxonomy and species identification in biodiversity research and for the implementation of effective conservation and protection measures for vulnerable and sensitive ecosystems. We address key challenges of the taxonomy field and provide recommendations to improve the characterization of marine diversity in poorly known and unexplored environments.
This paper examines some of the challenges facing Taxonomy and conservation of benthic marine biodiversity in the Southwestern Atlantic, an ecologically rich but understudied region spanning the continental margins of Brazil, Uruguay, and Argentina. The area supports high levels of species diversity and endemism, shaped by complex geomorphological and oceanographic features-from continental shelves and submarine canyons to deep-sea plains and unique coastal habitats. This region is distinguished by its vast environmental heterogeneity, supporting ecosystems that range from tropical reefs to temperate and even subantarctic benthic zones. However, significant knowledge gaps persist due to a combination of difficulties, such as scarcity of trained specialists, limited institutional backing, and chronic underfunding. This results in inadequate documentation of species, particularly invertebrates, and undermines conservation efforts, especially as benthic systems face accelerating threats from human activities such as bottom trawling, habitat destruction, pollution, and deep-sea exploitation. The paper underscores the crucial role of taxonomy in generating foundational biodiversity data necessary for effective conservation policies. It calls for renewed investment in taxonomic research, advocating for its recognition as a cornerstone for informed environmental management, robust scientific understanding, and inclusive conservation strategies, in the face of mounting anthropogenic pressures.
South Africa has one of the highest stranding records in the world for both pygmy (Kogia breviceps) and dwarf (K. sima) sperm whales and as such offers a unique opportunity to study these little-known species. Data and samples from animals stranded along the South African and Namibian coastline between 1960 and 1999 were analysed to determine basic life history parameters for the two species. Teeth from 80 K. breviceps and 45 K. sima from South Africa and an additional 27 K. breviceps and one K. sima from Australia were available for age determination. A good correlation between cemental and dentinal age estimates was found for both species, although cemental readings may not be as reliable in K. sima as they are for K. breviceps. Length at birth for K. breviceps was about 120 cm and the weight around 53 kg, while it was about 103 cm and 14 kg for K. sima. The asymptotic length for K. breviceps was calculated as 306.04 cm by 286.08 cm for females and males. Assuming one growth layer group (GLG) to be equal to one year, both sexes reached physical maturity at about the same age of 15 years. A life expectancy between 16 and 23 years was determined for the species. For K. sima, the asymptotic length was 249.14 cm in females and 263.75 cm in males. This corresponds to 13 and 16 years of age for females and males, respectively. A life expectancy of 17-22 years was determined for K. sima. Reversed sexual dimorphism is suggested for K. breviceps, while there appears to be little size difference between the sexes in K. sima. Reproductive organs from 19 male and 25 female K. breviceps and 19 male and 26 female K. sima were examined to determine reproductive status. The onset of sexual maturity was estimated to be at about 262 cm and around five years in female K. breviceps and at about 215 cm and around five GLGs in female K. sima. The ovulation rate of 0.9 per year for K. breviceps indicated that, on average, ovulations occurred about every 13.3 months. The gestation length is approximately 11 months and conceptions occur from April to September and births possibly occurring from March to August in K. breviceps. In K. sima, the ovulation rate of 0.7 per year indicates that ovulations occur about every 17.1 months (or roughly one and a half years) and gestation length is 11-12 months. Both conceptions and births occurred between December and March and 11.5 % of mature females were found to be simultaneously lactating and pregnant. These data indicated that K. sima may also show annual reproduction, if the conditions are right, although that may be facultative and some animals may only reproduce every two years. The reproductive strategy determined for both Kogia species indicated that a relatively high percentage of females was simultaneously lactating and pregnant, but the accumulation rate of corpora showed that although K. breviceps may have an annual reproduction, at least some K. sima females may only reproduce every two years. Both species exhibited seasonal reproduction, but while K. breviceps appeared to have a protracted mating and calving season of six months, K. sima exhibits a shorter mating and calving season over the period of four months with births occurring during the warmest part of the year. Reproductive organs from 19 K. breviceps and 19 K. sima males were examined to determine their reproductive status. In male K. breviceps, attainment of sexual maturity (ASM) occurred between 2.5 and 5 years, 241-242 cm and 210.0-233.6 kg, while it occurred between 2.55 and three years of age in male K. sima, a body length of 197 cm and body weights between 111.8 kg-124.0 kg. The maximum combined testis weight made up 1.04 % of the total body weight in K. breviceps and 2.00 % in K. sima. Based on data on testes size, sexual size dimorphism, signs of intraspecific fighting, and group size a polygynous mating system with a roving male strategy was proposed for both species.
Max Egon Thiel worked as curator of the aquatic invertebrates collection at the Zoological Museum in Hamburg until 1963. Specialising in marine planktonic megafauna, he compiled a broad review of the research history on the Scyphozoa (Coronatae, Cubomedusae, Semaeostomeae) including the Staurozoa (as Stauromedusae), written in German. After publishing major parts in 1936 and 1938, World War II delayed further chapters until 1959 and 1962. A complete bibliography covering references up to 1970 was not printed until 1977. The final section on the taxon Rhizostomeae was completed as a typescript before his death, but was never published. In the present paper, the authors provide a synopsis of the published volumes in English. Following Thiel's original outline, the research history, as well as reviews of the current knowledge at the time about morphology, histology, ontogeny (life cycle), physiology, ecology, and phylogeny of the taxa are presented. The paper is complemented by two electronic supplements: A translated and revised version of the left-behind typescript of Max Egon Thiel about the taxon Rhizostomeae, and the revised digital list of references published in Thiel (1977).
The morphology of members of the order Rhizostomeae is revisited considering all life cycle stages, but with emphasis on the medusa. The current classification of the group is presented, and some aspects of species diversity are discussed. The main issues investigated since the 1970s are briefly presented by decade.
Cetaceans are a critical component of marine ecosystems, acting as top predators in mesopelagic trophic webs. In the Macaronesian biogeographical region, cetacean populations face threats from various anthropogenic activities. Evaluating cryptic oceanic species like kogiids whales is challenging due to insufficient biological and ecological data, making conservation assessments and management efforts harder to achieve. Kogia breviceps and K. sima comprising the family Kogiidae, are morphologically similar, widely distributed, and elusive, with most information originating from stranded specimens and few at sea observations. This study examines data from Kogia species stranded in the Canary Islands between 1977 and 2024 and analyzes sighting data obtained between 1999 and 2024. Between 1977 and May 2024, there were 111 stranding events involving 114 kogiid individuals along the Canary Islands' coasts: 86 events (88 individuals) were pygmy sperm whales, 14 events (15 individuals) were dwarf sperm whales, and 11 events with 11 individuals, were unidentified Kogia species. Additionally, 36 kogiid sightings were recorded, of which 34 originated from dedicated surveys and 2 from opportunistic sightings. Of these sightings, 14 (39%) were K. breviceps, 9 (25%) were K. sima, and 13 (36%) were unidentified Kogia. Twenty-nine sightings (80.5%) of kogiids were recorded in the waters off the eastern coast of the islands of Lanzarote and Fuerteventura. The data indicate that the waters around the Canary Islands are an important habitat for Kogia whales. The findings establish a baseline for future research and underscore the necessity of accurately assessing conservation pressures on pygmy and dwarf sperm whales in the region.
The genus Kogia includes two species that are some of the least known cetacean species around the globe. Here, we investigated the occurrence, behavior, and habitat suitability of dwarf sperm whales (K. sima) off St. Vincent and the Grenadines (Eastern Caribbean). Small boat dedicated surveys were conducted during May and June of both 2022 and 2023 along the south and west coast of the island of St. Vincent. A total of 2260 km was surveyed and 33 sightings of dwarf sperm whale were recorded, which was also the most frequently sighted cetacean species (37.5% of all cetacean sightings). Group size varied from 1 to 20 individuals (mean = 2.08, SD = 3.23). Traveling and breaching were the most commonly recorded behavioral categories and occurred at an equal proportion (28.6%). The distribution of dwarf sperm whales was restricted to the south and southwest portion of St. Vincent in depths ranging from 95 to 1104 m (mean = 650 m). Habitat suitability (in relation to depth and slope) was investigated using an ensemble model using three algorithms (GLM, GAM, and MaxEnt). The model revealed that slope, and to a lesser extent depth, were important in explaining the habitat suitability of dwarf sperm whales. This preliminary research highlights the existence of a globally important area for dwarf sperm whales off St. Vincent, where encounter rates are significantly higher than in any other known island-associated habitat.
Rhizostomeae species attract our attention because of their distinctive body shape, their large size and because of blooms of some species in coastal areas around the world. The impacts of these blooms on human activities, and the interest in consumable species and those of biotechnological value have led to a significant expansion of research into the physiology and functional biology of Rhizostomeae jellyfish over the last years. This review brings together information generated over these last decades on rhizostome body composition, locomotion, toxins, nutrition, respiration, growth, among other functional parameters. Rhizostomes have more than double the carbon content per unit of biomass than jellyfish of Semaeostomeae. They swim about twice as fast, and consume more oxygen than other scyphozoans of the same size. Rhizostomes also have faster initial growth in laboratory and the highest body growth rates measured in nature, when compared to other medusae groups. Parameters such as body composition, nutrition and excretion are highly influenced by the presence of symbiotic zooxanthellae in species of the Kolpophorae suborder. These physiological and functional characteristics may reveal a wide range of adaptive responses, but our conclusions are still based on studies of a limited number of species. Available data indicates that Rhizosotomeae jellyfish have a higher energy demand and higher body productivity when compared to other jellyfish groups. The information gathered here can help ecologists better understand and make more assertive predictions on the role of these jellyfish in their ecosystems.
The substantial development of microscopic techniques and histological examination methods during the past five decades allowed for many new insights into the histology and microanatomy of Rhizostomeae. The present review focuses on new findings about histologically important structures: nerves, senses, muscles, gonads, zooxanthellae and nematocysts. Different ontogenetic stages of rhizostome species were included in the literature research, supplemented with the authors' unpublished data and figures. The overview of the research results reveals that the application of chemo- and immunohistochemical techniques have provided deeper insights into neuronal and sensory structures and their interconnections. Modern microscopic methods led to new findings on the histological gonadal organization and details of the processes of gametogenesis, fertilization, cleavage, gastrulation, and brooding. Advanced optical methods also allowed for a better understanding of Rhizostomeae-zooxanthellae associations and the morphology and function of nematocysts. Improvements in molecular biology allowed for more precise identification of zooxanthellae associated with rhizostome species. Although there has been significant progress in all of the research subjects covered here, we identify several knowledge gaps and conclude with some recommendations for future research.
The genus Kogia includes two extant species, the dwarf sperm whale (Kogia sima) and the pygmy sperm whales (K. breviceps). Due to their elusive behavior at the surface, which limits opportunities for observation, they are amongst the least known species of cetaceans and knowledge of their ecology mostly comes from stranded individuals. Although they have overlapping ranges, dwarf sperm whales seem to be distributed preferentially in warmer tropical and subtropical waters, while pygmy sperm whales tend to be associated with more temperate waters. Both species have previously been recorded in the western Indian Ocean, but little is known about their distribution patterns. Data from different sources, including vessel-based and aerial surveys, environmental DNA and strandings were compiled to report on the occurrence of Kogia around the remote oceanic island of Reunion. The combination of sightings data, eDNA detections and stranding events indicated that the dwarf sperm whale was more common than the pygmy sperm whale and seems to use the territorial waters of Reunion on a regular basis. The northern part of the island in particular might provide suitable habitats for the species. Groups of 1-5 individuals were sighted and occurred mainly over the insular slope, in 1310 m deep waters and 8.2 km from the shore on average; no clear seasonality pattern could be determined. Stranding data were consistent with a calving period during the austral summer and highlighted the vulnerability of these species to human activities.
