John K. Keesing

Jellyfish blooms in China: Dominant species, causes and consequences

Three jellyfish species, Aurelia aurita, Cyanea nozakii and Nemopilema nomurai, form large blooms in Chinese seas. We report on the distribution and increasing incidence of jellyfish blooms and their consequences in Chinese coastal seas and analyze their relationship to anthropogenically derived changes to the environment in order to determine the possible causes. A. aurita, C. nozakii and N. nomurai form blooms in the temperate Chinese seas including the northern East China Sea, Yellow Sea and Bohai Sea. N. nomurai forms offshore blooms while the other two species bloom mainly in inshore areas. Eutrophication, overfishing, habitat modification for aquaculture and climate change are all possible contributory factors facilitating plausible mechanisms for the proliferation of jellyfish blooms. In the absence of improvement in coastal marine ecosystem health, jellyfish blooms could be sustained and may even spread from the locations in which they now occur.

Recurrence of the world’s largest green-tide in 2009 in Yellow Sea, China:Porphyra yezoensis aquaculture rafts confirmed as nursery for macroalgal blooms

In the summer of 2008, the worlds largest green-tide occurred in the Yellow Sea, China. The hypothesized cause was the expansion of Porphyra yezoensis aquaculture along the Jiangsu coastline and the re-occurrence of a green-tide in 2009 was predicted. In this study, satellite and field images showed the formation of the June 2009 green-tide which again originated from the Jiangsu coast. The responsible species, its source and biomass accumulation were studied to support the previous hypothesis. Morphological and phylogenetic analysis demonstrated the homology of Ulva prolifera in the 2008 green-tide with the U. prolifera from P. yezoensis aquaculture rafts. About 91-505kg/ha of U. prolifera was attached to the P. yezoensis aquaculture rafts and a total biomass of 4956 tonnes was estimated during the harvesting of P. yezoensis. This is sufficient to seed a bloom when they are dislodged from the rafts as a result of harvesting practices.

Inter- and intra-annual patterns of Ulva prolifera green tides in the Yellow Sea during 2007–2009, their origin and relationship to the expansion of coastal seaweed aquaculture in China

The large green-tide events that occurred in the Yellow Sea in 2008 (3489km(2)) and 2009 (4994km(2)) are shown to be novel events preceded only once by a much smaller event in 2007 (82km(2)). The blooms originated in the coastal area of Jiangsu province and spread north-east towards the Shandong Peninsula. The blooms grew at different rates and mesoscale variability in surface winds explained the differences in the spatial and temporal patterns of blooms in 2008 and 2009. The 2009 bloom was tracked to its origin immediately offshore of extensive intertidal flats between Yancheng and Nantong where recent rapid expansion of Porphyra aquaculture has occurred. We review published hypotheses which have been advanced to explain the occurrence of blooms and in light of our findings, we conclude that the accumulation and disposal of waste Ulva prolifera from Porphyra aquaculture rafts is the most likely cause of the blooms.

A Review of Sea Cucumber Aquaculture, Ranching, and Stock Enhancement in China

ABSTRACT Sea cucumber aquaculture has flourished as a result of increasing demand coupled with declining wild fisheries and has been facilitated by technical progress in the production and grow-out phase of larvae and small juvenile sea cucumbers. China has developed a large and successful sea cucumber aquaculture industry based on the temperate species Apostichopus japonicus (Selenka, 1867). China consumes most of its domestic sea cucumber production (193, 705 tons: 2013), exporting only a few dozen tons. Much of the success of sea cucumber aquaculture in China came from advances in culture methods, especially for the early stages of broodstock conditioning, larval production and settlement, and the critical early juvenile development stage. These artificial approaches to production are a precondition for all aquaculture models, and the scientific procedures and management protocols must be strictly adhered to for success. Similarly, the grow-out phase of sea cucumber production in China has evolved from attempts using disused fish and shrimp ponds to new, dedicated ponds developed to meet the more sensitive requirements of sea cucumbers for water quality and substrate type and to the use of ocean ranching. Various diseases have affected this industry and become barriers to its sustainable development. To achieve higher survival rates and better production quality, the trend has been toward ocean ranching of sea cucumbers and stock enhancement, and production levels have increased significantly in recent years. While cost-effective methods for sea cucumber aquaculture close to their point of consumption is good news for wild stocks of sea cucumbers in different parts of the world, there is a potential downside in the environmental impact of such extensive production methods. The influence of sea cucumber aquaculture on the environment and the influence of the environment on sea cucumber aquaculture are important issues relating to ecological security and sustainability.

Contrasting Trends in Populations of Rhopilema esculentum and Aurelia aurita in Chinese Waters

Rhopilema esculentum and Aurelia aurita are the most common scyphozoan species in Chinese waters. Here the population trends of R. esculentum and A. aurita are described and compared. The possible causes of their contrasting population trends are discussed by reviewing the status of existing information and introducing new data collected on blooms and reproduction of A. aurita in northeastern China. The population change of R. esculentum was described based on the annual harvest of R. esculentum in Chinese waters since 1955. It is generally accepted that a stock enhancement program has been successful in increasing the total catches of R. esculentum. However, the catches have declined since 1998, and this may be due to current stock enhancement levels exceeding the carrying capacity of the fishery ground or deterioration in the coastal marine environment. In contrast, blooms of A. aurita are causing increasing problems in the coastal waters of northern China with suitable settlement substrate provided by expansive coastal aquaculture implicated in these population increases. In addition to anthropogenic influences such as fishing, stock enhancement, and the proliferation of coastal infrastructure, the variation in reproductive and life history traits between R. esculentum and A. aurita may also explain the different recruitment potentials of the two species.

Chapter 25 – Heliocidaris erythrogramma

Heliocidaris erythrogramma is a sea urchin species endemic to Australia, where it inhabits temperate and subtropical rocky reefs on the west, south and east coasts. Two subspecies, Heliocidaris erythrogramma erythrogramma and Heliocidaris erythrogramma armigera, are recognized from the western area of its distribution. This review covers all known aspects of the biology and ecology of H. erythrogramma, including distribution and habitat, genetic and environmental influences on phenotypic expression in different populations, reproductive biology, larval development and settlement, growth, mortality, movement and feeding. Heliocidaris erythrogramma has a lecithotrophic mode of larval development. This has made it a useful subject for experimental studies of the factors that influence settlement and metamorphosis, including some that suggest the species may be resilient to near future changes to ocean temperature and pH. Research over the last decade has made large advances in understanding the ecological role of H. erythrogramma as an herbivore with a significant role in structuring marine plant communities and the way this role can be affected by fishing of predators of sea urchins.

Abiotic factors influencing biomass accumulation of green tide causing Ulva spp. on Pyropia culture rafts in the Yellow Sea, China

Annually recurrent green-tides in the Yellow Sea have been shown to result from direct disposal into the sea of fouling Ulva from Pyropia aquaculture. The role abiotic factors play in Ulva biomass accumulation on rafts was studied to find ways to mitigate this problem. Dissolved inorganic nitrogen (DIN) was very high at all sites, but the highest Ulva biomass was associated with the lowest DIN and anthropogenic N. Under luxuriant background nutrient conditions, variability in temperature and periods of emersion, rather than pH, light and salinity determined Ulva biomass. Two dominant species of Ulva displayed differing tolerances to temperature and desiccation which helped explain why Ulva prolifera dominates floating green-tides. Rather than trying to mitigate green-tides only by reducing nutrient pollution, an earlier harvest of Pyropia in southern Jiangsu Province especially before temperatures increase greatly above 10°C during April, could reduce the biomass of U. prolifera disposed from rafts.

First record of photosynthetic cyanobacterial symbionts from mesophotic temperate sponges

Cyanobacterial symbionts may enable sponges to play a critical role in bentho-pelagic coupling, recycling nutrients at the benthic surface and providing a key requirement for ecosystem function. This is the first study to investigate the depths to which these symbioses are viable and the first record of photosynthetic sponges (i.e. sponges having a symbiotic relationship with photosynthetic cyanobacteria) from mesophotic temperate habitats. Sponges with high levels of photosynthetic cyanobacteria occurred at depths of up to 50 m, medium levels to 75 m and low levels to 150 m off south-western Australia. The proportion of sponges that showed no epifluorescence increased greatly with depth. Cyanobacterial symbionts sequenced from sponges at 40 and 50 m belonged to the genera Synechococcus and Synechocystis. Our results verify that the domain of photosynthetic sponges is not just tropical or shallow water temperate environments. Sponges made up the highest biomass of biota across all the sites we sampled from depths of 30–150 m and we hypothesise that photosynthetic cyanobacterial symbionts may be important in facilitating sponges to dominate habitats at these depths off Australia’s oligotrophic west coast.

Reproductive biology of the sand dollar,Peronella lesueuri(L. Agassiz, 1841) (Echinoidea: Clypeasteroida: Laganidae), in south-western Australia

The reproductive biology of the sand dollar Peronella lesueuri was studied between 2009 and 2011 in Cockburn Sound, a large coastal embayment in south-western Australia. Individuals of P. lesueuri did not display sexual size-dimorphism, and the population was found to have a sex ratio of 1:1. Maturity occurred over the range of 80–115 mm with all sand dollars larger than 115 mm having distinct gonads. Monthly histological analysis of gonads and changes in oocyte proportions over time indicated that P. lesueuri has an annual reproductive cycle; gametogenesis occurs in spring and spawning in summer. Differences in the rate of gametogenesis between 2009/2010 and 2010/2011 may have been influenced by higher temperatures experienced in 2010/2011. P. lesueuri have large ova (mean = 210 μm), which suggests the species has lecithotrophic larval development.

Chapter 17 Ecology of Heliocidaris erythrogramma

Publisher Summary This chapter describes the ecology of Heliocidaris erythrogramma ( H. erythrogramma ). Studies that have provided a good insight into the ecology of H. erythrogramma include those on physiology in relation to nutrition, population genetics, and some aspects of feeding. It is commonly known as the “purple sea urchin” and is endemic to Australia, being distributed on rocky reefs from the intertidal zone. It occurs in a variety of habitats throughout its range, from moderate energy, open rocky shores to estuaries. In moderate wave-energy sites, it occupies crevices in the reef. The fertilization success of H. erythrogramma is examined in the field by measuring fertilization rates of eggs from spawning females upstream of a spawning male. The important role of H. erythrogramma in the complex interactions that structure Australian temperate macroalgal reef systems is increasingly recognized, which would lead to more studies that take a modeling approach incorporating population dynamics that represent the interactions and predict ecosystem dynamics. H. erythrogramma moves mostly at night and shows little fidelity to individual crevices and shelters. It feeds both by grazing or scraping on the substrate and capturing drift algae.