Severe tissue damage in Atlantic cod larvae under increasing ocean acidification

Ocean acidification, caused by increasing atmospheric concentrations of CO2 (refs 1-3), is one of the most critical anthropogenic threats to marine life. Changes in seawater carbonate chemistry have the potential to disturb calcification, acid-base regulation, blood circulation and respiration, as well as the nervous system of marine organisms, leading to long-term effects such as reduced growth rates and reproduction(4,5). In teleost fishes, early life-history stages are particularly vulnerable as they lack specialized internal pH regulatory mechanisms(6,7). So far, impacts of relevant CO2 concentrations on larval fish have been found in behaviour(8,9) and otolith size(10,11), mainly in tropical, non-commercial species. Here we show detrimental effects of ocean acidification on the development of a mass-spawning fish species of high. commercial importance. We reared Atlantic cod larvae at three levels of CO2, (1) present day, (2) end of next century and (3) an extreme, coastal upwelling scenario, in a long-term (2; months) mesocosm experiment. Exposure to CO2 resulted in severe to lethal tissue damage in many internal organs, with the degree of damage increasing with CO2 concentration. As larval survival is the bottleneck to recruitment, ocean acidification has the potential to act as an additional source of natural mortality, affecting populations of already exploited fish stocks.

The Russell Cycle. An update and review of trends in zooplankton and fish larvae off Plymouth 1924-2009. Occasional Publication of the Marine Biological Association 24

Regular plankton sampling off Plymouth by the Marine Biological Association (MBA) has been carried out from the early 1900s. Much of the sample analysis and description of the results was carried out by Sir Frederick Russell and Professor Alan Southward (AJS), the latter having completed the organisation and transfer of the paper records to digital files. The current authors have transferred the main data files of AJS on zooplankton and fish larvae to the MBA long-term database (including various editing and checking against original analysis records and published data) together with adding the data for 2002-2009. In this report the updated time-series are reviewed in the context of earlier work, particularly with respect to the Russell Cycle. It is not intended as an exhaustive analysis. Brief details of the sampling and comments on data processing are given in an appendix.

Diel vertical migration of decapod larvae in the Portuguese coastal upwelling ecosystem: implications for offshore transport

The vertical distribution of decapod larvae off the northwest Portuguese coast was analysed in relation to associated environmental conditions from sampling during a 69 h period around a current meter mooring located on the shelf, approximately 21 km off the coast. Plankton samples were collected every 2 h at the surface with a neuston net and through the water column with a Longhurst Hardy Plankton Recorder (Pro-LHPR), allowing a very detailed resolution of larval vertical distribution. Environmental data (temperature, salinity, and chlorophyll a) were obtained every hour. To investigate the horizontal distribution of decapod larvae in relation to the coast, a plankton-sampling grid was carried out before the 69 h fixed station. Larvae of shelf decapod species were widely distributed over the shelf, while those of inshore species were found much closer to the coast. Decapod larvae (zoeae and megalopae) showed clear diel vertical migrations, only appearing in the upper 20 m at night, a migration that did not appear to be affected by physical conditions in the water column. Larval densities were highly variable, 0.01 to 215 ind. m super(-3) for zoeae and 0 to 93 ind. m super(-3) for megalopae, the zoeae being generally more abundant. The results indicated that during the day larvae accumulate very close to the bottom. The diel vertical migration behaviour is discussed as one of the contributing mechanisms for larval retention over the shelf, even with offshore transport conditions promoted by coastal upwelling, and is hence of major relevance for the recruitment success of decapod species that inhabit inshore and shelf zones of coastal upwelling systems.

Predator–prey reversal: A possible mechanism for ecosystem hysteresis in the North Sea?

Removal of large predatory fishes from marine ecosystems has resulted in persistent ecosystem shifts, with collapsed predator populations and super-abundant prey populations. One explanation for these shifts is reversals of predator–prey roles that generate internal feedbacks in the ecosystems. Pelagic forage fish are often predators and competitors to the young life stages of their larger fish predators. I show that cod recruitment in the North Sea has been negatively related to the spawning-stock biomass of herring for the last 44 years. Herring, together with the abundance of Calanus finmarchicus, the major food for cod larvae, were the main predictors of cod recruitment. These predictors were of equivalent importance, worked additively, and explained different parts of the dynamics in cod recruitment. I suggest that intensive harvesting of cod has released herring from predator control, and that a large population of herring suppresses cod recruitment through predation on eggs and larvae. This feedback mechanism can promote alternative stable states and therefore cause hysteresis to occur under changing conditions; however, harvesting of herring might at present prevent a shift in the ecosystem to a herring-dominated state.

Distribution and Seasonal Cycles of Decapod Crustacean Larvae in Continuous Plankton Records from the North Pacific Ocean

Decapoda taken in Continuous Plankton Recorder (CPR) samples from the Pacific in 1997 and 2000-2003 have been identified and measured. Some previously un-described larval stages were referred to species and characteristics of these are described. Distributions and seasonal occurrence of decapod taxa in the samples are described and discussed with particular emphasis on the dendrobranchiate shrimp Sergestes similis and the brachyurans Cancer spp. And Chionoecetes spp. There is a prolonged larval season at low levels of abundance off the Californian coast but in the more northern waters there is a shorter productive period but numbers of larvae per sample are high, particularly in June. Larvae of Chionoecetes and other Oregoninae were found only from May to July.