Post-settlement Phase Research Articles

Structural changes in the hepatopancreas of the rock lobster, Jasus edwardsii (Crustacea: Palinuridae) during development from the puerulus to post-puerulus

There is evidence for non-feeding in pueruli of palinurid lobsters during their long-distance swim to the coast and the succeeding post-settlement phase until they molt to the juveniles. For a better understanding of the nutritional supply during the puerulus stage, structural changes in the hepatopancreas were studied in post-settlement pueruli and first-molt, postpueruli of the rock lobster, Jasus edwardsii, collected on the southeast coast of the North Island, New Zealand between 1989 and 1990. In newly settled (transparent) pueruli, the epithelium of the hepatopancreas is dominated by presumed “young R-(resorptive) cells”, which are devoid of lipid droplets, but show active uptake of material from the hemolymph through pinocytosis at the basal region. In the fully pigmented puerulus, the hepatopancreas is dominated by R-cells containing massive lipid droplets; also present are small numbers of F-(fibrillar) and B-(blister-like) cells. This increase of lipid inclusion in the R-cells corresponds to the reduction in size of the fat bodies as the lobster develops from the transparent to the pigmented puerulus. After the molt to the post-puerulus, the R-cells are compressed, and the lipid droplets almost disappear, while the B-cells increase both in size and number. A mechanism is proposed in the present paper to explain energy storage and utilization during the puerulus and post-puerulus stages, wherein the fat bodies and the lipid inclusions play a vital role.

The use of fresh food supplements to ameliorate moulting difficulties in lobsters, Homarus gammarus (L.), destined for release to the sea

. Compounded diets given to juvenile lobsters, Homarus gammarus (L.), during the critical post-settlement phase of their development induced moulting abnormalities that resulted in limb loss and deformity. These potentially lethal effects were minimized, and in some cases overcome, through the provision of a supplement of natural food given just once or twice each week. The degree to which a poor diet could be improved was proportional to the quality and frequency of supplementation. Both moult increment and frequency were affected by dietary regime. A quantitative index of general health was derived from selected physical attributes exhibited by juvenile lobsters, which was useful in assessing a combination of responses to different diets and supplements.

The crown-of-thorns starfish, Acanthaster planci, on the great barrier reef

Acanthaster planci, the crown-of-thorns starfish, is a large mobile starfish with a propensity for rapidly fluctuating populations, sometimes reaching very large numbers, on coral reefs of the Indo-Pacific region. The starfish eats hard corals, and large populations can cause rapid change in a coral reef by removing much of the live coral cover. The starfish life cycle includes a pelagic larval stage that lasts for about 2 weeks during the summer. The factors controlling the initiation and propagation of the outbreaks are not well-known. There are a range of hypotheses including physical effects, such as concentration of larvae by advective processes, and biological effects, such as change in nutrient levels influencing larval survivorship and changes in predator populations affecting the rate of population growth. Human impact on the system leading to changes in these parameters has also been suggested to have affected the size and frequency of starfish outbreaks. A range of modelling work on the Acanthaster phenomenon has been done, including non-spatial population models of the starfish and its predators and prey, spatial models of starfish aggregations and physical models of water circulation, i.e. larval transport models, at a range of spatial scales. Gaps in field data and modelling effort are identified. Some of the greatest problems lie in the following areas: • understanding the dynamics of adult starfish when they are at very low densities (non-outbreaking); • understanding the reproductive physiology of adult starfish with particular reference to range of conditions under which viable gametes are produced; • determining whether human activity has influenced the size and/or frequency of outbreaks over time scales of decades; • the processes regulating larval survivorship in the plankton and at the immediately post-settlement phase; • prediction of potential sites for recruitment, early detection of outbreak-size recruitment events and predicting the future course of starfish outbreaks after the initial recruitment has been detected.