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The reproductive cycles of two populations of Coscinasterias muricata from Port Phillip Bay, Victoria, Australia are described in terms of organ indices, oocyte development and progesterone levels. Both Governor's Reef and South Channel Fort populations exhibited clearly defined reproductive cycles with two spawning periods, during summer and during spring. In both populations, the pyloric caecal index and gonadal index showed inverse cycles suggesting nutrient translocation from the pyloric caeca to the gonads for gametogenesis. Physiological changes, such as decreases in pyloric caecal index, and increases in gonadal index and oocyte diameter were observed following the months of increased progesterone concentrations in the female pyloric caeca. These results indicate a role for this steroid in the reproductive cycle. The results from the Governor's Reef population suggest that the influence of progesterone on the reproductive cycle of female C. muricata is regulated by photoperiod. Results also provide evidence of a role for seawater temperature in the reproductive process of this species.

[article extract] Located in the mitochondria and endoplasmic reticulum, enzymes of the cytochrome P450 superfamily are involved in critical physiological processes including biosynthesis and metabolism of steroids, fatty acids and prostaglandins. In addition to metabolism of endogenous compounds, cytochrome P450 (P450) enzymes are involved in the biotransformation/detoxification of some organic xenobiotic compounds, including polyaromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). P450 reactions often lead to more water-soluble and generally less toxic metabolites that are further metabolised by phase II reactions, for example glutathione S-transferases, to form more readily excretable products. However, some P450 reactions involving exogenous compounds result in products that are more toxic than their parent compound, a process known as bioactivation. Changes in levels or activities of detoxification enzymes, such as total P450 and its isoforms, in response to organic contaminant exposure have been previously used in sea stars as specific biomarkers of this contaminant class. Therefore, thorough examination of the natural fluctuations of these enzymes must be undertaken to allow comparison with exposed organisms. The response of total P450 has been shown to be influenced by factors including season, temperature, organism gender, nutritional status and size in both marine vertebrates and invertebrates.

Concentrations of the essential trace metals copper and zinc were measured in the pyloric caeca of female Coscinasterias muricata sampled from Port Phillip Bay, Victoria, Australia at monthly intervals for 15 months. Results indicate that the concentrations of these metals appear to be regulated by the reproductive cycle. Peaks in zinc concentration occurred simultaneously with peaks in progesterone concentration in the pyloric caeca. These findings suggest that zinc plays a role in gametogenesis and ovarian development. Fluctuations in pyloric caeca copper concentration appear inversely related to the pyloric caecal index and associated with oocyte diameter, indicative of a role for this metal in oogenesis. The levels of cytosolic heat stable low molecular mass (LMM) proteins were examined throughout the sampling period. Heat stable LMM proteins (metallothionein-like) of 12 kDa and 7.5 kDa (apparent molecular mass) and the concentrations of copper appear to be related; although the exact nature of these proteins remains unknown. No such relationship was observed between the levels of heat stable LMM proteins and zinc.

Levels of cytochrome P450 enzymes were measured in pyloric caeca microsomes of the asteroid Coscinasterias muricata following exposure to sediment with nominal concentrations of 0, 0.1 or 2 ml crude oil kg −1 (dry weight) and subsequent depuration. No significant differences were observed in total cytochrome P450 levels or cytochrome P418 levels following the exposure period. However after five days of depuration, levels of total P450 in the pyloric caeca of C. muricata exposed to the highest oiled sediment concentration were significantly lower than in specimens exposed to the other treatments. Cytochrome P418 levels were inversely related to total P450 levels following exposure and subsequent depuration. Preliminary results show that levels of CYP1A-like immunopositive protein (CYP1A-like IPP) in exposed asteroids exhibited a concentration response relationship following the exposure period. Variations in CYP1A-like IPP levels observed during the depuration period may be influenced by the sublethal toxicity of hydrocarbons within the crude oil.