Reproductive variability over a four-year period in the sea urchin Evechinus chloroticus (Echinoidea : Echinodermata) from differing habitats in New Zealand

The endemic New Zealand echinoid, Evechinus chloroticus (Valenciennes), was sampled approximately monthly from September 1990 to October 1994 at three sites in Tory Channel, Marlborough Sounds, New Zealand. These channel site s (outer, mid and inner) were up to 20 km from the open ocean and differed in their shore type, exposure to wave action and macrophyte abundance. E. c hloroticus showed an annual reproductive cycle at each site, with gametogen esis commencing in the late austral winter and spawning in summer. Maximum gonad indices (reproductive potential) varied spatially, with the outer sit e generally having higher maximum gonad indices than the inner site, and te mporally, with maximum gonad indices occurring earlier in 3 of the 4 season s at the outer site than the inner site. The mid and inner sites showed muc h greater variation in maximum gonad indices (range 15.83 to 26.99% and 11. 87 to 20.90%, respectively) than the outer site (range 19.31 to 22.95%). Re productive output (weight of gametes released per gram echinoid) also varie d, with the different sites showing significantly different outputs in the different years. A regression of maximum reproductive potential against rep roductive output was significant (p < 0.001), and had a positive slope with an r(2) of 0.79. While, the initiation of gametogenesis was relatively syn chronous between sites and years, and is possibly cued by increasing daylen gth, it progressed at different rates among populations. Spawning did show spatial and temporal variability, occurring near the time of highest sea-su rface temperatures (<similar to>15 degreesC). The observed variations in re productive cycle may be related to small-scale variability in diet and envi ronmental conditions. Furthermore, asynchronous spawning, variable spawning duration, and variable reproductive output are likely to strongly influenc e annual recruitment variability in E. chloroticus, with different larval s ubpopulations contributing unequally in different years. The ecological con sequences of this, both for the ability of E. chloroticus to propagate itse lf in space and time and for the management of the developing E. chloroticu s fishery in New Zealand, are discussed.