ABSTRACT. 'No-take' marine reserves provide a valuable tool for managing marine resources as well as for providing relatively undisturbed habitat with which to assess modifications to ecosystems. We studied 2 marine reserves in northeastern New Zealand, the Leigh Marine Reserve (established 1975) and Tawharanui Marine Park (established 1982) in order to assess whether changes in protected predator populations had resulted in other indirect changes to grazers and consequently to algal abundance. Estimates of abundance of the most common demersal predatory fish Pagrus auratus indicated that adults of this species (i.e. large enough to prey upon urchins) were at least 5.75 and 8.70 times more abundant inside reserves than in adjacent unprotected areas. Overall, P auratus were also much larger inside reserves with mean total lengths of 316 mm compared with 186 mm in fished areas. The spiny lobster Jasus edwardsii displayed similar trends, and was approximately 1.6 to 3.7 times more abundant inside the reserves than outside. Lobsters within the reserves had a mean carapace length of 109.9 mm, compared with 93.5 mm outside the reserves. In one of the reserves, densities of the sea urchin Evechinus chloroticus had declined from 4.9 to 1.4 m-2 since 1978 in areas formerly dominated by it. Consequently, kelp forests were more extensive in 1998 than they were at the time of reserve creation. Urchin-dominated barrens occupied only 14 % of available reef substratum in reserves as opposed to 40"4 in unprotected areas. These changes in community structure, which have persisted since at least 1994, demonstrate not only higher trophic complexity than anticipated in Australasian ecosystems but also increased primary and secondary productivity in marine reserves as a consequence of protection. Trends inside reserves indicate large-scale reduction of benthic primary production as an indirect result of fishing activity in unprotected areas.

Tetrodotoxin (TTX) is a potent neurotoxin that has been identified in a range of phylogenetically unrelated marine and terrestrial organisms. Tetrodotoxin was recently detected in New Zealand in Pleurobranchaea maculata (the grey side-gilled sea slug). From June 2010 to June 2011 wild specimens were collected from 10 locations around New Zealand. At one site (Narrow Neck Beach, Auckland) up to 10 individuals were collected monthly for 6 months. Attempts were also made to rear P. maculata in captivity. Tetrodotoxin was detected in samples from eight of the ten sites. The highest average (368.7 mg kg−1) and maximum (1414.0 mg kg−1) concentrations were measured in samples from Illiomama Rock (Auckland). Of the toxic populations tested there was significant variability in TTX concentrations among individuals, with the highest difference (62 fold) measured at Illiomama Rock. Tetrodotoxin concentrations in samples from Narrow Neck Beach varied temporally, ranging from an average of 184 mg kg−1 in June 2010 to 17.5 mg kg−1 by December 2010. There was no correlation between TTX levels and mass. The highest levels correspond with the egg laying season (June–August) and this, in concert with the detection of high levels of TTX in eggs and early larval stages, suggests that TTX may have a defensive function in P. maculata. Only one larva was successfully reared to full maturation and no TTX was detected.

Early research into the distribution of juvenile snapper (Pagrus auratus) indicated that complex habitats were not important during early life stages. Recent studies in soft-sediment environments, however, have shown juvenile snapper to be more abundant in areas of complex habitat. No previous studies have investigated how and why this species uses both reef and soft-sediment habitats. Therefore, we examined the role of topographic complexity in influencing juvenile snapper distribution and habitat use, providing both field and laboratory evidence for the importance of complex benthic habitats for juvenile snapper and goatfish (Upeneichthys lineatus). Underwater visual censuses showed both species to be most abundant over sand flats adjacent to rocky reef habitats, a distribution that may balance the requirements of food acquisition and predator avoidance. In aquaria experiments, where juvenile snapper were given a choice between habitat with and without shelter, the use of shelter habitat increased significantly in the presence of a predatory threat. This demonstration of the use of complex habitat as shelter highlights the importance of benthic complexity for juvenile snapper and suggests that the management of essential habitats could enhance juvenile survivorship and should have an important role to play in sustainable management of exploited species.

Populations of the sea urchin Evechinus chloroticus were monitored at wave-exposed low-sediment reefs and wave-sheltered high-sediment reefs in the Hauraki Gulf, northeastern New Zealand. Urchin populations on both wave-exposed and sheltered reefs were dominated by adults. Wave-exposed reefs supported higher densities (2.7 to 9.6 ind. m ). Juvenile urchins (< 30 mm test diameter [TD]) were 25 times more abundant on wave-exposed reefs. Urchin settlement of 0.2 to 0.6 ind. 100 cm -2 was recorded at wave-exposed reefs but was undetectable at wave-sheltered reefs. Laboratory experiments were conducted to assess whether the volumes of sediment loads observed on sheltered reefs could affect the survivorship of early life stages of urchins in the absence of other environmental factors. Results indicated that fine sediments at one-third and two-thirds of concentrations found on wave-sheltered reefs inhibited the settlement of larvae and reduced the survival of urchin recruits (2 to 5 mm TD) and juveniles (10 to 30 mm TD). Survival rates of juveniles were higher than for more recent recruits, suggesting size-dependent mortality. A lack of significant differences between high and low treatments in all experiments suggests that urchin settlement and survival can be affected negatively at low levels of sediment that are common in natural environments.

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