Graeme J. Inglis

Ecology of Seagrass Seeds and Seagrass Dispersal Processes

Seagrasses began colonizing the marine environment 100 million years ago in the Cretaceaous (den Hartog, 1970) and, like their terrestrial, wetland, and freshwater angiosperm counterparts, established a highly effective method of dispersal seeds. While the terrestrial plant literature is replete with studies on all aspects of seed ecology, ranging from the importance of seed size and storage reserves, morphology, to dispersal and recruitment strategies (see reviews by Baskin and Baskin, 1998; Clark et al., 1998; Nathan and Muller-Landau, 2000; Higgins et al., 2003; Levin et al., 2003) research on the ecology of seagrass seeds has been remarkably sparse. These processes are integral to understanding the demography of natural plant populations and the absence of this information for seagrasses led to the historical paradigm that seeds were unimportant in seagrass bed dynamics. However, recent studies demonstrating higher than expected genetic diversity (Waycott, 1995; Reusch, 2002), patch development due to seed recruitment (Duarte and Sand-Jensen, 1990; Ole-

USING HABITAT SUITABILITY INDEX AND PARTICLE DISPERSION MODELS FOR EARLY DETECTION OF MARINE INVADERS

Eradication and control of invasive species are often possible only if populations are detected when they are small and localized. To be efficient, detection surveys should be targeted at locations where there is the greatest risk of incursions. We examine the utility of habitat suitability index (HSI) and particle dispersion models for targeting sampling for marine pests. Habitat suitability index models are a simple way to identify suitable habitat when species distribution data are lacking. We compared the performance of HSI models with statistical models derived from independent data from New Zealand on the distribution of two nonindigenous bivalves: Theora lubrica and Musculista senhousia. Logistic regression models developed using the HSI scores as predictors of the presence/absence of Theora and Musculista explained 26.7% and 6.2% of the deviance in the data, respectively. Odds ratios for the HSI scores were greater than unity, indicating that they were genuine predictors of the presence/ absence of each species. The fit and predictive accuracy of each logistic model were improved when simulated patterns of dispersion from the nearest port were added as a predictor variable. Nevertheless, the combined model explained, at best, 46.5% of the deviance in the distribution of Theora and correctly predicted 56% of true presences and 50% of all cases. Omission errors were between 6% and 16%. Although statistical distribution models built directly from environmental predictors always outperformed the equivalent HSI models, the gain in model fit and accuracy was modest. High residual deviance in both types of model suggests that the distributions realized by Theora and Musculista in the field data were influenced by factors not explicitly modeled as explanatory variables and by error in the environmental data used to project suitable habitat for the species. Our results highlight the difficulty of accurately predicting the distribution of invasive marine species that exhibit low habitat occupancy and patchy distributions in time and space. Although the HSI and statistical models had utility as predictors of the likely distribution of nonindigenous marine species, the level of spatial accuracy achieved with them may be well below expectations for sensitive surveillance programs.

Selectivity in vector management: an investigation of the effectiveness of measures used to prevent transport of non-indigenous species

Measures taken to control the spread of non-indigenous species by human vectors may act selectively by providing effective protection against some (but not all) species. Toxic ‘antifouling paints’ are used by boat owners to prevent the development of ‘fouling assemblages’ on the hulls of their boats, which reduce vessel speed and maneuverability. By reducing fouling, these paints also prevent transport of non-indigenous species. Using experimental surfaces mimicking boat hulls, we evaluated the effectiveness and selectivity of (1) antifouling paints, and (2) manual, in-water hull cleaning for preventing the transport of marine sessile invertebrates by recreational vessels. Different types of antifouling paints provided effective protection only against barnacles and bivalves. Other fouling taxa occurred on experimental surfaces after a period of only 2 months. Manual hull cleaning did not remove fouling completely, and even enhanced the risk of subsequent recruitment by some fouling organisms. Up to six times more individuals and colonies recruited to boat surfaces from which the existing fouling organisms had been removed manually than to surfaces that had been sterilized or contained intact fouling assemblages. Bivalves, colonial and solitary ascidians, encrusting bryozoans, hydroids, tubiculous polychaetes, and sponges consistently recruited in greatest abundance to manually cleaned surfaces. Individual taxa responded in complex, but predictable ways to the biogenic cues left by manual cleaning, so that different suites of organisms colonized surfaces that had originally contained fouling assemblages of local or non-local origin. Our study shows that widely adopted measures to control the spread of non-indigenous species by human vectors are often highly selective and, while effective for some taxa, do not prevent the transport of others.

DNA and morphological identification of an invasive swimming crab, Charybdis japonica, in New Zealand waters

Abstract Mitochondrial DNA sequences were used to identify an invasive swimming crab found in Waitemata Harbour, New Zealand. A 457 base sequence of the cytochrome oxidase 1 gene was compared in New Zealand specimens and nine species of Charybdis from Australia and Asia. The New Zealand specimens aligned with C. japonica. The diagnostic morphological characters of C. japonica were also checked in 54 specimens of the species collected in Waitemata Harbour, and concur with the mtDNA result. This is the first record of C. japonica establishing populations outside its native range. C. japonica, along with C. hellerii and the Lessepsian migrant C. longicollis, are the only known invasive species of Charybdis. C. japonica and C. hellerii are two of the few Charybdis species that inhabit the intertidal zone, and it is likely that the intertidal characteristics of these species contribute to their success as invasive species.

Adaptive multi-scale sampling to determine an invasive crab's habitat usage and range in New Zealand.

Patterns of local abundance and geographical distribution are often prime correlates of invasive species’ impacts on native ecosystems. Here we adaptively increased the spatial scale of delimitation surveys to determine the local abundance, range and habitat associations of the introduced portunid Charybdis japonica (Milne-Edwards, 1861) in New Zealand. The crab was first discovered in Auckland’s Waitemata Harbour in September 2000, and by April 2002 trapping surveys revealed the invader had spread widely throughout the Harbour. Experiments using three deployment times (1, 3 and 24 h) optimized detection rates prior to larger scale geographic surveys that defined the range of the introduced population. We surveyed >300 sites in coastal waters within the predicted range of larval dispersal and then 14 major shipping ports throughout New Zealand. C. japonica was abundant in the Waitemata Harbour and present in two nearby estuaries, but there was no evidence of spread to other shipping ports nationwide. Subtidal habitat associations were explored in the main area of infestation which indicated that the invader occupied a range of substrata from fine, silty muds to coarse, shelly sands. Although its distribution overlaps with the native portunid crab Ovalipes catharus, the invader was more abundant throughout Waitemata Harbour and occurred in muddy sediments where native portunids are rare. It is not yet clear whether the C. japonica population in New Zealand is self-sustaining, however if it persists and continues to spread, it is likely to have significant impacts on native estuarine benthic assemblages.

Use of the introduced bivalve, Musculista senhousia, by generalist parasites of native New Zealand bivalves

Abstract Introduced species are often thought to do well because of an escape from natural enemies. However, once established, they can acquire a modest assemblage of enemies, including parasites, in their new range. Here we quantified prevalence and effects of infection with copepods (family Myicolidae) and pea crabs (Pinnotheres novaezelandiae), in three mussel species, the non‐native Musculista senhousia, and two native mussels, Perna canaliculus and Xenostrobus pulex, at Bucklands Beach, Auckland, New Zealand. Copepod prevalence was highest in X. pulex (17.9%), whereas pea crab prevalence was highest in P. canaliculus (33.6%). Both parasites infected M. senhousia, but at a much lower prevalence. Dry tissue weight was significantly lower in P. canaliculus infected with pea crabs. In addition, we experimentally investigated host species selection by pea crabs. In an experimental apparatus, pea crabs showed a significant attraction to P. canaliculus, but not so for X. pulex or M. senhousia. When the mussels were presented in combination, pea crabs showed a weak attraction for X. pulex. Pea crab attraction to M. senhousia was not significant. It appears that the introduced M. senhousia largely escapes the detrimental effects of infection with either parasite species compared with native mussels occurring in sympatry.

Examining Residents’ Proximity, Recreational Use, and Perceptions Regarding Proposed Aquaculture Development

Competing interests related to marine resources have the potential to create conflict in the coastal zone. In many parts of the world marine farms exist in close proximity to areas that support recreation and tourism. The purpose of this study was to examine residents’ perceptions of proposed marine farm development related to their proximity to, and recreational use of, a coastal area in New Zealand. Residents from two areas were surveyed about their recreational use of the region and about perceptions related to marine farm development. Results indicated that those living closest to proposed marine farms used the area more often and in different ways, were most sensitive to marine farm development, and were less positive in their evaluations of marine farms, despite agreeing that marine farms can have positive economic consequences for nearby communities. Implications for using stakeholder input for the planning and management of marine farms are discussed.

Marine Invasions in New Zealand: A History of Complex Supply-Side Dynamics

New Zealand’s recent ecological history is often held up as a textbook example of the havoc that can be wrought by non-native species (Clout and Lowe 2000). The first human inhabitants of New Zealand arrived (by boat) just 800 years ago, and brought with them food crops and dogs. They arrived in a country where, already, many elements of the endemic fauna were in serious decline; an apparent legacy of the introduction of the Polynesian rat (Rattus exulans: ‘kiore’) by transient human visitors, some 1000 years before (Holdaway et al. 2002). In the eighteenth and nineteenth centuries, British immigrants to New Zealand brought with them a wave of new predators, plant pests and grazing animals. When Charles Darwin stopped in NZ on his Beagle voyage in 1835, the settled European population in NZ numbered fewer than 2000 but Darwin lamented the rampant spread of “very troublesome” weeds which had already “overrun whole districts” and the loss of native flightless birds, “annihilated” sic by introduced Norway rats (Rattus norvegicus) (Darwin 1889). Now, 170 years later, there are more than 4 million human inhabitants and 25,000 introduced plant species in New Zealand, with established exotics outnumbering native species (Beston 2005; NZ Plant Conservation Network 2006). Introduced species have significantly altered the natural landscape and ecological functioning of New Zealand’s environments. Deliberate and accidental introductions of organisms continue to occur at an alarming rate. In this chapter we discuss the status of marine invasions in NZ, some of the impediments to accurately defining that status and the importance of taking account of “supplyside” dynamics when assessing the risks of new introductions. “Supply-side” ecology is the term introduced into marine ecology in the late 1980s to describe the study of the processes of arrival of new members of populations (see also Johnston et al. this volume). Its importance was to re-emphasise the consequences of variability in the supply of recruits to adult populations. While not new, the concept served to refocus attention on the dynamics of reproductive success, oceanographic influences on dispersal, larval behaviour, the process of settlement, and features of the receiving environment that cause variations in

Comparison of the ectosymbionts and parasites of an introduced crab, Charybdis japonica, with sympatric and allopatric populations of a native New Zealand crab, Ovalipes catharus (Brachyura: Portunidae)

Abstract The success of biological invaders is often attributed to escape from specialist enemies in their natural range, such as predators and parasites. For enemy escape to have direct consequences in competitive interactions, invaders need to be less vulnerable to enemies than native competitors in the region they invade, but first the presence of these enemies must be established. We investigated the macroparasite and ectosymbiont fauna of the recently introduced portunid crab Charybdis japonica, and compared it with sympatric and allopatric populations of the native New Zealand portunid, Ovalipes catharus. A total of 468 crabs (350 O. catharus and 118 C. japonica) were collected from six harbours throughout New Zealand (Whangarei, Waitemata, Nelson, Lyttelton, Dunedin, and Bluff) and the identity, incidence and prevalence of ectosymbionts and parasites were compared among the different populations. Charybdis japonica and O. catharus harboured different ectosymbionts. Serpulid polychaete tubes occurred on the exoskeleton of 85.4% of C. japonica examined, but were absent from O. catharus. The bryozoan, Triticella capsularis occurred on 97.4% of O. catharus but was not found on C. japonica. Few endoparasites were present in either species. An unidentified juvenile ascaridoid nematode occurred in the hindgut of 5.9% of C. japonica, but was not found in sympatric populations of O. catharus. A second, unidentified species of ascaridoid nematode occurred in 7.1% of O. catharus from Nelson, but was not present in specimens from the five other harbours sampled. Melanised lesions were observed in the muscle tissue of almost half (46.6%) of the C. japonica examined. Histological examination showed these to be of two types: (1) spherical bodies resembling melanised trematode metacercariae; and (2) lesions consistent with wound repair. Lesions were not observed in O. catharus. Although the identity of parasites and epibionts carried by each species differed, both C. japonica and O. catharus had relatively low parasite species richness. We could not test whether the introduced portunid, C. japonica, is any less vulnerable to parasite enemies than the New Zealand portunid, O. catharus.

Using Temporal Sampling to Improve Attribution of Source Populations for Invasive Species

Numerous studies have applied genetic tools to the identification of source populations and transport pathways for invasive species. However, there are many gaps in the knowledge obtained from such studies because comprehensive and meaningful spatial sampling to meet these goals is difficult to achieve. Sampling populations as they arrive at the border should fill the gaps in source population identification, but such an advance has not yet been achieved with genetic data. Here we use previously acquired genetic data to assign new incursions as they invade populations within New Zealand ports and marinas. We also investigated allelelic frequency change in these recently established populations over a two-year period, and assessed the effect of temporal genetic sampling on our ability to assign new incursions to their population of source. We observed shifts in the allele frequencies among populations, as well as the complete loss of some alleles and the addition of alleles novel to New Zealand, within these recently established populations. There was no significant level of genetic differentiation observed in our samples between years, and the use of these temporal data did alter the assignment probability of new incursions. Our study further suggests that new incursions can add genetic variation to the population in a single introduction event as the founders themselves are often more genetically diverse than theory initially predicted.