Brendan P. Kelaher

Changes in habitat complexity negatively affect diverse gastropod assemblages in coralline algal turf.

The physical structure of a habitat generally has a strong influence on the diversity and abundance of associated organisms. I investigated the role of coralline algal turf structure in determining spatial variation of gastropod assemblages at different tidal heights of a rocky shore near Sydney, Australia. The structural characteristics of algal turf tested were frond density (or structural complexity) and frond length (the vertical scale over which structural complexity was measured). This definition of structural complexity assumes that complexity of the habitat increases with increasing frond density. While frond length was unrelated to gastropod community structure, I found significant correlations between density of fronds and multivariate and univariate measures of gastropod assemblages, indicating the importance of structural complexity. In contrast to previous studies, here there were negative relationships between the density of fronds and the richness and abundance of gastropods. Artificial habitat mimics were used to manipulate the density of fronds to test the hypothesis that increasing algal structural complexity decreases the richness and abundance of gastropods. As predicted, there were significantly more species of gastropods in loosely packed than in tightly packed turf at both low- and mid-shore levels. Despite large differences between gastropod assemblages at different tidal heights, the direction and magnitude of these negative effects were similar at low- and mid-shore levels and, therefore, relatively independent of local environmental conditions. These novel results extend our previous understanding of the ecological effects of habitat structure because they demonstrate possible limitations of commonly used definitions of structural complexity, as well as distinct upper thresholds in the relationship between structural complexity and faunal species richness.

Spatial patterns of diverse macrofaunal assemblages in coralline turf and their associations with environmental variables

Mats of articulated coralline algal turf are common on many rocky intertidal shores. The dense fronds provide a habitat for extremely diverse and abundant macrofaunal assemblages. Despite a large contribution to faunal biodiversity of rocky shores, little has been published about these assemblages. This study describes patterns of distribution and abundance of macrofauna in coralline turf on rocky shores around Sydney. In addition, the potential of environmental variables (sediment, epiphytes, length and density of coralline fronds) for determining these patterns was also investigated. Relatively consistent differences were found between macrofauna in low- and mid-shore areas at all times of sampling and on all shores. Although there was some variation among shores, there was generally significant variation in macrofauna between sites separated by tens of metres. Generally, a relatively small number of taxa were responsible for the great majority of dissimilarity between assemblages. Apart for the small bivalve Lasaea australis , however, these taxa varied between heights on the shore, among times of sampling and among shores. These data illustrate the important contribution that coralline turf has for biodiversity of faunal assemblages on rocky shores around Sydney. They also provide a basis for investigating biological processes and physical factors responsible for structuring patterns of biodiversity of macrofaunal assemblage in coralline turf.

Rapid loss of genetically based resistance to metals after the cleanup of a Superfund site.

Over the period 1953–1979, a battery factory on the Hudson River in New York released ≈53 tons of cadmium (Cd) and nickel hydride wastes into Foundry Cove. The most common aquatic benthic species, the oligochaete Limnodrilus hoffmeisteri, rapidly evolved resistance to Cd. The capacity for detoxification and internal storage of Cd resulted in a strong potential for trophic transfer of Cd through the aquatic food web. As a result of United States Superfund legislation, a major remediation effort in 1994–1995 removed the majority of the Cd, thereby removing the selective force for resistance. The cleanup of this cove resulted in the maintenance of resistant forms but then there ensued a rapid loss of resistance in ≈9–18 generations, showing the potential for ecological restoration to rapidly reduce the potential for trophic transfer of Cd through the ecosystem. This study demonstrates a genetic approach to the study of ecological restoration and connects a genetic indicator of restoration to transfer of toxic metals through ecosystems.

Ingestion of microplastic has limited impact on a marine larva

There is increasing concern about the impacts of microplastics (<1 mm) on marine biota. Microplastics may be mistaken for food items and ingested by a wide variety of organisms. While the effects of ingesting microplastic have been explored for some adult organisms, there is poor understanding of the effects of microplastic ingestion on marine larvae. Here, we investigated the ingestion of polyethylene microspheres by larvae of the sea urchin, Tripneustes gratilla. Ingestion rates scaled with the concentration of microspheres. Ingestion rates were, however, reduced by biological fouling of microplastic and in the presence of phytoplankton food. T. gratilla larvae were able to egest microspheres from their stomach within hours of ingestion. A microsphere concentration far exceeding those recorded in the marine environment had a small nondose dependent effect on larval growth, but there was no significant effect on survival. In contrast, environmentally realistic concentrations appeared to have little effect. Overall, these results suggest that current levels of microplastic pollution in the oceans only pose a limited threat to T. gratilla and other marine invertebrate larvae, but further research is required on a broad range of species, trophic levels, and polymer types.

ABSENCE OF A LARGE BROWN MACROALGA ON URBANIZED ROCKY REEFS AROUND SYDNEY, AUSTRALIA, AND EVIDENCE FOR HISTORICAL DECLINE1

Loss of habitat‐forming algae is increasingly prevalent in temperate marine ecosystems. Here, we document absence of an important habitat‐forming macroalga, Phyllospora comosa (Labill.) C. Agardh, along an urbanized coast in New South Wales (NSW), Australia. Dense Phyllospora canopies were common on shallow sublittoral reefs north and south of Sydney. In contrast, we did not find a single individual along ∼70 km of rocky coastline in the Sydney metropolitan region, despite historical evidence to suggest that it was very common half a century ago. Recolonization of this important habitat‐forming alga has not occurred on Sydney reefs despite improved water quality, protection of its habitat, and frequent long‐distance dispersal of Phyllospora wrack. While there are obvious limitations, historical information can be useful for identifying potential shifts in community structure to increase our understanding of contemporary ecological patterns.

Condition-specific competition allows coexistence of competitively superior exotic oysters with native oysters

1. Trade-offs between competitive ability and tolerance of abiotic stress are widespread in the literature. Thus, condition-specific competition may explain spatial variability in the success of some biological invaders and why, in environments where there is small-scale environmental variability, competitively inferior and superior species can coexist. 2. We tested the hypothesis that differences in abiotic stress alter the outcome of competitive interactions between the native Sydney rock oysters Saccostrea glomerata and exotic Pacific oysters Crassostrea gigas by experimentally testing patterns of intra- and interspecific competition across a tidal elevation gradient of abiotic stress at three sites on the east coast of Australia. 3. At low and mid-intertidal heights, exotic C. gigas were able to rapidly overgrow and smother native S. glomerata, which grew at c. 60% of the exotics rate. In high intertidal areas, where C. gigas displayed about 80% mortality but similar growth rates to S. glomerata, the native oyster was not affected by the presence of the exotic species. 4. Asymmetrical effects of the exotic species on the native could not be replicated by manipulating densities of conspecifics, confirming that effects at low and mid-intertidal heights were due to interspecific competition. 5. Our results suggest that the more rapid growth of C. gigas than S. glomerata comes at the cost of higher mortality under conditions of abiotic stress. Thus, although C. gigas may rapidly overgrow S. glomerata at low and mid tidal heights, the native oyster will not be competitively excluded by the exotic due to release from competition at high intertidal elevations. 6. The success of trade-offs in explaining spatial variation in the outcome of competitive interactions between C. gigas and S. glomerata strengthen the claim that these may be a useful tool in the quest to produce general predictive models of invasion success.

Foraging by the mud snail, Ilyanassa obsoleta (Say), modulates spatial variation in benthic community structure

We investigated the foraging behavior of the mud snail, Ilyanassa obsoleta, and its consequences for macrobenthic community structure on mud flats on Long Island, NY, USA. Field sampling demonstrated strong spatial heterogeneity in the population densities of I. obsoleta .W e experimentally tested three hypotheses: (i) I. obsoleta are strongly attracted to areas with high levels of detritus; (ii) local abundances of deposit-feeding annelids are limited by detritus; and (iii) the foraging activities of I. obsoleta negatively affects annelid assemblages. We manipulated the density of mud snails using inclusion fences and the levels of detritus using dried Ulva. Results showed that high densities of I. obsoleta were attracted to areas enriched with Ulva detritus. In addition, high densities of snails negatively affected abundances of annelids, with the opportunistic species, Capitella spp. and Paranais litoralis, being most affected. The addition of Ulva detritus had more specific effects on annelid assemblages. Only Capitella spp. showed a significant positive response, although previous evidence has demonstrated that higher experimental detrital inputs stimulated growth of other species of annelids and microphytobenthos. In an experimental treatment with enhanced detritus and low densities of snails, we found population abundances of opportunistic annelids (up to 200,000 m 2 ) substantially larger than has ever been recorded in 5 years of sampling. Because mud snails in natural areas actively search, locate and exploit areas with enhanced detritus and their foraging negatively affects abundances of opportunistic worms, I. obsoleta probably controls the upper limits of annelid abundance in the field. Foraging behavior of I. obsoleta therefore

Connectivity within and among a Network of Temperate Marine Reserves

Networks of marine reserves are increasingly being promoted as a means of conserving marine biodiversity. One consideration in designing systems of marine reserves is the maintenance of connectivity to ensure the long-term persistence and resilience of populations. Knowledge of connectivity, however, is frequently lacking during marine reserve design and establishment. We characterise patterns of genetic connectivity of 3 key species of habitat-forming macroalgae across an established network of temperate marine reserves on the east coast of Australia and the implications for adaptive management and marine reserve design. Connectivity varied greatly among species. Connectivity was high for the subtidal macroalgae Ecklonia radiata and Phyllospora comosa and neither species showed any clear patterns of genetic structuring with geographic distance within or among marine parks. In contrast, connectivity was low for the intertidal, Hormosira banksii, and there was a strong pattern of isolation by distance. Coastal topography and latitude influenced small scale patterns of genetic structure. These results suggest that some species are well served by the current system of marine reserves in place along this temperate coast but it may be warranted to revisit protection of intertidal habitats to ensure the long-term persistence of important habitat-forming macroalgae. Adaptively managing marine reserve design to maintain connectivity may ensure the long-term persistence and resilience of marine habitats and the biodiversity they support.

Changes in benthic assemblages near boardwalks in temperate urban mangrove forests

Boardwalks allow easy access to mangrove forests and are built to enhance their recreational and educational potential. Nevertheless, little is known about any potential impacts of boardwalks on plants and animals in the mangrove habitat. This study investigated the effects of disturbances associated with boardwalks on mangrove macrofauna. Influences at several spatial scales were examined by testing hypotheses about macrofaunal assemblages at different distances from a boardwalk. To examine the generality of findings about an impact, the hypotheses were tested for boardwalks in several mangrove forests around Sydney. At one location (Buffalo Creek), the assemblage of benthic macrofauna was affected within 3 m of the boardwalk. There were fewer of the amphipod Paracalliope australis, the gastropod Assiminea buccinoides and insect larvae near the boardwalk than in areas up to 24 m away. Similar local impacts were found around boardwalks in other mangrove forests, but the taxa affected differed from place to place. At Homebush and Woolooware Bays. there were more polychaetes and fewer gastropods directly adjacent to the boardwalk than in areas further away. Thus, boardwalks were associated with localised, but measurable disturbances to the macrofauna. Responses to disturbances differed from one location to another.

Effect of boardwalks on the semaphore crab Heloecius cordiformis in temperate urban mangrove forests

Boardwalks are used in management of mangrove forests because they are thought to solve problems of access by people while promoting recreational and educational opportunities. Nevertheless, boardwalks and the people using them may have negative effects on plants and animals of the mangrove habitat. This study investigated the potential impact of a boardwalk on the distribution and abundance of the semaphore crab Heloecius cordiformis in a mangrove forest near Sydney (New South Wales, Australia). To examine the generality of these findings, the hypotheses tested at this location were tested in another mangrove forest in the same catchment. At each location, there were more H. cordiformis in areas near the boardwalk than further away. Also, density of pneumatophores, cover of leaf litter and proportion of root-material in the sediment were significantly greater away from than near the boardwalk and all these variables were significantly negatively correlated with the abundance of crabs. Experimental transplantations of orthogonal combinations of sediment, root material, algae and pneumatophores demonstrated that the crabs respond to the softer sediment associated with boardwalks by increasing in abundance. Changes in density of pneumatophores, cover of algae, density of roots and type of mud did not influence the abundance of H. cordiformis. Minimising the effects of future anthropogenic disturbances can be best achieved by understanding the processes responsible for existing disturbances of a similar type. Experimental studies can demonstrate which aspects of boardwalks influence the abundance of H. cordiformis. Such studies should be more widely used in environmental management.