Dispersal carries added costs for bryozoans

Increased larval planktonic duration and post-recruitment competition influence survival and growth of the bryozoan Watersipora subtorquata. Michael A. Sams, Fletcher Warren-Myers, Michael J. Keough, Marine Ecology Progress Series 531: 179-191

For organisms with complex life cycles, longer time spent in the plankton by dispersing propagules can cause reduced survival, growth and fecundity, which could alter interactions between neighbours in the post-dispersal environment. We compared post-settlement performance of bryozoan Watersipora subtorquata colonies that developed from larvae of different natural and experimental planktonic durations over ca. 15 wk of colony growth. Settlers were situated either near established adults of the ascidian Botrylloides leachii or without competition. Increased larval planktonic durations reduced colony growth in the absence of competition; colonies that developed from longer or delayed larval durations were 2 to 3 times smaller than those that developed from shorter durations. Colonies that developed from longer larval periods (natural or experimental) also experienced higher mortality (75 to 100%) than those that settled quickly (20 to 42%), but these effects varied between experiments and seasons. In winter, W. subtorquata colonies of longer larval planktonic durations experienced greater mortality when adjacent to established B. leachii, whereas differences in colony growth due to planktonic duration were reduced by adjacent B. leachii. The influence of B. leachii varied between experiments in different seasons, however, and did not alter colony performance in summer. Our findings demonstrate that while increased larval planktonic duration can be costly for post-dispersal growth and survival, some differences can be mediated by species inter- actions and environmental variability. This suggests that while connectivity among populations that take longer to disperse may be limited, it may also be influenced in complex ways by the post-recruitment environment and not simply dispersal duration.


New paper: Worms help deal with nutrients, even when sediments are contaminated.

Influence of a burrowing, metal-tolerant polychaete on benthic metabolism, denitrification and nitrogen regeneration in contaminated estuarine sediments.  Joanne L. Banks, D. Jeff Ross, Michael J. Keough, Catriona K. Macleod, John Keane, Bradley D. Eyre.  Marine Pollution Bulletin 68 (2013) 30–37.

We investigated the effects of the burrowing cirratulid polychaete Cirriformia filigera (Delle Chiaje, 1828)
on benthic respiration and nitrogen regeneration in metal-contaminated estuarine sediments using laboratory
mesocosms. C. filigera is a dominant component of assemblages in the most severely contaminated
sediments within the Derwent estuary, southern Australia. In the presence of C. filigera sediment
O2 consumption doubled, with approximately 55% of this increase due to their respiration and the
remaining 45% attributable to oxidation reactions and increased microbial respiration associated with
burrow walls. Combined NO3 and NO2 fluxes were unaffected. The addition of labile organic matter
did not affect benthic fluxes, in the presence or absence of C. filigera, presumably due to the short timeframe
of the experiment and naturally enriched test sediments. The results suggest that a combination of
tolerance and burrowing activity enables this species to provide an ecosystem service in the removal of N
from contaminated sites.

New paper: New information to help study connectivity in seagrass.

Microsatellite primer development for the seagrass Zostera nigricaulis (Zosteraceae).  Timothy M. Smith • Paul H. York • Annalise M. Stanley • Peter I. Macreadie • Michael J. Keough • D. Jeff Ross • Craig D. H. Sherman.  Conservation Genetics Resources 5: 607-10.

Abstract Seagrasses are marine angiosperms with a worldwide distribution that form conspicuous beds in nearshore
habitats. Despite being universally recognised as a foundation species that performs a number of important
ecosystems functions (incl. sediment stabilisation, facilitation of biodiversity, nutrient cycling and carbon sequestration),
global seagrass habitats are in decline. Resilience—the ability to recover from disturbance without switching to an
alternative state—is paramount to the maintenance and persistence of seagrass habitats. Genetic diversity is a key
component of seagrass resilience and contributes to an understanding of population structure, connectivity between
populations, and reproductive strategies. Microsatellite primers were developed to investigate the resilience of the
seagrass Zostera nigricaulis, which dominates subtidal habitats in the bays of south-eastern Australia.We also tested
for cross-amplification of markers between Z. nigricaulis and previously developed markers for the sympatric species Z. muelleri to assess their applicability for use in assessing patterns of genetic diversity, population structure, and mating system. Using next-generation sequencing we isolated 11 novel microsatellite loci for Z. nigricaulis, 8 of which were polymorphic for the samples tested. Allelic diversity ranged from 1 to 8. None of the primer pairs developed for Z. nigricaulis cross-amplified in Z. muelleri; but 14 of 24 primer pairs previously developed for Z. muelleri amplified clearly in Z. nigricaulis samples with six of these showing polymorphism. The results demonstrate the applicability of the Z. nigricaulis microsatellite primers for use in the study of population genetics and limited cross-amplification with Z. muelleri.

New paper: Complex effects of invasive species: a marine pest alters nutrient processing, but not in a consistent way

Spatially variable effects of a marine pest on ecosystem function

D. Jeff Ross, Andy R. Longmore, Michael J. Keough.

The broad spectrum of anthropogenic pressures on many of the world’s coastal bays and estuaries rarely act in isolation, yet few studies have directly addressed the interactive effects of multiple pressures. Port Phillip Bay in southeastern Australia is a semi-enclosed bay in which nutrient management is a major concern. In recent years it has been heavily invaded by marine pests. We manipulated the density of one such invader, the European fanworm Sabella spallanzanii, and showed that it causes changes in the composition of macrofauna in the surrounding sediments, provides habitat for epibiota (both fauna and flora) on Sabella tubes, and reduces the biomass of microphytobenthos on the surrounding sediments. Of greatest concern, however, was the indirect impact on nutrient cycling. We suggest that the impacts on nutrient cycling are largely due to the feeding of Sabella and the epifauna on its tubes, capturing organic N before it reaches the sediment, excreting it back up into the water column as NH4, thereby bypassing sedimentary processes such as denitrification. Most notably, the efficiency of denitrification, the key ecosystem process that permanently removes N from the system, fell by 37–53 % in the presence of Sabella. Importantly though, this study also demonstrated significant spatial variability in fauna, geochemistry and the magnitude of Sabella effects. Given that the effect of Sabella is also likely to vary in time and with changes in density, all of these sources of variability need to be considered when incorporating the effects of Sabella in nutrient management strategies.

Oecologia 172: 525-538; see it at http://www.springerlink.com/openurl.asp?genre=article&id=doi:10.1007/s00442-012-2497-3

New paper: Hydroids slow mussel growth and eat their babies

Ruinous resident: the hydroid Ectopleura crocea negatively affects suspended culture of the mussel Mytilus galloprovincialis
Isla Fitridge & Michael J. Keough
Department of Zoology, University of Melbourne, Victoria, Australia

Hydroids are major biofouling organisms in global aquaculture. Colonies of the hydroid Ectopleura crocea have recently established in Australian commercial mussel leases culturing Mytilus galloprovincialis. This study examined the impacts of E. crocea on mussel culture at two stages of the production cycle: spatfall and grow-out. Hydroids most commonly fouled the body, edge and dorsal regions of the mussel shell and cause a reduction in the length (4%) and weight (23%) of juvenile mussels. They also consumed mussel larvae in the field and in the laboratory. Prey numbers of many taxa, including mussel larvae, were consistent in natural hydroid diets regardless of the temporal variation in prey availability, implying some selectivity in hydroid feeding. In the laboratory, E. crocea consumed settling plantigrade mussel larvae
more readily than trochophore or veliger larvae. Fouling by E. crocea is detrimental to mussel condition, and may affect the availability of wild mussel larvae in the commercial culture of M. galloprovincialis.

New paper: Biofouling leads to reduced shell growth and flesh weight in the cultured mussel Mytilus galloprovincialis

Michael Sievers, Isla Fitridge, Tim Dempster & Michael J. Keough

Biofouling 29: 97-107 (2013)

Competitive interactions between cultured mussels and fouling organisms may result in growth and weight reductions in mussels, and compromised aquaculture productivity. Mussel ropes were inoculated with Ciona intestinalis, Ectopleura crocea or Styela clava, and growth parameters of fouled and unfouled Mytilus galloprovincialis were compared after two months. Small mussels (≈50 mm) fouled by C. intestinalis and E. crocea were 4.0 and 3.2% shorter in shell length and had 21 and 13% reduced flesh weight, respectively, compared to the controls. Large mussels (≈68 mm) fouled by S. clava, C. intestinalis and E. crocea were 4.4, 3.9 and 2.1% shorter than control mussels, respectively, but flesh weights were not significantly reduced. A series of competitive feeding experiments indicated that S. clava and C. intestinalis did not reduce mussels’ food consumption, but that E. crocea, through interference competition, did. Fouling by these
species at the densities used here reduced mussel growth and flesh weight, likely resulting in economic losses for the industry, and requires consideration when developing biofouling mitigation strategies.