Invasive species Archives - The Sciku Project

July 6, 2020November 20, 2020

Invasive Species by Dr Phil Colarusso

Misplaced visitors
Cryptic hitchhikers on boats
Food webs are altered
By Phil Colarusso

While doing eelgrass restoration work in Gloucester, I became aware of a bluish-gray growth appearing on a large number of shoots. Shortly thereafter, I read in the Woods Hole journal Oceanus about a researcher who was seeing a new species of invasive tunicates (Diplosoma listeria) appearing on scallops, boat hulls, mooring lines and eelgrass on Martha’s Vineyard. The photo was of exactly the same thing I was seeing in Gloucester.

Tunicates are filter feeding organisms that can grow as small zooids in extensive colonies or as large solitary individuals. The colonial forms tend to be prolific breeders and filter enormous quantities of water. They can grow quickly and will cover just about any surface that is bare, including pilings, clam shells, algae and eelgrass. Recent research has shown that literally miles of the seafloor can be covered by one of these colonial species, smothering other sessile life and altering the availability of the habitat.

My team decided to conduct a study in a salt pond on Martha’s Vineyard, where these organisms had appeared to be particularly abundant. We initially had focused on the impact of these animals to the eelgrass in the pond, but quickly realized their prolific filter feeding may pose an additional risk to the food web of this small coastal pond.

Using stable isotopes, we determined the tunicates were feeding on the same resources as several commercially important shellfish species. Based on their high abundance, their prolific feeding rates and the small volume of the pond, our modelling suggested the tunicates could potentially filter a volume of water equivalent to the entire pond in somewhere between 1 and 17 hours. This represents a significant challenge for commercial shellfish stocks in these waters. You can see a video on this project here.

It is not always clear where and how these invaders arrive, but shipping is believed to be a major vector. Planktonic life forms and small creatures are carried in ballast water and along the hulls or larger vessels. Globalization has significantly increased shipping all over the planet and as a result the unintentional transportation of organisms as well. Early detection may allow for some level of control, but often once a new species is detected in the ocean, control options are untenable. Persistent monitoring is the most prudent tool in identifying and controlling the spread of non-native species.

Original research:

Colarusso, P. et al. (2016) Quantifying the ecological impact of invasive tunicates to shallow coastal water systems. http://dx.doi.org/10.3391/mbi.2016.7.1.05

Valentine, P.C. et al. (2007) The occurrence of the colonial ascidian Didemnum sp. on Georges Bank gravel habitat – Ecological observations and potential effects on groundfish and scallop fisheries. https://doi.org/10.1016/j.jembe.2006.10.038

Dr. Phil Colarusso is a marine biologist with US EPA Region I. He has been working on eelgrass restoration, conservation and research for 31 years. He and his team just recently had a paper on carbon sequestration rates in eelgrass in New England accepted for publication.

Enjoyed Phil’s sciku? Check out his other of his sciku Blue Carbon and Diving for Science.

August 29, 2019August 29, 2019

Spreading

Tiger mosquito,
spreading northwards, adapting.
Deadly time capsules.

Many mosquito species struggle to survive at low temperatures, preventing their spread into cooler climates and thus limiting the spread of diseases carried by the mosquitoes. Yet new research by Medley et al (2019) suggests that some mosquito species may be able to adapt part of their reproductive cycle to survive cold winters.

The Asian tiger mosquito is a vector for a number of pathogens, including Zika and dengue viruses. The species first arrived in the USA in Texas in 1985 and today the current range extends as far north New Jersey.

How has this tropical and sub-tropical species managed to survive the temperate conditions?

The secret lies with a process called diapause – a type of animal dormancy where development is delayed in response to unsuitable environmental conditions such as cold winters.

In the Asian tiger mosquito, the length of day or night (photoperiodism) can induce egg diapause – as the days get shorter with the approach of winter eggs become dormant and only start developing again once the days start to lengthen and temperatures are likely to be more suitable for the species.

In the new study the researchers found that northern diapause eggs survive northern winters a lot better than southern diapause eggs, but both northern and southern diapause eggs survive southern winters the same as each other. The research demonstrates the species adapting to colder conditions as it expands northwards over a period of around 30 years. Not only have northern populations adapted to northern climes by producing more eggs but those eggs are adapted to survive the northern winters better too.

Original research: https://doi.org/10.1111/1365-2664.13480

May 17, 2019May 17, 2019

Indigenous Engagement

The benefits of
indigenous engagement:
Ethics and Science.

Local knowledge and an awareness of local context can be integral to conducting a variety of research. However, one thing that’s less often considered is the impact of the diversity of the research team itself.

Conservation research by Ward-Fear et al (2019) into the impact of cane toads on yellow-spotted monitor lizards in Australia has unintentionally produced evidence of the scientific benefits of collaborating with local indigenous people.

Large cane toads are spreading through tropical Australia but are fatally toxic if eaten by yellow-spotted monitor lizards. Ward-Fear et al (2016) trained lizards with smaller, non-lethal cane toads and then compared the survival rates of trained and non-trained lizards in the wild over an 18 month period. They found that trained lizards had a greater survival rate than non-trained lizards, suggesting that the training helped the lizards to avoid eating the larger toxic cane toads.

Yet their study also revealed the importance of researcher diversity. In monitoring the population of lizards over 18 months, the research team included western scientists (professional, nonindigenous ecologists) and indigenous rangers (Australian-Aboriginal Traditional Owners of the region).

The indigenous rangers saw lizards from a greater distance, in more dense vegetation, under poorer light levels, and more frequently when the lizard was stationary. Additionally, when assessing the behavioural traits of the lizards, those that were spotted by the indigenous rangers were found to be more shy. What’s more, the ranger caught lizards appeared to benefit more from the training against the toxic cane toads.

All this highlights the importance of cultural diversity within research teams and in particular shows that indigenous collaboration can be utterly crucial for conservation efforts.

Original research:

Training of predatory lizards reduces their vulnerability to invasive toxic prey: https://doi.org/10.1098/rsbl.2015.0863

Collaboration with indigenous peoples can alter the outcomes of conservation research: http s://doi.org/10.1111/conl.12643

January 11, 2019January 11, 2019

Armyworms

Armyworms. Crop pests.
Inflict losses with our help.
Where will you strike next?

Crop pests cause vast economic losses worldwide, having a huge impact on the livelihoods of some of the most vulnerable populations. Originally from the Americas, the fall armyworm recently spread to sub-Saharan Africa, resulting in estimates of 20 to 50% maize yield losses. The armyworm appears to have arrived in sub-Saharan Africa as a result of passenger flights from America and has spread widely across the continent in only a couple of years.

Research by Early et al (2018) has considered where the pest might spread to next. By considering the armyworm’s life-history, current trade and transportation routes and the climates of countries that currently have populations of armyworms, the researchers were able to forecast the most likely next steps for this spreading species. In particular, the researchers highlight that the climactic conditions of South and Southeast Asia and Australia make these regions susceptible to invasion, with Australia, China, India, Indonesia, Malaysia, Philippines and Thailand the most vulnerable.

Original research: https://doi.org/10.3897/neobiota.40.28165

July 3, 2018July 12, 2018

Chestnut menace

Invading clonal

wasps. Chestnut menace spreading

yet no males required.

The Chestnut gall wasp arrived in Europe in 2006, imported accidentally from China. Since then it has begun to spread and devastate European Chestnut trees.

Bonal et al (2018) have now revealed that the European population has very low genetic diversity due to 1) the founding of the population by a small number of individuals, 2) an endosymbiont bacterial infection present within the population that is known to have male-killing tendencies and 3) it’s parthenogenetic reproduction strategy. This is where females are able to reproduce and produce female offspring without the need to be fertilised by males. No males have been observed in the European population and the females and their offspring are effectively clones of one another.

Original research: https://doi.org/10.1038/s41598-018-23754-z

March 13, 2018May 20, 2021

Reservoir or predator

African clawed frog –

reservoir or predator

of the fungal blight?

Amphibian populations worldwide are being devastated by a fungal infection (known as chytrid or Bd). As an invasive species and carrier of the fungal infection African clawed frogs are often blamed for the spread of chytrid and the current conservation crisis.

Research by Wilson et al (2018) suggests the story is more complicated than it at first seems though. Field studies in California suggest a 10% level of Bd infection in the frogs, with infected individuals having very low levels of infection. Additionally, larval clawed frogs appear to eat the Bd zoospores and may therefore actually be helping to reduce the negative impact and spread of the fungus. Unfortunately the study also suggests that the frog larvae also eat Daphnia, which are another predator of the Bd zoospores.

This latest research adds to growing evidence suggesting that African clawed frogs may not be as guilty as they seemed at first.

Original research: https://doi.org/10.1371/journal.pone.0191537

Interested in African clawed frogs? Check out these other Xenopus sciku: ‘Clawed frogs indicate‘, ‘Have frog, will travel‘, ‘Fungal culprit‘ and ‘Xenopus enrichment‘.

August 23, 2017May 20, 2021

Fungal culprit

Fungal culprit of

amphibian genocide –

Innocent scapegoat?

Amphibian populations are in the midst of a pandemic, the spread of chytrid fungus devastating species around the world. Conservationists have pointed a finger of blame at African clawed frogs: they are hosts of the fungus, have a degree of immunity and have spread around the world due to their use in research laboratories and hospitals.

The circumstantial evidence seems damming but research by Tinsley et al (2015) into long-standing UK populations suggests otherwise. Native amphibian species present alongside populations of African clawed frogs were not infected with chytrid fungus, despite the African clawed frogs themselves carrying it. What’s more, the African clawed frog populations have been present for decades yet surveys revealed continued high native species abundance. If fungal transmission from African clawed frogs were an issue then such levels of native amphibians would be unlikely.

It seems then that African clawed frogs may be scapegoats after all.

Interested in African clawed frogs? Check out these other Xenopus sciku: ‘Clawed frogs indicate‘, ‘Have frog, will travel‘, ‘Xenopus enrichment‘ and ‘Reservoir or predator‘.

June 9, 2017June 14, 2017

No saturation

Aliens spreading,

their invasion continues.

No saturation.

Increased globalisation over the past 200 years has helped to spread flora and fauna species around the world, with some non-native species disrupting local habitats to a devastating degree. Despite efforts to mitigate such invasions, the rate of alien species establishment appears to be increasing and no saturation point has been observed. Seebens et al, 2017.