Lights out! Clownfish can only hatch in the dark – which light pollution is taking away



Some 22% of the worlds’ coastlines are exposed to artificial light at night.
Emily Fobert, Author provided

Emily Fobert, Flinders University

Clownfish achieved worldwide fame following Finding Nemo, but it turns out these fish don’t do so well in the spotlight.

Our research, published in Biology Letters, found when clownfish eggs were exposed to low levels of light at night – as they would be if laid near a coastal town – not a single egg hatched.

This finding adds to the growing body of research on the health affects of light pollution, a rapidly spreading ecological problem.




Read more:
Light pollution: the dark side of keeping the lights on


What is light pollution?

Light pollution occurs when artificial light interferes with ecological systems or processes, usually at night.

Natural light at night, produced by the moon, stars, and other celestial bodies, is minimal. A full moon creates only 0.05-0.1 lux, which pales in comparison to the artificial light produced by humans, which can range from around 10 lux from an LED or low-pressure sodium streetlight, up to 2,000 lux from something like stadium lighting.

Clownfish were exposed to artificial light to see what effect it would have on their reproduction.
Emily Fobert, Author provided

Because nearly all organisms on Earth have evolved with a stable day-night, light and dark cycle, many biological events are now highly attuned to the daily, lunar, and seasonal changes in light produced by the reliable movements of the Earth and Moon around the Sun.

But artificial light can mask these natural light rhythms and interfere with the behaviour and physiology of individual creatures, and ecosystems as a whole.

The ocean is not exempt from these problems. Light pollution is spreading to marine habitats through urbanised coastlines and increasing marine infrastructure such as piers, harbours, cruise ships, and tropical island resorts where bungalows extend out into the lagoon, directly above coral reefs.

Why are clownfish at risk?

Clownfish, like many reef fish, are particularly vulnerable to light pollution because they don’t move around much in their adult stage. Clownfish can travel long distances in the first 2 weeks after hatching, but at the end of this period the young fish will settle in a suitable sea anemone that becomes their forever-home.

Once clownfish find a suitable anemone they stay put forever.
Emily Fobert, Author provided

This means that if a fish chooses an anemone on a shallow reef in an area that is heavily lit at night, they will experience chronic exposure to light pollution throughout their life; they won’t just move away.

Clownfish also lay their eggs attached to rock or other hard surfaces, so in areas exposed to light pollution the eggs will experience continuous artificial light (as opposed to many fish that lay and fertilise eggs in open water, so they are immediately carried away by ocean currents).

What we found

To test how artificial light affects clownfish reproduction, we examined the common clownfish (Amphiprion ocellaris) in a lab experiment.

Five breeding pairs of fish experienced a normal 12-hour daylight, 12-hour dark cycle, while another five pairs of fish had their “night” period replaced with 12 hours of light at 26.5 lux, mimicking light pollution from an average coastal town.

For 60 days, we monitored how often the fish spawned, how many eggs were fertilised, and how many eggs hatched. While we saw no difference in spawning frequency or fertilisation rates between the two groups of fish, the impact of the artificial light treatment on hatch rate was staggering. None of the eggs hatched, compared with an average of 86% in the control group.

Clownfish attach their eggs to rocks or other hard surfaces, leaving them at the mercy of their immediate environmental conditions.
Emily Frobert, Author provided



Read more:
Why does Nemo the clownfish have three white stripes? The riddle solved at last


At the end of the experiment we removed the artificial light and monitored the fish for another 60 days to see how they would recover. As soon as the light at night was removed, eggs resumed hatching at normal rates.

Clownfish, like many reef fish, have evolved to hatch after dusk to avoid the threat of being eaten. Newly hatched baby clownfish, like most coral reef fish, are small (about 5mm long) and transparent. Hatching in darkness likely means they are less visible to predators as they emerge from their eggs.

Our findings show that the presence of artificial light, even at relatively low levels, can disrupt this crucial process, by masking the environmental cue – darkness – that triggers hatching. As many reef fish share similar reproductive behaviours to clownfish, it is likely artificial light will similarly interfere with the ability of other fish species to produce viable offspring.

Healthy, fertilised clownfish eggs did not hatch in the presence of artificial light.
Emily Frobert, Author provided

The larger problem

Light pollution is one of the most pervasive forms of environmental change. An estimated 23% of land surface (excluding the poles) and 22% of coastal regions are exposed to light pollution.

And the problem is only growing. The reach of light pollution across all land and sea is expanding at an estimated rate of 2.2% per year, and this will only increase with the rising global human population.




Read more:
Saving Nemo: how climate change threatens anemonefish and their homes


Although research on the ecological impacts of light pollution is arguably only in its infancy, the evidence for negative consequences for a range of insects, birds, amphibians, reptiles, and mammals, including humans, is stacking up.

Our new research adds another species to the list, and highlights the importance of finding ways to manage or reduce artificial light, on land and below the waves.The Conversation

Emily Fobert, Research Associate, Flinders University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

New research could lead to a pregnancy test for endangered marsupials



Knew you were coming: a koala cub on the back of the mother.
Shutterstock/PARFENOV

Oliver Griffith, University of Melbourne

Many women realise they are pregnant before they’ve even done the test – perhaps feeling a touch of nausea, or tender, larger-than-usual breasts.

For a long time, biologists had thought most marsupials lacked a way to recognise a pregnancy.

But new research published today shows a marsupial mum knows – in a biological sense – when she’s carrying a young one before they make their journey to the pouch.




Read more:
All female mammals have a clitoris – we’re starting to work out what that means for their sex lives


This knowledge changes how we think pregnancy evolved in mammals. It may also help in breeding programs for threatened or endangered marsupials by contributing to new technologies such as a marsupial pregnancy test.

Marsupials do things differently

When people think of marsupials – animals that mostly rear their young in a pouch (although not all marsupials have a pouch) – kangaroos and koalas tend to spring to mind. But marsupials come in a range of shapes and sizes.

A red-necked wallaby with a joey.
Pixabay/sandid

Australia has about 250 species of marsupials, including wombats, possums, sugar gliders, the extinct Tasmanian tiger, and several endangered species such as the Tasmanian devil.

In addition to Australia’s marsupial diversity, there are also 120 marsupial species in South America – most of which are opossums – and just one species in North America, the Virginia opossum.

One thing all marsupials have in common is they give birth to very small, almost embryonic, young.

An opossum with two day old young.
Oliver Griffith, Author provided

Because marsupial pregnancy passes so quickly (12-40 days, depending on the species), and marsupial young are so small and underdeveloped at birth, biologists had thought the biological changes required to support the fetus through a pregnancy happened as a follow on from releasing an egg (ovulation), rather than a response to the presence of a fetus.

Marsupial pregnancy is quick

One way to explore the question of whether it is an egg or a fetus that tells the marsupial female to be ready for pregnancy is to look at the uterus and the placenta.

In marsupials, just like in humans, embryos develop inside the uterus where they are nourished by a placenta.

Previously, biologists thought all of the physiological changes required for pregnancy in marsupials were regulated by hormones produced in the ovary after ovulation.

If this hypothesis is right, then the uterus of pregnant opossums should look the same as the uterus of opossums that ovulate but don’t have the opportunity to mate with a male.

To test this hypothesis, my colleagues at Yale’s Systems Biology Institute and I examined reproduction in the grey short-tailed opossum.

Grey short tailed opossum with young.
Oliver Griffith

Signs of pregnancy

We looked at two groups of opossums: females that were exposed to male pheromones to induce ovulation, and females that were put with males so they could mate and become pregnant.

We then used microscopy and molecular techniques to compare females from the two groups. Contrary to the current dogma, we found that the uterus in pregnancy looked very different to those females that did not mate.

In particular, we found the blood vessels that bring blood from the mother to the placenta interface were only present in pregnancy. We also noticed that the machinery responsible for nutrient transport (nutrient transporting molecules) from the mother to the fetus was only produced in pregnancy.

While hormones may be regulating some aspects of maternal physiology, the mother is certainly detecting the presence of embryos and responding in a way that shows she is recognising pregnancy.

How this knowledge can help others

Given that recognition of pregnancy has now been found in both eutherian (formerly known as placental) mammals like ourselves and marsupials with the more ancestral reproductive characters, it appears likely that recognition of pregnancy is a common feature of all live bearing mammals.




Read more:
Sexual aggression key to spread of deadly tumours in Tasmanian devils


But this knowledge does more than satisfy our curiosity. It could lead to new technologies to better manage marsupial conservation. Several marsupials face threats in the wild, and captive breeding programs are an important way to secure the future of several species.

Two Tasmanian devils.
Pixabay/pen_ash

One such species is the Tasmanian devil, which faces extinction from a dangerous contagious cancer. Captive breeding programs may be one of the only mechanisms to ensure the species survives.

But management can be made more difficult when we don’t know which animals are pregnant. Our research shows that maternal signals are produced in response to the presence of developing embryos. With a bit more research, it may be possible to test for these signals directly.

New reproductive technologies are likely crucial for improving outcomes of conservation programs, and this work shows, that to do this we first need a better understanding of the biology of the animals we are trying to save.The Conversation

Oliver Griffith, ARC DECRA Fellow, University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Coral reproduction on the Great Barrier Reef falls 89% after repeated bleaching


Morgan Pratchett, James Cook University

The severe and repeated bleaching of the Great Barrier Reef has not only damaged corals, it has reduced the reef’s ability to recover.

Our research, published today in Nature, found far fewer baby corals are being produced than are needed to replace the large number of adult corals that have died. The rate at which baby corals are settling on the Great Barrier Reef has fallen by nearly 90% since 2016.

While coral does not always die after bleaching, repeated bleaching has killed large numbers of coral. This new research has negative implications for the Reef’s capacity to recover from high ocean temperatures.

How coral recovers

Most corals reproduce by “spawning”: releasing thousands of tight, buoyant bundles with remarkable synchronisation. The bundles burst when they hit the ocean surface, releasing eggs and/or sperm. Fertilised eggs develop into larvae as they are moved about by ocean currents. The larvae settle in new places, forming entirely new coral colonies. This coral “recruitment” is essential to reef recovery.




Read more:
Explainer: mass coral spawning, a wonder of the natural world


The research team, led by my colleague Terry Hughes from the ARC Centre of Excellence for Coral Reef Studies, measured rates of coral recruitment by attaching small clay tiles to the reef just before the predicted mass spawning each year. These settlement panels represent a standardised habitat that allows for improved detection of the coral recruits, which are just 1-2mm in size.

Almost 1,000 tiles were deployed across 17 widely separated reefs after the recent mass bleaching, in late 2016 and 2017. After eight weeks they were collected and carefully inspected under a microscope to count the number of newly settled coral recruits. Resulting estimates of coral recruitment were compared to recruitment rates recorded over two decades prior to the recent bleaching.

Australian Academy of Science.

Rates of coral recruitment recorded in the aftermath of the recent coral bleaching were just 11% of levels recorded during the preceding decades. Whereas there were more than 40 coral recruits per tile before the bleaching, there was an average of just five coral recruits per tile in the past couple of years.




Read more:
Tropical marine conservation needs to change as coral reefs decline


Reef resilience

The Great Barrier Reef (GBR) is the world’s largest reef system. The large overall size and high number of distinct reefs provides a buffer against most major disturbances. Even if large tracts of the GBR are disturbed, there is a good chance at least some areas will have healthy stocks of adult corals, representing a source of new larvae to enable replenishment and recovery.

Larvae produced by spawning corals on one reef may settle on other nearby reefs to effectively replace corals lost to localised disturbances.

It is reassuring there is at least some new coral recruitment in the aftermath of severe bleaching and mass mortality of adult corals on the GBR. However, the substantial and widespread reduction of regrowth indicates the magnitude of the disturbance caused by recent heatwaves.

Declines in rates of coral recruitment were greatest in the northern parts of the GBR. This is where bleaching was most pronounced in 2016 and 2017, and there was the greatest loss of adult corals. There were much more moderate declines in coral recruitment in the southern GBR, reflecting generally higher abundance of adults corals in these areas. However, prevailing southerly currents (and the large distances involved) make it very unlikely coral larvae from southern parts of the Reef will drift naturally to the hardest-hit northern areas.

It is hard to say how long it will take for coral assemblages to recover from the recent mass bleaching. What is certain is low levels of coral recruitment will constrain coral recovery and greatly increase the recovery time. Any further large-scale developments with also greatly reduce coral cover and impede recovery.




Read more:
The 2016 Great Barrier Reef heatwave caused widespread changes to fish populations


Reducing carbon emissions

This study further highlights the vulnerability of coral reefs to sustained and ongoing global warming. Not only do adult corals bleach and die when exposed to elevated temperatures, this prevents new coral recruitment and undermines ecosystem resilience.

The only way to effectively redress global warming is to immediately and substantially reduce global carbon emissions. This requires that all countries, including Australia, renew and strengthen their commitments to the Paris Agreement on climate change.

While further management is required to minimise more direct human pressure on coral reefs – such as sediment run-off and pollution – all these efforts will be futile if we do not address global climate change.The Conversation

Morgan Pratchett, Professor, ARC Centre of Excellence for Coral Reef Studies, James Cook University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Article: Kangaroo Reproductive Systems


The following link is to an article dealing with the reproduction of Kangaroos, which are set up to deal with the Australian landscape reality.

For more, visit:
http://grist.org/list/kangaroo-genitals-are-weirder-than-you-ever-thought-possible-2/