Tag Archives for light

Under the moonlight: a little light and shade helps larval fish to grow at night



Jeffrey Shima, Author provided

Jeffrey Shima, Te Herenga Waka — Victoria University of Wellington; Craig W. Osenberg, University of Georgia; Stephen Swearer, The University of Melbourne, and Suzanne Alonzo, University of California, Santa Cruz

At night on any one of hundreds of coral reefs across the tropical Pacific, larval fish just below the sea surface are gambling on their chances of survival.

Our latest research shows the brightness of the Moon could play a major role in that struggle for survival by affecting the availability of prey and keeping predators away.

Understanding how that works could help in fisheries management, specifically the prediction of changes to harvested fish stocks that allow us to anticipate how many adult fish can be taken without destabilising the fishery.

Many fish populations experience boom-and-bust cycles largely because parents routinely produce millions of offspring that have very low, but fluctuating, survival rates.

The large number of larval fish that are produced means any environmental conditions — for example, increased nutrients — that improve survival odds even only marginally can lead to a big influx in the number of surviving offspring.

Several sixbar wrasse swim above a reef.
Adult sixbar wrasse in courtship.
Author?, Author provided

When the Sun goes down

In the past we failed to take into account the influences the night may have on fish development.

In our research we found the daily growth rates of the larvae of sixbar wrasse (Thalassoma hardwicke) around the island of Mo’orea, in French Polynesia, are strongly linked to phases of the Moon.



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Their growth appears to be maximised when the first half of the night is dark and the second half of the night is bright.

Cloudy nights obscure the Moon, and thus allowed us to check our models by contrasting growth on cloudy versus clear nights, which confirmed the effect of moonlight on growth of these fish.

Phases of the Moon

We found that on the best nights of the lunar month for sixbars, around the last Quarter Moon when the Moon rises around midnight, larval fish grew about 0.012mm a day more than average.

But on the worst nights, around the first Quarter Moon when the Moon is overhead at sunset and sets around midnight, they grew about 0.014mm a day less than average.

From First Quarter to Full Moon then Last Quarter.
Phases of the Moon from the Southern Hemisphere.
Wikimedia, CC BY-SA

For a typical larval sixbar of 37.5 days old, that means its growth is 24% more on the best night than on the worst one. This is important, as growth is inextricably linked to survival and ultimately fisheries productivity.

We think the Moon affects larval growth in this way because of how it changes the movements of deeper-dwelling animals, those that migrate into shallow water each night to hunt for food under the cover of darkness.

Zooplankton — potential prey for larval sixbars — respond quickly to the arrival of darkness, and move into the surface water to supplement the diets of sixbars.

Micronekton, such as lanternfishes, which hunt larval fishes, may take much longer to reach surface waters and seek out their prey, due to their migration from much deeper depths.

Four graphs showing different phases of the Moon and the amount of predator/prey during each phase.
Four graphs showing the larval fish (in yellow) and the amount of predator (red shading area) and prey (brown shading area) rising to the surface during each phase of he Moon.
Proceedings of the Royal Society B, Author provided

As a consequence, prey availability for sixbars in surface waters may be hindered by early nocturnal brightness while the arrival of predators may be impeded by late nocturnal brightness.

Thus, larval fish grow best when their predators are absent but their prey are abundant — around the last Quarter Moon.

In contrast, around the first Quarter Moon, prey are suppressed but predators are not, leading to the slowest growth.

During the New Moon, when the surface waters remain dark throughout the night, influxes of both prey and predators may be high, with the latter preventing the larval fish from enjoying the increased numbers of prey.

On the other hand, during the Full Moon, when surface waters are well-lit, the movement of prey and predators may be suppressed, reducing the risk to the fish but also eliminating their food.

Impact on fishing

More research is needed to quantify these lunar effects on other marine populations. But our findings to date are good news for those working to strengthen fisheries management, given that phases of the Moon are predictable and cloud cover that can modify moonlight is being measured by satellites.

A diver underwater keeping watch on one of the sixbar wrasse fish.
Observing the sixbar wrasse spawning.
Author?, Author provided

This makes the incorporation of moonlight into existing fisheries management models relatively simple.

We think this will have implications around the world, not just in the tropics. This is because the nightly upward movements of deep-water animals is ubiquitous — it is the largest mass migration of biomass on the planet, and it happens everywhere.

The suppressive effect of moonlight on this movement of potential predators and prey is also a global phenomenon.

We evaluated effects of the Moon on growth of larval temperate fish in an earlier study and found a similar effect (moonlight enhanced growth).



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The effect is stronger and more nuanced in our latest study, most likely because the waters in the tropics are comparatively clear.

Our findings also hint that other factors which affect night-time illumination of the sea may disrupt marine ecosystems. This includes the reflection of artificial lights from coastal cities, suspended sediments in the water column, and changes in cloud cover due to climate change.

In the future, we may be able to harness this extra information to help forecast fish population change to better guide the management and conservation of fisheries around the world.The Conversation

Jeffrey Shima, Professor of Ecology, Te Herenga Waka — Victoria University of Wellington; Craig W. Osenberg, Professor of Ecology, University of Georgia; Stephen Swearer, Professor of Marine biology, The University of Melbourne, and Suzanne Alonzo, Professor of Ecology & Evolutionary Biology, University of California, Santa Cruz

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

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Daylight robbery: how human-built structures leave coastal ecosystems in the shadows



Human-built structures are home to a wide variety of creatures.

Martino Malerba, Monash University; Craig White, Monash University; Dustin Marshall, Monash University, and Liz Morris, Monash University

About half of the coastline of Europe, the United States and Australasia is modified by artificial structures. In newly published research, we identified a new effect of marine urbanisation that has so far gone unrecognised.

When we build marinas, ports, jetties and coastal defences, we introduce hard structures that weren’t there before and which reduce the amount of sunlight hitting the water. This means energy producers such as seaweed and algae, which use light energy to transform carbon dioxide into sugars, are replaced by energy consumers such as filter-feeding invertebrates. These latter species are often not native to the area, and can profoundly alter marine habitats by displacing local species, reducing biodiversity, and decreasing the overall productivity of ecosystems.

Incorporating simple designs in our marine infrastructure to allow more light penetration, improve water flow, and maintain water quality, will go a long way towards curbing these negative consequences.

Pier life

We are used to thinking about the effects of urbanisation in our cities – but it is time to pay more attention to urban sprawl in the sea. We need to better understand the effects on the food web in a local context.



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Most animals that establish themselves on these shaded hard structures are “sessile” invertebrates, which can’t move around. They come in a variety of forms, from encrusting species such as barnacles, to tree-shaped or vase-like forms such as bryozoans or sponges. But what they all have in common is that they can filter out algae from the water.

In Australian waters, we commonly see animals from a range of different groups including sea squirts, sponges, bryozoans, mussels and worms. They can grow in dense communities and often reproduce and grow quickly in new environments.

The sheltered and shaded nature of marine urbanisation disproportionately favours the development of dense invertebrate communities, as shown here in Port Phillip Bay.

How much energy do they use?

In our new research, published in the journal Frontiers in Ecology and the Environment, we analysed the total energy usage of invertebrate communities on artificial structures in two Australian bays: Moreton Bay, Queensland, and Port Phillip Bay, Victoria. We did so by combining data from field surveys, laboratory studies, and satellite data.

We also compiled data from other studies and assessed how much algae is required to support the energy demands of the filter-feeding species in commercial ports worldwide.

In Port Phillip Bay, 0.003% of the total area is taken up by artificial structures. While this doesn’t sound like much, it is equivalent to almost 50 soccer fields of human-built structures.

We found that the invertebrate community living on a single square metre of artificial structure consumes the algal biomass produced by 16 square metres of ocean. Hence, the total invertebrate community living on these structures in the bay consumes the algal biomass produced by 800 football pitches of ocean!

Similarly, Moreton Bay has 0.005% of its total area occupied by artificial structures, but each square metre of artificial structure requires around 5 square metres of algal production – a total of 115 football pitches. Our models account for various biological and physical variables such as temperature, light, and species composition, all of which contribute to generate differences among regions.

Overall, the invertebrates growing on artificial structures in these two Australian bays weigh as much as 3,200 three-tonne African elephants. This biomass would not exist were it not for marine urbanisation.

Colonies of mussels and polychaetes near Melbourne.

How does Australia compare to the rest of the world?

We found stark differences among ports in different parts of the world. For example, one square metre of artificial structure in cold, highly productive regions (such as St Petersburg, Russia) can require as little as 0.9 square metres of sea surface area to provide enough algal food to sustain the invertebrate populations. Cold regions can require less area because they are often richer in nutrients and better mixed than warmer waters.

In contrast, a square metre of structure in the nutrient-poor tropical waters of Hawaii can deplete all the algae produced in the surrounding 120 square metres.

All major commercial ports worldwide with associated area of the underwater artificial structures (size of grey dots) and trophic footprint (size of red borders). Trophic footprints indicate how much ocean surface is required to supply the energy demand of the sessile invertebrate community growing on all artificial structures of the port, averaged over the year. This depends on local conditions of ocean primary productivity and temperature. Ports located in cold, nutrient-rich waters (dark blue) have a lower footprint than ports in warmer waters (light blue).

Does it matter?

Should we be worried about all of this? To some extent, it depends on context.

These dense filter-feeding communities are removing algae that normally enters food webs and supports coastal fisheries. As human populations in coastal areas continue to increase, so will demand on these fisheries, which are already under pressure from climate change. These effects will be greatest in warmer, nutrient-poor waters.

But there is a flip side. Ports and urban coastlines are often polluted with increased nutrient inputs, such as sewage effluents or agricultural fertilisers. The dense populations of filter-feeders on the structures near these areas may help prevent this nutrient runoff from triggering problematic algal blooms, which can cause fish kills and impact human health. But we still need to know what types of algae these filter-feeding communities are predominantly consuming.



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Our analysis provides an important first step in understanding how these communities might affect coastal production and food webs.

In places like Southeast Asia, marine managers should consider how artificial structures might affect essential coastal fisheries. Meanwhile, in places like Port Phillip Bay, we need to know whether and how these communities might affect the chances of harmful algal blooms.The Conversation

Mussels in the port of Hobart.

Martino Malerba, Postdoctoral Fellow, Monash University; Craig White, Head, Evolutionary Physiology Research Group, Monash University; Dustin Marshall, Professor, Marine Evolutionary Ecology, Monash University, and Liz Morris, Administration Manager, Monash University

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

Article: Light Overnight Camping


The link below is to an article that looks at packing light for overnight camping trips.

For more visit:
http://www.australiangeographic.com.au/outdoor/lightweight-camping-gear-how-to-pack.htm

News Report on Aboriginal Population Growth Prior to European Occupation of Australia


I have come across an interesting news article on the Aboriginal population prior to European occupation of Australia. Though not exactly wilderness or environmental news, the article does shed some light (or at least sparks interest) on the Australian situation prior to European colonisation of our country. Of particular interest is the suggested impact on the Tasmanian Tiger on mainland Australia.

For more visit:
http://www.abc.net.au/news/stories/2011/05/11/3214132.htm

 

ALL AUSSIE ADVENTURES: With Russell Coight


Most people who know me know that I love the Australian bush and wilderness, and whenever I can I like to be able to get away from it all and head bush for a while.

Here in Australia there have been a number of television shows over the years that have explored the Australian outback and bush. A couple of years ago a different style of exploring Australia television shows hit the small screen – it was called ‘All Aussie Adventures,’ with Glenn Robbins playing the host Russell Coight. It was a send up of these types of shows and it always gave viewers a bit of a laugh with its light comedy.

Anyhow, I found some of the show on the Internet and thought I’d post some here for those interested in Australia from a somewhat different angle. A word of warning though – don’t take too much that Russell Coight says seriously (you’ll be led astray).

Visit the television shows web site at:

http://www.bigcoight.com/

 

Below: These clips show most of the first episode of All Aussie Adventures.