From sharks in seagrass to manatees in mangroves, we’ve found large marine species in some surprising places


Michael Sievers, Griffith University; Rod Connolly, Griffith University, and Tom Rayner, Griffith University

When we think of mangrove forests, seagrass meadows and saltmarshes, we don’t immediately think of shark habitats. But the first global review of links between large marine animals (megafauna) and coastal wetlands is challenging this view – and how we might respond to the biodiversity crisis.

Mangrove forests, seagrass meadows and saltmarshes support rich biodiversity, underpin the livelihoods of more than a billion people worldwide, store carbon, and protect us from extreme weather events.

Mangrove forests, seagrass meadows and saltmarshes are the three key vegetated habitats found in coastal wetlands.
Tom Rayner/www.shutterstock.com

We know marine megafauna also use these habitats to live, feed and breed. Green turtles and manatees, for instance, are known to eat seagrass, and dolphins hunt in mangroves.

But new associations are also being discovered. The bonnethead shark – a close relative of hammerheads – was recently found to eat and digest seagrass.




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The problem is that we’re losing these important places. And until now, we’ve underestimated how important they are for large, charismatic and ecologically important marine animals.

Counting wetland megafauna

Today our review of the connections between marine megafauna and vegetated coastal wetlands was published in the journal Trends in Ecology and Evolution. As it turns out, far more megafauna species use coastal wetlands than we thought.


Author provided/The Conversation, CC BY-ND

Before our review, the number of marine megafauna species known to use these habitats was 110, according to the International Union for Conservation of Nature (IUCN) Red List, which assesses species’ conservation status.

We identified another 64 species from 340 published studies, bringing the total number to 174 species. This means 13% of all marine megafauna use vegetated coastal wetlands.

We predominantly documented these habitat associations by electronic tracking, direct observation or from analysing stomach contents or chemical tracers in animal tissues.

Less commonly, acoustic recordings and animal-borne video studies – strapping a camera on the back of turtle, for instance – were used.

Deepening our understanding of how species use their habitats

In recent weeks, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) released a damming assessment of humanity’s stewardship of the natural world. Up to 1 million species were reported to be facing extinction within decades.




Read more:
‘Revolutionary change’ needed to stop unprecedented global extinction crisis


We need to dramatically change how we relate to and engage with species and their habitats, if we are to fix this problem.

But the question is, how can we make global change real, relevant and feasible at local and regional scales? And, as the international community rises to this challenge, what information is needed to support such efforts?

Our study suggests a critical first step to addressing the global biodiversity crisis is to deepen our understanding of links between species and their habitats. We also need to elevate how the evidence is used to both assess extinction risk and prioritise, plan and deliver conservation actions.

A juvenile lemon shark swimming in mangroves. More than half of the world’s coastal wetlands have been lost.
Shutterstock

More than half of all coastal wetlands have been lost globally and the rest are at risk from a range of serious threats, including deforestation. There is an urgent need to limit and reverse the loss of coastal wetlands to stop biodiversity loss, protect communities and tackle climate change.

Targeting places where high rates of mangrove loss intersect with threatened megafauna could lead to more efficient and effective conservation outcomes. Southeast Asia, Mexico and northern Brazil are such places.

In Southeast Asia, for example, the world’s largest mangrove forest is losing trees at a rate far exceeding global averages, largely due to aquaculture and agriculture. This is threatening the critically endangered green sawfish, which relies on these mangrove habitats.

Habitats should always be considered in assessments

The IUCN Red List assesses the extinction risk for almost 100,000 species. It provides comprehensive information on global conservation statuses, combining information on population sizes, trends and threats.

The wealth of data collected during species’ assessments, including habitat associations of threatened species, is one of the Red List’s most valuable features.

But our study shows many known associations are yet to be included. And for more than half of the assessments for marine megafauna, habitat change is yet to be listed as a threat.

‘Proportion species’ refers to all species within key taxonomic groups that are associated with coastal wetlands.
Author supplied

This is concerning because assessments that overlook habitat associations or lack sufficient detail, may not allow conservation resources be directed at the most effective recovery measures.

But it’s also important to note habitat associations have varying strengths and degrees of supporting evidence. For example, a population of animals shown to consume substantial amounts of seagrass is clearly a stronger ecological link than an individual simply being observed above seagrass.

The data on habitat associations must be strengthened in species assessments.
Shutterstock

In our paper, we propose a simple framework to address these issues, by clarifying habitat associations in conservation assessments. Ideally, these assessments would include the following:

  • list all habitat types the species is known to associate with
  • indicate the type of association (occurrence, grazing, foraging or breeding)
  • cite the source of supporting evidence
  • provide an estimate of the level of habitat dependence.

Data for decision making

Habitat loss is accelerating a global extinction crisis, but the importance of coastal habitats to marine megafauna has been significantly undervalued in assessments of extinction risk.

We need to strive to protect remaining coastal wetland habitats, not only for their ecological role, but also for their economic, social and cultural values to humans. We can do this by strengthening how we use existing scientific data on habitat associations in species assessments and conservation planning.The Conversation

Michael Sievers, Research Fellow, Global Wetlands Project, Australia Rivers Institute, Griffith University; Rod Connolly, Professor in Marine Science, Griffith University, and Tom Rayner, Science Communicator, Griffith University

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

Dugong and sea turtle poo sheds new light on the Great Barrier Reef’s seagrass meadows


Samantha J Tol, James Cook University; Alana Grech, James Cook University; Paul York, James Cook University, and Rob Coles, James Cook University

Just like birds and mammals carrying seeds through a rainforest, green sea turtles and dugong spread the seeds of seagrass plants as they feed. Our team at James Cook University’s TropWATER Centre has uncovered a unique relationship in the seagrass meadows of the Great Barrier Reef.

We followed feeding sea turtle and dugong, collecting samples of their floating faecal matter. Samantha then had the unenviable job of sifting through hundreds of smelly samples to find any seagrass seeds. These seeds range in size from a few centimetres to a few millimetres, and therefore can require the assistance of a microscope to be found. Once any seeds were found, they were stained with a chemical dye (Tetrazolium) to see if they were still viable (capable of growing).

PhD candidate Samantha Tol holding dugong poo collected from Cleveland Bay in Townsville.
TropWATER, JCU

Why is this important for turtles and dugong?

Green sea turtles and dugong are iconic animals on the reef, and seagrass is their food. Dugong can eat as much as 35 kilograms of wet seagrass a day, while sea turtles can eat up to 2.5% of their body weight per day. Without productive seagrass meadows, they would not survive.

This relationship was highlighted in 2010-11 when heavy flooding and the impact of tropical cyclone Yasi led to drastic seagrass declines in north Queensland. In the year following this seagrass decline there was a spike in the number of starving and stranded sea turtles and dugong along the entire Queensland coast.

The seagrass team at James Cook University has been mapping, monitoring and researching the health of the Great Barrier Reef seagrasses for more than 30 years. While coral reefs are more attractive for tourists, the Great Barrier Reef World Heritage Area actually contains a greater area of seagrass than coral, encompassing around 20% of the world’s seagrass species. Seagrass ecosystems also maintain vibrant marine life, with many fish, crustaceans, sea stars, sea cucumbers, urchins and many more marine animals calling these meadows their home.

These underwater flowering plants are a vital component of the reef ecosystem. Seagrasses stabilise the sediment, sequester large amounts of carbon from the atmosphere and filter the water before it reaches the coral reefs. Further, the seagrass meadows in the Great Barrier Reef support one of the largest populations of sea turtles and dugong in the world.

Seagrass meadows are more connected than we thought

Samantha’s research was worth the effort. There were seeds of at least three seagrass species in the poo of both sea turtles and dugong. And lots of them – as many as two seeds per gram of poo. About one in ten were viable, meaning they could grow into new plants.

Based on estimates of the number of animals in the coastal waters, the time it takes for food to pass through their gut, and movement data collected from animals fitted with satellite tags, there are potentially as many as 500,000 viable seeds on the move each day in the Great Barrier Reef. These seeds can be transported distances of up to 650km in total.

Green Island seagrass meadow exposed at low tide.
TropWATER, JCU

This means turtles and dugong are connecting distant seagrass meadows by transporting seeds. Those seeds improve the genetic diversity of the meadows and may help meadows recover when they are damaged or lost after cyclones. These animals help to protect and nurture their own food supply, and in doing so make the reef ecosystem around them more resilient.

Understanding recovery after climate events

Seagrass meadows have been under stress in recent years. A series of floods and cyclones has left meadows in poor condition, and recovery has been patchy and site-dependent.

This research shows that these ecosystems have pathways for recovery. Provided we take care with the environment, seagrasses may yet recover without direct human intervention.

The ConversationThis work emphasises how much we still have to learn about how the reef systems interconnect and work together – and how much we need to protect every part of our marvellous and amazing reef environment.

Samantha J Tol, PhD Candidate, James Cook University; Alana Grech, Assistant Director, ARC Centre of Excellence for Coral Reef Studies, James Cook University; Paul York, Senior Research Scientist in Marine Biology, James Cook University, and Rob Coles, Team leader, Seagrass Habitats, TropWATER, James Cook University

This article was originally published on The Conversation. Read the original article.