Bugles and Baselines – Nine Years of Bull Kelp Mapping around Mayne Island, B.C.
Kelly Fretwell and Rob Underhill
Have you ever made a bugle horn from a piece of washed-up bull kelp? If not, you’re missing out on a fine West Coast experience! Now is a good time to head to the beach and find a beautiful bulb from which to craft your instrument.
Bull kelp is an amazing species of brown algae with many values, some even more important than satisfying our craving for the sound of a good bugle horn. This species of brown algae—arguably the most impressive seaweed found in the Southern Gulf Islands—plays a number of important roles in our intertidal and nearshore ecosystems. As an annual species, bull kelp lives for only one growing season, yet it can grow to heights of nearly 40 metres (usually closer to 10 metres) from the tight grip of its root-like holdfast on the rocky ocean bottom to the tips of its long blades. Growing in dense beds, bull kelp forms underwater forests 1 that provide a safe living space for many marine creatures including sea stars, crabs, rockfish, and young salmon to find food and hide out from predators. In fact, kelp forests provide vital nursery habitat for many of our commercially and recreationally valuable fish and invertebrates.
In the fall and winter, as daylight hours diminish, temperatures drop, and storms increase in frequency, aging kelp ‘plants’2 break free from their holdfast anchors and are swept onto beaches and out to sea, or sink to the sea floor. Just as decomposing seaweed can help feed our vegetable gardens, so too does it provide life-giving nutrients to the animals living along our shorelines and on the ocean floor. Recent research found that the kelp that sinks to the sea floor may also be an important carbon sink, since kelp sucks up a lot of carbon during its rapid growing season3, and deposits it on the sea floor where it can remain for decades. The key role that bull kelp plays in providing habitat for an abundance of species has led scientists to consider it a foundation species within our nearshore ecosystems4. Consequently, a decrease or loss of this species would mean major changes to our coastal ecosystems.
Is Bull Kelp Increasing or Decreasing?
In order to help answer this question, the Mayne Island Conservancy has been mapping the extent of bull kelp beds around Mayne Island since 2010. During the last nine years we’ve learned a lot about bull kelp on our local shorelines, as well as the challenges of conducting marine monitoring on a shoe-string budget. Here are some of our main findings:
The distribution of bull kelp within our monitoring sites changes dramatically from year to year within its habitat (rocky bottoms at depths of 0-12m). This sort of variation is common with annual species like bull kelp, and may be caused by factors that do not ultimately impact long-term trends.
Between 2010 and 2018 we’ve recorded an overall decrease in the extent of bull kelp within our seven survey sites around Mayne Island, with decreases observed in six of seven sites. Check out the slideshow:
Two kelp beds within our monitoring sites show declines of more than 90% within our period of observations at Georgina Point and the north side of Georgeson Island. Both of these sites are exposed to greater influences from the Strait of Georgia than our other survey sites. The specific cause of their decline is not known.
Due to the natural year-to-year changes in bull kelp distribution and abundance, and the many factors affecting marine ecosystems, long-term data are required to confidently detect and predict trends in the health of bull kelp populations in the Salish Sea.
If Bull Kelp is declining, why is it happening?
There are a number of known and suspected causes for the decline of bull kelp or other species of kelp around the world and within the region. These causes include the following:
- Warming oceans – Other researchers have argued that warming sea temperatures have a negative effect on bull kelp, and some research shows that years of low kelp abundance correspond with years of warmer sea temperatures. Indeed, kelp forest declines and losses elsewhere in the world have been directly linked to warming waters. If this is a cause-effect relationship, then we can expect to see further decreases in bull kelp over time as waters continue to warm from climate change5. Researchers from Simon Fraser University are studying how warming temperatures may affect bull kelp in the Salish Sea, including researcher Braeden Shiltroth who joined us during our surveys in 2016.
- Losses of kelp around the world and within our region have been linked directly to increases in sea urchins, and indirectly to the animals that eat sea urchins, such as sea otters and sunflower sea stars. You may remember that scientists up and down the West Coast were recently sounding the alarm about something called Sea Star Wasting Disease. One of the species of sea star heavily impacted by the disease was the sunflower sea star; a predator of small and medium size sea urchins. Recent research from the Central Coast of British Columbia has described the complementary role sunflower sea stars have in maintaining urchin populations, and indirectly preventing the conversion of kelp forests to urchin barrens.
- Like other photosynthetic organisms, kelp relies upon access to sunlight for energy. Some studies show that seasonal blooms in phytoplankton reduce the clarity of the water, resulting in a negative impact on kelp species. In the Salish Sea, there are also seasonal decreases in water clarity resulting from the spring snow melt and the silt it carries down the Fraser River. This seasonal input of nutrients corresponds with increases in temperature, resulting in phytoplankton blooms that have a greater impact on the north side of Mayne Island; a possible cause or contributing factor in the decline of kelp beds around Georgina Point and north Georgeson Island.
In order to fully understand the annual variation in bull kelp extent, and to confirm any long term trends—such as the recent decrease shown by our data—we need to continue monitoring this important species. Without long-term monitoring programs, we have no way of detecting change in our environment.
Baseline Data – What is it and why is it important?
Mayne Island Conservancy’s kelp surveys collect what is known as baseline data: a set of information that provides a baseline against which future surveys can be compared. Baseline data provides an understanding of current ecological conditions, such as where species occur, how abundant they are, what species they interact with (known as ecological communities6), and the natural range of variability for these conditions. A repetition of such surveys over time is called long-term ecological monitoring, which allows scientists and resource managers to better understand the state of an ecosystem, and to track changes over time.
Ideally all aspects of our natural environment would be subject to long-term monitoring, but with limited time and resources, some species and ecological communities need to be prioritized. Bull kelp’s immense value to nearshore and intertidal ecosystems makes it a prime candidate, and so is one of two species we chose (with eelgrass (Zostera marina) as the other) for our long-term monitoring efforts.
Baseline data and monitoring help us see “the bigger picture” by providing context and insight to any changes that may occur — whether that change is the result of human impact or natural events (such as El Niño) — and help us understand what is ‘normal’ and what is not. For example, in 2015 sea star wasting disease struck midway through a study on kelp-sea otter-sea urchin interactions on BC’s Central Coast, allowing the researchers to compare pre-disease baseline data to surveys collected during and after the epidemic, ultimately revealing how important sea stars are to keeping sea urchin populations in check. Baseline surveys and continued monitoring can also provide measurable data to address concerns people may have based on their own observations – for instance, someone may notice their local kelp bed seems smaller than last year, but the context provided by long-term monitoring may show that last year was just a low year, or that overall kelp abundance within the region did not change, despite decreases in that location.
It is important to keep in mind that any given baseline is relative, however. Ecological baselines established now may be different from before the Industrial Revolution and European colonization, because by now human impact has altered most ecosystems in some way — with climate change (and associated ocean acidification) being the ever-present example looming over all natural systems. But establishing a baseline now can still provide data against which additional impacts can be measured; so if more stressors are added going forward — cumulative impacts like more boats transiting the Salish Sea or more pollutants and nutrients added to the water, or individual events like large oil spills — the impacts of those stressors can be better identified and hopefully mitigated.
What are considered ‘normal’ or ‘natural’ environmental conditions can and do change over time. These are called shifting baselines. For example, Pacific herring were an abundant seasonal visitor in the Southern Gulf Islands in the 1950’s -70’s, and those that lived here during that period considered that part of the normal cycle of nature. Now, it is very rare to see herring spawn on our shores, and our children will expect their absence, and consider it normal.
If you come across bull kelp washed up on a beach this winter, pause for a moment to think about the journey it has been on: how quickly it grew over the spring and summer, its ability to hold strong against the ocean’s forces, the foundational role it played in the ocean, and its continued value on shore or in the depths of the sea. Perhaps it belonged to one of the kelp beds we surveyed last summer, captured forever as data in the maps (see slide show above).
If you are interested in learning more about our bull kelp monitoring program please contact us —we are happy to share our results and methods. If you are interested in volunteering to participate as a Marine Citizen Scientist, give us a call or email.
Our Kelp Monitoring and other marine programs rely on donations to keep running. If you support the continuation of this work, please make a donation to our Healthy Shores; Now and Forever Campaign.
- Of the many large brown seaweeds that make up the kelps, bull kelp (Nereocystis luetkeana) and giant perennial kelp (Macrocystis pyrifera) (more commonly found on the exposed outer coastline of Vancouver Island than the inshore waters around the Gulf Islands) are the typical kelp forest species. Click here to learn more about kelp specific to the Capital Regional District.
- Kelp and other seaweeds are often referred to as plants, but they are not actually related.
- Seagrasses, mangroves, and other shoreline and marine plants that use carbon to grow can sequester up to 20 times the amount of CO2 as an equal area of terrestrial forest; this is known as blue carbon. Until recently, the contribution of kelp and other seaweeds to blue carbon storage were not considered, but a recent study estimated that up to 11% of all seaweed might end up as sequestering carbon at the bottom of the deep sea. Check out this article to learn more.
- Foundation species form the foundation of an ecosystem by creating or structuring habitat. More information on this and other important species types, such as keystone species, can be found here.
- For example, Northern California experienced large losses in bull kelp in recent years due to a one-two punch of temporarily warmer waters combined with the loss of sea urchin-eating sea stars to the now-infamous sea star wasting disease. The loss of sea stars meant the grazing sea urchins could mow down the kelp largely unchecked, while a temporary lull in the usual upwelling of cold water meant warmer temperatures.
- Ecological communities are composed of interacting populations of species living in a particular habitat or area. These species may interact with or influence each other in many ways, such as by interacting as predator and prey or by providing habitat or food.