Marine Ecosystems Q&A

With Marine Biologist Dr. Kristina Boerder

Owls Head has long been surrounded and shaped by the ocean. The rugged landscape reflects the legacy of the ice age, and the hardy ecosystems that developed after the ice retreated mirror the unique environment in which rare plant communities now thrive.

Land and ocean are inextricably connected; impacts on one will impact the other. Changing or disappearing ecosystems on land will lead to the collapse of marine ecosystems and vice versa. Often, this connection is not immediately apparent.

Q: What marine ecosystems are present around Owls Head?

A: The inshore marine ecosystems consist mainly of rockweed and eelgrass beds. Rockweed is a brown alga which grows on hard surfaces such as rocks, whereas eelgrass is a type of seagrass. Seagrasses are the only flowering plants that grow in the ocean. Eelgrass can grow in soft sediments such as sand and is mostly found in Northern, temperate, or cold waters.

Q: Why are rockweed and eelgrass beds so very important?

A: Both are so-called ‘ecosystem engineers.’ This means that these species create a special habitat, much like trees on land: a habitat in which other species can live, feed, spawn and hide. This, in turn, affects a whole range of species, from small invertebrates (like mussels and clams) to crustaceans (such as lobster and crabs), to fish (such as herring, juvenile salmon, and some flatfish).

Courtesy of Nick Hawkins Photography

Q: So how do rockweed and eelgrass beds benefit the environment?

These benefits make eelgrass beds very valuable – it has been estimated that eelgrass beds are worth in excess of $20,000 per hectare, per year.

Marine Biologist Dr. Kristina Boerder

A: Rockweed and eelgrass beds provide ‘ecosystem services,’ which are defined as benefits to humans. These benefits include:

  • Protection from coastal erosion by slowing down waves and currents and stabilizing sediment
  • Providing oxygen and nutrients
  • Enhancing water quality
  • Absorbing and storing carbon, which helps to mitigate climate change
  • Providing important habitat for many other species like fish, crustaceans and invertebrates such as scallops. These species feed, hide and spawn in these habitats. Eelgrass beds provide ‘nursery habitat’ to young fish by providing food and shelter from larger predators.
  • This, in turn, supports healthy fisheries, a reason why seagrass beds have been declared ‘Essential Fish Habitat.’

These benefits make eelgrass beds very valuable – it has been estimated that eelgrass beds are worth in excess of $20,000 per hectare, per year.

Q: What effects can the disappearance of these ecosystems have?

A: Coasts where eelgrass beds have disappeared are more prone to erosion as well as damage in storms, surges, and high tides. This often creates high costs to repair coastal infrastructure.

Water quality is reduced, and species that rely on eelgrass and rockweed to feed, hide, and spawn disappear. This can lead to reductions in the populations of invertebrates such as clams and scallops, crustaceans such as lobster and crab, and fish such as herring, salmon or flatfish. In the worst scenarios, local fisheries can suffer reduced catches.

What Threats Do Rockweed and Eelgrass Habitats Face?

A: Both rockweed and eelgrass have declined rapidly around the world due to a variety of impacts caused by humans. Human activity on land and at sea can jeopardize the health of rockweed and eelgrass habitats.

Common reasons that rockweed and eelgrass die off:

  • Open-net pen aquaculture has negative impacts on the marine environment in surrounding areas through the overload of nutrients from fish feed and feces especially when concentrated in coastal areas, the use of antibiotics and pesticides to fight disease and fish (sea) lice, and the spreading of diseases to wild fish.
  • Mechanical destruction of rockweed and eelgrass ecosystems can happen through dredging, trawling, or overharvesting
  • Invasive species such as the green crab, which rips out eelgrass to feed
  • The use of toxic substances on land, such as pesticides on lawns, agricultural fields, and golf courses. 
  • Warming waters due to climate change
  • Pollution with nutrients (“eutrophication”
  • Increased sedimentation

Eutrophication: Excess nutrients washed into coastal waters, for example from fertilization of agricultural land close to rivers or the coast, causes rapid growth of smaller algae, which overgrown rockweed and eelgrass and smother them.

Increased sedimentation can occur in any development where a lot of soil is shifted or the water flow is changed. This can be the construction of dams, roads, or large houses, the infill of coastal areas with soil or other material. The subsequent change to the way that water drains into the ocean (such as run-off of soil or sand from land during rain) decreases water clarity and reduces the amount of available sunlight, which rockweed and eelgrass need to grow.

Q: There is (or has been) construction along the coast in my area, but the eelgrass and/or rockweed is still there. How do we know that new coastal development will negatively affect the sea life nearby?

A: Every location is different and both rockweed and eelgrass beds can withstand a certain amount of damage, stress and disturbance, which can also occur naturally, as with storms. Certain characteristics along a shore can mitigate or worsen negative impacts. For example, currents that better disperse run-off lessen impacts, while factors such as sheltered bays can worsen the effects.

When there are too many negative impacts together, the health of coastal ecosystems will decline. Rockweed and eelgrass will not grow as well. They will become more vulnerable to diseases and predators, such as the invasive green crab.

Local eelgrass or rockweed beds might still be present and provide some or all of the ecosystem benefits mentioned above, but their health might be impacted. One additional stressor, such as increased nutrient concentrations or more sediment being washed into coastal waters, might push these ecosystems over the so-called “tipping point” – an ecological change so severe it cannot be reversed.

Q: The fisheries in my area are doing just fine despite development. How can this be explained?

A: Negative impacts on coastal ecosystems echo through food webs in a variety of ways. Depending on the scale and extent of negative impacts on rockweed and eelgrass beds, the abundance of some species might decline, while others take over or new species appear. Species that are highly specialized to certain conditions, certain prey, or are very sensitive to their environmental conditions usually suffer first, while others, such as some crustaceans and invertebrates, can be more resilient. However, if too many stressors and negative impacts occur, or they are too intense or prolonged, even these species might suffer. This may only become apparent after some time, for example, when fewer juvenile fish survive due to a lack of habitat to feed and hide in, thus resulting in fewer adult fish that can be caught in fisheries in following years.

Q: If these ecosystems disappear, can they come back?

A: Both rockweed and eelgrass are very unique in their abilities to grow in the areas where they do. If they disappear, barrens can be the result. If these ecosystems are gone or significantly altered, it can be very difficult and costly to bring them back. Scientists have been experimenting in restoring seagrass beds around the world by planting seagrass, but so far, successes are limited. Therefore, it is crucial to keep and protect eelgrass and rockweed beds, and protect these ecosystems and their key species by law.

Q: What can be done to help these ecosystems?

A: Keeping the coast wild and unaltered is very important.

Avoiding large developments or placing them far enough away from bodies of water, such as rivers, can be beneficial.

If construction needs to happen on a property, it should have as minimal an impact as possible. Existing structures that have negative effects on coastal ecosystems should be removed or relocated.

The use of fertilizers and pesticides should be restricted or prohibited near water.

Destructive fishing techniques such as dredging or trawling need to be kept out of sensitive coastal habitats and fishing should be conducted in a sustainable manner. Open-net pen aquaculture should be removed and/or shifted to integrated aquaculture on land.

Q: So, can there be a golf course in Owls Head without negative impacts on the marine environment?

A: Very unlikely. Due to the unique rugged landscape of Owls Head, extreme habitat alteration will be necessary to achieve a landscape suitable for golf. This will likely require the use of thousands of tons of infill, which will increase the amount of run-off and sedimentation into nearby lakes, streams, and coastal waters. To grow lawns, fertilizers and pesticides will be required. These will be washed into the water with heavy rains and storms. This alteration of the area will impact the coastal and marine ecosystems, potentially leading to a loss of species and biodiversity.

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