What are toxic phytoplankton and how do they occur?

The harvesting of mussels and other filter feeders, such as razors, has been restricted in Lamlash Bay, Whiting Bay and Pirnmill since May. COAST has been asked: “What exactly is a toxic phytoplankton bloom and why does it occur?”

In the marine environment, single-celled, microscopic plant-like organisms naturally occur in the surface waters of any body of water. These are phytoplankton sometimes known as microalgae, plant like organisms. Phytoplankton use sunlight to convert simple inorganic molecules, such as water and carbon dioxide, to complex organic compounds, such as protein, carbohydrates, and lipids.

The ocean waters that surround continental coastlines are the home of a large number of marine algae, making them the most productive areas for the commercial harvest of marine finfish and shellfish. They are important as they form the base of the food chain for many other marine organisms. However, about 2% of the thousands of species of marine phytoplankton are harmful or toxic and these can have negative effects on the environment, seabirds, fish and marine mammals; or on people who eat marine shellfish which concentrate these contained toxins.

Much of the time, microalgae are present at very low numbers, but when conditions are right, they can multiply rapidly and explosively, producing a noticeable discoloration in the water called a "bloom." These blooms can cover very large areas of the coastal ocean that are often visible from satellite observation of the earth. Large numbers of "blooming" algae can, at times, result in the presence of high levels of toxins or result in lower oxygen levels in seawater, thereby creating significant problems for marine life.

Two Centuries of Change in a Coastal Marine Ecosystem

Ruth H. Thurstan, Callum M. Roberts*
Environment Department, University of York, York, United Kingdom

Background: The Firth of Clyde is a large inlet of the sea that extends over 100 km into Scotland’s west coast.

Methods: We compiled detailed fisheries landings data for this area and combined them with historical accounts to build a
picture of change due to fishing activity over the last 200 years.

Findings: In the early 19th century, prior to the onset of industrial fishing, the Firth of Clyde supported diverse and productive fisheries for species such as herring (Clupea harengus, Clupeidae), cod (Gadus morhua, Gadidae), haddock (Melanogrammus aeglefinus, Gadidae), turbot (Psetta maxima, Scophthalmidae) and flounder (Platichthys flesus, Pleuronectidae).

The 19th century saw increased demand for fish, which encouraged more indiscriminate methods of fishing such as bottom trawling. During the 1880s, fish landings began to decline, and upon the recommendation of local fishers and scientists, the Firth of Clyde was closed to large trawling vessels in 1889. This closure remained in place until 1962 when bottom trawling for Norway lobster (Nephrops norvegicus, Nephropidae) was approved in areas more than three nautical miles from the coast. During the 1960s and 1970s, landings of bottomfish increased as trawling intensified.

The trawl closure within three nautical miles of the coast was repealed in 1984 under pressure from the industry. Thereafter, bottomfish landings went into terminal decline, with all species collapsing to zero or near zero landings by the early 21st century. Herring fisheries collapsed in the 1970s as more efficient mid-water trawls and fish finders were introduced, while a fishery for mid-water saithe (Pollachius virens, Gadidae) underwent a boom and bust shortly after discovery in the late 1960s.

The only commercial fisheries that remain today are for Nephrops and scallops (Pecten maximus, Pectinidae). Significance: The Firth of Clyde is a marine ecosystem nearing the endpoint of overfishing, a time when no species remain that are capable of sustaining commercial catches. The evidence suggests that trawl closures helped maintain productive fisheries through the mid-20th century, and their reopening precipitated collapse of bottomfish stocks. We argue that continued intensive bottom trawling for Nephrops with fine mesh nets will prevent the recovery of other species. This once diverse and highly productive environment will only be restored if trawl closures or other protected areas are re-introduced. The Firth of Clyde represents at a small scale a process that is occurring ocean-wide today, and its experience serves as a warning to others.

Read the full report Ecological meltdown in the Clyde

Leigh Howarth, a marine biologist from the University of York, has been surveying Lamlash Bay to help determine whether the No Take Zone (NTZ) will be beneficial in improving the local scallop population, a result seen all over the world for many species of fish and shellfish.
 

We are 2 months into the first year of a new annual dive monitoring scheme in Lamlash Bay. Progress was very slow at first due to a combination of bad weather and our lack of experience with the surveying process. However, we just completed our 35th survey, bringing our total area of the seabed covered to 5250 metres square, and the number of scallops recorded and measured underwater to 619.

What seemed as unachievable only last month, there are now only 5 more surveys left to conduct this summer. With no external funding, this great result is entirely down to the time and effort donated by COAST volunteers who either act as boatman (being in charge of transport, navigation and help in setting up the survey equipment on the seabed) or as a diver conducting the survey with myself. I am therefore very grateful to everyone who has helped in making this a hugely enjoyable and rewarding experience.

In particular, local diver and underwater photographer Angus Robson (see www.arransealife.co.uk) has really helped us turn the tide in terms of the number of surveys done. Angus has provided boat cover almost everyday regardless of the weather in exchange for the small reward of a  ham sandwich and an afternoon dive whilst myself and Howard wait onboard for a compulsory 2 hours in between dives to allow the built-up nitrogen to diffuse out of our bloodstream.

It is interesting how every dive has been completely different, especially considering the small area that is Lamlash Bay. Some dives we encounter very little life and just mud, other dives we encounter large maerl beds, hundreds of species and spawning aggregations of thousands of sea slugs. This is why we record everything we see, even if the specific data is not analysed in the forthcoming report. Long-term monitoring is essential in determining the success of NTZs and the data we collect now can be analysed and compared in 5, 10 or even 20 years time by government scientists, or perhaps by young, budding scientists such as myself. To see any effects generated by Lamlash Bay NTZ, whether they be ecological or physical, they all require data such as we are collecting.

A slideshow of photos of this summers surveys are now on the Gallery section of this website

Diving after the dredge

Visiting marine biologist Leigh Howarth is currently (July -Aug 2010) conducting the first diver scallop survey in Lamlash Bay to monitor the health of the scallop population since the introduction of Scotland’s first No Take Zone (NTZ). This will hopefully provide an important baseline for future monitoring of the Lamlash Bay NTZ.

"Preparation for the scallop survey has been hands-on. My first working day began with learning how to operate the dive boats and planning our survey procedures. We have since then been out diving every day, weather permitting of course."

"My first dive on Arran took place within Lamlash Bay NTZ. It was beautiful. The water was clear and not very cold, around 12°C, and the sealife was abundant. Just a few sights include: velvet swimming crabs, hermit crabs, squat lobsters, soft corals, sea pens, sea squirts, jellyfish, hydroids, dog fish, and interestingly, many commercially important species such as scallops, queenies, edible crabs, pollack, juvenile cod and juvenile flat fish. Lamlash Bay is clearly an important area worthy of its protected status."

“Interestingly, a week after my first dive, a scallop dredger was witnessed fishing very close to the boundaries of the No Take Zone over the course of a few days.  Once it had left the area, myself and COAST Chair, Howard Wood.  decided to investigate the state of the seabed after the dredger had left the area. Within seconds of reaching the seabed, the destruction brought about by the dredger was unmistakable. The seabed had literally been raked, leaving behind nothing but smashed up shellfish and sand. The scallops that had not been caught were left dead and broken by the teeth of the scallop dredge. Whilst crabs and lobsters had been torn to pieces, and delicate organisms that normally attach to boulders, cobbles and pebbles such as hydroids and sea squirts, were now free floating and dying. I have read many times about the destruction scallop dredging can bring, though I had never seen it first-hand.

Picture: Scallops  recovered during the dive, left broken after the pass of the dredger.

"After much planning, the scallop survey within Lamlash Bay is well under way, facilitated by COAST members. I have been shown an island hospitality ever since I stepped foot on Arran and want to say thank you to everyone I have met so far who have helped in the making of this project and made my experience here a very enjoyable one. The finalised report will be available in October.”

Please click here to read about the 'science behind the survey' And if you have any questions or comments please email me: This e-mail address is being protected from spambots. You need JavaScript enabled to view it .