Connect with us

Community

Uncovering A Mass Extinction Event: The Lake Rototoa Mussel Survey

Water quality scientist Ebi Hussain led a Project Baseline citizen science team to determine what was happening to New Zealand’s Lake Rototoa mussel population. Crying cockles and mussels, alive, alive, No!! Here are the deets.

Published

on

By Ebrahim (Ebi) Hussain
Header photo courtesy of Oliver Horschig.

Lake Rototoa, a cold, monomictic1 dune lake in a rural area northwest of Auckland, New Zealand, is in peril. With a maximum depth of 26m/85 ft, Rototoa is the largest and deepest of a series of sand dune lakes along the country’s western coastline. Known for its increasingly rare, diverse population of native submerged macrophytes i.e., aquatic plants, and large, freshwater mussel beds, this lake is under increasing threat from a deteriorated water quality. Although the exact cause of this deterioration is unclear, the likely culprit is a combination of factors: eutrophication, land use activities, pest invasion, and climate change.

In late 2019, the Project Baseline Aotearoa Lakes team noted signs of a freshwater mussel population collapse as well as other evidence of environmental degradation. This was alarming, as freshwater mussels are rapidly declining in New Zealand, and globally, with 70 percent of the species considered at risk or threatened.

Many people are unaware that freshwater mussels are an important part of a lake ecosystem; as biofilters and bioturbators, they filter out nutrients, algae, bacteria, and fine organic material which helps purify the water. The loss of these keystone  species has likely contributed to the decline in water quality seen at Lake Rototoa.

The team’s observations prompted the design of a collaborative project between Project Baseline Aotearoa Lakes and the Auckland Council Biodiversity Team. This project is the first of its kind in New Zealand; it aims to fill critical knowledge gaps and, for the first time, quantify mussel populations in Lake Rototoa in a scientific manner. 

Ebrahim Hussain installing the transect. This peg marks the beginning of the first transect across the mussel bed. Photo by Oliver Horschig.

This project is the first of its kind in New Zealand; it aims to fill critical knowledge gaps and, for the first time, quantify mussel populations in Lake Rototoa in a scientific manner. 

The first objective was to assess the mussel population statistics, including species composition, abundance, size class, and recruitment success. The second objective was to determine habitat preferences, bed locations, and bed limiting factors. In order to satisfy the project objectives, the team designed a bespoke survey methodology to collect all the required information in a standardized way.

Digging Into The Data

The initial series of dives focused on habitat mapping and collecting bed scale survey information. The team has mapped almost 5 km2/3.1 mi2 of lakebed and 2.2 km2/1.4 mi2 of mussel bed so far. This information provided critical insight into mussel bed formation and habitat preferences which the team used to inform the site selection for the more detailed follow up surveys. 

The first phase of surveys has been completed and the results are frightening. A total of 1604 mussels (Echyridella menziesii) were counted. The combined density across all three survey sites was 41.4 mussels per m2/3.8 mussels/ft2. Out of the 1604 mussels found, 1320 (82.3%) were dead and only 284 (17.7%) were alive. The dead mussel shells were in a similar condition to the live individuals indicating that they may have all died during a recent mass extinction event.

No juveniles were seen during the surveys and all the mussels were larger than 51 mm/2 in. The surveyed population is composed entirely of mature adults, 64.1% of live mussels were larger than 70 mm/2.8 in in length, 30.6% were between 61 to 70 mm/2.4 to 2.8 in and the remaining 5.3% were in the 51 to 60 mm/2 to 2.4 in size class.

Measuring an adult Echyridella menziesii, this individual is 78mm in length and approximately 15-20 years old. Photo by Oliver Horschig.

Individual dead mussels were not measured but were placed into approximate size classes, all dead mussels were larger than 51 mm/2 in with the majority of them being placed in the 61 to 70 mm and >70 mm size classes. The average age of the mussels surveyed was estimated to be between 20 and 30 years old based on their size. Some larger individuals were 80 to 100 mm long and were estimated to be around 50 years old.  

This aging population and lack of younger individuals indicates limited-to-no viable recruitment in the surveyed area for more than a decade. Considering that most of the live mussels were at the upper end of their life expectancy and that there was no evidence of recent recruitment, the long-term viability of the surveyed population is low. 

While the exact reasons for this population collapse are not known, recent lake surveys (fish, water quality, and macrophytes)  provide some indication of possible causes. Recent fish surveys indicate a significant drop in the number of  the primary intermediate host species. Both galaxiid and bully species are declining due to predation by pest fish species. Without these native fish, the mussels cannot effectively complete their life cycle.

The declining water quality of the lake is also a contributing factor. The lake’s change from an oligotrophic state, which is low in plant nutrients and high oxygen at depth, to a mesotrophic state with moderate nutrients, subjected it to increased eutrophication.  

Eutrophication causes an increase in bioavailable nutrients which stimulates algal growth and in turn causes high organic silting. This silt settles on the lakebed and decomposes creating areas of low dissolved oxygen, which can cause animal die offs. 

Some studies suggest that these mussels cannot survive at dissolved oxygen concentrations below 5mg/L and it is possible that the lake undergoes prolonged periods of low-dissolved oxygen during seasonal stratification. The wide scale coverage of benthic blue-green algal mats further points to periods of anoxia, or absence of oxygen, and general eutrophication. 



Mussel Mania

Due to the low nutrient concentrations and the filtration capacity of the extensive mussel population, Lake Rototoa historically had good water clarity. Mussel filtration rates generally match their food ingestion rate, but once they reach their food ingestion rate, no further filtration will occur. If there is a high concentration of food (phytoplankton and zooplankton) in the water, the filtration rate is likely to be low. This means that as the lake becomes more eutrophic, the algal biomass increases, and the mussel’s filtration rate will continue to decrease. 

An Echyridella menziesii bed, showing a mixture of live and dead adult sized mussels. Photo by Ebrahim Hussain.

This decrease in filtration rates will contribute to the declining visual clarity. The significant loss of mussel biomass and ultimately the loss of mussels in Lake Rototoa exacerbated the situation and may have facilitated a higher rate of eutrophication.

Sediment is also known to affect mussel populations, and there are signs of increased sedimentation; however, no clear evidence of smothering or suffocating was observed. The combination of the organic silt, sediment, and benthic algal growth can clog the mussel gills, so there are likely to be some sediment-induced population stressors.

In terms of bed extent and bed limiting factors, the team made several key observations. The mussels tended to prefer gentle slopes and did not occur in great densities on steep faced slopes/shelves. Water level, riparian vegetation extent, and wind/wave-induced disturbance appeared to dictate the upper extent. Mussel beds were generally established at a depth just below the permanent water line a short distance away from the end of the riparian edge. Fewer mussels were observed in shallow, exposed areas with visible signs of wind/wave-induced substrate disturbance. 

The establishment of aquatic plants, changes in substrate, thermoclines, and potentially anoxia limited the lower bed extent. Mussels were commonly found in lower numbers in amandaphyte stands within the wider bed area and were not found at all within dense charophyte meadows. Mussels tended to establish around isolated macrophyte stands rather than in them. The lower extent of the bed mirrored the start of the deeper charophyte meadows. The littoral zone had clearly defined sections of mussels in the shallower areas (1.5 to 5 m/5 to 16 ft ) and dense macrophyte dominated areas in the deeper portion (6 to 10 m), which were relatively devoid of mussels. 

Ebrahim Hussain counting and size classing mussels in a 0.25m 2 quadrate. Photo by Oliver Horschig.

In the absence of aquatic plants, the thermocline separating the warmer epilimnion above from the colder hypolimnion below appeared to dictate the lower bed extent. Almost no mussels were found past the thermocline, which was between 6 and 7 m/20 to 23 ft deep during the survey period. Since mussel bed establishment is not known to be thermally regulated, the limiting factor here may be anoxic conditions, commonly associated with hypolimnetic water. This assumption has not been validated, and a more detailed investigation of stratification profiles are planned for this upcoming year.

A clear limiting factor is the change in substrate seen past the 7 to 10 m/23 to 33 ft depth contour. The substrate changes from sand with a surficial layer of silt to a semi liquid silt/soft mud. No mussels or macrophytes were found in these areas, and the substrate does not appear to support bed establishment. Benthic algal mats covered the lower extent of some beds but did not clearly limit their establishment; since these mussels are mobile, presumably they will move if they are being smothered.

In Conclusion

Despite the concerning results, this project is a landmark event as it is the first study of its kind in New Zealand and the first detailed survey of the mussel population in Lake Rototoa. This project highlighted the pressures faced by our aquatic environments and exposed the ugly truth of what is going on below the surface. We have uncovered a mass extinction event that is currently occurring in our back yard that no one even knew was happening. 

We have uncovered a mass extinction event that is currently occurring in our back yard that no one even knew was happening.

Now more than ever, projects like this are critical. Our environments are under increasing pressure, and it is up to all of us to take action to ensure that we preserve these ecosystems for future generations.

The follow-up phases of this project are planned to be carried out this summer. The data we have collected thus far has enabled the Auckland Council to make informed decisions on how best to manage these threatened species and preserve native biodiversity. We hope that our continued efforts at this lake will contribute to preserving this ecosystem and prevent the complete extinction of these threatened species.

Footnotes:

  1. Cold monomictic lakes are lakes that are covered by ice throughout much of the year. During their brief “summer”, the surface waters remain at or below 4°C. The ice prevents these lakes from mixing in winter. During summer, these lakes lack significant thermal stratification, and they mix thoroughly from top to bottom. These lakes are typical of cold-climate regions. 

Dive Deeper:

InDepth V 1.6: Bringing Citizen Science To Lake Pupuke by Ebrahim Hussain

Learn more about Project Baseline
View their online database
Get involved 


Ebrahim (Ebi) Hussain is a water quality scientist who grew up in South Africa. As far back as he can remember he has always wanted to scuba dive and explore the underwater world. He began diving when he was 12 years old and he has never looked back. Diving opened up a new world for him and he quickly developed a passion for aquatic ecosystems and how they work. The complexity of all the abiotic and biotic interactions fascinates him and has inspired Ebi to pursue a career in this field.
He studied aquatic ecotoxicology and zoology at university, and it was clear that Ebi wanted to spend his life studying these subsurface ecosystems and the anthropogenic stressors that impact them. After traveling to New Zealand, Ebi decided to move to this amazing country. The natural beauty drew him in, and even though there were signs of environmental degradation, there was still hope. Ebi founded Project Baseline Aotearoa Lakes with the goal of contributing to preserving and enhancing this natural beauty as well as encouraging others to get involved in actively monitoring their natural surroundings.

Click to comment

Leave a Reply

Your email address will not be published. Required fields are marked *

Community

Hal Watts: Plan Your Dive

Known for his deep air diving exploits back in the day, 86-year-old Hal Watts, aka “Mr. Scuba,” is one of the pioneers of early scuba and credited with coining the motto, “Plan Your Dive. Dive Your Plan.” He founded the Professional Scuba Instructors Association International (PSAI) in 1962, which eventually embraced tech diving, but never relinquished its deep air “Narcosis Management” training. Italian explorer and instructor Andrea Murdock Alpini caught up with Watts and teased out a few stories from the training graybeard.

Published

on

By

Interview by Andrea Murdock Alpini 
English text by Vincenza Croce

Hal Watts, Terrence Tysall, and Bill Stone in March of 1993.  This was the last stop in the U.S. for a test dive of the Cis-Lunar Mk-4 rebreather prior to Stone’s San Agustin expedition (1994) for its first real sump dive.

“Plan your dive, dive your plan,” is a common refrain in diving, but it’s easy to forget the meaning of this phrase has changed over time.

The underwater explorers of the early days learned to plan their dives with watches, depth gauges, and US Navy tables. Back then, decompression tables were the Bible for divers—something miraculous, halfway between alchemy and physiology. Those trail-blazing divers defined what it meant to “plan” a dive.

But, at the time, the term “technical diving” did not exist; divers breathed air on the bottom as well as during decompression. Only after many years was oxygen added, followed by the famous jump into the hyperbaric chamber.  

Later came new innovations after a few decades of experiments: hyperoxygenated binary mixtures, the NOAA tables, Heli-air (i.e. the addition of helium in tanks loaded with air), the change in the speed of ascent, new molecules to be studied, new physiological and narcotic effects, and their consequent impacts on humans and their psyches.

In a very short time, diving traditions underwent a metamorphosis. The spool and the coral tank became a proper reel, the ascent bin and the plastic bag disappeared in favor of the buoyancy control device (BCD), the surface marker buoy appeared—and then, even later on, wrists were adorned with underwater computers instead of decompression slates.

Divers later renewed and revolutionized a niche discipline, transforming it into a sporting phenomenon and a vocation. Faced with imminent change, there is often nothing that can be done when an anomalous wave arrives; you cannot stop its irresistible force with the wave of a hand. And thus was the American revolution of underwater technique, where the means of exploration—read mixed gas and scooters—have become the end.

The self-proclaimed originator of the “plan your dive, dive your plan” motto was 86-year old Hal Watts, the founder of American didactic Professional Scuba Association International (PSAI) and a diving pioneer who once held the Guinness Book of World records for deep diving. Though the use of trimix grew in popularity, Hal continued to believe in deep air, in the ancient technique of coral fishermen. He supported wreck and cave diving—with decompressive mixtures and new configurations through PSAI; but, above all, he believed (and continues to believe) that deep air, if properly practiced, is a discipline with unique logistics, hidden dangers, and irresistible charms that can take you to a parallel world.

Hal Watts speaking at aquaCORPS tek.93 Conference

First of all, Hal, what was the dive that changed your way of seeing scuba diving? I mean, a dive that was like an epiphany, a dive which changed your point of view on a technical matter?

Hal Watts: Wow, you sure are really trying to test my old man memory. Now I’ll have to review some of my old logbook entries. 

The first scuba dive that really got my attention as to just how serious and dangerous scuba diving can be was on December 2, 1962. I was diving with Bob Brown, co-owner of Florida State Skindiving School in Orlando, Florida. I was a member of a dive club in Orlando known as Orlando Sport Diving Club. Bob and I had heard of a sinkhole in Ocala known locally as Zuber Sink as well as Blue Sink. Years later, I later leased the property and renamed it as Hal Watts’s 40 Fathom Grotto, and I eventually purchased the Grotto in mid-1979.

We had never talked to anyone about the sinkhole; therefore, we had no idea about the visibility or the depth. Up to this point, I had constructed my favorite BCD, using a large white Clorox plastic jug, which we tied to our twin tank system. We put air into the BCD from our “Safe Second Stage” mouthpieces. 

Bob and I tied our safety line to a tree on the bank of the sink and reviewed our dive plan. I am reminded of the motto I came up with, many moons ago—Plan your dive, dive your plan. 

We all know that motto. I didn’t realize that it was you who coined it.

It was back in the 1960s when I was writing course manuals for NASDS [National Association of Scuba Diving Schools] and opened up my Mr. Scuba dive shop.

Mr. Scuba’s Magic Bus!

But back to the dive at Zuber. I’ve failed to mention the fact that neither of us had been doing any dives below 30 m/100 ft. We followed the cave line down slowly, not paying enough attention to our depth. Before we realized it, we had hit the bottom, stirred it up, and had no clear water.

Lucky for us, I kept the cave diving reel in my hand, and Bob kept his hand on the line. I couldn’t see; however, I could feel Bob’s hand, squeeze his fingers tight on the line, grab his thumb, and give it the “thumbs up” signal. I don’t know how we managed it, but we were both able to use our NASDS safe second stages and add air into the Clorox “BCDs.” We were actually fated to begin an uncontrolled, too-rapid ascent. All of a sudden, we hit an overhead wall, which stopped our ascent at a depth of 9 m/30 ft. 

We looked at each other, and gave the OK hand signal. While decompressing, following the old Scubapro SOS mechanical computer, I started to pull up the loose line until the dive reel appeared. Wow, we sure had an awful lot of loose line floating around us. Were we extremely lucky? Of course, we were. Our problem was that we never planned our dive, and consequently, were unable to dive a plan.

After that dive, I worked with Scuba Pro and Sportsways to create the “Octopus,” or “safe second.” A while later, the octopus appeared for the first time in Scuba Pro catalogs. I was also the first to add a pressure gauge along with the Octopus.

Hal Watts set the world deep air record to 120m/390 ft in 1967

Ah yes, the “Safe Second.” That’s what NASDS called backup second stages, right? Sheck Exley (1949-1994), the legendary cave explorer with whom you were friends, was also credited with fitting a redundant second stage reg with a necklace. I want to ask you more about Exley, but first, I want to know: What are the best wrecks you ever dived?

This is really very hard to answer. I’ll have to list four, in the order that I dived them: the USS Monitor, Andrea Doria, Japanese wrecks located in Truk Lagoon, and the Lusitania in Ireland.

The most important would have to be the USS Monitor, a submarine used during the Civil War. A group of well-known USA divers applied to the National Oceanic and Atmospheric Administration (NOAA) for a permit to dive the Monitor, as she was located in protected waters. In addition to myself, the group consisted of: Gary Gentile, attorney Peter Hess, and several other well-known expert divers. At first, NOAA refused. Then, Peter Hess filed proper papers asking that we get the NOAA permit. To that end, we presented my Deep Air training material to the concerned NOAA group. I appeared as an expert witness and provided NOAA staff and their legal representatives with my internationally accepted training material and my record of training several world record deep air divers. Our deep air training has been accepted worldwide with zero diving deaths. After that, we received the permit. 

Other than the Monitor, my favorite deep wreck dive would be the Lusitania, which is a very personal and proud story for me. The main reason is because venture capitalist Gregg Bemis owned the diving rights to the Lucey at the time. Gregg had contacted me requesting that I train him on PSAI Narcosis Management Level V, on air—which is 73 m/240 ft—and then train him on trimix so he and I could dive to 91 m/300 ft on the Lusitania lying off the coast of Ireland. 

When word got out that I had enrolled Gregg in my Narcosis Management Course, a well-known international course director (a personal friend of mine) called and told me, “Hal, do not teach Gregg deep diving.” 

PSAI’s ad in aquaCORPS Journal circa 1994 offering deep air training.

He told me that he had been training Gregg at his facility, and that he was a “train wreck.” “He is from a very well-off family in Texas, and if you cause him any injuries, you will be sued and put out of business,” my friend said. Well, guess what? Gregg completed the 240 Level V Deep Air course, then our PSAI Trimix course. My wife, Jan Watts, Gregg, and I went to Ireland to dive the Lusitania. He and I made an awesome 91 m/300 ft trimix dive to the deck.

Diving on the Andrea Doria with Tom Mount, Peter Hess, and several great wreck divers was also an awesome dive. Last but not least was a great trip to Truk to dive on some of the Japanese wrecks.

Please tell us about Sheck.  What was your relationship with him like?

Sheck and I became friends and made several dives together, and one of my favorites happened when Sheck, his Mary Ellen, my wife Jan, and I were diving at 40 Fathoms. Sheck wanted to practice gas switches during descents. Sheck was practicing, getting ready for a planned very deep dive (I think in Mexico with Jim Bowden). The four of us swam to the east side of The Grotto, slowly following the wall during our controlled descent, watching Sheck practice gas switching. 

Sheck Exley and Hal Watts at a NSS-CDS conference

After reaching our planned depth of 73 m/240 ft, we began our controlled ascent up to our first planned deco stop. During our last deco stop on our 4.5 m/15 ft platforms, I noticed that Sheck had a funny look on his face and was messing with his drysuit between his legs. I remembered then that he had told me that he had an attachment installed in the drysuit that would allow him to pee underwater. He was clearly in a bit of discomfort and Mary Ellen, Jan and I just floated nearby and watched.

I’ve heard that Sheck later used diapers, or just cut it loose in one of his old neoprene drysuits on his big dives, so evidently he didn’t get that early p-valve to work. What about your friendship and job collaboration with Gary Taylor, your brother-in-arms and a co-owner of PSAI?

Andrea, get comfortable, since this question will take some time to properly answer.

I first met Gary in Miami, which is where we became friends when I was staying in his home and taking Tom Mount’s nitrox course.  I have a photo of Tom, Gary, and me gas blending on the floor of Tom’s garage. During the course, Tom was still using his worn-out hand written paper flip charts as his notes.

Gary was impressed with my deep air program and offered to put together an updated slideshow presentation for me to teach with. PSAI still uses an updated version of this system to date. Gary stayed with Tom until Tom thought he had sold IANTD [International Association of Nitrox and Technical Divers] to another individual. After that sale came about, Gary contacted me wanting to get more involved with PSAI. Being smarter than folks thought I was, I jumped at the chance to have Gary on the PSAI Team. Tom’s deal fell through, but Gary was totally involved with PSAI, and now is a partner and president of our agency. Thanks to Gary and Tom. 

Many, many years ago I was still taking some type of classes—I think regarding mixed gasses, maybe with Rebreathers—at Tom’s house. In fact, I was one of Tom’s instructors who did the final proofreading of one of Kevin Gurr’s manuals. Too far back to recall much about this mixed gas stuff—remember my reputation for being a deep air diver.

Tom Mount and Gary Taylor mixing up some trimix in the garage.

Speaking of the people with whom you’ve dived, was the aim of The Forty Fathom Scubapros Club?

Before I invested in a sinkhole in the Ocala, Florida, area—which was locally referred to as Blue Sink or Zuber Sink, and is now referred to as 40 Fathom Grotto—several diving buddies whom I had dived with and trained for extreme deep air diving—as well as cave exploring—got together and planned to dive The Grotto at least one Friday night per month. Within a short period of time, several other buddies joined our group, which eventually became known as The 40 Fathom Scubapro’s dive club. Each diver had to meet my requirements of training. 

Forty Fathom Grotto aka Zuber Sink
An early Sheck Exley mix course at Forty Fathom Grotto
An Eric Hutcheson drawing of Forty Fathom Grotto

Eventually, our group set specific personal requirements—being a good person, supporting our club safety rules, and making at least one 40 Fathom Grotto dive per month. We set a limit of 14 or 15 members. Three 40 Fathom members eventually set World Records for deep air: I was one, A. J. Muns, and Herb Johnson set ocean records, and later I set the air depth record for cave diving. Naturally, as time passed and we got older, our membership got smaller. It is notable that none of our club members have died during any scuba dive.

Finally, what led you to create the iconic motto, “Plan Your Dive. Dive Your Plan?” 

I used to be a private pilot, and we used to say, “Plan your flight, fly your plan.” This was back in probably 1961 when I had just started diving and there were so many instances where all the other divers would get in the water without saying anything. I’ve seen so many incidents and fatalities that could have been avoided through proper planning.

Dive Deeper

ScubaGuru: LXD 029 : Hal Watts – Record Deep Diver & Technical Diving Pioneer

Netdoc: Netdoc chats with Mr Scuba, Hal Watts

InDEPTH: The First Helium-based Mix Dives Conducted by Pre-Tech Explorers (1967-1988) by Chris Werner

Alert Diver.Eu: Rapture of the Tech: Depth, Narcosis and Training Agencies

Professional Scuba Association International: PSAI History


Andrea Murdock Alpini is a TDI and PSAI technical trimix and advanced wreck-overhead instructor based in Italy. He is fascinated by deep wrecks, historical research, decompression studies, caves, filming, and writing. He holds a Master’s degree in Architecture and an MBA in Economics for The Arts. Andrea is also the founder of PHY Diving Equipment. His life revolves around teaching open circuit scuba diving, conducting expeditions, developing gear, and writing essays about his philosophy of wreck and cave diving. He published his first book, Deep Blue: storie di relitti e luoghi insoliti (2018) and IMMERSIONI SELVAGGE, the new one is on the way, out on fall 2022. 

Subscribe for free
Continue Reading

Thank You to Our Sponsors

Subscribe

Education, Conservation, and Exploration articles for the diving obsessed. Subscribe to our monthly blog and get our latest stories and content delivered to your inbox every Thursday.

Latest Features

Trending