DIVE DRY WITH DR. BILL #889: MISSING IN ACTION?
Due to my self-imposed quarantine and a pinched nerve in my back making even walking a bit painful, I have not made a single dive in December of 2020. Like everything else, I hope 2021 is a much better year (although I have no intention of trying to match the 200 dives I made in 2020). Being of a "mature" age and compromised due to my cancers, my primary care physician says I will be in one of the early tiers to get the COVID vaccination which should offer a measure of safety.
Since I'm not diving this month, I've tried to reflect on what I saw on those 200 dives earlier this year... or, perhaps more appropriately, what I hadn't seen! My general impression is that biodiversity, at least in the dive park, was greatly reduced last year. I rarely saw a sea star other than the variable star (Linckia columbiae). They seem to have been somewhat immune to the sea star wasting disease of the past few years. I also saw a very few fragile rainbow stars (Astrometis sertulifera) and perhaps two of the formerly common giant spined or knobby sea stars (Pisaster giganteus).
I've already written about my concerns at seeing almost no flatfish such as the C-O sole (Pleuronichthys coenosus) and not a single California halibut (Paralichthys californicus). I may have seen one hornyhead turbot (Pleuronichthys verticalis) out by the wreck of the Suejac but wasn't fast enough to catch up to it to get video and a positive ID. Other fish species such as the kelp surfperch (Brachyistius frenatus) and kelp rockfish (Sebastes atrovirens) seemed much fewer than normal this year.
The beautiful shell-less snails known as nudibranchs were also rarely seen. Usually I can count on a few Spanish shawls (Flabellina iodinea) on each dive and occasionally a beautiful California blue dorid aka California chromadorid (Felimare californiensis). Apparently there was a population explosion of Price's aeolid (Flabellina pricei) but for me to see these tiny nudis would probably require prescription lenses. I don't think I saw a single sea hare, either the California (Aplysia californica) or the black (Aplysia vaccaria) on any of my dives. Even their molluscan relative, the California two-spot octopus (Octopus bimaculoides), was rarely encountered (at least by me). Fortunately the pink (Haliotis corrugata) and green (Haliotis fulgans) abalone populations seemed to be stable.
So what is the reason for this apparently diminished biodiversity in my home waters? The answer seems to be a mystery to me despite my 51 years of diving Catalina waters. I could blame aging eyes, but that would mainly explain the "absence" of smaller critters. Although water temperatures were warm much of the year, they were not so much out of the ordinary that I'd expect them as the culprit. It is possible some species went a bit deeper than I dove since I've become a fairly shallow (< 100 fsw) person in my advanced age. No more drops down to 200 fsw where I used to see many species not found at shallower recreational dive depths.
I keep up with dive reports from friends on the mainland and it doesn't seem as if they have noticed significant declines in biodiversity this past year. In fact, I'm a bit envious of the species many of them have filmed in the much cooler waters off Sandy Eggo. Many of those species are rarely (if ever) seen in our waters, possibly because they don't have larval forms that can make the journey across the San Pedro Channel. Others may have restricted travel outside their usual home areas due to COVID restrictions (ha ha, just kidding).
So, if any of my readers have hypotheses to explain this, I'd greatly appreciate hearing them because I'm stumped. As an ecologist, I like to be aware of the diversity of critters in a given ecosystem rather than focus on a single group. The paucity this past year (and the chilly waters of winter) have left me longing to travel to biodiversity hotspots in the South Pacific and Asia. Sadly, the cancers and COVID are not allowing that to happen.
© 2020 Dr. Bill Bushing. For the entire archived set of nearly 900 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: Knobby and fragile rainbow sea stars; kelp rockfish and California halibut; California blue dorid nudibranch and two spot octopus.
Due to my self-imposed quarantine and a pinched nerve in my back making even walking a bit painful, I have not made a single dive in December of 2020. Like everything else, I hope 2021 is a much better year (although I have no intention of trying to match the 200 dives I made in 2020). Being of a "mature" age and compromised due to my cancers, my primary care physician says I will be in one of the early tiers to get the COVID vaccination which should offer a measure of safety.
Since I'm not diving this month, I've tried to reflect on what I saw on those 200 dives earlier this year... or, perhaps more appropriately, what I hadn't seen! My general impression is that biodiversity, at least in the dive park, was greatly reduced last year. I rarely saw a sea star other than the variable star (Linckia columbiae). They seem to have been somewhat immune to the sea star wasting disease of the past few years. I also saw a very few fragile rainbow stars (Astrometis sertulifera) and perhaps two of the formerly common giant spined or knobby sea stars (Pisaster giganteus).
I've already written about my concerns at seeing almost no flatfish such as the C-O sole (Pleuronichthys coenosus) and not a single California halibut (Paralichthys californicus). I may have seen one hornyhead turbot (Pleuronichthys verticalis) out by the wreck of the Suejac but wasn't fast enough to catch up to it to get video and a positive ID. Other fish species such as the kelp surfperch (Brachyistius frenatus) and kelp rockfish (Sebastes atrovirens) seemed much fewer than normal this year.
The beautiful shell-less snails known as nudibranchs were also rarely seen. Usually I can count on a few Spanish shawls (Flabellina iodinea) on each dive and occasionally a beautiful California blue dorid aka California chromadorid (Felimare californiensis). Apparently there was a population explosion of Price's aeolid (Flabellina pricei) but for me to see these tiny nudis would probably require prescription lenses. I don't think I saw a single sea hare, either the California (Aplysia californica) or the black (Aplysia vaccaria) on any of my dives. Even their molluscan relative, the California two-spot octopus (Octopus bimaculoides), was rarely encountered (at least by me). Fortunately the pink (Haliotis corrugata) and green (Haliotis fulgans) abalone populations seemed to be stable.
So what is the reason for this apparently diminished biodiversity in my home waters? The answer seems to be a mystery to me despite my 51 years of diving Catalina waters. I could blame aging eyes, but that would mainly explain the "absence" of smaller critters. Although water temperatures were warm much of the year, they were not so much out of the ordinary that I'd expect them as the culprit. It is possible some species went a bit deeper than I dove since I've become a fairly shallow (< 100 fsw) person in my advanced age. No more drops down to 200 fsw where I used to see many species not found at shallower recreational dive depths.
I keep up with dive reports from friends on the mainland and it doesn't seem as if they have noticed significant declines in biodiversity this past year. In fact, I'm a bit envious of the species many of them have filmed in the much cooler waters off Sandy Eggo. Many of those species are rarely (if ever) seen in our waters, possibly because they don't have larval forms that can make the journey across the San Pedro Channel. Others may have restricted travel outside their usual home areas due to COVID restrictions (ha ha, just kidding).
So, if any of my readers have hypotheses to explain this, I'd greatly appreciate hearing them because I'm stumped. As an ecologist, I like to be aware of the diversity of critters in a given ecosystem rather than focus on a single group. The paucity this past year (and the chilly waters of winter) have left me longing to travel to biodiversity hotspots in the South Pacific and Asia. Sadly, the cancers and COVID are not allowing that to happen.
© 2020 Dr. Bill Bushing. For the entire archived set of nearly 900 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: Knobby and fragile rainbow sea stars; kelp rockfish and California halibut; California blue dorid nudibranch and two spot octopus.
