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Dive Dry with Dr. Bill

#665: Eco-Catastrophe Part Three: The Predators

If you've read my last two columns, you know how our current warm water episode, coupled with the presence of the invasive Asian seaweed Sargassum horneri, has impacted not only the primary producers in our marine ecosystems but also the invertebrates and fish that depend on them for food. High water temperatures created low nutrient levels thus limiting growth of the giant kelp that dominates our healthy marine environment, but also the many other native algae, thus allowing the non-native Sargassum to become dominant. With our native primary producers largely gone, replaced by the bitter tasting "devil weed," our local herbivores including abalone, top snails, sea urchins, kelp crabs and even species of plant-eating fish have little to eat. Some have exhibited limited growth, little or no reproduction or have just disappeared from our waters. Now let's look at how this impacts the upper levels of the food chains, the predators that munch on other critters.

Previously I mentioned that the filter and suspension feeders that live on our rocky reefs or in our sandy bottom habitats have also been impacted. First, the growth of plant plankton has undoubtedly decreased as witnessed by the great visibility underwater. With the phytoplankton gone, there is less for the zooplankton (animal plankton) to feed on and they decrease as well. When that happens, there is less food for the tube worms and other critters on sandy bottoms to feed on, as well as the tube worms, bivalves such as scallops and other filter feeders living on the rocky reefs. Add to that the dense growth of Sargassum and it is difficult to create water flow that reaches these filter feeders living under the thick seaweed.

Bat rays feed largely on juicy tube worms (Chaetopterus variopedatus) that are filter feeders living buried in the sand. Female sheephead feed on filter feeding bivalves such as clams and tube worms in sandy bottoms as well. When the filter feeders decrease in number, there is less food for them. Although male sheephead will often butt in on a female after it has dug its hole in search of food and take over, their much stronger jaws often have them feeding over the rocky reefs on filter feeders like scallops and algae eaters like sea urchins. Due to the impacts discussed last week, these foods are no longer as abundant either so these predators are also affected.

Some of you are probably unaware that in addition to scavenging on dead matter, your tasty lobster loves to dine on sea urchins. They are a good source of calcium since "bugs" don't drink milk (neither does Dr. Bill!). However, when sea urchins die off as so many purple and reds have, the "lobbies" don't have as much food. Growth and reproduction may slow down, and therefore they may remain undersized. Interestingly enough, I have not seen as many lobster molts as I normally do which adds credence to this. I hear most hoop netters and other bug hunters are not having a good year. One thing I have seen that surprised me are a number of "bugs" chowing down on sea cucumbers! Now males in some Asian cultures believe that "cukes" can enhance one's virility (I've never tested that myself), so perhaps the lobster are just trying to enhance reproduction. There has also been some evidence that the sea cucumbers are succumbing to a disease, possibly as a result of the warm water temperatures.

Another member of the Echinoderms (the spiny skinned animals) that has largely disappeared are the sea stars... perhaps better known to most of us as starfish. A terrible disease struck early last year that decimated species of starfish from Alaska to Mexico. The densovirus that was determined to be the cause is not new along the West Coast. However, some scientists believe it may have become so virulent and spread so quickly due to the three warm water Blobs that appeared last year off the West Coast: one in the Gulf of Alaska, one off Washington and Oregon and the third off southern California and Baja. Once again higher than normal temperatures may have caused direct impacts on another major group of marine predators.

Another observation I have made is the general absence of baitfish in our nearshore waters during the summer and fall. These include the jack mackerel, Pacific sardine and northern anchovy. All are planktivores (plankton eaters) and are undoubtedly affected by diminished plankton richness in our warmer, shallow nearshore waters. I have heard from some fishermen that they are being found further offshore in deeper depths, perhaps where colder water contains more nutrients and permits greater plankton growth. Recently as our nearshore waters have cooled a bit, I've started seeing baitfish in the shallows but only at night.

Warm waters have also allowed some predators from the south to stick around longer than usual. Last winter I was seeing yellowtail in the dive park as late as March and they are present in schools right now in November. And, of course, most of you have seen news reports about the hammerhead sharks that have entered our waters (as they have during other warm water episodes I have experienced here dating back to the late 1970s el Niño). The warm waters have also allowed smaller predators such as the cardinalfish, whitetail gregory (or damsel), the star-studded grouper and even tropical cornetfish to enter our region. There's been a change in the fauna, there'll be a change in you!

Another native species apparently affected indirectly by the warm water is the kelp surfperch. These small predators are usually fairly numerous in healthy kelp forests, but I haven't seen any in quite some time. My best guess is that without the protection of the kelp to hide in, they were easy prey for kelp bass to gobble up. I have to mention one native species that appears relatively unaffected by all this, the giant kelpfish. I am seeing lots of young giant kelpfish. Their parents have apparently turned traitor. After all, the common name kelpfish comes from their association with our giant kelp. Yet with most of our kelp forest decimated, the kelpfish have adopted the invasive Sargassum as appropriate nesting areas and nurseries!

I think after reading my last three columns you can see we are REALLY in hot water these days! Our marine ecosystems have undergone major changes at all levels of the food chain. Heck, the el Niño hasn't really hit us yet... and if global climate change continues to cause a warming trend in our waters as shown by hydrographic records dating back many decades and scientific experiments, we could be in trouble long-term. Of course this is absolutely frightening to me. As a kelp forest ecologist, I may have nothing to study in our waters. My options would be to move further north into colder waters, perhaps requiring a dry suit... or adapt and become a coral reef ecologist somewhere in the tropics where I can be surrounded by bikinis. I think you can guess my choice!

© 2015 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 29, 10:00 AM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. You can also watch these episodes in iPod format on YouTube through my channel there (drbillbushing). Please help me climb out of self-imposed poverty... buy my DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!

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Kelp surfperch and jack mackerel; traitorous giant kelpfish and yellowtail. .

This document maintained by Dr. Bill Bushing.
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