Field Notes: Storm Season on Catalina

The third storm of February came through on a Tuesday, and by Thursday morning the swell at the Catalina West End had dropped from six metres to a diveable two. These field notes cover Tidewright's first full winter at our Catalina restoration site: what eight weeks of North Pacific storm energy did to a young kelp forest, how we surveyed the damage between swells, and — the question every partner asks us — whether the seeded reef held. The short answer: mostly, yes. The long answer is more useful.

All site numbers below are Tidewright's own project figures from a single restored reef patch — illustrative of our method, not industry benchmarks.

The site going into winter

Our Catalina lease sits on a sloping granite reef on the island's exposed western shoulder, in ten to sixteen metres of water. It's exactly the kind of ground that used to carry giant kelp thick enough to foul a propeller, and exactly the kind that has spent recent decades cycling between sparse kelp and purple urchin barrens.

Going into the storm season we had, on paper:

• Roughly 9 hectares of reseeded reef, laid as seeded Holdfast lines across two winters (2024–25 and 2025–26 plantings)
• A canopy of one- and two-year-old giant kelp (Macrocystis pyrifera) — the two-year-olds approaching 12 metres of stipe length, the yearlings chest-high and supple
• A urchin-suppression zone maintained with our dive partners since the first lines went in
• Drifter 4 ("Pintail") and Drifter 7 ("Gullwing") working survey and maintenance circuits out of Two Harbors

February in the Southern California Bight is when the North Pacific sends its long-period groundswells down the coast, refracting around Point Conception and unloading on Catalina's west side. We'd planned for storms. Planning and living through them are different documents.

What a storm actually does to a kelp forest

There's a misconception — I held it myself, early on — that storms are simply enemies of kelp. The truth on Catalina is more interesting: winter storms are the forest's oldest pruning mechanism, and giant kelp evolved with them.

What six-metre swell does to a canopy, in sequence:

1. Drag loads multiply. Wave orbital motion at depth accelerates water back and forth through the forest. A mature Macrocystis plant carries a lot of sail area; drag forces rise steeply with wave height, and the weakest link — usually the holdfast's grip on the rock, or a stipe weakened by grazing snails — lets go.
2. Plants tangle and tear each other. Canopy rafts twist into ropes. Neighbouring plants braid together, and when one goes, it can take three with it.
3. Whole plants raft up and wash ashore. After each storm this winter, the island's west-side coves filled with drift kelp — tonnes of it — and the beaches briefly became the richest feeding grounds on the island. That export is not waste; drift kelp subsidises sandy-beach and deep-canyon food webs. Storms move the forest's productivity around.
4. Light reaches the bottom. This is the crucial one. Storm-thinned canopy lets sunlight hit the reef floor, where giant kelp's microscopic gametophytes and young sporophytes wait for exactly that: an open, lit patch of rock. Winter clearing followed by spring recruitment is the natural heartbeat of these forests.

So the goal of a storm-resilient restoration is not a forest that loses nothing. It's a forest that loses plants the way a wild forest does — from the canopy down, not from the reef floor up. What must not fail is the next generation holding on the rock below.

Riding it out

You don't fight a Catalina storm season; you schedule around it. Our rhythm for those eight weeks:

• Watch the forecast ensembles, not the single run. Swell models five days out gave us reliable windows. When a swell event was flagged, work shifted to: secure, batten, shelter.
• Get the Drifters off the water. The vessels are happiest at sea, but not that sea. Both Drifters ran for Cat Harbor on the leeward side before each swell arrived — a twelve-hour round trip that cost us survey days every time and was worth it every time. An autonomous vessel is only autonomous if it survives to next month.
• Buoy checks before and after every event. Our Holdfast line arrays have mooring and marker buoys that take the direct wave loading. Inspection dives in the calm before a storm found chafe points; inspection dives after found what chafed through.
• Shore work is not downtime. Storm days at Two Harbors were for seedline prep, spore culture checks, data backlog, and — honestly — watching the west side go white from the isthmus and feeling quietly humble.

The damage survey

By the first week of March the season's three big swells were through, and we ran the full post-storm survey: sonar lawn-mowing by the Drifters, diver transects on the seeded arrays, and canopy mapping from drone overflights timed to calm mornings. (The drone passes feed the same Canopy Ledger pipeline we use for all partner reporting.)

The honest tally from one storm season, Tidewright project figures:

• Canopy stipe density down ~35% on the two-year-old stands. Visually dramatic — the surface canopy that had been continuous in November was patchwork by March.
• Holdfast grip: the good news. Of the plants torn free, the overwhelming majority failed at the stipe or at wear points — snagged, braided, abraded — not by ripping their holdfasts off the rock. Attached bases were still there, alive.
• Seeded lines: ~92% of Holdfast line segments intact. Losses clustered where we expected: the two array corners that take refracted wrap-around swell, and one gully where storm-driven cobble had sandblasted a 20-metre stretch down to bare line.
• Recruitment lighting up. By late March, the diver transects were finding sporophyte recruits — little bronze ribbons five to fifteen centimetres tall — across the storm-opened patches. The pruning had done exactly what winter pruning is supposed to do.

For comparison, our baseline sonar history of the unrestored barren patch next door shows no such recruitment pulse. Bare urchin pavement stays bare; storms do it no favours. A forest with stock in the ground converts storm damage into turnover. A barren converts it into nothing.

What the storm season taught us

Three lessons are going into next winter's planting plan, and I'll put them here because they've changed how I brief crews:

First, plant for the corner cases, literally. Both of our worst line losses were on array edges exposed to wrapped swell. Next layout pulls the arrays back from those corners and accepts slightly less planted area in exchange for better survival geometry.

Second, the angle rules earned their keep. The arrays oriented to shed the prevailing northwest swell — our forty-degree rule, which deserves its own field note — came through with significantly less chafe damage than the short perpendicular "connector" runs we'd grandfathered in from the 2024 pilot. Those connectors are being re-laid this spring.

Third, storms audit your maintenance, not just your engineering. Every buoy that failed had been flagged for chafe at least once and deferred. Deferred maintenance is a loan the ocean collects with interest.

Standing on the isthmus in early April, watching baitfish flicker in the thinned canopy while yearling kelp put on its spring growth spurt, I kept thinking the same thing I wrote in the log: the site is behaving like a forest, not a garden. Forests take damage. Forests grow back through it. That's what we signed up to build.

Key takeaways

• Winter storms are a natural pruning force in kelp forests — giant kelp evolved with them, and storm-opened canopy triggers the light-driven recruitment the next generation depends on.
• Good restoration doesn't aim for zero storm loss; it aims to protect the base of the forest — holdfasts on rock and recruits in waiting — so damage converts into turnover rather than collapse.
• In one illustrative Tidewright Catalina season: roughly a third of canopy stipes lost, ~92% of seeded line segments intact, and a strong post-storm recruitment pulse across the thinned patches.
• Losses concentrated exactly where geometry predicted — swell-exposed array corners and cobble-scoured gullies — which is fixable in layout.
• Storm seasons audit deferred maintenance as much as engineering. Inspect before the swell, fix what you flag.

FAQ

Do storms destroy kelp restoration projects?

They can destroy poorly designed ones, and they will always take a toll. But a well-sited, well-laid project treats storm loss as expected turnover. Our Catalina site lost about a third of its canopy stipes in its first full storm season and came out the other side with holdfasts intact and the strongest recruitment pulse we've recorded there.

Why don't you build stronger lines that survive everything?

Because over-engineering creates its own problems — stiffer lines transfer wave load into the rock anchors, and indestructible lines torn loose become hazards. We'd rather engineer for controlled, survivable failure modes and let biology do the regrowing. The goal is a self-replacing forest, not a submarine fortress.

Can you work on the reef during storm season?

Between swells, yes — and those windows are valuable for inspection dives and repairs. During events, no: the Drifters shelter in Cat Harbor and the crew works ashore on seedline and data. Trying to work through a Catalina February is how boats and people get hurt.

Does the drift kelp washed ashore go to waste?

Far from it. Wrack lines of storm-cast kelp feed beach invertebrates, shorebirds and the microbial engines of sandy shores, and kelp that sinks offshore subsidises deep-sea food webs — one pathway by which kelp carbon reaches long-term ocean sinks. Storm export is a feature of kelp ecosystems, not a bug.